Research on the impact of quantitative configuration of spark plugs on combustion and emission characteristics in opposed free piston engine generators

The opposed free piston engine generator has emerged as an important research direction for breaking through the efficiency and emission limitations of conventional internal combustion engines, due to its compact structure, high efficiency, and flexible variable compression ratio. This study takes the OFPEG as the research object, establishes a combustion system simulation model, and calibrates the model based on experiment data. The study investigates in detail the influence of quantitative configuration of spark plugs on the in-cylinder working process of the OFPEG under different ignition timing. The results show that as the quantitative of spark plugs increases, the flame propagation speed in-cylinder is accelerated, and the combustion duration can be reduced by up to 14.4°ECA. However, when the ignition timing is advanced, the increase in the quantitative of spark plugs causes the combustion process in the cylinder to occur during the compression stroke, which is not conducive to improving system performance, resulting in a 59.32 % increase in NOx emissions. When the ignition timing is 12°ECA BTDC, the use of three spark plugs can achieve an indicated thermal efficiency of 42.32 % and an indicated power of 14.46 kW.