1998-02-23

Direct High Dynamic Flow Measurement in the Exhaust of Combustion Engines 980880

This paper describes a recently developed sensor, the High-Performance Flowmeter (HPF), which measures flow rates in raw, undiluted exhaust.The HPF is based on the principle of acceleration or deceleration of an ultrasonic pulse due to a flow of gas. It allows a two-directional detection of flow with high accuracy and high sampling rates. Formerly, all flow sensors were limited to low temperatures and low sampling rates when measuring the flow rates directly in raw exhaust. An entirely new principle has been developed for this generation of ultrasonic pulses which improves the performance of ultrasonic flow sensors dramatically. Using this principle, such flow sensors can be used for the first time to measure dynamic flow rates in raw exhaust at high temperatures with sampling rates up to several hundred hertz. The maximum temperature range of the medium of up to 800 °C (1500 °F) makes the sensor ideal to measure flow rates directly in unconditioned raw exhaust as well as in combustion air. The high dynamic and resolution directly indicates the internal flow dynamics and thermal behavior of the engine. The flow signal provides information about the condition of each engine cylinder as well as the total exhaust volume. Standardized flow rates can be calculated by measuring the temperature and the flow of the gas simultaneously. The mass emissions of all gases and respective gas components can be calculated dynamically if the HPF is used in combination with fast response analyzer benches,.This paper will give an overview about the sensor's design, its properties and advantages, as well as the experiences made with the HPF at PEUS facilities in Austria and USA. Also, comparisons to conventional methods of volume detection will be discussed.

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