Analysis of knocking combustion with methanol/iso-octane and ethanol/iso-octane blends in a spark-ignition engine

• Published in: Fuel (Guildford) 2021-01, Vol.284, p.118979, Article 118979
• Main Authors: Wei, Jianan, Feng, Hongqing, Liu, Haifeng, Zhu, Hongyan, Yue, Zongyu, Yao, Mingfa
• Format: Article
• Language: English
• Subjects: Alcohols; Combustion; Elastic waves; Ethanol; Heat; Heat release rate; Heat transfer; Integrals; Intensity of interaction; Isooctane; Knock; Methanol; Mixtures; Parameters; Pressure; Pressure oscillations; Spark ignition; Spark-ignition engine
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2020.118979

•Numerical simulation was carried out to simulate knock combustion of methanol/iso-octane and ethanol/iso-octane blends.•A new parameter I was come up for the description of the Intensity of interaction between flame core and pressure wave.•Dimensionless IIntegral was calculated basing on parameter I to evaluate the intensity of knock. The effects of methanol/iso-octane and ethanol/iso-octane blends on knock behavior were investigated under a known knocking condition with the mixing proportion of 10% and 30%. From the analysis of temperature, fuel consumption rate, heat release rate and pressure rise rate, the results revealed that iso-octane with 10% ethanol accelerated the combustion speed after the onset of knock, and demonstrated a higher heat release rate and pressure rise rate. However, its knock intensity was lower than that of pure iso-octane and methanol/iso-octane blends. In addition, methanol in blends enhanced the knock intensity of iso-octane especially under the blend ratio of 30%. Hence, to further analyze the reason of knock enhancement and the difference for two alcohols, a new parameter of I that measure the intensity of interaction between flame core and pressure wave was considered. It showed that methanol was more easily to induce the interaction between flame and pressure and thus resulted in more intense knock, compared with iso-octane and ethanol. The dimensionless integral IIntegral for M10 (0.0822/0.0799) and M30 (0.1193/0.0859) were higher than those of E10 (0.0320/0.0227) and E30 (0.0518/0.0236), respectively. Furthermore, the parameter I and its dimensionless integral IIntegral were compared with pressure oscillation and five knock criteria to verify its ability of describing knock, and it can be concluded that the parameter I and its dimensionless integral IIntegral were capable of evaluating the knock intensity from the view of pressure and heat release.