Particulate matter emissions are subject to legislation and can occur at significantly higher levels with Gasoline Direct Injection (GDI) engines than Port Fuel Injection (PFI) engines. This has to be linked to mixture preparation for which the fuel spray behaviour is fundamental. Spray behaviour is characterised here in terms of the saturation pressure ratio - the ratio of fuel saturation pressure to the in-cylinder pressure which can vary significantly during the cycle; especially when the engine is boosted. Mie scattering images with semi-quantitative analysis is used to quantify spray development, along with the use of a presence probability analysis. The particulate measurement experiments (using a Cambustion DMS500) show that fuel volatility has a beneficial impact on reducing particulate matter emissions, even if flash boiling does not occur. Flash boiling did not necessarily reduce the particulate number but it did reduce the mean particulate size
