emission control system
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What is an emission control system in vehicles?
An automotive emission control system limits the discharge of noxious gases from the internal combustion engine and other components. Sources of these gases include the engine exhaust, crankcase, and fuel tank.
To control crankcase emissions, leaked combustion gases are combined with ventilating air and returned to the intake manifold to be reburned. To control exhaust emissions, air-injection and exhaust gas recirculation (EGR) systems are used. In addition, catalytic converters convert hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust to water vapor, carbon dioxide, and nitrogen. Computerized control ensures efficient operation and precise air-fuel mixtures, while evaporative control systems reduce emissions from the fuel tank. Oxygen sensors help maintain the air-fuel ratio to protect the catalytic converter.
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Why do cars need emission control systems?
Emission control systems in cars limit the discharge of harmful gases from the engine, crankcase, fuel tank, and carburetor. These systems manage hydrocarbons, carbon monoxide, and nitrogen oxides, converting them into less harmful substances.
The positive crankcase ventilation valve (PCV) returns leaked combustion gases to the intake manifold for reburning. Exhaust emissions are controlled through air-injection and exhaust gas recirculation (EGR) systems, which lower combustion temperature to reduce nitrogen oxides. Catalytic converters use catalysts to convert hydrocarbons, carbon monoxide, and nitrogen oxides into water vapor, carbon dioxide, and nitrogen. Evaporative control systems and sealed fuel-tank caps also reduce emissions from fuel evaporation. Computerized controls further improve combustion efficiency, ensuring precise air-fuel mixtures and lower pollutant generation.
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What are common types of pollutants released by car engines?
Car engines release several types of pollutants. These include carbon monoxide, which is created by incomplete combustion, and nitrogen oxides, which form when high combustion temperatures cause nitrogen and oxygen to react.
Diesel engines also discharge particulate matter (soot) and odorous reactive nitrogen compounds. Additional pollutants from gasoline engines include unburned hydrocarbons, traces of acids, alcohols, and phenols. Air toxics such as benzene and formaldehyde are also released. Emission control systems, such as catalytic converters, air-injection systems, and exhaust gas recirculation (EGR), are employed to limit the discharge of these noxious gases.
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How does a catalytic converter help reduce pollution?
A catalytic converter is a component of automotive emission control systems that reduces noxious gases from internal-combustion engines. It consists of an insulated chamber containing a honeycomb structure or pellets coated with a catalyst. As exhaust gases pass through, hydrocarbons and carbon monoxide oxidize into water vapor and carbon dioxide, while nitrogen oxides are reduced to nitrogen and oxygen. The catalysts are either platinum-group metals or base metals such as chromium, nickel, and copper. This conversion requires a balanced air-to-fuel ratio.
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What role do sensors play in emission control systems?
Sensors play a crucial role in automotive emission control systems by monitoring and controlling various parameters.
Primarily, oxygen sensors made of zirconia monitor the air-to-fuel ratio in the internal combustion engine. This feedback is essential for the fuel injection system to maintain optimal A/F ratios, which protects the catalytic converter from damage.
Additionally, ceramic-based sensors gauge temperature, pressure, speed, and fuel level. Pressure sensors, for example, use alumina diaphragms to detect pressure changes in intake or exhaust manifolds. Computerized control systems utilize sensor data to improve combustion efficiency, reduce emissions, and ensure precise air-fuel mixtures.
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How do emission standards impact automotive emission control technology?
Emission standards significantly drive the evolution of automotive emission control technology. Governments establish air quality standards and conduct inspections, prompting manufacturers to develop more complex equipment to meet progressively stringent regulations.
These standards have led to engine modifications, including adjustments to air-fuel ratios, lowered compression ratios, and retarded spark timing. Emission-control devices like catalytic converters, exhaust-gas-recirculation systems, and fuel injection systems have emerged. The Bharat Stage VI (BS-VI) emission standards in India, for example, mandate low-sulfur fuel, filters, and catalytic converters to curb harmful emissions. Computer-controlled fuel-injection systems ensure precise air-fuel mixtures, enhancing combustion efficiency and reducing pollution.
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emission control system, in automobiles, means employed to limit the discharge of noxious gases from the internal-combustion engine and other components. There are three main sources of these gases: the engine exhaust, the crankcase, and the fuel tank and carburetor. The exhaust pipe discharges burned and unburned hydrocarbons, carbon monoxide, oxides of nitrogen and sulfur, and traces of various acids, alcohols, and phenols. The crankcase is a secondary source of unburned hydrocarbons and, to a lesser extent, carbon monoxide. In the fuel tank and (in older automobiles) the carburetor, hydrocarbons that are continually evaporating from gasoline constitute a minor but not insignificant contributing factor in pollution. A variety of systems for controlling emissions from all these sources have been developed.
In the crankcase—the portion of the engine block below the cylinders where the crankshaft is located—leaked combustion gases are combined with ventilating air and returned to the intake manifold for reburning in the combustion chamber. The device that performs this function is known as the positive crankcase ventilation valve, or PCV valve.
To control exhaust emissions, which are responsible for two-thirds of the total engine pollutants, two types of systems are used: the air-injection system and the exhaust gas recirculation (EGR) system. In EGR a certain portion of exhaust gases are directed back to the cylinder head, where they are combined with the fuel-air mixture and enter the combustion chamber. The recirculated exhaust gases serve to lower the temperature of combustion, a condition that favours lower production of nitrogen oxides as combustion products (though at some loss of engine efficiency). In a typical air-injection system, an engine-driven pump injects air into the exhaust manifold, where the air combines with unburned hydrocarbons and carbon monoxide at a high temperature and, in effect, continues the combustion process. In this way a large percentage of the pollutants that were formerly discharged through the exhaust system are burned (though with no additional generation of power).
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Another area for additional combustion is the catalytic converter, consisting of an insulated chamber containing ceramic pellets or a ceramic honeycomb structure coated with a thin layer of metals such as platinum and palladium. As the exhaust gases are passed through the packed beads or the honeycomb, the metals act as catalysts to induce the hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust to convert to water vapour, carbon dioxide, and nitrogen. These systems are not completely effective: during warm-up the temperatures are so low that emissions cannot be catalyzed. Preheating the catalytic converter is a possible solution to this problem; the high-voltage batteries in hybrid cars, for example, can provide enough power to heat up the converter very quickly.
In the past, gasoline fumes evaporating from the fuel tank and carburetor were vented directly into the atmosphere. Today those emissions are greatly reduced by sealed fuel-tank caps and the so-called evaporative control system, the heart of which is a canister of activated charcoal capable of holding up to 35 percent of its own weight in fuel vapour. In operation, fuel-tank vapours flow from the sealed fuel tank to a vapour separator, which returns raw fuel to the tank and channels fuel vapour through a purge valve to the canister. The canister acts as a storehouse; when the engine is running, the vapours are drawn by the resultant vacuum from the canister, through a filter, and into the combustion chamber, where they are burned.
Improvements in combustion efficiency are effected by computerized control over the whole process of combustion. This control ensures the most efficient operation of the systems described above. In addition, computer-controlled fuel-injection systems ensure more precise air-fuel mixtures, creating greater efficiency in combustion and lower generation of pollutants.