Spray guided Direct Injection Gasoline Engines are a key enabler to reducing CO2 emissions and improving the fuel economy of light duty vehicles. Particulate emissions from these engines have been shown to be lower than from first generation direct injection gasoline engines, but they may still be significantly higher than port fuel injected engines due to the reduced time available for mixture preparation and increased incidence of fuel impingement on the piston crown and combustion chamber surfaces. These factors are particularly severe in the period following a cold start.
Both nuclei and accumulation mode particle size and number concentration were measured using a Cambustion differential mobility spectrometer. These data are reported for different coolant temperature intervals during the warm-up period. The bulk composition was determined using thermo-gravimetric analysis, and PM mass fractions are given for different volatility ranges and for elemental carbon.
In addition to the above, a novel sample collection method was used to collect individual particles in different size ranges. Subsequent analysis by transmission electron microscopy allowed the morphology and composition of particles in the nuclei and accumulation mode size ranges to be reported.
PM number concentrations were shown to decrease during engine warm-up. In some cases the particle size also decreased. By mass, the majority of the particulate matter was volatile, with no more than 29 percent in the solid phase elemental carbon fraction, although this was dependent on operating point. Of this solid particulate fraction, dispersed elemental carbon particles of 5-10 nm diameters were detected in the nuclei mode. The larger solid particles detected were also found to be carbonaceous, and to exist as aggregates of larger (30-80 nm) particles.