By Jennifer Oredson, Technical Writer
Keeping apprised of the U.S. Environmental Protection Agency’s (EPA’s) complex diesel emissions regulations can be a challenge, but now that these requirements encompass not only mobile off-highway applications but also stationary applications, it’s up to the generator owner/operator to stay informed. When armed with the appropriate information, it will be relatively straightforward to source these products.
A complete listing of the emissions requirements for stationary diesel engines was published in the Federal Register in July 2006. Prior to this time, the EPA had exempted all stationary engines. Now engines used in stationary applicationssuch as diesel-powered generatorsare required to meet the same emissions levels as mobile off-highway diesel engines.
Off-highway diesel engines are a specific category of engines used in construction, agriculture or above-ground mining applications, to name a few. And certification procedures for these engines are well-established: Diesel emissions regulations have been a reality for mobile non-road engines since the early 1990s. The EPA had further divided non-road diesel engines into two categories: mobile and stationary. The EPA defines a stationary diesel engine as any internal combustion engine, except combustion turbines, that converts heat energy into mechanical work and is not mobile. For the generator market, this meant that tow-behind generators would count as mobile, but generators that remained in one place counted as stationary.
Now that emissions regulations for mobile and stationary non-road diesels have aligned, this distinction no longer applies. Engine manufacturers can simply supply off-highway engines for power generationwith the added fact that generator engines are usually optimized for fixed-speed operation.
“The EPA only regulates 0.3 percent of an engine’s total product of complete combustion,” said Doug Laudick, product manager with John Deere Power Systems, a diesel engine manufacturer. “The rest (99.7 percent) of engine exhaust is made up of natural elements in the air such as nitrogen, oxygen and water vapor. The two main emissions that are regulated are oxides of nitrogen (NOX) and particulate matter (PM). By the time diesel engines meet Final Tier 4 regulations, NOX and PM emissions will be reduced to almost nothing. More specifically, NOX will be reduced by more than 90 percent, and PM will be reduced by more than 95 percent.”
Diesel emissions regulations have been a part of the mobile off-highway industry for almost 20 years, but it’s a relatively new development for stationary off-highway engines. What is becoming of even greater importance, however, is the fact that mobile off-highway engines will continue to be suitable for power generation units. Because Interim Tier 4 and Final Tier 4 requirements have grown to include stationary non-road applications, engines for non-emergency generators must meet the same regulations as corresponding mobile non-road engines.
Exemption for Emergency Standby Generators
Because the industry adopted Tier 3 emissions regulations starting back in 2006, everyone’s eyes are turned to the Interim Tier 4 regulations that begin in 2011. Interim Tier 4 requirements started in 2008 for engines 19 kW 56 kW (25 hp 74 hp). But the deadline isn’t until 2011 for engines greater than 130 kW (174 hp) and 2012 for engines 57 kW 129 kW (75 hp 174 hp). For the power bands that the 2011 and 2012 regulations address, most engine manufacturers will use exhaust filters to meet the required emissions levels.
There is, however, an exemption for diesel engines used in emergency standby applications. The EPA defines an emergency standby application as one whose operation is limited to emergency situations, such as a hospital’s standby generator used only during a power failure.
“If the gen-set is used only as an emergency standby application, then the engine does not have to meet Interim Tier 4 regulations if an exhaust filter would be required to meet those emissions levels,” Laudick said. For example, John Deere PowerTech M 2.4L engines less than 57 kW (75 hp) meet Interim Tier 4 requirements without the need for an exhaust filter, so these engines will need to be used in both emergency and non-emergency gen-sets. On the other hand, John Deere engines 130 kW (174 hp) and greater will use exhaust filters to meet Interim Tier 4 regulations. That means these engines will not be required in emergency standby applications and Tier 3 engines may be used as part of the exemption.
This allows the continuing use of current Tier 3 engines for emergency applications for most power nodes because the majority of Interim Tier 4 engines will employ some form of after-treatment. But as of January 2011, non-emergency generators must use Interim Tier 4 engines.
“The reasoning behind the emergency standby exception all comes down to hours of use,” Laudick said. “An emergency generator is only going to run a handful of hours per year and therefore emissions from these engines are relatively low compared to non-emergency engines. Peak shaving is not considered emergency, and connection to the grid would exclude a generator from being labeled as an emergency unit.”
The emergency standby exception is a reflection of the EPA’s working with engine manufacturers to understand the available technologies and how they affect the marketplace. There is a point of diminishing returns in adding an emissions device that might be quite effective but adds substantially to the cost and complexity of an engine that likely will be used very few hours per year. To this end, a part of the regulations addresses stationary fire-pump engines, which likely would see even fewer hours of use and for which the regulations are even more relaxed.
Designating an emergency standby engine starts at the manufacturer level. An engine must be designated as “emergency” if it is in fact to be used for this type application, and it must have a label stating this.
“The emergency classification allows for unlimited use of the generator set, if in fact it is being used for a true emergency requirement,” Laudick said. “The only hour limitation is for the exercising and testing of the unit and is set at 100 hours per year.”
It’s important to note that this emergency standby exemption puts a greater level of responsibility on the owners and operators of these units, including two key requirements of fitting a non-resettable hour meter and keeping detailed records of operation with the unitin particular for what the EPA calls “maintenance checks and readiness testing.” These logs are critical to meet the EPA requirement that the engine be limited to true emergency use.
Interim Tier 4 Technologies
Now that non-emergency generator engines will have to meet the same stringent requirements as mobile non-road diesels, it’s time for generator owner/operators to educate themselves on these regulations and the technologies that will be used to meet them. Interim Tier 4 engines are inherently more complex, and most enginesspecifically those in the higher horsepower rangewill require some form of after-treatment or exhaust filter to meet the emissions regulations.
“It’s up to each manufacturer to decide what type of aftertreatment device will be used, but the general consensus is that most Interim Tier 4 engines will need some form of aftertreatment to be able to lower PM to the necessary levels,” Laudick said.
There are many types of aftertreatment devices, but two types that manufacturers have started talking about for Interim Tier 4 are diesel particulate filters (DPF) and selective catalytic reduction (SCR). While a few engine manufacturers have announced SCR as the Interim Tier 4 solution, most have announced that they will use some type of DPF.
“John Deere announced earlier this year that, for engine power ratings 130 kW (174 hp) and above, we will start with our Tier 3 PowerTech Plus engine platform, which included such technologies as cooled exhaust gas recirculation (EGR) and variable geometry turbochargers,” Laudick said. “Then we’ll add an exhaust filter for reducing particulates and we’ll increase the percentage of cooled EGR for NOX control.” John Deere will not use SCR for Interim Tier 4 because it claims the cooled EGR and exhaust filter technology path is simpler and more economical.
So what does this mean for the generator owner? It’s important to know what will change and what will stay the same when moving from Tier 3 to Interim Tier 4. Because most engines will require aftertreatment devices of some sort, one of the differences will likely be engine size. After-treatment devicescoupled with larger cooling packages in many instanceswill cause engines to take up more real estate.
“We plan to provide for Interim Tier 4 every power rating that John Deere provides today for Tier 3,” Laudick said. “Our generator customers should know that we will provide the same ratings, but the engine displacement might be different. For some of our Interim Tier 4 engines, we’ll be able to offer more power out of a smaller displacement than our Tier 3 models.”
Another end-user consideration for Interim Tier 4 engines is fuel economy. Interim Tier 4 engines will not necessarily consume more fuel than previous-tier engines. In fact, some engine manufacturers are talking about significant fuel economy gains. This fact is certainly important for owners of prime-power generators.
Maintenance is always a concern when it comes to engines, particularly considering new engine technologies. Many end users in the industry have assumed that Interim Tier 4 engines will require more maintenance because of their more sophisticated technology. On the contrary, with many engine brands, routine maintenance intervals for items such as oil and air filters changes remain the same.
Depending on displacement and configuration, the oil change interval for John Deere Interim Tier 4 engines will be either 500 hours or 250 hours. This is the same interval currently offered for its Tier 3 engines, Laudick said. One noticeable difference, though, will come with the addition of the exhaust filter. “The EPA requires an exhaust filter minimum service interval of 4,500 hours for engines 130 kW (174 hp) and greater and 3,000 hours for engines less than 130 kW (174 hp),” he said.
Engine oil type and diesel fuel quality have always been important, but the technologies needed to meet Interim Tier 4 emissions regulations make them even more so. Generator owners need to be aware that with the introduction of the exhaust filters, the type of engine oil used can have a significant impact on the proper functioning and service life of these devices. It is likely that many off-highway manufacturers will require the use of American Petroleum Institute CJ-4 oils in Interim Tier 4 engines. It will be important to always follow the manufacturer’s oil-type and service-interval recommendations.
Generator operators also need to be aware that fuel regulations are changing. Prior to July 2007, sulfur content levels of typical off-highway diesel fuel were 1,000 to 3,000 parts per million (ppm). Sulfur content in off-highway fuel was reduced to 500 ppm (low sulfur diesel) in 2007 and will be further reduced to 15 ppm (ultra-low sulfur diesel or ULSD) in 2010. These new, cleaner fuels will enable the use of aftertreatment devices on new engines and reduce emissions from the existing diesel engines.
“Emissions regulations are not only better for the environment,” Laudick said, “in many cases, they are better for our customers as well when you consider the new technologies that have led to increased engine performance and improved fuel efficiency. When you combine all of this with the environmental benefits, it’s good for everyone.”