燃料辛烷值对HCCI燃烧特征和排放特性的影响

Combustion Parameters and Emissions of HCCI Using Primary Reference Fuels and Their Mixtures

将一台4缸高速轻型柴油机中的一缸改装,使其具有独立的进排气系统和燃油供给系统,研究了参比燃料及其混合物在均质压燃过程中的着火时刻、燃烧速率和NOx、UHC、CO排放．考察了正庚烷、异辛烷和各种不同比例的混合物在常温、常压下各种负荷的燃烧特性．研究发现:随燃料辛烷值增加,第一阶段着火时刻推迟,燃烧持续期缩短,第一阶段反应结束时的压力升高量和温度升高量减少;第一阶段的累积放热量取决于燃料中高十六烷值燃料的浓度;第二阶段的着火时刻与第一阶段着火时刻呈线性关系;第二阶段燃烧持续期随当量比的增加而减小,且随辛烷值增加而延长;随燃料十六烷值和当量比增加,CO和UHC排放大幅度改善．

The basic combustion parameters including start of ignition timing, combustion duration, and CO, UHC, and NOx emissions of HCCI engines fueled with primary reference fuels and their blends were investigated in this article. A single-cylinder HCCI combustion engine, retrofitted from a four-cylinder high-speed diesel engine, is used in the tests. Two primary reference fuels, n-heptane and iso-octane, and their blends are evaluated. The experimental results show that, in the first-stage combustion, the start of ignition retards, the combustion duration shortens, and the pressure rising degree and the temperature rising at the end of the first-stage decrease with the increase of the research octane number. Furthermore, the cumulative heat release in the first-stage is strongly dependent on the concentration of n-heptane in the mixtures. The start of ignition in the second stage is linear with the start of the ignition in the first-stage. The combustion duration of the second-stage combustion decreases with the increase of the equivalence ration and increase with the octane number. The UHC and CO emission sharply decreases with the increase of the equivalence ratio and cetane number.