Final Report Summary - TIDE (Tangential Impulse Detonation Engine)
Executive Summary:
The TIDE project was aimed at developing a breakthrough propulsion system technology envisioned to trigger a step change in air transportation in the second half of this century. This new, radical approach to creating propulsion power aims at reducing the weight, the complexity, and the cost of the classical, air breathing, aviation engine and, thus, at significantly reducing the overall fuel consumption and, consequently, the total amount of pollutants emission.
The central idea of the proposed propulsion technology is the replacement of the gas turbine in a typical aviation engine of today by a simpler and at least as effective system. A power device able to replace the gas turbine in an aviation engine must, while providing the advantages discussed earlier, fulfil the functional role of the turbine. This role consists in converting the working fluid kinetic energy (velocity) and potential energy (pressure) into work used to propel the aircraft and to compress the air upstream of the combustor by means of blade rows forming divergent channel. The concept proposed in TIDE uses the conservation of impulse for the combustor exhaust jet released tangentially, to rotate the entire combustor assembly.
Even though the rotating combustor concept is, in itself, a breakthrough new technology, in order to trigger a step change in the propulsion technology of the future air transportation a radical approach to combustion is also proposed, namely supersonic combustion, that will allow efficient propulsion for supersonic and hypersonic flight, by means of a Pulsed Detonation Combustor (PDC).
Given the complexity of the task, and the limited resources available through the project, the scope of the project was limited. The main goal of the project is to prove the functionality and feasibility of the concept, opening the road towards developing a mature technology in the future. The project was successful in this respect,. Three PDC experimental models based on different geometrical configurations have been designed, manufactured and experimentally tested, and detonation was achieved in all three. The admission of air into the tested PDCs is controlled by a couple of aerodynamic valves created at the inlet by system of shock waves generated by the interaction of two incoming supersonic jets with Hartman resonators of various geometries. Thus, the operating frequency of the PDC can be raised significantly in comparison to the existing solutions in the literature, allowing the increase of the engine’s performances.
Currently, the limiting factor for the operating frequency of the TIDE PDCs is the frequency of the ignition spark. Further research efforts are needed to ensure self – ignition and self – sustained pulsed detonation, thus allowing a further major operating frequency increase.
A PDC demonstrator was designed, manufactured and tested during the project’s experimental program. Besides the proof of concept they provided, the experimental measurements carried out in the project allowed the selection of several very promising geometries for achieving an optimal jet – resonator interaction, and identified the critical geometrical parameters that control the operation of a PDC based on aerodynamic valves created by oscillating shock waves.
Numerical simulations of the TIDE compressor, operating under variable back pressure conditions, specific for a PDC driven engine, of the TIDE combustor, and of the entire TIDE engine were carried out with various degrees of success. Based on these, preliminary models for the compressor and for the entire engine were developed. Further research efforts are needed in order to optimize the engine components and to fully integrate them in an operational engine.
The results of the project were disseminated via a project website, seven peer reviewed scientific papers, participation in fairs and exhibitions, where a scaled model of the engine was presented, a TV interview, and several articles in popular science magazines. One of the most important achievements related to dissemination was the invitation the project consortium received to present TIDE at Aerodays 2015, in London, UK.
Project Context and Objectives:
Context
The TIDE concept proposes the use of conservation of impulse for the combustor exhaust jet released tangentially, to rotate the entire combustor assembly, thus eliminating the need for a turbine by a simpler and at least as effective system. The advantages of the approach are multiple. Firstly, the gas turbine represents about 25 % of the total weight of the engine, so, its replacement by a simpler system will lead to a decrease in engine weight. Secondly, the most important limitations for the modern gas turbine engines are related to the maximum temperature at the turbine inlet. As the turbine blade material can only withstand a certain maximum temperature, in order to maximize the temperature of the burned gas at the combustor exhaust, and therefore the performances of the engine, the turbine blades, especially for the first rows, need to be cooled. Given the dimensions and the complex geometry of the typical turbine blade, the design and machining of the cooling channels to and through the blades is a difficult and expensive process. The replacement of the turbine by a simpler power device would, therefore, simplify the design and the manufacturing of the engine and lower its costs. Thirdly, a gas turbine is a very complex machine, including a large number of rotating parts subjected to high temperature, and typically made from expensive and hard to machine materials. A simpler power device would lower significantly the time and the costs allocated to design, manufacturing and maintenance, while reducing the failure risks in both manufacturing and exploitation by reducing the number of parts. Finally, the dimensions of the engine, particularly its length, can also be reduced by replacing a series of turbine disks and stators by a more compact solution.
The combustor assembly contains several can combustors rotating together and connected together through a disk to a central shaft and enclosed in a pressurized shroud that rotates together with the combustor assembly. The shaft of the combustor assembly is connected, and provides power, to a compressor upstream of the combustor that provides pressure to the combustor shroud. The remaining energy will be used to power the aircraft, via a set of exhaust nozzles that collect the flow from each combustor and accelerate it to provide reactive thrust. The fraction of the energy transferred to the shaft is controlled through the shape of the rotating combustor nozzles, and the direction of the jet exiting the combustors. The tangential impulse transmitted to the central shaft balances the compressor work. The remaining energy, both potential (pressure) and kinetic (velocity) is extracted from the flow by means of the engine exhaust nozzle.
The combustors equipping the TIDE engine employ supersonic combustion, aiming for a radical increase in the efficiency of the propulsion system and its suitability for supersonic and hypersonic flight. The approach used by TIDE to supersonic combustion is the PDC.
The main challenge related to PDC and addressed by TIDE is the issue of operating frequency. The typical detonation frequency in PDEs is of the order 10 Hz while it is well known that high frequency PDC have several important advantages. Besides the obvious mechanical issues related to vibration and oscillating loads, the main limitation for the operating frequency of the PDC resides in the approach used to control the admission of the work fluid in the PDC. To ensure the correct air flow through the combustor, the classical PDE design proposes a set of valves that open and close the admission of the air, or air-fuel mixture, in the combustor. The main problem in this approach is the high wear experienced by the valves, even more so at high frequencies. Supplementary, the valves are subject to very high operating temperatures, and will induce pressure losses in the flow. TIDE focused on a valveless designs, based on a system of shock waves generated by the interaction of supersonic jets and Hartman resonators that provide carefully timed pressure gradients in the flow acting line an aerodynamic valve.
Another issue tackled by TIDE was the initiation of the detonation wave, strongly dependent on the inlet conditions. A solution to raise the temperature up to the self – ignition values of the fuel (Hydrogen, in TIDE), by means of the same system of shock waves was sough during the project, also based on the preheating of the air entering the PDC by the TIDE compressor upstream. As a backup solution, the use of an electronically controlled spark plug was considered.
Another problem that was investigated in TIDE was the optimal geometry of the PDC exit nozzle. Considering the fact that, in order to increase the overall TIDE engine efficiency, the combustors must provide the highest possible impulse on a direction other than along the combustor axis, the optimal direction with respect to the engine performances and constructive solution, as well as the minimization of pressure losses due to the deflection of the flow have was studied, and the required deflection angle was determined.
Also important was the definition of the optimal compressor geometry, taking into account the rotation of the downstream combustor, and the discontinuous discharge of the combustor shroud. A high frequency PDC somewhat alleviates the problem, but the effect on compressor stability had nevertheless to be assessed. Since the combustion process is supersonic, the need to decelerate the flow upstream of the combustor disappears; therefore, the presence of the compressor stator vanes was no longer required, thus reducing the pressure losses during the passage between the rotating and fixed blades.
Finally, the optimal fuel selection for the PDCs such as to allow the reliable initiation of the detonation wave was also of particular concern for the project research team. Most of the earlier research studies focused on gaseous fuels, mostly Hydrogen, methane, and propane. In TIDE, the first choice was propane, as it is the least dangerous fuel that may still undergo detonating combustion at usual pressures and temperatures. However, once a decision to aim for the self – ignition of the fuel, a more reactive fuel was selected, namely acetylene. Nevertheless, the numerical simulations carried out for the combustor indicated the occurrence of a very energetic hardly controllable explosion in the PDC, followed by flame flashback. Also, it proved extremely difficult to purchase high pressure acetylene supply systems, due, again, to safety concerns. Eventually, Hydrogen was selected as the TIDE PDC fuel, and the following detonation numerical simulations and experimental measurements were carried out using this fuel. Hydrogen also has the advantage of being ”greener”, as no carbon molecules are present in the combustion reactions, avoiding production of pollutants such as UHC, CO and CO2.
The most important result expected from the proposed project is to demonstrate that the power provided by the rotating PDCs can provide the energy to accelerate the compressor to the speed required for its design performance, with sufficient excess energy to power up the aircraft.
The power output of the PDC, estimated from the combined numerical simulations, theoretical cycle calculations and experimental measurements is, on average 1,732 kW (depending on the model, the power varies between 1,669 kW and 1,795 kW). The power required by the TIDE compressor at the design point is of 772 kW. This implies a usable TIDE engine power of around 960 kW, sufficient to power the engine.
A second achievement is expected to be the practical realization of a high frequency, self supporting ignition PDC. To achieve this, the combustor inlet was designed and tested to operate without mechanical valves, and the solution based on the system of shock waves generated by Hartman resonators was proven to prevent the detonation wave to propagate upstream.
The high frequency TIDE PDC is compact in all three spatial directions, allowing a significant reduction in engine dimensions and weight.
Due to the elimination of the classical engine turbine, the most important limitation of a gas turbine engine cycle, the maximum temperature is removed, the thermodynamic cycle estimated maximum temperature ranging between 2,860 K and 3,282 K (on average 3,071 K), and allowing an overall increase in the engine performance and efficiency. The project demonstrated, again based on a combination of theoretical considerations and experimental measurements the increase in theoretical cycle efficiency from 24 % to an average of 40.35 %.
Finally, the project provided a first attempt towards an integrated solution for the proposed concept, laying the foundation for building a demonstrator engine concept in the future.
Justification for all the values presented in this section is provided in the “Main scientific and technical results” section.
Objectives
Given the complexity of the task, and the limited resources available through the project, the scope of the proposed project was also limited, as it is not possible at this low TRL level to simultaneously address all possible issues raised by the new concept.
Instead, the main goal of the project is to prove the functionality and feasibility of the concept, opening the road towards developing a mature technology in the future. The proposed research focused on three modules, namely on the engine compressor, on the PDC that powers the engine, and on the assembly engine. As a result, the expected TRL at the end of the project was targeted to be 3 for the compressor and the entire engine, and 4 for the combustor. The objectives related to each module are presented in the following:
A. The compressor module.
The project focused on designing a stable and efficient compressor that can supply the PDCs with the required air flow and pressure, under the time variable downstream pressure conditions imposed by the operation of the PDCs valves. The objectives of the module are:
A1. Definition of the compressor operating parameters, constructive solution and geometry
A2. Numerical optimization of the compressor geometry
A3. Geometrical model of the compressor
B. The pulse detonation chamber module.
The project focused on designing, manufacturing and experimentally testing a PDC in order to demonstrate the capability of the PDC to power the TIDE engine. Due to the limited resources available compared the pre-existing TRL, the demonstrator that was manufactured and tested consisted of a single, stationary PDC.
The objectives of this module are:
B1. Definition of the combustor operating parameters, constructive solution and geometry
B2. Numerical optimization of the combustor geometry
B3. Geometrical model of the combustor
B4. Automated fuel injection and ignition system design
B5 Demonstrator design and manufacturing
B6. Experimental testing of the demonstrator
C. The overall engine module.
A first model of the TIDE engine concept was developed. The following objectives must be fulfilled, for this module:
C1. Definition of the engine operating parameters, performances, constructive solution and geometry
C2. Numerical simulation of TIDE flow path
C3. Geometrical model of the TIDE engine concept
Success metrics
At the beginning of the project, success metrics were defined as an indicator of the actual progress brought forward by the project, to allow the quantitative assessment of the success of the project:
The initial success metrics are presented below, along with the actual results of the project. It can be seen that most of the quantifiable objectives have been reached, and sometimes surpassed.
Table 1 – Success metrics and project achievements
Criterion Objective Result Variation [%]
Engine power [kW] 20-50 960 +1820
PDC operating temperature [K] 2,000 3071 +53.5
PDC operating frequency [Hz] 1,000 100 -90
PDC length [mm] 200 190 +5
PDC diameter [mm] 80 163 x 74 -55
Engine weight reduction [%] 20 33 +65
Increase in cycle thermal efficiency [%] 30 40.35 +34.5
TRL 3-4 3 (engine); 4 (PDC) 0
Two of the parameters require further consideration. First, the very large engine power must be regarded with sufficient reserve, as it results mainly from a estimation of the thermodynamic cycle of the engine, and does not take into account with sufficient accuracy the heat and pressure losses occurring in the supersonic flow in the real PDC, including shock wave losses, Also, the detonation combustion is assumed complete (even though a combustion completes coefficient is included in the calculations). Hence, it is very likely that the actual PDC power output is much lower. A better estimate of the PDC performances is provided by the engine flow numerical simulations, which indicate a cycle averaged thrust force of 6,125 N per PDC. Detailed numerical simulations and, most importantly, experimental measurements of the actual PDC thrust force are required to reach a reliable value for the energy output of the engine.
Secondly, the operating frequency is significantly lower than the targeted value, even if a significant increase with respect to the current state-of-the-art is obtained. The reason for the low operating frequency value was the need to use a spark plug for the ignition of the PDC, the PDC operating frequency being driven by the spark plug discharge frequency. Several solutions exist for this problem, and will be applied and tested in the future. Firstly, the incoming air will be preheated to values matching the compressor outlet temperature. Secondly, the intensity of the shock waves generated by the resonators will be increased through the aerodynamic optimization of the flow inside the PDC, based on the knowledge gained through the experimental campaign carried out in TIDE on the critical parameters controlling the flow aerodynamics and the generation of the oscillating shock waves.
Thirdly, an increase in the volume of the PDC experimental model will decrease the surface to volume ratio, diminishing the heat losses and improving the ignition conditions. It is noteworthy that the numerical simulations that neglect the heat losses, and the experiments carried out on a reduced scale experimental model that enhances heat losses, yield contradictory results with respect to the auto-ignition, indicating the key role heat and radical losses through the walls play in the ignition process.
Project Results:
The scientific and technical results of the project are presented in detail in the attached file "S&T results.pdf" (editable form in "S&T results.docx")
Potential Impact:
The results obtained in the project, and presented in the previous section, constitute the foundation for a marketable product in the next half of this century. A new, market available engine based on this concept will impact the air transport of the future in several ways.
First, the high efficiency cycle, together with the smaller dimensions implying lower weight and drag, will enable a decrease in the specific fuel consumption of the aviation engine. The high speed combustion process enhances the efficiency and completeness of the combustion process favourably impacting the engine emissions of greenhouse gas, especially as one can expect a continuing trend in toughening the pollution regulated restrictions in the future. It is also possible that due to the very small residence time characteristic for detonation, the NOx production to be diminished in comparison to classic deflagrations, but this issue require further numerical and experimental confirmation, since the higher reaction temperatures favour Nitrogen dissociation and thus may promote NOx formation.
The increased operating frequency of the PDC developed in TIDE allows increasing the specific impulse of the engine and allowing for a more compact combustor. Due to inertial effects, high frequency PDCs will also smooth out the mechanical vibrations in the engine and will improve the operating conditions for the compressor, which operates with fluctuating back-pressure. Even more importantly, PDC developed in this project has the potential for drastically stepping up the frequency once the detonation self – sustainability is solved, due to the demonstrated proper operation of the aerodynamic valves incorporated in the TIDE PDC.
The use of multiple PDCs operating out-of-phase, as proposed in this project, will reduce the overall noise emitted by the engine, which may be a significant problem, since detonations are much louder than classical deflagrations. Furthermore, the mechanical vibrations of the engine and the velocity fluctuations transmitted upstream are damped by the use of opposite phase pairs of PDCs. A secondary advantage of the TIDE concept compared to PJEs and classical PDEs is that it allows simple extraction of auxiliary power for the engine from the main shaft.
As it employs supersonic combustion, the TIDE engine will be an enabler for cheaper and easier supersonic or even hypersonic flight, contributing in increasing the mobility of the commercial customers and freight, an essential requirement for the future we imagine today. Also, the use of Hydrogen as fuel for the detonation combustion eliminates the emission of an entire set of Carbon (e.g. UHC, CO, CO2) and Sulphur based pollutants, which are common combustion products resulting from the use of typical aviation fuels, like kerosene, contributing to reduce the impact of Europe's air transport operations on the environment.
In themselves, the results of the present project demonstrated the viability of the PDC concept in laboratory conditions (TRL 4) and will provided a theoretical and numerical base for the full engine concept, raising its TRL to 3. Even if PDE has been a research topic for quite a while, by addressing some of the most important open issues raised by the concept, particularly the valveless PDC, the project will provide a much needed demonstration of PDE capabilities through its integration in a new concept engine.
At a European level, it should be noted that, historically, most of the work related to detonating combustion has been carried out in either the United State, or in Russia and its former empire. Together with other European efforts focused on the broader subject these days, the project provides a good opportunity for Europe to make up for the lost terrain and reduce the knowledge gap still existing.
The project also fostered European knowledge transfer between countries, as it involved partners from founding members of the EU (Belgium), later members (Sweden), new members (Romania), and also prospective members that recently gained the associated country status (Moldova).
Improved communication between scientists specialized in various fields is also a secondary result of the project. Since the research teams of the project involved many young researchers (note that two of the seven MC members are below 35 – dr. Cuciumita and dr. Saracoglu, and one below 40 – dr. Gherman), this enhanced communication may have quite an impact in the future cohesion and strength of European research.
Due to the complexity of the problem tackled in the project, and to the novelty of the concept, a significant number of open issues will still remain after the completion of the project. This creates an opportunity to develop subsequent research projects, where the results and the expertise accumulated through this one will be valorized and enhanced.
The project provided a knowledge increase in the field of supersonic combustion and new directions of research were opened for the consortium partners, also increasing the potential for new partnerships to be developed. The project will provide an excellent training ground for other related research interests of the consortium partners, such as space based applications, high speed aerodynamics, and combustion modelling, fields of interest for the European research community, where new research projects could be tackled with the knowledge gained here. The visibility and the prestige of the involved scientific and technical staff and of the host institutions was increased through the TIDE project and the specific research infrastructure available at the TIDE consortium partners was developed.
The project responds to the challenges of sustainable development, which implies meeting the needs of the present without endangering the ability of future generations to meet their own needs and development. Observing the sustainable development principle is a fundamental component in the project implementation. Through the planned activities, the project will tackle the main dimensions and themes of the European Union’s Sustainable Development Strategy, established through the Leipzig Charter, planning for actions that lead to a life quality continuous improvement, both for the current generations and for the future ones, and to an efficient use of resources and environment protection. This will be achieved both with respect to the environment protection issues, and to the economic and social component of the sustainable development concept.
The sustainable development environment component assumes the promotion of eco-efficient systems able to eliminate both the resource waste and the environment pollution and biosphere degrading processes that is systems that will not produce nature unusable or unrecoverable waste. From this point of view, the project promotes, by using non-Carbon based fuels, clean technologies and conducted research activities designed to reduce resources consumed by increasing the fuel efficiency of the aviation engine.
The organization of dissemination activities workshops aimed at the student body will impact upon raising the awareness of students and young engineers with respect to the scientific and technical innovation ongoing in the European aviation, raising their interest for a carrier in research and innovation, and preparing the new generation of young engineers for the challenges of the new century. The exposure of the young generation engineers and researchers to the concept developed in the project will help familiarizing them to it, enticing them to pursue further developments that will help putting the concept on the market in the future, and preparing them to readily accept the future major engine design change. Through its ground breaking character the project stand a significant chance of attracting high quality Romanian or foreign researchers interested in this promising new research field.
The proposed concept was introduced to major industrial partners by participating at the Aerodays 2015 event, and at the ASME TURBO Expo 2015 conference, in an effort to help catalyzing a quick response of the major aviation engines manufacturers to the proposed design change, once the concept becomes market ready.
Bringing the key results and benefits of the project to the general public attention will also help maximizing the project impact, by increasing the taxpayer confidence in the benefits of research for everyday life.
The dissemination of results towards the scientific community will accelerate the development of the concept and will foster the exchange of ideas and knowledge, which will help overcoming the existing challenges and also identify possible problems raised by the industrial application of the proposed concept, and propose new and better solutions.
Also, the increase in competitiveness brought by the project to the European aviation industry will be able to create new jobs, and contribute to a diminishing of unemployment, particularly for the young.
The main obstacle that might limit the expected impact is related to the yet unsolved issues related to the development of the concept that may still decrease the trust of the general scientific and industrial community in the concept, due to the yet low TRL. This obstacle may be overcome by further research efforts aimed at addressing the remaining problems and at further raising the TIDE concept TRL.
Another obstacle resides in the inertia of the aviation industry in adopting the new design, once this is market ready. To alleviate this, dissemination activities aimed at the industry stakeholders have to be enhanced in the future even at this still early stage, in order to increase awareness and plant the seeds for the new design transition once the concept is mature.
List of Websites:
Project website: tide.comoti.ro
Relevant contact details:
Romanian Research and Development Institute for Gas Turbines COMOTI
220D, Iuliu Maniu Blvd, Sector 6, 061126, Bucharest, Romania
Project coordinator:
Dr. Ionut PORUMBEL, tel. +40720090775, email ionut.porumbel@comoti.ro
Deputy coordinator and Engine Module leader:
Dr. Cleopatra Florentina CUCIUMITA, Tel. +4073285620, email cleopatra.cuciumita@comoti.ro
Scientific representative and Combustor Module leader
Dr. Constantin Eusebiu HRITCU, Tel. +40722368412, email eusebiu_hritcu@yahoo.com
Other management Committee members:
Dr. Bogdan George GHERMAN (Compressor Module leader), bogdan.gherman@comoti.ro
Dr. Florin Gabriel FLOREAN (Experimental Concept Validation WP leader), florin.florean@comoti.ro
Adrian TOMA (Manufacturing and Assembly leader), adrian.toma@comoti.ro
Legal advisor:
Leonard TRIFU, leonard.trifu@comoti.ro
Financial advisor:
Luminita PRECOB, luminita.precob@comoti.ro
Lund University
5c, Paradisgatan, 22100, Lund, Sweden
Partner team responsible and Numerical Simulations WP leader:
Prof. Dr. Johan REVSTEDT, Tel. +46462224302, email johan.revstedt@energy.lth.se
Von Karman Institute for Fluid Dynamics
72, Chaussee de Waterloo, 1640, Rhode Saint Genese, Belgium
Partner team responsible and Preliminary Concept Design WP leader:
Dr. Bayindir Huseyin SARACOGLU, Tel. +32 476 44 34 05, email saracog@vki.ac.be
Institute for Applied Physics
5, Academiei St., MD2028, Chisinau, Moldova (Republic of)
Partner team responsible and Geometrical Modeling and Design WP leader:
Tudor CUCIUC, Tel. +37360226707, email cuciuctud@yahoo.com
The TIDE project was aimed at developing a breakthrough propulsion system technology envisioned to trigger a step change in air transportation in the second half of this century. This new, radical approach to creating propulsion power aims at reducing the weight, the complexity, and the cost of the classical, air breathing, aviation engine and, thus, at significantly reducing the overall fuel consumption and, consequently, the total amount of pollutants emission.
The central idea of the proposed propulsion technology is the replacement of the gas turbine in a typical aviation engine of today by a simpler and at least as effective system. A power device able to replace the gas turbine in an aviation engine must, while providing the advantages discussed earlier, fulfil the functional role of the turbine. This role consists in converting the working fluid kinetic energy (velocity) and potential energy (pressure) into work used to propel the aircraft and to compress the air upstream of the combustor by means of blade rows forming divergent channel. The concept proposed in TIDE uses the conservation of impulse for the combustor exhaust jet released tangentially, to rotate the entire combustor assembly.
Even though the rotating combustor concept is, in itself, a breakthrough new technology, in order to trigger a step change in the propulsion technology of the future air transportation a radical approach to combustion is also proposed, namely supersonic combustion, that will allow efficient propulsion for supersonic and hypersonic flight, by means of a Pulsed Detonation Combustor (PDC).
Given the complexity of the task, and the limited resources available through the project, the scope of the project was limited. The main goal of the project is to prove the functionality and feasibility of the concept, opening the road towards developing a mature technology in the future. The project was successful in this respect,. Three PDC experimental models based on different geometrical configurations have been designed, manufactured and experimentally tested, and detonation was achieved in all three. The admission of air into the tested PDCs is controlled by a couple of aerodynamic valves created at the inlet by system of shock waves generated by the interaction of two incoming supersonic jets with Hartman resonators of various geometries. Thus, the operating frequency of the PDC can be raised significantly in comparison to the existing solutions in the literature, allowing the increase of the engine’s performances.
Currently, the limiting factor for the operating frequency of the TIDE PDCs is the frequency of the ignition spark. Further research efforts are needed to ensure self – ignition and self – sustained pulsed detonation, thus allowing a further major operating frequency increase.
A PDC demonstrator was designed, manufactured and tested during the project’s experimental program. Besides the proof of concept they provided, the experimental measurements carried out in the project allowed the selection of several very promising geometries for achieving an optimal jet – resonator interaction, and identified the critical geometrical parameters that control the operation of a PDC based on aerodynamic valves created by oscillating shock waves.
Numerical simulations of the TIDE compressor, operating under variable back pressure conditions, specific for a PDC driven engine, of the TIDE combustor, and of the entire TIDE engine were carried out with various degrees of success. Based on these, preliminary models for the compressor and for the entire engine were developed. Further research efforts are needed in order to optimize the engine components and to fully integrate them in an operational engine.
The results of the project were disseminated via a project website, seven peer reviewed scientific papers, participation in fairs and exhibitions, where a scaled model of the engine was presented, a TV interview, and several articles in popular science magazines. One of the most important achievements related to dissemination was the invitation the project consortium received to present TIDE at Aerodays 2015, in London, UK.
Project Context and Objectives:
Context
The TIDE concept proposes the use of conservation of impulse for the combustor exhaust jet released tangentially, to rotate the entire combustor assembly, thus eliminating the need for a turbine by a simpler and at least as effective system. The advantages of the approach are multiple. Firstly, the gas turbine represents about 25 % of the total weight of the engine, so, its replacement by a simpler system will lead to a decrease in engine weight. Secondly, the most important limitations for the modern gas turbine engines are related to the maximum temperature at the turbine inlet. As the turbine blade material can only withstand a certain maximum temperature, in order to maximize the temperature of the burned gas at the combustor exhaust, and therefore the performances of the engine, the turbine blades, especially for the first rows, need to be cooled. Given the dimensions and the complex geometry of the typical turbine blade, the design and machining of the cooling channels to and through the blades is a difficult and expensive process. The replacement of the turbine by a simpler power device would, therefore, simplify the design and the manufacturing of the engine and lower its costs. Thirdly, a gas turbine is a very complex machine, including a large number of rotating parts subjected to high temperature, and typically made from expensive and hard to machine materials. A simpler power device would lower significantly the time and the costs allocated to design, manufacturing and maintenance, while reducing the failure risks in both manufacturing and exploitation by reducing the number of parts. Finally, the dimensions of the engine, particularly its length, can also be reduced by replacing a series of turbine disks and stators by a more compact solution.
The combustor assembly contains several can combustors rotating together and connected together through a disk to a central shaft and enclosed in a pressurized shroud that rotates together with the combustor assembly. The shaft of the combustor assembly is connected, and provides power, to a compressor upstream of the combustor that provides pressure to the combustor shroud. The remaining energy will be used to power the aircraft, via a set of exhaust nozzles that collect the flow from each combustor and accelerate it to provide reactive thrust. The fraction of the energy transferred to the shaft is controlled through the shape of the rotating combustor nozzles, and the direction of the jet exiting the combustors. The tangential impulse transmitted to the central shaft balances the compressor work. The remaining energy, both potential (pressure) and kinetic (velocity) is extracted from the flow by means of the engine exhaust nozzle.
The combustors equipping the TIDE engine employ supersonic combustion, aiming for a radical increase in the efficiency of the propulsion system and its suitability for supersonic and hypersonic flight. The approach used by TIDE to supersonic combustion is the PDC.
The main challenge related to PDC and addressed by TIDE is the issue of operating frequency. The typical detonation frequency in PDEs is of the order 10 Hz while it is well known that high frequency PDC have several important advantages. Besides the obvious mechanical issues related to vibration and oscillating loads, the main limitation for the operating frequency of the PDC resides in the approach used to control the admission of the work fluid in the PDC. To ensure the correct air flow through the combustor, the classical PDE design proposes a set of valves that open and close the admission of the air, or air-fuel mixture, in the combustor. The main problem in this approach is the high wear experienced by the valves, even more so at high frequencies. Supplementary, the valves are subject to very high operating temperatures, and will induce pressure losses in the flow. TIDE focused on a valveless designs, based on a system of shock waves generated by the interaction of supersonic jets and Hartman resonators that provide carefully timed pressure gradients in the flow acting line an aerodynamic valve.
Another issue tackled by TIDE was the initiation of the detonation wave, strongly dependent on the inlet conditions. A solution to raise the temperature up to the self – ignition values of the fuel (Hydrogen, in TIDE), by means of the same system of shock waves was sough during the project, also based on the preheating of the air entering the PDC by the TIDE compressor upstream. As a backup solution, the use of an electronically controlled spark plug was considered.
Another problem that was investigated in TIDE was the optimal geometry of the PDC exit nozzle. Considering the fact that, in order to increase the overall TIDE engine efficiency, the combustors must provide the highest possible impulse on a direction other than along the combustor axis, the optimal direction with respect to the engine performances and constructive solution, as well as the minimization of pressure losses due to the deflection of the flow have was studied, and the required deflection angle was determined.
Also important was the definition of the optimal compressor geometry, taking into account the rotation of the downstream combustor, and the discontinuous discharge of the combustor shroud. A high frequency PDC somewhat alleviates the problem, but the effect on compressor stability had nevertheless to be assessed. Since the combustion process is supersonic, the need to decelerate the flow upstream of the combustor disappears; therefore, the presence of the compressor stator vanes was no longer required, thus reducing the pressure losses during the passage between the rotating and fixed blades.
Finally, the optimal fuel selection for the PDCs such as to allow the reliable initiation of the detonation wave was also of particular concern for the project research team. Most of the earlier research studies focused on gaseous fuels, mostly Hydrogen, methane, and propane. In TIDE, the first choice was propane, as it is the least dangerous fuel that may still undergo detonating combustion at usual pressures and temperatures. However, once a decision to aim for the self – ignition of the fuel, a more reactive fuel was selected, namely acetylene. Nevertheless, the numerical simulations carried out for the combustor indicated the occurrence of a very energetic hardly controllable explosion in the PDC, followed by flame flashback. Also, it proved extremely difficult to purchase high pressure acetylene supply systems, due, again, to safety concerns. Eventually, Hydrogen was selected as the TIDE PDC fuel, and the following detonation numerical simulations and experimental measurements were carried out using this fuel. Hydrogen also has the advantage of being ”greener”, as no carbon molecules are present in the combustion reactions, avoiding production of pollutants such as UHC, CO and CO2.
The most important result expected from the proposed project is to demonstrate that the power provided by the rotating PDCs can provide the energy to accelerate the compressor to the speed required for its design performance, with sufficient excess energy to power up the aircraft.
The power output of the PDC, estimated from the combined numerical simulations, theoretical cycle calculations and experimental measurements is, on average 1,732 kW (depending on the model, the power varies between 1,669 kW and 1,795 kW). The power required by the TIDE compressor at the design point is of 772 kW. This implies a usable TIDE engine power of around 960 kW, sufficient to power the engine.
A second achievement is expected to be the practical realization of a high frequency, self supporting ignition PDC. To achieve this, the combustor inlet was designed and tested to operate without mechanical valves, and the solution based on the system of shock waves generated by Hartman resonators was proven to prevent the detonation wave to propagate upstream.
The high frequency TIDE PDC is compact in all three spatial directions, allowing a significant reduction in engine dimensions and weight.
Due to the elimination of the classical engine turbine, the most important limitation of a gas turbine engine cycle, the maximum temperature is removed, the thermodynamic cycle estimated maximum temperature ranging between 2,860 K and 3,282 K (on average 3,071 K), and allowing an overall increase in the engine performance and efficiency. The project demonstrated, again based on a combination of theoretical considerations and experimental measurements the increase in theoretical cycle efficiency from 24 % to an average of 40.35 %.
Finally, the project provided a first attempt towards an integrated solution for the proposed concept, laying the foundation for building a demonstrator engine concept in the future.
Justification for all the values presented in this section is provided in the “Main scientific and technical results” section.
Objectives
Given the complexity of the task, and the limited resources available through the project, the scope of the proposed project was also limited, as it is not possible at this low TRL level to simultaneously address all possible issues raised by the new concept.
Instead, the main goal of the project is to prove the functionality and feasibility of the concept, opening the road towards developing a mature technology in the future. The proposed research focused on three modules, namely on the engine compressor, on the PDC that powers the engine, and on the assembly engine. As a result, the expected TRL at the end of the project was targeted to be 3 for the compressor and the entire engine, and 4 for the combustor. The objectives related to each module are presented in the following:
A. The compressor module.
The project focused on designing a stable and efficient compressor that can supply the PDCs with the required air flow and pressure, under the time variable downstream pressure conditions imposed by the operation of the PDCs valves. The objectives of the module are:
A1. Definition of the compressor operating parameters, constructive solution and geometry
A2. Numerical optimization of the compressor geometry
A3. Geometrical model of the compressor
B. The pulse detonation chamber module.
The project focused on designing, manufacturing and experimentally testing a PDC in order to demonstrate the capability of the PDC to power the TIDE engine. Due to the limited resources available compared the pre-existing TRL, the demonstrator that was manufactured and tested consisted of a single, stationary PDC.
The objectives of this module are:
B1. Definition of the combustor operating parameters, constructive solution and geometry
B2. Numerical optimization of the combustor geometry
B3. Geometrical model of the combustor
B4. Automated fuel injection and ignition system design
B5 Demonstrator design and manufacturing
B6. Experimental testing of the demonstrator
C. The overall engine module.
A first model of the TIDE engine concept was developed. The following objectives must be fulfilled, for this module:
C1. Definition of the engine operating parameters, performances, constructive solution and geometry
C2. Numerical simulation of TIDE flow path
C3. Geometrical model of the TIDE engine concept
Success metrics
At the beginning of the project, success metrics were defined as an indicator of the actual progress brought forward by the project, to allow the quantitative assessment of the success of the project:
The initial success metrics are presented below, along with the actual results of the project. It can be seen that most of the quantifiable objectives have been reached, and sometimes surpassed.
Table 1 – Success metrics and project achievements
Criterion Objective Result Variation [%]
Engine power [kW] 20-50 960 +1820
PDC operating temperature [K] 2,000 3071 +53.5
PDC operating frequency [Hz] 1,000 100 -90
PDC length [mm] 200 190 +5
PDC diameter [mm] 80 163 x 74 -55
Engine weight reduction [%] 20 33 +65
Increase in cycle thermal efficiency [%] 30 40.35 +34.5
TRL 3-4 3 (engine); 4 (PDC) 0
Two of the parameters require further consideration. First, the very large engine power must be regarded with sufficient reserve, as it results mainly from a estimation of the thermodynamic cycle of the engine, and does not take into account with sufficient accuracy the heat and pressure losses occurring in the supersonic flow in the real PDC, including shock wave losses, Also, the detonation combustion is assumed complete (even though a combustion completes coefficient is included in the calculations). Hence, it is very likely that the actual PDC power output is much lower. A better estimate of the PDC performances is provided by the engine flow numerical simulations, which indicate a cycle averaged thrust force of 6,125 N per PDC. Detailed numerical simulations and, most importantly, experimental measurements of the actual PDC thrust force are required to reach a reliable value for the energy output of the engine.
Secondly, the operating frequency is significantly lower than the targeted value, even if a significant increase with respect to the current state-of-the-art is obtained. The reason for the low operating frequency value was the need to use a spark plug for the ignition of the PDC, the PDC operating frequency being driven by the spark plug discharge frequency. Several solutions exist for this problem, and will be applied and tested in the future. Firstly, the incoming air will be preheated to values matching the compressor outlet temperature. Secondly, the intensity of the shock waves generated by the resonators will be increased through the aerodynamic optimization of the flow inside the PDC, based on the knowledge gained through the experimental campaign carried out in TIDE on the critical parameters controlling the flow aerodynamics and the generation of the oscillating shock waves.
Thirdly, an increase in the volume of the PDC experimental model will decrease the surface to volume ratio, diminishing the heat losses and improving the ignition conditions. It is noteworthy that the numerical simulations that neglect the heat losses, and the experiments carried out on a reduced scale experimental model that enhances heat losses, yield contradictory results with respect to the auto-ignition, indicating the key role heat and radical losses through the walls play in the ignition process.
Project Results:
The scientific and technical results of the project are presented in detail in the attached file "S&T results.pdf" (editable form in "S&T results.docx")
Potential Impact:
The results obtained in the project, and presented in the previous section, constitute the foundation for a marketable product in the next half of this century. A new, market available engine based on this concept will impact the air transport of the future in several ways.
First, the high efficiency cycle, together with the smaller dimensions implying lower weight and drag, will enable a decrease in the specific fuel consumption of the aviation engine. The high speed combustion process enhances the efficiency and completeness of the combustion process favourably impacting the engine emissions of greenhouse gas, especially as one can expect a continuing trend in toughening the pollution regulated restrictions in the future. It is also possible that due to the very small residence time characteristic for detonation, the NOx production to be diminished in comparison to classic deflagrations, but this issue require further numerical and experimental confirmation, since the higher reaction temperatures favour Nitrogen dissociation and thus may promote NOx formation.
The increased operating frequency of the PDC developed in TIDE allows increasing the specific impulse of the engine and allowing for a more compact combustor. Due to inertial effects, high frequency PDCs will also smooth out the mechanical vibrations in the engine and will improve the operating conditions for the compressor, which operates with fluctuating back-pressure. Even more importantly, PDC developed in this project has the potential for drastically stepping up the frequency once the detonation self – sustainability is solved, due to the demonstrated proper operation of the aerodynamic valves incorporated in the TIDE PDC.
The use of multiple PDCs operating out-of-phase, as proposed in this project, will reduce the overall noise emitted by the engine, which may be a significant problem, since detonations are much louder than classical deflagrations. Furthermore, the mechanical vibrations of the engine and the velocity fluctuations transmitted upstream are damped by the use of opposite phase pairs of PDCs. A secondary advantage of the TIDE concept compared to PJEs and classical PDEs is that it allows simple extraction of auxiliary power for the engine from the main shaft.
As it employs supersonic combustion, the TIDE engine will be an enabler for cheaper and easier supersonic or even hypersonic flight, contributing in increasing the mobility of the commercial customers and freight, an essential requirement for the future we imagine today. Also, the use of Hydrogen as fuel for the detonation combustion eliminates the emission of an entire set of Carbon (e.g. UHC, CO, CO2) and Sulphur based pollutants, which are common combustion products resulting from the use of typical aviation fuels, like kerosene, contributing to reduce the impact of Europe's air transport operations on the environment.
In themselves, the results of the present project demonstrated the viability of the PDC concept in laboratory conditions (TRL 4) and will provided a theoretical and numerical base for the full engine concept, raising its TRL to 3. Even if PDE has been a research topic for quite a while, by addressing some of the most important open issues raised by the concept, particularly the valveless PDC, the project will provide a much needed demonstration of PDE capabilities through its integration in a new concept engine.
At a European level, it should be noted that, historically, most of the work related to detonating combustion has been carried out in either the United State, or in Russia and its former empire. Together with other European efforts focused on the broader subject these days, the project provides a good opportunity for Europe to make up for the lost terrain and reduce the knowledge gap still existing.
The project also fostered European knowledge transfer between countries, as it involved partners from founding members of the EU (Belgium), later members (Sweden), new members (Romania), and also prospective members that recently gained the associated country status (Moldova).
Improved communication between scientists specialized in various fields is also a secondary result of the project. Since the research teams of the project involved many young researchers (note that two of the seven MC members are below 35 – dr. Cuciumita and dr. Saracoglu, and one below 40 – dr. Gherman), this enhanced communication may have quite an impact in the future cohesion and strength of European research.
Due to the complexity of the problem tackled in the project, and to the novelty of the concept, a significant number of open issues will still remain after the completion of the project. This creates an opportunity to develop subsequent research projects, where the results and the expertise accumulated through this one will be valorized and enhanced.
The project provided a knowledge increase in the field of supersonic combustion and new directions of research were opened for the consortium partners, also increasing the potential for new partnerships to be developed. The project will provide an excellent training ground for other related research interests of the consortium partners, such as space based applications, high speed aerodynamics, and combustion modelling, fields of interest for the European research community, where new research projects could be tackled with the knowledge gained here. The visibility and the prestige of the involved scientific and technical staff and of the host institutions was increased through the TIDE project and the specific research infrastructure available at the TIDE consortium partners was developed.
The project responds to the challenges of sustainable development, which implies meeting the needs of the present without endangering the ability of future generations to meet their own needs and development. Observing the sustainable development principle is a fundamental component in the project implementation. Through the planned activities, the project will tackle the main dimensions and themes of the European Union’s Sustainable Development Strategy, established through the Leipzig Charter, planning for actions that lead to a life quality continuous improvement, both for the current generations and for the future ones, and to an efficient use of resources and environment protection. This will be achieved both with respect to the environment protection issues, and to the economic and social component of the sustainable development concept.
The sustainable development environment component assumes the promotion of eco-efficient systems able to eliminate both the resource waste and the environment pollution and biosphere degrading processes that is systems that will not produce nature unusable or unrecoverable waste. From this point of view, the project promotes, by using non-Carbon based fuels, clean technologies and conducted research activities designed to reduce resources consumed by increasing the fuel efficiency of the aviation engine.
The organization of dissemination activities workshops aimed at the student body will impact upon raising the awareness of students and young engineers with respect to the scientific and technical innovation ongoing in the European aviation, raising their interest for a carrier in research and innovation, and preparing the new generation of young engineers for the challenges of the new century. The exposure of the young generation engineers and researchers to the concept developed in the project will help familiarizing them to it, enticing them to pursue further developments that will help putting the concept on the market in the future, and preparing them to readily accept the future major engine design change. Through its ground breaking character the project stand a significant chance of attracting high quality Romanian or foreign researchers interested in this promising new research field.
The proposed concept was introduced to major industrial partners by participating at the Aerodays 2015 event, and at the ASME TURBO Expo 2015 conference, in an effort to help catalyzing a quick response of the major aviation engines manufacturers to the proposed design change, once the concept becomes market ready.
Bringing the key results and benefits of the project to the general public attention will also help maximizing the project impact, by increasing the taxpayer confidence in the benefits of research for everyday life.
The dissemination of results towards the scientific community will accelerate the development of the concept and will foster the exchange of ideas and knowledge, which will help overcoming the existing challenges and also identify possible problems raised by the industrial application of the proposed concept, and propose new and better solutions.
Also, the increase in competitiveness brought by the project to the European aviation industry will be able to create new jobs, and contribute to a diminishing of unemployment, particularly for the young.
The main obstacle that might limit the expected impact is related to the yet unsolved issues related to the development of the concept that may still decrease the trust of the general scientific and industrial community in the concept, due to the yet low TRL. This obstacle may be overcome by further research efforts aimed at addressing the remaining problems and at further raising the TIDE concept TRL.
Another obstacle resides in the inertia of the aviation industry in adopting the new design, once this is market ready. To alleviate this, dissemination activities aimed at the industry stakeholders have to be enhanced in the future even at this still early stage, in order to increase awareness and plant the seeds for the new design transition once the concept is mature.
List of Websites:
Project website: tide.comoti.ro
Relevant contact details:
Romanian Research and Development Institute for Gas Turbines COMOTI
220D, Iuliu Maniu Blvd, Sector 6, 061126, Bucharest, Romania
Project coordinator:
Dr. Ionut PORUMBEL, tel. +40720090775, email ionut.porumbel@comoti.ro
Deputy coordinator and Engine Module leader:
Dr. Cleopatra Florentina CUCIUMITA, Tel. +4073285620, email cleopatra.cuciumita@comoti.ro
Scientific representative and Combustor Module leader
Dr. Constantin Eusebiu HRITCU, Tel. +40722368412, email eusebiu_hritcu@yahoo.com
Other management Committee members:
Dr. Bogdan George GHERMAN (Compressor Module leader), bogdan.gherman@comoti.ro
Dr. Florin Gabriel FLOREAN (Experimental Concept Validation WP leader), florin.florean@comoti.ro
Adrian TOMA (Manufacturing and Assembly leader), adrian.toma@comoti.ro
Legal advisor:
Leonard TRIFU, leonard.trifu@comoti.ro
Financial advisor:
Luminita PRECOB, luminita.precob@comoti.ro
Lund University
5c, Paradisgatan, 22100, Lund, Sweden
Partner team responsible and Numerical Simulations WP leader:
Prof. Dr. Johan REVSTEDT, Tel. +46462224302, email johan.revstedt@energy.lth.se
Von Karman Institute for Fluid Dynamics
72, Chaussee de Waterloo, 1640, Rhode Saint Genese, Belgium
Partner team responsible and Preliminary Concept Design WP leader:
Dr. Bayindir Huseyin SARACOGLU, Tel. +32 476 44 34 05, email saracog@vki.ac.be
Institute for Applied Physics
5, Academiei St., MD2028, Chisinau, Moldova (Republic of)
Partner team responsible and Geometrical Modeling and Design WP leader:
Tudor CUCIUC, Tel. +37360226707, email cuciuctud@yahoo.com
