The Effect of Fuel Composition on Ignition Delay and Knocking in Lean Burn SI Engine

Super lean burn technology is conceived as one of methods for improving the thermal efficiency of SI engines[1][2]. For lean burn, reduction of heat loss and the due to decrease in flame temperature can be expected. However, as the premixed gas dilutes, the combustion speed decreases, so the combustion fluctuation between cycles increases. Also, to improve the thermal efficiency, the ignition timing is advanced to advance the combustion phase. However, when the combustion phase is excessively advanced, knocking occurs, which hinders the improvement of thermal efficiency. Knocking is a phenomenon in which unburned gas in a combustion chamber compressed by a piston and combustion gas suffer compression auto-ignition. It is necessary to avoid knocking because the amplitude of the large pressure wave may cause noise and damage to the engine. Also, knocking is not a steady phenomenon but a phenomenon that fluctuates from cycle to cycle. Many studies have already been made on the knocking characteristics that occurred during stoichiometric combustion[3], but there have been no reports on knocking characteristics in super lean burn near the excess air ratio of 2.0. In order to establish super lean burn technology it is essential to grasp the knocking characteristics of super lean burn. In this research, we aim to clarify the factors that fuel composition affects auto-ignition of unburned gas using SIP common 5 component surrogate fuel.