An Experimental Study on the Knock Mitigation Effect of Coolant and Thermal Boundary Temperatures in Spark Ignited Engines

Paper #:
  • 2018-01-0213

Published:
  • 2018-04-03
Abstract:
Increasing compression ratio is essential to develop the future high-efficiency spark-ignited engines. However, it inevitably involves the knock occurrence during the combustion. Among a lot of methods, efficient cooling strategy of the engine components is considered as one of the practical ways to suppress knock occurrence. In this study, the effect of thermal boundary conditions on knock phenomena was observed while the temperatures of the cylinder thermal boundaries (head, liner and piston) were controlled independently. While controlling independently, by measuring the temperatures of each of them, the expansion of the detonation border line (DBL) and the advance of the ignition timing were investigated. The effect of the piston oil-cooling gallery was also investigated for further knock mitigation. In addition, the difference of the effect on two different type of single cylinder engines which are MPI and GDI type (CR=12) was also observed in this study. As the result, it was shown that 31.4%, 18.4% of DBL expansion was achieved at 1500 and 2000rpm, respectively. And approximately 0.2CA of ignition timing advance was achieved while decreasing 1°C of the coolant temperature. Piston oil-cooling gallery showed a great effect on knock mitigation by lowering the wall temperature efficiently, as well. It was clearly found that the cylinder head has the greater effect on knock mitigation in terms of the coolant temperature. However, by controlling the temperature of the thermal boundaries, decreasing temperature of the liner showed the greater effect on knock mitigation in terms of wall temperature due to the heat exchange during the intake process.
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