For manufacturers and operators of stationary diesel engines, approval of the EPA’s new federal emissions standards will bring increased costs and complexity—but also a more predictable regulatory landscape, to the extent that the federal standards may supersede those of local, regional, and state permitting authorities.

The EPA’s stationary diesel engine standards essentially parallel the four “tiers” of federal standards toward which the mobile diesel-engine world has been working for a decade, but with a separate implementation schedule. The standards would affect about 100,000 new stationary diesel engines manufactured each year.

These stationary diesel-engine standards impose emission reductions for carbon monoxide, non-methane hydrocarbons, oxides of nitrogen, and particulate matter, plus a substantial reduction in the sulfur content of diesel fuels and lubricants in Tier 4 (which is just beginning in the mobile engine world). Tier 4 entails a 90% reduction in oxides of nitrogen and particulates from the Tier 3 level---a major challenge for engine manufacturers, many of whom will comply by means of catalytic aftertreatment technologies that sulfur can contaminate.

For most stationary diesel engines, 2007 is the watershed year, when the EPA would begin requiring

• certification of all new stationary diesel engines to the nonroad mobile standards applicable to their model year and maximum engine power;
• purchase of emission-certified engines only; and
• availability and use of the new low-sulfur fuels.

For engines with a displacement of less than 10 liters per cylinder and more than 3,000 horsepower, the EPA would impose an intermediate set of standards for the 2007 through 2010 model years, then more stringent standards beginning with the 2011 model year.

The tiered standards wouldn’t apply to the largest engines, with a displacement of 30 liters or more. They would have to reduce oxides of nitrogen emissions by 90% or limit them to 0.40g/kWh (0.30 g/hp-hr), and reduce particulate emissions by 60% or limit them to 0.12g/kWh (0.09 g/hp-hr).

Less rigorous standards would apply to emergency engines, such as those powering generator sets, which typically operate only a few hours a month to ensure their readiness. Emergency engines fall into two categories, with the most lenient standards reserved for engines used to operate fire pumps.

A Bewildering Patchwork
In the absence of federal emissions standards, stationary diesel engines today are subject to a bewildering regulatory patchwork. “There are myriad districts, and myriad variations in the regulations that they impose,” says Allen D. Gillette, director of engineering at Generac Power Systems Inc., in Waukesha, WI.

“California has 35 air-quality management districts with disparate regulations,” Gillette continues. “The difference in regulations can be extremely confusing and challenging for both the equipment manufacturer and the end user. Sometimes there can be different interpretations within the same agency, depending on equipment location and even the personnel reviewing the permit application.

“All of our customers need to be aware of the local prevailing regulations before they begin to plan projects. Those regulations can change quickly and are subject to interpretation. You could have an EPA-certified nonroad diesel engine, and a local district still might not allow you to put it in. You could order a gen-set that meets local regulations and, by the time it gets built and installed, a new regulation is in place.

“Certification does not guarantee permitability,” says Gillette. “Many regulators will do a case-by-case risk analysis on a location with prevailing conditions. If you go above a certain risk threshold, they will disallow it.”

Steve Iverson, marketing manager for Cummins Power Generation in Minneapolis, MN, predicts that the federal standards will create more commonality among the states and air-quality management districts, providing “a consistent and clear target for us to shoot for so we can develop products to those standards.” He notes, though, that emission standards aren't consistent throughout the world, and “variability between countries also makes our job more challenging.”

Replace or Rebuild?
The EPA also has proposed emission standards for pre-2007 stationary diesel engines. If an older engine isn’t certified, it may comply by using emission test results from a similar engine, data from the engine’s manufacturer, data from vendors of pollution-control devices used with the engine, or a performance test. Bringing some older engines into compliance through any of these methods may involve considerable effort and expense.

“Equipment owners who wish to have emissions benefits should seriously consider scrapping or trading in their aging equipment,” advises John Madey, product manager at Iveco Motors North America in Carol Stream, IL. “New equipment will be more efficient and cost less to operate. This will force old equipment to work its way out of the marketplace via attrition and obsolescence.”

One way to recover at least some of an older engine’s residual value is to sell it to an offshore market. “I’ve known of larger diesels, 1 MW and up, that have gone to South America,” says Gillette.

If you’re in California, you may qualify for state money through the Carl Moyer Memorial Air Quality Standards Attainment Program to help you upgrade your equipment. Introduced in the 1998--99 fiscal year, the program had $18.6 million to spend in the 2004--05 fiscal year.

Nationwide, the 2005 energy bill that congress approved in July provides for a similar program, offering $1 billion over five years in grants and loans for states and organizations to clean up existing diesel engines or replace them with new, cleaner ones.

If you can’t afford to buy new equipment, several options exist to bring your old equipment into compliance. One is engine replacement. Some manufacturers offer new replacement engines, which are easy to install if the manufacturer followed the original engine’s mounting specifications. Otherwise, the new engine may not fit into the old one’s space without costly mounting modifications.

New replacement engines must meet the standards in force when they are built. “The rules are written to favor replacing an unregulated engine with the latest emissions-regulated engine,” says Cameron Larson, senior engineer--emissions standards at Kubota Engine America Corp. in Lincolnshire, IL.

Other benefits of installing a new engine include more horsepower and torque, and enhanced durability, according to Gillette.

Another alternative is a remanufactured engine, which the EPA says must be rebuilt “to its originally certified configuration for all the relevant tolerances, calibrations, and specifications that might affect emissions.” For standby generator engines, however, rebuilding is not a meaningful option. “Standby generators run very few hours each year and have very little impact on overall air quality,” says Mark Westphal, director of high range generator sets for Cummins Power Generation. “Their average life is 22 to 25 years. You’d have no need to rebuild them, and you couldn't even find parts after that period of time.”

In most instances, upgrading a prior-tier engine to the latest emission standards is less cost-effective than installing a new engine. “You can’t completely retrofit the newer diesel technologies onto an older engine,” Gillette says, “but you can add aftertreatment.”

Aftertreatment Options
Under the proposed federal emission standards, aftertreatment will not be required for emergency standby gen-sets---but that doesn’t prevent local authorities from insisting on it, especially in regions such as the Los Angeles Basin in California and the Houston-Galveston area in Texas, which have significant air pollution problems and aggressive air-quality management agencies.

Choosing the right aftertreatment option for a diesel engine depends on the equipment you’re trying to retrofit, the emissions it produces, and what your regulators will allow. Possibilities include

• A catalytic converter with a diesel oxidation catalyst (DOC). A ceramic or metal monolith coated with a precious metal, a DOC oxidizes pollutants to produce carbon dioxide and water. A DOC can remove from the exhaust stream more than 90% of carbon monoxide, 70% to 85% of hydrocarbons, and 20% to 40% of particulate matter, says John Stekar, chief executive officer of Catalytic Exhaust Products Ltd., in Brampton, ON, Canada.
• A selective catalytic reduction (SCR) system. Designed to combat oxides of nitrogen, SCR adds aqueous urea to the exhaust stream, which then passes through a catalytic converter where the catalyst removes up to 90% of oxides of nitrogen from the exhaust.
• Diesel particulate filters (DPFs). Made of ceramic materials, silicon carbide, or high-temperature paper, DPFs have porous walls with holes measured in microns that trap particles larger than the holes. Some are strictly mechanical and must be replaced frequently. Others have catalysts that oxidize trapped particulates. The catalyst may be applied to the filter, or added to the fuel. “We’re also working on an electrically regenerated DPF that uses electrical energy to increase the heat, thereby burning the filter clean,” Stekar says. Mechanical DPFs remove only particulates; catalytic DPFs can remove from the exhaust stream 85% of particulate matter and over 90% of carbon monoxide and hydrocarbons.
• Engine heating equipment. An engine heater employs a resistance heating element to preheat the lubricating oil and engine coolant. While not a total aftertreatment solution, heating an engine eliminates the noxious white smoke that accompanies cold starts. “The engine starts fast and produces drastically fewer emissions,” says Michael Floyd, communications manager at Kim Hotstart Mfg. Co. Inc., in Spokane, WA.

Floyd notes that preheating allows a standby or emergency gen-set to assume its full load within the 10-second window specified in National Fire Protection Association Standard 110. Approaching the same goal from a different perspective, the Canadian Standards Association requires maintaining engine temperature between 100°F and 120°F.

“Starting a large engine at that temperature provides oil pressure, which means less metal-to-metal grinding in the pistons,” Floyd says. “Preheating reduces overall wear and tear on an engine because it requires much less idling time. Regardless of engine size or ambient temperature, 90% of engine wear is due to low water-jacket temperature. So when any engine is started without preheating, that is when the most damage occurs.”

Retrofitting an aftertreatment device onto an old engine can help to reduce emissions, though perhaps not enough for the requirements you’re trying to meet. “Control devices have limitations,” Stekar says. “It’s the old analogy of trying to stop the blood from coming out of a head wound.”

Advanced Technologies
Although the EPA standards provide common goals for emissions reduction, individual diesel-engine manufacturers are pursuing those goals in different ways, mixing and matching a smorgasbord of technological options—microprocessor-based electronic engine controls and fuel-injection systems, combustion-chamber geometry that maximizes swirl and turbulence, turbochargers, and exhaust-gas recirculation (EGR).

Some companies won’t discuss what they’re doing; others proudly trumpet their progress. In the latter category:

• Peoria, IL--based Caterpillar Inc. calls its approach ACERT (Advanced Combustion Emissions Reduction Technology). It involves air- and fuel-management systems and advanced electronics. To meet the Tier 4 standards, Caterpillar says it may add a DOC.
• CERT uses turbochargers to force cool, clean air into the combustion chamber while the fuel system injects small, multiple shots of fuel at appropriate times. An electronic control module integrates the engine’s operation as well as hydraulics, the transmission, and other systems and components to optimize emissions, fuel economy, and performance.
• Cummins believes in-cylinder technology is more cost-effective than aftertreatment, says Westphal. “Each in-cylinder technology tends to incrementally lower emissions approximately 50%,” he says. “Aftertreatment uses brute force. You get a 90% reduction, but at a severe penalty in cost and reliability.”
• John Deere Power Systems of Waterloo, IA, has focused on the need to reduce oxides of nitrogen without increasing particulate matter. Deere and other manufacturers face a Hobson’s choice---the temperature-based inverse relationship between oxides of nitrogen and particulates. With a higher engine-cylinder temperature, combustion yields less particulate matter but more oxides of nitrogen. With a lower engine-cylinder temperature, combustion yields more particulate matter but less oxides of nitrogen. Adding to the complexity, particulate-removal devices can increase oxides of nitrogen by causing an afterburning reaction in the exhaust stream.

To optimize control of oxides of nitrogen and particulate matter, Deere is using cooled EGR and a variable-geometry turbocharger. Cooled EGR employs a valve to recirculate a measured amount of cooled exhaust gas back into the intake manifold to mix with incoming fresh air. This removes some oxygen from the engine’s air supply, reducing the peak combustion temperature. Critics of cooled EGR in stationary engines say it requires more frequent oil changes, and needs big fans and radiators that decrease the engine’s net power output. Another type, internal [uncooled] EGR, reduces oxygen concentration in the combustion chamber by recirculating hot exhaust gas directly into the combustion chamber, but because it’s hot, the benefits of internal EGR are limited. It also reduces the air/fuel ratio, increasing smoke and fuel consumption.

The turbocharger helps drive EGR, measuring the amount of exhaust gas that recirculates into the fresh-air stream. Variable-pitch vanes in the turbocharger adjust based on load and speed. An electronic control unit regulates the amount of EGR, the pitch of the turbocharger vanes, the air-to-fuel ratio, and the timing of multiple fuel injections.

• Iveco Motors expects all of its Tier 4 engines to be electronic and to have some aftertreatment technology. “We’re looking at cooled EGR and internal EGR, and at selective catalytic reduction (SCR) systems,” Madey says. “SCR allows the engine to have good fuel economy, and it gives the customer more flexibility for how the engine will operate.”
• Kubota is working on “simple, straightforward solutions,” Larson says. “We feel we can meet and exceed all the emissions regulations within the existing framework of a diesel engine.” He compares the addition of electronic control systems, EGR, and the like, to the automotive transition from the carburetor to electronic fuel injection.

“The end product is much better than in the past, and a lot more complex,” he says. “What matters is people’s perception of the complexity. On the gasoline engine, the result was credible improvements in economy, power, and reliability. We have the same potential for improving diesel engines.”

Looking Toward the Future
Instead of tweaking current diesel technology to meet the EPA standards, some researchers are developing new diesel-fueled engines as radically different from present models, as the latter are from Rudolf Diesel’s original engine patented in 1892.

One avenue of exploration is the use of materials that retain their strength at high temperatures, allowing an increase in combustion temperature to make an engine more efficient. An example is Inconel, a family of nickel-chromium-iron alloys. Some of these “super-stainless-steel” products contain molybdenum and columbium or niobium to stiffen and strengthen the nickel-chromium matrix without a special hardening treatment.

Also being studied is electronically controlled camless technology. In an engine without camshafts, the crankshaft controls the position of the pistons to discharge exhaust before admitting a fresh charge of air and fuel. Electronics regulate the timing and composition of each charge. In one camless approach, variable valve timing, valve operation relies entirely on solenoids that open and close valves electronically, allowing adjustment of the engine timing to optimize engine performance based on different speeds and loads.

FEV Engine Technology Inc., of Auburn Hills, MI, is working on a camless engine for military applications with funding from the Defense Advanced Research Projects Agency. FEV’s opposed-piston, opposed-cylinder (OPOC) two-stroke diesel engine lacks not only camshafts but also valves, the cylinder head, and all related drive systems.

OPOC differs from the more common four-stroke engine by having only two linear movements of the piston per cycle instead of four. The crankshaft resides between the two cylinders, each of which has two pistons moving in opposite directions. Intake and exhaust ports are at opposite ends of the cylinders. A turbocharger, driven by exhaust gases with an electrical boost, regulates pressure in the cylinders independent of the engine’s operation. This helps to maintain a constant fuel-to-air ratio and boosts exhaust-gas recycling, thus reducing oxides of nitrogen emissions.

Generac has introduced products based on the dual-fuel (also known as bi-fuel) concept, a diesel compression ignition engine capable of running on diesel fuel and natural gas. It would receive a dual-performance certificate, for a diesel-only mode of operation and a bi-fuel mode.

Because the natural gas burns cleaner, a dual-fuel engine could receive a regulatory mandate to use natural gas for a portion of its fuel mixture and/or running time. This would allow the engine to remain in overall average emission compliance throughout a specified time period. Such an engine also could cut back on diesel emissions during periods of adverse ambient-air quality without reducing its power output.

“We have several dozen such engines in the field now,” Gillette says. “They can accept various quantities of natural gas, up to about 90% gas and 10% diesel based on energy content. In a gas mode of operation, the diesel is primarily the ignition source, and after ignition the engine burns mostly natural gas.”

Municipalities have used dual-fuel engines since the 1950s, opting for whichever fuel was least costly. “In emergency duty, we’re looking for fuel redundancy in case either fuel is interrupted, and elongated run-time potential in an extended outage,” Gillette says. “In Florida after a hurricane, if you’ve kept a full tank of diesel fuel on hand, you can run gas early on and ‘miser’ the diesel. Then, if the gas gets interrupted, you still have a full tank of diesel. It gives you the ability to run longer.”

Costs of Compliance
The EPA estimates that meeting the stationary diesel emission standards will cost $57 million a year by 2015, and raise prices by 2.3% for irrigation systems, 4.3% for pumps and compressors, and 10% for generator sets and welding equipment.

Gillette estimates the cost increase for ultra-low emission diesel generating sets at 10% to 30%, depending on the degree of aftertreatment required. For Generac’s customers, he says, “the only advantage will be an easier installation and permitting process. They will have equipment with a pedigree. It will go in with less scrutiny, but they’ll pay more for it.”

Other industry sources are less precise, but all expect costs to increase. Madey says the costs of meeting Tier 3 standards are “a few percent---in the single digits---but Tier 4 is another ball game, still evolving.”

Some of the Tier 4 technologies now being tested won’t survive, Madey predicts. He foresees a shakeout by 2011 after serious field testing has occurred. “It will be up to the engine manufacturers to educate customers about the pros of their system; everybody else will educate them about the cons,” he says.

Which Tier 4 systems ultimately dominate will depend in part on the cost of fuel, Madey says. “Some systems are better than others in maintaining fuel economy,” he notes. “If fuel prices continue to climb, the emission technologies that reduce fuel economy will fall out of favor, and those that cause fuel economy to remain the same or increase will prevail. If fuel goes cheap again, whatever is cheapest to implement will win.”

From the perspective of an engine-parts manufacturer, “the original-equipment manufacturers (OEMs) are using metals and processes that add costs to the component parts. There is no way to avoid this because of the operating temperatures increasing to help meet the emissions standards,” says Russ Nardi, FP Diesel product planner at Federal Mogul Corp. in Southfield, MI. Federal Mogul supplies parts to the original-equipment manufacturers; its FP Diesel Engine Parts division sells to the aftermarket.

Nardi is concerned that the EPA and California Air Resources Board will force diesel engine rebuilders to use only replacement parts from OEMs when repairing or rebuilding an emission-certified engine. “This would severely limit the customer's options for cost savings and limit the locations available for repair,” he says. “This would also create a monopoly for the OEMs, effectively putting the aftermarket engine-parts makers out of business.”

Aftertreatment costs will depend on what technology is chosen or required, says Stekar. “A diesel particulate filter costs up to 10 times more than a diesel oxidation catalyst, depending on the filter media, the amount of catalyst on the filter, etc.”

Engine heaters are relatively inexpensive, costing $20 to $50 for a small direct-immersion block heater, and $200 to $600 for heaters at the top of Kim Hotstart’s product line, Floyd says.

Maintenance and Record-Keeping
On top of technology costs, users of the next generations of stationary equipment will face increased record-keeping and maintenance costs. Staying within the emission standards requires regularly changing oil, repairing fuel-injectors, cleaning filters, keeping critical belts tightened and sensors operational—and keeping records of what was done, so you’ll be ready for a pollution audit. You also may be subject to an in-field emission test.

“As a condition of your operating permit, you have certain obligations,” Gillette says. “If you obtain a permit for an emergency diesel generator that’s only going to run 200 hours a year, you have to show you’re only operating that much. If you’ve run 5,000 hours in a year, the regulators will find out. They’ll think you’re abusing the emergency standby nature of the equipment and accuse you of permitting it under false premises.

“With a car, there’s a difference. You might drive it 100,000 miles, I might drive it 400,000 miles. For a stationary application, regardless of its certification, it’s still subject to a stationary operating permit. The regulators will expect to see records of your usage, fuel type, etc. They’ll want to know its ultimate pollution profile.”

Gillette emphasizes that future generations of diesel engines will be required to operate at such low levels of emissions that compliance with the standards won’t be possible without proper maintenance.

“If you run too long without an oil change, or if you don’t repair your fuel injectors, clean your air filter or crankcase ventilation filter, or make sure the sensors and critical belts are appropriately tightened, your emissions may be affected to the point at which you’re not complying,” he says. “These engines will need to be finely tuned and kept that way. They won’t have that margin against the limit any more. They’ll have to be kept maintained.”

Dinosaur or Dominant?
Some pundits say the diesel engine is a dinosaur headed for extinction, to be replaced by fuel cells, microturbines, and hybrids of various kinds. Gillette disagrees. “In parallel with their vast improvement in emissions profiles, most diesel engines have been uprated in terms of power density—power output per kilogram or per liter,” he says. “As a power source, they are a very formidable option, as are modern spark-ignited natural-gas and bi-fuel reciprocating engines.

“Apart from the electronics, which are quite complex, a lot of the mechanical components in the new engines are simpler. The materials and processes used in their manufacture are becoming lighter, more reliable, quieter, and more fuel-efficient. They also have a lot more automation and diagnostics in place, to allow for good surveillance and maintenance programs.”

Larson also believes the emission-control effort will work and won’t diminish the dominant role that stationary diesel engines now play. “I’m an optimistic engineer,” he says. “The problems are going to be solved and the values inherent in a diesel engine will be there after all these emissions regulations go into effect.”

GEORGE LEPOSKY is a science and technology writer based in Miami, FL.

DE - November/December 2005