Although liquid hydrogen has a high storage requirement, it must be guaranteed to remain liquid at -250°C, otherwise it will vaporize and evaporate, but the energy density of liquid hydrogen is higher than that of high pressure gaseous hydrogen (which is compressed to 700 bar). 75%, so the use of liquid hydrogen vehicles can achieve a relatively long driving range, with all the practical benefits.
The core technical difficulty with liquid hydrogen is how to keep it at a very low temperature. One of Hydrogen 7's core technologies is its liquid hydrogen fuel tank. This fuel tank is located between the rear seat and the tailgate and has a double-walled structure consisting of a stainless steel plate of 2 mm thick and a 30 mm vacuum super insulation between the inner tank and the outer tank. This structure greatly reduces the heat transfer, and the middle layer can provide a heat insulation effect equivalent to about 17 meters thick styropor (a type of polystyrene). In addition, the connection between the inner tank and the outer tank uses a carbon fiber sandwich, which greatly avoids heat transfer. BMW said that the effect of this thermal insulation technology is unprecedented in practical applications. For a simple example, adding boiled coffee to this kind of fuel tank can keep it warm for more than 80 days before it is reduced to a suitable amount for drinking. temperature. Such efficient insulation can keep the liquid hydrogen under a pressure of 3-5 bar for a long time at a constant temperature of about -250°C. Even a trace amount of evaporated hydrogen will be discharged through an evaporation management system with reasonable pressure and purification.
Because the temperature in the fuel tank is so low, the gaseous hydrogen vaporized from the fuel tank must be preheated with the heat provided for this purpose from the engine cooling system piping before entering the fuel mixing process.
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