Natural gas fuels:
CNG and LNG

 

CNGCompressed Natural Gas

Compressed Natural Gas

 

Liquified Natural Gas

Liquified Natural Gas

Compressed Natural Gas (CNG)

Clean-burning natural gas has become the alternative fuel of choice for transit, refuse, and many other heavy-duty vehicles.  High-strength and lightweight materials allow CNG pressures up to 3,600 PSIG, providing increased fuel storage capacities while keeping the total system weight low.

Agility's CNG fuel systems are designed to take advantage of all of the latest technological developments and pass the operating benefits through to the end user.  Single fuel systems can hold up to five storage cylinders, while large bus systems can carry as many as twelve cylinders with a fuel capacity of over 27,000 SCF (194 diesel gallon equivalents).

Vehicles equipped with Agility's fuel systems comply with all Federal, state, and local regulations, and have an excellent track record for safety and reliability in the most demanding fleet applications.

In choosing CNG over LNG, a fleet operator should consider the relative advantages and disadvantages of CNG as a fuel.

CNG Advantages CNG Disadvantages
  • Unlimited hold times with no fuel loss
  • More mature technology
  • Gas / vapor instead of cryogenic
  • Simple fuel tanks and pressure management
  • System design can be customized for application
  • Cost of compression - energy and maintenance with a compression station
  • Size of storage tanks
  • Possible weight disadvantage

 

CNG Conversion Formulas

Pounds of CNG Fuel
Lbs. of CNG @ 3,600 PSI = Water Volume (cu. in.) multiplied by 0.0079
Lbs. of CNG @ 3,000 PSI = Water Volume (cu. in.) multiplied by 0.0069

Standard Cubic Feet (SCF)
SCF @ 70°F and 3,600 PSI = Water Volume (cu. in.) divided by 5.861
SCF @ 70°F and 3,000 PSI = Water Volume (cu. in.) divided by 6.657

Diesel/Gasoline Gallon Equivalents
Gasoline Gallon Equivalent (GGE) = SCF of Natural Gas divided by 123
Diesel Gallon Equivalent (DGE) = SCF of Natural Gas divided by 139

 

Liquefied Natural Gas (LNG)

Natural gas fuel for vehicles is also available in liquid form. For certain applications where weight and vehicle range are critical, LNG may be the perfect choice.  LNG systems operate at low pressure and can store as much as 2.5 times the fuel in the same space as conventional CNG systems.  LNG is transported and stored at extremely low temperatures and requires the use of vacuum-insulated storage tanks.

The Agility product development team has extensive experience working with cryogenic (-260°F) piping systems and has designed fuel systems holding as many as four storage tanks that mount on the roof or over the engine for transit applications.  LNG fuel systems incorporate a proprietary Agility pressure control manifold, which reduces the number of system components and allows multiple storage tanks to operate as a single unit.  All LNG systems include an integral containment pan designed to protect the passenger or engine compartment in the event of any fuel leakage.

The California Highway Patrol and the Texas Railroad Commission approve these systems.

In choosing LNG over CNG, a fleet operator should consider the relative advantages and disadvantages of LNG as a fuel.

LNG Advantages LNG Disadvantages
  • Fewer tanks / less space requirements
  • Greater fuel density
  • Lower weight storage
  • The complexity of tanks
  • Pressure and temperature management of fuel to engine is more complex
  • High maintenance cost of cryogenic parts
  • Use the fuel or lose it
  • Reliability is challenging
  • The life cycle fuel cost over CNG may
    be higher

 

LNG Pressure - Temperature - Density

Pressure (PSI) Temperature (°F) Density (Lbs/Gal.)
0 -259 3.54
50 -223 3.29
100 -200 3.11
150 -186 2.97
200 -175 2.85
250 -167 2.76
300 -158 2.68
350 -150 2.60