Besides the under hood equipment , the CNG cylinder is a crucial component required for a CNG system.
There are four CNG cylinder manufacturers in North America:
All make composite cylinders but Faber steel cylinders are very commonly used in CNG aftermarket conversions in North America. Canadian installation regulations limit the pressure to 3000 psi while US installation regulations allow 3600 psi. The higher pressure allows the cylinder to carry more CNG but adds to the cost of the conversion because higher cost components must be used to withstand this higher pressure.
Because of the low cost of natural gas in many parts of the USA (especially Utah), many people try to do a DIY conversion themselves. Due to the liability issues of CNG conversions, CNG components (like CNG cylinders) are generally not available to the public.
CNG tanks are bulky compared to a gasoline tank that holds an equivalent amount of energy. Very roughly, a CNG cylinder holds about 1/3 of the energy capacity of a gasoline tank. By its nature, a CNG tank must be cylindrical in design to withstand the extremely high storage pressure. Cylinders are not ideal for placement inside a vehicle and a great deal of usable storage space must be sacrificed in order to have a reasonable operating range.
Additional range can often be added which the obvious loss of even more cargo capacity. Commuters would likely not miss their trunk space very much if they had another general purpose car available when they needed the extra carrying capacity. For additional operating flexibility, natural gas vehicles are commonly dual fuelled. When the natural gas is completely consumed, the car is easily switched back to gasoline operation. This is best option for most people but there are very few CARB-certified bi-fuel conversions available. EPA certification is easier to obtain and is therefore more common. To maximize the payback of the conversion, the vehicle should obviously be operated on CNG as close to 100% as possible. More storage capacity reduces the inconvenience factor but can potentially improve the payback on the conversion.