物理化学学报 >> 2016, Vol. 32 >> Issue (12): 2879-2890.doi: 10.3866/PKU.WHXB201609303

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双燃料发动机缸内分层激光诱导荧光实验及化学动力学模拟研究

唐青龙,刘海峰*(),李明坤,尧命发   

  • 收稿日期:2016-08-19 发布日期:2016-11-30
  • 通讯作者: 刘海峰 E-mail:haifengliu@tju.edu.cn
  • 基金资助:
    国家自然科学基金(51320105008,91541205)

Study on In-Cylinder Charge Stratification of a Dual-Fuel Engine Using Fuel-Tracer Laser-Induced Fluorescence and Chemical Kinetic Simulation

Qing-Long TANG,Hai-Feng LIU*(),Ming-Kun LI,Ming-Fa YAO   

  • Received:2016-08-19 Published:2016-11-30
  • Contact: Hai-Feng LIU E-mail:haifengliu@tju.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(51320105008,91541205)

摘要:

双燃料压燃(RCCI)是一种很有前景的发动机新型燃烧方式,能在小负荷到中高负荷范围内实现发动机高效清洁燃烧,为了将RCCI拓展到更高负荷,需要对其缸内燃油分层和燃烧过程开展更深入研究。本文在一台双燃料光学发动机上采用燃油-示踪剂平面激光诱导荧光法(PLIF),对RCCI着火前缸内燃油分层进行定量测量,选用甲苯作为示踪剂,利用266 nm脉冲激光激发甲苯荧光,发动机转速1200 r·min-1,平均指示压力6.9×105 Pa,气道喷射异辛烷,缸内在上止点前10°喷射正庚烷。采用燃油-气体绝热混合假设,对PLIF测量结果进行温度不均匀性修正,以上止点后5°曲轴转角下的测量结果为例,不修正相比修正测试区域内的最大当量比高估15%。根据实验结果,利用Chemkin软件分析了活性、浓度和温度分层对燃烧滞燃期的影响,结果显示燃料活性分层和浓度分层共同决定RCCI的着火滞燃期,其中活性分层影响要大于浓度分层,而温度分层对着火滞燃期影响很小。RCCI燃烧过程自发光的高速成像结果表明,着火过程首先出现在燃烧室边缘的高活性区域,随后火焰向燃烧室中心处的低活性区域发展,碳烟辐射光图像显示碳烟主要形成于燃烧室边缘的高活性区域。

关键词: 激光诱导荧光法, 双燃料压燃, 燃油分层, 光学发动机

Abstract:

Dual-fuel compression ignition, or reactivity controlled compression ignition (RCCI) is a promising strategy for engines to achieve high efficiency and clean combustion from low to mid-high load. To extend the operating range to high engine load, further examination of the in-cylinder fuel stratification and combustion processes is required. In this paper, fuel-tracer planar laser-induced fluorescence (PLIF) was used to quantify the fuel stratification of RCCI in an optical engine. Toluene was chosen as the tracer, which was mixed with isooctane and n-heptane. A laser of 266 nm was used to stimulate the toluene fluorescence. The engine was run at 1200 r·min-1 under a load of 6.9×105 Pa IMEP (indicated mean effective pressure). Iso-octane was delivered via the intake port and n-heptane was injected directly into the cylinder at-10° CA (crank angle) after top dead center (ATDC). A fuel-gas adiabatic mixing assumption was adopted to correct temperature non-uniformity of the PLIF images. As an example, the results obtained at 5° CA ATDC gave an overestimated maximum equivalence ratio in the diagnostic region before any correction of 15%. Based on the measurements, the effects of reactivity, concentration and temperature stratification on ignition delay of RCCI were evaluated using Chemkin software. The results indicated that the reactivity stratification and concentration stratification dominated the ignition delay of RCCI, with the reactivity stratification being more significant than the concentration stratification. The temperature stratification had only minor effects on the ignition delay. The high-speed imaging of the RCCI combustion showed that the initial ignition sites emerged at the edge of the combustion chamber where the local fuel reactivity or fuel concentration was high. The flames then progressed into the center of the combustion chamber where the fuel was leaner and less reactive. The soot emissions shown by the soot radiation images mainly formed in the high reactive region.

Key words: Laser-induced fluorescence, Dual-fuel compression ignition, Fuel stratification, Optical engine

MSC2000: 

  • O643