天然气发动机怠速燃烧排放特性试验

在一台CNG发动机上研究怠速工况条件下,点火提前角(θi)和过量空气系数(λ)对燃烧排放性能的影响规律。节气门全关,参数调节时,步进电机自动调节,将发动机转速控制在800 r/min。θi在上止点前40～10°CA BTDC变化,λ=1.1时指示热效率和燃烧速度最高;随着λ增加,最高指示热效率所对应的θi越大;θi过大或过小,都会加剧循环变动;λ1.3,平均指示压力循环变动(CoVimep)明显增加;λ=1.1时,NOx排放最高。

Combustion and Emission Characteristics of a CNG Engine at Idle Condition

The rule of ignition advance angle(θi) and excess air ratio(λ) influencing on the combustion and emissions characteristics is investigated on a CNG engine at idle condition.The throttle valve is fully closed.When the parameters are changed,the stepper motor is adjusted automatically to control the engine speed at 800 r/min.When the ignition advance angle is changed from 40 to 10o crank angle(CA) before top dead center(BTDC),the maximum indicated thermal efficiency(ITE) and the maximum burning speed are observed at λ=1.1.As the excess air ratio λ increases,the maximum ITE is corresponding to a greater θi.The CoVimep will be increased if the ignition is too early or too late.When the excess air ratio λ is more than 1.3,the CoVimep increases obviously.When λ=1.1,NOx emissions get the highest level.