The misfire degree and its effects on combustion and pollutant formation of subsequent cycles: A study on a high speed gasoline engine

Abstract

Misfire has attracted lots of researcher?s attention as a common engine fault, but most researchers focus on misfire diagnosis. For motorcycle engines, misfire is more worth to investigate because of the more extensive operation windows. The misfire degree is detected by experiment and its effect mechanism on subsequent cycles is investigated through simulation. Its effect is analyzed through two aspects: 1) misfire cycle leaves about 10.8% fuels that participate in next cycle working process, leading to richer fuel/air mixture. But 13.8 % lower of in-cylinder peak pressure than normal scenario is observed. Then interaction between flame propagation and flow field is discussed. The effect of misfire on flow field intensity is small, but it changes flow field structure largely. This change evolves persistently during subsequent processes, superimposing the lower temperature brought by misfire of last cycle, resulting in slower flame propagation and thus lower thermal efficiency for misfire scenario. This impact can last 3-4 subsequent cycles until gradually fades away; 2) for pollutants formations, the NO emission is lower for misfire scenario due to the lower in-cylinder temperature, but HC emission is higher. Although higher CO is produced during main combustion phase for misfire scenario, it converts to CO2 more largely during post flame stage, resulting in almost the same final amount relative to normal scenario.

The effect of pipe-line structure on the flammability characteristics of hydrogen-air premixed gas under end-opening conditions

“…The gradual development and concentration of vortices lead to the gradual increase of turbulence intensity in the pipe. Higher turbulent kinetic energy accelerates the flame propagation and combustion speed [23]. The farther the flame front is from the ignition end, the more obvious the flame tip stretches (shown in Fig.…”

“…The flame propagation process is mainly affected by the mixture composition and the interaction between flame propagation and flow field structure [23]. Figures 4 to 6 show the flame structure and flow field distribution in each pipe structure, and the instantaneous state of flame propagation is reflected by different colour.…”