A New Intermittent Aspirated Probe for the Measurement of Stagnation Quantities in High Temperature Gases

Abstract

This paper presents the design, manufacture, and testing of a new probe for the measurement of temperature and pressure in engine environments. The probe consists of a choked nozzle located in the flow and a system downstream including a cooler, a flow measuring device, and a valve. It operates in two modes: In the first mode the valve is open, the probe is aspirated, and the nozzle is choked. The mass flow through the probe is measured using instrumentation placed downstream of the cooler, so that it does not have contact with the hot flow. In the second mode, the valve is closed, and the stagnation pressure is measured using the same instrumentation downstream the cooler. The total temperature is computed as a derived variable from the measurements of stagnation pressure and mass flow rate. There are a number of advantages of the probe over existing methods of temperature measurement. The measurement inaccuracy due to conduction and radiation errors and calibration drift found in thermocouples is significantly reduced; it can measure both stagnation temperature and pressure, halving the instrumentation costs; it has no wiring or transducer in the sensor head; the system can self-calibrate while located within an engine. This paper describes the design of a probe for use in engine environments. The probe prototype is tested up to 900 K and is shown to have an accuracy of ±6 K.