While industry observers don’t put hard and fast numbers on the life cycles of natural-gas vehicles (NGVs), their observations indicate the vehicles are capable of providing many more years of service than their traditionally fueled counterparts.
It’s an engine that “burns cleaner with less pollution, and the engine of the vehicle will most likely last much longer with lower noise level operation,” notes Nabil Sahlani, innovator-in-chief at CNG-One, a collaborator with quasar energy group.
Stephen Yborra, director of market development for Natural Gas Vehicles for America concurs that because natural gas engines run clean, they last longer. While he doesn’t have an anecdotal story from the refuse sector, he compares it to the transit sector-MARTA in Atlanta-whose vehicles share similar qualities to a refuse vehicle of a heavy-duty cycle moving a lot of weight with ongoing dead stops and starts.
Yborra points out that bus agencies typically “rebuild” a bus for a second life at around 250,000 to 300,000 miles. MARTA has more than 400 buses that run nearly 24 hours a day. While a diesel bus may require a complete rebuild, a natural-gas bus may only need the replacing of a few rings and it can run for another 300,000 miles, Yborra says, adding that this can be a selling point to get a premium price in the secondary vehicle sale market.
Also important in the secondary market is that there are some regions, such as southern California, that mandate alternative fuels for waste collection route bids.
“Sometimes those bidders that want to go up against the big boys want to have a natural-gas truck running, either because it’s required or they get a better review because they get extra points for being clean,” Yborra says. “They don’t have to buy a new natural-gas truck. They can buy one that someone is rotating out of their fleet.”
The overall life cycle and cost of natural-gas solid waste vehicles depends on many factors, says Curtis Dorwart, Mack vocational marketing product manager.
“In some cases, some customers report a life cycle cost that is less than a diesel truck, while others report it to be more,” notes Dorwart. “Where is the truth? At the end of the day, the fuel cost difference between natural gas and diesel on a diesel-gallon equivalent [DGE] basis is the one point that generates the most interest.”
Acknowledging that achieving a lower operating expense is a main driver in a vehicle selection and that fuel costs take the top slot on a balance sheet these days, Dorwart points out that “anyone considering going with natural gas needs to pencil out all the associated costs beyond the very attractive DGE price, such as the acquisition cost of the trucks, weight and payload impact, fueling infrastructure-including the operational cost of fueling-maintenance facility preparation, engine oil, and training and inspections, among other factors.”
Yborra notes there are many vehicles that are factory offered with the natural-gas engines in the refuse sector. They are primarily Cummins-Westport spark-ignited engines, the 8.9-liter engine in particular, although the company is launching a new 12-liter spark-ignited engine using the same technology, he says.
Cummins-Westport’s ISL G engine runs on natural gas. Introduced in 2007, it was the first heavy-duty engine to meet 2010 US Environmental Protection Agency and California Air Resources Board emissions standards.
Among its many applications, it is suitable for larger refuse and dump trucks up to 66,000 GVW points out Charles Ker, director of industry relations and refuse segment for Cummins Westport.
In addition to compressed or liquefied natural gas (LNG), the ISL G also can operate on up to 100% biomethane-renewable natural gas made from biogas or landfill gas that has been upgraded to pipeline and vehicle fuel quality.
The ISL G engine block is shared with the Cummins ISL9 diesel. It is designed for optimal piston ring and bearing life, improved coolant flow and targeted piston cooling for increased reliability and durability. Life-to-rebuild and rebuildability are the same as for diesel engines, as is the factory-based warranty.
The 8.9-liter ISL G uses stoichiometric cooled exhaust gas recirculation (SEGR) combustion, designed for a high-performance natural-gas engine. The cooled EGR system passes a measured quantity of exhaust gas through a cooler to reduce temperatures before mixing it with fuel and the incoming air charge to the cylinder.
Cooled EGR, in combination with stoichiometric combustion (the theoretical or ideal combustion process in which fuel and oxygen are completely consumed, with no unburned fuel or oxygen in the exhaust), provides a number of benefits.
Cooled EGR, in place of large amounts of excess air used in lean-burn technology, lowers combustion temperatures and knock tendency. SEGR combustion also is designed to improve power density and fuel economy in contrast with lean-burn and traditional stoichiometric engines.
Compared with previous Cummins Westport lean-burn natural-gas engines, the ISL G torque at idle is improved more than 30%, with a fuel economy improvement of up to 5%.
The ISL G combustion technology uses three-way catalyst (TWC) aftertreatment, which consists of passive, maintenance-free devices packaged as part of the muffler and provide consistent emissions control.
That is in contrast to active aftertreatment such as a diesel particulate filter (DPF) or selective catalytic reduction (SCR).
The refuse sector has embraced the NGV technology, especially major players such as Waste Management and Republic Services, Yborra points out.
“Both have publicly stated a number of times that they’ve seen a reduction in their overall maintenance costs for refuse collection recycle vehicles,” he says. “When you get into heavy-duty vehicles that are employing larger loads, which might be transfer vehicles-that’s what the new 12-liter will be better suited to.”
The driving factor is the base of the technology, the TWC exhaust system, Yborra says. He compares it to a maintenance-free, three-way muffler on a car.
It is unlike a two-part diesel system, which entails an initial exhaust flow and a lot of particulate matter, says Yborra, adding that diesels have a two-part, “fairly complicated” exhaust aftertreatment system that has to be maintained for it to work effectively versus the maintenance-free natural-gas system.
Particulate filter regeneration burns off particulate into a finer ash after sensors indicate increased back pressure from silt capture, he says, adding that the ash has to be blown down to clean the ceramic brick that traps the soot particles.
The second stage is the selective catalytic reduction that uses diesel exhaust fluid through a dosing system into the secondary muffler to handle chemical byproducts, Yborra says.
“You’ve got two integrated exhaust after-treatment systems, one of which is maintenance intensive and can be fuel intensive, particularly in refuse, because you’re not operating at high rates of speed and temperatures by which you can get that “˜cooking the soot’ as it goes,” he says.
“Every once in a while, you have to go into that mode where it shuts you down and goes into a 20-minute regen cycle. You’re trying to be productive, but the truck indicates it has to clean the muffler right now. It doesn’t happen every day, but it’s something that happens, and you’re out of commission until it’s done doing its cycle.”
The benefit of the TWC is there is not the extra cost associated with diesel muffler systems, and it does not weigh as much, Yborra notes.
The downside of NGVs is they have an engine with spark plugs that require replacement, he says.
“They are typically Iridium spark plugs, which means that they’re fairly expensive because they are operating in a fairly hot environment. And we’re combusting natural gas, so the spark plugs are specific to operating in that heavy-duty sparking within that environment where natural gas is being used,” Yborra says.
The low-ash oil is more expensive than standard oil, he adds.
A vehicle’s oil life can be extended through an oil analysis, Yborra says. Although diesel has more carbons per atom than methane, and the oil may look “good” with an operator assuming an oil change is not needed, the oil may have reached its change point because another factor is its various properties, such as viscosity, he adds.
Yborra says a question that often comes up is whether one can convert a diesel engine to one that runs on natural gas; he advises against that.
“You start running natural gas, you’re dealing with more heat,” he says. “Maybe you have to adjust the flow of the water pump. Maybe you have to adjust the surface area of the radiator. On the Peterbilt 320 LCF, it has a different radiator package.
“When you bought a truck, it was sized a certain way. We are dealing with more heat rejection, and that’s designed in, but it’s specific to why you just can’t take a diesel and easily convert it,” he adds. “It’s not just the engine; it’s all of the peripheral systems that tie into the engine.”
While weight may be saved with natural gas in contrast to the weight of a diesel engine and exhaust aftertreatment system, weight is added with CNG cylinders, Yborra points out.
“The CNG fueling package is certainly going to add weight compared to the comparable amount of diesel fuel in a simple diesel tank,” he says. “I tend to think that transit buses, school buses, and trash trucks have more braking concerns than big over-the-road truckers because they spend longer times moving forward, braking, moving forward, braking. If you add weight, you may add wear on the brakes.”
Another factor is the fuel system. That cylinders need to be inspected every 36,000 miles or 36 months means ensuring there is someone trained to do such inspections, Yborra points out.
“You’re usually looking for just any other kind of what might be an abnormal wear, which is very rare in the refuse industry,” he says. “If they’re doing appropriate maintenance, they should inspect those cylinders. They may choose to inspect the various other parts of the system.”
The includes checking the hydraulics to ensure they’re not leaking, checking the fuel lines, and inspecting the brake linings as well, because solid waste vehicles carry a lot of weight, Yborra adds.
Given the assumed life cycle issues, those in the industry say certain maintenance practices are necessary to sustain and extend NGV life cycles.
With the Cummins-Westport engine, the high-energy ignition system of the ISL G is designed for better performance and longer service intervals and improved spark plug and coil durability, plus self-diagnostics, says Ker.
Longer engine life is derived from the high-efficiency lube cooler, which lowers oil temperatures for longer engine life. The combination full-flow and bypass oil filter improves filtration while minimizing oil filter replacement and disposal costs.
The Electronic Control Module (ECM) provides full monitoring and control of engine sensors, fuel system and ignition system and full interface capability to Cummins INSITE and diagnostic service tools. ECM gives Original Equipment Manufacturers and end users the ability to tailor performance of the engine to fit the vehicle mission.
Truck customers receive full engine coverage for two years or 250,000 miles.
Maintaining a CNG vehicle requires different considerations. In addition to the cylinder inspections Yborra references, Sahlani points out that there are two other primary maintenance considerations one must keep in mind:
- At every CNG fill-up, operators should check the filling receptacle for leaks at the line connection and the nozzle “O” ring hook-up, and visually check the exposed fittings and connections for a natural-gas leak, smell, or oil residue.
- Every 24,000 miles or once per year, whichever comes first, operators should check the CNG filter, if equipped, and replace the element.
Natural-gas engines will drive some changes in maintenance routines, so careful consideration and planning are necessary, notes Dorwart.
Service intervals for the engine oil is more frequent than for diesel, says Dorwart.
“A specific type of oil-low ash-must be used with natural-gas engines,” he says. “Failure to do this will result in internal engine damage and the aftertreatment system, causing a significant cost to the owner. Spark plugs and coils will have to be replaced and the valves have to be adjusted more frequently than on diesel engines.”
Maintaining a good cooling system is time well spent, since natural-gas engines run hotter than diesel, Dorwart says.
Cummins Westport ISL G maintenance intervals for refuse trucks in hours/miles/kilometers/months, with maintenance performed at whichever occurs first:
- Check CAC cooler, piping and air cleaner: 250/3,000/5,000/3
- Oil and filter: 500/6,000/10,000/6 (using motor oil formulated for natural gas)
- Spin-on fuel filter: 1,000/12,000/20,000/12
- Spark plugs: 1,500/18,000/30,000/18
- Standard coolant: 2,000/24,000/40,000/24
- Overhead adjustment: 2,000/24,000/40,000/24
For the ISL G, an initial valve adjustment must be performed after 1,000 hours (15,000 miles/24,140 km) of operation and is critical to achieving longer engine life.
The company’s recommended daily checks:
- Fuel filters-filtration and separation of oil from the fuel is important for trouble-free operation, protecting the engine against damage. The fuel filter has a valve that must be opened daily by hand to drain any collected water or oil. There will usually be some fuel in the filter under pressure. Water or oil in the filter will come out first.
- Air intake piping and all clamps and air system connections, including the restriction gauge
- Crankcase breather tube
- Radiator hose
- Filter hoses and air cleaner restriction indicator
- Coolant recovery tank level (fill when cold)
- Oil level
- Retighten the valve by hand
While many people consider fueling stations when making NGV purchases, “they don’t always think all the way through with regards to upgrading their repair garages,” points out Jim Dong, vice president with Raymundo Engineering. “It is important so that the costs are considered and a good decision is made when the owner opts for CNG.”
Dorwart agrees, saying that depending on the fuel type, LNG or CNG, and fire codes in a given operation area, some additional practices and precautions may need to be addressed.
“Just getting to the point of being able to service a natural-gas vehicle inside a shop may pose a problem,” says Dorwart. “LNG, for instance, does not have an odor, while CNG, like natural gas piped into a home, is odorized. This may drive additional costs and changes in the way maintenance is approached.”
Dong designs CNG vehicle fueling stations and upgrades to vehicle repair garages to accommodate the indoor repair of CNG vehicles.
“With regard to refuse vehicles that are powered by CNG, if the owner wants to repair those vehicles indoors, then certain modifications must be provided to allow that to happen according to various codes,” Dong says, referring to compliance with the International Fire Code and the National Electrical Code.
“In both documents, ventilation is usually the key to upgrading the repair garage to be co-compliant,” he says. “We’re talking about spark-proof ventilation to ventilate the space in the event of a release of natural gas. The fire code allows the ventilation to be activated by a continuously monitoring methane-gas detection system, otherwise the ventilation system must be activated continuously. Most clients will opt for methane gas detection with a ventilation interlock.”
While basic mechanical tools can be used in CNG maintenance, one that should be added to the mix is a methane CH4 gas leak detector, Sahlani points out.
Before any servicing, those providing the service must exercise safety precautions for high-pressure systems, he adds.
There also are rules regarding allowing heating systems in CNG repair garages, Dong says.
The heating systems must meet those rules and if not, they need to be removed and replaced “if you want to retain a heating system in the repair garage area,” he says. “There is no real need to make all of the electrical devices in a repair garage to be explosion-proof as long sufficient ventilation is provided.”
Usually vehicles do not have a full load of CNG when they are brought in, Dong says.
“But there are times when after a vehicle is fueled that someone discovers a leak in the system or some problem that requires maintenance and requires the vehicle to be brought indoors,” he says.
“Generally, bringing a vehicle in with a full fuel load is not a good idea. A maintenance garage usually has a defueling panel that allows the owner to remove CNG fuel from the vehicle from a relatively full load down to just a couple hundred pounds of pressure.”
That enables a vehicle to enter a repair garage with a nominal amount of fuel. In the event of a release, the entire fuel load is not being released in the building, Dong says.
Dong also favors the use of a portable, hand-held methane gas detector to detect leaks prior to a vehicle entering a maintenance building.
Yborra, who does webinars on maintenance safety, says there is a “fair amount of confusion in the application of the codes” regarding modifications to facilities.
“There are natural-gas vehicles that can be brought into garages for regular maintenance with very little modification. Most maintenance on a vehicle is considered minor and doesn’t involve the CNG system,” he says.
Yborra points out that most major fleets at one time or another must do repair work on their CNG system, which would by definition of codes be considered major repair work and should have a partner facility, either separate or isolated, where that part of the facility can be modified to accommodate that special work.
There have to be appropriate ventilation considerations, such as no open flames in that part of the garage, he adds.
“Being that it is compressed natural gas and natural gas is lighter than air, it’s not a fuel that goes to the floor, it goes to the ceiling,” he says. “What most major fleets do is isolate the fuel system by turning off the supply from the tanks. There is usually enough fuel in the system to at least start the vehicle to move it. Some people will leave the fuel on and as soon as they start to pull in, they’ll turn off the fuel and run the engine, so now there’s an engine that has completely isolated the fuel even if nothing is being done with the fuel system.
“Even if someone is going to do tire rotation, an inspection and maybe lube some axle joints, it’s a good practice to isolate the fuel system from the rest of the vehicle. When it’s ready, you turn it back on, start the engine and away you drive.”
The National Fire Protection Association’s NFPA-52 and NFPA-30A are the governing documents for natural-gas vehicles and stations, Yborra says.
The latter addresses motor fuel dispensing facilities and repair garages.
“NFPA 52 makes reference to the fact that you should always have written manuals and procedures so that your staff is appropriately trained,” Yborra says. “It is the overall governing document about stations, vehicles, designs, and safety. Facilities can be modified to accommodate natural-gas vehicles for major repair work. The issue is understanding major repair work, what percentage of the time it’s being done and can that activity be isolated to one place rather than modifying an entire garage just to bring a vehicle in and out.”
Propane is different, Yborra points out.
“Propane is heavier than air, so propane has its own set of rules for garages,” he says. “It has to do with ventilation rates that are more like gasoline or diesel, meaning close to the floor.”
The Clean Vehicle Education Foundation, of which Yborra is director of market analysis, education, and communications, publishes a document titled [ITALIC]Guidelines for Determining Modifications Required for Adding Compressed Natural Gas and Liquefied Natural Gas Vehicles to Existing Maintenance Facilities.
The foundation distinguishes between routine maintenance versus major repair and suggests an organization evaluates such activities and limit modifications to a space specifically set aside for handling those infrequent repairs involving a CNG system to greatly reduce modification costs, Yborra says.
There is special training required for servicing the Cummins Westport ISL-G and ISX-G engines, Dorwart points out.
“The rollout of this training is under way and will take some time to cover all of the dealers and service facilities,” he says. “Beyond the engine itself, it is important to note that the fuel system needs to be periodically inspected by someone trained in such matters. The fuel storage containers have a finite life, so keeping track of your equipment and having trained technicians knowledgeable about fuel system inspection and maintenance should not be taken lightly.”
There are many connection points in a natural-gas fuel system that are potential leak points, Dorwart says.
“Staying on top of all the valves, fittings and piping to make sure they are in good order is a must,” he says, adding that he believes that investment in methane detection tools to locate fuel system trouble spots is also important, as well as knowing the proper type of thread sealant to use on all of the fittings.
Cummins Westport offers a “Natural Gas Academy,” an online tutorial that demonstrates, among other factors, how to maintain a natural gas engine. It can be found at http://goo.gl/Ty4mep.
Training also can be obtained by the local gas utility and local clean cities organizations will sponsor training for CNG vehicle maintenance, says Dong. The Natural Gas Vehicle Institute also provides training, he adds.
Among the training considerations is CSA certification for CNG fuel system inspection to inspect and approve the cylinders every three years or 36,000 miles. The CSA Group develops standards for gas-fired products and alternative energy standards and is accredited by the American National Standards Institute, says Sahlani.
