Hydrogen Mole Fraction Distributions Inferred from Inverse-LIF Measurements on High-pressure Hydrogen Injections

The mixing of fuel and ambient in a compression-igniting combustion engine is a critical process, affecting ignition delay, burn duration, and cycle efficiency. This study aims to visualize and quantify hydrogen mole fraction distributions resulting from high-pressure (10 MPa) hydrogen injections into an inert, pressurized (1 MPa) nitrogen ambient at room temperature. Using inverse planar laser-induced fluorescence, in which the ambient rather than the jet is seeded with a fluorescent tracer, two different injectors (nozzle hole sizes of 0.55 and 0.65 mm) and two different tracers (toluene and acetone) are compared. It is concluded that a non-intensified CCD camera for fluorescence detection is superior to the use of an intensified one, due to the linear behavior on contrast. The two injectors produce similar jets in terms of jet penetration and angle. Jet penetration derived from inverse-LIF measurements agree with Schlieren data on nominally the same jets, but the hydrogen mole fractions are generally 2.5-5 percent lower than those obtained by planar Rayleigh scattering. Quasi-steadiness and self-similarity were found for ensemble-averaged mole fraction distributions of both injectors, which aligns with theory and highlights the importance of using RANS simulations or time-averaged experiments for future comparisons.