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).