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EMA European Office, C.P. 65, CH-1231 Conches, Switzerland

Telephone: +41 22 784 3357 Facsimile: +41 22 784 3349

EMA is a Non Governmental Organization in Special Consultative Status with the Economic and Social Council of the United Nations

Two North LaSalle Street

Suite 2200

Chicago, Illinois 60602

Tel: 312/827-8700

www.enginemanufacturers.org Fax: 312/827-8737

April 13, 2007

Mr. Jaime Pagan

Energy Strategies Group

US Environmental Protection Agency

D243-01

Research Triangle Park, NC 27711

RE: Follow-up Issues on CI NSPS Rule for Greater Than 30 Liters Engines

Dear Mr. Pagan:

In our discussions and correspondence with EPA staff on open issues regarding the NSPS 

regulation for CI (Compression Ignition) engines, one outstanding issue is our continuing 

concern about the emissions standards for engines greater than 30 liters in areas where lower 

quality fuels are being used. This issue was discussed in our letter to you dated September 29, 

2006, and in a follow-up email with Mr. Horowitz on December 1, 2006.

Briefly, our concern is with the ability of engine-based power systems to meet the NOx 

and PM limits established in the CI NSPS when higher sulfur fuels or fuels mixed with used 

lubricating oil are allowed by the NSPS. This issue is primarily limited to the US Territories and 

Alaska where low sulfur diesel fuel may not be available and where the local population relies on 

the use of diesel engines for the production of primary power. As we discussed, the use of high 

sulfur, lower quality fuels will create problems with the successful use of SCR (Selective 

Catalytic Reduction) and ESP (Electro-static Precipitators) that are needed to reach the strict 

emissions limits established in the final CI NSPS. Additionally, even if technically feasible, 

meeting the limits will be of such high cost as to severely impact the captive local population 

that relies on these engine facilities as their only viable source of power. 

In previous discussions on this issue, EPA indicated that lower sulfur fuel oils were likely 

to be available in US territories and Alaska. However, this low sulfur fuel, even if available, 

will be more expensive. Depending on location and availability, the light, low sulfur fuel can be 

as much as two times the cost of heavier diesel fuel. Given the economics and small population 

size in some of these remote locations, it is not likely that local operators will voluntarily opt to 

use low sulfur fuel when a much lower cost option is available. In addition, even if low sulfur 

fuel is available, many locations still maintain the practice of mixing used engine lube oils. 

Doing so introduces several heavy metal contaminants to the fuel which will be harmful to any 

SCR systems deployed. 
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The use of SCR also requires a minimum flue gas temperature (dependent on the sulfur 

content of the fuel) to prevent clogging of the elements of the reactor that will be especially 

challenging to maintain in plants with frequent start-ups and shut-downs. With respect to the use 

of ESP, there is very limited experience with this technology in stationary engine power plants. 

The established PM emission limit requirement in the CI NSPS is also very strict. In comparison 

to the European Union Best Available Technology (BAT) level published in the guidelines 

“Integrated Pollution Prevention and Control, Reference Document Best Available Techniques 

for Large Combustion Plants (July 2006)” the NSPS PM standard is about 2.5 times more 

stringent and is thus beyond best determined technology for large stationary engines. 

Consequently, we believe that the fuel issues discussed earlier in the territories and 

Alaska are not satisfactorily resolved and that some relief from the emissions standards for 

engines greater than 30 liters are still needed.

Another issue of concern is the large discrepancy between stationary engine emissions 

standards for engines near the 30 liters cut point. For engines in the 25-30 liters size class, EPA 

has established emissions limits based on marine engine standards (Table 3 of the Preamble) of 

11.0 g/kW for NOx +THC and 0.5 g/kW for PM. However, if the engine is designed with a > 30 

liters displacement, the emissions standard drops significantly to 1.6 g/kW NOx and 0.15 g/kW 

PM. This large difference in the applicable emissions standards creates a strong incentive to use 

smaller engines, especially in areas where only higher sulfur fuels are available, since the 

engines less than 30 liters in size are likely to be able to achieve the emissions standards without 

aftertreatment even when using higher sulfur fuels. This causes disruptions in the market and 

works against larger, more efficient engines.

As an example, one engine manufacturer has a current engine model that has a cylinder 

size less than 30 liters and a new model that is greater than 30 liters. The newer model has many 

improvements, provides owners more flexibility is power range, and is nearly 3% more energy 

efficient. However, the current CI NSPS regulation would require the newer engine to meet 

much lower emissions standards and would require the addition of aftertreatment, thus adding 

significantly to the capital and operating costs. Because the CI NSPS emission standards for 

engines less than 30 liters are much less stringent, prospective owners are likely to choose the 

older, less efficient and higher emitting engine based on cost alone. EMA does not believe that 

this is a logical or desired outcome.

As a solution, EMA again requests that EPA consider revising the emission standards 

applicable to engines greater than 30 liters/cylinder in two ways.

First, relief needs to be provided in areas where low sulfur fuels are not required. Even if 

low sulfur fuel is available in these areas, the cost differential is sufficient to expect that it will 

not be used, thus creating significant concerns about the technological and cost-effective 

feasibility of meeting the emissions standards for those applications.

Second, the very large differential in emissions standards between engines less than 30 

liters and greater than 30 liters needs to be resolved by providing more equivalent standards for 

engines greater than 30 liters when operating on the same fuel. One way to address this 
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disruption is to establish different emission standards based on plant size within the >30 liter 

engine category. Engine unit size can vary considerably from 2.5 MW to 80 MW for engines in 

the greater than 30 liter displacement size category, and a power plant often consists of multiple 

engine units. EMA recommends that EPA maintain the current emission standards for plant 

sizes greater than 20 MW, but establish less stringent emission standards for plants less than or 

equal to 20 MW. This recommendation is similar to the regulatory approach used in Europe

where large thermal power plants (>50 MWth, about 20MW output) have to use BAT and 

smaller plants have less stringent emissions standards.

EMA again recommends that the following emissions standards be established for plants 

less than 20 MW:

NOx 12.4 g/kWhr

PM 0.54 g.kWhr

EMA understands that EPA is still working on issues related to the CI NSPS and would 

appreciate your efforts to address the above issues in the near future. Since the final rule and its 

emission standards are in effect and there currently are real-world issues related to these topics, 

EMA requests that the issues be resolved as soon as it is practical to do so.

Please do not hesitate to call me if you have any questions.

Very truly yours,

Joe Suchecki

Director, Public Affairs