Experimental Study on the Burning Rate of Methane and PRF95 Dual Fuels 2016-01-0804
Natural gas as an alternative fuel offers the potential of clean combustion and emits relatively low CO2 emissions. The main constitute of natural gas is methane. Historically, the slow burning speed of methane has been a major concern for automotive applications.
Literature on experimental methane-gasoline Dual Fuel (DF) studies on research engines showed that the DF strategy is improving methane combustion, leading to an enhanced initial establishment of burning speed even compared to that of gasoline. The mechanism of such an effect remains unclear.
In the present study, pure methane (representing natural gas) and PRF95 (representing gasoline) were supplied to a constant volume combustion vessel to produce a DF air mixture. Methane was added to PRF95 in three different energy ratios 25%, 50% and 75%. Experiments have been conducted at equivalence ratios of 0.8, 1, 1.2, initial pressures of 2.5, 5 and 10 bar and a temperature of 373K. At stoichiometric conditions, experiments in an SI engine have been also performed.
It has been found that methane and all DFs have their fastest burning rate at stoichiometric conditions whereas PRF95 at rich conditions (Φ=1.2). At lean conditions (Φ=0.8), all DFs resulted in faster combustion than PRF95, whereas methane is the slowest of all. At rich conditions, DF75 and DF50 are slower than methane. The transition mechanism between the constant volume combustion experiments and those in the engine environment resulted in a larger increase in the burning speed of methane and all DFs in comparison to that of the liquid fuel.