The influence of ethanol blends on particulate matter emissions from gasoline direct injection engines

Particulate Matter (PM) legislation for gasoline engines and the introduction of gasoline/ethanol blends, make it important to know the effect of fuel composition on PM emissions. Tests have been conducted with fuels of known composition in both a single cylinder engine and V8 engine with a three-way catalyst. The V8 engine used an unleaded gasoline (PURA) with known composition and distillation characteristics as a base fuel and with 10% by volume ethanol. The single cylinder engine used a 65% iso-octane - 35% toluene mixture as its base fuel. The engines had essentially the same combustion system, with a centrally mounted 6-hole spray-guided direct injection system. Particle size distributions were recorded and these have also been converted to mass distributions. Filter samples were taken for thermo-gravimetric analysis (TGA) to give composition information. Both engines were operated at 1500 rpm under part load. The tests with the single cylinder engine used lambda of 0.9, 1.0 and 1.1 with an ignition timing sweep of 15-45°bTDC. The trends with the stoichiometric and weak mixtures were less clear (the PM emissions being at low levels), but with lambda of 0.9 the trends were clear. For the rich mixture, advancing the ignition timing increased both PM number and mass emissions, and the use of E10 reduced the number emissions by a factor of 25-65 and the mass emissions by a factor of 2-10. The V8 tests were at stoichiometric with injection timing sweeps during induction (120 to 360°bTDC), with a reduction in both PM number and mass due to reactions in the catalyst. The earlier injection gave lower PM emissions and this was attributed to there being more time for mixture preparation, leading to a more homogeneous mixture. The addition of 10% ethanol led to an increase in PM emissions (both in terms of mass and number).