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On Track Toward Cleaner Large Engines

New emissions reduction strategies focus on locomotives and ferry boats

By Steven Fritz

Steven Fritz, shown in front of a 4,000-horsepower locomotive engine installed on SwRI's locomotive engine test platform in San Antonio, is a principal engineer in the Engine and Emissions Research Department within the Engine, Emissions and Vehicle Research Division. He leads SwRI's activities in locomotive exhaust emissions characterization and established the SwRI Locomotive Technology Center in 1992. To date, more than 100 locomotives have been tested. Fritz has led numerous projects involving characterizing both regulated and unregulated exhaust emissions from locomotive diesel engines covering 1,000 to 6,000 horsepower.

Although they remain among the most efficient means of transporting large volumes of freight, diesel-powered trains and marine vessels are subject to ever-increasing demands for greater fuel efficiency and lower exhaust emissions, just as their 18-wheeled diesel cousins on the highways. Environmental Protection Agency locomotive exhaust emission regulations, which took effect in 2000, are unique in that they apply not only to new locomotives but also to the existing fleet of approximately 20,000 locomotives in operation today that were manufactured between 1973 and 2000. Because these existing locomotives must be upgraded to meet EPA regulations during their next overhaul cycle, Southwest Research Institute (SwRI ) provides support for the industry in new engine research and in development of cost-effective emission reductions for the in-use fleet.

While railroads are one of the world's most efficient modes of transportation, diesel locomotive engines are subject to federal exhaust emission regulations that apply not only to new units, but also retroactively to locomotives built as long as three decades ago.

The approach to solving efficiency and emission problems in large compression-ignition engines follows generally along the lines that have been applied earlier to diesel truck engines. However, their sheer size and specialized applications require unique solutions. The nation's Class 1 railroads use approximately 4 billion gallons of diesel fuel each year. When fully phased-in, the new emission standards will reduce locomotive oxides of nitrogen (NOx) emissions by nearly two-thirds and hydrocarbon (HC) and particulate matter (PM) emissions by half. If emission controls were to cause even a 2 percent fuel economy penalty, it would cost the industry as much as $80 million per year.


Locomotive engines spend much of their operational lifetime running at idle, whether parked on a siding to make way for an oncoming train or waiting in a switchyard while railcars are being collected and coupled to make up a new train.

The large engines, some with as many as 20 cylinders, do not provide power directly to the wheels, but instead turn a generator that provides electricity for traction motors that drive the wheels. The engine also powers all critical accessories and environmental systems aboard the train, such as air brakes for the whole train and heating and air conditioning for the locomotive cab. For this reason, and for safety when operating in remote areas where a dead battery might result in a long delay, locomotives are frequently left idling in switchyards and on sidings.

In areas with cold climates, letting the engines idle prevents coolant water from freezing in the radiators. Locomotives typically use no antifreeze because undiluted water is a more efficient cooling agent. An antifreeze-based cooling system would require 20 percent more cooling capacity, which would be difficult to accommodate because even modern locomotives' cross-sections must fit railroad tunnels built more than 100 years ago. One fuel-saving approach examined by the SwRI team was to reduce the amount of time a locomotive's main engine is kept running when it is not actually pulling a train.

A locomotive with a 2,200-horsepower diesel electric powerplant was involved in a program in which an auxiliary power unit was installed to meet critical energy demands when the main engine was shut off.

APU Applications

The Texas Emission Reduction Plan (TERP), established by the Texas Legislature in 2001 and administered by the Texas Commission for Environmental Quality (TCEQ), provides grants and incentives for improving air quality in the state.

In a TERP-funded program in which a grant was provided to a manufacturer of auxiliary power units (APU), SwRI engineers were asked to evaluate the performance of a typical locomotive with an APU installed. The four-cylinder, diesel-powered APU is designed to meet critical energy demands when the main engine, a 2,200-horsepower diesel-electric powerplant, is shut off. Funded by a TERP grant, EcoTrans Technologies LLC, a joint venture of International Road and Rail and CSX Transportation, asked the SwRI team to gather baseline data from two switcher locomotives in normal configuration, then quantify any emissions reductions from the same two locomotives fitted with an APU.

Two switcher-service locomotives were supplied by the Burlington Northern Santa Fe (BNSF) Railroad for the test program. SwRI engineers installed an automatic switch that would turn off the locomotive's main engine after 30 minutes in "park." Sensors would then monitor battery power, air pressure, and water and oil temperatures. If a sensor reached a critical level, the APU would be started automatically to charge the batteries and circulate and heat the main locomotive engine water and oil, while also maintaining air pressure for the train's air-brake system. The APU-equipped locomotives were placed into regular freight service in the Houston-Galveston area of Southeast Texas and monitored for one year.

SwRI engineers and technicians also measured emissions from the APU itself at various load levels. In addition, they installed a global positioning system (GPS) recording device to monitor the engine's movements and a data transmitter that used cell-phone technology to download data reports from the two locomotives to engineers in San Antonio on a weekly basis.

Institute staff members repeatedly disassemble engines to inspect components such as this piston from a diesel-electric locomotive engine. Modern locomotive engines may have 12, 16 or 20 cylinders.

Positive Results

After a year of monitored operation, each of the APU-equipped locomotives saved some 22,000 gallons of diesel fuel compared to a normal engine. That fuel reduction translated into a net 4.8-ton annual reduction of NOx for each locomotive in the East Texas area.

In addition to its fuel-saving potential, the APU also proves an economical means of installing cab upgrades in aging locomotives. Most older locomotives were not built with cab air conditioning, and because they operate on 74-volt DC electrical systems, modifying off-the-shelf cooling equipment for installation in the cab is difficult and expensive. With an APU providing 60 Hz, 120-volt AC power to the cab, any of a number of commercial air conditioning units could be installed at a fraction of the cost.

Control circuitry is shown for a small diesel auxiliary power unit installed in a locomotive to supply engine cooling and electrical power while the main engine is shut off.

Follow-On Locomotive Engine Research

SwRI is working with EcoTrans on a follow-on program to evaluate the potential for further emissions reductions by installing custom-designed fuel injectors for the locomotive main engine.

For this TERP-funded project, the follow-on work is funded by the TCEQ New Technology Research and Development (NTRD) Program, and involves assessing the NOx emission reduction potential of fuel injectors specifically designed for NOx reductions from the EMD 645-E engines used in these switcher locomotives. SwRI performed the testing that led to the development of the specifications for these new fuel injectors, and, in this new program, will test the final product as installed in the two BNSF locomotives that were equipped with the APUs. As a result, NOx reductions from these two locomotives will be reduced not only due to the automatic shut-down systems, but also when they are pulling trains. The existing SwRI data-loggers installed on the locomotives will be modified to include monitoring of the main engine operation so that overall NOx emission reductions can be calculated.

SwRI has acquired a test locomotive, WC6624, that can accommodate General Motors ElectroMotive Division (EMD) engines of 8, 12, 16 and 20 cylinders.

Recognizing the need to test bare engines, before they are installed in either a locomotive or a marine vessel, SwRI obtained an EMD SD45 locomotive which serves as a "test cell on wheels." The SD45 locomotives were equipped with 20-cylinder engines, which means that they will accommodate EMD 20-, 16-, 12- and 8-cylinder engines. The locomotive is equipped with all of the necessary components to support engine operation, such as the lubricating oil cooler, the jacket water radiators, the alternator and associated control circuitry, and an on-board load grid to dissipate the power generated by the engine. Since commissioning WC6624 in the fall of 2003, SwRI has performed project work using its 12-645-E3B test engine and external customer-supplied engines for both locomotive engine development work and for marine engine certifications.

Most line-haul locomotives are equipped with the "dynamic brake" feature in which the electric motors used for traction are reverse-excited to become generators for slowing the train. The electrical power generated is dissipated in resistance grids. Locomotives with the self-load feature can dissipate the main alternator power into these "dynamic brake" resistance grids. WC 6624 is equipped with dynamic brake grids capable of dissipating the full engine power, and these grids are used to load the stationary locomotive.

Dynamic braking can generate prodigious amounts of energy, amounting to 4,000 to 5,000 horsepower. However, since no technology exists to capture or store such large bursts of energy efficiently, the excess electricity is diverted to resistance heaters, or "toaster grids" atop the locomotive, which dissipate the energy as waste heat.

Ferries such as this one, operating on the Gulf Coast near Galveston, Texas, are powered by large, 12-cylinder diesel engines similar to those that power railroad switcher locomotives. SwRI engineers are logging operating characteristics of these engines to assist the Texas Department of Transportation in reducing NOx emissions from its ferry fleet.

Ferry Boat Engines

A program for the Texas Department of Transportation (TxDOT), funded by the Houston-Galveston Area Council of Governments (H-GAC), involves investigating emissions reduction technologies on ferries operating between Galveston and Point Bolivar. Those diesel-powered ferries are equipped with 12-cylinder engines similar to those used in switcher locomotives. The program's goal is to reduce NOx emissions by 70 percent, which would amount to a savings of 1,600 pounds of NOx per day based on fuel consumption of 1.8 million gallons of diesel per year.

One promising technology for achieving that goal involves the use of selective catalytic reduction (SCR) of exhaust gases. However, this technology requires that exhaust temperatures be maintained at sufficiently high levels to allow the catalyst to operate efficiently. The SwRI team believes that if exhaust temperatures are sufficient, SCR systems could be installed in the space currently occupied by the mufflers in the ferries' center sections without significant structural modification to the boats.

Two in-service ferries were fitted with instruments to record and log engine speeds, loads and exhaust temperatures over a three-day period of continuous operation. Once this baseline information is processed, it will be used by TxDOT in an upcoming request for proposals to reduce NOx emissions from the TxDOT ferry fleet at Galveston.

Locomotive control systems limit engine operation to specific speed and load conditions, while the same engine in marine applications experiences a much broader range of speeds and loads. This difference in operating characteristics between these two applications of the same engine can influence the approach used to reduce NOx emissions.


Medium-speed diesel engines are the workhorse of the locomotive industry in North America, and these same engines are also very popular in industrial marine applications, and also for primary and emergency electrical power generation. Although each sector faces somewhat different timetables on emission regulations from the EPA, the general approaches to developing and applying emission reduction technologies are very similar. SwRI's experience in emission measurements on these large engines, combined with broad expertise in automotive, truck and marine engine emission measurements and emission reduction technologies, have resulted in a unique facility that will continue to serve this industry.

Comments about this article? Contact Fritz at (210) 522-3645, or


The author greatly acknowledges the team effort of the Locomotive Technology Center, particularly the support and expertise of Eddie Grinstead, John Hedrick, Eugene Jimenez, James Height and Kathy Jack, all of the Department of Engine and Emissions Research.

Published in the Spring 2004 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Joe Fohn.

Spring 2004 Technology Today
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