|The Sierra Lobo liquid hydrogen storage system (vacuum jacket not shown). Click to enlarge.|
Sierra Lobo will test its No-Vent Liquid Hydrogen Storage and Delivery System, currently under development under contract with the Department of Defense (DOD), in a custom Hydrogen Internal Combustion Engine (HICE) Silverado truck provided by Electric Transportation Engineering Corporation (eTec) (earlier post).
The No-Vent system, specifically developed to eliminate hydrogen boil-off in ground and space transportation systems, is derived from liquid hydrogen (LH2) storage system technologies originally developed under several Department of Defense contracts that Sierra Lobo is now integrating for dual-use (military and commercial) hydrogen vehicle applications.
The No-Vent system cools the storage tank walls and intercepts environmental heat leak before it reaches the liquid, thus providing for the storage and dispensing of liquid hydrogen without venting.
|Operating conditions of the Sierra Lobo high-efficiency Pulse Tube Cryocooler. Click to enlarge.|
The system that will be integrated into the HICE Silverado consists of a 10 kg liquid hydrogen, super-insulated tank with a nominal operating pressure of 550 kPa (80 psia), an active-cooling loop around the tank, a low-pressure, drop cooling loop helium circulation blower, and the Sierra Lobo two-stage pulse tube cryocooler driven by a long-life linear compressor. The active-cooling loop is connected to the pulse tube cryocooler at the 2nd stage cold heat exchanger, which operates at 20 K (-253°C).
In an article for the newsletter of the Ground Testing Committee of the American Institute of Aeronautics and Astronautics (AIAA), Sierra Lobo said that the pulse tube cryocooler is the key component to this active-cooling system.
The pulse tube cryocooler is capable of lifting 4 W at 20 K, at the second stage, and can simultaneously lift about the same wattage at 80 K, on the first stage. The cooling capacity of the first stage will be used for cooling thermal shields that will further minimize heat leak into the hydrogen tank.
Approximately 600 W of electrical input power will be required to drive the compressor. This input power will be provided by off-board facility power or plug power when the vehicle is parked. Heat will be rejected at the aftercooler flange at 300 K using the vehicle on-board water cooling system.
The pulse tube cryocooler was designed and built by Sierra Lobo and is the most efficient hydrogen cryocooler of its size in the world at 12 percent of Carnot.
The No-Vent Liquid Hydrogen Storage and Delivery System will be mounted in the bed of the Silverado and will take up one third of the space that a comparable compressed-gas storage system would occupy.
While eTec currently has several HICE vehicles that are powered by compressed hydrogen in operation throughout North America, the eTec HICE Silverado delivered to Sierra Lobo, Inc. will be the first eTec HICE vehicle to be powered using liquefied hydrogen (LH2) technology.
With technical assistance from project partner, Roush Industries, eTec led the conversion of the eTec HICE Silverado. Based on the full-size 2007 Chevrolet Silverado 1500 HD pickup truck utilizing the Vortec 6.0 Liter V8 engine, the vehicle was customized to Sierra Lobo’s specification and underwent internal modifications to meet the technical demands and requirements needed to run on a liquefied hydrogen fuel system.
The eTec HICE Silverado is the only production HICE vehicle participating in the Department of Energy’s Advanced Vehicle Testing Activity under the FreedomCar and Vehicle Technologies Program.