Authored by: Christopher J. Hollerback
Copyright © 2007 SAE International
Closed-loop refueling is an evolutionary dispensing method designed for the rapid and environmentally secure filling of vehicles equipped with single or multiple fuel tanks. The principle is based on the utilization of high-pressure fuel flow in conjunction with an equal amount of vacuum under positive mechanical connection. This retrofit system connects, dispenses, and disconnects while containing virtually 100% of raw fuel and hydrocarbon-laden vapor to avoid small-volume releases. This is achieved through a single-connection dispensing gun to a mating receiver assembly mounted on the refueling vehicle.
Exploring an evolutionary method of fluid transfer designed to attain maximum resource utilization through enhanced environmental and labor efficiencies by way of positive mechanical connection. In commercial fleet maintenance operations, such as vehicle refueling, the objective is to maximize resources (e.g. labor and commodity products in the form of fuel and other essential fluids) in the most cost-effective and efficient manner. This is balanced with the need to be environmentally responsible in the process. The time required to replenish fuel is currently regulated by maximum gallons per minute (GPM) established to safely manage and limit potential fluid releases and varies by product for the specific application. Gasoline dispensing is regulated to a standard of 10 GPM while the less volatile diesel fuels, commonly dispensed in larger quantities and to more tanks than gasoline, is permitted at 30 GPM. Both fuels are assumed to be handled under safe practices and monitored to ensure that the product goes where it is intended - into the fuel tanks.
The potential for “small-volume release” (spills) commonly arises when maintenance personnel are tasked with additional checks that divert attention from the refueling process to focus on other maintenance items. One such task includes additional fluid checks like oil level, washer solvent, and coolant. Physical inspections are also required ranging from belt tension to battery checks and tire pressures. These seemingly simple tasks that enable vehicles to remain in service can easily become overlooked due to the number of units within large fleets, and the pressure for personnel to return each vehicle to the road in an expedited manner.
By combining tasks and safely increasing fuel flow rates through closed loop fueling, it is perceived that greater efficiencies can be realized in a cost-effective and environmentally sound manner during the refueling process.
WHAT CONSTITUTES A SMALL-VOLUME RELEASE?
Mathew A. Lahvis, of Shell Global Solutions (US), and author of “Evaluation of Potential Vapor Transport to Indoor Air Associated with Small-Volume Releases of Oxygenated Gasoline in the Vadose Zone” states that “Small-volume releases of gasoline may be liquid or vapor and occur as a result of routine fueling operations, equipment repair, or leaky joints and connections in UST systems. In the case of liquid release, the volume is not of sufficient magnitude for the released product to contact groundwater. Rather, individual constituents of the gasoline migrate to groundwater by diffusion and advection. Resulting effects on groundwater are the function of the magnitude (volume and rate) of product released, its composition, the physiochemical properties of the constituents that compose the released gasoline, and the prevailing hydrogeologic conditions of the vadose zone in which the product is released.” 1 While Mr. Lahvis references gasoline, specifically, it is understood that such releases occur with all types of combustible fluids during transfers.
WHAT ARE THE COMMON ISSUES OF CURRENT METHODS AND HOW CAN THEY BE ADDRESSED?
* Ground contamination due to fuel spills and overfills;
* Fugitive aromatic vapors in the form of volatile organic compounds (VOCs) or polycyclic aromatic hydrocarbons (PAHs) ;
* Potential operator health risks due to repeated exposure to fumes and raw fuel;
* Inefficiencies in mechanical nozzle designs which make it necessary to monitor the refueling process to avoid unwanted small-volume releases.
These problems are universal in all refueling operations, whether it involves a personal-use automobile or an entire commercial vehicle fleet.
The focus of this writing will concentrate on an alternative method to improve efficiencies within commercial vehicle refueling operations. By implementing a system that is essentially a scaled down version of Stage I Vapor Recovery (dual line delivery method used for bulk fuel transfer from tanker truck to underground storage tanks (UST) at service stations or travel plazas.) these negative issues can be eliminated.
The principle of this system is based on the utilization of high-pressure fuel flow in conjunction with an equal amount of vacuum to return previously lost fuel in the form of vapor to a usable state. In addition, the positive mechanical connections capture and return fluid that would otherwise be lost as a ground contaminate.
The vacuum occurs in the return path to remove both vapors and associated tank pressure to complete the closed loop by returning vapor to the originating UST. The balance of pressure and vacuum also circumvents the activation of OEM pressure relief valves (PRV) or spring-loaded vents, present in current fuel caps, to maintain the closed loop integrity during the fueling process.
This proposed system connects, dispenses, and disconnects while containing virtually 100% of raw fuel and hydrocarbon-laden vapor. This single-connection, multi-coupling dispensing gun mates to a vehicle-mounted receiver assembly that does not impede OEM fuel caps.
WHAT ARE THE BASIC VEHICLE MODIFICATIONS NEEDED FOR USE WITH THE TCFS METHOD?
Two basic components are required, a universal mount receiving box (complete with integral dust cover) and one manifold for each fuel tank on the vehicle. The manifold is installed on each tank in a similar fashion in which aftermarket diesel tank heaters are installed. Hoses are fitted in series to each manifold with the final vacuum return connecting back to the receiving box to complete the basic loop.
The receiving box is designed to hold two quick connect couplings as the basis for the mechanically contained closed loop delivery method of liquid fuels. The first coupling delivers fuel via hose, plumbed through to the tank-mounted manifold to a “down tube” inside each fuel tank to expedite bottom filling. This method was selected to eliminate the foaming of fuel associated with air inclusion common with splash fill nozzles. The fuel is delivered under pressure below the existing fluid level within the receiving tank and allows fuel to be introduced at a substantially higher velocity. Vacuum, applied in the return coupling, is utilized to maintain a near-zero tank pressure balance and removes vapors from the ullage segment of the fuel tanks during the refueling process.
For commercial applications, additional couplings are included to remotely fill reservoirs with various maintenance fluids such as oil, washer solvent, coolant or urea for greater maintenance efficiencies.
WHAT ARE THE BASIC DISPENSING GUN DESIGN ELEMENTS OF THE TCFS METHOD?
The dispensing gun is larger than a standard splash fill nozzle and is therefore supported by a tool balancer to assist operation with minimal operator effort. The multiple hoses are suspended with the balancer to prevent abrasion and to minimize trip hazards within the refueling work envelope.
Elemental features of the prototype design study have included numerous safety considerations.
The dispensing gun self-aligns in a polarized orientation with the vehicle’s receiving conduit box to prevent cross-connection. Insertion and ejection of the dispensing gun is assisted by a fulcrum lever and mechanical cam to overcome the compound spring pressures of the multiple hydraulic push-to-connect fittings. This cluster configuration is also connected to an internal solenoid that is designed to release the dispensing head automatically upon completion of fluid transfer. The solenoid can also be activated by a panic stop switch located above the handle assembly.
During refueling, the dispensing gun is mechanically connected to the vehicle’s receiver. To prevent premature movement of the vehicle, which could damage either the vehicle or the dispensing equipment, an integrated magnetic switch is activated to lock out an electrical circuit on the vehicle such as a transmission neutral switch or an electro/pneumatic brake assembly while the dispensing gun is connected. This switch returns to the closed position upon removal of the dispensing gun, restoring normal operation to vehicle movement. In the event that a vehicle does move during connection, the dispensing gun is equipped with fracable hose fittings to minimize damage to the fueling equipment.
Technically the gun can be connected to an existing island dispenser in place of a standard nozzle for the basic fuel delivery system. A vacuum source retrofit to the pump is required to complete the closed loop. However to take advantage of the high-speed delivery that can be safely achieved with this method, the standard pump would also require an upgrade.
A flow meter and flow switch, located in the return side of the dispensing gun, serves to measure returned vapor and detect fluid to trigger solenoid release. This is a designed safety in the remote chance that a supply pump continues to run. Fluid and vapor are returned to the underground storage tank (UST). The vacuum return hose is sized on a 1:1 ratio with the pressurized fluid delivery hose to insure unrestricted flow in the event of fluid return.
This closed loop method is intended as a close proximity data exchange through the use of radio frequency identification (RFID). Through the utilization of RFID in conjunction with an engine control module (ECM) or on-board diagnostics (OBD) useful information such as engine error codes, maintenance reminders or even payment transaction authorizations can occur at the pump, without paper or even a credit card.
HOW DOES THIS METHOD COMPARE TO TRADITIONAL REFUELING DEVICES?
Current fueling methods in a “failure mode” result in fluid loss through filler necks or PRV’s. These devices are designed to prevent tank ruptures which would result in contamination of the work envelope as a small-volume release. This type of fluid loss cannot be recovered for reuse for its intended purpose. Closed loop fueling circumvents the possibility of tank rupture and recovers 100% of reusable fluid and hydrocarbon-laden vapor for the intended purpose.
The one common factor of existing fueling systems is that they all vent to the immediate atmosphere. As a result, they become a source of ground and atmospheric contamination.
1. Open filler necks on medium trucks, heavy trucks, and school buses
a. Fill device: most common “splash fill” nozzle
b. Various diameters of fill necks
c. Common trait: used as vent
d. Prone to overfill and spill
2. Vapor recovery nozzle for gasoline applications in consumer vehicles
a. 95% effective for recovering VOC vapor
b. Marginally effective in recovering some fuel in overfill condition
c. Not a full mechanical seal
d. Not designed for diesel applications
3. Pressure fill: municipal bus, train, and off-road equipment
a. Common trait: pressure relief valve (PRV) as tank safety
b. Prone to overfill and back pressure spill on disconnect due to undersized PRV imbalance and pressure buildup bypassing worn seals
c. PRV’s atomize fuel into the immediate atmosphere—odor release; particulates settle on equipment and attracts and holds dirt; cakes in layers after repeated fills
d. Examples of systems:
* Emco Wheaton2: diesel locomotive and bus applications;
* Adel Wiggins3: off-road, heavy equipment and diesel locomotives;
* Identic4: single tank bus applications
e. Pressure systems as a rule fill one tank per connection. Exception: Adel Wiggins can fill dual tanks, but still relies on PRV for high pressure refueling applications
WHAT ARE THE ADVANTAGES OF A CLOSED LOOP FLUID TRANSFER?
1. A sealed mechanical connection removes human error from the possibility of accidental fluid or vapor release due to diversions that may take an attendant away from monitoring the fuel flow process required with conventional nozzle filling.
2. Outside air inclusion is eliminated during fueling of a closed loop system, allowing returning vapor to be accurately measured. The calculations of returned hydro carbons (HCs) that were previously lost during conventional fueling processes may qualify as a new and additional revenue source in the form of tradable carbon credits under Cap and Trade venues such as proposed under the Kyoto Protocol.
3. Retrofit manifolds installed on the top of connected fuel tanks deliver fluid through a “down tube” dispensing liquid below existing fluid level within the tanks. This bottom fill method eliminates air inclusion and prevents foaming of fuel normally associated with “through the cap” individual tank splash fill nozzle methods currently in use.
4. Higher pressures of fluid with a 1:1 balance from vacuum return allows a greater volume of fuel delivery (GPM) at a zero tank pressure. Consequently, existing pressure relief safeties will not engage, confining all vapor and fluid to maintain the closed loop.
5. In the event of a mechanical failure that prevents the fluid pump from shutting down, fluid (instead of flowing outside the tank through a PRV or open filler neck) is allowed to return to the UST (through filtration) freely from the same 1:1 dimensioned vacuum line.
6. Manifolds adapted to the fuel tanks mechanically maintain a maximum fill level of 80% under any circumstances including fuel returned through the vacuum return line.
7. A flow switch within the dispensing gun shuts down the fuel meter and electronically disengages all pump activity as a final safety in this closed loop configuration.
8. If used consistently, this system would minimize condensation associated with current “open cap” fueling methods in humid climates. This sealed method does not allow tanks to be exposed to, or ingest ambient outside air containing moisture. Conversely, dust and particulate matter cannot enter a closed loop system in windy or arid environments, further protecting fuel supply from contamination.
9. The unique connection insures that only authorized vehicles can be fueled making this method a high security device to protect fuel supplies.
This innovative refueling method is presented as an alternative to current vented refueling devices. As a retrofit system for captive fueling commercial fleets this proposed method offers significant advantages as an environmental safeguard and the ability to dispense fuel at flow rates previously unattainable to expedite fleet mobilization. Current proof of concept methods suggest that fueling time alone can be safely reduced by 2/3’s over conventional nozzle fill dispensing. Adding in the additional liquid transfer capability promotes an efficient method of fluid management along with RFID enhancement. With collaborative industry efforts, and support of a standardized system, this method offered as an OEM option would promote change toward environmental stewardship by limiting small-volume releases during the refueling process. The TCFS method also offers a more efficient means of secure transactional equipment within the commercial fueling industry. While this method is presented to the commercial environment, the basic principal applies to all fueling aspects and is viewed as a possible new source for tradable carbon credits.
1. 1 Author: Matthew A. Lahvis, Shell Global Solutions (US) Inc Excerpt from American Petroleum Institute (API) (Jan. 2005), No. 21 publication titled: "Evaluation of Potential Vapor Transport to Indoor Air Associated with Small-Volume Releases of Oxygenated Gasoline in the Vadose Zone"
2. Emco Wheaton, 2480 Bristol Circle, Oakville Ontario(Canada)L6H5S1 www.emcowheatoncanada.com
3. Adel Wiggins Group, 5000 Triggs St., Los Angeles California (USA) 90022 www.adelwiggins.com
4. Identic AB, Vargmotesvagen 1C, 186 30 Vallentuna
5. Christopher J. Hollerback holds patent # US 7,082,969 with international patents pending for the TCFS method.
Chris Hollerback is a Michigan born native with an inherent interest in transportation and a passion for automotive design. His youth was spent customizing and painting muscle cars and vans. He became involved in fueling processes as a mechanical and design consultant for a robotics based Venture Company headed up by his father in the mid 80’s. Chris realized that the current fueling practices could be enhanced in both environmental and maintenance efficiencies but would require modifications to the basics of delivery systems. This was not a direction the robotics organization could pursue at the time.
In 2003 Chris focused on independent research which has resulted in the award of a U.S. patent in 2006 for the “Total Containment Fueling System” (TCFS) method and has international patents pending.
Mr. Hollerback currently resides in Colorado.