The Effect of Intermittent Engine Misfire and Air to Fuel Ratio Excursions on Exhaust Catalyst Temperature

The effect of ignition induced misfire on exhaust catalyst temperature has been investigated using an engine bench and a computer model. The effects of misfire rate, exhaust gas flow rate and catalyst condition are reported and conditions that would lead to the melting of a ceramic catalyst are predicted.

The modelling techniques have been extended to predict the effect of a fast air to fuel ratio transient on catalyst temperature. Measurements of catalyst temperature during a simulated deceleration using fast response thermocouples have shown that a short lived temperature increase does occur.