NDTnet 1998 Aug, Vol.3 No.8

Abstract

The exhaust gas flow from the cylinders of piston engines is a complicated highly dynamic process. Flow velocity, pressure and temperature are fluctuating fast and markedly, especially during motor charge changes. A knowledge of the transient behaviour of these parameters is decisive for future motor developments with regard to pollutant emissions. A method for the high temporal resolved measurement of the exhaust gas mass flow and the temperature has been developped. The following criteria had to be taken into account:
• Applicability for measurements in all exhaust pipe sections up to the exhaust connection branch
• Resistance to high temperatures and thermal shocks

The method is based upon the ultrasonic time-of-flight technique developped already for the intake pipe(1). An air borne ultrasonic transducer oriented at an angle with regard to the pipe axis generates an ultrasonic pulse travelling from one side of the exhaust pipe to the other side. Here the pulse is detected by means of a second transducer. As a function of flow velocity the sound path is deviated resulting in a variation of the time-of-flight. The time-of-flight is measured. After interchanging the transmitter-receiver functions of the transducers, a second time-of-flight measurement is performed. The time-of flight difference is proportional to the flow velocity; the temperature is calculated with the time-of-flight values of both measurement steps.

The research activities centered on the realization of the high-temperature stable air borne ultrasonic sensors. At the present state of development, the sensors are applicable for exhaust gas temperatures up to 400° C without water cooling and up to 600° C with water cooling. It is intended to extent the temperature range up to 1000° C.

The sensors and the measurement method were tested at a motor test stand. The average values of exhaust gas flow and temperature were in good agreement with the values determined from fuel / air consumption. It was demonstrated that the technique can be used up to 6000 revolutions per minute.

1.A. von Jena and V. Magori in F&M 100 (1992) 3

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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