Evaporation and mixing of ethanol-water mixture in a heavy duty common rail diesel engine intake air

Limited crude oil resources and growing environmental awareness have provided enormous motivation to seek new techniques utilising alternative fuels for diesel engines. In this study, testing on a heavy duty common rail diesel engine was carried out to examine the evaporation and mixing of aqueous ethanol in the inlet air. The engine was maintained at 1800 RPM and 926 Nm torque. Aqueous ethanol was added at different energy substitution rates (5%, 15% and 20%). Two different types of jet configurations (3-jets and 5-jets) were used to inject an ethanol/water mixture into the air stream. Exhaust emissions of oxides of nitrogen (NO_x), carbon monoxide (CO), hydrocarbons (HC), oxygen and carbon dioxide (CO₂) were measured. In general, the injection of ethanol resulted in reduction in the NOx whereas CO emission increased with increase in the rate of ethanol injection. To verify whether the aqueous ethanol was mixed and evaporated thoroughly, the temperatures across the pipe cross section were measured using a rotational two temperature probe device. For 5% energy substitution rate, the temperature distributions for both 3 and 5 jets were found to be uniform and ethanol was well mixed with air. However as the injection increased to 15%, the mixing of aqueous ethanol and compressed air did not occur homogenously across the pipe. Further for 20% substitution rate, the temperature across the pipe dropped sharply suggesting that 20% of ethanol/water mixture is above the maximum evaporation limit. To estimate the theoretical maximum amount of ethanol, the equilibrium temperature of the mixture was calculated. The results showed that a 5-jet configuration provided a better mixing compared to a 3-jet configuration.