Experimental Analysis of Diesel-Ignited Methane Dual-Fuel Low-Temperature Combustion in a Single-Cylinder Diesel Engine

Abstract

This paper focuses on the effect of diesel injection timing, intake boost pressure, and diesel injection pressure on diesel-methane dual-fuel combustion performed in a single-cylinder research engine. The engine was operated at a constant speed of 1,500 revolutions per minute (rpm) while percentage of methane energy substitution (PES) and load were maintained at 80% and 5.1 bar net indicated mean effective pressure (IMEP), respectively. The start of injection (SOI) of diesel was varied from 250 crank angle degrees (CAD) to 350 CAD while keeping the injection pressure at 500 bar and intake boost pressure at 1.5 bar. Advancing SOI from 330° to 300° reduced indicated specific NOx (ISNOx) emissions from 11.9 g/kW·h to less than 0.02 g/kW·h; further advancement of SOI did not yield any significant ISNOx reduction. Net indicated fuel conversion efficiency (IFCE) increases from 29.4% at 350 CAD SOI to 40.5% at 300 CAD SOI. Combustion efficiency trends are consistent with unburned hydrocarbon (HC) and carbon monoxide (CO) emission trends. Moreover, smoke emissions were lower than 0.1 filter smoke number (FSN) for all SOIs. A diesel injection pressure sweep from 200 to 1,300 bar at 300 CAD SOI showed that very low injection pressures lead to apparently more heterogeneous combustion and higher ISNOx, indicated specific CO (ISCO), and indicated specific HC (ISHC) emissions, whereas smoke, IFCE, and combustion efficiency remained unaffected. An injection pressure of approximately 500 bar appeared to be optimal for early SOIs. Finally, an intake boost pressure sweep from 1.1 to 1.8 bar at 300 CAD SOI and 500 bar injection pressure showed that ISNOx and smoke remained fairly low at all conditions (ISNOx<0.15 g/kW·h; smoke<0.1 FSN); however, increasing boost pressure resulted in an increase in both ISHC and ISCO emissions while combustion efficiency and IFCE were reduced.