What is a diesel oxidation catalyst?

A diesel oxidation catalyst breaks down pollutants in diesel engine exhaust. It is usually within the exhaust muffler and consists of a honeycomb structure coated with precious metals.

When heated by the exhaust, the precious metals act as a catalyst, causing a chemical reaction without being part of it. Nitrogen dioxide comes into contact with the catalyst and breaks apart, limiting air pollution. Additionally, when the fuel mixture is rich and unburnt fuel passes through the exhaust, the heated catalyst burns a portion of the fuel. Vehicle manufacturers have included a diesel oxidation catalyst for several years, but a conversion system can easily be retrofitted to a vehicle.