There is also a second oxidation reaction that happens inside the catalytic converter, which turns any unburned hydrocarbons into carbon dioxide and water. What this all amounts to is less smoke and odour coming out of the exhausts of cars now than before catalytic converters were mandated by Australian authorities during the 80s for all cars sold here. It is also worth noting catalytic converters are one reason we must use unleaded fuel in cars today, as leaded fuel, which is no longer sold in Oz, prevents the catalysts from breaking down the pollution in the exhaust gases.
To solve those problems, cities, states and the federal government create clean-air laws that restrict the amount of pollution that cars can produce. Over the years, automakers have made many refinements to car engines and fuel systems to keep up with these laws.
One of these changes came about in with an interesting device called a catalytic converter. Catalytic converters are amazingly simple devices, so it is incredible to see how big an impact they have.
In this article, you will learn which pollutants are produced by an engine and how a catalytic converter deals with each of these pollutants to help reduce vehicle emissions. 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.
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 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 These emissions are mostly benign, although carbon dioxide emissions are believed to 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:. Gallon for gallon, new lawn mower engines contribute 93 times more smog-forming emissions than new cars. It's no wonder that the EPA and the state regulators of California are trying hard to get golf ball-sized catalytic converters into lawn mower and other small engines. However, just like in the s, the lawmakers are being met with a powerful lobby. Four smaller lawn mower engine manufacturers have refuted this charge.
California democrats and the EPA think it has more to do with the bottom line. Pending regulations proposed in California could reduce emissions by the equivalent of , cars per day [source: Barringer ]. 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 [source: Chemicool ].
In the catalytic converter, there are two different types of catalyst at work, a reduction catalyst and an oxidation catalyst. 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.
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Road tests. The substrates are the backbone of the converter. This is where the proprietary mix of precious metals and the washcoat allow the conversion process to take place. Coatings are engineered for high temperature durability and optimal catalytic activity, as well as OBD system compatibility. Converters are available in single- or multiple-substrate designs. The mat cushions the converter substrate, holding the ceramic catalyst in proper alignment and accommodating for thermal expansion of the body.
Another vital part of an emissions control system, these sensors are placed before and after the catalytic converter on an OBDII vehicle. They are designed to monitor the O2 levels in the exhaust gas and are also used to evaluate the status of the converter. This information along with data provided by the mass air flow, MAP manifold absolute pressure and engine sensors, allow the PCM to adjust fuel controls. The precious metals introduced onto the substrate serve as catalysts that chemically process raw exhaust gases.
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