Zero-Emission Locomotives on U.S. Railways?

Written by Alex Luvishis, Ph.D

Based on emerging technologies in batteries, hydrogen fuel cells and renewable natural gas, zero-emission motive power is a possibility.

In 2025, the U.S. EPA Tier 5 standard and the European Euro7 standard should come into effect. Both standards limit the emission of harmful substances by trains and locomotives to very low values. In particular, in the Tier 5 standard, in comparison with Tier 4, the value of NOx (oxides of nitrogen) decreases from 1.3 g/dHp-hr to 0.2 g/dHp-hr, and the value of PM (particulate matter) from 0.03 to 0.00. Thus, the standard requires zero PM emissions and almost zero NOx emissions.

Typically, long before standards change, locomotive factories design and manufacture prototype locomotives that meet the requirements of these standards. Already today, prototypes and many production locomotives have been manufactured that meet these requirements.

Depending on the primary energy source, three types of new rolling stock can be distinguished.


The EMD Joule battery-electric switcher locomotive from Progress Rail with power of 2,400 kWh will operate on the network of the Port of Los Angeles. These locomotives should be delivered in 2021.The locomotive is expected to operate for up to 24 hours without recharging, depending on the initial charge and load conditions. The six-axle electric locomotive is equipped with a modern asynchronous traction drive and has a capacity of 3,200 hp.

In October 2018, Wabtec (then GE Transportation) announced a plan to build a main line battery-electric locomotive in conjunction with BNSF. This locomotive is built on the Evolution Series diesel locomotive platform at the company’s plant in Erie, Pa. The body of the locomotive contains lithium-ion batteries with a total energy of 2,400 kWh, traction inverters similar to those used on diesel-electric locomotives with an AC drive, and a microprocessor control system. The locomotive, called the FLXdrive but designated as a BEL44C4D, is currently being tested as the middle unit in a three-unit consist, placed in between two Wabtec Tier 4 diesel-electrics. It is undergoing testing on freight trains between Barstow and Stockton, Calif., (approximately 370 miles) to accumulate train braking energy that will be used in traction mode. Fuel consumption by the diesel locomotives is expected to be reduced by 10-15%.

Thus, accumulator-type switching and main line locomotives have already been developed and will be delivered to the U.S. railways in the coming years. The traction units themselves have zero emission of harmful substances. However, for the complete absence of emission of harmful substances during their operation, it is necessary that the energy that is used to charge the battery traction units is green, that is, it is obtained from renewable energy sources—hydro-, wind and solar power plants.

Hydrogen Fuel Cells and Hybrids

On some modern hybrid trains and locomotives, fuel cells with proton-exchange membranes (PEMs), energy storage devices and an asynchronous traction drive are used. The two-car Alstom Coradia iLint train is the world’s first hybrid train with PEM fuel cells on board. Each of the cars contains a roof structure with compressed hydrogen cylinders totalling 94 kg, and a fuel cell module manufactured by Hydrogenics (a Canadian company now owned by Cummins) with a capacity of 198 kW. Under each car is a 110 kWh lithium-ion battery manufactured by Akasol, with converter equipment: an inverter, a converter for auxiliary needs and a pulse converter that matches the voltage at the output of the fuel cell module with 800V output of the traction battery. Each motor bogie is equipped with a 125 kW asynchronous traction motor. The train has 150 seats. The maximum speed of the train is about 90 mph. The range is 400-500 miles. 

Launched in September 2018 on the railroads of Lower Saxony in Germany, two Coradia iLint trains accumulated 100,000 km (just over 60,000 miles) of operational mileage by May 2019. It is expected that 21 such trains will be in service in 2021. After 2022, at least 48 of these trains will operate on German railways. In the coming years, HFC (hydrogen fuel cell) trains will appear on 10 railways around the world. Most of the trains have already been contracted.

In 2024, HFC passenger trains are expected to appear on U.S. railways. The San Bernardino County Transportation Authority, California, has contracted with Stadler to supply 5 FLIRT H2 HFC trains. The new train is based on the FLIRT electric multiple-unit, but will consist of three cars, the end units of which are cab cars with passenger cabins; the center car with equipment that houses fuel cells, hydrogen storage structures and a motor bogie with asynchronous traction motors. The train is expected to have 108 seats and a top speed of 80 mph.

In 2009, BNSF demonstrated a “hydrogen hybrid” fuel cell switcher locomotive, the HH20B, a modernization of the RJ Corman Railpower GG20B “Green Goat” series hybrid switcher locomotive. The HH20B uses a fuel cell unit instead of a 200 kW diesel generator set. Two 150 kW plants with solid-polymer electrolyte PEM cells from the Canadian company Ballard are used as fuel cells. The DC traction motors are controlled by pulse converters. The hydrogen necessary for fuel cell operation is stored in the form of gas in 14 cylinders with a pressure of 350 atmospheres. The total supply of hydrogen on the locomotive is 70 kg. The fuel cell modules are located in the place of the diesel engine on the GG20B hybrid locomotive, with hydrogen cylinders housed in a well-ventilated elongated hood above the batteries. The locomotive passed long-term operational tests in various climatic conditions. It was found that the amount of hydrogen on board the locomotive was enough for an average of 11.3 hours of operation. The refueling time for hydrogen cylinders is 25-45 minutes.

Canadian Pacific expects to have a prototype main line HFC locomotive within a few years. 

Modernized Diesel Engines

With the transition from Tier 3 to Tier 4 and the use of diesel fuel, exhaust gas cleaning systems have been used to reduce NOx and PM. To reduce NOx emissions, an SCR (selective catalytic reduction) neutralization system and exhaust gas recirculation are used, with particulate filters to reduce the PM.

If you use natural gas as a fuel by upgrading the engine, you can reduce emissions of harmful substances to the level of Tier 4 compliance without exhaust gas cleaning devices. Based on the Cummins 1SX12N engine, the KOFSG11.9400 series six-cylinder, 11.9L engine offers 400 hp. The engine has been used in 12,000 natural gas-fueled trucks, and in switcher locomotives on the Indiana Harbor Belt (IHB). Unlike other U.S. railroads that use LNF (liquefied natural gas), the IHB has converted two-thirds of its locomotives to CNG (compressed natural gas).

When using natural gas as a fuel, it is possible to significantly reduce emissions of harmful substances and meet the requirements of Tier 4, but not to achieve zero emissions. OptiFuel USA uses modified diesel engines and RNG (renewable natural gas) to achieve zero emissions. RNG, or synthetic natural gas is biogas from which impurities have been removed. By increasing the quality of methane-based biogas to the quality of natural gas, it becomes possible to distribute gas to consumers through the existing gas network.

The KOFSG11.9400 engine can run on any combination of RNG, CNG or LNG. When the engine is running on petroleum-based natural gas, NOx emissions are small, but not zero. When the engine is running on a combination of petroleum-based and renewable gases, NOx and PM are zero, as confirmed by IHB switcher locomotive tests.

Main line locomotives can also be built using modified engines and a combination of RNG and CNG/LNG. OptiFuel showcased a multi-engine power supply for a long-distance locomotive comprising four KOFSG11.9400 engines and an upgraded 2,700 kW Cummins QSK60 engine. The total capacity of the five diesel generator sets is 4,300 kW. In addition to diesel generator sets, the unit is also equipped with a small storage battery. This locomotive will use 83% natural gas as fuel, and will have a 20% higher efficiency compared to conventional diesel locomotives, at half the fuel cost. OptiFuel will modernize switching locomotives with body lengths from 13.4m to 20.7m. 

Prospects for Zero Emission Locomotives

On a large number of European railways, the completion time of the transition to locomotives with zero emissions of harmful substances is defined as 2050. U.S. companies like OptiFuel are more ambitious, saying this can be achieved in the U.S. by 2035. It cannot be ruled out that new breakthrough technologies will appear during this time.

Based on the technologies existing today, the prospects for battery-electric switcher locomotive are associated with a further decrease in the cost of lithium-ion batteries and an increase in the specific energy (Wh/kg) of such batteries, which will increase the energy storage of energy storage units and reduce their weight and dimensions.

Prospects for a battery-powered main line electric locomotive are associated with an increase in energy storage capacity, optimization of control, regulation and safety systems, and the use hybrid freight consists on all U.S. railways.

The prospects for switcher and main line locomotives with modernized engines and RNG depend upon development of technologies that will allow the production of large quantities of inexpensive RNG.

Broad prospects should open up for switching and, possibly, main line locomotives with fuel cells.The prospects are associated with a reduction in the cost of PEM fuel cells. A continuous decrease in their cost requires automation of the production process, an increase in the number of products. Over the 10 years from 2008 to 2018, the cost of Ballard’s fuel cells dropped by 70%.

An important method to reduce the cost of PEM fuel cells is to reduce the cost of their components, in particular, catalysts. Platinum and its alloys with no-less-precious palladium are most often used as catalysts in fuel cells. The use of nanotechnology makes it possible to create catalysts that are cheaper than platinum ones. In the U.S., France and South Korea, catalysts for fuel cells have been developed that are much cheaper and surpass them in efficiency and service life. 

New fuel cell switcher locomotives will be hybrids with permanent-magnet synchronous traction motors, variable frequency drive and regenerative braking.

Alex Luvishis, Ph.D. was head for 18 years of the laboratory that developed control systems for the first еlectric locomotives with asynchronous (AC) traction motors in the former USSR. He also headed, for seven years, the rolling stock department at the Institute of Technical Information of Railway Transport in Moscow. Dr. Luvishis is the author of more than 100 articles on electric traction drives and the book “Hybrid Rail Vehicles,” published in 2009. His interests are asynchronous traction drive systems of modern rolling stock and hybrid drive systems for trams, suburban and regional trains and switcher and main line locomotives. He has lived in the U.S. since 1999.

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