Effect of Fuel and Combustion System on the Pre-Ignition of Boosted SI engines

摘要

Downsizing of gasoline engines is one of the key technologies for a substantial progress in CO_2-emissions reduction. Additional benefit in de-carbonisation is gained by the use of fuels with bio-components. Thus, future gasoline engines will demand a combination of downsizing and flex-fuel capability. Both enhanced downsizing and new fuels lead to challenges due to irregular combustion phenomena. This contribution presents pre-ignition results obtained on a highly boosted engine for different fuels and injection systems by a combination of engine testing, optical diagnostics and CFDR. The investigation of the role of combustion system on pre-ignition focuses on the mixture formation. It is observed here that direct injection with an optimized DI injector lay-out can reduce pre-ignition propensity significantly compared to advanced port fuel injection due to the charge cooling. Furthermore a substantial effect of DI injector lay-out is observed, since wide spray shapes with enlarged fuel liner impingement reveal a higher pre-ignition propensity due to the different thermal state of the charge. The investigation on the effect of fuel on pre-ignitions focuses mainly on fuels with varying ethanol contents. With increasing ethanol content the pre-ignition propensity decreases. Furthermore E85 and E100 show no tendency for glow ignition in the tested engine, although substantially higher load levels are achieved.