Abstract
The increasingly strict worldwide emission regulations for internal combustion engines force car manufacturers to exploit innovative combustion technologies. One expects a change from pure thermal engines to more advanced internal combustion engine. A high engine compression ratio with high EGR dilution has an impact on increasing engine efficiency. A compelling concept to burn diluted combustion can be a DM-TJI combustion system, which consists of a pre-chamber and main chamber connected with one or more small orifices. This technology effectively achieves diluted combustion by improving engine dilution tolerance and knock performance. This paper focused on the impact of engine speed with variation in pre-chamber nozzle orifice diameter. Experiments were conducted with three different pre-chamber nozzle orifice diameters of 1.25, 1.5, and 1.75 mm with an engine speed range from 1500 to 2300 rpm. A numerical analysis was conducted to investigate the nozzle orifice diameter effect on the engine speed beyond 2500 rpm. Engine speed variation affects the performance of each orifice’s diameters. Small orifice diameter performs better for lower engine speed, and large orifice diameter performs better for higher engine speed. The 1.25 mm orifice diameter provided fast combustion. However, when the engine speed increases, the combustion stability suffers. Orifice diameter of 1.5 mm has better combustion stability in all tested speed ranges and higher efficiency in the speed range of 1500–2000 rpm, with a maximum indicated efficiency of 44.18%. The 1.75 mm orifice diameter performs better in the high engine speed ranges between 2100 and 2300 rpm, with a maximum indicated efficiency of 44.56% at an engine speed of 2300 rpm. This study has demonstrated the capability of the DM-TJI system to work with a high level of EGR dilution (up to 45%) and delivered a better indicated efficiency than the conventional spark ignition engines.
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