Experimental investigation of impacts of engine hardware, operating parameters and combustion performance on particulate emissions in a DISI engine

With increasing concern over ultrafine Particulate Matter (PM) emissions from Direct Injection Spark Ignition (DISI) engines and ever tightening emissions legislation, substantial research work is required to obtain a better understanding of influence of advanced engine technologies on particulate formation and oxidation. In this work, experimental investigation of engine-out particulate emissions were carried out on a single cylinder spray-guided DISI engine. With regard to effects of engine hardware on PM emissions; impacts of fuel spray angle, fuel flow rate and intake valves' lift and camshaft phasing were examined over a wide start of injection sweep window. Injector tests highlighted a complex relation between injector characteristics and engine operating parameters with PM emissions as a result of fuel impingement and poor mixture preparation. Valvetrain tests indicated some benefits from engine throttling by valve lift and intake camshaft phasing in particulate number concentration reduction at low load. This was associated with increased intake flow turbulence and improved mixture preparation. Number-weighted particle size distribution was also affected by intake valve modes at low load. Nevertheless, at high load, impacts of variable valve lift and camshaft phasing on particulate number concentration and size distribution became negligible. Furthermore, combustion phase indicators were studied in order to probe impacts of combustion performance on PM emissions. While no satisfactory correlation of initial flame development with PM emissions was identified; shorter rapid-burning angles were observed with lower particulate number concentrations.