Modelling and Experimental Investigations of Supercharged HCCI Engines

This paper focuses on supercharged HCCI engines employing internal EGR that is obtained by the use of negative valve overlap. In HCCI engines, the absence of throttling coupled with the use of high compression ratio to facilitate auto-ignition and with the use of lean mixtures result in improved fuel efficiency. High dilution is required to control the auto-ignition and it also results in reduction of the production of NOx. To compensate for the charge dilution effect, the method used to recover the loss of power is to introduce more air in to the engine which allows introducing also more fuel while maintaining high lambda. A supercharger is required to introduce the required amount of air into the engine.

The modelling investigation performed with Ricardo WAVE® coupled with CHEMKIN® and experimental investigation for supercharged HCCI show significant improvement in terms of extension of load range and reduction of NOx over the naturally aspirated HCCI and also over SI operation. Thus the operation window of HCCI can be greatly extended by supercharging technology in order to get low emission and higher power.

The modelling and experimental work in the paper refer to two engines - a single cylinder engine supercharged with compressed air fed from the shop supply and a Jaguar V6 engine equipped with a mechanically coupled positive displacement supercharger. The effect of valve timing, lambda and pressure ratio on the operation of supercharged engines has been investigated. Modelling investigation is showing very good consistency with experimental results. Modelling performed for the V6 engine also shows the requirement of a supercharger of an appropriate size.