| A modified CFR Cetane engine was used to study combustion characteristics and emissions of minimally processed coal liquids (MPCLs). The principal modifications to the engine were the air and fuel heating systems and improved instrumentation. The MPCLs tested were derived from simple distillation of coal liquids. The coal liquids were the by-products of coal gasification of Elkhorn bituminous and North Dakota lignite using an atmospheric air-blown Wellman-Galusha and pressurized oxygen-blown Lurgi gasifiers, respectively. Measurements of fuel consumption, cylinder pressure, ignition delay, and emissions were made at each operating condition. A constant fuel viscosity was maintained in the injection system by heating the MPCLs prior to injection.; The operation conditions were controlled to observe the effect of pressure and temperature on the ignition characteristics of the test fuels. MPCLs, diesel fuel, and two reference fuels of low cetane number were evaluated in the engine. The inlet air was varied from room temperature to a maximum of 533K. The compression ratio was varied from 13 to 31. The equivalence ratio was held at 0.60 by monitoring the exhaust CO{dollar}sb2{dollar} levels. The engine speed was kept constant at 900 RPM with a synchronous AC motor.; The engine operated successfully on 100% MPCLs. Precautions had to be taken to prevent gum deposits on the fuel injection system. To successfully ignite the MPCLs in the engine, the engine intake temperature was maintained at 339K for both fuels and compression ratio was adjusted to 22 for Lignite and 21 for Elkhorn.; A three dimensional non-linear regression program was used to fit the parameters of an Arrhenius type equation to ignition delay, pressure, and temperature data. Activation energy correlated with Cetane number for all test fuels except for alpha-methylnaphthalene. The Cetane numbers of MPCLs were estimated to be close to that of the secondary reference fuel, U12 (21 Cetane number). Under similar engine operating conditions, maximum cylinder pressure, maximum rate of heat release, and thermal efficiency of the MPCLs were in the same range of diesel fuel. NO{dollar}sb{lcub}rm x{rcub}{dollar} emissions of MPCLs were also similar to that of diesel fuel. However exhaust soot concentrations of MPCLs were substantially higher than that of diesel fuel. |
