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.

Ambient temperature influence on catalytic outlet—inlet temperature difference

“…For this purpose an alternative manual procedure was devised using computer-controlled sound signals that helped the driver make the necessary speed changes. This approximate manual simulation of the ECE 15 test driving schedule for six consecutive cycles is illustrated and presented in reference [14].…”

“…For this purpose an appropriate microprocessor-controlled assessment system was designed and installed on a test vehicle. The results of reference [14] indicate that the catalyst outlet±inlet temperature dierence is also in¯uenced by the ambient temperature. According to experimental results obtained during this research, as the ambient temperature increases, the outlet±inlet temperature dierence of the catalyst also tends to increase linearly.…”

“…According to the experimental results presented in the previous sections, there is a correlation between catalytic converter eciency and ambient temperature. This correlation was not included in the catalytic converter eciency evaluation algorithm presented in an earlier paper by the present authors [14], where the eciency inspection was based exclusively on the outlet±inlet temperature dierence. By measuring the ambient temperature T b and applying equation ( 5) twice for the calculation of ÁT mx and ÁT min for the measured ambient temperature T b using stored reference ambient temperature T a , a new algorithm for the catalytic converter eciency monitoring is created.…”

“…The present paper describes the ambient temperature in¯uence in catalyst diagnostic monitoring based on the outlet±inlet temperature dierence. As mentioned in reference [14], this is an alternative approach that can be used for catalyst eciency assessment based on time integration of the outlet±inlet temperature dierence…”

Συστηματα Διαγνωστικου Ελεγχου Αποδοσης Τριοδικου Καταλυτικου Μετατροπεα

“…Κάθε σήμα ήταν ενδεικτικό του σταδίου που αντιπροσώπευε, ενώ η διάρκεια του σήματος ήταν ίση με τη διάρκεια του σταδίου. Με τη χρήση ακουστικών, ο οδηγός του οχήματος εκτελούσε τον κύκλο, φροντίζοντας με τη βοήθεια του ταχυμέτρου να διατηρεί τη σωστή ταχύτητα για κάθε στάδιο[72]. Το αποτέλεσμα αυτής της πρωτότυπης προσομοίωσης του κύκλου παρουσιάζεται Συνολικά εκτελέστηκαν σαράντα πειράματα αυτού του είδους κάτω από διαφορετικές καιρικές συνθήκες (κρύο, ζέστη, βροχή κ.λπ.…”