| This paper used the GT-POWER software, combined with SI turbulence combustion model. Based on the influence on flame speed affected by different oxygen concentration, this paper analyzed the influence on combustion characteristics of gasoline engine affected by oxygen concentration under theoretical air-fuel ratio. In order to analyze the total effect by the oxygen concentration and different influencing factor, this paper selected four different oxygen concentrations. Further more, this paper analyzed the energy and the availability changes of gasoline engine under different oxygen concentration. 1. The influence on combustion characteristics of gasoline engine affected by oxygen concentration under theoretical air-fuel ratio:①. The maximum burn rate and the maximum heat release rate happen at the crank angle when 50% fuel burned. When the oxygen concentration increases, the maximum burn rate and the maximum heat release rate increases before this angle, and decreased after this angle.②. When the oxygen concentration increases, the combusting lagging period and the 0-50% fuel burn duration decrease, the 50-75% fuel burn duration decrease, but the 75-90% fuel burn duration and the main burn duration increase, the total combustion duration decreases a little, the total combustion duration is shortest when the oxygen concentration is 25%.③. When the oxygen concentration increases, the coefficient of residual gas decreases, the average temperature and the maximum temperature increase, the time when the maximum temperature happens is earlier than before, the heat transfer and exhaust energy increase.④. When the oxygen concentration increases, the pressure, the brake mean effective pressure, the maximum rate of pressure rise and the maximum pressure increase, the time of the maximum pressure and of the maximum rate of pressure rise are earlier than before, the brake power and torque increase and have the same maximum increase rate of 21%, the brake efficiency and the brake specific fuel consumption have a maximum decrease rate of 2%. Before the maximum rate of pressure rise, when the oxygen concentration increase, the rate of pressure rise increase, and after the maximum rate of pressure rise, the rate of pressure rise decrease when the oxygen concentration increase.⑤. When the oxygen concentration increases, the NOx increases rapidly, but the increase rate is shorter and shorter when the oxygen concentration is higher and higher. When the oxygen concentration changes from 21% to 23%, 25% and 27%, the NOx increase rate changes from 36.2% to 50.7% and 56.2%.2. The total effect by the oxygen concentration and different influencing factor under theoretical air-fuel ratio:①. Influence of speed: When the oxygen concentration increases, the power and the torque increase at the same speed.②. Influence of intake pressure: When the intake pressure increases, the power and the torque increase linearly. When the oxygen concentration increases, the power and torque increase at the same intake pressure, and the increase rate is higher when the intake pressure is higher. When the intake pressure is 16.8% lower than the standard air pressure, the 27% oxygen concentration can reach the same dynamic performance as the standard air pressure.③. Influence of intake temperature: When the intake temperature increases, the power and the torque decrease. When the oxygen concentration increases, the power and the torque have the maximum increase rate of 21%.④. Influence of load: When the load increases, the power and the torque increase. When the oxygen concentration increases, the power and the torque at 3% load of 27% oxygen concentration are higher than which at full load of 21% oxygen concentration.⑤. Influence of compression ratio: When the compression ratio increases, the power and the torque increase. When the oxygen concentration increases, the power and the torque increase. Compared with the example engine of 21% oxygen concentration, in order to reach the same dynamic performance, the 25% oxygen concentration can get 30.9% decrease rate of compression ratio. ⑥. Influence of displacement: When the displacement increases, the power and the torque increase. When the oxygen concentration increases, the power and the torque increase. Compared with the example engine of 21% oxygen concentration, in order to reach the same dynamic performance, the 27% oxygen concentration can get 19% decrease rate of displacement.3. Basic analyse of the second law of thermodynamics:When the oxygen concentration increases, the percentage of heat transfer and exhaust energy increase, the percentage of work decreases, the percentage of the availability of heat transfer and exhaust energy increase, the percentage of the availability of work decreases. This indicates that, when the oxygen concentration increases, the average cylinder temperature and exhaust temperature increase, so the availability of heat transfer and exhaust energy increase. The decrease of thermal efficiency makes the percentage of the availability of work decrease. Furthermore, the decrease of availability lost means that to increase the oxygen concentration can increase the availability efficiency of the second law of thermodynamics.
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