A Comprehensive Model for Pilot-Ignited, Coal-Water Mixture Combustion in a Direct-Injection Diesel Engine

Abstract

A combustion model has been developed for a direct-injected diesel engine fueled with coal-water slurry mixture (CWM) and assisted by diesel pilot injection. The model combines the unique heat and mass transport and chemical kinetic processes of CWM combustion with the normal in-cylinder processes of a diesel engine. It includes a two-stage evaporation submodel for the drying of the CWM droplet, a global kinetic submodel for devolatilization, and a char combustion submodel describing surface gasification by oxygen, carbon dioxide, and water vapor. The combustion volume is discretized into multiple zones, each of whose individual thermochemistry is determined by in-situ equilibrium calculations. This provides an accurate determination of the boundary conditions for the CWM droplet combustion submodels and the gas phase heat release. A CWM fuel jet development, entrainment, and mixing submodel is used to calculate the mass of unburned air in each of the burned zones. A separate submodel of diesel pilot fuel combustion is incorporated into the overall model, as it has been found that pilot fuel is required to achieve satisfactory combustion under many operating conditions. The combustion model is integrated with an advanced engine design analysis code. The integrated model can be used as a tool for exploration of the effects of fuel characteristics, fuel injection parameters, and engine design variables on engine performance, and in the assessment of the effects of component design modifications on the overall efficiency of the engine and the degree of coal burnout achieved.

Clean Coal Diesel Demonstration Project

“…While these model results were in agreement with modeling work done later (13,14), some preliminary experiments reported by Kakwani (l5) indicated that much higher engine speeds appeared to be possible. These results were corroborated in a project with Detroit Diesel Corporation and SwRI (16,18,21) conducted in 1990-93 and performed a 1900-rpm Detroit Diesel 8V -149 engine used in mine haul truck applications.…”

“…• General Electric, Texas A&M, and DDC used modeling of coal ignition and combustion in medium-speed reciprocating engines to guide selection of coal particle size in the slurry, and mixture preparation for satisfactory ignition (12,13,14,15,16). …”

Coal-fueled high-speed diesel engine development. Final report, September 28, 1990--November 30, 1993

“…In order to identify problems with the CWS ignition and combustion at high engine speeds and assess the effectiveness of possible design solutions, a coal combustion model developed at Ricardo North America was used to simulate the 149 diesel engine (Wahiduzzaman et al, 1990). The model was c_brated for the 149 two-stroke engine by performing a simulation of the diesel-fueled engine at the 1900 rpm, (125 bhp/cylinder) operating condition for which engine test results and cylinder pressure data was available.…”