Rocket engine testing: thrust, pressure and vibration characterization

Rockets are exposed to very high stresses, especially during launch. To prevent malfunctioning during operation, rocket components – and especially rocket engines – undergo extensive testing and inspection. For example, new or modified rocket engines require testing to ensure that no combustion instabilities will occur. When using liquid propellant, the supply mechanism needs to be characterized and optimized. Measuring the dynamic ignition pressure is essential for a safe rocket launch

Thrust, dynamic pressure and vibration characterization

Fuel efficiency in solid propellant for solid rockets, or fuel mixture in the case of liquid rockets, is a major concern for rocket engine designers. Characterizing the thrust of the engine itself provides a clear understanding of how much thrust can be produced with a given nozzle design. This allows engineers to compute the specific impulse of the combustion material and study the different phases during the functioning of a rocket engine, such as ignition, burn-in and switch-off. Customer-specific 6-component dynamometers based on piezoelectric technology are often used for such investigations.

This approach also provides an in-depth understanding of the injection and mix of fuel components, ignition time, and combustion: essential knowledge to verify the reliable performance of a rocket engine and drive the development of propulsion technologies. Piezoelectric pressure and acceleration sensors from Kistler span the extreme range of ultra-high temperature stability and dynamics required to tackle the challenges encountered in extreme thrust chamber environments.

Important technologies for dynamic characterization

Depending on the type of rocket engine, high-frequency dynamic measurements are of interest during thrust characterization. Force solutions must have natural frequencies of at least 1 500 to 3 000 Hz.

Piezoelectric force measurement technology allows both quasi-static and dynamic measurement with high resolution. The piezoelectric measuring chain allows a focus on the lower dynamic signals. This capability enables high-fidelity measurements of the low-level signals originating from thrust instabilities.

Single and multicomponent force sensors from Kistler can be configured in dynamometers to satisfy specific application requirements, ensuring flexibility for adaptation to other dynamometer designs as requirements evolve.

Static pressure monitoring and characterization

Last but not least, static pressure monitoring is another important measurement in rocket engine testing. This process, performed on a rocket engine test bench, includes monitoring and controlling of propellant flow as well as measuring the static pressure in the combustion chamber. Monitoring and control of propellant flow for liquid propellant rocket engines requires static pressure sensors. Piezoresistive pressure sensors from Kistler utilize a cavity-etched, micro-machined, silicon sensing element and are suitable for applications with media that are compatible with silicone oil filled capsules.

Important technologies for static monitoring and characterization

Long-term static pressure measurement requires piezoresistive technology with inherent operation from 0Hz up to 2 kHz, unlike piezoelectric sensors which only allow quasistatic operation.

Depending on the use and installation of the pressure sensor, inherent protection against igniting explosive environments may be required.

Piezoresistive pressure sensors utilize an oil-filled and cavity etched, micro-machined, silicon sensing element which provides inherent 0.1%/year long-term stability.

Benefits

High-frequency dynamic force measurement up to 750 Hz

Dynamic pressure measurement directly in the combustion chamber up to 700 °C thanks to high-temperature piezoelectric pressure sensors

Dynamic characterization of liquid propellant fuel supply with cryogenic piezoelectric pressure and acceleration sensors 

Long-term measurement of static pressure with piezoresistive pressure sensors

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