Investigations into the storage and use of hydrogen as an automotive fuel

This thesis describes an investigation into the use of hydrogen as a fuel for automotive use. Due to problems of backflash into the engine intake when hydrogen is used as the sole fuel, a dual-fuel system using petrol and hydrogen together was studied. Using this system, a spark-ignited engine has been run at all speeds with a wideopen throttle, and the specific fuel consumption and BTE figures indicate a greater part load efficiency than those from a throttled engine. The performance and emissions curves of the engine are presented, both at the standard compression ratio of 8.9:1 and at a higher compression ratio of 11.7:1. Emissions data indicate reduced levels of CO, and NOx at part load due to the very lean mixtures used. No problem of backfiring was experienced since the concentration of hydrogen was very low. A vehicle was modified to run on such a dual-fuel system, and details of this modification are also presented. A major problem with using hydrogen as an automotive fuel is its on-board storage. This is discussed in some detail, with particular reference to the use of metal hydrides as storage media. Metal hydride tanks are now commercially available, and a detailed mathematical model of such a tank has been developed to describe its behaviour under both hydriding and dehydriding conditions. In contrast to other hydride models previously reported in the literature, this model simulates an actual, commercially available containment vessel, rather than that of an abstract ideal situation. Thus the model provides a convenient means of predicting the time taken to release or absorb given amounts of hydrogen. These are calculated from the heat transfer characteristics and diffusion properties of particular metal alloys. Comparisons are given between the actual operating characteristics and those simulated by the model. A brief discussion of the reaction kinetics of hydriding certain metal alloys is also included.