Comparison of Propane and Methane Performance and Emissions in a Turbocharged Direct Injection Dual Fuel Engine

With increasingly restrictive $NOx$ and particulate matter emissions standards, the recent discovery of new natural gas reserves, and the possibility of producing propane efficiently from biomass sources, dual fueling strategies have become more attractive. This paper presents experimental results from dual fuel operation of a four-cylinder turbocharged direct injection (DI) diesel engine with propane or methane (a natural gas surrogate) as the primary fuel and diesel as the ignition source. Experiments were performed with the stock engine control unit at a constant speed of 1800 rpm, and a wide range of brake mean effective pressures (BMEPs) (2.7–11.6 bars) and percent energy substitutions (PESs) of $C3H8$ and $CH4$⁠. Brake thermal efficiencies (BTEs) and emissions (⁠$NOx$⁠, smoke, total hydrocarbons (THCs), CO, and $CO2$⁠) were measured. Maximum PES levels of about 80–95% with $CH4$ and 40–92% with $C3H8$ were achieved. Maximum PES was limited by poor combustion efficiencies and engine misfire at low loads for both $C3H8$ and $CH4$⁠, and the onset of knock above 9 bar BMEP for $C3H8$⁠. While dual fuel BTEs were lower than straight diesel BTEs at low loads, they approached diesel BTE values at high loads. For dual fuel operation, $NOx$ and smoke reductions (from diesel values) were as high as 66–68% and 97%, respectively, but CO and THC emissions were significantly higher with increasing PES at all engine loads.