Hydrogen Combustion using Port-fuel Injections in a Heavy-Duty Optical Diesel Engine Converted to Spark Ignition Operation

This study examines the use of hydrogen as a fuel for internal combustion engines to decrease greenhouse gas emissions. The focus is on hydrogen combustion at leaner mixture conditions, which has the potential to increase efficiency and reduce NOx emissions. While metal engine experiments have established these benefits, there are only a few optical studies on pure hydrogen combustion under lean operating conditions. This study reports optical measurements performed in a heavy-duty optical diesel engine converted to spark-ignition operation with port-fuel injections and varying spark timing, at air-excess ratios (lambda) of 2.5 and 3. The engine was equipped with a flat-shaped optical piston that allowed for bottom-view imaging of the combustion process. High-speed natural combustion luminosity images were recorded, along with in-cylinder pressure measurements. The results showed that advancing the spark timing shifted the combustion phasing towards TDC, thus increasing the peak combustion pressure for both tested lambda values. The peak combustion pressure decreased at the higher lambda operating point. The shortest combustion duration was associated with the minimum COV of IMEPg, indicating the optimal spark timing configuration for pure hydrogen combustion under lean conditions. The study also analyzed the high-speed natural combustion luminosity images to determine the flame front propagation speed, which increased rapidly during the early stage of combustion, reached a peak, and then decreased. The highest peak flame front propagation speed of 19.62 m/s was observed for a spark timing of -20°CA aTDC at a lambda value of 2.5.