Rudolph Diesel, A Patent, and Coal

Rudolf Diesel –
A Patent and Coal

Andrew Prestridge | October 5, 2020

Any Kind of Fuel

We’re all familiar with the fact that diesel fuel goes into diesel engines - but truthfully when Rudolf Diesel patented the original Diesel Engine concept in 1895, it had the universal claim the engine could burn, “any kind of fuel, whether solid, liquid, or gas.” And furthermore, the invention and perfection of diesel fuel came much later. Over a century later - diesel fuel is the most common fuel used today, but how did we get here?

Portrait of Rudolf Diesel

Portrait of Rudolf Diesel c. 1900

Simple Beginnings

Rudolf Diesel was born in March of 1858 in France to Bavarian immigrants. He excelled academically and was taught by Carl von Linde the noted German Scientist famous for the invention of refrigeration. Diesel learned about the theoretical Carnot cycle from Linde, which is the thermodynamic cycle representing the perfect conversion (no entropy) of heat into work. The Carnot cycle can also be used to analyze refrigeration cycles.

Pressure and Volume in a theoretical Carnot Cycle

Chasing the Carnot efficiency ideal in the construction of a new engine design became the guiding light for Rudolf - The technical concept and research basically set the bar, he just needed to make the most efficient engine possible. The results are the modern diesel engine we know today.

Rudolf Diesel – Father of the Diesel Engine

Mechanically, Diesel started by studying steam engines, powered by coal, and was able to compare their low efficiency to the Carnot cycle. He then moved to the newer internal combustion engines, powered by gasoline, which still struck him as inefficient. The drive for the highest possible fuel efficiency led Diesel in a unique direction. Strong castings were required to achieve the combustion pressures for the diesel engine, a hard earned lesson that left Diesel injured on several occasions due to explosions. The difficult problems became clear, the system to inject and distribute the different types of fuel at the correct time and duration during the combustion cycle.

In early 1890 he had a chance to follow his personal aspirations to make an efficient engine and by 1893 he had filed the first German patent: DRP 67207. This mechanical work on the diesel engine was done in Germany at the MAN company headquarters in Augsburg Germany.  

Long stroke diesel engine prototype, from Diesel's first US patent

Long stroke diesel engine prototype, from Diesel's first US patent

His first US patent titled "Method of and Apparatus for converting heat into work" (US 542,846 July 1895) very clearly describes how the diesel engine works and relates it back to a Pressure-Volume(PV) chart. The diesel chart is crafted in the same manner for the Carnot cycle. The patent also shows the iconic diagram of a very long stroke diesel engine prototype

Diesel's Choice(s) of Fuels

While "Diesel fuel" is synonymous with "diesel engines," when Rudolf Diesel was first inventing his engine he had envisioned a wide variety of potential fuel options. In 1895 the main options available were:

Plant (Vegetable) Oils – e.g. Olive Oil

Olive Oil or Peanut Oil are common oils still in use today (more often for cooking than burning), they contain saturated and unsaturated fats. Because many vegetable oils become rancid, they are not commonly found in industrial uses (unless further refinement is made). Recently vegetable oils have been recycled from restaurant fat-frier's and used as biofuel in diesel engines. This type of fuel oil was definitely available and could have been a fuel choice, but it is not mentioned in either patent.

Animal Oils – e.g. Whale Oil

Whale Oils were used for Illumination prior to the widespread use of kerosene. This type of fuel oil was less likely to be a choice, and also was not mentioned in either patent.

Mineral Oils – e.g. Kerosene

Formed from ancient Phytoplankton (plant) and Zooplankton (animal) these marine life forms rain their organic matter onto the seafloor. The formation of Mineral Oil takes many millions of years undergoing increased heat and pressure from geologic processes as the layers of organic matter transform to Mineral Oil and migrate into traps.

In 1856, the Polish chemist Ignacy Lukasiewicz setup the world’s first mineral oil refinery in Ulaszowice Poland to produce kerosene at scale. This was less than 900km from Munich and Augsburg where Diesel was developing his engine. Germany had no native mineral oil production in 1895, as of today they only rank 62nd in global mineral oil reserves. Kerosene was a natural fuel choice, it was relatively abundant and nearby.


Diesel had previously experimented with ammonia while working with Linde. Linde used ammonia as the refrigerant in his systems so Diesel was familiar with this gas. Concentrated ammonia gas or liquid is both toxic and hazardous. It would have been available from the distillation of coal, and Diesel was familiar with ammonia during his earlier experiments with Linde. Diesel does mention this as a fuel choice in his patent.

Pulverized Coal Dust

Diesel also considered Coal Dust “Pulverulent solid fuel” which Germany had in supply and probably on a large scale, but as we know today it proved impractical in many applications and would have poor emissions. Germany ranks number 7 in global coal reserves today. Anthracite coal was the national fuel of choice, as it was readily available. He did spend a fair amount of his patent discussion on the fuel supply and injection system for pulverulent solid fuel.


It is very clear that Diesel did not want his patents to specify any one fuel, but rather show how many different fuels could be used. He most commonly used the generic term “fuel”, but here are some other options he discussed; Neutral Gas, Pulverulent solid fuel, anthracite, gas, fluid fuel, petroleum and ammonia vapour. He relied on mechanical variants of the Bunsen burner to distribute fuel for an even burn inside the combustion chamber. His universal fuel claim is that his engine can burn "any kind of fuel, whether solid, liquid, or gaseous."

The Second "Internal-Combustion Engine" Patent

His second US patent titled “Internal-Combustion Engine”, focuses on the mechanism unique to each fuel choice. (US 608,845, August 1898). Rudolf is the inventor, but this time the rights are assigned to “The Diesel Motor Company of America, of New York”. This patent was previously filed in Spain, France, Belgium, Luxemberg, Italy, England, Switzerland, Germany, Hungary, Austria, and Denmark. Diesel used the Attorney “A Faber du Faurf".

This second patent is clearly about the mechanisms to accommodate different fuel types. There is absolutely no mention of any lubrication system the mechanical device needed or the oils it would require. This is par for patents to stay focused narrowly on the claims, but even the drawings showing many moving parts and contact surfaces are devoid of any oiling system components such as zerks, oiling ports etc.

Figures 1 and 2 Show the Pressure-Volume Diagram with constant temperature lines and the Diesel Cycle. The ideal cycle as you recall is the Carnot Cycle. Figure 2 shows how the injection of fuel at pressure can alter the Carnot Cycle to improve efficiency. Although not shown, the x-axis on these graphs is Volume, and the y-axis is Pressure. The curved lines from 1-2 or 3-4 are lines of constant temperature.

Fuel Feed Mechanism

Figure 3 is a cutaway section of an engine to show the fuel-feed mechanism. Mixing of the Fuel occurs prior to entry into the cylinder. Figures 4, 5, and 6 also show varying fuel-feed methods where the fuel is mixed in the cylinder.

C-Cylinder, P-Piston, V-Air Valve, D-Nozzle dictating 2-3 behavior on the above figures, n-needle valve, T-Hopper to contain Pulverulent solid fuel, r-rotary distributing valve, L-Gas Tank with compressed gas pressure(air, combustible gas or a mixture), m-inlet gas pipe, L is connected to C by pipe S and Hopper T, R-Pressure Regulating valve, B-Counterweight to adjust pressure in Cylinder, Q-connecting rod, Governor (not shown) connects to the rod Q. Also Diesel notes that one could use liquid fuel in the hopper T. K and V are not explained in the Patent, but it appears that K is some sort of modified piston bowl and V is an exhaust valve.

Figure 7 shows different nozzle (Bunsen Burner tip) designs to evenly distribute fuel into the combustion chamber. Figures 8, 9 and 10 show the mechanism for operating the injector timing and duration. Figure 9 shows a more complex mechanism to operate valve Y found in Figure 8. At the end of the mechanism of Figure 9 is a large Bevel Gear to finally connect the diesel motor and the horsepower it generates to a machine. Like a car, boat, truck, airplane, water pump, etc.

Figures 11, 12 and 13 relate to the different bunsen burner arrangements inside the piston.

The patent very much demonstrates the claims for Diesel's mechanical ideas the ongoing research and innovation of the diesel engine is all about the Carnot cycle at the heart, and improving injection, timing and more to optimize performance. Today emissions have caused fuel innovation to make Ultra Low Sulfur Diesel (ULSD), Bio-Diesel, and Synthetic Fuels. Pulverized coal - just did not happen.

PS. Nobody is perfect, and if you read the Patent carefully even Diesel had a few of the figures mixed up with their descriptions. Oops!

Rudolf Diesel and His Patent

Quest for Efficiency

Diesel was looking to maximize efficiency and get as close as possible to the theoretical limit of the Carnot Cycle.

Diverse Fuel Options

Diesel envisioned a wide array of possible fuel options, many more than just the "diesel fuel" we use today

Burner Design and Arrangement

Diesel outlined a variety of burner designs and arrangements to accommodate the diverse fuel options


  • What did he use from a refrigerator for the fuel system

  • Absolute superb read .

    Kevin Clarvis

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