Corrective knock control and performance of a retrofitted 2.9 L heavy-duty spark-ignition engine operating in gasoline–hydrogen bi-fuel mode

The direct utilization of renewable hydrogen has emerged as a promising pathway toward decarbonizing hard‑to‑electrify sectors. A particularly relevant application is mobile machinery powered by heavy‑duty internal combustion engines. Although hydrogen combustion offers clear advantages, it also presents several challenges, including a pronounced susceptibility to abnormal combustion phenomena that necessitate careful control. In the present work, a commercial Deutz G 2.9 L4 four‑cylinder spark‑ignited engine originally designed to operate on gasoline was retrofitted for bi‑fuel (gasoline/hydrogen) operation. Two novel strategies for abnormal combustion control were developed and successfully implemented. The first strategy involves regulating the hydrogen injection pulse (hydrogen trim) and imposing an appropriate hold time during which hydrogen supply is reduced. The second strategy consists of injecting very small amounts of gasoline through the original fuel injectors simultaneously with the hydrogen supply. The procedures developed to implement these measures are described and are primarily based on the analysis of the signal provided by the knock sensor originally installed on the engine block. Both strategies proved highly effective, as they enabled precise intervention on the cylinder identified as experiencing abnormal combustion and, more importantly, on the cycle immediately following the detonating event. This approach effectively suppressed the propagation of pressure waves that might otherwise amplify and ultimately result in engine damage. While a strategy based on gasoline injection can be justified for retrofitted engines that retain the original gasoline injectors, the control of hydrogen injection is more straightforward in dedicated hydrogen-fueled internal combustion engines.