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Emission Control Systems

The parts of a vehicle that are designed to reduce air pollution are called emission control systems. These systems focus on minimizing crankcase, evaporative, and tailpipe exhaust emissions. The first emission control systems were introduced in the late 1960s as vehicle add-ons. By 1971, the government mandated evaporative emission control systems on all U.S. vehicles. Four years later, the government began requiring auto makers to install catalytic converters, another emission control, on all new vehicles. In this post, we’ll explain more about the various types of emissions and how emission control systems work to reduce vehicle air pollution.

Types of Vehicle Emissions

Vehicles contribute to air pollution in three primary ways, all of which are outlined below.

  1. Crankcase emissions. Unburned fuel and the byproducts of combustion reactions comprise crankcase emissions. The positive crankcase ventilation (PCV) system recirculates these gases back into the car’s engine where they reburn.
  2. Evaporative emissions. Gasoline vapors emitted by the carburetor and fuel tank. By sealing the vehicle’s fuel system and keeping the vapors in a canister for reburning, these fumes are prevented from entering the atmosphere.
  3. Tailpipe exhaust emissions. These emissions contain unburned hydrocarbons, carbon monoxide, and nitrogen oxides. Several emissions control systems minimize the creation of these pollutants, including the catalytic converter and special fuel calibration.

Catalytic Converters

Catalytic converters are an integral component of vehicle emission control systems. Catalytic converters reduce the emission of both unburned hydrocarbons and carbon monoxide. Unburned hydrocarbons are primarily responsible for the formation of smog, while carbon monoxide is one of the deadliest vapors vehicles emit. The addition of a converter in a vehicle reduces the amounts of these two pollutants by almost 90%. Currently, vehicles use a three-way catalytic converter that uses computerized feedback to control the concentrations of nitrogen oxide in the exhaust.

Exhaust Gas Recirculation (EGR)

EGR is a type of emissions control system that focuses on reducing nitrogen oxide. This system works by recirculating part of the engine’s exhaust back to the cylinders of the engine. The exhaust is mixed with incoming air to dilute it, thereby raising the specific heat capacity of the gas. Nitrogen oxide forms much faster at higher temperatures, so by raising the heat capacity, EGR limits the formation of nitrogen oxide. In a typical engine, about 5%-15% of the exhaust gas is recirculated back to the engine through EGR. Certain EGR systems may reduce the efficiency of an engine, thus creating a tradeoff between nitrogen oxide emissions reduction and engine efficiency.