A Study of the Dilution Effects on Particle Size Measurement from a Heavy-Duty Diesel Engine with EGR

A study of particle size distributions was conducted on a Cummins M11 1995 engine using the Scanning Mobility Particle Sizer (SMPS) instrument in the baseline and downstream of the Catalyzed Particulate Filter (CPF). Measurements were made in the dilution tunnel to investigate the effect of primary dilution ratio and mixture temperature on the nuclei and accumulation mode particle formation. Experiments were conducted at two different engine modes namely Mode 11 (25% load - 311 Nm, 1800 rpm) and Mode 9 (75% load - 932 Nm, 1800 rpm). The nanoparticle formation decreased with increasing dilution ratios for a constant mixture temperature in the baseline as well as downstream of the CPF II for Mode 11 condition. At Mode 9 condition in the baseline, the dilution ratio had a little effect on the nanoparticle formation, since the distribution was not bimodal and was dominated by accumulation mode particles. However, the effect of dilution ratio on nanoparticle formation could be clearly seen downstream of the CPF II at Mode 9 condition and the nanoparticle formation decreased with increasing dilution ratios. The dilution ratio had no significant effect on the accumulation mode particle formation at both the modes in the baseline and downstream of the CPF II. The mixture temperature had no significant effect on the nanoparticle and accumulation mode particle formation for a constant dilution ratio at two different modes in the baseline and downstream of the CPF II. It was concluded that for the MTU dilution tunnel, the nano-particle formation decreases at higher dilution ratios (>40:1) and in addition to making measurements at lower dilution ratios (<15:1), the future particle size measurements will also be made at higher dilution ratios where less nanoparticles are formed.