Emissions and Efficiency of Turbocharged Lean-Burn Hydrogen-Supplemented Natural Gas Fueled Engines

Abstract

The use of hydrogen fuel to supplement conventional hydrocarbon engine fuels is of interest as a means of developing hydrogen supply infrastructure, without the challenges of developing dedicated hydrogen-fueled vehicles. Mixing hydrogen with natural gas is the most straightforward means of implementation as both can be mixed and stored in conventional high pressure compressed gas cylinders. The primary benefit of hydrogen supplementation for IC engines is to allow leaner operation than with operation on natural gas alone while maintaining high combustion efficiency. Results from both engine and vehicle studies confirm that hydrogen supplementation improves the NO_x–hydrocarbon emission trade-off compared to natural gas as a result of leaner operation. The difference between the leanest air–fuel ratio for hydrogen-containing mixtures and the leanest air–fuel ratio for natural gas decreases with engine load. Thus, the extent of improvement in the NO_x–hydrocarbon trade-off diminishes at high loads. As a result, the extent of improvement in real-world use will depend on driving cycle. Finally, fuel consumption is a third dimension in the NO_x–hydrocarbon trade-off. As a result, not only the emissions but also the impact on fuel consumption must be taken into account in selecting the air–fuel ratio, spark timing, and other factors that constitute an engine calibration.