Road to Hydrogen

There is an inevitable trend towards hydrogen replacing the fossil fuels. However, there is a huge gap in between. An obvious step is the use of liquified methane or LNG before moving on to hydrogen.

Approximate energy density of liquid methane is 55 MJ/kg and the density of the liquid is 657g/L. Approximate energy density of jet fuel is 43 MJ/kg and the density of the liquid is 840 g/L. For the same volume, both fuels have similar energy capacity. The main disadvantage of liquid methane is the weight of the tank. For small volumes the weight of the tank compared to the total weight exceeds 70 percent. Even for a 50-ton tank, more than 30 percent of the total weight belongs to the cryogenic tank.

The road to hydrogen requires economical low weight cryogenic tanks for sure. Even with technological advancements the weight cannot be reduced dramatically. This brings design restrictions on liquid methane powered vehicles. Either, fuel storage tanks should be enlarged for the same range to compensate for the additional weight or smaller range should be accepted. Another problem with the storage is cryogenic tanks cannot be formed in any shape. The wings of a plane can store jet fuel. However, liquid methane could only be stored inside the fuselage of a plane. This design restriction allows lighter hollow wings, but longer fuselage to accommodate the liquid methane tank.

On the other hand, the thick steel hull of a ship can be modified to store liquid methane with less weight penalty. The trucks would have special chassis where part of it doubles as a storage tank to reduce the effect of heavy tanks. Double purposing would be a solution in many of the vehicle designs to overcome the weight penalty.

The handling of liquid methane also requires heavier and more expensive hardware on the servicing stations and on the vehicle itself. As the use of liquid methane or LNG expends the prices would go down and parts may get lighter. On my next article, I would like to propose a commercial plane utilizing liquid methane or LNG as fuel.