LNG Vehicle Fuel Tanks - Systems

CRYOGENIC FUELS INC. LNG Vehicle Fuel Systems Engineering Services CFI VEHICLE FUEL TANKS

Technology Overview

There are two operating capabilities of the CFI tank design that represent a significant advancement in the "state of the art" for cryogenic containers. These capabilities are summarized as follows:

Fuel Delivery:

The most outstanding performance feature of the CFI vehicle fuel storage tank is the capability to withdraw "liquid only" fuel from the tank for delivery to the engine. Conventional "industrial gas" cryogenic containers must withdraw a combination of both vapor and liquid in order to maintain the operating pressure of the tank. The withdrawal of pure methane vapors has been demonstrated to "weather" the residual LNG in the fuel tank and as a result it is necessary to use, re-liquefied, 99% methane content LNG in these types of tanks.

The "liquid only" operating capability of the CFI tank design eliminates any possibility of LNG weathering and regular, less expensive, industrial LNG may be used in the CFI fuel tank. It should be pointed out that weathering is the term used to describe the "increase in the heavier hydrocarbons" in LNG as the methane gas component is withdrawn from the tank and combined with the liquid fuel flow to the engine. These heavier hydrocarbons, such as excess ethane, can cause engine damage.

Pressure Management

Pressure variations of as much as 40 to 60 psi are a continuing problem with "industrial gas" tanks that are used as LNG vehicular fuel tanks and the LNG must be heated (conditioned) to increase its saturation pressure to compensate for these pressure variations. The CFI tank operating pressure is maintained totally independent of the saturation temperature of the LNG and it is not necessary to precondition the LNG. A conventional pressure regulator, combined with a short length of "heat exchange" tubing, is used to build pressure at the maximum rate of 2 psi per operating hour. The pressure build process requires only droplets of liquid, on an intermittent basis, to maintain the specified tank operating pressure. The desired tank operating pressure is normally pre-set at 10 to 15 psi above the specified engine operating pressure.

Code Compliance

The LNG vehicle fuel tanks designed and patented by Cryogenic Fuels are manufactured, tested and certified in compliance with the National Fire Protection Association (NFPA) Code For Liquefied Natural Gas Vehicular Fuel Tanks & Fueling Facilities, 2002 Edition.

Design Criteria

The tanks are of all stainless steel construction and consist of an inner pressure vessel suspended within an outer tank by means of a non-metallic central support beam. This rugged beam design is combined with multi-layer insulation and a high order vacuum to reduce the amount of "heat leak" into the cold LNG in the inner tank. The result is a thermal protection system that is, at a minimum, four (4) times more efficient than, conventional "industrial gas" cryogenic tanks.

Model C-100-26-2 Tank Plumbing Schematic


The CFI vehicle fuel tank is available in six (6) diameters, 16" to 30" X 32" to 78" in length. Thermodynamic, structural analysis and general design information is compiled and available for 52 tank configurations.


Testing And Certification Model C-100-26-1 Model C-100-26-2 Shock – Vibration The CFI tank design has successfully completed, dynamic structural testing, consisting of 3.5 "G" cyclic shock loads, conducted at tank operational temperature and pressure. The testing simulated 500,000 miles of heavy-duty truck operational service. Federal Hwy. Administration (FHWA) 30’ & 10’ Drop Test Crash test simulation on the Model C-100-26-2 LNG fuel tank was successfully performed under DOE Contract No. DE-FCO2-O1CH11084.