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Particulate Matter (PM) emissions from gasoline direct injection (GDI) engines, particularly Particle Number (PN) emissions, have been studied intensively in both academia and industry because of the adverse effects of ultrafine PM emissions on human health and other environmental concerns. GDI engines are known to emit a higher number of PN emissions (on an engine-out basis) than Port Fuel Injection (PFI) engines, due to the reduced mixture homogeneity in GDI engines. Euro 6 emission standards have been introduced in Europe (and similarly in China) to limit PN emissions from GDI engines. This article summarises the current state of research in GDI PN emissions (engine-out) including a discussion of PN formation, and the characteristics of PN emissions from GDI engines. The effect of key GDI engine operating parameters is analysed, including air-fuel ratio, ignition and injection timing, injection pressure, and EGR; in addition the effect of fuel composition on particulate emissions is explored, including the effect of oxygenate components such as ethanol.

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Particulate emissions from Gasoline Direct Injection (GDI) engines have been an important topic of recent research interest due to their known environmental effects. This review paper will characterise the influence of different gasoline direct injection fuel systems on particle number (PN) emissions. The findings will be reviewed for engine and vehicle measurements with appropriate driving cycles (especially real driving cycles) to evaluate effects of the fuel injection systems on PN emissions. Recent technological developments alongside the trends of the influence of system pressure and nozzle design on injector tip wetting and deposits will be considered. Besides the engine and fuel system it is known that fuel composition will have an important effect on GDI engine PN emissions. The evaporation qualities of fuels have a substantial influence on mixture preparation, as does the composition of the fuel itself. Recently a number of studies have attempted to link fuel composition with PN emissions, developing a variety of indices including the PM index (Aikawa et al.) and the PN index (Leach et al.). An extensive literature search has been carried out and the PN index evaluated against these data. In addition the PM index and PN index are compared. The results of the review show that the Aikawa index should be applied when the fuel quality is known by lab reports, whereas the Leach index is relevant when only minimal information about a fuel is known, even the latter giving a relatively good prediction of PN emission trends from fuels in GDI engines.

The use of direct injection spark ignition (DISI) engines for passenger cars has increased; providing greater specific performance and lower CO2 emissions. DISI engines, however, produce more particulate matter (PM) emissions than Port Fuel Injected (PFI) engines. Forthcoming European exhaust emissions legislation is addressing concerns over health effects of PM emissions. Accordingly, research into PM emission formation has increased.A model developed by Aikawa et al. (2010) for PFI engines correlated PM number emissions with the vapour pressure and the double bond equivalent (DBE) of the components of the fuel. However there was no independent control of these parameters. This study investigates a particulate emissions index for DISI engines.A single-cylinder optical access Spray Guided DISI engine was used to develop a Particulate Matter Number emissions Index (PN index) -modified from the PM index using industry standard measurements -through the use of model and commercially available fuels.Model fuels were designed using Raoult's law and UNIFAC such that the DBE and vapour pressure of the fuel mix could be varied.Engine tests were conducted, independently varying the DBE and the vapour pressure of the fuel. PM number emissions were measured using a Cambustion DMS500, the results were analysed alongside observations of the fuel spray to investigate the PN index.The PN index has also been used to evaluate emissions from two commercially available EN228 fuels. The results demonstrate that the trend of the PN index is followed both with model fuels and commercial gasolines.