Numerical simulation on the effects of n-butanol combined with intake dilution on engine knock.

The improvement in thermal efficiency of GDI engine is severely limited by knocking. The effects of n-butanol combined with intake dilution on engine knock and thermal efficiency were studied in this paper. The results show that the combustion activity of n-butanol containing OH functional group can be improved by blending a small amount, and then the detonation intensity and thermal efficiency can be improved. When a high proportion of n-butanol is mixed, the knock strength and thermal efficiency will be reduced due to the effect of low calorific value and latent heat of vaporization. In particular, the maximum value is reached when 15% n-butanol is employed. The spontaneous combustion tendency is reduced by intake dilution, and the influence degree is reduced in the order of EGR dilution, compound dilution and air dilution, which is caused by the different amount of CO 2 in the three dilution gases. When R A = 1.2 and R A-E = 1.2, the knock intensity of GDI engine burning Bu15 is reduced by 96.3% and 98.4%, respectively. Therefore, when n-butanol combined with composite dilution is selected, the occurrence of knocking can be suppressed, while ensuring high thermal efficiency. Current study can provide theoretical guidance for knock suppression of GDI engines. • The mechanism about the intake dilution improving the performance of GDI engines. • When the Bu15 is employed, the peaks of both thermal efficiency and knock intensity. • When R A-E = 1.2, engine knock intensity of burning Bu15 is reduced by 98.4%. • Thermal efficiency can be improved by n-butanol combined with compound dilution. [ABSTRACT FROM AUTHOR]