What are Engine Emissions?

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  • Written By: J. Leach
  • Edited By: Michelle Arevalo
  • Last Modified Date: 13 September 2019
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Engine emissions are gases and particulates that are expelled by a motor or other mechanical device. Particulates are small dust particles. Internal combustion engines, like the ones used in vehicles, emit emissions from the engine exhaust, the fuel tank, and the motor itself. Automobile exhaust is composed of carbon dioxide, carbon monoxide, methane, and formaldehyde. The exhaust also contains particulates and water vapor.

Engines also produce hydrocarbons when fuel is not consumed efficiently. Hydrocarbons are compounds that are made of carbon and hydrogen. Methane is a hydrocarbon and is a greenhouse gas that contributes to the greenhouse effect.

Greenhouse gases, like methane, accumulate in Earth’s atmosphere and become a barrier that traps heat close to the planet’s surface; this is the greenhouse effect. Hydrocarbons are also thought to contribute to global warming. Global warming is the alteration of a planet’s temperature, which affects weather patterns, climates, crops, and disease. Vehicles are now being manufactured with the reduction of carbon engine emissions in mind.

The fuel tank and the carburetor are insulated to limit the amount of fuel vapor that they exude. The carburetor is a device that supplies the engine with a blend of air and fuel. When the engine is not in use, fuel vapors flow into a canister which contains activated charcoal. The charcoal absorbs the fuel vapors. These vapors are then expelled into the combustion chamber and destroyed when the engine is started.


Vehicle engine emissions are controlled in three ways. The first controls and limits the amount of fuel in the mixture injected by the carburetor. This ensures that more fuel is thoroughly consumed, because this helps reduce the amount of byproducts produced, and the resulting emissions. The second method of engine control allows hydrocarbons to flow back into the engine to be further consumed by the combustion process. Finally, the catalytic converter gives the hydrocarbons and particulates an additional area to be consumed and destroyed.

The catalytic converter helps to reduce the emissions of hydrocarbons, carbon monoxide, and nitrogen oxides. The Environmental Protection Agency (EPA) in the U.S. is invested with the authority to regulate engine emissions, as well as to monitor the air quality in general. The EPA issued a federal regulation that required all car manufacturers to equip automobiles with catalytic converters, and by doing so, reduced the emissions of unburned hydrocarbons by 85%.

In the U.S., the Clean Air Act Amendment of 1990 has helped to effectively reduce engine emissions. Large engines and automobiles are burning fuels more efficiently, and their contributions to air pollution have been greatly reduced. Smaller engines are also being improved and their fuel efficiency increased. Therefore, those contributions to pollution have also been decreased.


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