experimental tank fuel

Wednesday, September 4, 2024

September fuel price decrease: Here’s how much you’ll save per tank in most popular vehicles

Motorists stand to save between R30 and R73 per tank from September 4. Picture: Supplied

Published 19h ago

Most South Africans will be waiting until after Wednesday to fill their tanks, with significant decreases for both petrol and diesel set to come into effect.

From September 4, the price of both grades of petrol will decrease by 92 cents per litre, while diesel will come down by between 79 cents (500ppm) and R1.05 (50ppm).

But is it really worth delaying that refuel until the decreases take effect?

Refuelling a small hatchback like the Suzuki Swift with 32 litres will cost approximately R30 less after the decrease kicks in, while a medium sized car will save you up to R50 per tank and a larger bakkie or SUV should cost about R73 less to fill up.

Keep in mind that our calculations are based on the vehicle’s maximum tank capacity minus five litres, or 10 litres in the case of the larger bakkies. The diesel tank cost is an estimation as the price for this fuel type is not fixed.

The bottom line is that most motorists who fill up three times or more in the month stand to save more than R100 per month and this can only be good news for the economy.

Although many are seeing green shoots in the economy, household budgets remain under significant financial pressure as interest rates remain at a 15-year high. This appeared evident in last month’s new vehicle sales figures , which saw a 4.9% year-on-year decline overall, although the budget end of the passenger car market did see modest growth.

WesBank’s communications head Lebo Gaoaketse believes that many potential car buyers have delayed their purchase decisions in hope of an interest rate cut in September.

“While inflation data looks positive to allow a reduction in the prime lending rate, the difference won’t make immediate impactful savings to indebted consumers, but it should begin a rate-cutting cycle that would benefit the market.”

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Next pair of Red Hill tanks set for cleaning

PEARL HARBOR, Hawaii — Personnel from the Navy Closure Task Force-Red Hill are scheduled to begin cleaning a second set of fuel tanks at the Red Hill Bulk Fuel Storage Facility on Sept. 4.

What You Need To Know

The first step involves venting (or degassing) tank 6 to eliminate volatile compounds, the same process previously used for tanks 7 and 8. the venting is achieved by pushing clean air from the bottom of the tank and releasing it through a complex ventilation system the navy closure task force-red hill installed nine air quality monitoring stations in and around the facility, including at the halawa correctional facility, to track changes in air quality, measure potential volatile organic compound levels, and collect atmospheric data including air speed, wind direction, temperature, humidity and barometric pressure nctf-rh continuously monitors the air quality to ensure emissions from ventilation are maintained at less than the hawaii department of health’s limit of 38 parts per million by volume total volatile organic compounds in the event that volatile organic compound levels exceed the doh limit during operations, nctf-rh will alert regulators, hawaii emergency management agency and the honolulu department of emergency management.

The first step involves venting (or degassing) tank 6 to eliminate volatile compounds, the same process previously used for tanks 7 and 8. The venting is achieved by pushing clean air from the bottom of the tank and releasing it through a complex ventilation system, thereby ensuring a safe working environment within the tank. Personnel also take steps to keep outside air from being contaminated, according to the task force.

“To date, the air quality emissions levels from venting have remained within state emission limits,” said Rear Adm. Marc Williams, NCTF-RH deputy commander. “The team will remain deliberate with safety measures to ensure ventilation of the tanks is done in a manner that will not pose a risk to human health as we move forward with tanks 5 and 6.” 

NCTF-RH installed nine air quality monitoring stations in and around the facility, including at the Halawa Correctional Facility, to track changes in air quality, measure potential volatile organic compound levels, and collect atmospheric data including air speed, wind direction, temperature, humidity, barometric pressure.

NCTF-RH continuously monitors the air quality to ensure emissions from ventilation are maintained at less than the Hawaii Department of Health’s limit of 38 parts per million by volume total volatile organic compounds. 

During the degassing phase, air quality monitoring data will be updated hourly on the NCTF-RH mobile app, and daily on the NCTF-RH website. The data will be updated daily during ventilation operations. 

The task force said it has a series of fail-safes and redundancies to mitigate risk and safeguard the area around the tanks. In the event that volatile organic compound levels exceed the DOH limit during operations, NCTF-RH will alert regulators, Hawaii Emergency Management Agency and the Honolulu Department of Emergency Management. The public will also be notified via the NCTF-RH app, website  and a press release to the media. Anyone with questions or concerns may contact the Navy Call Center at 808-210-6968.    

For more information about NCTF-RH, visit  navyclosuretaskforce.navy.mil  or download the free mobile app by searching for “NCTF-Red Hill” in the Apple App store or Google Play store.    

Michael Tsai  covers local and state politics for Spectrum News Hawaii. He can be reached at  [email protected] .

Adding Aux Fuel Tanks To Your Airplane

We’ve all been in that place where more fuel would have meant a faster and better trip. with many planes, that dreamed-of additional capacity is possible..

Range on planes like this Bonanza can go from good to great with the addition of retrofit aux fuel tanks. Photo via shutterstock.

Who doesn't want a little more range  from their favorite airplane? Or, rather specifically, more endurance. After all, airplanes deliver their horsepower from burning fuel at a more or less fixed rate, consumed in gallons per hour. The number of miles covered, on the other hand, is utterly dependant on the wind's velocity; your actual mileage may vary. But we have all probably had the thought: "If I just had another hour of fuel, I could make this leg nonstop."

Installing an auxiliary fuel system to eliminate the temptation to land "on fumes" or, worse yet, to exhaust one's fuel supply short of the destination, is not an inexpensive or easy solution. That said, there are proven, well-engineered aux fuel systems to be had for the most popular planes, and you'll find that some airplanes on the market have already had them installed, should you be shopping for a new ride. We'll discuss what's available and how they work.

To Tank Or Not To Tank

Is installing auxiliary tanks a good idea? It depends on your needs and plans for the airplane. How often do you make trips that stretch your available fuel supply, requiring an extra stop to complete the mission? If this occurs only a couple of times per year, you're probably better off leaving the plane as it is. Frequent cross-country jaunts, on the other hand, can justify adding tankage.

Will add-on fuel tanks increase the airplane's resale value? In the case of some short-legged designs that came from the factory with insufficient fuel supply, definitely. But if the stock fuel capacity is adequate for the great majority of potential buyers, not so much. In general, I always assume that spending money on improvements to your airplane gains only half the expense in immediate resale value. The rest should be recovered in the satisfaction of flying it for a few years.

No solution is free of consequences. Hauling an extra 40 gallons of gas around means your payload is cut by 240 pounds, unless the tank installation includes an extra gross weight allowance, which, in some cases, it does. And the system itself adds to the aircraft's empty weight. More weight means less performance, requiring a recalculation of the takeoff distance and time-to-climb charts. I knew of a tricked-out Cessna 340 that could legally carry only two people if all of its add-on tanks were topped off. In addition, the usable cruise altitudes, and the single-engine ceiling, were reduced as it struggled to climb with the extra load.

However, it's very comforting to know you've got plenty of gas to go the distance. IFR flying is predicated on being able to dodge some weather, shoot an approach to unknown conditions that might not work out, and then divert to an alternate to land with fuel enough to reach yet another airport if that one didn't work out. That often means you'll need to take off with six hours of fuel on board just to make a three-hour trip. For an airplane to be considered "fully IFR capable," it needs to have more than a panel full of radios; it needs to have legs.

Even if you're operating carefully VFR, do you really want to sit in an airplane for over five hours? Most passengers need a break in no more than three hours, so stopping to refuel isn't necessarily a burden. Spending the money to install auxiliary tanks that aren't used that often may be a needless extravagance.

Some airplanes, however, were short-changed at the factory, particularly if they've been modified with larger, thirstier engines. A modified Cessna 152 or Grumman AA-1 with its horsepower boosted from 108-110 to 150 is a two-hour cruiser with standard tanks. A lot of Beech Bonanzas from the 1940s and ’50s have been modified with larger engines but were left with only 39 gallons of standard fuel supply. The early 250-hp Piper Comanches came with the 60-gallon tanks of the 180-hp version, begging for a tip-tank modification.

Beech's first turbocharged Bonanza A36, the A36TC, had the 74-gallon tanks of its normally aspirated sibling, hardly enough to keep it aloft for four hours. The follow-on B36TC hoisted 102 gallons, so it's obvious why so many A36TC's have had tip tanks added to feed the TSIO-520 engine. Turbine-converted airplanes, like the Silver Eagle P210, Soloy 206 and turboprop Bonanzas, will obviously need extra fuel for the thirstier turboprop engine.  

Given the need, there are options in add-on fuel systems. Wingtip fuel tanks are a commonly seen modification, sometimes gaining a takeoff weight increase to offset some of the payload limitations. Putting extra fuel on the tips is a better engineering option than adding weight in the fuselage, allowing the wing's span to share the load instead of increasing bending movement at the root. The drag of the tip tank may be offset somewhat by its end-plate effect by controlling tip vortexes. Adding a rear fuselage tank, by comparison, will cause the C.G. to move aft, something to be done with caution because it decreases pitch stability.  

In homebuilt airplanes, the designer sometimes starts out with a simple header tank located forward of the cabin but, as bigger engines are installed, will be forced to add wing root tanks to replenish the suddenly insufficient header tank. High-wing EAB types can dump the fuel in by gravity, while low-wing homebuilts will need a pump to lift the gas. Designers of twin-engine airplanes may resort to wingtip tanks to supplement fuel in the wings, or there can be nacelle tanks added aft of the engines.  

Tanking The Bonanza

The Beech Bonanza, whose incredible production run is closing in on 75 years, is a particularly fertile field for auxiliary fuel tank installations. The original Bonanza 35's 39-gallon wing-tank fuel system was soon outgrown as horsepower increased in either stock form or through modification. A factory-installed STC added a 20-gallon rear fuselage tank, available up to the 1954 E35. Some of these older airplanes have even had wingtip tanks installed for a total of five fuel sources. The F35 of 1955 introduced auxiliary wing bladders, used until the 1960 M35, after which the optional-but-always-ordered long-range tanks simplified fuel management.

You can forget about adding an aft-fuselage tank to an old Bonanza that wasn't built with one, so wingtip fuel is really the only way to go at this point. Even the 74-gallon factory tanks in the more modern Bonanzas aren't always enough, as we mentioned earlier. Two tip tank options exist;  General Aviation Modifications  (GAMI), Inc., in Ada, Oklahoma, now offers the 20-gallon tip tanks previously made by J.L. Osborne in Victorville, California, and  D'Shannon Aviation, Inc. , of Buffalo, Minnesota, sells its own wingtip tank system. Both work well, using electric pumps to move the fuel into depleted wing tanks.

The Osborne by GAMI system uses welded aluminum tanks, while the D'Shannon tanks are made of fiberglass, allowing the incorporation of a sight-gauge window to confirm fuel level in addition to the electric gauges. D'Shannon's tanks are canted slightly, reportedly improving roll control. If you're purchasing an existing modified Bonanza, either is worth consideration.  

D'Shannon Aviation has had 50 years of experience with its Bonanza tip tanks, which now have a 20-gallon capacity; older installations offered 15 gallons per side. The latest engineering improvements tailor airflow for maximum efficiency, and an aileron-rebalancing kit is included. Reportedly, the tanks help with the Bonanza's dutch-roll characteristics. The kit price is $13,850, with installation time requiring about 50 hours, plus or minus; we were told that $1,450 of the cost of the kit is represented by the new AeroLED lights that come with it.

Osborne by GAMI tanks have a long history as well, dating back to the 1950s. They incorporate LED lighting, feature flush filler caps and quick drains, and are said to improve aerodynamic efficiency and stability. The kit price is currently $12,995 and will cost about $20,000 installed.  

Adding tip tanks to a Bonanza can result in an approval to operate at higher gross weights. Both the D'Shannon and GAMI tanks' extra weight allowance varies by model and, in some cases, requires additional weight to be fuel in the tips. However, the matter of increasing takeoff weight may not be entirely tied to a tip tank installation. D'Shannon offers a Genesis STC to extend gross weight, allowing operation in Normal Category certification instead of the Utility Category carried by most Bonanzas. This resets maneuvering speed and other POH parameters.

Navion Fuel Systems

The J.L. Osborne tip tanks, originally sold under the "Brittain" name, were offered for Navions as well as Bonanzas. The Navion's unique factory fuel system had two 20-gallon wing tanks filled by a single port, with an optional aft-fuselage tank holding an extra 20 gallons. Without the rear tank option, the addition of 20 gallons per side with the Osborne tip tanks gave a very desirable increase in range. In addition, a 250-pound gross weight increase was part of the Osborne tanks' approval for the older Navions. A total 108-gallon supply, including tip tanks, was available in the final Navion Rangemaster model.  

Piper Comanche Tip Tanks

The PA-24 Comanche is a fine airplane, but for the first three years of its production, it held only 60 gallons of fuel, not quite enough for the 250-hp version, which is the reason an extra 30 gallons became available in auxiliary wing tanks by 1961. On the early Comanches, one frequently sees Osborne tip tank installations holding 15 gallons each, and they are sometimes found even when the optional 90-gallon fuel system is installed. The Twin Comanche is also a favorite target for adding wingtip tanks. According to GAMI, very few of the Osborne systems for Navions or Comanches were sold in recent years. The new owners will support existing installations with parts and tech support for as long as possible.

More Range For Cessnas

While other options have been pursued for adding fuel capacity to Cessnas, most notably Dave Blanton's 17-gallon Javelin baggage compartment tank in C-170s, the most successful kits are those from  Flint Aero  in El Cajon, California. Flint tips, as they are frequently called, have been around since 1967 and are seen on Cessnas all over the world. They mimic the look of standard Cessna wing profiles instead of adding a bubble on the end of the wing. As with other tip systems, an electric pump moves the fuel to the standard tanks after room is obtained.

Flint Aero's kits result in added wingspan in some cases by locating the tank in an extension of the stock wing, which results in improved climb performance. Many Flint tanks, however, can be internal, preserving the original wingspan by removing the close-out rib and slipping the fiberglass tank inside the wing.  

Approval for legacy Cessnas covers the 150/152, strut-braced 170 and 180 series, and some older 210s. These internal tanks add a total of 23 usable gallons at the cost of 34 pounds of additional empty weight. Estimated time required for the installation is 45 to 60 hours. An average cost of the conversion is around $10,000.

Cantilever-wing Cessna 210s, particularly the turbocharged models, can benefit from the addition of Flint Aeros' wet wingtips. They add a total of 32.5 gallons and increase overall wingspan by 26 inches, which improves high-altitude performance. Pre-1972 airplanes pick up an extra 400 pounds of gross weight. Kit cost is $19,307, with 55 to 70 hours required for installation.

Cessna 182s and 210s are probably the most likely models to carry Flint auxiliary fuel systems, although bush operators also like more gas for their 206 and 180/185 airplanes. The lighter end of the Cessna line doesn't see as much need for add-on fuel unless bigger engines find their way into the cowling. That said, Skyhawks with standard 42-gallon tanks, rather than later-optional 52-gallon supply (inherited from the Model 175), do find themselves short-changed in even a light headwind.

Other Aux Tank Options

Ingenuity abounds, it seems, when it comes to putting extra fuel into airplanes. Not all approvals are applicable to other aircraft models in a series, and some of the older STCs are no longer supported. If considering the purchase of an airplane with existing aux tank modifications, be sure to get all the paperwork and check out the availability of parts, if needed.  

In all cases, the value of an auxiliary fuel system will be related to the existence of an STC holder that's still in business. Orphan equipment adds little to resale worth. Check out the opinions on type-club forums to see what other owners say about their modifications. Extra fuel is worth a lot when you're struggling to get home against a stiff headwind. 

Facts About Refueling Airplanes

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Experimental Tanks & Fighting Vehicles

Armor | battlefield, just as with aircraft, the realm of armored fighting vehicles has seen its fair share of experimental types envisioned..

Zero-Boil-Off Tank Experiments to Enable Long-Duration Space Exploration

Do we have enough fuel to get to our destination? This is probably one of the first questions that comes to mind whenever your family gets ready to embark on a road trip. If the trip is long, you will need to visit gas stations along your route to refuel during your travel. NASA is grappling with similar issues as it gets ready to embark on a sustainable mission back to the Moon and plans future missions to Mars. But while your car’s fuel is gasoline, which can be safely and indefinitely stored as a liquid in the car’s gas tank, spacecraft fuels are volatile cryogenic liquid propellants that must be maintained at extremely low temperatures and guarded from environmental heat leaks into the spacecraft’s propellant tank. And while there is already an established network of commercial gas stations in place to make refueling your car a cinch, there are no cryogenic refueling stations or depots at the Moon or on the way to Mars. Furthermore, storing volatile propellant for a long time and transferring it from an in-space depot tank to a spacecraft’s fuel tank under microgravity conditions will not be easy since the underlying microgravity fluid physics affecting such operations is not well understood. Even with today’s technology, preserving cryogenic fuels in space beyond several days is not possible and tank-to-tank fuel transfer has never been previously performed or tested in space.

Heat conducted through support structures or from the radiative space environment can penetrate even the formidable Multi-Layer Insulation (MLI) systems of in-space propellant tanks, leading to boil-off or vaporization of the propellant and causing tank self-pressurization. The current practice is to guard against over-pressurizing the tank and endangering its structural integrity by venting the boil-off vapor into space. Onboard propellants are also used to cool down the hot transfer lines and the walls of an empty spacecraft tank before a fuel transfer and filling operation can take place.  Thus, precious fuel is continuously wasted during both storage and transfer operations, rendering long-duration expeditions—especially a human Mars mission—infeasible using current passive propellant tank pressure control methods.

Zero-Boil-Off (ZBO) or Reduced Boil-Off (RBO) technologies provide an innovative and effective means to replace the current passive tank pressure control design. This method relies on a complex combination of active, gravity-dependent mixing and energy removal processes that allow maintenance of safe tank pressure with zero or significantly reduced fuel loss.

Zero Boil-off Storage and Transfer: A Transformative Space Technology

At the heart of the ZBO pressure control system are two proposed active mixing and cooling mechanisms to counter tank self-pressurization.  The first is based on intermittent, forced, subcooled jet mixing of the propellant and involves complex, dynamic, gravity-dependent interaction between the jet and the ullage (vapor volume) to control the condensation and evaporation phase change at the liquid-vapor interface. The second mechanism uses subcooled droplet injection via a spraybar in the ullage to control tank pressure and temperature. While the latter option is promising and gaining prominence, it is more complex and has never been tested in microgravity where the phase change and transport behavior of droplet populations can be very different and nonintuitive compared to those on Earth.

Although the dynamic ZBO approach is technologically complex, it promises an impressive advantage over the currently used passive methods. An assessment of one nuclear propulsion concept for Mars transport estimated that the passive boil-off losses for a large liquid hydrogen tank carrying 38 tons of fuel for a three-year mission to Mars would be approximately 16 tons/year. The proposed ZBO system would provide a 42% saving of propellant mass per year. These numbers also imply that with a passive system, all the fuel carried for a three-year Mars mission would be lost to boil-off, rendering such a mission infeasible without resorting to the transformative ZBO technology.

The ZBO approach provides a promising method, but before such a complex technological and operational transformation can be fully developed, implemented, and demonstrated in space, important and decisive scientific questions that impact its engineering implementation and microgravity performance must be clarified and resolved.

The Zero-Boil-Off Tank (ZBOT) Microgravity Science Experiments

The Zero Boil-off Tank (ZBOT) Experiments are being undertaken to form a scientific foundation for the development of the transformative ZBO propellant preservation method. Following the recommendation of a ZBOT science review panel comprised of members from aerospace industries, academia, and NASA, it was decided to perform the proposed investigation as a series of three small-scale science experiments to be conducted onboard the International Space Station. The three experiments outlined below build upon each other to address key science questions related to ZBO cryogenic fluid management of propellants in space.

The ZBOT-1 Experiment: Self-Pressurization & Jet Mixing

The first experiment in the series was carried out on the station in the 2017-2018 timeframe. Figure 2 shows the ZBOT-1 hardware in the Microgravity Science Glovebox (MSG) unit of the station. The main focus of this experiment was to investigate the self-pressurization and boiling that occurs in a sealed tank due to local and global heating, and the feasibility of tank pressure control via subcooled axial jet mixing. In this experiment, the complicated interaction of the jet flow with the ullage (vapor volume) in microgravity was carefully studied. Microgravity jet mixing data was also collected across a wide range of scaled flow and heat transfer parameters to characterize the time constants for tank pressure reduction, and the thresholds for geyser (liquid fountain) formation, including its stability, and penetration depth through the ullage volume. Along with very accurate pressure and local temperature sensor measurements, Particle Image Velocimetry (PIV) was performed to obtain whole-field flow velocity measurements to validate a Computational Fluid Dynamics (CFD) model.

Some of the interesting findings of the ZBOT-1experiment are as follows:

• Provided the first tank self-pressurization rate data in microgravity under controlled conditions that can be used for estimating the tank insulation requirements. Results also showed that classical self-pressurization is quite fragile in microgravity and nucleate boiling can occur at hotspots on the tank wall even at moderate heat fluxes that do not induce boiling on Earth. 
• Proved that ZBO pressure control is feasible and effective in microgravity using subcooled jet mixing, but also demonstrated that microgravity ullage-jet interaction does not follow the expected classical regime patterns (see Figure 3).
• Enabled observation of unexpected cavitation during subcooled jet mixing, leading to massive phase change at both sides of the screened Liquid Acquisition Device (LAD) (see Figure 4). If this type of phase change occurs in a propellant tank, it can lead to vapor ingestion through the LAD and disruption of liquid flow in the transfer line, potentially leading to engine failure.
• Developed a state-of-the-art two-phase CFD model validated by over 30 microgravity case studies (an example of which is shown in Figure 3). ZBOT CFD models are currently used as an effective tool for propellant tank scaleup design by several aerospace companies participating in the NASA tipping point opportunity and the NASA Human Landing System (HLS) program.

The ZBOT-NC Experiment: Non-Condensable Gas Effects

Non-condensable gases (NCGs) are used as pressurants to extract liquid for engine operations and tank-to-tank transfer. The second experiment, ZBOT-NC will investigate the effect of NCGs on the sealed tank self-pressurization and on pressure control by axial jet mixing. Two inert gases with quite different molecular sizes, Xenon, and Neon, will be used as the non-condensable pressurants. To achieve pressure control or reduction, vapor molecules must reach the liquid-vapor interface that is being cooled by the mixing jet and then cross the interface to the liquid side to condense.

This study will focus on how in microgravity the non-condensable gases can slow down or resist the transport of vapor molecules to the liquid-vapor interface (transport resistance) and will clarify to what extent they may form a barrier at the interface and impede the passage of the vapor molecules across the interface to the liquid side (kinetic resistance). By affecting the interface conditions, the NCGs can also change the flow and thermal structures in the liquid.

ZBOT-NC will use both local temperature sensor data and uniquely developed Quantum Dot Thermometry (QDT) diagnostics to collect nonintrusive whole-field temperature measurements to assess the effect of the non-condensable gases during both self-pressurization heating and jet mixing/cooling of the tank under weightlessness conditions. This experiment is scheduled to fly to the International Space Station in early 2025, and more than 300 different microgravity tests are planned. Results from these tests will also enable the ZBOT CFD model to be further developed and validated to include the non-condensable gas effects with physical and numerical fidelity.

The ZBOT-DP Experiment: Droplet Phase Change Effects

ZBO active pressure control can also be accomplished via injection of subcooled liquid droplets through an axial spray-bar directly into the ullage or vapor volume. This mechanism is very promising, but its performance has not yet been tested in microgravity. Evaporation of droplets consumes heat that is supplied by the hot vapor surrounding the droplets and produces vapor that is at a much lower saturation temperature. As a result, both the temperature and the pressure of the ullage vapor volume are reduced. Droplet injection can also be used to cool down the hot walls of an empty propellant tank before a tank-to-tank transfer or filling operation. Furthermore, droplets can be created during the propellant sloshing caused by acceleration of the spacecraft, and these droplets then undergo phase change and heat transfer. This heat transfer can cause a pressure collapse that may lead to cavitation or a massive liquid-to-vapor phase change. The behavior of droplet populations in microgravity will be drastically different compared to that on Earth.

The ZBOT-DP experiment will investigate the disintegration, coalescence (droplets merging together), phase change, and transport and trajectory characteristics of droplet populations and their effects on the tank pressure in microgravity. Particular attention will also be devoted to the interaction of the droplets with a heated tank wall, which can lead to flash evaporation subject to complications caused by the Liedenfrost effect (when liquid droplets propel away from a heated surface and thus cannot cool the tank wall). These complicated phenomena have not been scientifically examined in microgravity and must be resolved to assess the feasibility and performance of droplet injection as a pressure and temperature control mechanism in microgravity.

Back to Planet Earth

This NASA-sponsored fundamental research is now helping commercial providers of future landing systems for human explorers. Blue Origin and Lockheed Martin, participants in NASA’s Human Landing Systems program, are using data from the ZBOT experiments to inform future spacecraft designs.

Cryogenic fluid management and use of hydrogen as a fuel are not limited to space applications. Clean green energy provided by hydrogen may one day fuel airplanes, ships, and trucks on Earth, yielding enormous climate and economic benefits. By forming the scientific foundation of ZBO cryogenic fluid management for space exploration, the ZBOT science experiments and CFD model development will also help to reap the benefits of hydrogen as a fuel here on Earth. 

PROJECT LEAD

Dr. Mohammad Kassemi (Dept Mechanical & Aerospace Engineering, Case Western Reserve University)

SPONSORING ORGANIZATION

Biological and Physical Sciences (BPS) Division, NASA Science Mission Directorate (SMD)

Related Terms

• Biological & Physical Sciences
• ISS Research
• Science-enabling Technology
• Technology Highlights

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NASA’s Zero-Boil-Off Tank Experiments To Enable Long-Duration Space Exploration

NASA ’s Zero-Boil-Off Tank experiments address the challenge of managing cryogenic propellants in space, crucial for future Moon and Mars missions, with potential Earth-bound benefits in hydrogen energy applications.

Do we have enough fuel to get to our destination? This is probably one of the first questions that comes to mind whenever your family gets ready to embark on a road trip. If the trip is long, you will need to visit gas stations along your route to refuel during your travel.

NASA is grappling with similar issues as it gets ready to embark on a sustainable mission back to the Moon and plans future missions to Mars. But while your car’s fuel is gasoline, which can be safely and indefinitely stored as a liquid in the car’s gas tank, spacecraft fuels are volatile cryogenic liquid propellants that must be maintained at extremely low temperatures and guarded from environmental heat leaks into the spacecraft’s propellant tank. And while there is already an established network of commercial gas stations in place to make refueling your car a cinch, there are no cryogenic refueling stations or depots at the Moon or on the way to Mars.

Furthermore, storing volatile propellant for a long time and transferring it from an in-space depot tank to a spacecraft’s fuel tank under microgravity conditions will not be easy since the underlying microgravity fluid physics affecting such operations is not well understood. Even with today’s technology, preserving cryogenic fuels in space beyond several days is not possible and tank-to-tank fuel transfer has never been previously performed or tested in space.

Propellant Management in Space: Overcoming Boil-Off

Heat conducted through support structures or from the radiative space environment can penetrate even the formidable Multi-Layer Insulation (MLI) systems of in-space propellant tanks, leading to boil-off or vaporization of the propellant and causing tank self-pressurization. The current practice is to guard against over-pressurizing the tank and endangering its structural integrity by venting the boil-off vapor into space.

Onboard propellants are also used to cool down the hot transfer lines and the walls of an empty spacecraft tank before a fuel transfer and filling operation can take place. Thus, precious fuel is continuously wasted during both storage and transfer operations, rendering long-duration expeditions—especially a human Mars mission—infeasible using current passive propellant tank pressure control methods.

Introducing ZBO: A New Horizon in Fuel Efficiency

Zero-Boil-Off (ZBO) or Reduced Boil-Off (RBO) technologies provide an innovative and effective means to replace the current passive tank pressure control design. This method relies on a complex combination of active, gravity-dependent mixing and energy removal processes that allow maintenance of safe tank pressure with zero or significantly reduced fuel loss.

Zero Boil-off Storage and Transfer: A Transformative Space Technology

At the heart of the ZBO pressure control system are two proposed active mixing and cooling mechanisms to counter tank self-pressurization. The first is based on intermittent, forced, subcooled jet mixing of the propellant and involves complex, dynamic, gravity-dependent interaction between the jet and the ullage (vapor volume) to control the condensation and evaporation phase change at the liquid-vapor interface.

The second mechanism uses subcooled droplet injection via a spraybar in the ullage to control tank pressure and temperature. While the latter option is promising and gaining prominence, it is more complex and has never been tested in microgravity where the phase change and transport behavior of droplet populations can be very different and nonintuitive compared to those on Earth.

Although the dynamic ZBO approach is technologically complex, it promises an impressive advantage over the currently used passive methods. An assessment of one nuclear propulsion concept for Mars transport estimated that the passive boil-off losses for a large liquid hydrogen tank carrying 38 tons of fuel for a three-year mission to Mars would be approximately 16 tons/year. The proposed ZBO system would provide a 42% saving of propellant mass per year.

These numbers also imply that with a passive system, all the fuel carried for a three-year Mars mission would be lost to boil-off, rendering such a mission infeasible without resorting to the transformative ZBO technology.

The ZBO approach provides a promising method, but before such a complex technological and operational transformation can be fully developed, implemented, and demonstrated in space, important and decisive scientific questions that impact its engineering implementation and microgravity performance must be clarified and resolved.

The Zero-Boil-Off Tank (ZBOT) Microgravity Science Experiments

The Zero Boil-off Tank (ZBOT) Experiments are being undertaken to form a scientific foundation for the development of the transformative ZBO propellant preservation method. Following the recommendation of a ZBOT science review panel comprised of members from aerospace industries, academia, and NASA, it was decided to perform the proposed investigation as a series of three small-scale science experiments to be conducted onboard the International Space Station . The three experiments outlined below build upon each other to address key science questions related to ZBO cryogenic fluid management of propellants in space.

The ZBOT-1 Experiment: Self-Pressurization & Jet Mixing

The first experiment in the series was carried out on the station in the 2017-2018 timeframe. Figure 2 shows the ZBOT-1 hardware in the Microgravity Science Glovebox (MSG) unit of the station. The main focus of this experiment was to investigate the self-pressurization and boiling that occurs in a sealed tank due to local and global heating, and the feasibility of tank pressure control via subcooled axial jet mixing. In this experiment, the complicated interaction of the jet flow with the ullage (vapor volume) in microgravity was carefully studied.

Microgravity jet mixing data was also collected across a wide range of scaled flow and heat transfer parameters to characterize the time constants for tank pressure reduction, and the thresholds for geyser (liquid fountain) formation, including its stability, and penetration depth through the ullage volume. Along with very accurate pressure and local temperature sensor measurements, Particle Image Velocimetry (PIV) was performed to obtain whole-field flow velocity measurements to validate a Computational Fluid Dynamics (CFD) model.

Some of the interesting findings of the ZBOT-1experiment are as follows:

• Provided the first tank self-pressurization rate data in microgravity under controlled conditions that can be used for estimating the tank insulation requirements. Results also showed that classical self-pressurization is quite fragile in microgravity and nucleate boiling can occur at hotspots on the tank wall even at moderate heat fluxes that do not induce boiling on Earth.
• Proved that ZBO pressure control is feasible and effective in microgravity using subcooled jet mixing, but also demonstrated that microgravity ullage-jet interaction does not follow the expected classical regime patterns (see Figure 3).
• Enabled observation of unexpected cavitation during subcooled jet mixing, leading to massive phase change at both sides of the screened Liquid Acquisition Device (LAD) (see Figure 4). If this type of phase change occurs in a propellant tank, it can lead to vapor ingestion through the LAD and disruption of liquid flow in the transfer line, potentially leading to engine failure.
• Developed a state-of-the-art two-phase CFD model validated by over 30 microgravity case studies (an example of which is shown in Figure 3). ZBOT CFD models are currently used as an effective tool for propellant tank scaleup design by several aerospace companies participating in the NASA tipping point opportunity and the NASA Human Landing System (HLS) program.

The ZBOT-NC Experiment: Non-Condensable Gas Effects

Non-condensable gases (NCGs) are used as pressurants to extract liquid for engine operations and tank-to-tank transfer. The second experiment, ZBOT-NC will investigate the effect of NCGs on the sealed tank self-pressurization and on pressure control by axial jet mixing. Two inert gases with quite different molecular sizes, Xenon, and Neon, will be used as the non-condensable pressurants. To achieve pressure control or reduction, vapor molecules must reach the liquid-vapor interface that is being cooled by the mixing jet and then cross the interface to the liquid side to condense.

This study will focus on how in microgravity the non-condensable gases can slow down or resist the transport of vapor molecules to the liquid-vapor interface (transport resistance) and will clarify to what extent they may form a barrier at the interface and impede the passage of the vapor molecules across the interface to the liquid side (kinetic resistance). By affecting the interface conditions, the NCGs can also change the flow and thermal structures in the liquid.

ZBOT-NC will use both local temperature sensor data and uniquely developed Quantum Dot Thermometry (QDT) diagnostics to collect nonintrusive whole-field temperature measurements to assess the effect of the non-condensable gases during both self-pressurization heating and jet mixing/cooling of the tank under weightlessness conditions. This experiment is scheduled to fly to the International Space Station in early 2025, and more than 300 different microgravity tests are planned. Results from these tests will also enable the ZBOT CFD model to be further developed and validated to include the non-condensable gas effects with physical and numerical fidelity.

The ZBOT-DP Experiment: Droplet Phase Change Effects

ZBO active pressure control can also be accomplished via injection of subcooled liquid droplets through an axial spray-bar directly into the ullage or vapor volume. This mechanism is very promising, but its performance has not yet been tested in microgravity. Evaporation of droplets consumes heat that is supplied by the hot vapor surrounding the droplets and produces vapor that is at a much lower saturation temperature. As a result, both the temperature and the pressure of the ullage vapor volume are reduced. Droplet injection can also be used to cool down the hot walls of an empty propellant tank before a tank-to-tank transfer or filling operation. Furthermore, droplets can be created during the propellant sloshing caused by acceleration of the spacecraft, and these droplets then undergo phase change and heat transfer. This heat transfer can cause a pressure collapse that may lead to cavitation or a massive liquid-to-vapor phase change. The behavior of droplet populations in microgravity will be drastically different compared to that on Earth.

The ZBOT-DP experiment will investigate the disintegration, coalescence (droplets merging together), phase change, and transport and trajectory characteristics of droplet populations and their effects on the tank pressure in microgravity. Particular attention will also be devoted to the interaction of the droplets with a heated tank wall, which can lead to flash evaporation subject to complications caused by the Liedenfrost effect (when liquid droplets propel away from a heated surface and thus cannot cool the tank wall). These complicated phenomena have not been scientifically examined in microgravity and must be resolved to assess the feasibility and performance of droplet injection as a pressure and temperature control mechanism in microgravity.

Back to Planet Earth

This NASA-sponsored fundamental research is now helping commercial providers of future landing systems for human explorers. Blue Origin and Lockheed Martin, participants in NASA’s Human Landing Systems program, are using data from the ZBOT experiments to inform future spacecraft designs.

Cryogenic fluid management and use of hydrogen as a fuel are not limited to space applications. Clean green energy provided by hydrogen may one day fuel airplanes, ships, and trucks on Earth, yielding enormous climate and economic benefits. By forming the scientific foundation of ZBO cryogenic fluid management for space exploration, the ZBOT science experiments and CFD model development will also help to reap the benefits of hydrogen as a fuel here on Earth.

Project Lead

Dr. Mohammad Kassemi (Dept Mechanical & Aerospace Engineering, Case Western Reserve University)

Sponsoring Organization

Biological and Physical Sciences (BPS) Division, NASA Science Mission Directorate (SMD)

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Experimental Study of Electrostatic Hazards during Simulated Aircraft Fuel Tank Loading by Ground Fueling Systems 04-14-02-0006

This also appears in sae international journal of fuels and lubricants-v130-4ej.

Electrostatic discharge during aircraft refueling operations has long been recognized as a safety hazard. To reduce the chances of this happening, different practices were developed, the most common being the addition of a static dissipator additive (SDA). Nowadays, the SDA is a well-established requirement in all the leading jet-fuel specifications and is in widespread use in commercial and military aviation industries. To deepen the understanding of the electrostatic behavior of nonconductive jet fuel and SDA, the Israeli Air Force (IAF) has conducted small-scale refueling tests in a simulated aircraft fuel tank. In these tests, the effect of flow rate, residence time, SDA concentration, bounding, grounding, and the method of filling were evaluated by measuring the electrostatic field strength generated. The simulation of the aircraft fuel tank was obtained using a nonconductive plastic tank jointed with a small faucet at the bottom. As such, the results were referred to as the worst-case scenario of fueling operation. Through this arrangement it was possible to ratify the common techniques applied for diminishing electrostatic hazards—i.e., increasing the electrical conductivity of the fuel, decreasing the flow rate, and increasing the residence time of the fuel

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Rapid Prototyping and Experimental Design

Epoxy and fuel resistance tests, part 2-choosing an epoxy for a fuel tank.

This is the penultimate article in the rapid prototyping series for now, and the last of our discussions on shop experiments. In the next article, we will look at a couple of opportunities for further education for those interested in learning more about composites and experimental design.

Last time we discussed some of the basic properties concerning epoxies. Based on that information, we conducted a set of tests designed to determine which epoxy would be best for a particular application, in this case the construction of a composite fuel tank.

To minimize pinholes, PrimeTex (left) has very little open area compared to regular carbon fiber.

Which Epoxy to Choose?

Like strength, chemical resistance of epoxy systems is strongly tied (among other factors) to the degree of crosslinking achieved in the cured part. For this reason, when constructing composite fuel tanks, the biggest advantage you can give yourself is to (a) choose a system with a proven history of success when used for fuel tanks, and (b) post cure the tank to the highest permissible temperature.

The SR-1 race plane that has been the basis of this series has integral wing fuel tanks. One proven method of sealing such tanks is to use a novolac sealer like Rhino (Jeffco) 9700, which forms a thick (.05-.15 inch, depending on application technique and number of coats) surface coat for sealing the inside of the tank. This is the factory specified method used on Lancairs, for example.

Close-up of typical coupons (left) and coupon in a test jar (right). Labeling nomenclature indicates epoxy brand (J=Jeffco, M=MGS, Z=E-Z Poxy), post cure temp (3=30 C/86 F, 5=50 C/122 F, 8=80 C/176 F), environment (V=avgas, E=ethanolated mogas, A=acetone). Each test had two coupons. Thus, the coupon on the left is E-Z Poxy, 50 C post cure, avgas exposure, coupon 1 of 2.

Unfortunately this method is somewhat heavy and thus not ideal for the SR-1, which is a severely weight-critical aircraft. However, Rutan-style aircraft builders (Long-EZs, etc.) have successfully built wing strake fuel tanks without sealer for years. Based on personal and forum discussions on this topic, I decided to seal my tanks by applying (over the existing sandwich skin) a skim layer of neat resin, followed by another skim layer of resin mixed with cabosil (to the consistency of petroleum jelly), followed by a final layer of Hexcel PrimeTex 284 carbon fiber with an approximately 40/60 fiber/resin ratio. (If you have read previous articles in this series, you will recognize 40/60 as being a very resin-rich layup.) PrimeTex 284 differs from bog-standard 284 in having very low open area, thus minimizing pinholes.

The next question was which epoxy would be most fuel resistant? Now, I have no intention of ever putting alcohol-laced mogas into the tank (a major reason for tank failures, as alcohol attacks epoxy). But while some tanks are fuel proof simply by virtue of having walls thick enough so that any chemical degradation never has a chance to make a hole through them, the thinness of my sealing layer (about .020 inch) meant that I wanted to assure that I had the most chemically resistant epoxy coating possible. I therefore decided to test three different epoxies for chemical resistance.

Figure 1: Test Matrix. Two coupons were used for each test for a total of 54 coupons.

The test matrix consists of three epoxies, three post cure treatments, and three chemical environments, giving 27 test permutations, with two coupons per test (see Figure 1), for a total of 54 coupons tested over a period of 18 months.

According to various sources, E-Z Poxy E-Z 10 resin with E-Z 87 slow hardener is the epoxy of choice for fuel tanks for Rutan aircraft builders. According to EAA technical counselor and former Shell “Answer Man” for epoxy resins, Gary Hunter, E-Z 87 is the only aromatic amine hardener available for homebuilders, as compared to aliphatic and cycloaliphatic amines, which are more common in commercially available systems. While from a health and safety standpoint aromatic amines are nastier than the aliphatic/cycloaliphatic amines, they are superior for chemical resistance.

According to Gary, MGS 285/287 uses the aforementioned cycloaliphatic amine hardener, and is what I use generally for SR-1 parts, so I also wanted to test that system (it is also what the underlying wing skin is made with). Finally, I chose Jeffco 1307/3176, as it is a less expensive system that is popular among homebuilders.

Neither aviation gas (left) nor mogas test coupons (middle) showed any obvious physical degradation. Acetone coupons (right) showed moderate to severe degradation.

Jeffco acetone test coupons clearly show the effect of post curing in providing chemical resistance protection. (Left) Room-temperature post cure, (Middle) 122 F post cure, (Right) 176 F post cure.

Coupon Preparation

All coupons were initially cured for 24 hours at room temp (approximately 85 F), followed by no post cure or a 24-hour post cure at 122 F or 176 F. Coupons were nominally 4.0×1.5x 1/8 inch, and were tested for Barcol hardness and weighed before being placed in a 16-ounce glass jar filled with either 100LL, 93 octane E10 auto gas, or acetone. The percentage of ethanol in the E10 mogas was 8.4%, as determined by a water admixture test.

Although one would not normally expect to have parts subjected to long-term immersion in a solvent like acetone, it was included as a means of examining the performance of coupons in a strong solvent environment, as a sort of proxy for a longer-term test. Whether this can be used to infer/extrapolate performance in a less harsh but longer-term environment is definitely debatable, and possibly specious. As Peter Meszaros of Airheart Distributing (North American distributors of MGS epoxy) points out by way of illustration, a paper towel soaked in acetone holds up just fine, but one soaked in water quickly disintegrates. So the acetone tests should be viewed in that light, but the results were nonetheless interesting and confirm Gary’s exoneration to builders that there is no substitute for post curing to achieve chemical resistance.

The test began June 19, 2016 and ended January 9, 2018. At the end of the test, coupons were removed and allowed to dry, then weighed.

Figure 2. Barcol hardness versus post cure temperature for different brands of epoxy.

None of the coupons immersed in either 100LL or 93 octane E10 mogas showed any visible signs of deterioration. No particular difference among coupons based on brand or post cure was discernible. Almost all coupons, however, did gain weight over the period of the test, with weight gain from avgas being least and acetone being greatest. As can be seen in Figure 3, post curing reduced the amount of weight gain.

Figure 3: Warmer post cure temperatures reduced the amount of coupon weight gain.

Coupons immersed in acetone showed degradation ranging from slight to severe. Figure 4 shows a graphic representation of these coupons, with degradation being given a number value based on a subjective assessment of the degree of degradation, with 1 representing no degradation and 4 representing severe degradation. E-Z Poxy and MGS performed similarly, but surprisingly Jeffco outperformed both. That said, differences in post curing had a larger impact on degradation than differences in epoxy brand. This again appears to confirm Gary’s position that the most important consideration when constructing parts for chemical resistance is achieving a good post cure.

Figure 4: Higher post cure temperatures reduced the amount of coupon degradation from acetone (1 represents no degradation and 4 represents severe degradation).

It should be noted that with only two coupons per sample, these results lack any statistical significance. The results should be interpreted as observed trends.

That wraps up our look into epoxy. Next time we’ll finish up the series with a look at continuing education classes by Abaris Technology of Reno, Nevada, and Micro-Measurements of Raleigh, North Carolina. Until then, happy building.

Acknowledgements: Many thanks to Gary Hunter and Peter Meszaros for answering my questions while I was preparing these epoxy articles. Klaus Savier of Lightspeed Engineering provided access to his post curing oven for the coupon tests as well as his Barcol hardness tester. Ricardo Stary, the 2016 SR-1 Project intern, fabricated the coupons.

E-Z Poxy for Fuel Tanks

The E-Z Poxy line of products has a long history of use in the aviation industry, being originally developed for the Long-EZ kit aircraft. Of the hardeners, E-Z 83B, 87B, and 92B are almost identical, with only a slight variation in accelerator to help vary gel time. The differences in fuel resistance between these three should be negligible.

E-Z 84B is a bit different. All hardeners have a similar resistance to diesel fuel (containing 5% biodiesel), with a slight advantage given to E-Z 84B over the 83B/87B/92B group of products. However, when exposed to gasoline (containing 10% ethanol) the E-Z 83B/87B/92B group of hardeners are definitely more fuel resistant than E-Z 84B. In addition, when directly exposed to solvents (50/50 isopropyl alcohol/xylene blend), 83B/87B/92B are almost twice as resistant as E-Z 84B. Bottom line, for the best fuel and solvent resistance use E-Z 10A Resin with either E-Z 83B, 87B or 92B Hardeners.

—Mike Schroeder, Endurance Technologies

Note: Mike doesn’t mention post curing, which we have shown to be the single most important factor in chemical resistance. 83B and 87B have identical post cure Tg, so either one should be fine for use in fuel systems as long as they are appropriately post cured.

Shot Bags by Lowing Light & Grip

When starting my race plane project, I visited a friend’s composites shop and noticed a number of leather, lead-filled shot bags holding things down. Searching where to buy some for myself, I came across steel shot bags offered by Lowing Light & Grip (LLG). Adam Boeskool, the company’s product manager, donated a few bags to the SR-1 project in return for feedback that might help him develop a set of bags for the experimental aircraft industry.

Lowing Light & Grip shot bag kit for homebuilders. The company makes shot bags for the film industry, but has supplied bags to big names in aerospace as well.

I find the bags incredibly useful. I mostly use them to stabilize things, for example when sanding, and also to hold templates and cloth in place when cutting carbon fiber. From a health safety point of view, I like that the shot is steel instead of lead. The butterfly grips make them much easier to pick up and move than handleless bags, and the canvas conforms nicely over parts. Mine were on the heavy side though, so I thought the shapes and weights could be improved for homebuilders. Based on that feedback, Adam put together a set of three bags (see photo) and shipped them to Jay Pratt at RV Central (a builder assist center) for additional feedback (Jay also received his bags free of charge in return for feedback).

Jay really likes his bags. “I don’t know how I’d live without them at this point. I use them almost every day for all sorts of tasks. I have a couple of 25-pound, round, metal-forming bags, but I don’t use them nearly as much as I now use these. They are just too heavy and not really the right shape. The LLG tube weight is fantastic for sanding, drilling, and deburring.

“I use them on the workbench more than anywhere else, and for composites work. For example, when riveting the stabilizer skins, the tube weight stabilizes the part so it’s much easier to rivet. And the fairings that come with the RV kits aren’t exactly known for the best fit, so when we rework them for a tighter fit, we lay up the fiberglass, put on a sheet of wax paper, then use the weight to hold it tight against the structure. We’ve done that with tail fairings and also the RV-8 canopy fairing, where I prop it up against the fuselage with a broom stick.

“I’m pretty amazed how much I have used them. I even use them for non-aviation stuff—I used one to help change a bike tire the other day.”

The shot bag kit for homebuilders is $115, plus about $35 for shipping. Would Jay pay that much for a set? “Well, homebuilders can be pretty tight. But knowing what I know now—yes, for sure. I’ve probably spent that much just on lead shot. I would recommend these to anybody; they are very useful.” LLG carries many other sized weights as well, which you can see at their website, www.lowinglight.com .

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• Corpus ID: 108425747

Aircraft Fuel Tank Inerting System

• R. L. Johnson , J. Gillerman
• Published 1 July 1983
• Engineering, Environmental Science

7 Citations

Advanced air separation module performance evaluation, the oxygen concentration measurement of an aircraft fuel tank inerting system, numerical study of the influence of ambient pressure on the inerting effect of an aircraft fuel tank inerting system, analysis of the influence of on-board temperature and pressure control system on inert gas generating performance of hollow fiber membrane, evaluating and augmenting fuel-saving benefits obtained in aircraft formation flight.

• Highly Influenced
• 15 Excerpts

Benefits of Formation Flight of Extended Duration Considering Fuel Burn

Nist special publication 984, related papers.

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