How does a catalytic converter work? Q
Answered by Paul Etheridge, Head of Business Development at Ricardo Motorcycle, and Dr Franz Berndt, Head of Thermodynamic Development at Ricardo Motorcycle Catalytic converters were introduced en masse on bikes in the early 2000s. This device is found inside the motorcycle’s exhaust and reduces harmful exhaust emissions. It does this by acting as the catalyst for a series of toxin-reducing reactions in the exhaust pipe.
Most modern units are made of stainless steel and coated with precious metals including platinum, rhodium and palladium to provide the required catalytic reactions.
There is a reduction of carbon monoxide (CO) to carbon dioxide, an oxidation of unburnt fuel (hydrocarbons, HC) to carbon dioxide and there is also a reduction of nitric oxide to nitrogen, carbon dioxide and oxygen.
In order for these reactions to take place, the motorcycle must operate within a very narrow air-to-fuel ratio, which is supposedly 14.5kg of air to 1kg of fuel. If you don’t do this and you run an engine rich, then the catalyst efficiency for reducing HC and CO will reduce. If you run a bike lean, then the reaction for nitric oxide won’t take place.
To prevent this, a Lambda sensor measures the amount of oxygen in the exhaust. This then sends messages to the bike’s computer to adjust the air-fuel ratio accordingly. Finally, the catalyst must operate above an exhaust temperature of about 300 degrees centigrade for the reactions to take place.
Catalysers have evolved over time and the number of holes in them dictates the number of cells per square inch. In the early days, this was maybe 100 cells per square inch. The more holes they have, the more back pressure they create in the exhaust. Nowadays they have around 200-300 cells per square inch for increased conversion efficiency. This higher density of cells will then affect your bike’s performance, depending on where the catalyst is in the exhaust.
Precious metals help zap dangerous exhaust emissions