A modified CFR Cetane engine was used to analyze combustion characteristics and emissions of minimally processed coal liquids (MPCLs). To aid in combustion of the coal liquids, the ability to heat the fuel and inlet air was added. The MPCLs are derived from atmospheric distillation of coal liquids. The coal liquids are byproducts of coal gasification of Elkhorn bituminous and North Dakota lignite using the atmospheric, air blown Wellman-Galusha and pressurized, oxygen blown Lurgi gasifiers, respectively.The MPCLs were compared with three reference fuels: diesel No. 2, U12 (21 cetane number) and #-methyl napthalene (0 cetane number). The inlet air was heated from 340 to 535 K and the compression ratio was varied from 13 to 31 to provide sufficient range in temperature and pressure necessary for the combustion of low cetane number fuels. At each operating condition, fuel consumption, cylinder pressure, ignition delay, and emisions were measured. By monitoring the exhaust CO2 levels, the overall equivalence ratio was held at 0.60. The engine operated successfully on 100% MPCLs. By comparing to the ignition characteristics of the reference fuels, the cetane number rating on the MPCLs is estimated at about 21.A three dimensional nonlinear regression program was used to fit the parameters of an Arrhenius type equation to the engine's ignition performance. Activation energy was found to correlate with apparent cetane number for the full boiling range fuels.Under similar engine operating conditions, maximum cylinder pressure, maximum rate of heat release, thermal efficiency, and NOx of the MPCLs were similar to those of diesel fuel. Exhaust soot concentrations of MPCLs, however, were substantially higher than levels found burning diesel fuel.