by Wendy Leavitt, contributing editor

It is fair to say that natural gas has become the darling of the alternative fuel world, at least for now. The price differential between natural gas and diesel or gasoline is compelling, as is the fuel’s “green” emissions profile and the fact that the U.S. is producing lots of natural gas right here at home.

Compressed natural gas (CNG), in spite of its shorter operating range and generally lower GVW limitations, has enjoyed an early lead over liquefied natural gas (LNG). For many local or regional operations, it can be a rightsized solution for everything from beverage delivery vehicles to transit buses, sanitation trucks to the pickups in use by the parks department.

If you are considering adding CNG vehicles to your own business, it is critical that you do your homework first. Natural gas requires some special considerations at virtually every step of the deployment process.

Understanding the choices
First of all, there is not just one type of CNG engine available. There are several choices, each with different performance characteristics. A Houston-based company called Nat G Conversions offers a good overview of the various types of CNG vehicles available:

Dedicated: A dedicated CNG vehicle is one that runs only on CNG.

Mixed fuel: Any vehicle that blends CNG with diesel or other fuels. In practice, there are some engines, like the Cummins Westport ISX, that use a small amount of diesel, but basically act as dedicated CNG engines. And some engines, like the Cummins Westport ISL G, can operate on either CNG or LNG.

Dual fuel: A dual-fuel system blends natural gas with diesel by injecting it into the turbocharger; however, the vehicle can still run on 100% diesel. That means if you run out of CNG you can keep going. Depending on the load, a dual-fuel system will use up to 50% CNG on average.

Bi-fuel: Bi-fuel systems are also called “switchable” systems because you can switch between gasoline and CNG.
The good news about all-CNG vehicles is that you don’t need to worry about buying two different fuels or about mandated emissions aftertreatment in the case of diesel; however, it does limit practical operating range. The good news about dual-fuel and bi-fuel vehicles is that so-called “range anxiety” goes away.

In heavy-duty vehicles, dual-fuel, compression-ignited engines are slightly more fuel-efficient than spark-ignited, dedicated natural gas engines. However, a dual-fuel engine increases the complexity of the fuel-storage system by requiring storage of both types of fuel.

OEM or retrofit?
More truck OEMs are beginning to offer CNG vehicles that can be purchased right through a truck dealership. But most of the light- and medium-duty CNG vehicles in operation around the U.S. today resulted from a conversion process or retrofit, according to CNG Now, a website sponsored by companies in the natural gas industry.

Certified installers will usually only perform a CNG conversion on new or nearly new vehicles, CNG Now notes, and they use CNG “conversion kits” to do so. These kits must meet Environmental Protection Agency (EPA) and/or California Air Resources Board (CARB) requirements. Different states have different requirements, so you will want to make sure you know what the requirements are in your area before moving ahead with a CNG conversion.

Fueling and GVW
Andy Douglas, national sales manager for specialty markets at Kenworth Truck Co., recently prepared a brief guide to help fleets considering natural gas, either CNG or LNG. He stresses the importance of taking into account the operating range for natural gas vehicles as well as the load you need to carry. “In general, if your operating range is over 400 mi., it is usually best to go with LNG,” Douglas says. “Under 400 mi., CNG can be an option. CNG can be used up to 66,000 lbs. GVW, with some severe-duty applications going up to 80,000 lbs. GVW.”

The task of building out a natural gas fueling infrastructure in the U.S. and Canada has been picking up speed over the past year, so range will, over time, become less of an issue. Even if natural gas is readily available along most truck lanes, drivers will still have to accept the fact that more frequent fuel stops are a reality with natural gas—especially CNG. The good news is that drivers don’t need special training to pump CNG, and many CNG stations compress the gas into onsite storage cylinders, notes Douglas, which allows it to be dispensed quickly.

There is sometimes a tendency to over-spec when choosing natural gas fuel tanks, Douglas adds, since operators are in the habit of carrying a two- or three-day supply of diesel onboard. However, “in many cases, it is often impractical to carry much more than a day’s supply of natural gas,” he says. “Natural gas fuel tanks can also be expensive, so consider carrying only enough fuel for a full day’s work, plus a 10% reserve.”

How about ROI?
Chesapeake Energy is certainly not a small fleet, but this mega-operation has lessons to offer about the ROI on CNG trucks that are applicable to carriers of any size. Chesapeake began to convert its entire fleet of almost 6,000 vehicles (80% trucks and 20% sedans and SUVs) to run on compressed natural gas in late 2007. According to Nate Pumphrey, director of fleet operations for the company, the conversion project has been going well. What’s more, the payback is there, too.

“You have to remarket CNG vehicles where there is a demand and where there is [infrastructure and maintenance] support,” Pumphrey notes. “We trade our vehicles at 90,000 mi., while they are still under powertrain warranty. Recently, we’ve actually begun seeing residual values. There is an extremely strong demand for CNG vehicles at auction. Natural gas vehicles can command $5,000 to $6,000 more than their gasoline-powered counterparts.
“We are cycling them back pretty early, we know,” he adds. “There is a temptation to keep them longer for the fuel cost-saving benefit, but it is a balancing act when you factor in maintenance. The CNG vehicles require an additional filter change. And every three years, the fuel tanks have to be inspected and recertified. On the other hand, the cleaner fuel is reducing some maintenance costs. Most of our vehicles run about 30,000 mi. per year.
“If other fleets would like to see our numbers, we are an open book,” Pumphrey says. “We are excited to share information about this.”

Maintaining CNG trucks
Maintenance also requires some special considerations when it comes to natural gas-powered vehicles. If you do your own maintenance, your shop will require some upfitting to make it safe to service CNG trucks.

For starters, shops must have methane detection systems and adequate air flow to comply with applicable federal codes, primarily the National Fire Protection Association Code 52 and Code 30. Heating systems will probably also have to be replaced, particularly those that use an open flame, such as waste oil heaters. States and municipalities may also have additional regulations of their own concerning maintenance of natural gas vehicles.

While natural gas-powered vehicles have much in common with gasoline and diesel vehicles, technicians working on natural gas trucks should be trained and certified, as well. Technician training programs are beginning to spring up around the country, such as at West Virginia University’s National Alternative Fuels Training Consortium.

Many fleets using natural gas vehicles are electing to outsource maintenance rather than make the required investment in facilities and training. Ryder, for example, expects maintaining natural gas vehicles to become a differentiating factor for the company, according to Scott Perry, vice president-supply management for Ryder Fleet Management Solutions. “Maintaining natural gas vehicles is a major obstacle [for truckers] to market entry,” he says.

Truck OEMs are also stepping up to help natural gas customers put good maintenance programs into place. “Dealer service is key,” says Douglas. “We will not build a [natural gas] truck without a great service plan in place. That is what needs to be done.”