Liquefied Natural Gas (LNG)

LNG is natural gas chilled to about 260 degrees below zero Fahrenheit, which turns it liquid and shrinks it enough that a tank holds far more energy than the same tank of compressed gas. It is kept in double-walled, vacuum-insulated pressure vessels rather than the high-pressure cylinders CNG uses.

That density is the whole reason to consider it, and the reason it suits so few public fleets. More energy by volume means longer range, so LNG is used in medium and heavy-duty vehicles that cover distance. CNG covers light, medium and heavy duty and is stored at up to 3,600 psi in ordinary cylinders, which is simpler in every respect that matters to a municipal yard.

The operational catch is that the fuel is only liquid because it is cold. A vehicle that sits for long stretches lets its tank warm and vent, so an asset used intermittently is the wrong candidate. Most government duty cycles return to a yard every night and cover moderate distance, which is exactly the profile CNG serves and exactly the profile that wastes LNG’s advantage.

Where it does appear in the public sector it is usually long-haul transit or regional heavy-duty work, and the decision is dominated by the fueling facility rather than the vehicles.