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Particulate Emissions from Homogeneous Charge Compression Ignition (HCCI) combustion are routinely assumed to be negligible. It is shown here that this is not the case when HCCI combustion is implemented in a direct injection gasoline engine. The conditions needed to sustain HCCI operation were realized using the negative valve overlap method for trapping high levels of residual exhaust gases in the cylinder. Measurements of emitted particle number concentration and electrical mobility diameter were made with a Cambustion DMS500 over the HCCI operating range possible with this hardware. Emissions of oxides of nitrogen, carbon monoxide and unburned hydrocarbons were also measured. These data are presented and compared with similar measurements made under conventional spark ignition (SI) operation in the same engine. Under both SI and HCCI operation, a significant accumulation mode was detected with particle equivalent diameters between 80 and 100 nm.

In catalyst heating operation for DISI (Direct Injection Spark Ignition) engines, split injection has been generally known to improve combustion stability which is critical for the trade-off between tailpipe emissions and vehicle idle NVH. This is also the case for a spray guided DISI engine employing multi-hole injectors and with both injector and spark plug centrally located in the chamber. There are some special challenges with regard to combustion robustness because of the close proximity between injector and spark plug. Investigations have been carried out through engine testing and CFD simulation to ensure combustion robustness. For catalyst heating operation, the first injection occurs during induction, which forms a relatively well mixed but lean mixture in the cylinder before ignition, and the second injection occurs close to ignition, which produces a stratified fuel rich mixture in the central region of the combustion chamber.

Extensive simulation was carried out to investigate cam strategies for SI engine part load operation. Performance of the engine with dual independent variable cam timing (VCT) system is assessed. Over a wide range of part load operating conditions, engine performance parameters, such as fuel consumption, were expressed in forms of contour maps as a function of intake and exhaust cam timings. Based upon the simulation results, cam timings were optimized for various part load conditions. A cam strategy incorporating intake and exhaust cam retard was developed to improve fuel economy and emissions. Influences of intake and exhaust cam timing on the gas-exchange and combustion processes were also analyzed. It was shown that the fuel economy improvement by dual independent VCT is achieved primarily through reduction of pumping loss. Effects of in-cylinder charge motion and the use of differential intake cam profiles on fuel economy were examined.

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.