NRMM emissions regulations in Europe: What they mean for diesel powered generating systems White PaperBy Gonzalo Fincheira Paliza, Sales Application Engineer, Cummins Power Generation and Aniruddha Natekar, Territory Manager, Cummins Power Generation

On December 16, 1997, the European parliament published Directive 97/68/EC. This directive encompasses regulations limiting emissions of gaseous and particulate pollutants from internal combustion engines which are installed in non-road mobile machinery (NRMM). This directive has been amended several times and includes the diesel-powered generating systems from installation since 2002 (limits are applicable since 2007). The last amendment changing emissions standards was in 2004. Since December 31, 2007 this directive has harmonized the emissions regulations for mobile generating sets have been harmonized all throughout Europe, but the different member states can choose to have local legislation on their emissions for stationary sets. Depending on the kilowatt output of the machine, the emission requirements as well as the time frame in which the manufacturers have to comply may differ.

Emission RegulationsDiesel-powered generator sets remain the preferred choice for standby and emergency power systems around the world. The growth of applications in recent years involving distributed generation has caused more diesel generator sets to be used for utility peaking and commercial load-shedding. This is due to their proven reliability, low life-cycle cost, high efficiency, ready availability, ease of installation, operational flexibility and high-quality electrical performance.

Cummins Power Generation offers a wide range of products meeting Stage IIIA for NRMM established by the European commission, Tier levels established by the EPA in USA and TaLuft_2g.

Compared to previous years, NOX and PM emission requirements have been reduced significantly as we have moved up the tier levels. It is also worth noting that the fuel being used has undergone some change as well. For example, the sulfur content has gone down from 1000 ppm to 10 ppm for ultra low sulphur diesel (ULSD).

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The Regulatory Landscape:

In the last 15 years, the European Commission has been concerned with pollution and air quality in the member states. Directives and regulations have been put in place to control those emissions.

The NRMM directive covers mobile generating sets and does not include stationary machines, therefore in simple terms it primarily impacts rental generator sets. The latest emission levels to be met are stated in Stage IIIA (measured in g/kWh), which only comments on the instantaneous levels to be met. Depending on the power of the machine, it does not consider the time that the set will be running during the year, as is the case with other regulations.

In contractual agreements with customers, it is pos-sible that these standards will have to be met for a stationary diesel generating set. This is not a legal requirement, but it is a common market specification.

Due to the nature of the European Union, the member states are free to follow different more stringent rules than the European Commission directives. Such is the case for several countries, including France and Germany, that regulate stationary generating sets.

FIGURE 1 - NRMM emissions evolution for fixed speed engines

Germany follows TALuft which is similar to the French regulation. It is also stringent on NOx, which is also measured in mg/m^3. The TALuft does not apply for emergency stand-by equipment seeing as these will only run for a few hours a year. The TALuft emission levels are hard to meet without the installation of af-tertreatment. Engines with a rated thermal input equal or higher than 3MW need to comply with 0.5 g/m^3.

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The TaLuft has been used historically across Europe as an industry standard, thus it is a typical market specification. Nevertheless, the market does not specify the current TALuft regulation but an older version of it: the 2 grams TALuft. Most suppliers understand this as the best emission level that can be achieved without the use of aftertreatment. TALuft 2g is often a contractual requirement on stationary diesel generator sets, even for stand-by operation. This is a de-facto standard for Cummins Power Generation.

It is important to note that different countries, even different cities, may have different rulings and it is easy to get lost and not understand which ones to comply to. A good example of this is the Industrial emission directive; this directive only applies to combustion plants with a combined power of higher than 50MW and does not consider individual combustion plants with a rated thermal input of less than 15MW, However, small generator sets are occasionally asked to comply. In Figures 2

and 4 you can see, the typical values for TALuft2g and the evolution of NRMM emissions with their implementation date.

To limit the emissions of typical pollutants, France follows the “Arrêté type: Rubrique nº 2910” for any combustion application including diesel engines. This rule is stringent about nitrous oxides emissions (measured in mg/m^3) and is very difficult to meet without aftertreatment. It does however mention an application in which the genset does not run for more than 500 hours per year in which case it is more permissive. The world of emissions is an ever changing environment, and this regulation is undergoing new changes that should soon be released.

With these sorts of requirements, most prime power applications across central Europe use gas engines that have better fuel economy and emit less nitrous oxide than diesel engines.

Engine Emissions at prime rating corrected to 5% O2 content, are in compliance with the following TA-Luft Standards (see test conditions below):

Test Methods: TA-Luft emissons recorded per ISO 8178.

Diesel Fuel Specification:Cetane Number: 40-48, Sulfur (Wt. %): 0.03 - 0.05. Reference: 40CFR89 Subpart D Appendix A, table 5; ISO8178-5; ASTM D975 No.2-D

Reference Conditions: Air Inlet Temperature: 25oC (77oF). Fuel Inlet Temperature: 40oC (104oF). Barometric Pressure: 100 kPa (29.53 in Hg).Humidity: 10.7 g/kg (75 grains H2O/lb) of dry air; required for NOx correction. Restrictions: Intake Restriction set to a maximum allowable limit for clean filter; Exhaust Back Pressure set to maximum allowable limit.

Tests conducted using alternate test methods, instrumentation, fuel or reference conditions can yield different results.

TA- Luft:

NOx : 2000 mg/nm3

CO : 650 mg/nm3NMHC : 150 mg/nm3

Particulates : 130 mg/nm3

Test Conditions:

FIGURE 3

FIGURE 2

kVA, 80 hz Standby kW (HP) 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 201718 - 33 18 - 36 (24 - 48) 8.0 / 1.5 / 5.5 / 0.8 (7.5) / 5.5 / 0.538 - 55 37 - 55 (19 - 74)

7.0 / 1.3 / 5.0 / 0.4 (4.7) / 5.0 / 0.466 56 - 74 (75 - 99)70 - 110 75 - 129 (100 - 173) 6.0 / 1.0 / 5.0 / 0.3 (4.0) / 5.0 / 0.3138 - 550 130 - 560 (174 - 751) 6.0 / 1.0 / 3.5 / 0.2 (4.0) / 3.5 / 0.2

Stage II Stage IIIA

CPG Genset Power

NOx / HC / CO / PM (g/kW-hr) [Conversion: (g/kW-hr) x 0.7457 = g/bhp-hr](NOx+HC / CO / PM (g/kW-hr) [Conversion: (g/kW-hr) x 0.7457 = g/bhp-hr]

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Other European directives: It is also worth pointing out two more directives that drive the NRMM to lower emission standards. These directives are the National Emissions Ceiling (NEC) Directive and the Ambient Air Quality (AAQ) and Cleaner Air for Europe Directive.

The NEC directive protects countries within the European Union from receiving the pollutants that their neighbors emit. To control these pollutants the European Commission has decided to limit the maximum amount of a substance, expressed in kilo-tones, which may be emitted from a Member State in a calendar year. Thus, as industry develops, the emissions of the individual machines have to be lowered in order to accommodate this ceiling.

The AAQ directive establishes the need to reduce pollution to levels which minimize harmful effects on human health, paying particular attention to sensitive populations, and the environment as a whole. This directive divides the territory depending on their usage such as, rural, urban, industrial, etc. It imposes, among other things, the need to define a list of the main emission sources responsible for pollution (map) and the total quantity of emissions from these sources (tonnes/year).

Fuel:Understandably, it is difficult to get a clean output from any process that has a dirty input. Fuel quality has changed greatly over the years thereby increasing power output and decreasing its adverse effects on aftertreatment devices. The sulfur content, for example, affects the functioning of aftertreatment devices. The sulfur content has reduced from 10000 ppm to 10 ppm over the past 10 years or so enabling an extension to the useful life of catalyst used in aftertreatment devices.

The development of fuels for compression ignited (C.I.) engines does not stop at reduced sulfur percentages. Manufacturers continue to look at alternative fuels, innovative fuel systems, and new control strategies to improve the overall efficiency of the engine. Biodiesel is one such viable option. It is a fuel comprised of methyl/ethyl ester-based oxygenates of long chain fatty acids derived from the transesterification of vegetable oils, animal fats, and cooking oils. These fuels are commonly known as Fatty Acid Methyl Esters (FAME). Biodiesel properties are similar to that of diesel fuel, as opposed to gasoline or gaseous fuels, and thus are capable of being used in compression ignition engines.

Due to certain challenges associated with the fuel (Fuel quality, oxidation stability, contamination, microbe growth, etc), engine manufacturers are skeptical about the use of 100 percent biodiesel (B100). Blends of biodiesel with regular diesel are therefore widely used for prime and continuous applications, with B5 and B20 being highly popular in the market depending on complexity of the engine and the application. The number alongside the letter ‘B’ indicates the percentage of biodiesel in the blend. B5 would have 5 percent biodiesel; B20 would have 20 percent, and so on.

FIGURE 4

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• Diesel oxidation catalyst (DOC): DOC is a flow through device that consists of a canister containing a honeycomb-like structure or substrate. The substrate has a large surface area that is coated with an active catalyst layer. DOC is capable of achieving over 95 percent reduction in CO and HC. More specifically, DOCs utilize palladium and platinum catalysts to reduce the particulate matter (PM), hydrocarbon based soluble organic fraction (SOF), and carbon monoxide content of diesel exhaust by simple oxidation.

• Diesel particulate filter (DPF): Particulate matter is the most visible form of pollutant coming out of an exhaust pipe. It is the main constituent of black smoke or soot which has lead to the demise of diesel engines on a non commercial scale. DPF’s or particulate matter (PM) traps are designed to physically capture PM from the exhaust stream. They can either be simple mechanical filters requiring frequent replacement, or they can be catalytic filters that provide periodic or continuous oxidation (regeneration) of the trapped particulates into CO2. PM traps with continuous regeneration have already reached a high level of commercialization and are being employed on stationary diesel engines in areas with strict PM emissions regulations. Ultra-low sulfur diesel fuel is needed to prevent contamination of the conversion catalysts. However, filtration efficiencies up to 90 percent have been demonstrated.

Combustion:In essence, this is a process where chemical energy from fuel is converted into mechanical energy at the crankshaft. Of the exhaust contents, a small part by volume are major pollutants which are controlled by regulatory bodies. For diesel engines, combustion is a constant pressure heat addition. Therefore the method of adding fuel and the injection timing in relation to the crank position plays an important part. Additionally the in cylinder temperatures and pressures must be considered. Advancements in this field allow for multiple injections which help engines cope with varying load demands in an efficient way, see figure 4.

Aftertreatment:Exhaust aftertreatment reduces emissions by a great margin. Optimizing engine design, fuel systems, and advanced control strategies certainly help a great deal, and aftertreatment strategies can be seen as the next step. This level of emission control is what the stage IV regulations and other local regulations aims to achieve. The following methods have already gained practical levels of commercialization in various applications:

• Selective catalytic reduction (SCR): This is a very effective method for curbing NOx emissions and is basically aqueous urea injection into the exhaust stream passing over a suitable catalyst. SCR can reduce NOx up to 98 percent. Systems consist of an SCR catalyst, urea injection system, urea tank, pump and a control system. See Figure 5.

FIGURE 5

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Other advancements include:• Exhaust gas recirculation (EGR): A well proven

method of reducing NOx in internal combustion engines. By recycling a portion of the inert gases of the exhaust gas stream with incoming engine air, combustion temperatures are reduced, and therefore so is NOx formation. While not employed widely in stationary diesel engines at the present time, EGR may be used on selected engines to achieve compliance with regulations.

• Variable geometry turbo chargers (VGT) with inter-coolers: Allows for variable boost by changing the angle of the vanes. This greatly reduces the turbo lag at low load without compromising maximum boost at higher loads.

• Combustion chamber geometry: Design goals include achieving the optimum compression ratio and thorough mixing of fuel and air prior to combustion. Designs that optimize the air swirl and turbulence provide the best mixing and therefore the lowest emissions consistent with high power output.

• Common rail injection systems with fuel pressures up to 1,800 bars (26,000 psi): Injection timing, injection pressure, nozzle design and electronic injection systems have all proved significant in controlling both NOx and PM. Retardation of injection timing along with increased injection pressure has been shown to reduce NOx without significantly increasing the production of hydrocarbons (HC) or PM. Higher injection pressures and multiple injection events per cycle improve fuel atomization and combustion chamber penetration that simultaneously improve fuel economy while reducing PM.

• Electronic engine management: The addition of electronic sensors and microprocessor-based controls has greatly improved fuel efficiency and power output while decreasing the production of both NOx and PM. By controlling fuel quantity, injection timing, turbocharger boost pressure and other factors, electronic engine controls maintain optimum combustion efficiencies by compensating for load, temperature, fuel energy content, barometric pressure and even engine wear.

It is worth noting that all these advancements have pushed the thermal efficiency of the diesel engine from about 33 percent to over 40 percent.

ConclusionSince December 9, 2002, the European Commission harmonized emissions requirements for mobile diesel engines with the existing Non Road Mobile Machinery regulations. These regulations keep getting tighter, and as movement is made towards Stage IV requirements, a steep rise will be seen in the use of aftertreatment strategies bringing significant reduction in NOx and PM levels. Some installation locations are already familiar with the aftertreatment strategies which represent the best available control practices, but now these solutions will be applicable to a much larger population of generator sets. Thanks to the technological refinements taking place today, the electric power industry will continue to enjoy the performance advantages that diesel generators offer well into the foreseeable future.

For additional technical support, please contact your local Cummins Power Generation distributor.

To locate your distributor, visitwww.cumminspower.com.

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About the author

Aniruddha Natekar started with Cummins Power Generation in 2007 and currently holds the position of Territory Manager for the western region. Ani started with Cummins as a senior application engineer interfacing between engineering and front line sales. He provided engineering solutions and recommendations to customers and promoted Cummins’ technical expertise in key industry functions. Most recently Ani lead the marketing functions for highly competitive and crucial segments in the north America market. He provided key inputs in redesigning product lines and established short term initiatives as well as long term strategies to sustain market leadership in these sensitive markets.

Aniruddha has an M.S. in automotive engineering from Lawrence Technological University (Southfield, Michigan) and a B.S. in mechanical engineering from the University of Pune (India). He has held positions in research and development, market research, engineering and product development with a number of automotive companies prior to joining Cummins.

About the author

Gonzalo Fincheira is a graduate from the Ramon Llull University (Barcelona) with masters in chemical and mechanical engineering. He started with Cummins Power Generation in 2011 as an application engineer.

Gonzalo´s focus is on assisting clients and distributors with technical guidance on pre-sales for standard commercial product and application-specific issues for unique projects. Gonzalo is also engaged with the sales force supporting technical training and seminars.

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