The effect of energy density and wall temperature and their interaction on the knock intensity of isooctane/air and n-heptane/air mixtures was investigated on a rapid compression machine. Results show that with the increase of energy density and wall temperature

the knock intensity of both fuels increases significantly. For isooctane/air mixture

the effect of energy density on knock intensity is significantly enhanced with the increase of wall temperature. Moreover

the influence of wall temperature on knock intensity is also significantly enhanced with the increase of energy density. However

the n-heptane/air mixture basically does not have the above relationship

and its knock intensity is always at a higher level

which indicates that the energy density and wall temperature have different influence on the knock intensity for different active fuels.