Effects of Different Injection Timings on the Performance and Emission Characteristics of the Direct-Injection Compressed Natural Gas Engine

摘要

The primary objective of this research is to investigate the effects of different injection timings such as early, partial and late fuel injection timings on the performance and emission characteristics of the direct injection compressed natural gas (DI-CNG) engine. The research was conducted by experiment using single cylinder four stroke spark-ignition direct injection CNG engine at stoichiometric mixture, wide open throttle (WOT) and different injection timings. The results showed that by advancing the injection timing (early injection timing) produce a better brake torque across all engine speed compared to the other injection timing under the same operating conditions. While, partial injection timing gives out the lowest brake specific fuel consumption as it produces the least friction mean effective pressure inside the cylinder during the combustion process which lowered the amount of work done by the piston. At lower engine speed (up to 3000 rpm), BSNOx emission was notably lower at late injection timing. Drastic reduction in BSCO emissions was observed as more complete combustion process occurred at the operating condition under consideration. As the speed was increased above 3000 rpm, there is increase in BSCO emission. Early injection timing recorded the lowest BSUHC emission as homogeneous fuel mixture provides a complete combustion process which reduces the BSUHC emission. In addition, late injection timing increases the BSNOx and BSUHC emissions because of the lower quality of combustion process at that operating condition. From the foregoing, it is reasonable to say that the use of late injection timing to control BSNOx and BSUHC emission concentrations in DI-CNG engine is greatly discouraged. Thus it can be concluded that, the implementation of early and partial injection timing in DI-CNG engine is a viable approach towards realizing high performing internal combustion engine and curbing global warming by drastically reduce the emission of BSNOx, BSCO and BSUHC in DI-CNG engine.