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A zero-dimensional cycle simulation model coupled with a chemical equilibrium model and a two-zone combustion model has been extended to predict nitric oxide formation and emissions from spark-ignited, lean-burn natural gas engines. It is demonstrated that using the extended Zeldovich mechanism alone, the NOx emissions from an 8.1-liter, 6-cylinder, natural gas engine were significantly under predicted. However, by combining the predicted NOx formation from both the extended Zeldovich thermal NO and the Fenimore prompt NO mechanisms, the NOx emissions were predicted with fair accuracy over a range of engine powers and lean-burn equivalence ratios. The effect of injection timing on NOx emissions was under predicted. Humidity effects on NOx formation were slightly under predicted in another engine, a 6.8-liter, 6-cylinder, natural gas engine. Engine power was well predicted in both engines, which is a prerequisite to accurate NOx predictions.

Several investigations have shown that the operation of spark ignition engines on methanol can cause unusually high levels of wear during conditions of warm-up and cold-weather operation. This engine wear occurs principally in the upper cylinder bore and ring are as, and corrosion plays an important role in the mechanism. The present study examines the theory that the corrosion is caused by combustion residues that form when liquid alcohol on the cylinder wall evaporates and burns. Combustion residues were found when shallow pools of alcohol fuels were burned in an apparatus designed to simulate a water-cooled cylinder wall. The residues contained water, alcohol, formaldehyde, acetaldehyde, formic acid, acetic acid, and methylenehydroxy-peroxide; they reacted rapidly with cast iron to form iron formate and FeO(OH). This study explains previous test results on cylinder bore and ring wear in methanol and ethanol fueled engines.