Application and extension of diesel spray theory in analysis of methanol spray characteristics under high-pressure injection conditions

Methanol has received widespread attention as a kind of alternative fuel for internal combustion engines because of its wide range of sources, low price, low combustion emission pollution, and carbon neutrality. Meanwhile, the relatively developed diesel spray theories have a great reference value to theoretical analysis of high-pressure methanol injection. Based on the optical experiment of the methanol sprays under high-pressure injection conditions, the empirical models for predicting spray tip penetration, spray angle, spray area, and spray volume of diesel were used to calculate the parameters of the methanol sprays. These calculation values were then compared with the experimental values to establish empirical models of high-pressure methanol spray characteristics. On this basis, an assessment of the adaptability of the diesel spray similarity theory applied to the high-pressure methanol sprays was conducted under similarity conditions. The results show that Wakuri's model has the best predictive performance on the methanol spray tip penetration (the average relative error is 4.31%), and Inagaki's model provides the most precise predictions on the methanol spray angle (the average relative error is 2.63%). After correcting the constants, empirical models that can describe the methanol spray characteristics in this experiment were proposed. In terms of the similarity theory, the diesel spray similarity theory shows good adaptability to the spray tip penetration and spray angle of the high-pressure methanol sprays with nozzle diameters of 0.12 mm and 0.15 mm under similarity conditions. The above results can serve as a basis for extending diesel spray theory to methanol and for the upsizing or downsizing design of direct injection methanol engines with different bore sizes of the same series.