The Application of an Enhanced Ignition Delay Model to HCCI Engines and Comparison to Engine Measurements

The paper describes the application of an enhanced ignition delay model, developed by Yates and co-workers, to the operation of a single cylinder HCCI engine. The ignition delay description was further expanded in this paper to incorporate the effects of air-fuel ratio changes (to cater for lean operation) and residual exhaust gas. Variable combustion (heat release) duration was added, yielding improvement on the common assumption of a fixed duration.

The model was compared to measurement performed in a variable compression ratio, single cylinder Ricardo E6 engine and the paper details the engine preparation, test procedure and results. A variety of fuels were tested and modelled and results for two fuels (n-heptane and methanol) were presented in the paper. These two fuels represent extremes of autoignition resistance (with octane numbers of 0 and 106, respectively).

Comparison between modelled and measured data yielded discrepancies in three areas: the combustion duration, ignition phasing and the existence of cool flame heat release. All three discrepancies were traced to simplifications in the engine and ignition delay model.