THE MAGAZINE FOR COMPUTER APPLICATIONS
Circuit Cellar Online offers articles illustrating creative solutions
and unique applications through complete projects, practical
tutorials, and useful design techniques.

ALL ABOARD THE CLEAN ENGINE

Automotive Emissions and Onboard Diagnostics

by John West & Mark Stachew

Start ý Why Onboard Diagnostics? ý Major Components ý Catalytic Converter ý Oxygen Sensor ý EGR ý Fuel System Adaptive Learning ý Misfire Detection ý The Need for Speed ý New Regulations ý 0 to 100 KB in 6 Seconds ý Sources and PDF

CATALYTIC CONVERTER

All exhaust gases pass through a catalytic converter that is mounted on the exhaust pipe. It filters these gases through a dense honeycomb structure coated with precious metals such as platinum, palladium, and rhodium (see Figure 1). Chemical reactions occur on these surfaces to convert the pollutants into less harmful gases. Catalytic converters store oxygen on lean mixtures (less than optimal amount of fuel) and release oxygen on rich mixtures (more than optimal amount of fuel).

Figure 1ýHere you can see the catalytic converter cross section.

The primary pollutant produced on the lean swing is nitrous oxide. Oxygen is removed from nitrous oxide by the converter, resulting in nitrogen gas, a harmless emission. On the rich cycle, the primary pollutant is carbon monoxide. By adding the oxygen that was stored on the lean cycle to the carbon monoxide, carbon dioxide is produced.

PREVIOUS • NEXT