Modeling Investigation of Different Methods to Suppress Engine Knock on a Small Spark Ignition Engine

Abstract

Knock is the main obstacle toward increasing the compression ratio and using lower octane number fuels. In this paper, a small two-valve aircraft spark ignition engine, Rotax-914, was used as an example to investigate different methods to suppress engine knock. It is generally known that if the octane number is increased and the combustion period is shortened, the occurrence of knock will be suppressed. Thus, in this paper, different methods were introduced for two effects, increasing ignition delay time in end-gas and increasing flame speed. In the context, KIVA-3V code, as an advanced 3D engine combustion simulation code, was used for engine simulations and chemical kinetics investigations were also conducted using chemkin. The results illustrated gas addition, such as hydrogen and natural gas addition, can be used to increase knock resistance of the Rotax-914 engine in some operating conditions. Replacing the traditional port injection method by direct injection strategy was another way investigated in this paper to suppress engine knock. Some traditional methods, such as adding exhaust gas recirculation (EGR) and increasing swirl ratio, also worked for this small spark ignition engine.