Micro Gas Turbine
The Micro Gas Turbine (MGT) is the key to our fuel-flexible energy system. It is a single engine capable of running on multiple sustainable fuels. The MGT consists of 5 main components: compressor, recuperator, combustion chamber, turbine, and generator. These components generate the energy that powers the car by converting heated air into electricity. Unlike a conventional engine, combustion does not take place directly inside the turbine itself. This allows for much greater control over combustion temperature and speed, enabling the use of different fuels without major modifications. Fuels such as biomethanol and biogas have very different flame characteristics and energy contents, yet both can be combusted effectively within the turbine’s combustion chamber.
In addition, a micro gas turbine is compatible with a Solid Oxide Fuel Cell (SOFC). Integrating an SOFC into the MGT system has the potential to elevate both efficiency and fuel flexibility to an entirely new level. We are currently conducting research into this promising long-term extension: a hybrid MGT–SOFC architecture.
We are implementing this technology in a city car, in order to deliver a proof of concept on a small scale. This is a major technical challenge with great potential for innovation. But the technology also has strong potential for sectors such as heavy-duty transport, maritime applications, and even aviation.
HOW IT WORKS
In this engine, air first enters at the compressor, where it is compressed. The compressed air then flows into the recuperator, where it is preheated using heat from the exhaust gases. Next, this warm air enters the combustion chamber, where fuel is injected and ignited. The resulting hot, high-energy gases expand through the turbine causing it to rotate at high speed. This rotational energy is converted into electrical energy by the generator connected to the turbine shaft. After the whole process, the exhaust gases flow back through the recuperator before being released to the atmosphere.
Compressor
Draws in fresh air and compresses it, increasing pressure to prepare the airflow for efficient heating and combustion.
Generator
Converts the rotational energy into electrical energy to to charge the batteries and power the car.
Turbine
Spins at around 180,000 rpm thanks to the hot, high-energy air. This rotational power drives both the compressor and generator via a shared shaft.
Recuperator
Recovers heat from the exhaust gases and transfers it to the incoming compressed air, significantly improving overall system efficiency.
Combustion Chamber
Heats the compressed air to high temperatures around 900 °C. by combusting sustainable fuels, providing the energy needed to drive the turbine.
CHALLENGES AND DEVELOPMENT
To increase compactness, the turbine, compressor and generator are all configured on the same shaft. This raises one of our most difficult challenges, which is to find a generator that can generate around 3 kW of electricity, can withstand the 900 degrees Celsius heat transfer of the turbine, and can rotate at 180,000 revolutions per minute.
Due to the compact size of the system, maintaining high efficiency is inherently difficult. Relative to the system volume, there is a large surface area exposed to ambient air, resulting in proportionally higher heat losses. To counteract this, we recover heat from the exhaust gases using a heat exchanger and feed it back into the inlet airflow. This reduces the amount of fuel required to reach and maintain high operating temperatures.
Last year, when working with an externally fired gas turbine, compressed air was used to start the system, which proved to be highly challenging. This year, we are taking a different approach. We plan to use the generator as an electric motor to spin up the system to approximately 70,000 rpm. From that point onward, the combustion chamber is sufficiently hot and the combustion process stable enough for the gas turbine to take over. Once this happens, the generator switches from motor mode to power generation mode. A key ongoing challenge remains the development of a generator that can handle these extreme rotational speeds while maintaining high efficiency and mechanical stability.
