汽车专业英语第二章第六节

• 化油器设计成带有喉管的形式，喉管是空 气通道中一段狭窄的部分。空气流过化油 器的喉管时速度增加，在喷嘴的开口处形 成低压区。大气压力作用在储存汽油的浮 子室上。燃油便被压入伸向喉管低压区的 喷管里。这样燃油从喷管末端喷射到气流 中。
• (2) Float Chamber
• The float chamber is a reservoir for storing and supplying fuel to the carburetor. As the engine uses fuel, the float chamber replenishes it automatically. The float chamber works on the same basic principle as the holding tank in a flushing toilet. A float rests on top of the fuel in the reservoir. As fuel is used, the float level drops. When the float drops, a needle valve is opened.
• The main circuits of the carburetor ：
• Idle and Low-Speed Circuit • Main Metering Circuit • Power-Enrichment Circuit • Accelerator (Pump) Circuit • Choke Circuit
2.6.4 Carburetor Fuel System
• 1. Fuel pump:
• Most cars today have a mechanical fuel

pump. This pumps fuel out of the tank
and through the fuel lines to the
• 凸圆旋转带动油泵中的摇臂运动。油泵中 可膜片变形的泵膜通过膜片回位弹簧和膜 片拉杆与摇臂相连。
• 2. Carburetor
• Complete burn • theoretical requirement - 14.7:1
• Excess-air factor λ: • λ=air mass supplied/ theoretical requirement • 过量空气系数
• 化油器输送的燃油与流经化油器的空气量 成一定比例。踩下加速踏板，节气门开度 变大，化油器吸入的空气增加。化油器可 提供较浓或较稀的混合气，这取决于发动 机转速、负荷、温度和油门开度等因素。 为满足复杂的要求，化油器的结构也很复 杂，其上有很多内部通道和部件。
• (1) Venturi 喉管
• An automobile carburetor is designed with a venturi chamber. The venturi is simply a narrowed portion in the air passage. Air moving through the throat of the carburetor speeds up as it travels through this narrowed passageway. The increased air speed through the venturi creates a lowpressure area at the opening of the fuel nozzle. Atmospheric pressure pushes down on a fuel reservoir within the carburetor known as the float chamber. Fuel is forced through a tube that extends into the lowpressure area of the venturi. Thus, fuel sprays through the end of the tube into the air stream.
发动机工况
1)冷启动 2)后启动阶段 3)暖机 4)加速 5)部分负荷 6)全负荷 7)怠速 8)超速 9)发动机限速 10)高海拔
• The main function of the carburetor：
• Metering • correct proportions of fuel and air • Atomization • spray of fine particles to great air • Distribution • uniform mixture delivered to manifold
• 2. Carburetor
• A carburetor delivers fuel in proportion to the amount of air flowing through it. As you press on the accelerator pedal, the throttle valve opens wider to draw more air through the carburetor. The carburetor provides richer or leaner mixtures, de油pe门nd开in度g on a number of factors: engine speed, load, temperature, and throttle position. To meet complicated demands, a carburetor is a highly intricate device, with many internal passages and parts.
• 2.6.1 Gasoline :
• Gasoline must vaporize easily. This characteristic, called volatility, is important. However, it must not vaporize too easily, or it will turn to vapor inside the fuel tank or fuel lines. Inside the fuel line, fuel vapor may block the flow of liquid gasoline. This is called vapor lock. Vapor lock is common in fuel lines where the inlet side of the pump is exposed to high temperatures.
carburetor or injection system. In most
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the an
electr传ic送fuel pump. This pump mounts
in the fuel tank with the fuel pickup and
the fuel-gauge-sending unit.
• 当前大多数汽车采用机械汽油泵，汽油泵 从油箱抽出汽油，通过油管送到化油器或 喷射系统。大部分汽车的汽油泵安装在缸 体上。一些汽车采用电动汽油泵，汽油泵 安装在油箱上，附带有油量传感器和燃油 表油量传送装置。
• The rotation of the lobe moves a rocker arm in the pump. Inside the pump, a flexible diaphragm connects to the rocker arm though a diaphragm spring, pull rod and link.
• 两种基准参考燃料正庚烷和异辛烷分别被 定义成辛烷值为0和辛烷值为100，将它们 混合产生与实验样本相等敲缸强度的爆震。
混合物中异辛烷的百分比就认为是实验样
本的辛烷值。这样，依照实验方法，如果 匹配的混合物由15%的正庚烷和85%异辛 烷组成，那么按照所用的实验方法，对比 实验样本的辛烷值就是85。
CHAPTER 2 INTERNAL COMBUSTION
ENGINE
2.6 Gasoline Fuel System
• What’s the meaning of the air/fuel ratio (A/F)?
• A/F is stated in term of weight, different fuel has different ratio.
• 在点火前增加燃烧室内可燃混合气的压力 有助于提高发动机的功率，这是通过把可 燃混合气压缩到一个极小的体积来实现的。 高的压缩比不仅增加发动机的功率，而且 会带来更多的有效功率。但随着压缩比的 增加，爆震的可能性也会增加。
• Two primary standard reference fuels, normal heptane and iso-octane arbitrarily assigned 0 and 100 octane number, respectively, are then blended to produce the same knock intensity as the test sample. The percentage of isooctane in blend is considered the octane number of the test sample. Thus, if the matching reference blend is made up of 15% n-heptane and 85% isooctane, the test sample is rated 85 motor or research octane number, according to the test method used.