Processing of coal tars and their combustion characteristics in a diesel engine

Liquid fuels produced from the effluent of coal gasifiers have been used to fuel a diesel engine. North Dakota lignite and Elkhorn bituminous coals were gasified in a pressurized, oxygen blown Lurgi gasifier and an atmospheric, air blown Wellman-Galusha gasifier, respectively. The high viscosity raw effluents are unsuitable for direct use in a diesel engine's fuel injection system. Therefore, the raw coal liquids were distilled at atmospheric pressure to discard up to 20% water and to select a fraction with a boiling range acceptable in a diesel engine. The effects of pressure and temperature on the ignition characteristics of the coal liquids, diesel reference fuel, and two low cetane number reference fuels were evaluated in a CFR cetane engine. The inlet air was heated (maximum of 533 K) and the compression ratio was varied from 13 to 31 to provide sufficient ranges in temperature and pressure to evaluate the Arrhenius parameters of the ignition delay equation. The coal liquids ran successfully in the engine without apparent damage to the engine or fuel system. Both coal derived liquids exhibited ignition characteristics similar to the 21 cetane number reference fuel. The NO_x levels were comparable with diesel fuel. The soot concentrations, however, were substantially higher with the coal derived fuels than diesel fuel at all operating conditions.