Analytical Evaluations of Ignition Options for a Coal/Water Slurry Fueled Engine

An engine cycle simulation was developed to investigate the ignition and combustion characteristics of coal slurry fuels in a reciprocating internal combustion engine. The simulation describes the compression and expansion strokes of an engine using submodels for cylinder gas mixing, wall heat transfer, solid coal particle combustion, coal devolatilization, and liquid evaporation and combustion. The submodels together with a thermodynamic analysis of the cylinder gas yield instantaneous cylinder conditions and overall indicated engine performance. The engine parameters and operating conditions were selected to be representative of a locomotive engine operating at 1000 RPM. Engine and fuel parameters investigated include engine inlet conditions (temperature and pressure), coal particle size and size distributions, fuel additives, and coal properties. Inlet conditions were found to be important parameters affecting the ignition and combustion characteristics. Increases in the initial (at BDC) gas temperature or pressure improved the ignition characteristics of the fuel in the engine. Ignition characteristics of coal/water slurries were also improved with the addition of small amounts of diesel oil. Smaller particle size slurries exhibited better ignition qualities and resulted in higher peak indicated thermal efficiencies than larger particle size slurries. Results obtained using monosize sauter mean diameter (of a distribution) particles agreed well with the results for the corresponding distribution. Finally, ignition was achieved at lower initial gas temperatures for higher reactivity coals.