## 1 Introduction
Based on previous research, the addition of hydrogen to diesel offers significant advantages in terms of enhancing performance and reducing emissions. However, the widespread adoption of hydrogen is limited by its expensive storage costs. A possible solution is on-board generating of hydrogen-rich gas from other compounds through the recovery of exhaust heat [13]. The most commonly employed methods for on-board hydrogen production include steam reforming, autothermal reforming, catalytic dissociation, and partial oxidation. A comparative study of three on-board approaches for generating hydrogen, namely steam reforming, autothermal reforming, and partial oxidation from diesel fuel, was conducted by [PERSON] and [PERSON] [14]. The results demonstrated that the adoption of all three methods could improve engine efficiency. Among the methods, steam reforming proved to be the most effective method, resulting in an 8% increase in global efficiency compared to the baseline. The enhancement achieved by autothermal reforming was slightly lower than that of steam reforming. In contrast, the global efficiency improvement from partial oxidation was significantly less compared to the other two methods. [PERSON] et al. [15] studied hydrogen production methods from ammonia dissociation catalytic decomposition and ammonia reforming by recovering the exhaust heat from a gasoline direct injection (GDI) engine. The results indicated that different methods yielded similar improvements in fuel economy and CO2 emissions. The sources of on-board hydrogen production can be diverse. Coal, natural gas, methane, methanol, ethanol, gasoline, ammonia, biomass, and some other fuels have been utilized for hydrogen production. Methanol is the most commonly used feedstock for hydrogen production due to its abundant resources and relatively high hydrogen production rate. Two practical approaches for generating hydrogen from methanol are steam reforming and catalytic dissociation; both approaches are endothermic reactions and require external energy input. Engine exhaust gas energy can be recovered and used as a heat source. In terms of hydrogen yield, steam reforming produces more hydrogen than catalytic dissociation for the same mass of methanol, but it requires more reaction energy and additional water. In our latest study [16], a methanol catalytic dissociation system was successfully implemented in a spark-ignition gasoline engine. The composition of syngas, which varies depending on the feedstock used for generating hydrogen, can have a significant impact on the performance and emissions of a diesel engine. In a study conducted by [PERSON] et al. [17], a diesel engine was fueled with three different syngas compositions under various loads. The results demonstrated that at higher loads, better performance was achieved with a decrease in the fraction of hydrogen (H\({}_{2}\)), while higher levels of carbon monoxide (CO) and hydrocarbon (HC) emissions were observed with an increase in the CO fraction. Similar findings were reported by [PERSON] [18], who found that increasing the H\({}_{2}\)/CO ratio in syngas led to reduced HC and CO emissions in an HCCI engine. [PERSON] and [PERSON] [19] conducted experimental and numerical studies on a diesel engine fueled with a mixture of diesel, nitrogen (N\({}_{2}\)), and syngas. The results revealed that the introduction of syngas + N\({}_{2}\) into the diesel fuel reduced nitrogen oxide (NOx), CO, and soot emissions under specific operating conditions, albeit increasing fuel consumption at all test points. Additionally, [PERSON] et al. [20] carried out a modeling study on the ignition characteristics of a hydrogen-methanol-diesel mixture. They reported that low and intermediate concentrations of hydrogen in the mixture had minor effects on the first and second stages of ignition delay times, while high concentrations of hydrogen significantly reduced the ignition delay.