Study on characteristics of methanol evaporating spray based on empirical formulas and similarity theory

Abstract

With global carbon neutrality in mind, methanol has garnered significant attention from the internal combustion engine industry. High-pressure methanol direct-injection can realize diffusive combustion and high substitution rate, which can enhance the engine efficiency and decrease the carbon emission. Therefore, optical visualization experiments on methanol evaporation spray were conducted to clarify the behavior of high-pressure direct injection methanol spray, and the spray empirical formulas and similarity analysis were applied to expand the theory of methanol spray. Initially, spray characteristics of diesel and methanol were compared to assess the applicability of diesel spray theories to methanol. Based on this, empirical formulas for diesel spray were applied to methanol spray to identify those that can better describe methanol spray characteristics. Finally, spray similarity theories based on Chikahisa’s geometric similarity theory and Inagaki’s optimized Wakuri’s momentum theory were applied to methanol sprays to verify whether they exhibit similarities as diesel sprays. It shows that among the empirical formulas for spray tip penetration, Arai’s formula showed the best predictive performance with an average relative error of 3.19%. For spray angle formulas, Arai’s formula also demonstrated the highest predictive accuracy, though the relative error reached 10.78%. After correcting the coefficients of Arai’s formula, the average relative error between the corrected spray angle predictions and experimental values decreased to 3.4%. When using similarity theory to analyze methanol spray characteristics, the spray tip penetration generally followed similarity theory rules, while the spray angle did not yield satisfactory results after similarity scaling.