Injection Process of the Synthetic Fuel Oxymethylene Ether: Optical Analysis in a Heavy-Duty Engine
Oxygenated synthetic fuels such as oxymethylene ether (OME) are a promising approach to reduce the emissions of diesel engines and to improve sustainability of mobility. The soot-free combustion of OME allows an optimization of the combustion process to minimize remaining pollutants. Considering the injection system, one strategy is to decrease the rail pressure, which has a positive impact on the reduction of nitrogen oxides without increasing the particle formation. Furthermore, due to the reduced lower heating value of OME compared to diesel fuel, an adaptation of the injector nozzle is recommended. This work describes a method for analyzing the injection process for OME, using the Mie scattering effect in an optically accessible heavy-duty diesel engine. The design of the 1.75 l single cylinder engine allows operation up to 300 bar peak cylinder pressure, providing optical access through the piston bowl and through a second window lateral below the cylinder head. An algorithm processes the data of the high-speed camera by cleaning the Mie signal and determining the progress of the liquid penetration length (LPL) for each injection jet. Based on this method various injectors with different flow rates and nozzle geometries were examined. The results show, that the LPL primarily depends on the in-cylinder pressure, which can be described by an injector-specific quadratic polynomial function. The rail pressure influences the opening and closing behavior of the injector, while the LPL remains unaffected. The findings are usable for optimizing the injection system or other components, e.g. the piston geometry for the operation with OME.