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A study of combining gasoline engine downsizing and controlled auto - ignition combustion

Moxey B., Cairns A., Ganippa A., Zhao H., Bassett M.

Journal of KONES

2012

Vol. 19, No. 1

289-300

In recent years European automotive CO2 emissions targets have largely been met through increased diesel sales. However, the distillation of crude oil results in high proportions of both gasoline and diesel fuel and ultimately this has resulted in Europe being "diesel lean" at times. In order to meet future global emissions goals, in the short term it will be necessary to improve the fuel consumption of the gasoline engine and in the longer term source sustainable alternatives to crude oil. The objective of the current work was to investigate the optimum trade-off between the opposing engine operating requirements of gasoline engine downsizing and Controlled Auto-Ignition (CAI) combustion for use in a family-sized passenger car. Experimental fuel consumption and emissions data were produced for four sizes of spark ignition engine, varying from 1 to 2 litres in capacity. The additional benefits of two experimentally developed CAI operating methodologies were evaluated in each engine using drive cycle simulation software. The first CAI mode was based on novel use of combined internal and external EGR to attain higher loads. The second involved the adoption of turbocharging at part-load for yet higher output via so-called lean-boosted CAI. It was concluded that, for such a vehicle, a compromise exists where best fuel economy can be obtained from a moderately downsized CAI-capable engine. Compared to the baseline 2 litre engine, it was possible to obtain fuel economy benefit equivalent to that offered from an aggressively downsized 1 litre unit but using a moderately downsized 1.4 litre CAI engine, without the need for any complex boosted operation or expensive emissions aftertreatment systems. As capacity was reduced below 1.4 litres, the benefit of CAI diminished at an accelerated rate due to progressive failure to capture key higher load sites visited across the European drive cycle.