Experimental study on ultra-lean hydrogen combustion using a dedicated cold spark plug ignition system

This study presents an experimental assessment of a prototype cold-spark ignition system developed for hydrogen-fueled spark-ignition engines. Experiments were conducted on a single-cylinder research engine. First, ignition performance of the H 2 cold-spark system was compared with a conventional J-gap spark plug at λ = 1.7 by varying spark advance, engine speed, and throttle valve opening. Then, lean-burn operation and ignition limits were investigated by varying excess air ratio and spark timing at fixed operating conditions. Finally, combustion stability and NOx emissions were evaluated under ultra-lean conditions exploring different engine speeds and loads. Results demonstrate stable combustion up to λ = 2.9, with cycle-to-cycle variability at maximum brake torque consistently below 3% and IMEP exceeding 2 bar. NOx emissions decreased sharply with increasing λ, approaching near-zero levels for λ between 2.6 and 2.9. Enhanced flame kernel development with the cold-spark system led to improved combustion stability under ultra-lean conditions.