## 1 Introduction
Additionally, hydrogen's capability to produce power without emitting carbon compounds positions it as a superior alternative in the quest for cleaner automotive technologies; however, it depends on the type of hydrogen production, as so-called black, brown, grey, and blue hydrogen is indicated [24]. When used in spark ignition engines, hydrogen combustion produces no carbon monoxide (CO), CO2, hydrocarbons (HC), or particulate matter (PM) emissions, making it an exceptionally clean fuel choice [25; 26]. Hydrogen's high burning velocity and broad flammability range, in contrast to traditional fossil fuels, elevate the risk of flashbacks, pre-ignition, and accidental explosions [27; 28; 29]. Moreover, the combustion of pure hydrogen produces a high combustion temperature, leading to the formation of nitrogen oxides [30; 31; 32]. Using hydrogen as fuel at excess air ratios higher than 1.3 reduces NO\({}_{\rm x}\) emissions by up to six times compared to emissions at a stoichiometric mixture. Lean air-hydrogen mixtures combust at lower temperatures, which are not enough to support NO\({}_{\rm x}\) formation [33; 34]. Adjusting spark timing can also help reduce NO\({}_{\rm x}\) emissions. At an excess air ratio of 1.4, retarding the spark timing by just 4 CAD (crank angle degrees) results in a 17% reduction in NO\({}_{\rm x}\) emissions. For instance, at an excess air ratio of 1.6, retarding the spark timing leads to a 70% reduction in NO\({}_{\rm x}\) emissions [35]. Selecting the specific mixture formation method like'spark-plug mildly stratified charge', NOx emissions are limited to less than 10 ppm [36]. Due to its low energy density under standard temperature and pressure, hydrogen requires specialized storage solutions. For instance, a fuel cell vehicle requires approximately 5-6 kg of hydrogen, compressed to 700 bar, to achieve a driving range of 500 km [37]. Combusting hydrogen in an internal combustion engine (ICE) requires an even greater amount of hydrogen to be stored on board the vehicle. According to modelling results from Chalmers University of Technology, hydrogen fuel cell vehicles demonstrate nearly twice the efficiency of ICEs, with a lower fuel consumption of 1.05 kg-H\({}_{2}\) per 100 km under the Worldwide Harmonised Light Vehicles Test Procedure driving cycle (WLTC), compared to approximately 1.79 kg-H\({}_{2}\) per 100 km for hydrogen combustion vehicles [38]. Replacing petrol with hydrogen to achieve a driving range of at least 500 km presents significant challenges, primarily due to the increased amount of hydrogen that needs to be stored in the vehicle. Also, hydrogen is highly flammable, and special composite H\({}_{2}\) fuel tanks must be used for hydrogen storage. For fuelling systems, stainless steel lines are required, along with a special pressure reducer equipped with a flame arrestor. A hydrogen leak detection system should also be installed, incorporating hydrogen sensors that provide warnings and can automatically shut off the tank's main stop valves in the event of a leak. In case of a fire, a pressure relief system should vent hydrogen away from the vehicle and passengers to minimize the risk of explosions. Additionally, automatic shut-off valves should be installed to automatically close solenoid valves on the hydrogen tanks during a crash, isolating the fuel supply. Even with the installation of safety systems, dual-fuel technology remains a potential alternative for reducing greenhouse gas emissions and fossil fuel consumption. One potential solution to the storage challenge is implementing a dual-fuel system. In this approach, hydrogen can be used as an additive or substitute for a small portion (up to 15% by mass) of conventional fuel [39]. This strategy reduces the required hydrogen storage, lowering the overall vehicle mass while simultaneously contributing to a reduction in tailpipe emissions [40]. Hydrogen enables the increase of air excess ratios up to two, without substantially prolonging the combustion duration and reducing NO\({}_{\rm x}\) emissions.