Characteristics of Evaporating Spray for Direct Injection Methanol Engine: Comparison between Methanol and Diesel Spray

Abstract

In the context of global efforts to pursue carbon neutrality, the research on the application technology of methanol fuel in internal combustion engines has ushered in a new peak. In order to provide a theoretical basis for the development of direct injection methanol engines, the spray characteristics of methanol with high-pressure direct injection were studied. Based on the visualization experimental device of constant volume vessels, the diffused background-illumination extinction imaging (DBI) and schlieren methods were applied to examine the distinctions in the evaporating spray properties between methanol and diesel under different injection pressures and ambient temperature conditions. Furthermore, aiming to maximize the potential of methanol fuel in compression ignition engines, under the premise that the alternative fuel can obtain the same total fuel energy as diesel, two different injection strategies of methanol were proposed and evaluated through the coordination of the nozzle hole diameter, injection pressure and injection duration. It reveals that it is easier for methanol spray to evaporate because of the lower boiling point, which results in a shorter spray tip penetration and wider spray angle compared with those of diesel, especially under the middle-level ambient temperature (600 K) condition. These deviations are also observed under different injection pressure conditions. However, affected by the lower energy density, the strategies of injecting the same fuel energy of methanol with that of diesel prolong the methanol spray tip penetration, enlarge its spray area and sacrifice the methanol evaporation performance. It is necessary for the geometrical design of the combustion chamber to coordinate with the hole diameter and injection pressure selection to deal with the huge distinctions in the spray characteristics between methanol and diesel fuel.