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Catalytic Converters
| What is a catalytic converter and how does it do what they do. |
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The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the NOx emissions. When an NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2.
Oxidation Catalysts:Palladium (Pd) and platinum (Pt) metals in very small amounts convert the hydrocarbons of unburned gasoline and carbon monoxide to carbon dioxide and water. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. But where did this oxygen come from?
The Control System:The third stage is a control system that monitors the exhaust stream, and uses this information to regulate the air/fuel mixture. There is an oxygen sensor mounted in front of the catalytic converter, meaning it is between the engine and the converter. The O2 sensor tells the engine ECU how much oxygen is in the exhaust. The ECU can increase or decrease the amount of oxygen in the exhaust by adjusting the air/fuel mixture. In this way the ECU can make sure that the engine is running as close to the stoichiometric point, and also ensure there is enough oxygen in the exhaust to allow the oxidization catalyst to burn the unburned hydrocarbons and CO.
The catalytic converter does an efficient job of reducing the vehicle emissions, but there are ways it can be improved. One of the biggest drawbacks is that it only works at a fairly high temperature. When you start your car cold, the catalytic converter does next to nothing to reduce the vehicle emissions.
| More... » Part 1 » Part 2 » Part 3 » Part 4 » Part 5 |
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