Effect of diesel from direct coal liquefaction–biodiesel blends on combustion, performance and emission characteristics of a turbocharged DI diesel engine

•Diesel from direct coal liquefaction (DDCL) was studied on a common rail diesel engine.•DDCL-biodiesel blends were fueled on engine to improve combustion and emissions.•A “model” of MD change with disease progression is proposed.•Retarded injection and EGR were introduced to further decrease exhaust emissions.

In this study, the performance and exhaust emissions of diesel engine fueled with diesel from direct coal liquefaction (DDCL)–biodiesel blends consisting of 0%, 20% and 40% biodiesel are investigated. In order to decrease nitric oxides (NOX) and soot emissions, retarded injection and cooled exhaust gas recirculation (EGR) strategies are introduced. Experiments are conducted on a four-cylinder, four-stroke, direct injected diesel engine without any modification. It is found that compared with pure DDCL, DDCL–biodiesel blends can reduce maximum pressure rise rate and gain lower combustion noise and mechanical load of diesel engine. In addition, there is hardly any difference for combustion phase between test fuels. Both exhaust emissions and fuel consumption are reduced due to the improved combustion by fuel properties of biodiesel, such as cetane number and fuel oxygen. When EGR rate is increased to 40%, with an increment of biodiesel in blends, NOX, carbon monoxide (CO) and equivalent brake specific fuel consumption (BSFC) are still decreased, and soot emission is increased. Anyway, both exhaust emissions and equivalent fuel consumption are controlled to a quite low level under retarded injection for DDCL–biodiesel blends.