An experimental study on particle evolution in the exhaust gas of a direct injection SI engine

The measurement results for exhaust nucleation mode particles in internal combustion engines are not easy to repeat and very sensitive to the measurement processes in laboratory experiments. In this study, particle numbers and size distributions were measured at different sampling points along an exhaust system of a single-cylinder gasoline direct injection engine, which consists of an exhaust plenum chamber and circular steel pipes. Different injection timings and two fuels including gasoline and ethanol were tested. Particle evolution in the exhaust gas was analyzed. One sampling point upstream and five sampling points downstream the exhaust plenum chamber were measured with the exhaust temperature dropping from 630 degrees C to 170 degrees C. For gasoline, when the sampling point shifts from the upstream to the downstream of the exhaust plenum chamber, the particle number concentrations of accumulation mode decrease by 7%-10%, and the particle number concentrations of nucleation mode decrease by 50%-98%. A trade-off between the particle number concentrations of nucleation mode and accumulation mode with varied injection timings is observed downstream of the exhaust plenum chamber, indicating that coagulation between solid core particles and accumulation mode particles occurs in the exhaust plenum chamber. It is concluded that intensive particle coagulation occurs inside the exhaust plenum chamber, leading to reduction of solid core particle number concentration and the resultant different measurement results of nucleation mode particles in the downstream exhaust gas. For ethanol, the particle number concentration reduction is less than 20% regardless injection timings due to the ultra-low accumulation mode particles. The particle number concentration reductions along the five sampling points downstream of the exhaust plenum chamber are negligible.