Adaptive Pulse Repetition Frequency Technique for an Ultrasonic Transit-Time Gas Flowmeter for Hot Pulsating Gases

Abstract

A technique of using an adaptive pulse repetition frequency (PRF) to operate an ultrasonic contrapropagation transit-time gas flowmeter (UFM) is introduced. This adaptive PRF technique allows transient measurements of hot (up to 450 • C) and pulsating (up to 1.5 kHz) gas flows. Such conditions occur in the exhaust gas of a combustion engine. Here, a UFM with the widely used fixed PRF technique is not applicable, because the large gas temperature variations would prevent a reliable detection of ultrasonic pulse arrival times. Coherently reflected waves are generated within the gas because of the unavoidable acoustic impedance mismatch between the gas and the transducers, and, depending on the gas temperatures, these echoes overlap with the main signal. The adaptive PRF technique overcomes this problem and allows correct pulse detection over the whole temperature range required. The UFM utilizes special high-temperatureresistant capacitance ultrasonic transducers (CUTs) to meet the requirements in terms of operating temperature range and dynamic response. Results, which are obtained with a preliminary laboratory prototype, are presented for the exhaust gas mass flow rate in a ∅ 50-mm pipe measured at gas temperatures of up to 450 • C and at PRFs of up to 5.5 kHz, which is an increase in frequency response of one order of magnitude in comparison to existing measurement systems.Index Terms-Adaptive pulse repetition frequency (PRF), capacitance ultrasonic transducer (CUT), exhaust gas, high temperature, mass flow sensor, pulsating gas flow, ultrasonic flowmeter.

Study of the influence of temperature on the measurement accuracy of transit-time ultrasonic flowmeters

“…The elasticity causes the fluid to resist compression and have a tendency to return to its original state, but the inertia of mass produces too much movement. The two conditions of the wave are provided 18 .…”

Methodology for instantaneous average exhaust gas mass flow rate measurement

“…lt retains the strong oscillation, which cannot be used later to determine the average volume flow rate because of the "square root error", caused by nonlinear relationship between differential pressure and flow, as is widely discussed by Nakamura et al [29]. Such measurement errors can be clearly seen in the development of other exhaust gas flow meters ( [16,17,19,29]), where negative flow values are also observed.…”

“…Ultrasonic flow meters, are among the most effective to flow measure even if pulsating or backflow is present [29], but have some disadvantages because they are affected by the temperature, density and viscosity of the fluid [35,37]. Different techniques have been developed to overcome these problems like the work developed at the University of Leoben [16] [17,18] and the flow meter developed by AVL [3,19].…”

Multipath ultrasonic gas flow-meter based on multiple reference waves

“…UFM can be based on different principles, among which the transit-time method is one of the most widely adopted due to its numerous advantages [2][3][4]. In the transit-time UFM, at least one pair of transducers is applied with their centerlines inclined to the axis of gas pipeline at a designed angle.…”