Community Research and Development Information Service - CORDIS

FP7

COMETNANO Report Summary

Project ID: 229063
Funded under: FP7-NMP
Country: Greece

Final Report Summary - COMETNANO (Technologies for Synthesis, Recycling and Combustion of Metallic Nanoclusters as Future Transportation Fuels)

Executive Summary:
COMETNANO was an EU-funded, 3-year project focusing on the evaluation of metallic nanoparticles as potential fuels for Internal Combustion Engines (ICEs). It proposed, for the first time, an integrated approach studying the synthesis of metallic nanoparticles, their controlled combustion under realistic conditions and the recycling of spent fuel via utilization of renewable means. All these aspects, constituting the innovative overall concept of the project, were investigated either at a proof-of-principle or at a proof-of-concept level. Ideally, the combustion of metals produce energy, without generation of the well-known harmful emissions of conventionally fuelled ICEs such as petrol or diesel, as the only product is the respective metal oxide. The project’s main goal was to investigate the in-principle feasibility of metallic nanofuels combustion under ICE conditions and subsequently propose integrated strategies that have minimal or no environmental impact for the complete life-cycle of such novel fuels. Preliminary studies, based on the natural availability, non-toxicity, market price and intrinsic power density of a variety of metals, concluded that promising candidate metallic nanofuels could be boron, aluminium and iron. Preliminary engine-like tests performed in shock tube and combustion vessel rigs, suggested that iron nanofuel constituted the preferred choice among those initially proposed and evaluated. Hence, efforts during the last 18 months of the COMETNANO project focused on the completion of systematic combustion studies of iron-air under both ‘engine-like’ and real engine conditions. Relevant studies for aluminium-air combustion systems were also continued, as a secondary project aim, primarily due to scientific interest.
Comprehensive iron-air combustion studies carried out during the project elaborated on the fundamental mechanism of iron nanoparticles combustion. Based on experimental data, customized simulation models, describing the main principles/phenomena controlling dispersion flow, injection and combustion processes were developed. The most important aspect of combustion-related work were the efforts made to operate a simple ICE engine on iron nanofuel, including nanopowder grades specifically produced for the needs of the project and others commercially acquired. Relevant tests indicated that the in-principle operation of an ICE running on iron nanofuel is feasible. Nonetheless, engineering problems related to clogging of engine or injector valves, which lead to undesirable phenomena, must be resolved if metallic combustion is to become applicable. It should be highlighted that the aforementioned engineering challenges cannot be regarded as prohibitive for the proposed concept. Despite their intrinsic difficulties, they relate to aspects potentially manageable via solutions that could emerge from further relevant R&D efforts on ICE design engineering and materials science, in the route towards implementation of purpose built systems that would allow optimized use of an iron nanofuel. After their in-principle validation, conventional and novel synthesis methods of tailored iron nanoparticles were intensified with the aim of providing adequate amounts of iron nanofuels for the conduction of project studies related to injection, combustion and fuel/combusted fuel handling under flow conditions. At the same time, a process regarding upgrading of a typical iron-based waste fraction from steel industries to a value-added high purity ferrous product that could be utilized for the synthesis of iron nanoparticles was developed. Its validation at a level of several kg processing for the preparation of purified precursors was successful. In addition, a novel system for the preparation of metallic nanoparticles was developed, constructed and successfully tested at a proof-of-concept level. COMETNANO project also assessed potential impacts of the utilized nanoparticles on human health. To date, such issues are not well established and additional effort is needed in this particular field. Of primary importance is the introduction of exposure limits legislation based on the number concentration of NPs. Moreover, experimental studies conducted indicated that efficient solutions for the virtually 100% containment of utilized nanoparticles exist and are based on the mature and optimized technology of diesel particulate filters. Relevant systematic measurements have confirmed that the aforementioned goal is achievable in the short-term. Moreover, studies –under relevant emulating conditions– on partial system-failure scenarios were conducted and measurements were compared to the existing mass based occupational limits, as issued by OSHA, with the aim of determining the extend of system damaging up to which these limits are not exceeded. At the same time, simple fail-safe modules were incorporated. In conjunction to this and in the absence of relevant systematic literature data, fundamental-level protocols related to the assessment of the toxicity of the combusted metallic fuels were designed and applied. The strategies considered for the feasibility of the proposed concept of metallic nanofuels were subjected to preliminary economic evaluation and simplified ‘well-to-wheels’ study. Results indicated that, under certain conditions, costs calculated for the case of iron nanofuel are comparable to the respective ones for conventional fuels case and less costly than other environmental-friendly, state-of-the-art approaches (i.e. hydrogen fuel-cell engines and Li-ion batteries). This is under the prerequisite that all major challenges related to such a technology, including further improvements in materials synthesis aspects, will be successfully resolved.
COMETNANO project introduced a novel technology/concept with a potential significant impact upon the emergence and development of green mobility solutions providing an alternative fuel with virtually no emissions of harmful gases and the spent fuel being recycled by renewable energy means. Such a technology could potentially extend the lifetime of internal combustion engines (a mature technology) using metal nanoparticles instead of polluting fossil fuels, on the prerequisite that all major system modification required will be efficiently implemented via continuation of systematic relevant R&D efforts, to which COMETNANO will be the pioneering one. At the same time, within the 3-year duration of the project, ‘side-activities’ with respect to the synthesis of metallic nanoparticles with tailored properties and to the exploitation of industrial byproducts/discarder fractions yielded several important results and novel systems. Those, after implementation of required improvements and their optimization via continuation of relevant research work, can be directly applicable to an industrial-scale level for a variety of nanostructured materials to be used in a multitude of energetic or high-tech applications. Such results/systems, after their necessary optimization, could become simpler, more robust and less costly alternatives to currently employed state-of-the-art systems/concepts for the production of a variety of nanoparticles/nanostructured materials requiring accurately regulated atmospheres for their preparation.

Project Context and Objectives:
The COMETNANO project comprised of eight work packages (WPs), with six of them being dedicated to its Research and Development (R&D) aspects and two of them related to its administrative management and dissemination and exploitation of results produced. The main scientific and technological outcomes of the project, within its 3-year duration, are summarized below per WP. The titles of the R&D WPs and a brief description of their major objectives are also provided.

WP1: Evaluation of candidate metal-fuels and their sources

Major Objectives were:
- To evaluate several candidate metal-fuels and their sources in terms of efficiency, availability, costs and handling.
- To perform a comparative-to-conventional and other environmental-friendly technologies study.

During the initial project period, the task of choosing suitable candidate metal-fuels as well as their respective sources to be employed for the needs of the project has been completed. The candidate-fuels chosen were iron, aluminium and boron, in the form of nanoparticles with a typical average size of primary particles in the range of 20-100nm (nanoparticles). This choice was based on the energy content, the abundance, the relevant safety/toxicity aspects, and the preliminary economic data of these metals as well as on the fundamental structuring characteristics that these metals should possess in order to be in-principle suitable for engine-like combustion. The potential sources considered for the production of respective metallic nanoparticles included both commercial materials (i.e. oxides, ‘coarse’/micron-sized metallic powders to be formulated into the respective nanopowders and/or appropriate salts) as well as relevant discarded/waste fractions, which were examined in terms of their ‘upgradability’ via suitable and economically feasible techniques. Two such fractions were considered: an iron-based/mill-scale slag and an aluminium-based slag (‘aluminium ash’). In the case of the iron-based slag, an efficient process for its purification to obtain a relatively pure iron source was described in detail. Due to the promising results obtained at a preliminary level, it was chosen to be further studied and optimized within the framework of WP3 studies, as described in the relevant section below. Preliminary considerations for ‘aluminium ash’ showed that the development of a similar refinement process is feasible; however there appeared to be several significant economic drawbacks and based on the current experience of COMETNANO’s industrial partners, this particular candidate-source was decided to be abandoned. The respective metallic nanoparticles precursors’ preparation and synthesis routes that were suggested by COMETNANO included a combination of conventional and well-established processes with promising emerging technologies that are expected to become key-methods for the tailoring of materials nanostructuring in the near-to-mid-term future (i.e. aerosol-based synthesis processes and plasma-aided synthesis of nanoparticles). It was made clear that for practical purposes and in order to perform all relevant experiments that were needed in order to verify the feasibility of various important project activities proposed (e.g. combustion and the required fundamental oxidation characteristics of metal nanoparticles), a significant amount of commercial nanopowders was necessary to be acquired and employed for the efficient and timely progress/completion of such activities. The completion of Task 1.1 signified the successful completion of project’s milestone M1, entitled ‘‘Decision on candidate metals specific sources and definition of required processes for nanoparticles production per source and element’’.
Shortly after the project’s mid-term, it was considered necessary that a basic economic analysis should be conducted in order to obtain a first idea on the cost assessment of the metallic fuels proposed (at least within an order of magnitude). The analysis was being updated during the whole 2nd period of the project and it was also conducted under certain fundamental pre-requisites referring to the efficient resolution of all technological challenges related to the in-practice implementation of metal-fuelled engines in the mid-to-long term horizon and to pollutants emissions-related systematic taxation of fossil-fuel based ones. The major aforementioned challenges are briefly stated in WP4 section of this report. The main conclusions of this economic study was that the iron nanofuel prepared according to the proposed environmental-friendly processes, could be comparable or lower than the respective liquid hydrocarbons under certain conditions. The key parameter to achieve this was to increase the number of 1-step regenerations of the spent fuel (oxide) by directly reducing it with renewably generated hydrogen, so that at least 10-20 combustion cycles could be performed with the use of recycled fuel without notable degradation of its nano-scale characteristics. Subsequently, it was necessary to transform the multi-combusted degraded spent fuel into an appropriate precursor that would allow its ‘radical regeneration’ (i.e. in terms of its metallic nature and of its nanostructuring) via a more complex process involving liquid chemistry based and other steps.
On the other hand, the Al nanofuel case was found to be much more challenging. On one hand the 1-step regeneration of the spent fuel was not feasible due to fundamental thermodynamic restrictions and on the other hand the calculated costs for Al formulation into a suitable nanopowder via thermal-spray based methods were relatively high. The necessary modifications in order to achieve elimination of the significant environmental impact of the conventional Al production method was an additional challenge but it is believed than in the long-term, their industrial-scale implementation could become feasible.
The case of boron was not examined, within the framework of such an economic analysis, since its combustion at a proof-of-principle level (please refer to WP4 section of this report) under ICE-conditions was not identified as feasible and therefore had been excluded from further studies as early as project month 18.
During the final stages of the project and as more information from the other project WPs was becoming available the conduction of additional studies became possible. Example include a simplified but realistic ‘well-to-wheel’ analysis on metallic nanoparticles as ICE fuels and a simple comparative analysis of metal-fuelled engines technologies versus other state-of-the-art environmental-friendly ones. With respect to the ‘well-to-wheels’ analysis, a simplified study concerning the assessment of the existence of practically adequate iron worldwide reserves and production rates that would both allow the in-principle future utilization of iron-fuelled engines was made. The main conclusion was that, even under the ‘extreme’ assumption of covering the global transportation energy demands with the aid of iron fuelled engines, worldwide reserves are enough for a period of 60-90 years, without taking into account the recycling concept that COMETNANO concept is based upon. However, such a dramatic transition would require substantial increase in iron worldwide production rates (i.e. 7-8-fold as compared to year 2009). Regarding the comparison to hydrogen fuelled fuel cell based engines and to the option of fully electric vehicles, the comparative estimated costs – by taking into account all assumptions/pre-requisites briefly described above – all three options yielded figures that are within the same order of magnitude. However, under the prerequisite that at least 10 combustion cycles could be achieved using the same recycled iron nanofuel batch, the technology introduced in COMETNANO has a clear advantage against the other two alternatives.

WP2: Simulation of nanoparticles flow-management, injection and combustion

Major Objectives were:
- The numerical simulation of the fundamental aspects of metallic nanoparticle combustion, injection of the fuel (port/direct injection) and overall circulation/feed/collection of nanoparticles dispersion of a candidate Internal Combustion Engine (ICE).
- The provision of basic information concerning the desired properties of the nanofuels and required design modifications of the involved sub-systems, so that conditions are retained in a range of acceptable operating efficiency.

The main goal of WP2 was the implementation of suitable simulation models with respect to the important phenomena referring to the flow characteristics of air/metal nanoparticles aerosols, their injection according to concepts that are similar to the ones applied in ICEs (direct injection, port injection) as well as to the combustion mechanism of the metallic nanofuels. The implementation of such activities would allow a basic numerical description of main aspects involved during the aforementioned phenomena and some of the peculiarities of the utilization of metallic nanoparticles as fuels, while it would also provide theoretical background to the in-principle feasibility of handling and combustion of such novel fuels. Finally, it would also contribute to the basic definition of the engine system main sub-components.
The realization of a combustion model that would aid in the identification of the basic aspects of the combustion mechanism of metallic nanoparticles was acknowledged as the most novel and challenging activity of WP2. It was initiated with the conduction of an extensive literature review that aimed at the determination of all relevant information available so far. The detailed analysis of available data on metal nanoparticle combustion characteristics revealed positive indications on the possibility to perform combustion of the nanopowders under consideration during an engine cycle. It was concluded that existing literature data were not directly applicable to internal combustion engine conditions and specific experiments were necessary in order to proceed with the introduction of a suitable combustion model. Preliminary experiments in a basic research engine permitted the implementation of a simple single-zone (gas phase) model. Such a model provided very preliminary but important indications on the engine combustion characteristics of nanoparticles. It is important to note that, at that preliminary stage, the solid phase (particles) and the temperature differences between particles and gas phase were neglected from the thermodynamic analysis of the engine cycle. However, such results had to be experimentally confirmed by means of particle temperature measurements. Based on the aforementioned simplified combustion model, a more rigorous two-zone model was adopted, which included both gas and solid phase. It must be noted that the one-zone model underestimated the experimental data for the case of Fe and Al (i.e. peak combustion temperatures recorded), while the improved two-zone version was in good agreement with the respective first experimental campaigns of WP4. Peak temperatures of the gas phase were determined to be above the NOx formation threshold for the case of aluminium and below this threshold for the case of iron. Such indications appeared critical in the context of obtaining virtually zero emission combustion. The experimental validation of the proposed model, with the aid of WP4 activities, facilitated its continuous improvement via insertion of required modifications. Upon completion of the relevant simulation activities, the developed engine numerical simulation methodology had been formulated in such a way that very good agreement with the respective real engine combustion data was achieved.
Modelling of the high-pressure injection system initially facilitated the design of a lab-scale device able to operate successfully under engine-like conditions. The simulations revealed useful information in terms of mass flow rate, range of pressure and timings, which were of fundamental importance in order to maximise the efficiency of the system. A single shot pneumatic injection system was initially considered in order to understand the main phenomena that can be found during the nanoparticles injection process. The behaviour of the injection system, in several operating conditions, in terms of its main flow characteristics had been studied and defined via simulation for the Al and Fe nanofuels. Upon finalization of CFD (Computational Fluid Dynamics) calculations, the aim of realistically defining the behaviour of metallic nanoparticles during the injection process was accomplished. This information provided the boundary conditions for CFD spray characterization in WP4. The model was successfully validated against experimental data obtained from relevant WP4 studies.
Modelling of the particle feeding system (i.e. Task 2.3) primarily focused on the air-dispersed metallic fuel conditioning (i.e. deagglomeration) via appropriate strategies incorporated in the overall arrangement. Deagglomeration via shockwave formation was considered and based on the CFD results, the final design proved adequate in achieving the pressure and/or velocity gradients. The model was in good agreement with the respective experimental measurements conducted, within the framework of WP4.
In conclusion, the activities and subsequent results obtained from the overall WP2 studies contributed to the successful completion of project milestone ‘M4: Definition of a simplified metal fuelled ICE: Sub-components, operating conditions and nanofuel specifications’. Such a contribution derived from the strong interaction established between WP2 and WP4.

WP3: Tailoring of metal-nanoparticles and regeneration of burned fuel by direct/indirect utilization of ‘solar H2’

Major Objectives were:
- Synthesis of several candidate metal-fuel nanoparticles via aerosol-based, thermal-spray and other techniques capable of tuning the materials in the nano-level.
- Identification and preparation of suitable precursor materials for the above synthesis activities.
- Identification and application of suitable passivation techniques for the synthesised nanoparticles.
- Identification and application of techniques suitable for the regeneration of burned fuels with emphasis of solar-H2 utilization as medium or energy source.
- Detailed characterization of synthesised, combusted and regenerated metallic nanofuels.

During the 1st period of the project (month 1-month 18), the synthesis of iron nanoparticles has been demonstrated either via direct aerosol-based synthesis conditions or from reduction of suitable iron oxide nanopowders (including the ones synthesised via aerosol-based methods), under certain conditions that have been determined with the aid of detailed parametric studies. These conditions were also suitable for the regeneration of combusted iron nanofuels (i.e. iron oxides), as demonstrated by relevant experimental campaigns. Two different practical and simple to be implemented passivation strategies of the produced iron nanoparticles were defined.
Synthesis of aluminium-based nanoparticles via a plasma-spray aided method was feasible, as identified from the conduction of relevant proof-of-principle tests and the required system modifications, in order to fully demonstrate the preparation of nanoparticles that will possess the metallic aluminium phase, are currently being implemented. For the case of boron, plasma-based synthesis of boron-based nanoparticles was practically evaluated as infeasible, at least with respect to potential application at a scalable-level. The preparation of suitable Fe-precursors from the iron –based slag, with the aid of a process that has been developed within the framework of the project, was demonstrated at the lab-scale level. Synthesis of Fe nanoparticles either via ASP or by direct reduction of the purified powder with the aid of H2 has been achieved. The oxidation characteristics of Fe, Al and B nanopowders were determined at a basic level via Thermo-Gravimetric Analysis and spark-aided oxidation tests, in a nanopowder ‘free combustion’ mode. It was shown that the ‘in-house’ iron nanoparticles are more readily oxidized than the respective commercial ones.
During the 2nd project period, further improvement and successful scaled-up evaluation of the process, developed within the framework of COMETNANO project, for the purification of calamina slag and the subsequent preparation of suitable precursors were made. In addition, further experimental campaigns for the preparation of iron nanoparticles, based on the conditions and experimental protocols already defined during the 1st project period, were continued. An improvement was made with respect to energy requirements for the reduction with hydrogen of iron oxide nanoparticles. Furthermore, synthesis of aluminium-based nanoparticles via a plasma-spray aided method (APS) with the aid of a suitable system that was developed and constructed within the framework of the project was successful, as identified from the conduction of relevant proof-of-concept tests. The utilization of improved Fe-precursors from the iron-based slag, with the aid of the processes already defined during the 1st project period was further demonstrated at a lab-scale level. Proof-of-concept studies at the aerosol-based synthesis pilot-scale unit for the production of iron oxide nanoparticles, subsequently reducible via exposure to hydrogen to metallic ones, were also completed successfully. The production rate was measured at 40 g?h-1 and the repeatability of this value was verified.
Simplified studies on the effect of repeated ‘spark-aided free combustion’/regeneration-by-H2 cycles on the nanostructuring/oxidation characteristics of Fe nanopowders showed that, depending on the iron grade (i.e. commercial or in-house prepared from two different iron-oxide precursors), this number can in-principle be in the range of 2-5. Based on the relevant range identified in WP1 for the iron nanofuel to be cost-competitive with respect to conventional fossil-fuels (please refer to the relevant section), further improvement is clearly needed.
With respect to the important project milestones M3 and M4 requirements that refer to the feasibility of the examined nanoparticles synthesis and regeneration techniques as proposed by WP3, in continuation of the progress reported in the 1st periodic report, it was concluded that:
- All requirements have been successfully met for the case of iron and aluminium metals. For the case of iron, the aforementioned fulfilment has already been reported at the end of the 1st project reporting period (please refer to 1st project periodic report for details). However, the relevant additional experimental campaigns and in particular the scaled-up tests further substantiated that fact. With respect to aluminium, the fulfilment of the two milestones was signified by the successful plasma-based synthesis of Al nanoparticles that was completed during the 2nd project period.
- Production of boron nanoparticles with the aid of the techniques proposed within the framework of this project was not feasible, which essentially meant that WP3 failed in addressing the suitable conditions to be employed for this specific case.
Another important issue that needs to be highlighted is the fulfilment of the fundamental objective of WP3 to function as the metallic nanofuel supplier of the project. Indeed, following the in-principle fulfilment of major requirements with respect to the feasibility of the preparation of these ‘nanofuels’ that was made evident in the 1st project periodic report, WP3 produced adequate quantities of several grades of metallic nanoparticles that were all fed to the experimental campaigns of WP4-WP6 for their evaluation.

WP4: Injection, combustion and flow-management studies

Major Objectives were:
- Studies under ‘engine-like’ combustion conditions for the in-principle evaluation of combustion feasibility and the determination of basic combustion parameters/characteristics.
- Studies under real-engine combustion conditions with the aid of a Compression-Ignition ICE.
- Evaluation of potential fouling and/or clogging issues as well as basic evaluation of potential NOx formation.
- Development and evaluation of suitable injection and air dispersed metallic nanofuels flow/management systems.

Studies involving shock tube experiments and post-analysis of combusted samples permitted the characterization of Al, Fe and B combustion at high pressure and temperature conditions (i.e. ‘piston engine’-like). In all cases, combustion was feasible. However boron required extremely high ignition temperatures, which indicated that its combustion may not be feasible in a reciprocating engine. The oxidation of iron nanoparticles proceeded according to a solid state reaction. The combined analysis of shock tube and the post analysis of spent, iron oxide fuel samples collected from the shock-tube suggested that iron oxidation proceeded according to a solid state reaction, primarily governed by the surrounding temperature and consequent chemical and diffusional kinetics. Aluminium combustion was slightly different, since it evolved at relatively lower temperatures, indicating a diffusionally controlled combustion mechanism at the initial stages, followed by rupture of the particle’s oxide shell and direct exposure of molten metal to the oxidising environment. Peak temperatures encountered for iron-oxidiser combustion suggested no possibility of NOx formation. In contrast, aluminium-oxidiser combustion revealed peak temperatures close to or slightly higher than the NOx formation threshold. The shock tube results during the 2nd period of the project were of a reassuring nature as they largely confirmed the key findings from the preliminary tests. That was achieved via conduction of a large number of tests and relevant post analysis of the combusted samples. Continuous improvement of the system diagnostics/measuring modules allowed the refinement of the findings of the 1st project period with respect to combustion duration, ignition temperatures, main oxidation mechanisms involved etc.
Preliminary engine tests confirmed the possibility to ignite and in-principle burn both aluminium and iron nanoparticles in the time scale of the compression-expansion engine stroke. With respect to boron, the shock tube results were confirmed, since no ignition of particles was detected by the pressure sensor of the engine. Al and Fe tests revealed different combustion characteristics, a finding which was in qualitative agreement with the respective shock tube results. These real engine tests have clearly confirmed the possibility to in-principle realize single combustion cycles with nanoparticles without critical drawbacks. Visible analysis of the engine oil after combustion tests showed pollution with solid particles. However no visible wearing issues were identified at that stage.
The CFD calculations (WP2) and the inert tests carried out with different injection systems have been used to develop the final high-pressure lab-scale direct injection system. Once the system was built, the aerosol macroscopic characteristics were analyzed obtaining a behavior similar to gaseous sprays. The design, construction of a high-pressure, high-temperature combustion test rig (i.e. combustion vessel) was completed and set into operation. Initial data gathered provided the first useful information for the characterization and validation of the test rig itself and the development of the engine-like combustion measurement procedure. Results produced via systematic experimental combustion campaigns in the combustion vessel were in agreement with the ones reported above for the shock-tube case. Moreover, the combustion/regeneration experimental campaign described in WP3, was repeated with the aid of this particular test-rig, which was more representative to an engine-like combustion process. The conclusions were in general agreement with those described in WP3, indicating that after 3 combustion cycles, there were signs of iron nanofuel deterioration.
With respect to the particle feeding/flow management system, preliminary, evaluation tests performed for commercial powder dispersers highlighted the nature of problems related to lack of concentration control and aerosol production repeatability. Initial efforts focused on the design of a pneumatic system that would control the aerosol produced by means of powder fluidization inside a tank. All tests performed with the proposed pneumatic system revealed that maintaining aerosol concentration control for a relatively long period would be extremely challenging. Based on that, it was decided to design a new feeder employing a mechanical component to carry the powder into the main airstream creating the aerosol, while simultaneously sealing the powder tank compartment from this airstream. This first version of the custom-build feeder was tested for a series of nanopowders, representative of the grades of the nanofuel powders planned to be used for the engine tests. Results suggested sufficient feed rate control of adjustable nature. Incorporated with the convergence-divergence nozzle, the feeding system led to powder deagglomeration factors of approximately 10. Unfortunately, upon usage of the first version of the feeder with commercial iron and aluminium nanopowders (APPS of 40-60 nm), severe clogging problems were encountered. Following these difficulties encountered with the continuous aerosol dispersion and management system in the first part of the project (refer to mid-term report), it was decided to assign a group of the overall project team to the continuation of development of an integral system aiming at continuous powder feeding into the engine, while another group focused on the development of a batch-type powder injection system. The first group finished the design and manufacturing of an improved powder feeder, which incorporated mechanisms focused on the solution of the aforementioned clogging problems. This final version of the continuous powder feeder system was completed at the start of the 2nd period of the project. The second group proceeded with a design relying on a pneumatically controlled one-way check valve sized to inject controllable quantities of powder on a cycle-to-cycle basis. This direct injection (DI) system was initially installed in a transparent vessel in order to measure fundamental injection parameters, such as penetration length, spray angle in conjunction to injection timing and duration. The DI valve was then installed into the engine, allowing the conduction of combustion tests with known and controllable quantity of powder injected during each engine combustion cycle and, consequently, enabling the estimation of energy balance of iron-air combustion. Unfortunately, the high reactivity of iron, made it impossible to properly time the injector for optimal combustion. Therefore, a significant portion of the energy content of the charge injected into the cylinder was added to the pumping losses during the compression stroke. This, in turn, rendered the determination of a representative, realistic thermal efficiency of the iron-air combustion process, impossible. A faster response valve could improve the situation significantly. Nonetheless, the experiments performed with the use of the direct injector, strengthened the feasibility level of metal fuelled combustion inside an internal combustion engine. Moreover, similarly to the observations made from the shock tube, the engine results implied that iron-air combustion proceeded in the solid state. Also important were the findings with respect to the probability of NOx formation by burning iron inside the engine. The engine as well as specifically designated combustion vessel results, suggested that NOx formation has a very low probability.
As already mentioned, design efforts towards the completion of an integral powder dispersion and flow management system were continued and successfully concluded. The final design version of the continuous powder feeder was tested and found to perform adequately with a variety of nanopowders. Powder feed rates were fully adjustable and continuous at feed rates relevant to those required for the Lombardini research engine. The overall flow management system, composed of the feeder, the de-agglomerating nozzle and all necessary flow diagnostic sensors, was incorporated to the engine during project month 26. Information on these tests is provided in WP5.
Following the tests performed with the batch injector, as well as those conducted with the use of the continuous powder feeding system, the engine was dismantled and thoroughly checked for signs of excessive wear. It was found that the piston rings and upper surface of piston crown had been worn out at a notable level. It should be noted that this was also suggested by the slight decrease in motoring pressure and increase in engine blow-by towards the later runs of the engine with metal powder fuel. The worn out state of the piston rings also led to the accumulation of significant amounts of powder inside the crankcase, contaminating the engine oil and reducing its lubricating capacity.
In conclusion, based on the WP4-related results obtained during the project and in relation to relevant project milestones:
- Iron and aluminium nanoparticles combustion was found to be in-principle feasible under both engine-like and real engine conditions. The combustion of boron was not feasible under engine-like conditions due to its high ignition temperature requirements that are outside typical ICE specifications. Thus, the critical requirement/project milestone for the verification of at least one metallic fuel combustion under engine-like conditions was fully met.
- The implemented flow management system, via incorporation of customized modifications, was also successful in generating metallic nanoparticles/air aerosols of tunable concentrations for an adequate time period, while on the other hand the efficient particulates containment has been achieved. Thus, the relevant project milestone was also fulfilled for this case.

WP5: Construction of a lab-scale test-cell for metal-fuels testing

Major Objectives were:
- Design and construction of a test-cell for the evaluation of the performance of a customized system embedding a simplified engine fuelled by the synthesized metallic nanofuels.
- Evaluation of candidate metallic nanofuels under realistic conditions.

WP5 constituted the integration of the flow management, injection, engine, exhaust and particle collection subsystems developed within the framework of WP4 and WP6. The resulting integral test-cell would be used for the conduction of the crucial runs of the engine on metal fuel for a finite time period. Results obtained would be used as the ultimate evaluation of the project’s main principles.
As included in the parts of this document describing the activities of WP4 and WP6, all system components were designed, manufactured and tested. The only central deviation from the initial plan was caused by the absence of a scaled up injector unit from the final engine-rig proposed. The powder feeder, engine and exhaust and collection sub-systems were incorporated together for the final runs with continuous metal fuel feeding during the final stages of the project. The integrated test-cell, together with all necessary diagnostic sensors and electronic controls, was assembled as required. A second version of the overall system was also implemented, in which case the powder feeder and flow management system was replaced with a shot-to-shot injector placed overhead of the engine cylinder.
The final version of the powder feeding and dispersion management unit was implemented. This unit was designed to provide continuous iron powder feed rates within a range suitable for the simple experimental engine utilized. It also facilitated a specialised system for the fragmentation of the larger powder agglomerates present in the dispersion. Detailed technical information with respect to the overall performance of the feeding unit was identified, as required prior to its coupling with the engine. The engine used for the overall test cell was a single cylinder, 350cc, CI engine, with one intake and one exhaust valve.
A set of tests was conducted for the overall system described above, with the feeder providing the engine with a continuous powder feed of iron nanofuel for 40-60 seconds. The powder-air dispersion provided by the feeder entered the combustion chamber through the inlet, poppet type valve of the engine. Unfortunately, clogging problems primarily related to the engine valves, prevented systematic continuation of these tests. More specifically, the valves of the engine remained open due to powder accumulation on the valve seats, resulting to pre-ignition of the charge inside the intake line. Another factor that contributed to these pre-ignition problems related to the poor passivation of the commercial iron powder purchased for the completion of the tests. A few successful continuous fuel feeding runs were eventually completed with the use of the iron nanopowder, produced within the framework of project activities (WP3). After analysis of the results, it was found that there was a window, where at least 100 consecutive firing cycles, with positive net work production, were achieved. Such finding was a further strong indication that, if certain engineering problems related to clogging of the system could be overcome, combustion of iron metal fuel inside an ICE is a feasible and sustainable process.
The completion of WP5, also marked the partial achievement of the project milestones requesting for the “Final definition of a test-cell to be employed for candidate metal fuels evaluation” and the “Evaluation of the test-cell operation”. To be fully legitimate, one could argue that both of these milestones were principally - but not fully - complete, due to the absence of a suitable injection system from the final test-cell and also because the maximum period of attainable continuous operation of the metal-fuelled engine was not sufficient to allow comparative evaluation of several grades of metallic nanofuels.

WP6: Environmental impact and health assessment studies under failure conditions

Major Objectives were:
- Investigation of the potential environmental impact and health effect of controlled nanoparticles leakages to the surrounding environment.
- Exhaust measurements of nanoparticles concentration under normal and abnormal (system-failure) operation.
- Literature studies with respect to relevant existing regulations and important scientific findings regarding the health effects/toxicity of nanoparticles of interest.

As required by the DoW/Annex I, during the last 18 months of the project some basic experiments in order to evaluate the efficiency of the proposed particulates containment technology inside a candidate flow-management system have been conducted. Nanoparticle collection tests revealed that the use of a standard wall-flow particulate filter system proved adequate in filtering the high aerosol concentrations produced with the current feeding system. Under normal operations of the system, filtration efficiency for NPs of <100 nm was 99+%, while that for NPs of > 100 nm ranged from 90 to 99%, depending on DPF loading. Nanoparticle levels inside the lab (during the tests) were measured at 0.015 mg/m3, which is 20-25 times lower than the current legislation exposure limits. For tests under abnormal conditions of the dispersion system, it was found that neither in the case of a failure in the intake line nor in that of a failure of the particulate filter the particle concentrations inside the lab and/or in the intake and exhaust lines surpassed the maximum permissible occupational exposure limits.
With respect to the effects of metallic NPs in human health, recent studies have linked NPs to increased chances of respiratory system or heart related diseases. Nanoparticle toxicity is strongly related to particle size; with smaller particles being more toxic. A fundamental conclusion is also the fact that further development is needed, so that new and more tailored-to-nanoparticles standards and exposure limits are imposed by the relevant regulations/legislation. In particular for iron oxide NPs, a number of research works have been published that aim to characterize and evaluate their biophysical reactivity and toxicological effects in vitro and in vivo, which do not always result in homogenous conclusions, and even tend to be contradictory, sometimes. In this framework, an experimental campaign to evaluate the oxidative stress levels by monitoring the Reactive Oxygen Species (ROS) generation potential of iron oxide NPs, both in acellular and cellular systems, was performed.
In conclusion, the work completed within the framework of WP6 revealed that no in-principle detrimental effects with respect to human health and to the environment were identified for the materials examined and the version of the flow management system implemented, under the pre-requisite that such a system would be equipped with proper, relatively simple and readily available failsafe modules.

Project Results:
The COMETNANO project comprised of eight workpackages (WPs), with six of them being dedicated to its Research and Development (R & D) aspects and two of them related to its administrative management and dissemination and exploitation of results produced. The main scientific and technological outcomes of the project, within its 3-year duration, are summarized below per WP. The titles of the R & D WPs and a brief description of their major objectives are also provided.

WP1: Evaluation of candidate metal-fuels and their sources

Major Objectives were:
- To evaluate several candidate metal-fuels and their sources in terms of efficiency, availability, costs and handling.
- To perform a comparative-to-conventional and other environmental-friendly technologies study.

During the initial project period, the task of choosing suitable candidate metal-fuels as well as their respective sources to be employed for the needs of the project has been completed. The candidate-fuels chosen were iron, aluminium and boron, in the form of nanoparticles with a typical average size of primary particles in range of 20-100nm (nanoparticles). This choice was based on the energy content, the abundance, the relevant safety/toxicity aspects, and the preliminary economic data of these metals as well as on the fundamental structuring characteristics that these metals should possess in order to be in-principle suitable for engine-like combustion. The potential sources considered for the production of respective metallic nanoparticles included both commercial materials (i.e. oxides, ‘coarse’/micron-sized metallic powders to be formulated into the respective nanopowders and/or appropriate salts) as well as relevant discarded/waste fractions, which were examined in terms of their ‘upgradability’ via suitable and economically feasible techniques. Two such fractions were considered: an iron-based/mill-scale slag and an aluminium-based slag (‘aluminium ash’). In the case of the iron-based slag, an efficient process for its purification to obtain a relatively pure iron source was described in detail and due to the promising results obtained at a preliminary level, it was chosen to be further studied/optimized within the framework of WP3 studies, as described in the relevant section below. Preliminary considerations for ‘aluminium ash’ showed that the development of a similar refinement process is feasible; however there seemed to be several significant economic drawbacks and based on the current experience of COMETNANO’s industrial partners, this particular candidate-source was decided to be abandoned. The respective metallic nanoparticles precursors’ preparation and synthesis routes that were suggested by COMETNANO included a combination of conventional and well-established processes with promising emerging technologies that are expected to become key-methods for the tailoring of materials nanostructuring in the near-to-mid-term future (i.e. aerosol-based synthesis processes and plasma-aided synthesis of nanoparticles). It was made clear that for practical purposes and in order to perform all relevant experiments that were needed in order to verify the feasibility of various important project activities proposed (e.g. combustion and the required fundamental oxidation characteristics of metal nanoparticles), a significant amount of commercial nanopowders was necessary to be acquired and employed for the efficient and timely progress/completion of such activities. The completion of Task 1.1 signified the successful completion of project’s milestone M1, entitled ‘‘Decision on candidate metals specific sources and definition of required processes for nanoparticles production per source and element’’.
Shortly after the project’s mid-term, it was considered necessary that a basic economic analysis should be conducted in order to obtain a first idea on the cost assessment of the metallic fuels proposed (at least within an order of magnitude). The analysis was being updated during the whole 2nd period of the project and it was also conducted under certain fundamental pre-requisites referring to the efficient resolution of all technological challenges related to the in-practice implementation of metal-fuelled engines in the mid-to-long term horizon and to pollutants emissions-related systematic taxation of fossil-fuel based ones. The major aforementioned challenges are briefly stated in WP4 section of this report. The main conclusions of this economic study was that the iron nanofuel, prepared according to the proposed environmental-friendly processes, could be comparable or lower than the respective liquid hydrocarbons under certain conditions. The key parameter to achieve this is to increase the number of 1-step regenerations of the spent fuel (oxide) by directly reducing it with renewably generated hydrogen, so that at least 10-20 combustion cycles, without notable degradation of its nano-scale characteristics, are feasible. Subsequently, it is necessary to transform the multi-combusted degraded spent fuel into an appropriate precursor that would allow its ‘radical regeneration’ (i.e. in terms of its metallic nature and of its nanostructuring) via a more complex process involving liquid chemistry based and other steps.
On the other hand, the Al nanofuel case is much more challenging, since on one hand the 1-step regeneration of the spent fuel is not feasible due to fundamental thermodynamic restrictions and on the other hand the calculated costs for Al formulation into a suitable nanopowder via thermal-spray based methods are relatively high. The necessary modifications in order to achieve elimination of the significant environmental impact of the conventional Al production method is an additional challenge but it is believed than in the long-term, their industrial-scale implementation will become feasible.
The case of boron was not examined, within the framework of such an economic analysis, since its combustion at a proof-of-principle level (please refer to WP4 section of this report) under ICE-conditions was not identified as feasible and therefore had been excluded from further studies as early as project month 18.
During the final stages of the project and as more information from the other project WPs was becoming available, additional studies such as a simplified but realistic ‘Well-to-wheels’ analysis on metallic nanoparticles as ICE fuels and a simple comparative analysis of metal-fuelled engines technologies versus other state-of-the-art environmental-friendly ones have been completed. With respect to the ‘Well-to-wheels’ analysis, a simplified study concerning the assessment of the existence of practically adequate iron worldwide reserves and production rates that would both allow the in-principle future utilization of iron-fuelled engines was made. The main conclusion was that, even under the ‘extreme’ assumption of covering the global transportation energy demands with the aid of iron fuelled engines, worldwide reserves are enough for a period of 60-90 years, without taking into account the recycling concept that COMETNANO concept is based upon. However, such a dramatic transition would require substantial increase in iron worldwide production rates (i.e. 7-8-fold as compared to year 2009). Regarding the comparison to hydrogen fuelled fuel cell based engines and to the option of fully electric vehicles, the comparative estimated costs – by taking into account all assumptions/pre-requisites briefly described above – all three options yielded figures that are within the same order of magnitude. However, under the assumption that >10 combustion cycles could be achieved for the iron nanofuel, under the already explained concept, the COMETNANO technology has a clear advantage against the other two alternatives.

WP2: Simulation of nanoparticles flow-management, injection and combustion

Major Objectives were:
- numerical simulation involving in-cylinder combustion process, injection of the fuel (port/direct injection) and overall circulation/feed/collection of nanoparticles dispersion of a candidate Internal Combustion Engine (ICE).
- provision of basic information concerning the desired nanofules properties and required design modifications of the involved sub-systems, so that conditions are retained in a range of acceptable operating efficiency.

The main goal of WP2 was the implementation of suitable simulation models with respect to the important phenomena referring to the flow characteristics of air/metal nanoparticles aerosols, their injection according to concepts that are similar to the ones applied in ICEs (direct injection, port injection) as well as to the in-cylinder combustion of the metallic nanofuels. The implementation of such activities would allow a basic numerical description of main aspects involved during the aforementioned phenomena and some of the peculiarities of the utilization of metallic nanoparticles as fuels, while it would also provide theoretical background to the in-principle feasibility of handling and combustion of such novel fuels. Finally, it would also contribute to the basic definition of the engine system main sub-components.
The realization of a realistic combustion model was identified as the most novel and challenging activity of WP2 and started with the conduction of an extensive literature review that aimed at the determination of all important parameters/constraints/phenomena available so far. The detailed analysis of available data on metal nanoparticle combustion characteristics revealed positive indications on the possibility to perform combustion of the nanopowders under consideration during an engine cycle. It was concluded that existing literature data were not directly exportable to realistic engine combustion conditions and specific experiments were necessary in order to proceed with the introduction of a suitable combustion model. Preliminary experiments in a real “low cost” engine permitted the first implementation of a simple single-zone (gas phase) model. Such a model provided very preliminary but important indications on the engine combustion characteristics of nanoparticles. It is important to note that, at that preliminary stage stage, the solid phase (particles) and the temperature differences between particles and gas phase were neglected for the thermodynamic analysis of the engine cycle. However, such results had to be experimentally confirmed by means of particle temperature measurements. Based on the aforementioned simplified combustion model, a first version of a more realistic two-zone model (“gas+solid phase model”) has been introduced. It must be noted that the one-zone model underestimates the experimental data for he case of Fe and Al (i.e. peak combustion temperatures recorded), while the improved two-zone version was in good agreement with the respective first experimental campaigns of WP4. Peak temperatures of the gas phase seemed to be above the NOx formation threshold for the case of aluminium and below this threshold for the case of iron. Such indications appeared very interesting in order to obtain real zero NOx emission combustion. The experimental validation of the proposed model, with the aid of WP4 activities, facilitated its continuous improvement via insertion of required modifications. Upon completion of the relevant simulation activities, the developed engine numerical simulation methodology had been formulated in such a way that very good agreement with the respective real engine combustion data was achieved.
The modelling of the high-pressure injection system has initially facilitated the design of a lab-scale device able to operate successfully under engine-like conditions. The simulations revealed useful information in terms of mass flow rate, ranges of pressure and timings, which were of fundamental importance in order to determine under which conditions the system would operate more efficiently. A single shot pneumatic injection system was initially considered in order to understand the main phenomena that can be found during the nanoparticles injection process. The behaviour of the injection system, in several operating conditions, in terms of its main flow characteristics had been studied and defined via simulation for the Al and Fe nanofuels. Upon finalization of CFD (Computational Fluid Dynamics) calculations, the aim of realistically defining the behavior of metallic nanoparticles during the injection process was accomplished. This information provided the boundary conditions for CFD spray characterization in WP4. The model was successfully validated against experimental data obtained from relevant WP4 studies.
Modelling of the particle feeding system (i.e. Task 2.3) primarily focused on the air-dispersed metallic fuel conditioning (i.e. deagglomeration) via appropriate strategies incorporated in the overall arrangement. Deagglomeration via shockwave formation was considered and based on the CFD results, the final design proved adequate in achieving the pressure and/or velocity gradients. The model was in good agreement with the respective experimental measurements conducted, within the framework of WP4.
In conclusion, the activities and subsequent results obtained from the overall WP2 studies contributed to the successful completion of project milestone ‘M4: Definition of a simplified metal fuelled ICE: Sub-components, operating conditions and nanofuel specifications’. Such a contribution derived from the strong interaction established between WP2 and WP4.

WP3: Tailoring of metal-nanoparticles and regeneration of burned fuel by direct/indirect utilization of ‘solar H2’

Major Objectives were:
- Synthesis of several candidate metal-fuel nanoparticles via aerosol-based, thermal-spray and other techniques capable of tuning the materials in the nano-level.
- Identification and preparation of suitable precursor materials for the above synthesis activities.
- Identification and application of suitable passivation techniques for the synthesised nanoparticles.
- Identification and application of techniques suitable for the regeneration of burned fuels with emphasis of solar-H2 utilization as medium or energy source.
- Detailed characterization of synthesised, combusted and regenerated metallic nanofuels.

During the 1st period of the project (month 1-month 18), the synthesis of iron nanoparticles has been demonstrated either via direct aerosol-based synthesis conditions or from reduction of suitable iron oxide nanopowders (including the ones synthesised via aerosol-based methods), under certain conditions that have been determined with the aid of detailed parametric studies. These conditions were also suitable for the regeneration of combusted iron nanofuels (i.e. iron oxides), as demonstrated by relevant experimental campaigns. Two different practical and simple to be implemented passivation strategies of the produced iron nanoparticles were defined.
Synthesis of aluminium-based nanoparticles via a plasma-spray aided method was feasible, as identified from the conduction of relevant proof-of-principle tests and the required system modifications, in order to fully demonstrate the preparation of nanoparticles that will possess the metallic aluminium phase, are currently being implemented. For the case of boron, plasma-based synthesis of boron-based nanoparticles was practically evaluated as infeasible, at least with respect to potential application at a scalable-level. The preparation of suitable Fe-precursors from the iron –based slag, with the aid of a process that has been developed within the framework of the project, was demonstrated at the lab-scale level. Synthesis of Fe nanoparticles either via ASP or by direct reduction of the purified powder with the aid of H2 has been achieved. The oxidation characteristics of Fe, Al and B nanopowders were determined at a basic level via Thermo-Gravimetric Analysis and spark-aided oxidation tests, in a nanopowder ‘free combustion’ mode. It was shown that the ‘in-house’ iron nanoparticles are more readily oxidized than the respective commercial ones.
During the 2nd project period, further improvement and successful scaled-up evaluation of the process, developed within the framework of COMETNANO project, for the purification of calamina slag and the subsequent preparation of suitable precursors were made. In addition, further experimental campaigns for the preparation of iron nanoparticles, based on the conditions and experimental protocols already defined during the 1st project period, were continued. An improvement was made with respect to energy requirements for the reduction with hydrogen of iron oxide nanoparticles. Furthermore, synthesis of aluminium-based nanoparticles via a plasma-spray aided method (APS) with the aid of a suitable system that was developed and constructed within the framework of the project was successful, as identified from the conduction of relevant proof-of-concept tests. The utilization of improved Fe-precursors from the iron-based slag, with the aid of the processes already defined during the 1st project period was further demonstrated at a lab-scale level. Proof-of-concept studies at the aerosol-based synthesis pilot-scale unit for the production of iron oxide nanoparticles, subsequently reducible via exposure to hydrogen to metallic ones, were also completed successfully. The production rate was measured at 40 g?h-1 and the repeatability of this value was verified.
Simplified studies on the effect of repeated ‘spark-aided free combustion’/regeneration-by-H2 cycles on the nanostructuring/oxidation characteristics of Fe nanopowders showed that, depending on the iron grade (i.e. commercial or in-house prepared from two different iron-oxide precursors), this number can in-principle be in the range of 2-5. Based on the relevant range identified in WP1 for the iron nanofuel to be cost-competitive with respect to conventional fossil-fuels (please refer to the relevant section), further improvement is clearly needed.
With respect to the important project milestones M3 and M4 requirements that refer to the feasibility of the examined nanoparticles synthesis and regeneration techniques as proposed by WP3, in continuation of the progress reported in the 1st periodic report, it was concluded that:
- All requirements have been successfully met for the case of iron and aluminium metals. For the case of iron, the aforementioned fulfilment has already been reported at the end of the 1st project reporting period (please refer to 1st project periodic report for details). However, the relevant additional experimental campaigns and in particular the scaled-up tests further substantiated that fact. With respect to aluminium, the fulfilment of the two milestones was signified by the successful plasma-based synthesis of Al nanoparticles that was completed during the 2nd project period.
- Production of boron nanoparticles with the aid of the techniques proposed within the framework of this project was not feasible, which essentially meant that WP3 failed in addressing the suitable conditions to be employed for this specific case.
Another important issue that needs to be highlighted is the fulfilment of the fundamental objective of WP3 to function as the metallic nanofuel supplier of the project. Indeed, following the in-principle fulfilment of major requirements with respect to the feasibility of the preparation of these ‘nanofuels’ that was made evident in the 1st project periodic report, WP3 produced adequate quantities of several grades of metallic nanoparticles that were all fed to the experimental campaigns of WP4-WP6 for their evaluation.

WP4: Injection, combustion and flow-management studies

Major Objectives were:
- Studies under ‘engine-like’ combustion conditions for the in-principle evaluation of combustion feasibility and the determination of basic combustion parameters/characteristics.
- Studies under real-engine combustion conditions with the aid of a Compression-Ignition ICE.
- Evaluation of potential fouling and/or clogging issues as well as basic evaluation of potential NOx formation.
- Development and evaluation of suitable injection and air dispersed metallic nanofuels flow/management systems.

Studies involving shock tube experiments and post-analysis of combusted samples permitted the characterization of Al, Fe and B combustion at high pressure and temperature conditions (i.e. ‘piston engine’-like). In all cases, combustion was feasible, however boron showed quite high ignition temperatures and such behaviour provided an indication that its combustion may not have been feasible in a piston engine. The oxidation of iron nanoparticles proceeded according to a solid state reaction. The combined analysis of shock tube and the post analysis of spent, iron oxide fuel samples collected from the shock-tube suggested that iron oxidation proceeded according to a solid state reaction, primarily governed by the surrounding temperature and consequent chemical and diffusional kinetics. Aluminium combustion was slightly different, since it evolved at relatively lower temperatures, indicating a diffusionally controlled combustion mechanism at the initial stages, followed by rupture of the particle’s oxide shell and direct exposure of molten metal to the oxidising environment. Peak temperatures encountered for iron-oxidiser combustion suggested no possibility of NOx formation. In contrast, aluminium-oxidiser combustion revealed peak temperatures close to or slightly higher than the NOx formation threshold. The shock tube results during the 2nd period of the project were of a reassuring nature as they largely confirmed the key findings from the preliminary tests. That was achieved via conduction of a large number of tests and relevant post analysis of the combusted samples. Continuous improvement of the system diagnostics/measuring modules allowed the refinement of the findings of the 1st project period with respect to combustion duration, ignition temperatures, main oxidation mechanisms involved etc.
Preliminary test engine tests confirmed the possibility to ignite and in-principle burn both aluminium and iron nanoparticles in the time scale of the compression-expansion engine stroke. With respect to boron, the shock tube results were confirmed, since no ignition of particles was detected by pressure sensor of the engine. Al and Fe tests put in evidence different combustion characteristics and in qualitative agreement with the respective shock tube results. These real engine tests have clearly evidenced the possibility to in-principle realize single combustion cycles with nanoparticles without critical drawbacks. Visible analysis of the engine oil after combustion tests showed pollution with solid particles, however no visible wearing issues were identified at that stage.
The CFD calculations (WP2) and the inert tests carried out with different injection systems have been used to develop the final high-pressure lab-scale direct injection system. Once the system was built, the aerosol macroscopic characteristics were analyzed obtaining a behavior similar to gaseous sprays. The design, construction and set into operation of a high-pressure, high-temperature combustion test rig (i.e. combustion vessel) has been completed and subsequently provided the first useful information for the characterization and validation of the test rig itself and to develop the engine-like combustion measurement procedure. Results produced via systematic experimental combustion campaigns in the combustion vessel were in agreement with the ones reported above for the shock-tube case. Moreover, the repeated combustion/regeneration experimental campaign described in WP3, was repeated with the aid of this particular test-rig, as more representative to engine-like combustion process. The conclusion was in general agreement with the one described in WP3, indicating that after 3 combustion cycles, the iron nanofuel deteriorated.
With respect to the particle feeding/flow management system, preliminary, evaluation tests performed for commercial powder dispersers highlighted the nature of problems related to lack of concentration control and aerosol production repeatability. Initial efforts focused on the design of a pneumatic system that would control the aerosol produced by means of powder fluidization inside a tank. All tests performed with the proposed pneumatic system revealed that maintaining aerosol concentration control for a relatively long period would be extremely challenging. Based on that, it was decided to design a new feeder employing a mechanical component to carry the powder into the main airstream creating the aerosol, while simultaneously sealing the powder tank compartment from this airstream. This eeder was tested for a series of nanopowders including emulating nanostructured powders and grades of metallic and oxidized nanopowders; all results suggested sufficient concentration control. Incorporated with the convergence-divergence nozzle, the feeding system led to powder deagglomeration factors of approximately 10. Unfortunately, upon usage of the system with commercial iron and aluminium nanopowders (APPS of 40-60 nm), severe clogging problems were encountered. On the other hand, the efficient particulates containment inside the system has been achieved via the utilization of conventional means, such as employment of Diesel Particulate Filters upstream of the exhaust point (this strategy is analyzed in detail in WP6 part of this report). A new improved design, incorporating mechanisms that focus on this particular clogging problem, has been completed at the end of the 1st project period. Following these difficulties encountered with the continuous aerosol dispersion and management system in the first part of the project (refer to mid-term report), it was decided to assign a group of the overall project team to the continuation of development of an integral system aiming at continuous powder feeding into the engine, while another group focused on the development of a batch-type powder injection system. In the latter case, the design relied on a pneumatically controlled one-way check valve sized to inject controllable quantities of powder on a cycle-to-cycle basis. This direct injection (DI) system was initially installed in a transparent vessel in order to measure fundamental injection parameters, such as penetration length, spray angle in conjunction to injection timing and duration. The DI valve was then installed into the engine, allowing the conduction of combustion tests with known and controllable quantity of powder injected during each engine combustion cycle and, consequently, enabling the estimation of energy balance of iron-air combustion. Unfortunately, the high reactivity of iron, made it impossible to properly time the injector for optimal combustion. Therefore, a significant portion of the energy content of the charge injected into the cylinder was added to the pumping losses during the compression stroke. This, in turn, rendered the determination of a representative, realistic thermal efficiency of the iron-air combustion process, impossible. A faster response valve could improve the situation significantly. Nonetheless, the experiments performed with the use of the direct injector, strengthened the feasibility level of metal fuelled combustion inside an internal combustion engine. Moreover, similarly to the observations made from the shock tube, the engine results implied that iron-air combustion proceeded in the solid state. Also important were the findings with respect to the probability of NOx formation by burning iron inside the engine. The engine as well as specifically designated combustion vessel results, suggested that NOx formation has a very low probability.
As already mentioned, design efforts towards the completion of an integral powder dispersion and flow management system were continued and successfully concluded. The final design of the powder feeder incorporated additional features to overcome the clogging problems inside the powder tank (for information on the clogging problems encountered with the first version of the feeder, refer to the mid-term report). The system was tested and found to perform adequately with a variety of nanopowders. Powder feed rates were fully adjustable and continuous at feed rates relevant to those required for the Lombardini research engine. The overall flow management system, composed of the feeder, the de-agglomerating nozzle and all necessary flow diagnostic sensors, was incorporated to the engine during project month 26. Information on these tests is provided in WP5.
Following the tests performed with the batch injector, as well as those conducted with the use of the continuous powder feeding system, the engine was dismantled and thoroughly checked for signs of excessive wear. It was found that the piston rings and upper surface of piston crown had been worn out at a notable level. It should be noted that this was also suggested by the slight decrease in motoring pressure and increase in engine blow-by towards the later runs of the engine with metal powder fuel. The worn out state of the piston rings also led to the accumulation of significant amounts of powder inside the crankcase, contaminating the engine oil and reducing its lubricating capacity.
In conclusion, based on the WP4-related results obtained during the project and in relation to relevant project milestones:
- Iron and aluminium nanoparticles combustion was found to be in-principle feasible under both engine-like and real engine conditions. The combustion of boron was not feasible under engine-like conditions due to its high ignition point that is outside of the general/common ICE specifications. Thus, the critical requirement/project milestone for the verification of at least one metallic fuel combustion under engine-like conditions was fully met.
- The implemented flow management system, via incorporation of customized modifications, was also successful in generating metallic nanoparticles/air aerosols of tunable concentrations for an adequate time period, while on the other hand the efficient particulates containment has been achieved. Thus, the relevant project milestone was also fulfilled for this case.

WP5: Construction of a lab-scale test-cell for metal-fuels testing

Major Objectives were:
- Design and construction of a test-cell for the evaluation of the performance of a customized system embedding a simplified engine fuelled by the synthesized metallic nanofuels.
- Evaluation of candidate metallic nanofuels under realistic conditions.

WP5 constituted the integration of the flow management, injection, engine, exhaust and particle collection subsystems developed within the framework of WP4 and WP6. The resulting integral test-cell would be used for the conduction of the crucial runs of the engine on metal fuel for a finite time period. Results obtained would be used as the ultimate evaluation of the project’s main principles.
As included in the parts of this document describing the activities of WP4 and WP6, all system components were designed, manufactured and tested. The only central deviation from the initial plan was caused by the absence of a scaled up injector unit from the final engine-rig proposed. The powder feeder, engine and exhaust and collection sub-systems were incorporated together for the final runs with continuous metal fuel feeding during the final stages of the project. The integrated test-cell, together with all necessary diagnostic sensors and electronic controls, was assembled as required. A second version of the overall system was also implemented, in which case the powder feeder and flow management system was replaced with a shot-to-shot injector placed overhead of the engine cylinder.
The final version of the powder feeding and dispersion management unit was implemented. This unit was designed to provide continuous iron powder feed rates within a range suitable for the simple experimental engine utilized. It also facilitated a specially system for the fragmentation of the larger powder agglomerates present in the dispersion. Detailed technical information with respect to the overall performance of the feeding unit were identified, as reuiqred prior to its coupling with the engine. The engine used for the overall test cell was a single cylinder, 350cc, CI engine, with one intake and one exhaust valve.
A set of tests was conducted for the overall system described above, with the feeder providing the engine with a continuous powder feed of iron nanofuel for 40-60 seconds. The powder-air dispersion provided by the feeder entered the combustion chamber through the inlet, poppet type valve of the engine. Unfortunately, clogging problems primarily related to the engine valves, prevented systematic continuation of these tests. More specifically, the valves of the engine remained open due to powder accumulation on the valve seats, resulting to pre-ignition of the charge inside the intake line. Another factor that contributed to these pre-ignition problems related to the poor passivation of the commercial iron powder purchased for the completion of the tests. A few successful continues fuel feeding runs were eventually completed with the use of the iron nanopowder, produced within the framework of project activities (WP3). After analysis of the results, it was found that there was a window, where at least 100 consecutive firing cycles, with positive net work production, were achieved. Such finding was a further strong indication that, if certain engineering problems related to clogging of the system could be overcome, combustion of iron metal fuel inside an ICE is a feasible and sustainable process.
The completion of WP5, also marked the partial achievement of the project milestones requesting for the “Final definition of a test-cell to be employed for candidate metal fuels evaluation” and the “Evaluation of the test-cell operation”. To be fully legitimate, one could argue that both of these milestones were principally - but not fully - complete, due to the facts that a suitable injection system was absent from the final test-cell and due to the fact that the maximum period of attainable continuous operation of the metal-fuelled engine was not sufficient to allow comparative evaluation of several grades of metallic nanofuels.

WP6: Environmental impact and health assessment studies under failure conditions

Major Objectives were:
- Investigation of the potential environmental impact and health effect of controlled nanoparticles leakages to the surrounding environment.
- Exhaust measurements of nanoparticles concentration under normal and abnormal (system-failure) operation.
- Literature studies with respect to relevant existing regulations and important scientific findings regarding the health effects/toxicity of nanoparticles of interest.

As required by the DoW/Annex I, during the last 18 months of the project some basic experiments in order to evaluate the efficiency of the proposed particulates containment technology inside a candidate flow-management system have been conducted. Nanoparticle collection tests revealed that the use of a standard wall-flow particulate filter system proved adequate in filtering the high aerosol concentrations produced with the current feeding system. Under normal operations of the system, filtration efficiency for NPs of <100 nm was 99+%, while that for NPs of > 100 nm ranged from 90 to 99%, depending on DPF loading. Nanoparticle levels inside the lab (during the tests) were measured at 0.015 mg/m3, which is 20-25 times lower than the current legislation exposure limits. For tests under abnormal conditions of the dispersion system, it was found that neither in the case of a failure in the intake line nor in that of a failure of the particulate filter the particle concentrations inside the lab and/or in the intake and exhaust lines surpassed the maximum permissible occupational exposure limits.
With respect to the effects of metallic NPs in human health, recent studies have linked NPs to increased chances of respiratory system or heart related diseases. Nanoparticle toxicity is strongly related to particle size; with smaller particles being more toxic. A fundamental conclusion is also the fact that further development is needed, so that new and more tailored-to-nanoparticles standards and exposure limits are imposed by the relevant regulations/legislation. In particular for iron oxide NPs, a number of research works have been published that aim to characterize and evaluate their biophysical reactivity and toxicological effects in vitro and in vivo, which do not always result in homogenous conclusions, and even tend to be contradictory, sometimes. In this framework, an experimental campaign to evaluate the oxidative stress levels by monitoring the Reactive Oxygen Species (ROS) generation potential of iron oxide NPs, both in acellular and cellular systems, was performed.
In conclusion, the work completed within the framework of WP6 revealed that no in-principle detrimental effects with respect to human health and to the environment were identified for the materials examined and the version of the flow management system implemented, under the pre-requisite that such a system would be equipped with proper, relatively simple and readily available failsafe modules.

Potential Impact:
The direct potential impact attributed to the core concept of COMETNANO, as already described above, is by-definition a long-term one. It could be realized under the pre-requisite that further R&D efforts will be promoted to further investigate, improve and more importantly encourage efficient practical solutions to the technological challenges identified within the 3-year duration of this project. In line with this, if the concept of CometNano is further promoted, it is expected to have a significant impact on the development of a novel, environmental-friendly fuel that could potentially become the future replacement of conventional (fossil-based) fuels. This in turn could contribute to the realization of the zero-emission engine (at a full life-cycle level) with obvious advantages to the environment and to the quality of human life.
On the basis of the above, COMETNANO introduced a framework which is completely new, environmental-friendly and outside of the mainstream thinking. One could eloquently sum up the viability of the concept in the following excerpt “…It is pertinent to ask how one can be concerned with the economics of a technology that does not exist especially when its use is envisioned for a time at least 50 years into the future. Certainly, a typical cost-benefit analysis is inappropriate; if such a criteria were invoked in the 19th and early 20th century by potential entrepreneurs, it seems likely that they would have decided not to invent the telephone, oil refinery, automobile, aircraft, etc…’’
The COMETNANO project, being oriented towards the European policy of sustainable development, focused on an integrated, ‘full fuel-cycle’ approach of metallic nanoparticles management and aimed at the minimization of environmental pollution. This could be achieved via both the direct/indirect utilization of renewable hydrogen for the regeneration of burned fuel, as well as the attempt to include suitable discarded/waste fractions as candidate raw materials for the initial synthesis of metal-fuel nanoparticles. In terms of the regeneration process, by proposing a ‘recyclable metal-fuel concept’, a novel way of efficient ‘hydrogen storage’ during the reduction process of the metal oxide is introduced. Thus, metal nanoclusters become an alternative energy carrier that averts the significant difficulties of hydrogen safe storage and transportation. In this way, a radically novel means for the realization of the pursued ‘renewable hydrogen economy pathway’ is pursued.
A more direct and short-term potential impact is expected from its ‘side-activities’, processes and concepts developed within the framework of COMETNANO. More specifically:

- The suitability and efficiency of the process developed for the exploitation of the iron-based slag in order to prepare precursors suitable for the preparation of iron-based nanoparticles has been demonstrated at a relatively scaled-up proof-of-concept level. A relevant patent application titled ‘Nanoscale particles & method of manufacture thereof’ (more details are provided in Section B of this report) was filed. Evident such an activity can potentially induce an ‘adding value’ process for these relatively abundant and low-cost by-products, thus stimulating the interest of large industrial metal producers.
- The system/concept designed, constructed and at a proof-of-concept tested and verified for the production of aluminium nanoparticles also constitutes another potential aspect with short-term impact in the demanding sector of preparing various nanostructured materials requiring tailored atmospheres/conditions for their preparation. Although this system requires further optimization for the efficient tackling of its moderate efficiency, its relatively reduced complexity, robustness and inherent scalability makes it a candidate alternative to the energy-intensive, costly and delicate state-of-the-art systems currently employed.
- The powder feeder module, designed and implemented for the needs of the flow management studies of the project also constitutes a system that could provide efficient solutions to currently challenging problems of powder handling in industrial applications related to the preparation of optimized construction materials (e.g. cement).

As a conclusion, COMETNANO project promoted a radically novel approach by introducing an alternative energy carrier (i.e. iron metal) and by describing an integrated concept that did not focus on only one aspect of the main idea proposed but also took into account/investigated all relevant steps for the implementation of the complete lifecycle of that idea.

List of Websites:
Project Website: www.cometnano.org

Project Coordinator:
Dr.Athanasios G. Konstandopoulos
agk@cperi.certh.gr
http://apt.cperi.certh.gr/

Project Contact Point
Dr. George Karagiannakis
gkarag@cperi.certh.gr
http://apt.cperi.certh.gr/

Related information

Reported by

CENTRE FOR RESEARCH AND TECHNOLOGY HELLAS
Greece
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