Experimental database with renewable fuels
Within the framework of ENERXICO, advanced modelling tools for high-fidelity combustion simulations have been developed to study the use of renewable fuels in future sustainable transportation systems. This includes both biofuels and power-to-liquid fuels, the so-called ‘e-fuels’, for which combustion characteristics need to be further understood before they can be applied in combustion systems with optimal efficiency and with minimum pollutant emissions.
The reliable use of these computational models demand for extensive validation from highly controlled experiments, such as the ones performed within ENERXICO. These experiments replicate the operating conditions that such advanced fuels will find in the combustion chamber of an engine in an optically accessible vessel. This means filling up a test volume with air of controlled composition at high pressure (up to 150 bar) and temperature (up to 730ºC), and injecting the fuel through a single-hole injector at realistic injection pressure (1500 bar). Compared to a real engine, where multi-hole injectors are used, and wall interaction as well as piston movement can occur, this is a much more simplified environment. However, conditions of the experiments are highly controlled, and highly advanced optical diagnostic tools can be used to quantify parameters that cannot be obtained from a normal operation of the engine.
Figure 1. Overall view of the experimental facility used to measure characterize renewable fuel combustion. The cylinder in the center is the spray vessel, with different optical accesses and cameras around that make possible to quantify the flame relevant parameters.
In terms of optical diagnostics, advanced tools for combustion analysis have been used. Those include high speed cameras recoding 25000 images per second to resolve all the information occurring within an injection process, which lasts just 4 milliseconds. The radiation of the flame has been recorded both in the visible and ultraviolet wavelength ranges, from which information on when ignition occurs and what the flame length is has been acquired. Adequate imaging devices allow to determine the time-resolved spread of the fuel in the combustion chamber, as well as the amount of soot particulates formed within the flame. Finally, high-power laser light sources are used to quantify information on the presence of relevant combustion species within the flame.
Some of these data are available at CMT website.
Figure 2. Comparison of schlieren visualization recordings of fuel under investigation in the Enerxico project. Images correspond to experiments under the same operating conditions and timing after start of injection with the fuel denoted in the corresponding figure caption.