Correlations between particulate matter emissions and gasoline direct injection spray characteristics

• We explored impacts of purposed-designed GDI fuel delivery systems on engine-out particulate matter emissions.
• We studied effects of fuel flow rate and spray angle on PM emissions for homogeneous and heterogeneous in-cylinder mixtures.
• We investigated influence of location and relative timing of fuel impingement on engine-out particulate matter emissions.

The present work investigates impacts of fuel delivery system on Particulate Matter (PM) emissions in a latest generation gasoline Direct Injection Spark Ignition (DISI) engine. Particulate number concentration and size distribution were studied over a wide size range for homogeneous and heterogeneous in-cylinder fuel/air mixtures at different engine speeds/loads. Various fuel spray angles and fuel flow rates were employed to investigate effects of fuel wetting and mixture preparation on particulate emissions. Experimental results highlighted intricate relation between particulate formation/oxidation and engine operating parameters that dictates optimum spray characteristics for lowest PM emissions. The study revealed fuel impingement on hot piston surface during early injection timings and consequent fuel pyrolysis and diffusion flame result in PM size distributions with a peak in accumulation mode (particle diameter ≥50 nm). On the other hand, late fuel impingement on cylinder liner and insufficient time for mixture preparation, result in PM size distributions with a peak around 10-15 nm in nucleation mode. It was concluded that for the latter case, condensation of unburned hydrocarbons was more significant than adsorption into exiting particles’ surface.