It will be better to fully understand first what really happens inside a catalytic converter before knowing the latest updates on catalytic converters. Automakers describe them as devices that help lessen the toxicity of the vehicle’s exhaust before they are released to the atmosphere.

Car engines today need to control the amount of fuel they burn so they can reduce emissions.   They try to keep the air-to-fuel ratio very close to the calculated ideal ratio, or  the stoichiometric point. Once the ratio has been reached,  all of the fuel will be burned using all of the oxygen in the air.

A catalytic converter is tasked to reduce these elements:

Carbon monoxide (CO) - a poisonous gas that is colorless and odorless

Hydrocarbons or volatile organic compounds (VOCs) - produced mostly from unburned fuel that evaporates

Nitrogen oxides (NO and NO2, together called NOx) - contributes to smog and acid rain, and also causes irritation to human mucus membranes.

Most cars today use a three-way catalytic converter. “Three-way” refers to the three regulated emissions it helps to reduce the elements previously stated. The converter uses two different types of catalysts, a reduction catalyst and an oxidation catalyst. Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and 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.

The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the NOx emission. The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning them over a platinum and palladium catalyst. The last stage is a control system that monitors the exhaust stream, and uses this information to control the fuel injection system. An oxygen sensor is  mounted upstream of the catalytic converter, that tells he engine computer how much oxygen is in the exhaust. In turn, the engine computer can increase or decrease the amount of oxygen in the exhaust by adjusting the air-to-fuel ratio.

This entry was posted on Wednesday, July 18th, 2007 at 7:40 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.