6.3 Combustion and knock tendency
The optimized water/fuel combination is then deeply investigated to evaluate the effect of water injection on knock. The original fuel-only case is used as a reference. As visible from Fig. 7 below, the charge temperature in the combustion chamber at the spark time is lower for the water injection case. Combustion is slightly slowed down by the combination of lower temperatures and higher residual gas concentrations. This results in a decrease of the incylinder pressure peak, visible in Fig. 8 (a), and in a simultaneous drop of the end-gas reactivity, since for the water case there is no signal of any autoignition heat release, Fig. 8(b). A visual confirmation is reported in Fig. 9, where the flame front distribution at 740°CA is reported.