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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.

Multiple fuel injections with higher injection pressure are a way to improve diesel engine performance and lower emissions of unburned HCs, smoke, particulate matter and carbon monoxide (CO). However this method leads to a higher level of NOx emissions. A combination of higher pressure split injection and exhaust gas recirculation (EGR) has potential in controlling NOx emissions and engine performance simultaneously. The focus of this study is to investigate the effect of variation in injection pressure with split (pilot and main) injection, (with and without cooled EGR) on engine performance and emissions. The engine used is a common rail direct injection V6 Diesel fitted with turbo-charged variable turbine geometry (VTG) turbochargers, fuelled with ultra low sulphur diesel (ULSD).