A Timed Fuel-Injection Spark-Ignition Engine Operated by Methanol Fuels 900355
The combustion in a spark ignition engine was studied when it was fueled by neat methanol using the timed injection method at the intake port. The measurements from this fueling were compared with those obtained from a carburetor fueled operation. In the study, results of the cylinder pressure analysis and the in-cylinder high-speed photographic observation showed that the reaction in the timed methanol engine combustion had multiple-stage combustion processes. The multiple-stage reaction was pronounced based on the double spikes in heat release history and droplets individually burning in the mixture. The injection time for the best methanol fueled engine operation seemed to be that right after the intake valve opening when the lowest specific fuel consumption was obtained with smallest cyclic variation in the pressure-time history and when the lowest emissions (NOx, UHC and HCHO) were produced. Some heating of the fuel in the timed injection improved various engine functions, i.e., emission, efficiency and cyclic variations. The brake thermal efficiency with the timed injection method was lower than that with the carburetor fueling method. However, when the fuel temperature was increased both efficiencies approached each other particularly when the mixture was slightly leaner than stoichiometric. The water content and EGR in the mixture exhibited a similar effect on the combustion processes in the timed methanol injection engine; both contents decreased NOx emission, increased UHC, and caused cyclic variation in pressure-time history. When the period of time for the in-cylinder mixture increased by injecting earlier in the timed injection, emissions of UHC and HCHO increased in this method. This was explained by excessive mixing in the stratified charge of the timed injection fueling.