Measurements of Three-Way Catalyst Performance Under a Stepwise Constant Idle Speed Schedule

The present paper analyses the results from a series of experiments involving tests of catalysts under a stepwise constant engine idle speed schedule in the form of a step pyramid. This test speed schedule consists of an acceleration sequence formed by a number of abrupt speed increments followed by constant speed periods, and a deceleration sequence formed by the same speed changes executed in the reverse order. During the experiments the CO, HC, as well as the catalyst outlet - inlet temperature difference were monitored. The experimental results indicated that as the catalyst efficiency deteriorated with age, the rise of pollution levels was accompanied by significant changes in the CO and temperature difference signals. The HC signal was not as strongly affected.

There are positive indications that the outlet - inlet temperature difference signal can be used as an input to a microcontrolled catalyst efficiency assessment system, capable of operating under driving conditions. However, further experimentation is required for the development of the catalyst efficiency evaluation algorithm, since under load the increased mass flow and exhaust gas temperature would strongly effect catalytic efficiency.