Experimental study on knocking combustion in compressionignition engines under high-altitude conditions

Abstract

Diesel engine combustion becomes very rough or even detonation under high altitude conditions, which is harmful to components durability. In this study, combustion characteristics were experimentally investigated on a V6 heavy-duty diesel engine using by a plateau simulation test bench to simulate altitude conditions of 1000 m, 3000 m and 4500 m. Results show that extremely high peak pressure rise rates of above 50bar/°CA exist at low speeds under the altitude of 4500 m. This indicates that not only does knocking combustion exist in spark-ignition (SI) engines, but also can be found in compression-ignition (CI) engines. Knock intensity (KI) is calculated by the pressure oscillation with high-pass filtering (HPF). Approach of cycle to cycle variation was adopted to study combustion characteristics on the comparisons of knock and non-knock states. Also, the correlation between KI and peak pressure rise rate was revealed through the linear regression method.