Extinguishment and reignition are important in the development of electrically controlled solid propellants (ECSPs) with on-demand control. An experimental study was carried out to explore the ignition, quenching, reignition, and combustion characteristics of an ECSP based on a co-oxidizer of sodium nitrate and ammonium perchlorate. In total five propellants were studied with varying ratios of sodium nitrate and ammonium perchlorate using polyethylene oxide as the binder. All formulations were solution cast, however, thermogravimetric analysis revealed no detectable residual solvent present in the final compositions, which may be an important factor for improving long term storage and alleviating variations in performance. Ignition delay was characterized over a range of voltages (80 – 200 V), with a blended oxidizer (25/75 sodium nitrate/ammonium perchlorate) formulation demonstrating the fastest ignition. High frequency reignition resulted in faster ignition delays, while very low frequency reignition resulted in longer ignition delays in comparison to the initial ignition delay. The low frequency reignition behavior was likely associated with the formation of inhibiting compounds. Propellant formulations with majority concentrations of sodium nitrate demonstrated pressure deflagration limits greater than a measurable limit of 13.8 MPa. Burning rates were measured as a function of pressure and applied voltage, and a modified Saint-Robert’s burning law was created coupling the combined effects of pressure and voltage over the experimental range. Burning rates increased with increasing ammonium perchlorate concentration.
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.
