Among the existing concepts to help improve the efficiency of spark ignition engines on low load operating points, Controlled Auto-Ignition™ (CAI™) is an effective way to lower both fuel consumption and pollutant emissions at part load without major modifications of the engine design. The CAI™ concept is founded on the auto-ignition of a highly diluted gasoline-based mixture in order to reach high indicated efficiency and low pollutant emissions through a low temperature combustion.Previous research works have demonstrated that the valve strategy is an efficient way to control the CAI™ combustion mode. Not only the valve strategy has an impact on the amount of trapped burnt gases and their temperature, but also different valve strategies can lead to equivalent mean in-cylinder conditions but clearly differentiated combustion timing or location. This is thought to be the consequence of local mixture variations acting in turn on the chemical kinetics.In the present study, 3D CFD computations and optical diagnostics are combined to explore the local mixture differences due to the choice of valve strategy. The mixture characteristics are then linked to the experimentally observed differences in terms of autoignition location and timing, combustion duration and pressure rise.The results provide an insight into the effects explaining the suitability of the Negative Valve Overlap (NVO) strategy for low CAI™ loads and the capability of the Exhaust Gas Re-Breathing (EGRB) strategy to reach higher loads.
Influence of the Local Mixture Characteristics on the Combustion Process in a CAI™ Engine
Sae Int. J. Fuels Lubr
Sae International Journal of Fuels and Lubricants
2008 SAE International Powertrains, Fuels and Lubricants Congress ; 2008
Sae International Journal of Fuels and Lubricants ; 1 , 1 ; 1133-1149
2008-06-23
17 pages
Aufsatz (Konferenz)
Englisch
Influence of the Local Mixture Characteristics on the Combustion Process in a CAI™ Engine
British Library Conference Proceedings | 2008
|Combustion characteristics of H2-CO-CO2 mixture in an internal combustion engine
Kraftfahrwesen | 2001
|Influence of Mixture Formation on Injection and Combustion Characteristics in a Compact GDI Engine
SAE Technical Papers | 2002
|A Study of Mixture Injected SI Engine - Part 1 : Mixing Process and Lean Combustion Characteristics
British Library Online Contents | 1995
|