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7 7.1 IntroductIon Power Train Applications The chemist’s role is not limited to materials and analysis of designed components. The role also extends into power train applications and processes. “Power train,” refers to the set of components that generate power (engine) and deliver power (transmission, differential, and drive shafts) to the road. The combustion process, lubrication of components, and cooling requirements—along with ways to improve these processes and requirements—must be understood. The automotive chemist’s tools and training allow for these challenges to be met properly as we head into the future. 7.2 Fuel combustIon The combustion and airflow system in an automobile delivers a fresh charge of air and fuel into the combustion chamber and then converts the chemical energy into mechanical energy by the combustion process. Equation 7.1 shows how the process works: CH 3 8 + [ 5O2 + N2]( air)→ 3CO2 + 4H2O+ N2+ Heat (7.1) It is very important for the power train designers to understand this process because the combustion airflow system influences efficiency, emissions, performance, heat rejection, structural requirements, and noise. Figure 7.1 shows a simple example of the combustion airflow system for a conventional spark injection (SI) engine. The air and fuel are mixed together in the intake system, inducted through the intake valve into the cylinder, and mixed with residual gas. The mixture is then compressed and combustion is initiated toward the end of the compression stroke by a spark discharge. A turbulent flame is initiated at spark discharge. The combustion process can be thought of as a controlled burning process rather than an explosion. Figure 7.2 shows the cylinder pressure versus crank angle for the four-stroke engine used in automobiles. The crank angle in degrees expresses the minimum spark advance for best torque (MBT). Maximum engine torque is expressed where the spark timing is at the MBT point. Likewise, the specific fuel consumption will be at a minimum at the MBT point. The optimum air–fuel ratio can be expressed as the stoichiometric or theoretical combustion ratio. This is the mixture in which fuel will be burned completely. In other words, all the carbon will be converted to carbon dioxide, all hydrogen converted to water, and all sulfur converted to sulfur dioxide. If there are unburned components in the exhaust gas, such as C, H 2, or CO, the combustion process is incomplete. Carbon monoxide is produced if there is insufficient oxygen to oxidize the fuel fully. Nitrogen 95
96 The Role of the Chemist in Automotive Design Cylinder Pressure Kilo Pascals 2000 1600 1200 Airflow Air Box Valve train Exhaust manifold 800 400 Converter Muffler 0 EGR Exhaust CO 2 H 2 O CO HC NO x Intake Compression Expansion Exhaust –360 –180 0 Crank Angle 180 360 FIgure 7.2 Crank angle versus cylinder pressure. PCV, Purge FIgure 7.1 Diagram of internal combustion engine. Spark Piston Coolant Intake manifold Fuel injection
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THE ROLE OF THE CHEMIST IN AUTOMOTI
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CRC Press Taylor & Francis Group 60
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Contents Preface...................
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Contents ix 6.6 Thermal Properties
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Contents xi 11.4 Glass Microspheres
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The Author Herman Phlegm was born i
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2 The Role of the Chemist in Automo
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10 The Role of the Chemist in Autom
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3 3.1 IntroductIon Component Materi
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Component Materials in Automobiles
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HVAC System Overview and Refrigeran
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152 The Role of the Chemist in Auto
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190 Index Carbon dioxide emissions,
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192 Index heat exchanger designatio
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194 Index Power train, 95 Power tra
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