Anhydrous ammonia (NH3) is an energy-dense, ultra-clean-burning liquid fuel that can be made from water and air using hydroelectric power. Ammonia holds promise as a domestically-produced, renewable, and clean fuel.
By John H. Holbrook
You’re probably asking yourself what an article about internal combustion engines operating on ammonia fuel is doing in a journal whose primary emphasis is hydroelectric power generation. Well, the answer may surprise you. Anhydrous ammonia (NH3) is an energy-dense, ultra-clean-burning liquid fuel, and it can be made from simply water and air using hydroelectric power, or other clean renewable power.
NH3 has roughly half the energy density of gasoline or diesel fuel, with all of its energy coming from hydrogen. Its combustion products are merely nitrogen and water vapor since it contains no carbon, and therefore it emits zero greenhouse gases as it delivers its power. NH3 has an octane rating of approximately 120 and can be operated directly in a gasoline-type (spark ignition) or in a diesel-type (combustion ignition) engine, the latter with a small amount (about 5 percent) of a high cetane fuel, such as biodiesel, blended in. NH3 also can be used to power direct ammonia fuel cells.
A history of the use of anhydrous ammonia
Fritz Haber won the Nobel Prize in 1917 for being the first person to show that nitrogen could be fixed (converted from nitrogen in the air to a chemical form accessible by plants) in an efficient process to produce NH3 at large production scales. Since that time, billions of tons of NH3 have been made by that process and have helped to increase crop production to meet the earth’s food needs.
In the 1930s, engineers from Norway and Italy demonstrated vehicles whose standard piston engines could operate on NH3 as a fuel. Largely, these demonstrations were driven by shortage of gasoline, rather than a desire to decrease emissions.
In the 1940s during World War II, Belgium ran its commercial transportation buses on an ammonia-rich fuel blend with heating oil. Those buses ran for thousands of miles during the war.
In the 1960s, ammonia was chosen as the fuel of choice for the U.S. military’s Energy Depot concept because it could be synthesized in the field. Also in the 1960s, the X-15 rocket plane set speed and altitude records using ammonia as a fuel.
Current, future opportunities
Energy independence, freedom from fossil fuels, greenhouse gas emissions, and rising gasoline prices are all reasons why ammonia fuel is coming onto the world stage. Ammonia and hydrogen are the only practical fuels that oxidize/ combust with zero greenhouse gas emissions. But, ammonia is considerably easier to store and transport than hydrogen. It also has a higher energy density than hydrogen. In fact, ammonia has the highest hydrogen density by volume of any liquid fuel — some 50 percent higher than cryogenic liquid hydrogen itself. Thus, motorists would not have to sacrifice driving range if their vehicles operated on ammonia.
Anhydrous ammonia fuel can be produced from simply water and air using clean, inexpensive electricity such as that from hydroelectric projects. That’s because NH3 is inherently a carbon-free fuel. The only other fuel that can make a similar claim is elemental hydrogen (H2), but, as just mentioned, hydrogen suffers significant problems as a practical fuel in storing sufficient energy in small volumes. On the other hand, NH3 can be synthesized from hydrogen and nitrogen. The hydrogen comes from electrolysis of water (it takes about 55 kilowatt-hours to make an amount of H2 with an energy equivalent of 1 gallon of gasoline). The nitrogen comes from the tried-and-true industrial process of air separation. The hydrogen and nitrogen are then combined at high temperature and pressure over proven and inexpensive catalysts (i.e., the Haber-Bosch process) to produce anhydrous ammonia.
This process of producing NH3 (for fertilizer) using hydropower was used extensively on a commercial scale in numerous countries until the 1980s. About that time, many of those “e NH3” plants had to be shut down because they could not compete with the price of NH3 produced using natural gas (essentially methane, CH4, to provide the H2 for the NH3 molecule, and to power the conversion process). Today, however, new technologies are being developed that will make “green ammonia,” i.e., ammonia produced without fossil fuels to supply the H2, and which are expected to challenge or beat the price of ammonia produced with natural gas or coal.
This S10 pickup — operating on 80 percent NH3/20 percent gasoline — made a trip from Detroit to San Francisco in the summer of 2007.
In the future, ammonia will power fuel cell vehicles as well as stationary fuel cell power systems. Certainly, development of direct ammonia fuel cells is well under way. But the real promise of ammonia fuel is that it can be used in internal combustion engines (ICE) today, although no major automaker is currently producing ammonia-fueled vehicles.
On the other hand, there has been considerable progress in the last few years in demonstrating the performance and promise of ammonia-fueled ICEs. For example, the Canadian company Hydrofuel recently announced the availability of equipment and services to convert gasoline-powered vehicles to run on 100 percent NH3. This company first began work on ammonia ICEs in the early 1980s.1
In another example, in the summer of 2007, a Michigan team drove an S10 pickup, operated on 80 percent NH3/20 percent gasoline, from Detroit to San Francisco.2 The pickup has two separate fuel tanks and can be operated on the ammonia blend or on straight gasoline. The Michigan developers state that this “dual-fuel” feature will allow for a seamless transition to ammonia fuel by providing gasoline back-up operation.3
In a third example, a company headquartered in Iowa, Hydrogen Engine Center (HEC), is concentrating on ammonia ICEs for stationary power applications. The company has a 65-kW engine reliably pumping irrigation water in the San Joaquin Valley. The unit operates on an ammonia-rich blend with propane, but the goal is to have it operating on 100 percent NH3 within two years. For this irrigation pump application, the use of an ammonia-fueled engine to replace a gasoline or diesel engine is crucially important because of the increasingly strict air emissions standards in the valley. HEC is putting a great deal of its development focus on ammonia-fueled engines, believing ammonia to be a key fuel for the future.4
This 65-kW engine, powered with an ammonia-rich blend with propane, is used to pump irrigation water in the San Joaquin Valley.
There is also ongoing development of diesel-type engines operating on ammonia for both highway and marine applications, as well as stationary back-up generators. Since ammonia has such a high octane rating, it will not compression-ignite in a diesel and thus needs a high-cetane additive. Recent efforts are examining the most effective ways of carrying out the blending step. Both emulsions and co-injection are being examined.5 Results for both approaches are encouraging.
Because ammonia can be synthesized from water and air, and then used to fuel a variety of generators, it offers significant promise as a means for storing energy, such as time-variable wind or solar energy. The key to success for ammonia as a renewable fuel will be the availability and performance of efficient electric power generators that will operate on ammonia. The previous examples of ammonia ICEs point to hope for continued success at achieving those goals and providing a new tool for managing our energy resources.
Mr. Holbrook may be reached at 1161 Viewmoor Court, Richland, WA 99352; (1) 509-396-2082; E-mail: john. firstname.lastname@example.org.
- www.hydrofuelNH3.com and www. youtube.com/watch?v=L0hBAz6MxC4
- www.energy.iastate.edu/becon/ downloadNH3/AmmoniaMtg07.html
- www.hydrogenenginecenter.com and www.energy.iastate.edu/becon/ downloadNH3/2007/HEC.pdf
- www.energy.iastate.edu/becon/ downloadNH3/2007/Agosta_NH3. pdf; www.energy.iastate.edu/becon/ downloadNH3/2007/Kong_NH3.pdf
John Holbrook is the director of AmmPower LLC, a consulting company focusing on stationary and vehicular applications of ammonia as a fuel. He also is the chief executive officer of NHThree LLC, a company commercializing a high-efficiency “green” ammonia synthesis technology. And, he is co-chair of the Ammonia Fuel Network, a non-profit associa- tion promoting and growing the use of ammonia as an emission-free fuel. John spent almost three decades in technology development and project management in the U.S. Department of Energy national laboratory system.