Feasibility study of an on-board natural gas to dimethyl ether reactor for dimethyl ether preinjection and enhanced ignition

Dual fuel (CI) engines provide an excellent means of maintaining high thermal efficiency and power while reducing emissions. This is particularly true in situations where the main CI fuel does not exhibit good autoignition characteristics, such as diesel engines operating on natural gas usually in stationary applications such as a pipeline installation. This paper explores the feasibility of chemically synthesizing DME from natural gas on-board and using it as an ignition source for a dual fuel engine. Conversion from diesel to dual fuel operation merits substantial benefits in PM emission reduction. Assuming a 5% pilot amount, a once through process has been modeled and a first law analysis (using practical isentropic efficiencies) demonstrates that this combined system can be operated with a reduction of between 5%-10% of the equivalent diesel efficiency. Significant quantities (similar to 30 vol %) of hydrogen are introduced to the natural gas as a byproduct of the DME synthesis process. The corresponding increase in combustion efficiency must be validated by experiments to determine DME and H-2 requirements for successful pilot ignition of the natural gas/H-2 mixture.