Abstract
Due to its intrinsic characteristics of spark-ignited engine, engine operation under high compression ratio can bring to high efficiency but also can invoke the knock which can cause mechanical failure. Because knock is highly dependent on in-cylinder thermal boundary condition, it is important to investigate the relationship between in-cylinder condition and wall temperature. Therefore, this study mainly focuses on the effect of cylinder wall temperatures on knock phenomena. Dual-loop coolant passages for cylinder head and liner facilitated the control of independent coolant temperature. It was enabled to investigate the effect of each component. By temperature measurements around the combustion chamber, as a coolant temperature variation does not affect a lot to the other’s wall temperature, it was verified that independent wall temperature control was achieved. Also, piston surface temperature was found to be governed by liner wall temperature. In addition, by refined experimental methodologies, the knock mitigation effect was observed by the load limit expansion. It was found that head cooling strategy has a significant role on knock mitigation. For deeper understanding, 3D CFD simulation was used in this study. As the result, it was found that the intake port wall is highly influential on the heat transfer to gas during the gas induction phase. In addition, excluding the heat transfer in the intake port, it was found that the liner cooling strategy has a remarkable potential to reduce the gas temperature for knock suppression.