Advances in traceable calibration of cylinder pressure transducers

Abstract

Accurate and reliable dynamic pressure measurements are needed for optimizing performance in modern combustion engines, manufacturing processes and aerospace applications. Besides fast pressure transients, these applications subject dynamic pressure transducers to elevated temperatures. Both of these quantities effect the sensitivity of transducers. Therefore, transducers should be calibrated at conditions that corresponds to the operating environment. To answer these needs, the National Metrology Institute VTT MIKES has developed its drop weight dynamic pressure primary standard further. Developments include improved control and measurement of the falling weight, extension of the pressure range to combustion engine pressures down to 3 MPa and a heating option for dynamic pressure transducers under calibration. These advances enable traceable calibration of cylinder pressure transducers at conditions relevant to engine applications. The overall uncertainty (k = 2) of calibration is estimated to be around 1.7%. The performance was demonstrated by calibrating a piezoelectric pressure transducer in the pressure and temperature range from 7 MPa to 30 MPa in 20 °C, 120 °C and 180 °C, respectively. As a result, traceable calibrations of dynamic pressure transducers can be performed at conditions relevant for engine applications. This improves the reliability and accuracy of in-cylinder pressure measurements.

Recent Developments of Dynamic Pressure Measurements in Combustion Engines

“…The calibrator is based on the reference sensor principle with traceability to SI through the VTT CPS calibrated at VTT MIKES using the dynamic pressure primary standard. The working principle is as follows (see Figure 1): An electromechanical actuator excites the impact mass (2), which hits the piston (3) giving rise to a pressure pulse inside the chamber (4) to which the sensors (up to 4 sensors) are connected through the sensor ports (5). Pressure pulses generated with the calibrator have a half-sine shape and a duration of about 2 ms, which corresponds well to pressure pulses inside ICEs.…”

“…Dynamic pressure sensors are typically calibrated at ambient temperatures using static pressure measurements standards, which might cause errors up to 10 % when sensors are used at dynamic conditions and elevated temperatures inside an engine. To provide traceability to the International System of Units (SI), the National Metrology Institute of Finland (VTT MIKES) has developed a dynamic pressure primary standard [2]. Although providing the most accurate realization of the unit -typical calibration uncertainties (k = 2) around 2 % -it is not considered practical for dayto-day calibration work as it requires a highly skilled operator, and it is laborious to use.…”

Effect of the Dynamic Response of a Side-Wall Pressure Measurement System on Determining the Pressure Step Signal in a Shock Tube Using a Time-of-Flight Method

“…Metrological traceability to the International System of Units (SI) requires the development of appropriate primary standards for dynamic measurements of pressure [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. The aperiodic shock tube pressure generators show a potential to provide SI-traceable dynamic calibrations for pressure sensors [ 17 , 18 , 19 , 20 , 21 ].…”

Comparing the adiabatic and isothermal pressure dependence of the index of refraction in a drop-weight apparatus

“…It is therefore of interest to investigate whether a dynamic calibration might mitigate this difference. Several groups are working towards this goal, see for example [2,[8][9][10][11][12][13]. A particular challenge is the transfer of SI traceability from static pressure, where well established primary standards are available, to dynamic pressure, where work on providing standards with the required characteristics (pressure range, frequency range, uncertainty) is still in progress.…”

“…Several principles have been used to construct devices for the non-destructive generation of strong pressure pulses, i.e., stronger than can in general be reached by shock tubes [14,15]. They include, for example, fast opening valves [7], the use of a commercial drop-weight apparatus [16], a dropweight apparatus designed for secondary calibrations using two piezoelectric sensors [8,17], a drop-weight apparatus measuring pressure via the monitoring of the deceleration of the piston [9,18,19], an air gun [16], a pressure-tank setup [10], or optical absorption spectroscopy [11]. Diamond anvil cells [20], well known for the very high pressures they can exert on small samples, necessarily need to be smallvolume devices, too small to permit attaching a customer's transducer (typical sensor casings use M10 or M12 threads).…”