This work is a numerical study of the use of ammonia and hydrogen in a high-pressure-dual-fuel (HPDF) combustion. The main fuels (hydrogen and ammonia) are direct injected and ignited by a small amount of direct injected pilot fuel. The fuels are injected using a dual fuel injector from Woodward L’Orange, which can induce two fuels independently at high pressures up to 1800 bar for the pilot fuel and maximum 500 bar for the main. The numerical CFD-model gets validated for of hydrogen-HPDF with experimental data. Due to safety issues at the test rig it was not possible to use ammonia in the experiments, so it is modelled using the numerical model. It is assumed that the CFD-model also gives qualitative correct results for the use of ammonia as main fuel, so a parameter study of ammonia-HPDF is made. The results for the hydrogen-HPDF show, that hydrogen can be used in the engine without any further modifications. The combustion is very stable, and the hydrogen ignites almost immediately when it enters the combustion chamber. The results of the ammonia combustion indicate, that the HPDF combustion mode can handle ammonia effectively. It seems beneficial to inject the ammonia at higher pressures than hydrogen. Also pre-heating the ammonia can increase the combustion efficiency.

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Further improvement of hydrogen combustion in port fuel injection engines is limited by backfire. To overcome this drawback of hydrogen port fuel injection engines it is essential to locate and understand the reasons for the inflammation of a backfiring cycle. To contribute to this understanding a minimal invasive lateral optical access was developed for a medium speed large bore engine. The access uses a UV enhanced endoscope to investigate the OH radical’s natural chemiluminescence to locate the inflammation of a backfiring cycle in the combustion chamber. The investigations are carried out at high engine load. The optical investigations were based on a thermodynamic screening. This included the variation of the start of the hydrogen port fuel injection and the engine’s backpressure. These experiments prove the influence of exhaust backpressure and the start of injection on the probability of backfire. As higher backpressure leads to an increased probability of backfire, the SoI strategy has also a decisive influence. An optimum start of injection timing with less backfire under high backpressure was experimentally determined at 300°CA with respect to 720°CA as FTDC. The conducted optical investigations show that backfire starts by ignition by hot residual gasses during the first cycle located under the exhaust valves. Furthermore, the results show ongoing combustion in the intake manifold leading to serious damage of the engine if not prohibited.

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