Hotfire-Test Case-Study IPL

When a self-built rocket engine fires for the first time on its test stand, only a few seconds decide whether months of design work translate into reliable data or into a dramatic failure. In that one second, an enormous amount depends on the sensors and on the people who understand them. How a French student team turned that combination into an international scientific award is the subject of this article.

How the Innovative Propulsion Lab Won an EUCASS Award with Our Thermocouples

Thermocouples in hotfire tests are the unobtrusive lead actors in any serious engine development programme. They deliver the data that later defines design choices, material selection and safety margins, and they do so under conditions that very few components can endure. This is exactly where the Innovative Propulsion Lab, a French student team in propulsion research, used sensors from our manufacture during the past season. The collaboration produced a scientific paper that was awarded the Best Student Paper Award at a major aerospace conference. This case study explains how it came about and what industrial users can take from it.

Who the Innovative Propulsion Lab Is

The Innovative Propulsion Lab, or IPL, is a student research team based in France. The group develops liquid rocket engines, that is, propulsion units running on liquid propellants, and operates its own hotfire test stand. Unlike many academic projects, this is not about model rockets with solid fuel, but about engines whose complexity and safety requirements demand significant engineering effort.

We at Therma supported the team with sensors for the first time last year. The request came from a research environment in which our products have been used by university motorsport teams for years, so the cooperation fit our work without friction. What started as a single sponsorship has since grown into a partnership that spans several project phases and that the team has also documented publicly on LinkedIn.

What sets a liquid rocket engine apart from a hobby project

A liquid rocket engine routes fuel and oxidiser separately into a combustion chamber and regulates combustion through pumps, valves and injector geometries. That makes it controllable but technically far more demanding than a simple solid propellant motor. For sensor work it means many measurement points, steep temperature gradients and very high reliability requirements.

Why student teams matter in propulsion engineering

Student propulsion teams are often the first to test new configurations because they have no legacy systems to maintain. They iterate quickly, document openly and work closely with research institutions. That iteration speed makes them very valuable practical partners for us.

Why Thermocouples Are Crucial in Hotfire Tests

A hotfire test holds the engine firmly anchored to a test stand and brings it to a controlled ignition. The objective is not flight but a complete characterisation of the unit under realistic load. Thermocouples in hotfire tests are the fastest and most robust way to record temperatures on hot components.

Measurements typically occur at several points simultaneously, for example on the combustion chamber, the nozzle, propellant lines and structural elements. From the curves at these measurement points you can reconstruct heat flux, verify material limits and calibrate model calculations. Without that data, you fly blind through the design.

For a deeper technical look at sensor selection in aerospace contexts we recommend the pillar article Temperature sensor in rocket testing and aerospace. It covers the fundamental requirements, material questions and the comparison criteria between thermocouples and resistance thermometers in aerospace applications.

What hotfire means

Hotfire denotes the controlled ignition of an engine on the ground, usually within a defined burn window of a few seconds up to several minutes. During that time, every subsystem runs in real operation. Sensors that fail here are missing at the moment that matters most.

Which measurements are safety relevant?

Safety relevant measurements include temperatures on combustion chamber walls, nozzle throats and components immediately downstream of the injection. They also include structural temperatures at locations where materials are loaded by heat and pressure at the same time. Each of these measurement points contributes to the decision whether a test continues or aborts.

Why response time and robustness matter together

A response that is too slow swallows the actual temperature peak, while a fragile design does not survive the mechanical loads on the test stand. Both have to be solved at the same time, and that is the domain of mineral insulated sheath elements and carefully engineered installations.

Which Sensors the Team Used from Our Range

In the team’s setup last season, two product families from our manufacture were essentially in use. The selection was driven less by datasheet comparison than by the actual installation situation and the expected temperature class. In our view that is the only sensible order when sensors have to perform under real conditions.

Specifically, we supplied the screw-in thermocouple type K with fibreglass for measurement points with threaded ports on pressure-bearing components, together with the surface thermocouple type K with Kapton for flat structural measurements on the engine housing. Both designs are part of our standard ranges of screw-in thermocouples and surface thermocouples, all manufactured at our site in Lindlar.

The main reasons for this exact configuration:

• Screw-in design with fibreglass insulation for a tight, high-temperature-resistant connection to pressure-bearing components
• Surface sensor with Kapton adhesive foil for fast application without drilling or component preparation
• Fibreglass insulation with excellent heat resistance even in close proximity to hot components
• Designs that a student team can install and replace safely on its own, without specialised tooling

Screw-in thermocouple type K with fibreglass

This design sits in a thread and brings the sensor tip in a defined way into the medium or component to be measured. Fibreglass insulation supports high continuous temperatures and is much more tolerant of mechanical abrasion on the sheath than pure plastic insulation.

Surface thermocouple type K with Kapton

The sensor is bonded to a component surface and reads the surface temperature without penetrating the part. For structural measurements under time pressure ahead of a hotfire, that is a very pragmatic solution.

Why the design says more about the result than the measuring range

A type K thermocouple can in theory work in many configurations around a rocket engine. What actually decides the quality of the measurement is where and how the sensor is fitted, how well it is thermally coupled and how fast it reacts to changes. The mechanical design is almost always the decisive lever.

How the Hotfire Test Was Run

On the test stand, the engine was firmly fixed, the propellant and oxidiser lines were connected and all sensors were wired to a reference junction and a data acquisition system. The team’s instrumentation was distributed across the combustion chamber, the nozzle area and load-bearing structures, supplemented by control points on the supply lines. The setup is classic for hotfire test stands and differs only in detail from industrial engine test rigs.

Ignition runs in sequence, starting with propellant supply, followed by initial ignition and a defined burn window. During that time the thermocouples record a fast temperature rise, a typically short plateau and then a decay. Emergency shutdowns are pre-programmed in such sequences and are triggered from threshold values on exactly these sensors.

The team obtained very clean data sets from the resulting curves. Clean data in this context means low noise, plausible rise gradients and clear repeatability across multiple ignitions. That is the precondition for any further scientific evaluation. The team also published video impressions from the test stand and the sensor installation in two Instagram posts, one showing the setup with mounted instrumentation and one showing the hotfire itself:

Sensor positions on the engine

Sensors were placed on the combustion chamber wall, the nozzle throat, the propellant line and several structural points. This distribution captures heat not just locally but as a path through the engine.

What makes a clean measurement curve

A clean measurement curve shows a clearly identifiable rise, an expected plateau and a consistent decay without erratic jumps. Where such jumps do appear, they can be traced to specific causes such as a material change or a sensor failure.

From the Data Set to an Award Winning Paper

From the measurement series of the past season, the IPL team wrote a scientific paper and submitted it to the European Conference for AeroSpace Sciences. The conference was held in Rome in 2025 and is one of the most relevant forums for student and professional contributions to propulsion research. The paper is publicly available as a PDF and describes the thermal characterisation of the engine over the hotfire sequence.

At that conference the contribution was honoured with the Best Student Paper Award. From our point of view this is the most rewarding form of validation that sensor work can receive. It does not appear in a marketing text but in a peer-review-grade source that other researchers can cite.

EUCASS as a proving ground

EUCASS brings together teams from academic research, industry and space agencies. Anyone whose paper holds up here has presented a methodology that survives in front of a technically demanding audience. For a student team that is an exceptional accomplishment.

Why good data is the start of good research

A scientific work is only as solid as the data on which it stands. If the sensors already wobble on the test stand, even the best evaluation cannot turn the result into a sound finding. That is why the quality of a paper often begins weeks before the writing, at the engine itself.

What IPL Is Planning for Race2Space in the United Kingdom

The 2026 season takes the team to a new venue. With a redesigned and considerably more powerful engine, IPL is participating in the Race2Space competition in the United Kingdom. Race2Space is aimed at student propulsion teams and sets requirements that go a clear step beyond the previous hotfire campaign.

Race2Space as the next benchmark

Race2Space requires a documented safety and test concept, a qualified engine and an on-site demonstration. Sensors here become not only measurement equipment but part of the regulatory evidence.

Why type T is sensible for some measurement points?

Type T performs reliably in a range where many other pairings are either inaccurate or thermally over-specified. Where measurements concern propellant temperatures, coolant paths or structural points below combustion chamber temperature, that property is valuable.

Why We Support Student Teams in Aerospace

For more than three decades our work has had a clear application focus, originally industrial and then increasingly in motorsport up to Formula 1. The bridge to aerospace grew out of this organically, because many of the requirements are similar, including high temperatures, short response times, mechanical loads and reproducible measurement integrity. Student teams have become regular customers in this world for us.

These collaborations are not a marketing exercise but a technical feedback channel into our own production. We learn from unusual installation situations, from the rapid iteration of the teams and from the requirements that arise from the respective competitions. Where our sensors hold up under those conditions, they also hold up in industrial applications.

The main reasons we actively look for this work:

• Direct practical feedback from extreme applications that a typical factory test stand rarely produces
• Stress test for our designs that keeps our standards sharp
• Contribution to the next generation in propulsion and instrumentation engineering, one of the thinner areas in the German and European engineering pipeline

From motorsport to aerospace

Motorsport has taught us how to handle high accelerations, broad vibration spectra and rapid temperature swings in very tight installation situations. The same requirements appear almost one to one in a liquid rocket engine, just in a different domain.

What we learn from student projects

Student teams ask questions that an established industrial customer would not ask, simply because they have no routine in the way. These questions regularly lead to small but meaningful improvements in our designs.

What Engineers Can Take from This Case Study

Even though hotfire tests are rare in everyday industry, the underlying logic holds in many areas. Wherever sensors must work under temperature, pressure and mechanical load at the same time, the mechanical design comes before the datasheet. That is the most important translation of this case into the daily work of an industrial engineer.

The second lesson lies in response time. A measurement point that reacts too slowly produces smooth and apparently plausible curves in which the actual events are missing. In safety-critical applications this is often the difference between a documented event and a missed anomaly.

The third lesson is consultation. Before sensors are ordered, a conversation about installation situation, medium and load profile pays off. We know this from motorsport, from aerospace and from classic industry, and in all three areas an early discussion saves substantial time later. If you have a comparable task in front of you, please get in touch.

When a custom solution is worthwhile

A custom build is worthwhile as soon as a standard geometry does not match the installation situation, or as soon as tolerances beyond the standard range are required. We typically deliver such custom dimensions within one to two weeks.

Conclusion

A first sponsorship request from the Innovative Propulsion Lab has grown into a partnership that ended, for now, with a Best Student Paper Award at EUCASS 2025 in Rome. For us this is the most credible form of validation, because it does not come from a marketing environment but from a scientific assessment. For the team, it confirms that a carefully built hotfire campaign and solid sensors are an excellent foundation for research work.

The next stop is Race2Space in the United Kingdom, with a more powerful engine and an adapted sensor suite. We will stay close to the project, watch the next iteration with interest and welcome the line that runs through all of this. If you are facing a comparable measurement task in industry, please feel free to talk to us.