Abstract
Spark ignition engines with direct injection, especially those with spray guided combustion strategy, have a high potential regarding fuel efficiency and therewith CO2-emissions at part load operation. This benefit mainly results from the lean operation which is realised with a highly stratified mixture at part load. Consequently thermal efficiency and charge cycle efficiency increase significantly. Due to the limited air intake mass of natural aspirated engines, the highly efficient stratified operation is applicable to low loads only. Boosting enables to increase the air intake mass and therewith the air-fuel ratio, so that stratified operation can be extended to higher loads. Hence low fuel consumption can be achieved in a larger area of the engine map. Further in the conventional stratified operation points the fuel consumption can be decreased with increasing the air-fuel ratio by boosting.
This paper presents investigation results which have been carried out on a single cylinder DI engine with spray guided combustion strategy. The engine was equipped with a compressor. A strategy is shown which enables the extension of the stratified charge engine map. The airfuel- ratio was increased significantly.
The measurement results show that a significant reduction of the fuel consumption in the stratified charge operation was achieved with this boosting strategy. By thermodynamic analyses of the engine process, the effects of boosting on charge cycle efficiency and thermal efficiency was evaluated.
Keywords:boosting, extended stratified operation, DISI