Abstract:
Micro combustion process of micro IC engine is very sensitive to changes of equivalent ratio and speed. The laminar flow finite rate model and methanol chemical reaction mechanism is adopted to simulation its premixed laminar combustion process. And then, the influence law of equivalent ratio and speed on micro combustion characteristic is explored, and the critical operation parameters are investigated. Finally, the thermal ignition theory and chemical reaction kinetics theory is adopted to explore the influence of equivalent ratio on micro combustion characteristic mechanism. The results show that simulation results agree well with experiment. When equivalent ratio increases from 0.6 to 1.1, the combustion rate, the pressure and the temperature increase, pressure peak increases by about 1.5E+6 Pa and the maximum temperature increases by about 1 300 K. Since then, with the increase of ratio equivalent, the combustion rate, the pressure and the temperature also reduce. Moreover, the research reveals the mechanism that equivalent ratio affects micro combustion characteristic. In dilute zone, equivalent ratio mainly affects micro combustion performance by temperature changes. As equivalent ratio increases, fuel concentration and released heat increase, thus the temperature and the pressure increase, and then combustion ratio increases. In thick zone, equivalent ratio mainly affects micro combustion performance by oxygen changes. As equivalent ratio decreases, oxygen volume and reaction rate decrease, thus combustion ratio decreases, and then the temperature and the pressure decrease. When the speed lifts, the time for combustion is shortened, thus the complete combustion level reduces and the temperature and the pressure drop. Because of relatively large heat loss and short residence time of micro combustion, the complete combustion operation area of micro engine is narrow. The lean burn limit to realize complete combustion is about 0.9 in our experiments, and the highest speed is about 6 000 r/min. It is worth to being paid attention to when the micro IC engine is designed.
