Emission testing is a key importance in aircraft development in the modern age. Since this is the time for low and zero emission flight, confirming how low the emissions can be, is practically a necessity. With the internal combustion engine test stand at Ulm University, performance tests have been started in order to compare emissions, efficiency, and power concerning various fuel types. The results obtained during flight tests, as shown, are a base measurement for comparison of non-hybrid small aircraft. There are a couple key points to take away from the initial emission measurements.
Especially noticeable in the graph is that NOx emissions and CO emissions have an inverse relationship because of combustion properties at different engine temperatures, combustion air temperature, and air/fuel ratio. The CO2 concentration is similar at different Manifold Air Pressures (MAP) and altitudes. These initial results of a non-hybrid aircraft give insight into what should be improved for a hybrid battery-ICE aircraft, like using bioethanol based fuels for carbon neutrality, and finding ideal operating point to balance the NOx and CO emissions.
General aviation fuel is currently low leaded, and as the tests move towards zero lead, low biofuel content, and high biofuel content fuel, we will be able to see the comparable power of the engine at different RPMs. Throughout measurements, the goal is to see that the low biofuel content fuel can run the engine at a similar or increased power and efficiency; this would allow for biofuel based aviation fuels to replace general aviation gasoline. As automotive fuels have adapted to contain bioethanol, similarly, this could occur for aviation fuels, leading the regional and small aircraft industry to sustainability and suitability for the modern world and technologies.
