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Overview Of The Parts Responsible For Your Car’s Emissions Control System

By George Rossmore

A generation ago, automobiles lacked safeguards that prevented vapors from being released into the atmosphere. Research has since shown, of course, that these vapors (i.e. hydrocarbons, oxides of nitrogen, and carbon monoxide) are harmful to people and the environment. They are generated while your engine is in operation. Most of the vapors are released through your vehicle’s exhaust pipe, but much of it evaporates before it reaches that point.

In the late 1970s, legislation was passed to reduce the volume of emissions released by vehicles. Within a few years, most cars rolled off the factory floor equipped with an early version of today’s emission control system. In those early systems, an oxygen sensor was located somewhere in the exhaust path. It would monitor the exhaust and send the resulting data to the car’s computer. The computer would then modify the air-fuel mixture in order to minimize the emissions.

While automotive technology has evolved dramatically since then, the basic design for the emissions control system has remained largely the same (with a few notable changes). In this article, we’ll take a brief look at the individual components involved.

EGR Valve

This component monitors the level of oxides of nitrogen (NOx) in the exhaust that flows between the intake and exhaust manifolds. The valve opens and a small vacuum draws exhaust into the intake manifold. This reduces the combustion temperature of your engine because the presence of exhaust gas thins the air-fuel blend within the cylinders.

The combustion process – and specifically, the high temperatures – that occurs within each of the cylinders produces NOx. The EGR valve, in diluting the air-fuel blend, also dilutes the power of the combustion process. This lowers the temperature, and thus lowers the volume of NOx.

Catalytic Converter

This component is located in the exhaust path prior to the muffler and tailpipe. It collects gases produced during combustion and released from the cylinders through the exhaust valves. Inside the catalytic converter is a sheet of catalyst material. As carbon monoxide and hydrocarbons enter the component, this sheet causes a chemical reaction. As a result, the harmful elements are left behind while harmless elements, such as carbon dioxide, nitrogen, and water vapors, exit the tailpipe.

PCV Valve

In addition to leaving the cylinders through the exhaust valves, gases produced during combustion are also found in the crankcase. The crankcase is the housing for the crankshaft. A system called the positive crankcase ventilation (PCV) system is responsible for removing these gases and sending them to the intake manifold. There, they are re-burned during combustion. The PCV valve is the heart of this system.

The challenge with redirecting gases back to the engine is that they can lean out the air-fuel mix within the cylinders. That affects your engine’s performance. The PCV valve’s job is to control the volume of air that makes it back into the engine.

Gas Tank Emissions Container

Fuel evaporates, which releases hydrocarbons into the atmosphere. Decades ago, laws were passed to minimize the volume of hydrocarbons that resulted from this process. Hence, a fuel evaporation control system was designed to sit within a car’s gas tank and collect vapors from evaporated fuel. This system was basically a container with charcoal material inside. The charcoal collects the vapors and holds them until the engine is started and warmed. Then, the vapors are released through a valve, and vacuumed into the engine to be burned during combustion.

While each of the parts described above play a critical role in minimizing emissions, the catalytic converter is generally considered the most important component. Its development was largely responsible for spearheading the reduction of pollutants from vehicles. That said, each component is essential to the operation of your car’s emissions control system.

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Article Citation
MLA Style Citation:
Rossmore, George "Overview Of The Parts Responsible For Your Car’s Emissions Control System." Overview Of The Parts Responsible For Your Car’s Emissions Control System. 23 Jun. 2010. 28 Dec 2014 <>.

APA Style Citation:
Rossmore, G (2010, June 23). Overview Of The Parts Responsible For Your Car’s Emissions Control System. Retrieved December 28, 2014, from

Chicago Style Citation:
Rossmore, George "Overview Of The Parts Responsible For Your Car’s Emissions Control System"

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