Effect of Compression Ratio on the Combustion of a Pressure Charged Gasoline Direct Injection Engine 2000-01-0250
Pressure charging of S.I. engines is one possibility of enhancing torque and power significantly. Moreover, for engines with gasoline direct injection the disadvantage of a reduced volumetric efficiency due to DI-specific intake ports can be reduced and the possible engine map area with stratified charge may be enhanced. However, the compression ratio is a very important parameter for admissible boost pressure and full load torque as well as for part load fuel consumption. In this paper, the effects of a varied compression ratio in terms of full load behavior, knocking sensitivity, fuel consumption, emissions, stability of combustion and exhaust gas temperature at λ=1 as well as for stratified charge are investigated. The effects show clear advantages for a high compression ratio in part load fuel consumption and combustion stability. Stratified charge is possible until up to 3000 rpm/8 bar IMEP. At high load, however, with reduced compression ratio nearly constant fuel consumption (due to lower knocking sensitivity) and significantly higher full load results, combined with lower HC emissions, can be achieved. A further reduction of the compression ratio leads to slightly higher full load torque and lower emissions, but results in deteriorated fuel consumption at part load and full load.