乙醇-正庚烷燃料均质压缩过程着火与燃烧特性的研究

详细研究了乙醇正庚烷混合燃料实现均质充量压缩过程的自燃着火特性和燃烧特性。在单缸HCCI发动机上，开展了正庚烷、10％～50％乙醇正庚烷燃料在1800r／min下不同负荷时的试验研究。研究表明，在正庚烷中加入30％～40％比例的乙醇，HCCI运行的平均指示压力可以从0．34MPa拓展到0．52MPa，大负荷下的指示热效率达到50％，但低负荷热效率显著降低。由于乙醇较高的辛烷值，随燃料中乙醇比例的增加，低温反应明显推迟，发生低温反应的起始温度相应升高，峰值放热率降低，并且当乙醇比例达到50％以后，观察不到明显的低温反应。由此导致高温着火时刻推迟，燃烧持续时间延长。正庚烷、10％～30％乙醇正庚烷的HC较低，但是乙醇比例达到40％后，HC显著升高。CO排放在平均指示压力0．15～0．25MPa最高，负荷增加后得到改善。在供给相同的循环热量条件下，随乙醇比例增加，最大燃烧压力以及对应时刻、着火时刻都呈现明显的变动。

Experimental Study on the Auto-Ignition and Combustion Characteristics of Homogenous Charge Compression Ignition Combustion with Ethanol/N-heptane Blends by Port Injection

This paper investigates the auto-ignition,combustion,and emission characteristics of homoge- nous charge compression ignition(HCCI)combustion engines fuelled with ethanol and n-heptane blended fuels.The experiments were conducted on a single-cylinder HCCI engine using neat n-heptane,and 10%, 20%,30%,40%,and 50% volume of ethanol blended fuels at engine speed of 1 800 r/min.The results show that,when ethanol fraction in blends is 30% to 40%,the maximum HCCI operation range can be ex- tended to 0.52 MPa,and the indicated thermal efficiency can reach up to 50% at large engine loads.How- ever,the thermal efficiency will deteriorate at low engine load.Due to high value of octane number for ethanol,the cool-flame reaction will be postponed,and the initial temperature of the cool-flame will in- crease,and the peak value of the low-temperature heat release decreases with the increase of ethanol frac- tion.HC emission decreases at small fraction of ethanol while it increases at large ethanol fraction.CO gets its peak value at indicated mean effective pressure from 0.15 MPa to O.25 MPa,and it will decrease with further increase of load.In the case of operation stability of HCCI combustion,for a specific supplied energy per cycle,the cycle-to-cycle variation of the maximum combustion pressure and its corresponding crank angle,and ignition timing deteriorated with the increase of ethanol additive.