The Impact of Tier 4 Emission Regulations on the Power Generation Industry White Paper
By Aniruddha Natekar, Sales Application Engineer, Cummins Power Generation Santhosh Sorab, Marketing Manager, Cummins Power Generation
Regulations for diesel engine emissions have been in existence for almost 40 years. They focused mainly on the on-highway engines
The first set of emission regulations for non-road engines was introduced with the Tier 1 regulation in 1996, and since then the EPA has tightened emission regulations, driving engine manufacturers to pursue
until 1996, when non-road engines
technological advancements. Compared
were brought into focus as well.
to previous EPA emissions requirements,
The Environmental Protection Agency (EPA) “non-road” category of engines refers to engines used in mobile applications such as farm equipment, construction equipment and mobile power sources, including generator sets on trailers and other portable industrial engines used in temporary off-road/off-highway applications.
current allowable levels of nitrogen oxide (NOx) and particulate matter (PM) — the two main pollutants in diesel engines — have been reduced significantly.
The Impact of Tier 4 Emission Regulations on the Power Generation Industry
Off-highway Emissions Evolution Stationary engines are defined as any engine that is permanently installed or located on-site for a minimum
9.2
period of 12 months. All other
Tier 1/Stage 1 (1996)
applications are considered mobile
NOx [g/kW-hr]
02
applications and must meet Tier 4 Final regulations starting in 2014 for some power categories. By 2015, all power categories are mandated by the EPA to meet Tier 4 standards.
2.0
Currently, Tier 4 is the strictest engines mandated by the EPA. Tier 4
Tier 2/Stage II (2001)
4.0 Tier 3/Stage IIIA (2005)
Moving to Tier 4 emissions requirement for diesel
6.4
90% Lower
has been phased in, for most of the power range, since the introduction of the EPA’s Tier 4 interim (Tier 4i)
0.4
Tier 3 Interim/Stage IIIB (2011)
Tier 4 FInal/Stage IV (2014)
0 0.02 90% Lower
0.2
0.54
PM [g/kW-hr]
requirement. The interim requirement is typically less stringent on one of the components of the diesel exhaust emissions — either NOx or PM. Since 2008, the Tier 4 requirement has been in effect for engines below 25 hp, and the Tier 4i requirement has been in effect for engines in the 25– 48 hp range. For engines that are greater than 48 hp and fall within the EPA’s targeted power ranges, Tier 4i has been in effect since 2011– 2012. The transition to the final Tier 4 requirement is being phased in between 2013 – 2015, depending on the power range. Please note that these power ranges are based on the mechanical output of the engine and not the
Emergency Power The Tier 4 regulations impact diesel engines used in power generation, industrial applications, oil and gas markets, and mining, as well as mobile equipment mounted on trailers. However, stationary emergency generators greater than 49 hp are exempt from this requirement and are allowed to stay at current Tier levels. These include only those standby generators which provide power in the event of disruption of the normal power source. Generators used for peak
electrical output of the generator set.
shaving or prime power will still need to comply with
Tier 4 levels have resulted in a reduction in exhaust
applications must meet Tier 4.
emissions levels of more than 95 percent. Also note that the quality of fuel has changed dramatically through the years — dropping from 500 ppm of sulfur in low sulfur diesel to a recent 15 ppm of sulfur in ultra-low sulfur diesel.
the Tier 4 interim or Tier 4 regulations. All mobile
03
Non-attainment Areas and Local Regulations In the U.S., certain state and local emissions standards for diesel-powered generator sets require an additional level of control, primarily for NOx and PM. While the EPA-designated “non-attainment areas” represent a fraction of the land area of the country, they are typically found in heavily populated areas. The U.S. metropolitan areas that meet the National Ambient Air Quality Standards (NAAQS) are said to be in “attainment” for specific contaminants. Those areas not meeting the standards are said to be in “non-attainment.” Check with the local air quality regulator or your local power generation equipment provider for the most recent information.
Solution Strategy PM and NOx are the two most significant diesel engine exhaust constituents and have been considered as two sides of a see-saw. High temperatures and excess oxygen are conducive to the formation of NOx. Lowering the in-cylinder temperatures and oxygen content does reduce NOx; however, it decreases the fuel conversion efficiency and increases soot (or PM) production. Placing a limit on both these constituents at the same time has challenged engine manufacturers to develop innovative, alternative solutions.
(A) Technological Solutions All existing technologies meeting the Tier 4 emission levels can be classified under one of the following: 1. In-cylinder technology, or 2. Aftertreatment systems
2. Multiple fuel-injection capability provides more combustion control and improved part load performance — in terms of emissions and fuel consumption — without sacrificing power. 3. Advanced fuel-injection systems, like modular common rail fuel injection, provide improved stability, cold start and transient response while maintaining power densities. 4. Solenoid-controlled electronic injectors add precision to the delivery of fuel. 5. New engine control modules with improved sensors control engine operating parameters more precisely and are critical to maximizing power output. 6. High-durability Ferrous Cast Ductile Pistons: Stronger than aluminum, especially when operating at higher temperatures; help deliver optimum power output. 7. Charge air cooling to reduce the temperature of the turbocharged air before it enters the combustion chamber. 8. Cooled exhaust gas recirculation, which potentially recycles a part of the exhaust to drop combustion chamber temperatures and reduce emissions at part loads. The intercooling would further aid in dropping in-cylinder temperatures. 9. Variable geometry turbocharger gives precise control of airflow at all engine speeds and loads and effectively provides necessary pressure differential to drive EGR. 10. ‘Miller Cycle’ philosophy using Variable Valve Actuation (VVA) allows for late intake valve closing, thereby reducing the effective compression ratio, resulting in lower compression temperature and therefore lower NOx. Despite these innovations, there are limits to what in-cylinder technologies can do before one starts
In-cylinder technology may include:
approaching the mechanical limits of the currently
1. New combustion bowl geometry for optimum combustion.
existing hardware. A closer look at the emission schedule also reveals that as the engine power increases, the emission levels actually tighten. This calls for something beyond the realm of in-cylinder technological advancements as they stand today.
The Impact of Tier 4 Emission Regulations on the Power Generation Industry
For aftertreatment systems, again there are multiple
Some important things to note on aftertreatment
strategies. Depending on the requirement, some or
technology:
all of the following may be used:
Other than the obvious downside of additional costs,
1. A diesel oxidation catalyst (DOC), which is a flowthrough device where exhaust gasses are brought in contact with materials that oxidize unburnt hydrocarbons and reduce emissions.
the increase in technology does come with significant
2. Selective catalytic reduction (SCR) units comprise a system where a “reducer� is added to the exhaust flow to create the reactions in a catalyst chamber. 3. Diesel particulate filters (DPF) are devices designed to physically capture the PM from the exhaust stream. With advanced fuel-injection systems, it is possible to eliminate DPF through in-cylinder mechanisms. Cummins Power Generation employs high-pressure common rail fuel-injection systems to eliminate DPF for Tier 4 in a majority of our engine platforms. This allows enhanced fuel efficiency while meeting emissions norms at the same time.
challenges that need to be carefully addressed. Cooling the exhaust gas before recirculating, for example, is an effective method for reducing incylinder temperatures to reduce NOx. However, this could lead to increased engine heat rejection, leading to an impact on the cooling system design and size. Similar challenges also exist for aftertreatment solutions ranging, from packaging and space constraints to thermal management and serviceability. With some aftertreatment devices like DPF, there could be a significant amount of back pressure, requiring precise, duty cycle-based control of temperatures and dosing frequency for regeneration. Most aftertreatment devices also require high temperatures to reduce emissions,
UQS & DEF Tank
NOx
SCR
DOC
AMOX
DEF Doser, Module
NOx
04
VGT provides additional heat to DOC & SCR for efficient NOx conversion
VGT
DirectFlow air filter
Intake throttle
QSB6.7 - HPCR Bosch QSL9 - Cummins XPI
EGR valve
05
which could be a challenge under light loading. To overcome the challenge with light loads, Cummins incorporates an intake throttle mechanism for generator applications, which ensures optimal air to fuel ratio by precisely controlling air flow.
(B) Transition Program for Equipment Manufacturers (TPEM) The U.S. EPA created the TPEM program to provide original equipment manufacturers (OEMs) with flexibility to comply with the new emission regulations. This program basically allows equipment manufacturers to produce a specific percentage or number of units with engines meeting the previous Tier standards. The program is only available for applications that are considered non-road.
Conclusion With the introduction of Tier 4 emission regulations by the EPA, the industry has progressively moved toward cleaner and greener energy solutions. Tier 4 brings a significant reduction in both NOx and PM levels, which requires a new generation of diesel engines and aftertreatment devices. With appropriate technology selection, the transition to Tier 4 can be not only a transition to the latest EPA regulation, but also a transition to a cleaner and more efficient technology.
06
The Impact of Tier 4 Emission Regulations on the Power Generation Industry
About the authors Aniruddha Natekar started with Cummins Power Generation in 2007. As a sales application engineer, he provides technical recommendations on installations and engineering support to customers, assists the sales force with technical training, and supports technical seminars. 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 held positions in R&D, market research, engineering and product development with a number of automotive companies prior to joining Cummins Power Generation.
Santhosh Sorab is a marketing manager with Cummins Power Generation. He started with Cummins in 2010 in product planning and is currently responsible for marketing and product requirements on Cummins Power Generation’s Tier 4 Final product development. Santhosh has significant experience working with diesel emissions regulations and emissions control technologies from his past work in the automotive industry. Santhosh holds an MBA from Thunderbird School of Management and has completed his B.S. in electronics engineering from Vishweshwariah Technological University in Bangalore, India.
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