Experimental investigation of combustion and particle emissions under different combustion modes on a heavy-duty diesel engine fueled by diesel/gasoline/diesel from direct coal liquefaction

In an effort to contribute in further reducing pollution and fuel consumption, the effects of various combustion modes on the combustion process and emissions were investigated on a modified single cylinder from a six-cylinder engine using diesel, gasoline, and diesel from direct coal liquefaction (DDCL). The engine was run at 1000 r/min with an indicated mean effective pressure (IMEP) of 0.7 MPa. Additionally, we experimentally evaluated the impact of exhaust gas recirculation (EGR) and did comparisons among the tested fuels. Gasoline was injected into the intake port to form a homogeneous mixture and compression ignition, which led to homogeneous charge compression ignition (HCCI). Diesel was injected near top dead center (TDC), which was dominated by diffused combustion depending on the mixing rate of diesel and air. DDCL was also injected near TDC. In comparison with diesel, DDCL has a longer ignition delay (ID) than diesel due to low cetane number and high volatility. It also had a heat release rate between that of gasoline and diesel. Among the tested fuels, gasoline displayed the highest gross indicated thermal efficiency, followed by DDCL, and then diesel. Moreover, emission test results showed that gasoline had the lowest NOx and soot emissions, but had the highest CO and HC emissions. Different particle modes were present under different EGR conditions. For instance, at an EGR ratio lower than 20%, the particles of the tested fuels were composed mainly of nucleation-mode particles. When the EGR ratio was higher than 20%, the particles of DDCL and diesel were of accumulation-mode, whereas those of gasoline were of small-diameter nucleation-mode.