Experimental and Simulation-assisted Investigations of PFI and DI Combustion Concepts for Hydrogen-fueled Large Bore Engines

The use of hydrogen as a fuel in large bore engines for power generation or combined heat and power applications is a promising way to reduce greenhouse gas emissions. With water vapor being the major combustion product, the combustion of hydrogen yields no carbon dioxide, sulfur oxides and particulate matter emissions and only traces of hydrocarbons from lubricant entering the combustion chamber can be detected in the exhaust gas. The formation of nitrogen oxides (NOx) can be suppressed by operating the engine at relatively high excess air ratios. The advantages of low emission levels can come at the expense of straightforward engine operation as some physical and chemical properties of hydrogen, for instance the low minimum ignition energy and wide flammability range, pose challenges regarding abnormal combustion phenomena, such as knock and pre-ignitions.
In the present study, results of simulation-based and experimental investigations of a hy-drogen-fueled single cylinder research engine equipped with external and internal mixture formation are presented and compared with regard to differences in NOx emissions and engine operation. Simulation results show that for internal mixture formation mixture homo-geneity is lower compared to external mixture formation, which might lead to higher NOx emissions and higher risk of abnormal combustion. The experimental investigations indi-rectly confirm the simulation results, as for internal mixture formation NOx emissions are higher and the engine operating range is smaller compared to external mixture formation. Strategies to lower NOx emissions in internal mixture formation operation are presented and assessed based on efficiency penalties.