Do you know the meaning of “T”?

“T” (Turbocharging) ：涡轮增压，轿车排量后面加上一个T，如宝来的1.8T ： 不带T 动力为1.8L 带T 动力相当于2.4L 其最大功率与未装增压器的时候相比可以增加40%甚至更高。这样也就意味着同样一台发动机在经过增压之后能够产生更大的功率。但是耗油量却比1.8发动机并不高多少。 在另外一个层面上来说就是提高燃油经济性和降低尾气排放。

Chapter 3 Turbocharging

Content 3.1 Introduction purpose, three kinds of turbocharging and comparison 3.2 Energy available in the exhaust (self-study) 3.3 Principle and thermodynamics of exhaust turbochargers the main components, characteristics of turbine and centrifugal compressor 3.4 Spark ignition engines turbocharging

Preview task 3 1.What’s the primary purpose of Turbocharging? And What’s the accomplish methods? 2.What’s three main components of turbocharger? Please describe the operation principle and characteristics of centrifugal compressor.

3.1 Introduction pV=nRT, 发动机的有效功率 Brake power is proportional to inlet air density. If the inducted air is compressed to a higher density than ambient, prior to entry into the cylinder, the maximum power an engine of fixed dimensions can deliver will be increased. This is the primary purpose of supercharging.

Three basic methods are used to accomplish this： 1) mechanical supercharging 机械增压 Where a separate pump or blower 鼓风机or compressor, usually driven by power taken from the engine, provides the compressed air. 发动机输出轴直接驱动机械增压器，实现对进气的压缩。

2) turbocharging 涡轮增压 where a turbocharger--a compressor and turbine on a single shaft is used to boost the inlet air (or mixture) density. Energy available in the engine's exhaust stream is used to drive the turbocharger turbine which drives the turbocharger compressor which raises the inlet fluid density prior to entry to each engine cylinder. 压气机与涡轮同轴相连，构成涡轮增压器。涡轮在排气能量的推动下旋转，带动压气机工作，实现进气增压。

3) pressure wave supercharging 气波增压 Uses wave action in the intake and exhaust systems to compress the intake mixture. An example of a pressure wave supercharging device is the Comprex,气波增压器 which uses the pressure available in the exhaust gas stream to compress the inlet mixture stream by direct contact of the fluids in narrow flow channels. 利用进气及排气系统中的波动效应来压缩进气，著名的气波增压器(Comprex)就是其中之一。

comparison The most arrangements use a mechanical supercharger and turbocharger. Mechanical superchargers have the added complication of a mechanical drive, and the compressor efficiencies are usually such that the overall economy is reduced. Turbocharging is a particular form of supercharging in which a compressor is driven by an exhaust gas turbine. It uses power of exhaust gas to compress the induction air so that turbocharged engines are powerful and economical. Turbochargers have been used for a long time on larger compression ignition engines, and are now being used increasingly on automotive compression ignition and spark ignition engines.

Red color represents high-temperature exhaust gas，blue color represents fresh air

3.3Principle and thermodynamics of exhaust turbochargers 中间体 The turbocharger has three main components: 1. A turbine, which is almost always a radial inflow turbine 2. A compressor, which is almost always a centrifugal compressor 3. The center housing/hub rotating assembly (CHRA). 径流式涡轮 离心式压气机

The compressor draws in ambient air and compresses it before it enters into the intake manifold at increased pressure. This results in a greater mass of air entering the cylinders on each intake stroke. The power needed to spin the centrifugal compressor is derived from the high pressure and temperature of the engine's exhaust gases. The turbine converts the engine exhaust's potential pressure energy and kinetic velocity energy into rotational power, which is in turn used to drive the compressor.

A turbocharger may also be used to increase fuel efficiency without any attempt to increase power. It does this by recovering waste energy in the exhaust and feeding it back into the engine intake. By using this otherwise wasted energy to increase the mass of air, it becomes easier to ensure that all fuel is burned before being vented at the start of the exhaust stage. The increased temperature from the higher pressure gives a higher Carnot efficiency卡诺循环.

3.3.1 Operation principle and characteristics of radial-flow turbine 径流式涡轮 Two types of turbines are used in turbochargers: 1) Radial-flow turbines径流式涡轮 Which is similar in appearance to the centrifugal compressor; however, the flow is radially inward not outward. Radial flow turbines are normally used in automotive or truck applications. 2) Axial flow turbines轴流式涡轮机. Locomotive, stationary, or marine---use axial flow turbines.

3.3.2 Operation principle and characteristics of centrifugal compressor The centrifugal compressor consists of a stationary inlet casing, a rotating bladed impellor有叶片的工作轮, a stationary diffuser (with or without vanes), and a collector or volute蜗壳 to bring the compressed air leaving the diffuser to the engine intake system. 进气道：收集气流顺畅进入工作轮 工作轮：对气体压缩 扩压器：工作轮出口气体进一步压缩 涡 壳：使增压气体顺畅进入气缸

3.3.2 Operation principle and characteristics of centrifugal compressor Fig. 3.13 indicates, on a diagram, how each component contributes to the overall pressure rise across the compressor. Air at stagnation state is accelerated in the inlet to velocity and pressure reduced to due to the convergent逐渐减小的 passage. Then the air distributes circumferentially圆周 into passages constructed by impeller blades and rotates rapidly with the blades. The work transfer to the air occurs in the impeller叶轮. It can be related to the change in gas angular momentum via经过 the velocity components at the impeller entry and exit. Compression in the impeller flow passages increases the pressure to and velocity to.

3.3.2 Operation principle and characteristics of centrifugal compressor The diffuser converts as much as practical of the air kinetic energy at exit to the impeller to a higher pressure by slowing down the gas to velocity in carefully shaped expanding passages. Finally, in the collector, which is an expanding volute, the pressure rises to and the velocity is lowered to. In a word, with a series of energy transferring, most of the mechanical work of compressor impeller, which derived from the turbine, is converted into pressure energy of the air.

3.4 Spark ignition engines turbocharging 汽油机涡轮增压 Turbocharging the spark ignition engine is more difficult than turbocharging the compression ignition engine. Spark ignition engines require a wider air flow range (owing to a wider speed range and throttling), a faster response, and more careful control to avoid either pre-ignition or self-ignition. The fuel economy of a spark ignition engine is not necessarily improved by turbocharging. To avoid both knock and self-ignition it is common practice to lower the compression ratio, thus lowering the cycle efficiency. This may or may not be offset抵消 by the frictional losses representing a smaller fraction of the engine output.

3.4 Spark ignition engines turbocharging The turbocharger raises the temperature and pressure at inlet to the spark ignition engine, and consequently pressures and temperatures are raised throughout the ensuing processes. The effect of inlet pressure and temperature on the knock-limited operation of an engine running at constant speed, with a constant compression ratio, is shown in Fig.3.16. Higher octane fuels and rich mixtures both permit operation with higher boost pressures and temperatures. Retarding the ignition timing will reduce the peak pressures and temperatures to provide further control on knock. Unfortunately there will be a trade-off in power and economy and the exhaust temperature will be higher; this can cause problems with increased heat transfer in the engine and turbocharger. Reducing the compression ratio is the commonest way of inhibiting抑制 knock and retarding推迟 the ignition is used to ensure knock-free operation under all conditions.

一般来说，涡轮增压都是利用发动机排出的废气惯性冲力来推动涡轮室内的涡轮，涡轮又带动同轴的叶轮，叶轮压送由空气滤清器管道送来的空气，使之增压进入汽缸。当发动机转速增快，废气排出速度与涡轮转速也同步增快，叶轮就压缩更多的空气进入汽缸，空气的压力和密度增大可以燃烧更多的燃料，相应增加燃料量和调整一下发动机的转速，就可以增加发动机的输出功率了。 涡轮增压装置主要是由涡轮室和增压器组成。首先是涡轮室的进气口与发动机排气歧管相连，排气口则接在排气管上。然后增压器的进气口与空气滤清器管道相连，排气口接在进气歧管上，最后涡轮和叶轮分别装在涡轮室和增压器内，二者同轴刚性联接。

经典的BORA 1.8T 涡轮增压发动机

涡轮增压套件 半开式工作轮

10ZJ型涡轮增压器

罗茨式压气机