Experimental study on in-cylinder combustion and exhaust emissions characteristics of natural gas/diesel dual-fuel engine with single injection and split injection strategies

On a non-road, high-pressure common-rail engine, natural gas/diesel dual-fuel (NDDF) combustion mode was performed. The way natural gas energy substitution percentage (ESP) and pilot diesel injection timing affected the combustion process, emission properties and fuel economy regarding NDDF engine with single injection strategy and split injection strategy was experimentally investigated at 25% load of 1800 rpm. Results show that under the two injection strategies, as ESP increased, NDDF combustion altered from single-stage to two-stage slowly, the combustion center (CA50) was delayed, the combustion duration increased, the soot and NO emissions declined, and the brake thermal efficiency (BTE) presented an increase-to-decrease change trend. As the combustion phase of split injection strategy was wholly advanced, the ignition delay period was shortened, the cyclic coefficient of variation (COV) and HC emission declined, and the BTE elevated. Additionally, the advanced injection timing would make NDDF heat release gradually advance, resulting in advanced CA50, extended ignition delay, lengthened combustion duration, lowered unregulated emissions, and increased BTE. The increase in peak heat release rate and BTE of split injection strategy was accompanied by decreased HC and aldehyde emissions. For NDDF engine possessing optimized split injection strategy, the BTE reached 37.79% and the COV reached 1.49% at ESP= 60%.