二甲醚/甲醇混合燃料HCCI燃烧特性数值模拟

为了研究混合气浓度及燃料掺混对二甲醚/甲醇混合燃料HCCI（homogeneous charge compression ignition）燃烧特性的影响，对不同过量空气系数和二甲醚掺混比下的醇醚混合燃料HCCI燃烧过程进行了模拟计算，分析了缸内温度、压力、压力升高率、放热率和燃料消耗路径随过量空气系数和二甲醚掺混比的变化关系。结果表明，随过量空气系数增大，缸内压力、温度、放热率和压力升高率峰值减小，相位推迟，过量空气系数太大时，CO的进一步氧化反应会受到阻碍，使缸内产生大量的CO残留；随二甲醚掺混比的增大，缸内压力、温度峰值增大，相位提前，压力升高率和放热率峰值减小；二甲醚HCCI燃烧放热率曲线存在3个峰值，第1个峰值出现上止点前曲轴转角30°，为二甲醚低温氧化放热，对应缸内温度为804 K，第2个峰值出现在上止点前曲轴转角15°，对应缸内温度为1 193 K，为甲醛等中间产物氧化生成CO时放热，第3个峰值为CO氧化，生成CO₂时放热，第2和第3个放热率峰值为二甲醚的高温氧化放热阶段，与甲醇掺混燃烧时，二甲醚的低温氧化反应对混合气的燃烧起到了促进作用。

Simulation study on HCCI combustion of DME/methanol fueled engine

To determine the effects of mixture concentration and fuel blending on the combustion performance of a dimethyl ether/methanol fueled HCCI engine, the combustion process under different excess air coefficients and dimethyl ether addition ratios was simulated. Parameters such as temperature, pressure, pressure rise rate and the heat release rate were examined, as well as the fuel consumption path. The results show that the peak values of the pressure, temperature, heat release rate and pressure rise rate decrease with the increase of the excess air coefficient, while the phases are delayed. Excessive excess air coefficient hinders the further oxidation reaction of CO, resulting in high CO residue. On the other hand, increasing the dimethyl ether (DME) addition ratio leads to higher peak values of pressure and temperature in the cylinder, advancing their phases, while the peak values of pressure rise rate and heat release rate decrease. The combustion heat release rate curve of dimethyl ether homogeneous charge compression ignition (HCCI) combustion exhibits three peaks. The first peak, occurring at a crane angle of 30° before topdead center (BTDC) with a temperature of 804 K, corresponds to the low-temperature-oxidation heat release of dimethyl ether. The second peak, appearing at a crane angle of 15° BTDC with a temperature of 1 193 K, corresponds to the heat release from reactions forming CO through formaldehyde and other intermediates. The third peak represents the heat release from CO oxidation when CO₂ is generated. The second and third exothermic rate peaks indicate the high-temperature oxidation exothermic stage of dimethyl ether. Additionally, when mixed with methanol, the low-temperature oxidation reaction of dimethyl ether promotes the combustion of the mixture.