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

With increasingly restrictive NO_x and PM 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-fueling a four-cylinder turbocharged 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 ECU at a constant speed of 1800 rev/min, and a wide range of BMEPs (2.7 to 11.6 bar) and percent energy substitutions (PES) of C₃H₈ and CH₄. Brake thermal efficiencies (BTE) and emissions (NO_x, smoke, THC, CO, and CO₂) were measured. Maximum PES levels of about 80–95 percent with CH₄ and 40–92 percent 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 fueling BTEs were lower than straight diesel BTEs at low loads, they approached diesel BTE values at high loads. With dual fueling, NO_x and smoke reductions (from diesel values) were as high as 66–68 percent and 97 percent, respectively, but CO and THC emissions were significantly higher with increasing PES at all engine loads.