Analysis of Dual Fuel Hydrogen/Diesel Combustion in Ultra Lean Conditions via Simultaneous UV and IR Imaging

Thanks to its reliability and high-performance characteristics combined with high technological innovation, the combustion engines powered by alternative fuels, such as hydrogen, can still represent a useful solution for achieving mobility with net zero emissions. The use of hydrogen in a dual-fuel engine with hydrogen and diesel (or HVO and other compatible renewable fuels) can reduce greenhouse gas emissions as well as particulate matter emissions while ensuring excellent performance. In this scenario, tests have been carried out on a dual-fuel single cylinder research engine to analyse the combustion evolution of hydrogen in ultra-lean conditions via optical diagnostics. At ultra-lean condition (=3.8), the hydrogen does not ignite by itself at desired crank angle; thus, diesel has been used to ignite the hydrogen premixed charge. An operating point at 1500rpm engine speed and at fixed engine load has been investigated. The in-cylinder pressure and the related data have been analysed as indicators of the combustion quality. 2D-digital imaging cycle resolved in both ultraviolet and infrared wavelength range have been performed and the flame propagation is evaluated. In particular, UV and IR cameras simultaneously acquired images of the hydrogen combustion and furnished information on the flame propagation via the detection of OH and low and high temperature reaction zones within the bowl, respectively. Results show that to control efficiently the hydrogen combustion it is necessary to phase properly the injection of diesel.