A Study on PCCI Combustion Control in Medium Speed Dual-Fuel Engine

To achieve simultaneous reduction of CO₂ and NO_x emission from the Dual-Fuel (DF) engine using natural gas and diesel fuel, Premixed Charge Compression Ignition (PCCI) type combustion is a promising technology. However, to apply this technology to the practical operation of the DF engine, combustion control is key challenge because the ignition of PCCI type combustion is governed by chemical reaction of natural gas/air and diesel fuel premixture and not controlled by direct control parameter such as spark timing of spark-ignition natural gas engine or diesel fuel injection timing of micro-pilot type DF engine. The focus of this study is to understand the effect of engine control parameters on DF-PCCI combustion characteristics to establish the combustion control strategy in medium speed DF engine. Engine experiments using a 4-stroke medium speed single cylinder engine were carried out. Firstly, early two stage diesel pilot injection was applied to realize DF-PCCI combustion. As a result, brake thermal efficiency was successfully improved by 2%pt compared with conventional micro-pilot combustion while achieving low NOx emission to meet the stringent emission standard. THC emission was successfully reduced at the same time. Secondly, the effects of engine control parameters on DF-PCCI combustion characteristics were investigated. Finally, DF-PCCI combustion control strategy in the medium speed engine is discussed and proposed based on the engine test results.