Comparisons of particle size distribution from conventional and advanced compression ignition combustion strategies

Abstract

Particulate size distribution measurements are of importance in engine research as stricter regulations on particulate matter emissions (both mass and number based) are being implemented. Particulate size distribution measurements can be very sensitive to the laboratory environment or experimental setup, making it difficult to compare results for different combustion strategies acquired in different labs. In this study, a comparison of particulate size distribution measurements over a wide variety of conventional and advanced combustion strategies was conducted using a four-stroke single-cylinder diesel engine test setup to eliminate lab-to-lab variations and enable direct comparison of particulate size distribution results for different combustion strategies. Eight combustion strategies are included in the comparison: conventional diesel combustion, diesel/gasoline reactivity controlled compression ignition, homogeneous charge compression ignition, two types of gasoline compression ignition (early injection and late injection), diesel low temperature combustion, natural gas combustion with diesel pilot injection, and diesel/natural gas reactivity controlled compression ignition. Measurements were performed at four different load-speed points with matched combustion phasing when possible; for several strategies, it was necessary to operate with slightly different combustion phasing. Particle size distributions were measured using a scanning mobility particle sizer. To study the influence of volatile particles, measurements were performed with and without a volatile particle remover (thermodenuder) at low and high dilution ratios. The results show that non-uniformity in the fuel distribution caused by direct injection results in increased accumulation-mode particle concentrations compared to premixed strategies even for low particulate mass advanced combustion strategies. Premixed combustion strategies (homogeneous charge compression ignition) and early injection gasoline compression ignition show higher nuclei-mode particle concentrations. Overall particle number and mass concentrations vary significantly between engine operating conditions and between combustion strategies.