We report the first application of a vertical-cavity surface-emitting laser (VCSEL) for calibration- and sampling-free, high-speed, in situ H₂O concentration measurements in IC engines using direct TDLAS (tunable diode laser absorption spectroscopy). Measurements were performed in a single-cylinder research engine operated under motored conditions with a time resolution down to 100 μs (i.e., 1.2 crank angle degrees at 2000 rpm). Signal-to-noise ratios (1σ) up to 29 were achieved, corresponding to a H₂O precision of 0.046 vol.% H₂O or 39 ppm·m. The modulation frequency dependence of the performance was investigated at different engine operating points in order to quantify the advantages of VCSEL against DFB lasers.

This paper describes the validation of a CFD code for mixture preparation in a direct injection hydrogen-fueled engine. The cylinder geometry is typical of passenger-car sized spark-ignited engines, with a centrally located injector. A single-hole and a 13-hole nozzle are used at about 100 bar and 25 bar injection pressure. Numerical results from the commercial code Fluent (v6.3.35) are compared to measurements in an optically accessible engine. Quantitative planar laser-induced fluorescence provides phase-locked images of the fuel mole-fraction, while single-cycle visualization of the early jet penetration is achieved by a high-speed schlieren technique. The characteristics of the computational grids are discussed, especially for the near-nozzle region, where the jets are under-expanded.Simulation of injection from the single-hole nozzle yields good agreement between numerical and optical results in terms of jet penetration and overall evolution. The 13-hole nozzle creates intense jet-to-jet interaction, with all jets merging into a single effective jet immediately downstream of the under-expanded region. This phenomenon (usually referred as Coanda Effect) is more challenging to the numerical simulation and requires higher level of detail in numerical simulation and grid resolution, with particular regard to the fields near the injector nozzle.

Mixture formation in an optically accessible hydrogen-fueled engine was investigated using Planar Laser-Induced Fluorescence (PLIF) of acetone as a fuel tracer. The engine was motored and fueled by direct high-pressure injection. This paper presents the evolution of the spatial distribution of the ensemble-mean equivalence ratio for six different combinations of nozzle design and injector geometry, each for three different injection timings after intake-valve closure. Asymmetric single-hole and 5-hole nozzles as well as symmetric 6-hole and 13-hole nozzles were used. For early injection, the low in-cylinder pressure and density allow the jet to preserve its momentum long enough to undergo extensive jet-wall and (for multi-hole nozzles) jet-jet interaction, but the final mixture is fairly homogeneous. Intermediately timed injection yields inhomogeneous mixtures with surprisingly similar features observed for all multi-hole injectors. Fuel is concentrated near the cylinder wall, an unfavorable scenario were the engine to be fired. Results for late injection depend more on the particular injector configuration. The 13-hole injector shows complete merging of all jets, consistent with results in the literature. The influence of intake-induced bulk-gas tumble is minor for the current injector and combustion-chamber configurations.