Hydrogen concentration measurements using spark induced breakdown spectroscopy in a real engine

This study develops spark induced breakdown spectroscopy (SIBS) for measurements of direct injected hydrogen concentration in a multi-cylinder engine operated at real conditions. To this end, calibration is performed in the air excess ratio (λ) range of 2.1 ∼ 2.9 and simultaneously, high-speed schlieren imaging of laminar hydrogen flame propagation is performed in an optical high-pressure constant volume combustion chamber (CVCC). To achieve real engine applications, the SIBS is further developed using a modified conventional spark plug for sapphire window insertion onto the positive electrode and guided arc formation via a newly designed nipple type ground electrode. Specifically, the peak spectra intensity ratio of H_α (656 nm) to O (777 nm) is used for calibration, which shows a linear correlation with λ. For the first time, the calibrated SIBS is applied to a real engine operated at 46.2 ∼ 63.9 Nm load and 2000 rpm with 3.5 MPa hydrogen direct injection. The results show lower local λ than the global λ despite early injection timing of 165 crank angles before top dead centre, indicating a significant influence of in-cylinder flow motion on the spatial distribution of hydrogen-air mixtures.