Knock characterization and development of a new knock indicator for dual-fuel engines

Abstract

Dual-fuel mode is a promising technique for natural gas utilization in internal combustion engines. However, for high loads operation, the engine risks to go through a hazardous knocking regime. Knock phenomenon is an abnormal combustion that can cause some disagreeable effects in engines where it occurs. It can even induce brutal irreparable engine damage under severe knocking conditions. The present paper aims first to highlight and characterize knock in dual-fuel engines fueled with natural gas as main fuel and diesel as pilot fuel. Description of this phenomenon is investigated in this type of engines. Knock behavior in dual-fuel engine is compared to spark ignition engine case. Cyclical variability of this phenomenon is studied. A new knock indicator, based on in-cylinder pressure analysis, is proposed in order to identify and evaluate knock in dual-fuel engines. In addition, knock effects on heat release, cylinder wall temperature and engine performance and emissions are examined. New techniques to delay knock appearance in this type of engines are investigated. It is found that the increase in pilot fuel quantity is an effective technique to delay knock onset in NG dual-fuel engines