Solid Fuel IC Engines

Gallery opened 13 Apr 2015

Updated: 11 June 2015

More on Diesel & Pawlikowsky
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It is fairly obvious that there are going to be serious challenges involved in burning solid fuel in an engine with piston and cylinder. That has not stopped people from trying, and trying very hard.

The obvious solid fuel is coal. It is much more abundant than oil, and so there have been many attempts to run petrol or diesel-type engines on pulverised coal. Interest waxes and wanes as the price of oil changes. There are fundamental problems; pulverised coal is highly abrasive, and it contains a percentage of ash that tends accumulate in the engine. The amount of ash varies with the type of coal, thus: anthracite 10 - 20%, bituminous coal 3 - 12%, sub-bituminous coal up to 10%, lignite 10 - 50%. Whatever sort of coal you use there are going to be substantial amounts of ash to deal with.


An early practical difficulty with the internal combustion engine was getting hold of a suitable fuel. Before petroleum products were available, various expedients were tried such as turpentine. However, there was a substance which was fairly readily available, and on ignition could be relied upon to produce a lot of hot gas. That substance was gunpowder. What could possibly go wrong?

George Medhurst, was a clockmaker in Pleasant Row, Clerkenwell. in London. In 1800 he was granted a patent for a "New Improved Method of Driving Carriages of All Kinds, without the Use of Horses, by means of an improved Aeolian engine..." which was British patent No 2431 for that year. (Patent numbering started from zero for each year in those days) This was essentially an ambitious proposal to cover the country with windmill-driven pumps that would charge reservoirs with compressed air, to drive vehicles; the gun-powder engine appeared on only one of the ten pages. This was 24 years before Sadi Carnot considered coal dust as a possible solid fuel.

Graces Guide has much more information on the career of George Medhurst.

Left: Medhurst's gunpowder-powered gun carriage: 1800

The single cylinder is here coloured grey. The crankshaft is directly coupled to the rear axle and there is no provision for declutching or changing gear. The toothed quadrants were intended to prevent side-forces on the piston and piston-rod.

The trumpet-like thing is a funnel for holding a small ready-use store of gunpowder; this was to be replenished from a larger storage funnel, and the inventor wisely warns that there should be a safe distance between the large funnel and the ready-use funnel. I do concur.

The vehicle seems rather lightly built for hauling around a great big cannon.

Left: The cylinder of Medhurst's gunpowder engine

With the piston fully to the left (at top dead-centre) the rotating cock connecting with the funnel would make half a turn and deliver a measured amount of gunpowder to the cylinder; this would then be ignited by "...a flint, agate, or diamond wheel placed within the piston" and rotated by a rack-and-pinion mechanism that operated when the piston reached the end of the cylinder. The cock was rotated at half crankshaft speed by a horizontal shaft driven from the crankshaft by right-angle gears.

When the explosion occurred, the piston F would move to the right, and the inventor expected such a high expansion ratio that with the piston fully to the right the pressure would be sub-atmospheric and valve G would be forced open by the outside pressure. When the piston moved left again the exhaust gases would be pushed out of G until the piston reached it and closed it. Gunpowder does not need an external air supply to explode, as it carries oxygen with it in the potassium nitrate, so there was no need to draw in a fresh charge of air.

The rightmost part of the cylinder was closed off with a cover B, and in conjunction with valve I was supposed to provide an air cushion to absorb the shock of the gunpowder explosions; as described, it is unlikely this could have worked.

Medhurst recommended that the charge per working cycle be 1/15 of a cubic inch of gunpowder to generate one horsepower. Since this would require an overall efficiency of 27%, completely impossible at the time, it seems unlikely that Medhurst carried out any practical tests of the gunpowder engine.

Left: Speculative indicator diagram for Medhurst's gunpowder engine

This later diagram gives a rough idea of the operation, if everything had worked as intended.

A charge of gunpowder is exploded and gives a peak pressure B, suitably chosen so that the cylinder pressure falls to atmospheric at C. At this point the exhaust valve would open and pressure would remain constant from C to E, instead of continuing to fall to D.

Looking critically at Medhurst's idea, could it have been made to work at all? There are objections:

1) The rotating cock that delivers the gunpowder charge makes me uneasy. It would seem to be all too easy for friction to ignite both the measured charge and the ready-use store of gunpowder in the small funnel.

2) When gunpowder burns, it does not turn completely into gas; about 55% by weight is solid, mainly potassium carbonate, potassium sulphate, and potassium sulfide. This causes musket fouling; a major factor in warfare for centuries. If the residues built up in musket barrels, there seems no reason why they would not build up in the cylinder here. The highly dubious ignition mechanism proposed would seem to be particularly vulnerable to this.

At the moment this is the only engine known to the Museum which actually uses an explosive as its fuel. Gunpowder is a low explosive; it burns relatively slowly, at subsonic speeds of propagation, as opposed to high explosives that detonate, producing supersonic shock waves. Nitroglycerine, for example, detonates producing shock waves through itself travelling at some 30 times the speed of sound; decomposition into a white-hot gas is near-instantaneous. The gases generated occupy more than 1200 times the original volume of explosive at ordinary room temperature and pressure, and the gas temperature is about 5000°C (9030°F). This is very different from burning, which depends upon available fuel regardless of pressure or shock. Considering these figures, a nitroglycerine engine might produce a lot of power in a small space, but somehow I am still not keen on the idea. Obviously it's crazy- I wonder how long a direct-injection nitroglycerine engine would run for?

And yet... you can bet that some people want to try it. See this suggestion from 2012. They also considered the notion at the HalfBakery in 2002.


The first known consideration of coal dust as a fuel was by the great French scientist and pioneer thermodynamicist Sadi Carnot in 1824, according to an article by Hans-Joachim Braun "The Coal Dust Motor 1916-1940" under the auspices of the Deutsches Museum, Munich.


According to the Braun article:

"The oldest known documentation regarding coal dust engines is an American patent from 1851 which described a type of coal dust turbine (2). In the period between 1890 and 1913 the Englishman McCullum worked through the development of coal dust engines and developed several versions, one of which was exhibited in Glasgow in 1901. He said that the fire safety regulations were the greatest hindrance to his progress (3)."

Neither the American patent nor any trace of Mr McCullum have been found. It is hard to see how British fire safety regulations would have hampered the work much, unless they (very sensibly) discouraged the storage of large amounts of pulverised coal, which is liable to self-heating and self-ignition.

References in the Braun article are to documents by Hans Wahl, who wrote a book called Verschleißbekämpfung bei Staubmotoren (Roughly: The Control of Wear in Dust Engines) in 1936. Dr. Ing. Hans Wahl studied at the University of Stuttgart Mechanical Engineering. In 1924 he took his first job in the chemical industry, where he was involved in the development of anti-knock agent for truck engines. From 1934 he was concerned with engine wear as part of the development of the RUPA coal dust motor; see below.


It is well-known that Diesel's early experiments were done using coal-dust as a fuel. Rudolf Pawlikowsky was one of his assistants, Vogel another. The usual account states that in 1892 an experiment with coal-dust as a fuel blew the compression indicator violently off the side of the cylinder, it shooting between Diesel and his assistant Vogel, and smashing into a wall. This incident is often reported as the complete destruction of the engine and the severe wounding of Diesel, but this appears to be mere exaggeration. One contributor to this site claims Diesel was killed! This would have slowed down the development of the Diesel engine somewhat.

For what actually happened, here is the account by Diesel himself, from his book " The Origin of the Diesel Engine" Springer, 1913:

"In spite of the lack of compression on the 10th August 1893, 20 days after the start of the experiments, with the engine driven by the line shafting and in the presence of my friend Vogel the first injection of fuel, which was Petrol was undertaken. We both awaited the results in tense anticipation."
"Ignition happened immediately, Diagram No. 1 showed an explosion pressure up to 80 atmospheres" In reality the pressure was somewhat higher, the indicator was destroyed by the powerful explosion and flew past our heads. Nothing happened to the engine, as very high pressures were anticipated and it was built like a cannon."

So in this incident the fuel was petrol, not coal dust, and the engine was being motored by an external power source rather than running by itself. This affair had nothing to do with abandoning coal-dust as a fuel. The problem with coal was not the pressures it created, but the abrasion in the engine; this is why Diesel turned to liquid fuel.

Left: Diesel's coal-dust injection system

The coal-dust was stored in the reservoir B, and measured amounts released by rotary valve D, just as in Medhurst's patent of 95 years earlier. When the injection valve E was lifted, the coal-dist was blown into the cylinder using high-pressure air stored in vessel A.

Based on Diesel's US patent 54 286 of 1895

Working for Diesel must have been a frustrating business for Vogel and Pawlikowsky. Diesel insisted on patenting their idea's as his own, which is hardly a recipe for harmony. A dispute of this sort caused Pawlikowsky to resugn from the Diesel project in 1898.


Rudolf Pawlikowski was a co-experimenter with Rudolf Diesel in his early researches, in which pulverised coal was the fuel. The difficulties caused Diesel to turn to liquid fuel, but Pawlikowsky was clearly made of sterner stuff and persisted with solid-fuel internal-combustion engines. According to the newspaper article below, by 1928 he considered himself successful.

The background to Pawlikowski's research was concern over Germany's very limited oil resources. Also, by around 1930 many 'experts' were claiming that the world oil reserves would be exhausted in 10 to 12 years. Germany however had very large coal reserves, second only to the USA. Between 1924 and 1933 Germany recorded over 20% of global hard coal production and over 75% of gobal brown coal production.

The major application considered for the coal-dust engines was peak-lopping on the electricity grid. When a peak in load came along, it would be much quicker to start an IC engine than get a steam plant on line. I am not aware that any mobile applications were envisaged.

Rudolf Pawlikowski was born in Dresden on 16th June 1868. He was born a Catholic, but is recorded as Protestant after 1871. He received a diploma in Mechanical Engineering from the Technical University of Dresden in 1893. He worked with Rudolf Diesel but resigned in 1898 over a dispute about credit for inventions. In February 1898 he joined Dessauer Maschinenfabrik, then in the same year became chief engineer at the Görlitz Maschinenbau AG. Here he seems to have been involved in evaluating industrial processes under development by other companies, such as Kesselhausentaschung, oxidation of nitrogen in the combustion engine, rayon, etc. These activities nade him financially secure, and from 1911 he devoted himself to the technical realization of the pulverized coal engine. He had invested about 2 million Reichsmark in the concept up to his death. He died on the 11th of October 1942 in Görlitz.

Left: Newspaper article on Pawlikowsky's engine

The secret of Pawlikowsky's success, if there was one, and if there was any success, seems to be the ejection of the ash via the exhaust ports, either by a blast of compressed air or a wash of lubricating oil.

The article raises a few questions. I am not convinced that the engine was 30 to 35% more efficient than a steam turbine, and I think you would have to be very devious with the comparison to make those figures viable. I am also extremely sceptical that the engine would work equally well on turf, sawdust, charcoal, rice dust, flour, or coke, as is claimed. I know flour can explode when suspended in air but I'm having some trouble taking it seriously as a fuel.

The headline is quite misleading as it implies the same engine has been run on coal for twelve years, which given the problems of abrasion and wear, would seem to be quite impossible.

This article is from the South-East Missourian, 27th Nov 1928.

Pawlikowsky took four letters of his name and called it the Rupa engine. It was intended that its main use would be in peak-lopping electricity generating stations, as the engines could be started and stopped much more quickly than steam plant. It does not appear to have had any commercial success, but the Museum staff are continuing their enquiries.

Left: This is Pawlikowsky's engine No 7: 1930

According to the legend at the bottom of the picture, this engine produced 140 horsepower. (PS in German) Given that it is as tall as a house, the power/weight ratio must have been less than impressive. It ran at a leisurely 166 rpm. The single cylinder had a bore of 500mm and a stroke of 720mm.

The fact that this is labelled as Motor No 7 indicates that there must have been quite a long and complex development process.

Left: The fuel valve assembly for one of Pawlikowsky's engines

This was considered the important and the most difficult part of the design.

The label at the top says the valve was for a 100 horsepower (PS) motor- presumably not Motor No 7 illustrated above, which was rated at 140 horsepower.

Left: Section of one of Pawlikowsky's RUPA engines

This engine has a bore of 420 mm, and a stroke of 630 mm; It produced 80 HP at 160 rpm. This implies it was neither RUPA No 7 nor the 100 HP engine of which the fuel valve is shown above

The fuel injection valve is at B, supplied with coal-dust by an Archimedean screw; a top view shows there were actually two screws side-by-side. There is a reservoir at c, and it looks as though the coal-dust is transported there by compressed air. Valve B is operated by a camshaft at the left, with engine speed controlled through the valves by the fly-ball governor at top left. The camshaft is driven from the engine crankshaft via a vertical shaft and two sets of skew gears.

Just below the camshaft is a small pump, with a pipe leading from it to the bottom of valve B; this presumably created an air-blast to inject the coal-dust, but it seems a rather small pump for the job. Just to the left of valve B is what looks like another small pump, driven by a cam on the camshaft. The apparatus on the right is driven by twisted belt from the engine crankshaft; it is clearly something to do with the coal-dust supply, but its detailed operation is currently enigmatic. The funnel-shaped thing at top right appears to be some sort of rotary separator, presumably for rejecting and recycling coal-dust particles that were too large.

From the Spanish journal Le Genie Civil, 9th Feb 1929

Left: Cylinder head of one of Pawlikowsky's RUPA engines

As as can be currently determined, Pawlikowski's designs differed from Diesel's in that instead of using compressed air to inject coal-dust into the combustion chamber via valves, he invented the idea of using "a pressure rise through partial combustion of dust inside a special pre-chamber (the "by-chamber") to force the fuel into the cylinder. This system...had many advantages, including the heating of the fuel/air mixture by compression in the by-chamber, and its heating by contact with hot chamber walls and hot air from the cylinder, so that it was dried, de-gassed and prepared for self-ignition."

This pre-chamber is presumably the structure visible just below the two feed-screws for the coal.

From the Spanish journal Le Genie Civil, 9th Feb 1929

In 1933 Pawlikowski took out US patent 1 926 304 "Powdered fuel for internal combustion engines" which specified the addition of a more combustible material to the coal-dust. Little detail about the engines is given, but it adds 'wood-meal, fallen leaves, animal carcasses' to the list of possible fuels.

In September 1939 German forces occupied Romanian territory to sieze the oil-fields of Ploiesti under the pretext of protecting the oil resources, and coal-dust engine abruptly became less relevant.

This article appeared in The Commercial Motor, 29th August 1941, when the security of oil supplies was no doubt on everyone's mind:

"Before Dr Diesel succeeded in running an engine on oil fuel he had failed in experiments with powdered coal.. That was over 40 years ago, as is indicated by the following note which appeared in a technical paper dated May 15, 1897: " A German engraver named Diesel has designed and brought out a new pattern motor. In this he has, it is stated, had the financial assistance of the great firm of Krupp. It is elaiined that the engine can run on oil, gas or coal dust." Coal dust, being something new in fuels in those early years, was put in italics."

"This is probably the starting of the interest in coal dust, powdered coal or pulverized fuel. its progress was very slow,and did not continue along the first line of application, namely, employment in an internal combustion engine. Diesel's difficulties were so great that he soon deserted this type of fuel and switched over to heavy oils of the hydrocarbon series, with the successful results of which we ale all aware."

"Abrasion of Cylinder Walls: his troubles centred on the apparent impossibility of preventing the ash in the coal, released by combustion, from causing excessive wear of the cylinder walls. This would surprise few of us, thinking of the amount of ash that falls out of a fire grate, even with the best of coals."

"Further, when we consider that the ash content of oil fuel to-day is a fraction of 1 per cent- it would not have been much higher in those days— and that it is a good coal that has as little as 4 per cent, most brands being of 10 per cent, and upwards, to 25 per cent. and over, we can visualize his troubles."

"The success of Diesel on oil was such that he never returned to his experiments on pulverized fuel. It is regrettable that his early death prevented him from participating to the full in the wonderful developments springing from his genius and energy."

"After a lapse of some years, one at least of Diesel's associates took up the dropped experiments and carried them through to a successful issue. Not, however, to the extent that road transport can participate using the system. It is in the realm of stationary engines that progress has been made."

"Reports have appeared from time to time in the Technical Press of the developments with an engine referred to as the "Rupa" made by a German concern under the direction of Mr. Pawlikovvsky, (sic) the co-experimenter with Diesel in the early researches, referred to above. Experiments in recent years have been carried out on brown coal, of which so much is available in Germany: The principle of operation of the Rupa engine is that of pre-combustion of the fuel in an ante-chamber, the pressure therein generated injecting the unconsumed fuel into the main cylinder. This system also minimizes the possibilities of ash trouble."

"In the pulverizing of the fuel, the ash content can be lowered to between 2 and 3 per cent. It is possible to bring it down to 1 per cent, but the cost of doing this has to be weighed against the requirements of such fuel, and the operation is usually carried so far only for certain purposes or processes."

"Coal's Advantage on Points: With oil at from three to four times the cost of coal, and allowing for the difference of calorific values in favour of oil (oil 19,500 BThU; coal 14,000 BThU, per lb.) and the cost of liner renewal as a result of ash wear, pulverized coal appears to hold the possibility of successful competition with oil in oil's sphere of activity."

The article is not exactly bursting with hard facts, probably because of its 1941 wartime provenance, but it does give some perspective. In fact, Pawlikowski's research appears to have been abandoned around this time.


Left: Petrol engine allegedly converted to powdered coal: 1956

This set-up seems to have a good deal in common with the Pawlikowsky engines. Note petrol carburettor still in place.

From Popular Mechanics, Mar 1956

Left: Account of engines converted to powdered coal: 1956

According to this account, making a Diesel engine run on coal dust is easy. Given the difficulties that other workers had, this report does not ring true. Popular Mechanics and similar magazines contained many articles about home inventors in every issue, and one suspects that their claims were not very carefully checked, if they were checked at all. I am not sure I can convince myself that the petrol version ran on 90% coal and 10% petrol. It would probably work with the proportions reversed, but not for long, I suspect.

I can't help wondering how his friend managed to blow up his house with coal dust.

From Popular Mechanics, Mar 1956


This is a list of patents that I have come across in researching this subject. It is not in any way complete, and omits patents after 1970.

  • Rudolf Pawlikowski 12 Sept 1933. US patent 1,926,304 "Powdered fuel for internal combustion engines"
  • David Krygsman 12 March 1946. US patent 2,396,429 "Internal-combustion engine"
  • Friedrich Nettel 12 March 1946. US patent 2,396,524 "Combustion engine and process"

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