Effect of Higher Content N-Butanol Blends on Combustion, Exhaust Emissions and Catalyst Performance of an Unmodified SI Vehicle Engine 2012-01-1594

To reduce exhaust emissions and dependency on petroleum-based fuels, various alcohols have been considered as gasoline substitutes for spark ignition engines. In the existing vehicle fleet, the use of ethanol, the most widely used alcohol, is practically limited to blends in relatively small concentrations with gasoline, due to its hygroscopicity, aggressivity, substantially lower heat content, and high latent heat. Butanol has relatively low toxicity, can be produced from biomass, and has higher energy density, lower latent heat, lower hygroscopicity and lower aggressivity than ethanol. In this study, the effects of blends of 30% and 50% of n-butanol (1-butanol) with gasoline on combustion process, engine control unit adaptation and exhaust emissions before and after a three-way catalyst were examined on a 1.2-liter, three-cylinder, four-valves-per-cylinder, naturally aspirated port-fuel-injected Skoda 1.2 HTP spark ignition engine coupled to an engine dynamometer. The adaptation of engine control unit and its effects on the fuel injection rates and air-fuel ratio, along with in-cylinder indicated pressures, exhaust gas temperatures and gaseous emissions were investigated at thirteen steady-state operating points. Where the engine maintained stoichiometric air-fuel ratio on gasoline, the engine control unit has adapted relatively successfully: stoichiometric operation was observed on both butanol blends, with lower HC both before and after catalyst, comparable CO, and slightly higher engine-out NO_x and lower or higher NO_x after the catalyst. With increasing rpm and loads, the engine control unit has retarded the spark timing to prevent excessive knock. Compared to gasoline, the duration of the early combustion stage was for butanol blends slightly shorter and the length of the main phase of combustion was generally comparable. Flame propagation was faster with higher butanol content. Where the engine employed commanded enrichment, the fueling rate was comparable among fuels, resulting in relative enleanment when operating on blends, with lower HC and CO, higher NO_x, and higher exhaust gas temperatures by up to 50°C. Maximum engine torque has decreased by up to 3%. Changes in cycle-to-cycle variability were non-uniform. The findings were generally positive, and while limited to the one engine tested, suggest some opportunity for further investigation of the use of higher content n-butanol blends as candidate fuels for existing fleets.