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Natural gas presents several challenges to engine manufacturers for use as a heavy-duty, lean burn engine fuel. This is because natural gas can vary in composition and the variation is large enough to produce significant changes in the stoichiometry of the fuel and its octane number. Similarly, operation at high altitude can present challenges. The most significant effect of altitude is lower barometric pressure, typically 630 mm Hg at 1600 m compared to a sea level value of 760 mm. This can lower turbocharger boost at low speeds leading to mixtures richer than desired. The purpose of this test program was to determine the effect of natural gas composition and altitude on regulated emissions and performance of a Cummins B5.9G engine. The engine is a lean-burn, closed loop control, spark ignited, dedicated natural gas engine. For fuel composition testing the engine was operating at approximately 1600 m (5,280 ft) above sea level.

A Second Law based analysis of the processes within a diesel engine is presented and compared with the traditional First Law analysis. The analysis technique is described and its assumptions outlined. Available energy additions, extractions, and destructions are examined and quantified for the various processes. Alternative approaches are presented for engine systems with or without secondary heat recovery devices to further quantify the relative importance of thermodynamic loss mechanisms. The technique is applied to a turbocharged diesel engine and used to track available energy throughout the engine cycle. The methods of analysis are applied to some simplified cases to demonstrate their usefulness in analyzing various engine processes.