It is reported by the authors that the combustion of super rich hydrogen mixture plume that is ignited in the middle or just after the injection can reduce NOx formation drastically without offering any trade-offs on thermal efficiency in high output power operation in high pressure direct injection hydrogen engines. In this study it was found that the location of the injected hydrogen jet in the combustion chamber and distance of ignition point from chamber wall were strongly sensitive to improving thermal efficiency. Fuel jet injected closely parallel with chamber wall in the vicinity of the wall damages air entrained to the jet, and resulted in increased unburned hydrogen in addition to increasing cooling loss to the chamber wall, both of which decreases thermal efficiency of the hydrogen engine. Ignition close to chamber wall also increased the cooling loss. Visualization of jet configuration and propagating flame in the combustion chamber based on laser shadowgraphy was effectively utilized to understand the phenomena mentioned above in the study. © 2013 The Japan Society of Mechanical Engineers.