Natural gas engines benefit from a favorable hydrogen-to-carbon ratio of the fuel molecule and relatively lower fuel cost per unit energy compared to diesel or other liquid petroleum fuels. However, their lower engine thermal efficiencies reduce the greenhouse-gas-emission and total-cost-of-ownership advantages for most heavy-duty vehicle applications, making the adoption of natural gas vehicles challenging. Hence improvements in spark-ignited natural gas engine efficiencies and base engine cost reductions can further the beneficial use of natural gas in heavy-duty vehicle applications. This project aims to drive simultaneous improvements in fuel efficiency and cost while achieving ultra-low emissions.
Cummins, Inc. undertook this research effort to develop a high efficiency, low emission 15-liter heavy-duty natural gas engine designed specifically for natural gas operation. Various design choices to optimize the engine for natural gas operation enabled a greater than 10 percent brake thermal efficiency improvement and a greater than 20 percent engine system cost reduction over commercially available natural gas heavy-duty engines. The engine also achieved diesel-like performance while still being able to deliver extremely low emissions equivalent to current natural gas engine products including 0.02 grams per brake horsepower hour of oxides of nitrogen emissions. This report summarizes the results of the development effort and innovations made to achieve the ambitious targets for emissions, efficiency, performance, and robustness. The project concluded that, with technology additions, a heavyduty natural gas engine can be nearly as efficient as a modern diesel engine but with the advantage of lower emissions.
