Highly Efficient and Clean Combustion Engine for Synthetic Fuels

This paper provides an overview of possible engine design optimizations by utilizing highly knock-resistant potential greenhouse gas (GHG) neutral synthetic fuels. Historically the internal combustion engine was tailored to and highly optimized for fossil fuels. For future engine generations one of the main objectives is to achieve GHG neutrality. This means that either carbon-free fuels such as hydrogen or potential greenhouse gas neutral fuels are utilized. The properties of hydrogen make its use challenging for mobile application as it is very diffusive, not liquid under standard temperature/pressure and has a low volumetric energy density. C1-based oxygenated fuels such as methanol (MeOH), dimethyl carbonate (DMC) and methyl formate (MeFo) have properties like conventional gasoline but offer various advantages. Firstly, these fuels can be produced with renewable energy and carbon capture technologies to be GHG neutral. Secondly, the C1-based fuels burn with significantly less pollutant emissions. A third advantage is the high knock resistance of those fuels. This inherits a drastic efficiency potential for spark ignition engines as the compression ratio and therefore the potential thermal efficiency can be directly increased. In the single cylinder engine, a compression ratio (CR) of ~20:1 is investigated proving the high knock resistance as well as the efficiency potential of MeOH and a mixture containing 65 vol% DMC and 35 vol% MeFo (C65F35). Special attention is paid to the direct injection strategy, which utilizes up to quadruple injections and 35MPa fuel pressure. Later on, a more moderate CR increase to 15:1 with a CFD optimized piston design is investigated at a state of the art four-cylinder engine (4CE) utilizing C65F35. The whole engine map is presented proving the real-world usability and efficiency potential of this fuel type in combination with the optimized piston. WLTC and RDE tests were performed, underling both the practicality and the efficiency potential in dynamic conditions. The 4CE tests are rounded off by showcasing the potential of lean operation with two different high-energy ignition systems (Corona and passive pre-chamber ignition). The performance investigation on both engines is accompanied by emission measurements utilizing standard exhaust analyzers, an FTIR-device and particle number counting systems.