Effect of injection-strategy on combustion, performance and emission characteristics in a DI-diesel engine fueled with diesel from direct coal liquefaction

•Diesel from direct coal liquefaction was studied on a common rail diesel engine.•Multiple-injection was introduced to decrease NOX and soot emissions.•Retarded main injection can reduce combustion noise and NOX, and causes a soot hump.•Injection strategy should be calibrated carefully to reduce NOX and soot.

The performance and exhaust emissions of diesel engine fueled with diesel from direct coal liquefaction (DDCL) with multiple-injection strategy were investigated in this study. Experimental study was conducted on a four-cylinder direct-injection engine, with the injection parameters (main injection timing, pilot injection quantity and timing, and post injection quantity and timing) adjusted to investigate their influences on combustion and emissions. It is found that with the retard of main injection timing, the ignition delay of main combustion is prolonged. Nitrogen oxides (NOX) are decreased by 64.1%, meanwhile, soot is less than 0.05 1/m. And main injection timing is fixed at −1° crank angle (°CA) before top dead center (BTDC), both the pilot and post injections are introduced to further reduce NOX and soot emissions. Pilot injection, especially early pilot injection (such as 44.5 °CA BTDC in this study), continues to reduce NOX emissions with an acceptable level of soot emission. Moreover, both retarding-main injection and pilot injection are the effective ways of reducing the combustion noise. Post injection can decrease NOX and soot emissions simultaneously. There is a specific post injection, at which minimum NOX and soot emissions are achieved, but a slight increase of hydrocarbon (HC) and carbon monoxide (CO) emissions are inescapable.