Numerical investigation the effects of the twin-spark plugs coupled with EGR on the combustion process and emissions characteristics in a lean burn natural gas SI engine

In this study, the single-spark natural gas (NG) SI engine was simulated by using the CFD coupled with detailed combustion mechanism, and validated against with the experiment data. Additionally, the axisymmetrically twin-spark plugs were placed diametrically opposite to each other in the combustion head of the NG SI engine, and fired simultaneously during the simulation cases to trigger two independent spark kernels. The results indicated that twin-spark plugs yielded approximate combustion phasing and better fuel conversion efficiency. Interestingly, in the early stages of flame propagation triggered by the twin-spark plugs configuration, two independent spark kernels looked remarkably similar to the iconic of "Taiji" diagram of the Chinese Taoism, and two independent flame kernels were obviously moved along with the flow. The strong flow pushed the flame front close to the side of the intake port of the NG SI engine equipped with the single-spark plug. While two independent flame fronts of the NG SI engine equipped with the twin-spark plugs were located separately at the intake and exhaust ports in the combustion chamber. Furthermore, two independent flame fronts mutually collided with each other, and generated more independent combustion block areas in the center of the combustion chamber. (C) 2020 Elsevier Ltd. All rights reserved.