High-speed visualization helps evaluate e-fuels under engine conditions
24 February 2021

Within the framework of ENERXICO, researchers at Universitat Politècnica de València are currently evaluating the performance of ‘e-fuels’ in transportation engines for applications where high-power density is mandatory. Such fuels can be synthesized starting from renewable hydrogen and CO2, which results in a low carbon print. Fuels under investigation are binary blends of Hydrotreated vegetable oil (HVO), which is representative of sustainable biofuels for compression-ignition engines, and two different e-fuels, namely Polyoxymethylene dimethyl ethers (OMEx), as well as Dimethothymethane (DMM). 

Current activity deals with tests under realistic engine conditions. For that purpose, a single-cylinder engine with optical accesses is used, where combustion can be isolated from other complicated engine processes. An overview of the test cell is shown in Figure 1. The experimental environment is very similar to that of a real engine, with a multi-hole injector, cylinder head and chamber dimensions. Operating variables (engine speed, fuel delivery, in-cylinder pressure and temperature) are also representative of those found in medium and heavy-duty vehicles. The availability of optical accesses allows for the recording of high-speed images that make a detailed description of the combustion process possible, from which the influence of the use of these fuels can be discussed in detail. 

Experimental information derived from in-cylinder pressure is complemented by images recorded at a rate of 25000 images per second to resolve each individual engine injection cycle. The radiation of the flame has been recorded both in the visible and ultraviolet wavelength ranges, from which information on combustion characteristics and potential particulate formation in the chamber is analysed.

Results show that replacing HVO with OMEx/DMM in higher proportions results in combustion characteristics similar to those of neat HVO fuel. Broadband natural luminosity, however, is reduced, which hints at reduced particulate formation in the combustion chamber (see Figure 2). This confirm that the selected e-fuels have a large potential for particulate reduction in those applications. Predicting the behaviour of such flames by means of computational tools will be a challenging target for the HPC models under development within ENERXICO.

Figure 1. Experimental test cell used in the study. At the top left part of the image, the optical engine is shown. At the bottom right part of the image the two high-speed cameras are observed.

Figure 2. Comparison of luminosity images for different fuel blends. Left to right correspond to 100% HVO, 30% DMM and 40% DMM. A decrease in luminosity can be observed when moving towards higher DMM fractions.