The refuse industry is experiencing a significant shift to CNG-powered trucks as haulers realize the benefits in comparison with conventional diesel-powered vehicles. Engineered for the extreme environment of the waste industry, CNG-powered trucks provide lower fuel costs and a greener image, among other benefits.
“Fuel cost is the number-one advantage,” states Curtis Dorwart, refuse segment manager for Mack Trucks, which has been manufacturing the TerraPro Series since 2009, and the cabover since 2010. Because of that, he says sales have been up every year.
With more CNG trucks on trash routes, attention must be directed to maintenance.
CNG Versus Diesel: Difficulty
Servicing a CNG-powered trash truck isn’t considered any more difficult than servicing a diesel-powered trash truck, but it is different. “You must understand that it is vastly different than your typical diesel injections system,” says Ken Shurboff, national technical communicator for McNeilus Companies, which is part of Oshkosh Corp.
The most common CNG fuel system on trucks does not include injectors. “Cummins/Westport utilizes a mixing chamber that closely resembles a carburetor on a gasoline engine,” continues Shurboff. The mixing chamber is a precision-designed component that interacts with the computer on the engine, constantly adjusting the fuel-air mixture for optimal performance. “We have found that water or oil suspended in the CNG can affect the mixing chamber in adverse, undesirable ways, so proper maintenance of the fuel supply may be considered by some as more intense. I tend to disagree with the evaluation of more intense. You have to keep water out of the diesel fuel; that requires filters designed to remove water, so filter change is, in my opinion, equal.”
Natural gas contains both water and methane, along with a few other byproducts. “When natural gas is compressed at the station, before it is transferred to a vehicle, it naturally becomes tainted by compressor oil known as “˜drip gas,'” explains Trevor Milton, of dHybrid Systems. Drip gas is extremely harmful to the engine and can quickly ruin a spark-ignited engine. For this reason, there is a filter that operates on the high-pressure side of the fuel system that filters it. This filter needs to be monitored and changed regularly to ensure no drip gas reaches the engine cylinders.
Tim Hooker, with Fontaine Modification Co., considers CNG and diesel simply two different types of technologies. A high-pressure CNG fuel storage system stores fuel at 3,600 psi, regulated down to the low-100s psi and delivered to the engine, as opposed to diesel fuel stored at minimum pressure as a liquid that is delivered by high-pressure direct injection (HPDI) to the engine. “The key is to deliver fuel in [the] cylinder at the proper flow and pressure rates that the engine requires to meet proper horsepower and torque demands.”
The biggest problem McNeilus customers have had, Shurboff says, results from the oil introduced by the CNG compressors that fill the tanks. “Too many of the filling units I have been around do not adequately remove the lubricating oil used in the compressors. At the pressures the natural gas is being compressed, there is quite a bit of heat being generated and in these conditions, the oil becomes suspended in the CNG.” In this state it transfers into the storage tanks on the trucks, where it cools and precipitates out of the CNG, settling into the storage tanks. This oil will work its way back into the delivery system, emulsifying with any moisture that is naturally suspended in the gas. This emulsified water/oil mixture tends to plug up filters intended to remove moisture, causing a lean-burn situation or giving the effect of running out of fuel. If not properly dealt with through more frequent filter changes, it can enter regulators, solenoids, senders, and the mixing chamber, all of which can be expensive to fix. Because of this problem, many companies have installed their own fueling stations to address this issue.
While it sounds onerous, the filter and tank inspections are the only regular service intervals you have with a CNG fuel system, Milton says.
To the daily inspection of fuel filters, Dorwart adds ignition coils and differential oil. Spark plugs should be replaced every six months. “Other than that, there’s not a lot of difference from a diesel truck, except for the fuel injectors.”
Spark plugs are a consideration not typically found on diesel machines, Shurboff confirms. “Unlike a car with spark plugs lasting 70,000 miles, CNG engines need to have the spark plugs [replaced] more often.” He estimates they need to be changed somewhere between 15,000 to 30,000 miles. “Since CNG is a unique fuel requiring an air-fuel mixture ratio between 5% and 15% with an octane rating of 117, the engine manufacturer is running the engine with a 16:1 compression ratio, also requiring the spark plugs to fire longer and hotter to get the fuel to burn.”
McNeilus’ exclusive CNG fuel management system features a control box that simplifies the system by incorporating a new manifold block that reduces the number of fitting connections and increases reliability. The fuel storage pods are equipped with boss-mounted, lightweight DOT Type 4 tanks and integrated three-sixteenth-inch steel guards for tank protection. CNC-formed high-pressure lines, O-ring face seal fittings, and high-pressure hoses with a working pressure of 5,000 PSI are also part of the system.
A unique aspect of CNG is that because natural gas is half as dense as air, any residue left in changing filters will quickly dissipate. Therefore, Shurboff points out, there is no diesel fuel spill to clean up, no hazardous waste to deal with.
CNG system
Cost Comparisons
The cost to maintain a CNG-powered truck is “about the same as a diesel motor, maybe slightly more over the long haul,” believes Milton.
Not everyone agrees. “Plugs are expensive,” says Dorwart. Parts are pricier, and because there’s less volume of CNG parts, there’s less opportunity for money-saving used parts.
“To my knowledge, it has not been an issue,” counters Fontaine’s Hooker. He says that because the current CNG engine platforms are based on diesel engines that have been modified to run on CNG, parts are the same on both engines-and are plentiful. “The truck dealers and engine distributors had a learning curve for stocking parts in the beginning, but it has improved.”
Sourcing parts for natural-gas fuel systems is no more complex than sourcing parts for other vehicle systems, claims Jim Zito director of vocational sales for Peterbilt. The company’s customers access parts through dealers and Paccar Parts distribution centers.
Similarly, Milton says parts are ordered directly through dHybrid Systems or through a service network like Peterbilt, Kenworth, or Volvo dealer groups. “The industry is still so new that they are being established and expanded as we speak.”
A CNG vehicle versus a comparable diesel unit does have a significant upcharge, Hooker admits. “The engine, transmission and fuel storage system add $30,000 to $50,000 to a unit. Depending on the fuel storage requirements, it could be more.”
However, there are savings in fuel costs, Hooker points out. “It is not unusual to see a 25% to 45% reduction in daily fuel costs to operate a CNG vehicle versus a diesel vehicle in the same application.” On the other hand, he adds, keep in mind the weight increase being added to the unit, because it could affect payload.
The acquisition cost of natural-gas vehicles is higher, but Peterbilt’s Zito estimates that investing in a natural-gas vehicle will pay for itself in fuel cost savings in about two to three years. From a strictly maintenance point of view, the vehicles themselves do not cost any more to maintain than their diesel-powered counterparts, he states. “The only significant cost difference from an aftermarket standpoint is if the customer or dealership makes an investment in a service facility equipped to maintain and repair natural-gas vehicles. This can be converted service bays or a new, purpose-built service area. While the regulations and requirements will vary by municipality, there are specific safety systems and other essential infrastructure. Some examples include natural-gas detectors, ventilation systems, and elimination of open flames and other possible sources of ignition.”
Shurboff estimates the cost of CNG at about one-third the cost of diesel but admits that infrastructure is very expensive. “Typically, a CNG truck will be an additional $20,000 to $40,000 initial purchase per unit. Fueling stations typically run $35,000 into the millions of dollars of initial investment, depending on how many trucks you want to fill up.”
“Space is another cost when looking
at truck,” he continues. “If you were to take the physical size of a 40-gallon diesel and equate this [to] a CNG tank of the same size, it would hold 10 DGE [diesel gallon equivalence].” Storage tanks on the trucks are typically a type 3 or type 4 storage vessel and that, without external damage and depending on manufacturer, they should last for 15 to 20 years. He says space is always an issue, since it can affect the hauling capability of the unit. However, he’s also seen some innovative installations that maximize payload and fuel-carrying capabilities.
Many of the companies converting to CNG have made the investment in bettering our environment to burn clean fuel, Shurboff says. “Anyone in it for the short haul would never make this amount of capital investment, and I applaud their commitment to be clean.”
Calling all CNG Trucks
Because CNG does not require all of the complicated aftertreatment that diesel uses, CNG vehicles have seen a decrease in service calls, Milton says.
Hooker agrees. “Service calls in general, in my opinion, are down for CNG vehicles versus diesel. The CNG vehicles don’t have the electronic and sensor issues that the SCR and DPF diesel units have been plagued with.”
The road call Shurboff most often sees is due to running out of fuel . . . or so the driver thinks. “This brings us back to the issue of oil from the filling stations plugging up the filters.”
He also saw some issues with the extreme cold weather causing problems, but much of that was attributed to education discrepancies among the drivers. “Whenever you drop from a high pressure to a low pressure, you will see a significant change of temperature that could cause a fuel regulator to freeze. This is why all CNG fuel regulators on the main fuel box are heated by the engine coolant. If the driver takes off without warming up the engine first, this can happen. By the time the mechanic gets there, the engine starts and runs just fine.” He mentions an issue with engine intake temperature sensors freezing during the extremely cold winter in the Midwest, but says it has been identified and corrected.
Zito doesn’t believe that natural gas vehicles are prone to greater frequency of maintenance or breakdowns. “Of course, as with all vehicles, we encourage customers to follow the recommended maintenance schedule most appropriate for their truck and their application.”
CNG truck
Training
With some basic training and safety requirements, it’s not difficult to service a CNG fuel system, Milton believes.
Natural gas systems are not more difficult to maintain, Zito concurs, but they do require different training, skills and facilities. Service technicians need special certification to work on natural gas engines and fuel systems. “It’s a different set of fundamentals, but it is by no means more difficult once the technician has received the proper training and certification.”
Training certification is also required to inspect the CNG systems, which in turn is required by law to occur every 36,000 miles or 36 months, or if the vehicle was involved in an accident over 5 mph or a fire, according to Shurboff.
Service technician training is offered by OEMs, engine manufacturers, and component suppliers of CNG systems, as well as by independent sources and outside organizations such as the Natural Gas Vehicle Institute. Clean Cities organizations sometimes provide free training.
Most states offer CNG service technician training now, Milton adds, although he says training is dependent on “each fuel system manufacturer and the new classes that states are putting together.”
There are many sources out there to help, Hooker says. He suggests that the key is to determine a company’s maintenance goals: six months to a year or long term. “Maintenance departments from big to small need to look at it in this manner. The training, tooling, and facility costs can be managed with confidence that the right decisions are being made.”
Training is important in order to protect technicians while they’re servicing CNG trucks. Shurboff offers some advice:
“One must work in a well-ventilated -environment while servicing CNG fuel systems and be very aware of the pressure in the fuel system.” CNG stores up to 5,000 psi. Employees need training to understand the system and how to depressurize it prior to servicing.
“My greatest fear in dealing with CNG is the untrained individual working on the high-pressure side without properly de-fueling the system,” continues Shurboff. De-fueling is relatively simple: the systems are designed to allow this easily; shutting off the fuel box and running the truck out of fuel is by far the most common method.
Feedback
Milton of dHybrid Systems says, that because mechanics are new to the CNG market, the verdict on endorsement is still out. However, he adds, the mechanics who are being trained in CNG service feel like they have a more stable job environment since not all mechanics know CNG.
What he calls “new industry technicians” welcome the new technology, Hooker observes, but it took a little more time for the “old school” mechanics to accept. “It really boils down to the desire of the individual and the company’s service department culture. A progressive company with good leadership seems to do well, and those with closed minds struggle. We are still seeing a shortage of technicians, and good ones are hard to find.”
Once they get past what Shurboff describes as the “bogus fear that they are working on a bomb,” he believes they adapt quickly. As with any other piece of equipment, he says that understanding what you’re dealing with is important.
“I’ve met some very competent individuals that, at first, were very leery of the whole concept, but after working on them became staunch supporters of the concept,” relates Shurboff. “These individuals have sent me pictures of trucks that have been in accidents or caught on fire, praising the safety features built into the CNG systems. Some even state [that] if this would have been a diesel-powered unit, there would have been nothing left to fix. Seeing the worst can drastically affect your opinion on choice of fuels.”
In fact, he says he doubts they miss changing injectors or the black oil they drain out of the engine pan. Neither do they have to deal with DEF after-treatment systems, which can be troublesome and labor-intensive. “CNG engines just require a catalytic converter for after-treatment,” he elaborates. “[It’s] very simple [and has] been on cars for over 20 years.”
One of the biggest complaints Dorwart received, like Shurboff, concerned cold weather operation during the “polar vortex” last winter. To remedy that, winter fronts -blankets in front of the radiator- and engine heaters were used. Because the engines then run hotter, it leads to more frequent valve adjustments: added maintenance.
Added maintenance means added cost -and switching to CNG already incurs expense. McNeilus’ Shurboff reports that many dealers have made the investment to convert their shops to be CNG compliant. That can be expensive, he says, since it affects heating, lighting, ventilation, garage doors, and methane-detection systems. “Others grumble, thinking it’s just a fad and it will go away.”
That’s unlikely. As dHybrid Systems’s Milton points out, CNG sales have increased. He credits the one- to two-year return on investment and fuel prices that are more stable than diesel fuel prices. “The more natural gas that is discovered, the cheaper the fuel becomes. On the contrary, diesel fuel continues to rise with each conflict the world sees.”
For those considering the costly switch to CNG, Hooker advises finding a -supportive dealer. “I still find dealers reluctant, dismissive, and uneducated,” he says. “I also find dealers who are very strong [on] the future of CNG and alternative fuel technologies. You can’t afford to have someone practice on your fleet: Do your homework.”
Benefits and Downsides
“CNG is not for everybody. Do your homework,” echoes Dorwart. He says that although diesel sales still dominate, there are costs and a learning curve even with the new diesel emissions regulations that can level the playing field.
“Smaller guys with less capital are taking a harder look at CNG,” he continues. “There are many benefits. You don’t need big power to pull. The trucks are home every night to slow fill. You have the ability to package fuel storage on the body, and you portray a green image.”
A green image can enhance a company’s overall image. According to a statement provided by Kelli Sandhurst, marketing representative for McNeilus Trucks, which fields more than 8,000 CNG-powered vehicles in the US, not only do CNG-powered vehicles run cleaner, save money, and reduce a company’s carbon footprint, they are much quieter when operating. That’s a significant benefit, especially on early morning residential routes.
CNG costs a little more, Dorwart says, “but no DPF or SCR offsets the cost.” He likes the simplicity of exhaust after-treatment with CNG.
The downsides Dorwart sees include acquisition cost, loss of payload, and the need for trained techs and a place to fill vehicles. In addition, the engine has less torque, which translates to less productivity. “It might require an overhaul sooner. It’s still early; we’ll see when they’re 10 to 15 years old.”
Another Point of View
As far as Jim Rogers, vice president of sales and marketing for E-Z Pack, which makes body and fueling systems, is concerned, it’s all about integration. The 50- to 75-gallon fuel tanks used to be saddle-mounted on the side of trucks or set on top of the body.
Lots of trucks carry 75-diesel-gallon equivalent (DGE) in five 15-gallon tanks that are 3 feet by 22 inches. Class 3 tanks have an aluminum core; class 4 tanks have plastic. Both feature a carbon wrap. “If the fiber wrap is damaged, there are issues,” says Rogers. Expensive issues: The tanks cost $5,000. Tanks mounted on top of the trucks ride 13 to 15 feet off the ground. “Tanks got damaged due to low bridges, trees, and overhead power lines,” he recalls. “Most cities don’t cut trees. Instead, the trucks break the branches.”
That led to the question of where to package the tanks for protection, safety and ease of maintenance. “Packaging, integrating, and protecting tanks is key,” says Rogers.
E-Z Pack developed a patent-pending design to integrate the tanks in the tailgate, where they are less prone to damage. This design does not extend the wheelbase, Rogers notes. “The trucks travel in urban areas, so we don’t want to shorten the turning radius.” Weight distribution is also a common issue solved by integration.
The modification adds to the initial cost, he acknowledges, but he calculates a payback period of two to three years, depending on the cost of fuel, and says the protection gives tanks a 20-year life.
For rearloaders, which still are used in rural and very congested urban areas, the tank is placed between the cab and the body in a cabinet. “Tanks on top are not the way,” concludes Rogers.
