Clean and efficient combustion requires an optimized combustion chamber. Such optimization depends on understanding phenomena such as the ignition rate and location as well as the associated chemistry of pollutant formation.
This integrated project will assess the effect of combustion chamber design properties on the ignition, local formation and reduction of NOx and unburned hydrocarbons (UHC) in gasoline engines. The project will deliver submodels which will be verified against engine data, for use in predictive multidimensional engine codes to permit the simultaneous minimization of both pollutants.
The validation process proved to be very successful, giving a high level of agreement between model predictions and experimental observations. For example, the NOx in the exhaust manifold is mainly due to Zeldovich NOx and not to prompt NOx formation. Furthermore, the NOx concentration reflects the integrated temperature and time history of the NOx formation process. The unburnt hydrocarbon emissions originate from three main sources. These are: the filling of crevice volumes with unburnt gas mixture, the adsorption and desorption of fuel vapour from oil layers on the cylinder walls, and valve leakage of unvapourised fuel deposits.
This project will be built from the hard and software tools developed in a previous EC project JOUE-CT90-0014 and an improved flamelet model with detailed chemistry. The advanced 2D laser diagnostics (LIF, PIV, LDA, mie scattering, single cycle flame contour analysis) will be revised and upgraded to the needs of practical applications in multidimensional computation. They will be applied to access the potential for further reduction of pollutant formation and to derive design criteria for improved combustion chambers and fuel characteristics.
Ignition: Universitat Stuttgart will model the reaction kinetics in the interface between the spark plasma and the unburned mixture. Cambridge University will extend the flamelet concept for turbulent intensity levels of order SL. Leeds University will measure turbulent flame speeds in homogeneous mixtures of reference fuels as function of pressure, temperature, equivalence ratio and turbulence intensity as well as length scales and quenching on approaching a cold wall. Daimler-Benz will complete experimental studies on flame kernel development in transparent engines as function of speed, load, ignition system, equivalence ratio and spark design.
NOx and UHC: Cambridge University will model the effects arising from the coexistence of rich and lean mixture pockets on NO and UHC formation using the flamelet concept and the strained flame library from Universitat Stuttgart. ENSMA will model the effects of mixture inhomogeneities on the effective turbulent burning velocity.
Universitat Stuttgart will quantify experimentally the structure and characteristic scales of inhomogeneous mixtures in the transparent square piston engine by applying advanced laser diagnostics and image proccesing. Universitat Heidelberg will identify local NO-sources and the temperature distribution in the square-piston engine using advanced 2D laser diagnostics. In addition the detailed reaction kinetics of NOx formation will be established and tested taking into account thermal NOx, prompt NOx in inhomogeneous flames and reaction channels via N20 and hydrocarbons species in detailed reaction schemes.
IFP will identify in-cylinder sources of UHC in a transparent engine having a cylindrical combustion chamber by using advanced 2D laser diagnostics. The results will be correlated with a UHC model accounting for flame quenching near walls and effects of crevices. Daimler-Benz will complement the HC data at IFP by results from preceding projects and by performing complementary measurements in the transparent square piston engine.
Imperial College will finalize the improved flamelet model for inhomogeneous mixtures, the submodels for ignition, UHC and the strained flame library and carry out test calculations as basis for verifications against engine results.
Funding SchemeCSC - Cost-sharing contracts
CB2 1PZ Cambridge
LS2 9JT Leeds