Analysis of the Combustion Mode Switch Between SI and Gasoline HCCI 2012-01-1105
The worldwide stricter emission legislation and growing demands for lower fuel consumption require for significant efforts to improve combustion efficiency while satisfying the emission quality demands. Homogeneous Charge Compression Ignition (HCCI) on gasoline engines provides a particularly promising and, at the same time, challenging approach, especially regarding the combustion mode switch between spark-ignited (SI) and gasoline HCCI mode and vice-versa.
Naturally aspirated (n.a.) HCCI shows considerable potential, but the operation range is air breathing limited due to hot residuals required for auto-ignition and to slow down reaction kinetics. Therefore it is limited to part-load operation. Considering the future gasoline engine market with growing potentials identified on downsized gasoline engines, it is imperative to investigate the synergies and challenges of boosted HCCI. Additional HCCI potentials can be realized through the additional breathing, resulting in extension of the operation map and further optimization of fuel efficiency and emissions.
One of the main challenges when running HCCI, especially boosted HCCI, is the combustion mode switch regarding torque stability, combustion robustness and noise limitation. Depending on the direction of the mode switch several dynamic effects especially in the intake system have to be considered and balanced through calibration. Some of these aspects will be addressed in this work by thermodynamic analysis of measured data on a 4-cylinder 2.0l direct injection gasoline engine. While running SI or controlled HCCI mode combustion mode switches were performed and optimized regarding the targets mentioned above. Meeting the thermodynamic requirements for a stable combustion on a cycle-to-cycle basis the results show feasible calibration strategies for successful combustion mode switches in both directions.