Mixture formation characteristics and feasibility of methanol as an alternative fuel for gasoline in port fuel injection engines: Droplet evaporation and spray visualization

Under the background of energy saving and emission reduction, methanol is considered an ideal alternative fuel for gasoline because of its renewability, high combustion efficiency and low emissions, while an issue is the cold start of methanol port fuel injection engines. To comprehensively understand the underlying mechanisms and the feasibility of methanol as a substitute of gasoline, a suspension method was first used to investigate the evaporation characteristics of methanol and gasoline droplets at low temperatures. Then an optical intake port was constructed based on the outer contour modification strategy and an optical distortion correction algorithm was proposed. The effects of inlet temperature, inlet flow rate and injection pressure on spray characteristics of methanol and gasoline were comparatively investigated. In addition, the influence of valve temperature on the characteristics of spray impingement on a valve was studied. The results showed that the difference between the evaporation rates of methanol and gasoline was small at 60-90 degrees C. The difference became obvious when the temperature was below 60 degrees C or above 90 degrees C. Reducing the ambient humidity may reduce this difference and improve the cold start performance of methanol engines. A higher inlet temperature slightly increased the spray area. A higher inlet flow rate and injection pressure significantly increased the spray area, but also caused serious wet wall problem. From the point of view of spray in the port, methanol was a feasible substitute for gasoline in the presence of inlet flow and at low injection pressure of 6 bar. The valve temperature should exceed 200 and 230 degrees C for methanol and gasoline, respectively to form vapor films that prevent fuel adhesion onto the valve. However, methanol may not be a suitable alternative fuel for gasoline when spray directly impacted on the valve in port fuel injection engines due to its much smaller spray area.