My first reaction when reading this sentence in the recent New Scientist article "Ammonia cleans up"  was disbelief. How can internal combustion engines run on ammonia? And, just assuming this is possible, when has ammonia been used as a fuel? After some historical research, I soon found that internal combustion engines – and diesel engines – can indeed be run on ammonia (which produces nitrogen and water when burned), and that ammonia actually has been used as a biofuel. As we shall see, ammonia fuelled a fleet of buses in Belgium during World War 2, something now long forgotten.
Fig. 1: A sketch showing one of Dr. Emile Lamm's ammonia engines, used to provide public transport in New Orleans between 1870 and 1872. Source: Wikipedia: Public domain.
And, in the early 1960s, ammonia was seriously evaluated as an engine fuel by none other than General Motors, in a project for the US army. This fuel, as we shall see in the next article, was to have been produced by “a mobile nuclear reactor” . Ammonia was also used with liquid oxygen to power the X-15 rocket plane, which "set speed and altitude records in the early 1960s” and still holds “the official world record for the fastest speed ever reached by a manned rocket-powered aircraft" . More recently, ammonia has been used in 2007 to power an S 10 pickup [bakkie], operated on 80% NH3 /20% gasoline, from Detroit to San Francisco .
Especially interesting to South African readers is the work being done by the Hydrogen Energy Center on ammonia ICEs [Internal combustion engines] for stationary power applications like irrigation pumps , and the future possibilities of ammonia for electric power generation . Ammonia is already being made experimentally using wind power in Minnesota . Even Albert Einstein used ammonia, in a design for a safe refrigerator he and his former student Leo Szilard patented in the US [20, 21, 22].
Fig. 2: An ammonia-powered bus, photographed after the successful inaugural trip in Brussels, in May, 1943. Note the cylinders of coal gas fixed to the roof, and the two standard cylinders (each holding 56,6 kg of ammonia) fixed to the front of the vehicle. Source: Ammonia Fuel Network (Illustration reproduced from Reference 2, p 215, published by the Energy Institute).
But before seeing the first (and last) mass use of ammonia as a biofuel – in Belgium, between 1943 and 1945 – let us look at two brief and very different attempts to use ammonia as a fuel. Although both failed, they give a good idea of the problems of using ammonia as a fuel. What follows shows that the first attempt to use ammonia for public transport (although not as a fuel) probably took place in New Orleans in 1870.
Ammonia power in New Orleans: in 1870
"The railroad company, having experimented with horsepower, cable power, and human power, then turned its attention to ammonia power" .
Today, most people associate the American city of New Orleans with the disastrous flooding hurricane Katrina caused there in 2005. Few people realise that this city is known for something else: the St Charles Street car line, the "oldest continuously operating street railway in the world" and one of the first passenger railroads in the United States, formally established on 9 February, 1833 , and still operational today.
In fact, the shape of New Orleans, actually comes from this same railway. As the city grew, new streets followed the curve of the railroad and river, rather than the usual grid of most American cities, because the original railway line, which connected the very beginnings of New Orleans, had followed the curve of the nearby Mississippi River. No fewer than four systems of powering the passenger cars have been used at various times: using horses, an overhead cable traction system, humans, ammonia, and, finally, electricity.
Between June 1870 and April 1872, the company experimented with ammonia-powered transport designed by a Dr. Emile Lamm (see Fig. 1). Exactly how this system worked is not described clearly in the source, other than that the ammonia engine was similar to a steam engine, except that a solution of water and ammonia provided the motive power . Presumably, a solution of ammonia in water was heated and the ammonia gas released drove a piston (in the same way steam does in a steam engine), before being recycled and reabsorbed in the water.
Fig 3: Flow sheet of Gazamo equipment. (Illustrations reproduced from .
While not successful in the long term - these engines were later converted to steam – this little known episode does show that ammonia was used in public transport as long ago as 1870, and that this strange system proved cheaper than using horses. . The steam engines that replaced them were also designed by Dr. Lamm. These were the so-called "fireless engines", where steam was stored in a pressure tank, and the passenger car then traveled until the steam tank was refilled from another depot. Although this system seems bizarre to modern readers, it must have been reasonably successful, as it was built under license in Paris and used extensively on Paris street railways until World War 1 [7 ].
Ammonia and Rudolf Diesel – a narrow escape
"It occurred to me that atomised fuel should be injected into compressed hot air instead of ammonia and, as it ignites, expanded in such a way that maximum heat could be put to useful work" .
In 1890, Rudolf Diesel and his family moved to Berlin from Paris, where he had been working at a refrigeration and ice plant for 12 years as a refrigeration engineer. As this work involved patents that he could not use after leaving, Diesel began work on something new: better, more efficient engines. After a building a steam engine that used ammonia vapour (maybe intended as an improvement on Dr. Emile Lamm's ammonia engine), he was conducting tests when it suddenly exploded. Lucky to escape with his life, he spent months in hospital followed by health and eyesight problems .
While recovering, he had a sudden flash of insight: that atomised fuel should be injected into compressed hot air , which formed the base of the revolutionary engine that now carries his name, the diesel.
Although years of hard work and testing separated this insight from the first workable prototype in 1895, it is strange to think that his ultimate success – and the Belgian bus engines that first used ammonia in 1943, came after an explosion caused by ammonia.
Using ammonia to power buses – successfully
"The first utilisation of liquid anhydrous ammonia as a fuel for motor-buses took place during the year 1943. The first motor-bus was equipped and put into service in April 1943, and since then eight buses operating on three lines have covered several tens of thousands of miles, leaving and arriving on schedule, thus maintaining an important public service for the Belgian civilian population" .
In October 1942, the management of the Belgian rail and road authority were confronted with a massive problem.No more diesel fuel would be available for motor buses. This meant that, unless another fuel could quickly be found, many Belgians would suddenly be without transport.
The engineers, together with Belgian specialists, made a rapid survey of possible alternate fuels. One option – liquid petroleum gas (the propane/butane mixture that is used today to power some vehicles) was speedily discarded because not enough was available. The other two options considered were compressed coal gas or producer gas. Both of these are what is called synthesis gas, a mixture of carbon monoxide and hydrogen, obtained by heating coal.Coal gas had then been produced for decades in Europe, by heating coal, and was still available. Producer gas, made from heating wood chips, had already been used since the early days of World War 2 to power cars, trucks, boats and just about anything else that normally ran on petrol or diesel.
The snag was that either of these options would have meant a loss of power of 25 – 40%  compared to diesel, and the buses were already carrying loads much higher than pre-war days, as the number of passengers had increased by at least 30% per bus . A last option was compressed coal gas. But, because of the relatively low BTU content of the then-produced gas, around 400 BTU per cubic foot, this would have meant carrying a large number of steel cylinders of compressed coal gas by each bus, just to carry enough fuel for one round trip. This would have further reduced the carrying capacity of the buses which was already strained to the limit.
As no effective replacement for diesel seemed possible, the bus service was discontinued in November, 1942, causing great inconvenience to the population . Then someone thought of ammonia.
Saved by ammonia
"The Gazamo process, which has been tested on the road principally during the severe winter of 1941-42, appears to be the first application on a fairly large scale, as about 100 vehicles were equipped for use of ammonia as fuel" .
Ammonia can be burned using the oxygen present in air, to produce nitrogen gas and water. The problem is getting it to burn. One way of managing this is to add hydrogen, or a source of hydrogen, to the ammonia/air mixture. Today, we know that the hydrogen does not need to be present as a gas, but can even be chemically bound to another atom like carbon, making methane, propane, natural gas or even biodiesel a suitable additive to make ammonia burn. For example, recent research shows that a 5% biodiesel and 95% ammonia blend works well in farm machinery .
Although patents for the use of anhydrous ammonia as motor fuel can be traced back to 1905, the first practical way of using ammonia as a fuel was that of Ammonia Casale, a Swiss company . This system, which involved the partial thermal decomposition of ammonia in a catalytic chamber heated with exhaust gases from the motor [to yield some hydrogen] was used to power a Fiat 509 600 km from Terni to Trieste with fixed stops for checks and statistical findings .
The ammonia patents had been further refined in the Gazamo process, which used cylinders of compressed coal gas and anhydrous liquid ammonia, and had already been exhibited at the Alternate Fuel Exhibition held in Brussels in June 1942. Thus it was that the engineers approached the developers of Gazamo process. Little did they realise their buses were about to make history. The first and last mass trial of ammonia to power public transport. Coal gas containing roughly 50% hydrogen is used to promote the ignition of the air-ammonia mixture .
On May, 1943, the first bus adapted to use ammonia and coal gas left for its inaugural run. Aptly entitled “Special”, it had cylinders of coal gas mounted on top of the roof, and two standard cylinders (each holding 56,6 kg of ammonia) fixed to the front of the vehicle (Fig. 2). Fig. 3 , gives an idea of how it worked.
The liquid ammonia (ammonia is quite easily kept in liquid form under moderate pressure) is first drawn from tank T, and then passes through a strainer L before entering the vaporiser E, that is heated with hot water from the engine's cylinder jacket. In the vaporiser, the ammonia first enters coil C, is mostly vaporised, and then completely vaporised when passing through chimney H. Another (optional) strainer G removes any last particles of foreign matter that might have escaped the first strainer L.
The compressed gas then passes through a regulator (R2), where the pressure is reduced to 1 – 2 psi. An atmospheric or "zero" regulator (A2) then acts as a very sensitive shut-off valve, to stop the flow of gas while the motor is at a standstill.
The ammonia then goes to the mixer/proportionator M, where it is mixed with coal gas, which has followed a very similar route (passing first through a filter F, then through a pressure regulator R1, then through atmospheric regulator A1, which acts as a shut-off valve. V1 is the filler valve, used for filling the coal gas cylinders, while V2 is the shut-off valve).
In modern motors using ammonia, we shall see that a computer is used to mix the proportions of ammonia and propane, biodiesel or gasoline before this goes into a sophisticated electronically-controlled fuel injection system. None of this technology was available in 1943. However, the resulting manual system worked surprisingly well. The driver used the control knobs K1(to regulate the coal gas flow) and K2 (for controlling the ammonia flow). By closing K2, the engine could be started on coal gas alone, and allow the jacket water (needed to gasify the ammonia) to warm up. By gradually opening K2 and closing K1, it was possible for the driver to obtain the proper mixture quite easily.
While doubtless less efficient than modern electronic systems currently under development (whose detailed working is kept confidential), this system nevertheless shows the main principles of how a diesel engine could be adapted to run on ammonia.
"Incidentally, the only serious incident which occurred during the two years of utilisation of ammonia as motor fuel (though not on the motor buses, which have an accident-free record, but on a private motor-car) was caused by a careless overfilling of an ammonia tank" .
One of the key concerns about using ammonia is safety, as it is poisonous in high concentrations. This much Rudolf Diesel had learned the hard way when his ammonia-based steam engine exploded, nearly killing him. One would thus have expected accidents, injuries and even fatalities when eight buses and other vehicles used liquid ammonia day in and day out for two years in the Belgian experiment. Especially when all these vehicles were filled up with liquid ammonia at just one specially adapted filling station in a large city, Brussels.
However, only one accident was recorded, when the careless overfilling of an ammonia tank (i.e. probably not leaving enough – at least 15%  – of the tank unfilled, for the liquid and gas to expand into) caused the car's fuel tank to explode, causing some material damage, but no casualties . No accidents were reported from the buses, and, remarkably, no injuries from ammonia vapour.
Neither is anything said of the ammonia levels in the exhaust. Belgians were probably so glad to have bus transport that they ignored any ammonia present in the exhaust gases of the buses (or the about 100 vehicles were equipped for use of ammonia as fuel , which must have included at least some motor-cars.
Because the engineers knew quite a bit more about engines than when Diesel had his near-fatal accident, no explosions were caused by ammonia in the buses' engines. As ammonia actually has a higher octane rating than normal gasoline and diesel fuel (of about 120 ), the compression ratio of the diesel buses was reduced from around 16:1 to 8,5 to 1 .
Results of using ammonia
"When properly installed and when adequate care is taken this motor fuel [ammonia] gives excellent results which compare favourably with those previously obtained with gas [or diesel] oil. There was no loss of lower, no corrosion, and no increase of the lubricating oil consumption" .
One of the problems of using ammonia is that it has about half the energy density of gasoline on a gallon-per-gallon basis . In other words, a vehicle would either need to carry ammonia at least 2,8 times by volume [of gasoline] and 2,35 times by weight [of gasoline]  to travel the same distance. Put another way, an aircraft using ammonia instead of conventional jet fuel in the same size fuel tanks would have its range cut roughly in half . So, ammonia would not be suitable for long-haul aviation – although, as we shall see in the next article, this limitation didn't stop it from being used as the fuel for North American X-15 rocket plane, and setting performance records that still stand.
But buses are not long-range aircraft, and the Belgian buses performed very well in the short-haul environment they were tested in. Six of the buses together covered more than 100 000 km on ammonia, according to statistics recorded between May and December of 1943 . While the consumption of fuel varied widely, not only from bus to bus, but even from month to month for the same bus (because the quality of the coal gas was erratic, and there were errors in the way it was measured out), this is not the main point.
The main advantage is far simpler, and has been long forgotten. Ammonia worked as a fuel for the buses, and worked well. While it was discarded as soon as diesel became available again in 1945, the Brussels trial showed ammonia can be used as a substitute to fuel diesel buses (and internal combustion engines) when no diesel or gasoline is available - especially buses that are running to and from rural areas. It was done very successfully in Belgium between May 1943 and May, 1945 (when World War 2 ended in Europe). It can be done again with buses elsewhere in the world, especially if sources of liquid ammonia – a chemical commonly produced for industry and agriculture – are available for refueling stations.
Put another way, ammonia can also be used as ethanol and methanol are currently: as 5%, 10% or higher blends with gasoline or diesel, to lessen the amount of imported oil needed. And adding 5%, 10% or even more ammonia to diesel or gasoline can be achieved without any food crops needing to be diverted to fuel, and affecting food prices. In fact, ammonia is already being made on a small scale directly from wind power. The next article will focus on more recent uses of ammonia as a fuel – recent being from after World War 2 to current research.
As we shall see in the next article, ammonia was again tested as a fuel for internal combustion engines after World War 2. The aim of the work seems like science fiction: using a nuclear reactor to produce a fuel for the US Armed Forces, using only water and air. The article begins with what was quite literally the high point of the use of ammonia as a fuel: to power the North American X-15, which still holds the official world record for the fastest speed ever reached by a manned rocket-powered aircraft .
For references see Part 2 of this article in the next issue of Energize).