Development of a skeletal surrogate mechanism for emulating combustion characteristics of diesel from direct coal liquefaction

A surrogate describing the oxidation characteristics of Diesel from direct coal liquefaction (DDCL) was proposed in this work. n-dodecane and decalin were chosen as representative species of alkane and cycloalkane hydrocarbons in DDCL according to compositional analysis results. A proportion of 24.6% n-dodecane and 75.4% decalin by mole was determined by emulating real DDCL properties including Cetane number (CN), Hydrogen-Carbon (H/C) ratio, lower heating value (LHV) and density. Sub-mechanisms of n-dodecane and decalin were constructed on top of a detailed C0C6 core mechanism and then sensitivity analysis was used to eliminate unimportant species and reactions. The final version of the skeletal DDCL surrogate mechanism consists of 131 species and 461 reactions. The skeletal mechanism was extensively validated against experimental data including ignition delay times, species concentration profiles and laminar flame speeds for each pure component. Furthermore, diesel engine experiments fueled with DDCL were conducted and the corresponding 3-D CFD simulation results show that the present skeletal mechanism gives reliable performance for combustion behavior as well as NOx and CO emissions predictions, indicating the proposed mechanism can be applied for modeling DDCL in practical engine applications.