Yahoo Autos What Does a Catalytic Converter Do and Why Do People Steal Them?
There are millions of cars on the road in the United States, and each is a source of air pollution. In an attempt to stem this pollution, cities, states and the federal government create clean-air laws that restrict the amount of pollution that cars can produce.
One of these auto production changes came about in 1975 with a device called a catalytic converter — but what does a catalytic converter do, exactly?
In this article, we'll go over the types of pollutants an engine produces and how a catalytic converter helps reduce vehicle emissions.
What Is a Catalytic Converter?
A catalytic converter is an emissions control device. The job of the catalytic converter is to convert harmful pollutants into less harmful emissions before they ever leave the car's exhaust system.
Catalytic converters are amazingly simple devices, so it is incredible to see how big an impact they have.
Air-to-fuel Ratio in a Car Engine
In order to reduce emissions, modern car engines carefully control the amount of fuel they burn. They try to keep the air-to-fuel ratio very close to the stoichiometric point, which is the ideal ratio of air to fuel.
Fuel Mixture
Theoretically, at this ratio, all of the fuel will be burned using all of the oxygen in the air. For gasoline, the stoichiometric ratio is about 14.7:1, meaning that for each pound of gasoline, 14.7 pounds of air will be burned.
The fuel mixture actually varies from the ideal ratio quite a bit during driving. Sometimes the mixture can be lean (an air-to-fuel ratio higher than 14.7), and other times the mixture can be rich (an air-to-fuel ratio lower than 14.7).
Types of Emissions
The main emissions of a car engine are:
Nitrogen gas (N2): Air is 78 percent nitrogen gas, and most of this passes right through the car engine.
Carbon dioxide (CO2): This is one product of combustion. The carbon in the fuel bonds with the oxygen in the air.
Water vapor (H2O): This is another product of combustion. The hydrogen in the fuel bonds with the oxygen in the air.
These emissions are mostly benign, although carbon dioxide emissions do contribute to global warming. Because the combustion process is never perfect, some smaller amounts of more harmful emissions are also produced in car engines. Catalytic converters are designed to reduce all three:
Carbon monoxide (CO) is a poisonous gas that is colorless and odorless.
Hydrocarbons or volatile organic compounds (VOCs) are a major component of smog produced mostly from evaporated, unburned fuel.
Nitrogen oxides (NO and NO2, together called NOx) are a contributor to smog and acid rain, which also cause irritation to human mucus membranes.
How Catalytic Converters Reduce Pollution
In chemistry, a catalyst is a substance that causes or accelerates a chemical reaction without itself being affected. Catalysts participate in the reactions, but are neither reactants nor products of the reaction they catalyze.
In the human body, enzymes are naturally occurring catalysts responsible for many essential biochemical reactions.
In the catalytic converter, there are two different types of catalyst at work: a reduction catalyst and an oxidation catalyst. Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium.
The idea is to create a structure that exposes the maximum surface area of catalyst to the exhaust stream while also minimizing the amount of catalyst required, as the materials are extremely expensive.
Most modern cars are equipped with three-way catalytic converters. This refers to the three regulated emissions it helps to reduce.
