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Metallic hydrogen (recombination energy) 216 [2] Specific orbital energy of Low Earth orbit (approximate) 33.0: Beryllium + Oxygen: ... Energy density by volume (MJ/L)
The higher the energy density of the fuel, the more energy may be stored or transported for the same amount of volume. The energy of a fuel per unit mass is called its specific energy. The adjacent figure shows the gravimetric and volumetric energy density of some fuels and storage technologies (modified from the Gasoline article).
Liquid hydrogen also has a much higher specific energy than gasoline, natural gas, or diesel. [12] The density of liquid hydrogen is only 70.85 kg/m 3 (at 20 K), a relative density of just 0.07. Although the specific energy is more than twice that of other fuels, this gives it a remarkably low volumetric energy density, many fold lower.
The liquefied hydrogen has lower energy density by volume than gasoline by approximately a factor of four, because of the low density of liquid hydrogen – there are actually more oxidizable hydrogen atoms in a litre of gasoline (116 grams) than there are in a litre of pure liquid hydrogen (71 grams).
Disadvantages of hydrogen as an energy carrier include high costs of storage and distribution due to hydrogen's explosivity, its large volume compared to other fuels, and its tendency to make pipes brittle. [146] If H 2 is to used as an energy source, its storage is important. It dissolves only poorly in solvents.
Although molecular hydrogen has very high energy density on a mass basis, partly because of its low molecular weight, as a gas at ambient conditions it has very low energy density by volume. If it is to be used as fuel stored on board a vehicle, pure hydrogen gas must be stored in an energy-dense form to provide sufficient driving range.
Energy density of fuels: horizontal per mass, vertical per volume. Kerosene is highlighted in red and hydrogen in blue. Hydrogen has a specific energy of 119.9 MJ/kg, compared to ~43.5 MJ/kg for usual liquid fuels, [3] 2.8 times higher.
The highest energy-density fuel (by weight) in common propellant combinations is hydrogen. However, gaseous hydrogen has very low (volume) density; liquified hydrogen has higher density but is complex and expensive to store. When combined with carbon, hydrogen can be rendered into the easily burnable hydrocarbon fuels.