Alternative fuel use is on the rise and, with it, alternative fuel vehicle upfits. When transitioning to compressed natural gas, or CNG, there are certain questions you should ask to be sure that you’re getting the proper vehicle fuel tank for the application. “What you have to look at first and foremost is the range of driving distance that the fleet needs. You can essentially work backwards from there: How much fuel and mileage are you going to need for this specific trip or application of the fleet?” explains Chris Hanners, alternative fuels product manager, Worthington Industries.
Certain tanks work better for certain applications—a fact that you should be aware of during the CNG vehicle specification process. “The end-customer should understand that there are different fuel tanks out there and it’s not just one that—specifically speaking—a fuel systems integrator would select,” says Hanners. Because the fuel tank is arguably the most vital piece of the fuel system—and certainly the most expensive—it’s important to know exactly what will best suit your fleet. “A CNG tank should be considered not only from the vehicle integrator’s point of view, but also the end-customer’s. For CNG fuel systems, several different CNG tanks can be selected or used.”
CNG FUEL TANK TYPES
One of the main factors in deciding which tank you’re going to use is weight. If you don’t care about the weight, Type I is the best option. Increasing payload is often an important objective; in order to decrease GVW, a Type III or IV tank would be better.
- Type I: Type I CNG fuel tanks are all-steel or all-metal tanks. If weight is not a factor, Type I tanks are the most robust, safest, and cost-effective.
- Type II: Type II CNG fuel tanks are steel or metal. The sidewall of Type II tanks is hoop-wrapped with carbon fiber to help lightweight the tank.
- Type III: Type III CNG fuel tanks are among the lightest. They have an aluminum metal liner and are encased in carbon fiber.
- Type IV: Type IV CNG fuel tanks are also among the lightest options. A Type IV tank actually has a plastic liner and is encased in carbon fiber.
“Wrapping the lighter tanks in carbon fiber is a pressure thing. In order to contain the pressure as you decrease the thickness of the metal wall or liner, you have to have something to support that. The carbon fiber contains the pressure while giving you the added benefit of being lighter,” says Hanners.
Below are a few questions fleet managers should ask before and during the CNG vehicle specification process.
WHAT TYPE OF CNG FUEL TANKS WILL YOU SPECIFY?
For most heavy-duty applications, you’re predominantly going to spec a Type III or Type IV tank. That’s because weight and payload are very important for heavy-duty trucks and that particular industry. That said, there are some differences between Type IIIs and Type IVs. They’re known for being the lightest tanks that you can get, but they do have some different performance characteristics.
Type III has an aluminum metal liner, which is essentially a gas-tight, seamless liner. This presents a couple of differences from a Type IV—from a fleet perspective. For instance, in a fast-fill situation (timely fill vs overnight fill), Type III tanks have the ability to dissipate heat much better than Type IV, which utilizes a plastic liner.
The Type IV’s plastic liner is not as good of a conductor of heat as Type III’s aluminum. When it is filled with CNG to the pressure of 3,600 psi, it quickly generates heat, which allows that pressure to build. The aluminum metal liner allows the heat essentially to conduct outward, which allows a more efficient fill.
Featured Image: Fleet operators who take an active role in the fuel system specification process of their new CNG-dedicated vehicles, including components like fuel tanks, can gain maximized driving range, increased safety, and improved total cost of ownership. In this image, the CNG fuel tanks are located in the cabinet behind the cab.
Above: Type III CNG fuel tanks feature a carbon fiber outer shell with an aluminum inner liner that is seamless—without welds, joints, or connections—virtually eliminating gas permeation.
HOW WOULD YOU VALIDATE THE DRIVING RANGE PLANS?
“Have an understanding of how you’re going to calculate your fuel range,” Hanners says. “When it comes down to it—although there are several different ways to calculate the capacity of gas that you will get—usable diesel gallon equivalence is the one that matters the most. How far are you going to get on a particular volume or capacity within your fuel system? You want to have as good of an understanding of that as possible, because the difference in tanks can impact that, as well as fuel systems providers.”
HOW WOULD A PRODUCT BE SUPPORTED LONG-TERM?
“The majority of tanks right now are qualified to a 15- or 20-year lifecycle. Some are even now pushing 25-year longevity,” Hanners says. “With those tanks basically having a lifecycle that will span or possibly outlive the life of the vehicle, you’re going to want to make sure that the product is supported if and when you encounter any issues with your tank throughout the life of the vehicle.”
Specifying a CNG fuel tank is just like any other upfit in that you should know what to get to maximize your fleet’s efficiency. Knowing what questions to ask before making the purchase is not only a smart move, it’s the right move.
FOR MORE INFORMATION:
Find out more about Worthington Industries’ CNG tanks and other products and services, visit www.worthingtonindustries.com.