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Model M15 gasoline fuels have been created from pure fuel components, to give independent control of volatility, the heavy end content and the aromatic content, in order to understand the effect of the fuel properties on Gasoline Direct Injection (GDI) fuel spray behaviour and the subsequent particulate number emissions. Each fuel was imaged at a range of fuel temperatures in a spray rig and in a motored optical engine, to cover the full range from non-flashing sprays through to flare flashing sprays. The spray axial penetration (and potential piston and liner impingement), and spray evaporation rate were extracted from the images. Firing engine tests with the fuels with the same fuel temperatures were performed and exhaust particulate number spectra captured using a DMS500 Mark II Particle Spectrometer.

A study has been undertaken with a single-cylinder engine, based on the Mitsubishi GDi combustion system, that has the option of either port injection or direct injection. Tests have been undertaken with pure fuel components (methane, iso-octane, toluene and methanol), and a representative gasoline that has also been tested with the addition of 10% methanol and 10% ethanol. The volumetric efficiency depends both on the fuel and its time and place of injection. For stoichiometric operation with unleaded gasoline, changing from port injection to direct injection led to a 9% increase in volumetric efficiency, which was improved by a further 3% when 10% methanol was blended with the gasoline. The improvements in volumetric efficiency will be used to quantify the extent of charge cooling by fuel evaporation, and these will be compared with predictions assuming the maximum possible level of fuel evaporation.