Effects of diesel from direct and indirect coal liquefaction on combustion and emissions in a six-cylinder turbocharged diesel engine

The aim of this study is to evaluate the effects of diesel from direct coal liquefaction (DDCL) and diesel from indirect coal liquefaction (DICL) on combustion and emissions. A six-cylinder turbocharged diesel engine fueled with DDCL, DICL, petroleum diesel (PD), 58% DDCL, and 42% DICL blended by volume (BD58) is used. The experiments are carried out at 1400 and 2300rpm engine speeds and various engine loads (10%, 25%, 50%, 75%, and 90% of the full-load). The results show that the brake thermal efficiency (BTE) of PD was higher than that of CTL (the maximum difference was 2%) at medium and high loads. At 10% load of 1400 rpm, the CO, HC and formaldehyde emissions of DDCL are 88.9%, 44.3% and 26.5% higher than those of PD respectively, and the CO, HC, and formaldehyde emissions of DICL are 30.1%, 15.3%, and 15.2% lower than those of PD. The differences among four fuels decrease rapidly with the increase of load. The NOX emissions of PD are the highest due to high nitrogen content (102.3 mu g/g) and low hydrogen-carbon (H/C) ratio. The fuel with higher cetane number has less formaldehyde emission at low loads, while the fuel with lower H/C has less formaldehyde emission at high loads. The particle size distribution shows a bimodal shape at different loads and the peak particle size of accumulation mode and nucleation mode all increases with the increase of load. The particulate emission of different fuels from high to low is the order of PD > DDCL > BD58 > DICL. In addition, the emissions of polycyclic aromatic hydrocarbons (PAHs) and toxicity equivalent (TE) of PD are highest at all loads. The proportion of soluble organic fractions (SOF) from DDCL, DICL, and BD58 is higher than that of PD.