Question

Difference between CNG and LPG

Answer 1

CNG is compressed natural gas – methane.

LPG is liquefied petroleum gas – propane.

There are many similarities between LPG and CNG, as well as some major differences…

What are the Differences between LPG vs CNG (Natural Gas)?

• LPG has a higher energy content than CNG, with 25MJ/L versus 9MJ/L, respectively.

• Storage pressure of LPG is less than 2 MPa whilst CNG is 20 – 25 MPa.

• For proper combustion, LPG requires an air to gas ratio of approximately 25:1 whilst natural gas requires a 10:1 ratio.

• LPG and natural gas appliances operate at different pressures – 2.75 kPa vs 1.1 kPa, correspondingly.

• LPG (propane) is denser than air at a relative density of 1.5219:1 vs natural gas (methane) at 0.5537:1, which is lighter than air.

• CNG cylinders have a tare weight approximately 3x heavier than comparable capacity LPG cylinders.

• LPG can be compressed into a liquid, increasing its energy density.

• LPG (propane) and natural gas (methane) have different chemical formulas: Methane is CH4. • Propane is C3H8.

Major Differences

The big difference is in volumetric energy density.

LPG has almost 3x the energy density with 25MJ/L for LPG versus only 9MJ/L for CNG.

In other words, for comparable capacity cylinders, the LPG cylinders will last more than twice as long.

Another major difference is that CNG is stored at pressures that can be more than 10x that of LPG.

LPG pressure is less than 2 MPa whilst CNG is 20 – 25 MPa.

This much higher pressure requires a much heavier and more expensive cylinder or tank.

This also means it is impractical to make them large enough to offset the energy density deficit, due to the size and weight required.

Hope this will help you :)