Engines running on the dual fuels of natural gas and diesel present technical challenges that require a thorough understanding of in-cylinder combustion physics. On the diesel side, engine knock and pre-ignition often limits substitution of natural gas for diesel fuel at high load, due to the high compression ratio of diesel engines. On the natural gas side, excessive incomplete combustion of the natural gas results in increased tailpipe emissions of methane and other pollutants. And, the chemical reactivity of the fuel can vary greatly, depending on the percentage of ethane and propane in the natural gas.
Woodward’s engine control unit (ECU) is designed with a high-speed, on-engine processor and control algorithms to take cylinder pressure for each cylinder, each cycle, and convert this high-speed information into combustion metrics such as center of combustion, rate of pressure rise, and peak pressure. With this data available, the ECU is able to control combustion phasing in reactivity controlled compression ignition (RCCI) combustion. Additionally, the combustion metric feedback can be used to maintain good combustion phasing during changes in substitution rates and also when the fuel quality changes.