eSpray: Einspritzung, Mischung und Selbstzündung von E-Kraftstoffen für CI-Motoren

Abstract

Liquid hydrocarbons produced from renewable energy, so-called e-fuels, in combination with compres-sion-ignition internal combustion engines will make a significant contribution to future carbon-neutral mobility. To achieve the best efficiency while minimizing the emissions, we need to understand these fuels’ physico-chemical behaviour. This project investigates the injection, mixture formation, and ignition of OME3-5 and 1-octanol in comparison with the diesel-like n-dodecane. The international research network consists of five institutes that contribute to the project with different methods and resources. The Professorship for Fluid Systems Technology at Friedrich-Alexander-Uni-versität Erlangen-Nürnberg (FAU) investigates the fuel sprays under diesel engine-like conditions with-out charge motion in the inert and reactive case. The Combustion Research Facility at Sandia National Laboratories (SANDIA) is also concerned with injection into quiescent atmosphere, but in a different facility and with different optical techniques, which together reduces experimental uncertainties. More practical investigations are carried out in the optical diesel engine of the Institute for Energy and Mate-rials Processes (formerly Combustion and Gas Dynamics) at the University of Duisburg-Essen (UDE). Here, the fuel spray and its ignition and combustion are characterized in multispectral images. Both FAU and UDE explore the relatively novel technique of mid-infrared imaging. The experimental results serve as input for CFD simulations at the Institute of Powertrains and Automotive Technology at Vienna Uni-versity of Technology (TUW). Models are developed for stand-alone injection as well as for the engine cylinder. To model the ignition and combustion of OME3-5, a reaction mechanism developed by the Department of Mechanical Engineering at Shanghai Jiao Tong University (SJTU) is implemented. The experimentally validated simulations provide additional information that is not accessible with experi-ments, which ultimately allows deeper insight into the physico-chemical behaviour of e-fuels. The results show that OME3-5 burns soot-free, regardless of the operating conditions. Not even soot precursors are formed with OME3-5. The reason for this is that this fuel has no C-C double bonds. Com-pared to the diesel-like dodecane, OME3-5 has a longer liquid penetration depth and a longer flame lift-off length. For use in existing diesel engines, this means that pistons with an adapted bowl geometry must be used to reduce potentially excessive wall-heat loads. OME3-5 has a shorter ignition delay than dodecane and the burnout phase (for the same fuel mass) is also shorter. Consequently, in an existing engine, the start of injection must be adjusted. Use of either OME3-5 or 1-octanol affects the injector hydraulics. In particular, multi-injections show a significant deviation in the opening and closing behav-iour for OME3-5 and 1-octanol compared with dodecane. The project’s results provide physical insight into engine combustion processes and can be understood as a design guide for future CI engines to exploit the full potential of the e-fuels investigated here. With e-fuels, not only carbon-neutral but also low-emission powertrains can be realized. Due to the soot-free combustion of OME3-5, high EGR rates are possible, which significantly reduces NOx emissions.