The Effect of an Oxidation Catalyst on Cold Start Diesel Emissions in the First 120 Seconds of Running

A diesel engine particulate emission rate can be 7 times greater when it is cold than when it is warm. It is recognized within the automotive industry that any catalyst, either diesel or gasoline, is unable to function efficiently when it is cold. The two way oxidation diesel catalyst is unable to oxidize CO to CO₂ and unburned hydrocarbons (uHCs) to CO₂ and H₂O, due to low start up exhaust temperatures. Add to this the inherently lower temperature of diesel exhaust, and it is possible that during urban driving the catalyst can take up to 10 minutes before receiving sufficient energy to start oxidizing the exhaust efficiently.

Work carried out at the University of Central England (UCE) suggests that although the catalyst is unable to oxidize CO and uHCs emissions during start and warm up, it has a secondary function of trapping the particulates produced, and reduce the tailpipe particulate emissions during the engine warm up phase.