分会场

高效清洁燃烧

摘要

In the global background of “Carbon Peak” and “Carbon Neutral”, natural gas shows a great advantage in energy-saving and pollution reduction. However, it suffers from lean combustion instabilities when applied to internal combustion engines. In this paper, the effect of turbulence enhancement on improving lean combustion performance of natural gas was investigated in an optical SI engine with high compression ratios. A variable swirl valve was designed and combined with intake tumble to achieve various turbulent flow and turbulent intensity. Particle image velocimetry (PIV) was employed to measure in-cylinder turbulent flow and high-speed photography was employed to capture combustion evolutions. The results show that in-cylinder turbulent intensity is enhanced as swirl is increased. There is little variation in the sensitivity of IMEP to spark timing, but the increase of combined-turbulence will greatly increase flame propagation speed and improve thermal efficiency. The analysis of flame images shows that turbulence intensity gradually increases in the radial orientation from the spark plug to the cylinder wall, which leads to an earlier flame kernel and a faster burning rate. This combined-turbulence can reduce the cyclic variations of early flame development and optimize the whole combustion process.

关键词

复合湍流;稀薄燃烧;早期火核;火焰速度;涡流比

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