Fuel for the Forces
New fuel-level sensing and communication technologies that permit real-time fuel management will help the Marine Corps keep its equipment moving to military hot spots when needed.
With a change in modern warfare tactics, the U.S. Marine Corps is asking Southwest Research Institute (SwRI) for help in developing ways to monitor the fuel assets needed to support vehicles and troops on the battlefield.
Fuel determines the distance that vehicles and aircraft can travel, making a plentiful supply essential for mechanized warfare. Acquiring and delivering this fuel to the battlefield can be a complex operation. Traditionally, military logisticians have sent massive quantities of supplies to the theater of operations to ensure that troops have adequate supplies. Thus, efficiency was sacrificed for effectiveness. As recently as Operation Desert Storm, logisticians overestimated combat supply requirements by more than 1 million tons. Following military action, U.S. forces abandoned excess supplies or turned them over to host nations rather than return them to the United States.
Need for modernization
The issue of providing troops with adequate fuel is further complicated as the U.S. Marine Corps evolves to a sea-based, rapid-response force. Rather than forming a large, relatively fixed supply base ashore, operations are conducted from offshore ships that can move quickly to other locations as the battle scene changes. To make this transition, existing military systems, procedures and doctrine must evolve accordingly. With this just-in-time supply requirement, the accuracy and timeliness of tracking and dispensing supplies, especially fuel, must be improved. Current fuel management relies upon voice communications and handwritten data collection, resulting in high error rates and reduced combat readiness. To provide real-time battlefield fuel management, the U.S. Marine Corps plans to incorporate state-of-the-art sensor and communication technologies to support the battlefield of the future.
The Naval Facilities Engineering Service Center (NFESC) is exploring technologies to improve fuel delivery and distribution on the battlefield. The latest fuel delivery prototype, called the Expeditionary Fuel System (EFS), is a modular concept that provides fuel in 400-gallon containers or functions as a bulk-delivery system that can transport up to 4,000 gallons of fuel. To complement this new fuel delivery system, NFESC began investigating level-sensing and communication technologies that permit real-time fuel asset management on the battlefield.
Fuel Automated Quantity Sensors
In 1999, the NFESC, under tasking from the Marine Corps and Office of Naval Research, contracted with SwRI to investigate sensors that could provide the Marine Corps with remote fuel management capabilities. The Marine Corps has an interest in developing Fuel Automated Quantity Sensors (FAQS) that can determine fuel quantity in its SIXCON fuel tank modules (900 gallons), collapsible fuel bladders (20,000 gallons), and the newly developed EFS prototype. While NFESC did not specify a single type of sensor for the three applications, the SwRI research team decided that having only one sensor type that meets all three requirements would simplify the sensor's integration into the military's supply process. To serve this need, the chosen sensor would have to work in both rigid and collapsible tanks. After the FAQS technology is developed and approved, it could have wide commercial and military application in areas such as automated vehicle refueling and fuel-farm management. Ultimately, FAQS technology will improve greatly battlefield awareness, combat readiness and combat service support.
Some of industry's most common techniques for gauging liquid level include ultrasonic sensors, pressure transducers and string potentiometers. Ultrasonic sensors use acoustic signals to measure the distance to the fuel's surface, while string potentiometers measure the same distance by the uptake of a string attached to a float in the fuel tank. Fuel volume is calculated using the dimension of the tank. Pressure transducers measure the pressure exerted by a column of liquid. The pressure is directly proportional to column height, which can be used to calculate the volume of liquid in the tank. The liquid density also must be known to calculate volume accurately from the pressure. Where applicable, SwRI engineers evaluated all three commonly used sensor types.
In the SIXCON module, the ultrasonic sensor performed exceptionally well -- as SwRI engineers expected based on the sensor's industry reputation -- and is likely to be the best candidate for a field solution. To evaluate the sensor, Institute engineers temporarily mounted the ultrasonic sensor in the manhole port on top of a SIXCON fuel tank. To provide the Marine Corps with an option, engineers also installed a pressure transducer in the drain port on the bottom of the SIXCON tank. In this evaluation, the pressure transducer also performed well.
Gauging fuel level in a collapsible fuel bladder is a challenge. The lack of rigid walls, the absence of empty space above the fuel in the tank and the varying position of the top of the bladder make most sensors difficult to use. The only solution to this fuel management problem is to measure the height of the flexible bag and relate that value to fuel quantity. The accuracy of this approach depends on the location of the sensor in the bladder and the slope of the ground on which the bladder is positioned.
Engineers mounted the string potentiometer through the vent pipe and the pressure transducer through the drain port underneath the bladder. Both sensors performed well; however, the string potentiometer measured inaccurately at low volumes. Several hundred gallons of fuel are required to raise the top of the bladder from its empty position. The string potentiometer could not register this low volume of fuel.
The design of the EFS fuel tank modules prevents the use of all sensors except pressure transducers. The research team mounted the transducers in the plumbing underneath the tanks, where flow and the tank's valve mechanism would not interfere with the sensor reading.
In all three types of fuel tanks, SwRI found that the performance of the pressure transducers satisfied the project goals. Rather than determining fuel height from the pressure measurements, Institute engineers calibrated the sensors directly to the amount of fuel in the tank, eliminating the need for a subsequent calculation. Some difficulty arose in calibrating the collapsible fuel bladder and the EFS. During the program, these tanks were calibrated with water and the calibrations were then corrected for fuel. Eventually, these systems will be recalibrated with fuel to increase measurement accuracy. To comply with Marine Corps procedures, Institute engineers installed a thermocouple in each tank so that all fuel quantities could be temperature corrected to 60° F.
Immediately prior to the start of this work at SwRI, the U.S. Army had awarded a large contract to install satellite communication and navigation equipment in Army vehicles. To provide a degree of commonality between the Army and the Marine Corps, the SwRI research team opted to use this system to transmit the FAQS information from the fuel storage tanks.
The Army-funded system consists of small satellite transceivers that can provide two-way communication services for fixed sites and mobile units. Typically, messages are relayed from a remote site through a satellite to a ground-based hub. Then, end users retrieve their messages by accessing the hub across the Internet.
To provide added value to the Marine Corps, SwRI chose to use a more innovative mobile-to-mobile routing system for this application. In the Institute approach, the information is rebroadcast from the hub through a satellite to a selected transceiver, which stores the data on a local workstation, ready for immediate access. Other users then retrieve the FAQS data as necessary. This method allows the data to be received anywhere in the world, even without Internet access.
An alternative, more conservative method of communication being considered by the Marine Corps is to use fielded radio equipment to transmit data from the fuel tanks to local collection sites. Radio operators can then retransmit the information via radio to other sites.
Limited field testing of the FAQS technology began in 2000. SwRI engineers successfully demonstrated the FAQS hardware for use in the collapsible fuel bladders and the EFS modules during the Combined Arms Exercise 7 at the U.S. Marine Corps Air Ground Combat Center in California. In the fall of 2000, NFESC sent the EFS modules to South Korea to participate in Foal Eagle, a joint exercise between the U.S. Marine Corps and the Republic of Korea Marine Corps. During Foal Eagle, FAQS data were relayed from South Korea to San Antonio, demonstrating the ability of the satellite communication link to operate on a worldwide basis. Additional exercises to demonstrate FAQS are planned.
In 2001, SwRI will continue to work with NFESC to prepare the FAQS data for incorporation into various military logistics systems, one of which is the Fuels Automated System (FAS) being implemented throughout the U.S. Department of Defense. For FAQS to be accepted by the military community, its ability to be integrated into the military's current and future logistic systems must be demonstrated successfully.
Comments about this article? Contact Hutzler at (210) 522-6978 or firstname.lastname@example.org or C.E. Thomas, program manager, Naval Facilities Engineering Service Center, 1100 23rd Ave., Port Hueneme, Calif. 93043 or email@example.com.
Published in the Spring 2001 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Maria Stothoff.