How Do Vehicles Control Emissions?


Most have probably heard a lot about emissions and why they need to be controlled. However, have you ever wondered what they are or how vehicles keep them under control?

The emissions themselves are a combination of burned and unburned substances such as hydrocarbons, carbon monoxide, nitrogen oxides and sulfur oxides that can come from the combustion chamber and the crankcase. In older vehicles, the emissions can also include gasoline fumes from carburetors. These emissions are controlled by both mechanical and technological systems.

Combustion Emission Controls

A significant aspect of the issues with emissions is the fuel that isn’t burned, so a key system returns this unburned fuel to the combustion chambers. This is achieved with a positive crankcase ventilation valve, or PCV valve, that combines leaked combustion gases with air, then pumps them back for combustion.

Emissions can also be limited by controlling the combustion itself. This is where electronic fuel injectors play a role. As of the mid-1990s, these completely replaced the old carburetor systems. A much more precise fuel-air mixture is created by the fuel injector systems to cut down on fumes and get more efficient burns.

Exhaust Emission Controls

More nitrogen oxides are produced with excess heat in the combustion chamber. To reduce this, an exhaust gas re-circulation system (EGR) system) takes a portion of the exhaust and routes it back to the combustion chambers. As a result, the temperature decreases, which helps reduce the amount of nitrogen oxides.

Past the EGR system, the exhaust goes through a catalytic converter, which has metal that converts the hydrocarbons, carbon monoxide and nitrogen dioxide into water, carbon dioxide and nitrogen.

Electronic Emission Controls

Precision is the key to truly controlling emissions. This is why the most crucial component of a modern emissions control system is the electronic control unit (ECU) of the car. This computer monitors the vehicle’s performance, then adjusts systems such as the fuel injector to make sure the vehicle is running as efficiently as possible. In addition, the ECU has the built-in capability to monitor the emissions, which allows it to adjust to run as cleanly as possible.

Controlling Emissions vs. Providing Power

The place where things can get difficult for manufacturers is trying to balance power with efficiency. While more efficient engines will use the least amount of fuel to move the car, generating less emissions, it also provides less acceleration or power. More power means more combustion and more emissions, particularly when you are asking for a lot of power in a short period of time for high acceleration.


Emission controls have significantly progressed since the smoggy 1970s when modern emissions standards were first introduced, and every year more advancements are made. Also, with the rise of hybrids and electric cars, the amount of average emissions per vehicle will just keep getting lower. Contact Asher Automotive with the link below for more information on how vehicles control emissions!

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