Three-way catalyst assessment via outlet—inlet temperature measurements: Driving tests

Abstract

This paper presents and discusses experimental data obtained during driving tests simulating the test cycle, ECE 15, and relates exhaust gas levels of hydrocarbon (HC) and carbon monoxide (CO) to catalyst outlet—inlet temperature differences. It also presents the preliminary results from the operation of a microcontrolled on-board diagnostics (OBD) II catalyst efficiency assessment system based on a statistical analysis of the catalyst outlet—inlet temperature difference thermocouple signal. There are indications that this system performs satisfactorily after an adequate warm-up period, if a sampling period in the order of 300—400 s is allowed. Although this operating principle is supported by considerable experimental evidence, there are several technical problems that must be overcome before it can comply to the OBD II requirements. Firstly, as engine loads increase, the efficiency of all catalysts tested is improved considerably by the high exhaust gas temperatures. Furthermore, as the catalyst outlet—inlet temperature difference tends to decrease, so does the sensitivity of the measurements. During driving, catalyst outlet—inlet temperature differences could also be affected by other external factors such as the car speed, rain or snow etc., or long-term temperature sensor drift. Present results indicate that catalyst outlet—inlet temperature difference is also influenced by the ambient temperature. A preliminary analysis of the data indicates that a linear relationship may exist between these two quantities, however, more tests are required for a statistical proof of this assertion. In spite of these problems, the results presented here tend to support the idea that a catalyst performance assessment system using temperature probes is technically feasible. However, further tests are required under various engine operating conditions and environments before a final conclusion can be drawn.