Particulate Emissions from a Direct-Injection Spark-Ignition (DISI) Engine

The numbers, sizes, and derived mass emissions of particles from a production DISI engine are examined over a range of engine operating conditions. Particles are sampled directly from the exhaust pipe using heated ejector pump diluters. The size distributions are measured using a scanning mobility particle sizer. The numbers and sizes of the emitted particles are reported for stratified versus homogeneous operation and as a function of fuel injection timing, spark timing, engine speed, and engine load. The principal finding is that particle number emissions increase by about a factor of 10 - 40 going from homogeneous to stratified charge operation. The particulate emissions exhibit a strong sensitivity to injection timing; generally particle number and volume concentrations increase steeply as the injection timing is retarded, except over a narrow portion of the range where the trend reverses. Under both homogeneous and stratified charge operation, advancing the spark timing leads to the emission of a higher number of particles and to an increase in particle size. Increasing speed and load both cause higher particulate emissions; however, for stratified charge operation these general trends are strongly influenced by injection timing. Data from a DISI engine equipped vehicle run over a transient FTP drive cycle show increases in PM (particulate matter) emissions that correlate with vehicle acceleration, as well as PM peaks that correlate with stratified charge operation. The net PM mass emission rate for the DISI vehicle is about 10 mg/mi, averaged over the three phase FTP cycle.