稀释方式对正丁醇-汽油HCCI发动机燃烧的影响

Effect of Dilution Ways on Combustion Characteristics in a HCCI Engine Fuelled with n-Butanol-Gasoline Blends

在一台单缸4冲程发动机上采用负气门重叠角策略,实现了均质充量压缩着火(HCCI),并研究了排气门相位和过量空气系数对正丁醇-汽油HCCI发动机燃烧特性的影响.结果表明,在相同的排气门关闭角下,随着正丁醇掺混比例的增加,缸内残余废气率增大,平均指示压力(IMEP)下降,而压力升高率增加.缸内残余废气稀释和空气稀释均能有效地降低正丁醇HCCI发动机的最大压升率,但与空气稀释相比,使用废气稀释时HCCI发动机的IMEP下降幅度较大.利用增加过量空气系数和推迟排气门相位的协同控制策略,可以在固定的IMEP下,推迟正丁醇HCCI发动机的着火时刻,降低其最大压升率.

Homogeneous charge compression ignition （HCCI）was achieved through the negative valve overlap strategy on a single cylinder four stroke engine fuelled with n-butanol-gasoline blends. The effect of exhaust valve timings and excess air ratios on the combustion characteristics of the n-butanol HCCI engine was investigated. Results show that with the increase of n-butanol volume fraction in the blends, residual gas fraction increases and indicated mean effective pressure （IMEP） decreases while the maximum rate of pressure rise increases at the same exhaust valve closing timings. The maximum rate of pressure rise can be effectively reduced by both residual gas dilution and air dilution for the n-butanol HCCI engine. However, the decrease in IMEP is larger with residual gas dilution as compared to air dilution. By com- bining increased excess air ratio with retarded exhaust valve closing timing, ignition timing of the n- butanol HCCI engine is delayed and its maximum rate of pressure rise is decreased at the fixed IMEPs.