Hydrogen Supplementation in SI Engines: Enhancing Efficiency and Reducing Emissions with a Focus on Knock Phenomena

This study investigates the impact of hydrogen supplementation on the performance, efficiency, and emissions of a spark-ignition internal combustion engine, with a specific focus on knock phenomena. A Nissan HR16DE engine was modified to operate in a dual-fuel mode using gasoline (E95) and high-purity hydrogen. Hydrogen was injected via secondary manifold injectors and managed through a reprogrammable MoTeC ECU, allowing precise control of ignition timing and fuel delivery. Experiments were conducted across various engine speeds and loads, with hydrogen mass fractions ranging from 0% to 30%. Results showed that increasing hydrogen content enhanced combustion intensity, thermal efficiency, and stability. Brake specific fuel consumption decreased by up to 43.4%, while brake thermal efficiency improved by 2–3%. CO, HC, and CO2 emissions were significantly reduced. However, NOx emissions increased with higher hydrogen concentrations due to elevated combustion temperatures. Knock tendency was effectively mitigated by retarding ignition timing, ensuring peak in-cylinder pressure occurred at 14–15° CAD aTDC. These findings demonstrate the potential of hydrogen supplementation to reduce fossil fuel use and greenhouse gas emissions in spark ignition engines, while highlighting the importance of precise combustion control to address challenges such as knock and NOx formation.