The research arm of United Technologies Corp. has developed a fuel tank made of a special composite material that could help get more natural gas vehicles on the road and reduce greenhouse gas emissions.
It's the first commercially viable conformable natural gas storage tank in the world, said Ellen Y. Sun, project leader for the tank's development at United Technologies Research Center (UTRC) in East Hartford, where all the innovation and engineering occurred.
It's conformable because it's flexible in size, flat and stackable, allowing the tank to be placed under a pickup truck bed or car trunk, for example, or perhaps elsewhere in a vehicle chassis.
The flat design also takes up less space in vehicles and stores more gas than traditional metal-cylinder tanks. It also weighs about half as much as a steel cylinder. A tank mock-up in the lab tipped the scale at about 80 pounds and measured 8 inches tall, 32 inches wide and 48 inches long.
"One of the main reasons why there are not too many natural gas vehicles, especially passenger vehicles in the U.S., is because of the storage technology," and the fact that tanks take up too much vehicle space, said Sun, a materials scientist who leads the advanced materials group at UTRC.
In a 2014 report on the Honda Civic natural gas vehicle, for example, Consumer Reports noted roughly half the trunk space was taken up by the tank, leaving only 6 cubic feet left for luggage.
Honda discontinued the vehicle after 2015 citing challenges with consumer demand and natural gas refueling infrastructure.
One advantage of UTRC's conformable tank is its flexibility, Sun noted. Tanks of different height, width and length can be made to fit into various spaces available on vehicles.
UTRC has licensed the tank technology to Adsorbed Natural Gas Products Inc. of Chester, N.J., to develop and produce the first commercially viable adsorbent-based, low-pressure natural gas storage tank for motor vehicles.
ANGP plans to use the tank for natural gas stored at 900 psi, much lower than the 3,200 psi to 3,600 psi typical for compressed natural gas. Adsorbed's natural gas technology uses a highly porous adsorbent material, activated carbon, in the tank to densely store natural gas molecules at the lower pressure. Under controlled depressurization, the molecules release and exit ANGP's storage system in response to engine demand.
"The industry has been waiting more than three decades for the union of low-pressure adsorbed natural gas technology and a conformable tank," said Bob Bonelli, ANGP co-founder and CEO. "UTRC's conformable tank provides 30 percent more storage capacity than multiple cylinders occupying the same envelope."
If that helps make natural gas vehicles more desirable, then the environment stands to benefit.
Switching from gasoline and diesel fuels to compressed natural gas can mean significantly lower amounts of carbon dioxide and air pollutants, including carbon monoxide, nitrogen oxide, nonmethane hydrocarbon, particulate matter, and toxic and carcinogenic pollutants, according to the U.S. Department of Energy. It can also help reduce America's dependence on foreign oil, thanks to natural gas' abundant supply.
Until gasoline prices plummeted late last year, compressed natural gas had historically been significantly cheaper than gasoline on a per gasoline gallon equivalent (GGE) basis, according to data reported in the quarterly Clean Cities Alternative Fuel Price Report from the Department of Energy. The latest report, based on data from the first two weeks of January, showed CNG at $2.09 GGE and gasoline at $1.98 per gallon.
UTRC's conformable tank design is ideal for lower-pressure adsorbed natural gas, enabling thinner tank walls and lower material costs, which ANGP hopes will lead to mass-market acceptance of its adsorbed natural gas storage technology for vehicles.
Using natural gas at lower pressure also saves significant money on fueling stations, said Matt Bonelli, ANGP's vice president of marketing.
Fuel dispensers need smaller, less expensive compressors and consume less energy, he said.
There also is an appliance that allows natural gas to be pumped at home from residential gas lines into vehicles, Bonelli said, and ANGP is looking into a home-refueling appliance that would plug into a typical 120-volt outlet, tap the home's natural gas supply and pressurize it to 900 psi to allow for home-based fueling.
Separately, General Electric had worked with a partner on a design for an inexpensive, high-speed home refueling appliance, but ended that program last year. GE researchers, though, are continuing to explore home-refueling technologies on their own, Todd Alhart, a spokesman for GE Global Research, said in an email.
While UTRC is working with ANGP to commercialize the tank technology for natural gas vehicles, UTRC also is exploring potential applications for the technology across other UTC divisions, from buildings to aerospace. It's too early to pinpoint specific applications, but there is a range of opportunities, Sun said.
"This particular application is for natural gas, but really the technology is for pressure vessels, so if there is a need to store pressurized gas or liquid inside a container and we wanted to maximize the usage of the space, this is the technology," Sun said. "This is essentially applicable for any application where a pressure vessel or pressure device is needed and space is a premium."
The tank can handle up to 3,600 psi. UTRC, which began developing the technology in late 2012, created prototypes for compressed natural gas applications in that psi range, David Parekh, corporate vice president of research and director at UTRC, said in a written statement. But when UTRC looked for ways to commercialize the technology, it partnered with ANGP to bring UTRC's design to the low-pressure market, he said.
Creating the tank, a carbon fiber reinforced polymer material, involved staff from myriad UTRC divisions, including design, structural analysis, manufacturing, advanced materials and technology transfer to market, Sun said.
"It really fits very well with the type of work we do here at UTRC, being the central research facility for UTC," Sun said. "We are really the innovation engine for UTC and developing game-changing technologies."
Matt Bonelli said UTRC's conformable tank technology is instrumental in what ANGP is trying to accomplish. The tank's weight is less than aluminum cylinder tanks ANGP built for its first-generation onboard storage system and stores more gas in the same space, "which is incredible," he said.
"So they've really given us the opportunity to help make this dream that people have had for over 30 years, a real reality," Bonelli said.
He hopes to see the comfortable tank system commercialized next year, when ANGP is targeting the second-generation, conformable tank system to be certified and ready to go.
"Right now we are in the process of choosing a manufacturer to first prototype and then we'll get going," Bonelli said.
"Certainly, there's something to be gained by a major auto manufacturer starting to design their vehicles to accept these types of systems," he said. "Right now, if you want a natural gas vehicle, your options are pretty limited in the U.S."
He thinks operators of light-duty fleets, including passenger cars and SUVs, will be interested in using the natural gas system using UTRC's tank because it's lighter, less expensive and stores more gas.
"We're focused for right now mostly on light-duty, because that's where the market opportunity is," he said.
According to the Department of Energy, there currently are limited light- and heavy-duty natural gas vehicles available from original equipment manufacturers. However, qualified system retrofitters can also reliably convert vehicles for natural gas operation.
Matt Bonelli thinks bi-fuel vehicles, for now, are the best option for people to use natural gas, tapping it for around-town driving and commuting, with the ability to switch to gasoline for longer trips.
"I think that natural gas is a great fuel source for vehicles to get us to bridge that gap from gasoline to maybe hydrogen some day — that would be fantastic," he said.