Energy & Fuels, Vol.20, No.1, 84-90, 2006
Effect of methanol addition into gasoline on the combustion characteristics at relatively low temperatures
A reliable and rapid cold start of the engine is related with the unburned hydrocarbon (HC) emissions as well as energy efficiency. Because combustion characteristics are relevant parameters for a reliable combustion process, an experimental investigation on the combustion characteristics has thus been made in a constant volume combustion bomb for methanol-gasoline blended fuel at relatively low temperatures. The effects of the equivalence ratio of the combustible mixture on the combustion pressure, ignition delay time, mass burning rate, and the flame propagation speed are mainly studied. It is shown that moderate methanol addition can slightly improve the combustion performance at low temperatures, compared to that of pure gasoline fuel, because methanol addition into gasoline results in the improvement of blend evaporation. The exhaust emissions are measured in terms of unburned HC, carbon monoxide (CO), and oxides of nitrogen (NOx) emissions. It is reported that the emissions of HC during the rich fuel/air mixture combustion at relatively low temperatures increase with the increasing addition of methanol into gasoline, because of the enhanced evaporation of blended fuel, compared to gasoline. However, in view of the separated optimization equivalence ratio for low temperature combustion, HC and CO emissions can be obviously reduced when moderate addition is used, because a leaner mixture has been supplied to realize rapid combustion for blended fuels. The flame speeds are investigated as well. It is shown that, at temperature ranging from 358 to 400 K, the suitable fuel/air ratio of blended fuels to realize fast flame propagation is about 1.3.