Optimization of the Air/Fuel Ratio for Improved Engine Performance and Reduced Emissions

Combustion processes inside the engine cylinder dictate engine power, efficiency and emissions. Following compression, burning proceeds as air and fuel mix to the composition necessary for combustion to take place. In the diesel engine, fuel is injected in the cylinder into high pressure and temperature air. The engine has less time to form the air-fuel mixture, which is less homogenous as a result. This creates periods during the combustion phase where the air to fuel relationship is non-optimized. This is particularly apparent during low-end operating cycles. Traditionally, efforts to reduce engine-out emissions have concentrated on fuel management. Development of two advanced technologies on turbocharged diesel engines have focused instead on air management with the optimization of this relationship of air to fuel. Test results indicate significant improvements that meet or exceed fuel management techniques designed to improve combustion efficiency, fuel economy, engine performance and emission reductions. This paper discusses these air management advancements based on steady-state and EPA transient cycle testing of two heavy-duty diesel engines.