Review of the hybrid gas - electric aircraft propulsion systems versus alternative systems

The continuously increasing interest in alternative aircraft propulsion systems is caused by the requirements and demands set by international institutions and government organizations. For instance, nowadays in the European Union, the objective called the European Green Deal seems most demanding. According to this regulation, the members of the European Union should ensure the net zero emission of greenhouse gases by the year 2050. This is why many efforts are devoted to finding ecological solutions for the aviation sector which almost completely relies on fossil fuels at the moment. One of the solutions, which has already proved beneficial for the automotive industry, is the hybrid gas-electric propulsion. Combining the advantages of the electric motors and batteries with the Internal Combustion Engines (ICE) creates an opportunity to reduce fuel consumption, thereby decreasing the greenhouse gas emission. However, challenges such as the immature batteries technology, complicated power management system or the cooling system for high power propulsion systems, among others, need to be dealt with. These all offer great potential for scientific studies, thus the associated literature is accumulating very quickly. The aim of this paper is to update the status and review the state of the art concerning aircraft with hybrid gas-electric propulsion systems. However, the other alternative propulsion systems are also described to indicate and emphasize drawbacks and benefits coming from the hybrid gas-electric propulsion.