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Content archived on 2024-05-29

Post-treAtment for the next Generation Of Diesel Engines

Final Report Summary - PAGODE (Post-treAtment for the next Generation Of Diesel Engines)

The aim of the PAGODE project was to provide a comprehensive, system-oriented development approach on potentially new after treatment processes that will be required by the next homogeneous charge compression ignition (HCCI) combustion systems, taking into account the future fuel generations.

The scientific objectives of this project were:
- to understand the complex kinetic mechanisms and chemical principles of CO/HC low temperature oxidation for the next generation diesel engines exhaust environment;
- to develop a robust, efficient, and accurate computational models to analyse, simulate and improve the performance of next generation catalytic converters (a transient one-dimensional model, and a single spatial dimension will be developed at a first step and then 2D and 3D calculations will be investigated and integrated).

The technological objectives were:
- to formulate, develop, test and optimise advanced new catalyst formulation for CO/HC low temperature oxidation;
- to design, develop and test emerging flexible low temperature oxidation technologies based on plasma concepts;
- to perform a powertrain system synthesis and evaluate, for next generation power trains, the needed requirements and boundary conditions to implement at their best the advanced after treatment processes in diesel engines.

This project worked through four main identified and focused directions, organised into respective work packages (WPs):

WP 1: Low temperature oxidation of CO and HC: fuel effect and oxidation mechanisms in advanced homogenous combustion processes.
The transverse work package WP1 was dedicated to the scientific and research activities on low temperature oxidation of high levels of CO and HC emissions, as created by HCCI-like combustion modes. This item was divided into data collection, complementary emissions measurements and modelling parts. From data collection and complementary emissions measurements part, the main objective was to get reliable data on CO and HC emissions and exhaust temperatures for the further system definition and to supply boundary conditions for the simulations tools. The modelling aim was then the development of innovative tools for the design and the improvement of exhaust lines using the developed advanced catalytic devices.

WP 2: Advanced new catalyst formulations for high CO, HC concentration and low temperature oxidation.
During WP2, fundamental investigation of advanced catalyst formulation for low temperature oxidation of high level of CO and HC was performed by Chalmers University in collaboration with CRF and JM. The work carried out between the three partners allowed us to determine the best catalyst components and preparation route to use for improved catalytic activities in respect to HCCI conditions. Newly developed technologies were benchmarked against the Johnson Matthey reference catalyst, current commercially available technology. Scale up studies of the new formulation (JM) and synthetic gas bench measurements (JM and CRF) were carried out to ensure that the newly developed catalyst has the same properties as the catalyst powder developed previously by Chalmers University. Progresses in terms of catalyst performance, conversion efficiency, low light-off temperature, poisoning effects, durability and precious content metal were monitored and reported during the project.

It was shown during this project that catalyst performance can be significantly improved with the new developed formulation. Testing of the advanced DOC formulation show that increasing CO concentration will increase performances due to positive order kinetics of CO regarding platinum supported on ceria. Low temperature oxidation was improved while minimising in the same time the cost of the DOC introducing larger amount of palladium in the catalyst formulation. Substituting platinum with palladium in DOCs results in precious metal cost saving and will improve thermal stability and performances in aged catalysts. Newly developed technology showed a big improvement compare to standard commercial diesel oxidation catalyst. Improvement on sulphur tolerance and support material stability can be obtained by adapting support material (mixed oxide components), layering of the catalyst and modifying precious metal distributions within the layers of the catalyst. Engine rich purges can be implemented in order to recover activity after sulphation and low sulphur fuel introduction will contribute to maintain high activity at low temperature. This project has proved that lowering emission pollutants can be achieved only with active collaboration between engine designs, high quality fuels and advanced emissions controls strategies.

WP 3: Emerging flexible low temperature oxidation technologies.
A major element of work package WP 3 was the incorporation of plasma technology into a diesel engine exhaust line. The work on this subject which was accomplished over the three year period took place on three different experimental levels and at three different corresponding locales. The three different experimental scales were laboratory-scale, synthetic gas bench (SGB)-scale, and engine test benchscale, and were performed at Supelec, PSA-Velizy, and IFP-Lyon, respectively. Electrical system design and construction for support of the experimental work on the SGB and engine test bench work was also done at Supelec.

Over the three-year period of the PAGODE project, significant progress was made over three different experimental scales on the subject of the emergent technology of plasma treatment of diesel exhaust gas coupled with oxidation catalysts. Two different ideas were tested on all three experimental scales, that of in-line plasma treatment of the gas upstream of the catalyst and then of ozone injection upstream of the catalyst. The idea for ozone injection upstream of the catalyst came about because of early laboratory-scale experiments as well as disappointing results in terms of the energy efficiency of the enhancement of catalyst performance by the in-line plasma treatment upstream up the catalyst on both the synthetic gas bench and engine test bench scales. In-line treatment of diesel exhaust gas upstream of a catalyst has been shown to have serious energy efficiency issues, combined with the need for a robust (expensive) ceramic-coated plasma reactor. Ozone injection addresses both of these issues, but its testing in the PAGODE project was exploratory and therefore not complete. Therefore, while plasma technology has been found to be lacking in certain aspects for this application, an alternative emergent technology has been identified and tested, and so further research and investigation is warranted.

WP 4: System synthesis for next powertrain generation.
The objective was to evaluate and optimise the newly developed concepts such as catalytic formulations and plasma reactor on the HCCI engine. Initially, ozoniser tests were not planned. However, regarding the potential identified during WP3, a full-scale ozoniser was also tested on the HCCI engine coupled with selected DOC formulations.

The full-size NTP reactor showed a quite limited positive assistance effect. Only a very small additional effect on HC was observed and this one tended to be far less efficient than DOC HC storage effect. The impact was higher on CO, with a maximum conversion comprised between 10 and 25 %. As a side effect, the plasma activation led to a significant NOx increase. Moreover, such a NTP reactor in the exhaust line remains fragile: two failures were encountered during the test phase. Due to the relatively high power requirement (500 W), the estimated fuel consumption penalty is estimated about 3 % and remains an issue.

Regarding the full-size ozoniser device, additional effect on HC and CO appeared mainly at very low temperature, with better results than for the NTP at idle. Furthermore, the ozoniser showed a better potential regarding NOx, although 25 % power less was consumed. About 50 % NOx reduction efficiency was observed (low absolute NOx level ranging from 5 to 30 ppm). The reaction mechanism for NOx reduction is not clear yet and further research work is necessary to better understand both gas and catalytic phase reactions. However, several key points remain to be solved such as ozone production efficiency with air as feed gas (only oxygen was tested during the tests), electric consumption to limit fuel consumption penalty, packaging, durability, cost... The temperature efficiency window has to be identified and the absence of by-products emissions like ozone, N2O must also be validated.

The results of PAGODE will help automobile industry to develop affordable innovative technical solutions dedicated to the future diesel engine. PAGODE is the place where complementary skills are joining their efforts to answer technological challenges on the after treatment of the next generation of diesel engine.