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怠速工况因其转速低、进气充量少、残余废气系数大、缸内平均温度低、气流运动弱等特点使得燃油雾化不良,混合气浓度分布不均,循环波动较大,经济性和排放性较差,因此针对车用增压柴油机怠速循环波动特性的研究对优化怠速控制策略,改善柴油机怠速稳定性能具有重要意义。为研究喷油压力、喷油定时以及冷却液温度等对高压共轨柴油机怠速循环波动的影响,在1台4缸水冷高压共轨柴油机上进行了怠速工况循环波动试验,通过测量连续多个循环的缸内压力统计获得的最大爆发压力Pmax、最大爆发压力对应转角φmax、最大压力升高率(dP/dφ)max的循环波动率CoV和波动率δ来评价发动机的循环波动。研究结果表明:怠速工况下,随着喷油压力的增加,缸内燃烧提前,最大爆发压力及其对应转角的循环波动率分别由2.9%、0.2%增加至4.2%、1.9%;在喷油定时从-2°ATDC增加至-14°ATDC的过程中,缸内最大爆发压力的循环波动由3.2%下降到2.3%然后再增加至3.5%,呈现出先减小后增加的变化趋势;怠速循环波动对冷却液温度变化比较敏感,当冷却水温从30℃增加到50℃时,缸内最大爆发压力波动率δPmax和循环波动率CoVPmax均急剧下降,而冷却水温进一步增加,怠速循环波动逐渐减弱。
Due to its low speed, low intake air charge, large residual exhaust gas coefficient, low average cylinder temperature and weak airflow, the idling condition makes the fuel atomized poorly, the concentration of the mixture unevenly distributed, the circulation fluctuates greatly, and the economy And emission is poor, therefore, the study of idling cycle fluctuation characteristics of turbocharged diesel engine is of great significance to optimize the idling control strategy and improve the idling stability of diesel engine. In order to study the influence of injection pressure, injection timing and coolant temperature on idling cycle fluctuation of high pressure common-rail diesel engine, a cyclic test of idling condition was carried out on a 4-cylinder water-cooled high pressure common rail diesel engine. Cyclic fluctuation of the engine is evaluated by the maximum burst pressure Pmax, the maximum explosion pressure corresponding to the rotation angle φmax, the cyclic fluctuation rate CoV and the fluctuation rate δ of the maximum pressure rise rate (dP / dφ) max obtained from the circulating in-cylinder pressure statistics. The results show that with the increase of injection pressure, the cycle fluctuation of cylinder combustion in advance, the maximum explosion pressure and its corresponding rotation angle increases from 2.9% and 0.2% to 4.2% and 1.9% respectively at idling condition. During the time when the oil timing increases from -2 ° ATDC to -14 ° ATDC, the maximum fluctuation pressure in the cylinder fluctuates from 3.2% to 2.3% and then to 3.5%, showing the trend of decreasing and then increasing. The idle speed When the cooling water temperature is increased from 30 ℃ to 50 ℃, the maximum in-cylinder burst pressure fluctuation δPmax and the circulating fluctuation CoVPmax decrease sharply, while the cooling water temperature further increases and the idle cycle fluctuation gradually decreases .