The internal combustion engine

In plain language

An internal combustion engine burns fuel inside a closed cylinder. The hot gas pushes a piston, and the piston turns a crankshaft that drives the wheels or other machinery. A steam engine, by contrast, burns fuel outside the cylinder to make steam, and the steam does the pushing.

Early engines were neither reliable nor efficient. Lenoir's engine of 1860 ran on gas but did not squeeze its mixture before it fired, so much of its energy was wasted. Otto's four-stroke engine of 1876 completed four steps in each cycle: it drew in a fuel and air mixture, squeezed it, fired it, and pushed out the exhaust. Later work by Diesel, Daimler, Maybach and Bosch added new ways to ignite the fuel and made engines fast and light enough for vehicles.

Technical explanation

The four-stroke cycle takes two turns of the crankshaft. On the intake stroke the piston draws a fuel and air mixture into the cylinder. On the compression stroke it squeezes the mixture. Near the top of that stroke the mixture is ignited, and the expanding gas drives the piston down on the power stroke. The exhaust stroke then pushes the burnt gas out. Otto's engine of 1876 used this sequence. Accelleron's company history also names Alphonse Beau de Rochas, who patented the cycle in 1862 with the mixture compressed before ignition.

Ignition has two main routes. In spark ignition, a magneto produces a high-voltage pulse that jumps the gap at a spark plug. Bosch's high-voltage magneto with spark plug, developed by chief engineer Gottlob Honold and applied for in January 1902, replaced the failure-prone break-spark rod used in earlier magnetos. A carburettor mixes petrol vapour into the incoming air. Wikipedia's entry on Wilhelm Maybach credits Daimler and Maybach jointly with a float-fed carburettor, dated to 1885, that mixed evaporated petrol with air. That date rests on this one entry.

In compression ignition, as in Diesel's design, air is compressed until it is hot enough to ignite the fuel when the fuel is injected. German patent DE 67207 describes feeding fuel in gradually while the piston moves outward, so that combustion takes place during expansion without a large rise in pressure. Cooling and lubrication are not described in this profile, because no primary source for them was checked.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Limitations and open problems

• The record for Otto's patent is thin. The museum story is the only source checked for patent number 532 and its August 1877 grant. A Google Patents record for DE 532 was checked, but it names no inventor and shows a filing date of 3 August 1877 with no grant date, so it does not confirm the link to Otto.
• The float-fed carburettor date and credit rest on one encyclopaedia entry, which dates the device to 1885 and credits Daimler and Maybach jointly. No second source was checked in this pass, so the date needs confirming before publication.
• The efficiency figure for Lenoir's engine (4.5 to 5 per cent) and the figure of 380 engines come from one company-magazine article. The article gives no further source for the engine count.
• Cooling and lubrication, which the brief asked this profile to cover, are not described. No primary source for them was checked in this pass.
• The English text of Diesel's patent on Google Patents is a machine translation, and the record names the applicant only as 'Individual'. The link between DE 67207 and Rudolf Diesel rests on the patent title and general knowledge, not on the page. The attribution and the description of the cycle should be checked against the German original and patent office records before publication.
• Most sources are secondary, such as company histories, a museum story and an encyclopaedia. Dates taken from company histories should be checked against patent office records before publication.

Possible future uses

Timeline

1. 1860Etienne Lenoir receives a patent for an air motor expanded by gas combustion, the spark-ignited gas engine that is an early internal combustion engine. Sources: [5]
2. Mar 1876The premiere run of Nicolaus Otto's four-stroke engine takes place in early March 1876. Sources: [1]
3. Aug 1877Otto's engine is granted German Reich patent number 532 in August 1877, according to the museum story. Sources: [1]
4. 16 Dec 1883Daimler and Maybach patent their first high-speed engine, which runs on ligroin, on 16 December 1883. Sources: [6]
5. 28 Feb 1892German patent DE 67207, a working method for combustion engines using compression ignition, is filed. The Google Patents record names the applicant only as 'Individual', so the link to Rudolf Diesel is not confirmed by the page. Sources: [2]
6. 24 Sept 1902Bosch delivers its first high-voltage magnetos, with spark plugs, to Daimler Motorenwerke, according to Bosch's Japanese company history. Sources: [4]

Glossary

Four-stroke cycle

An engine cycle with four piston strokes: intake, compression, combustion and exhaust.

Carburettor

A device that mixes petrol vapour with air in the right ratio before the mixture enters the cylinder.

Magneto

A generator that produces the high-voltage electric pulse used to make a spark plug fire.

Compression ignition

Ignition of fuel by the heat of air squeezed in the cylinder, without a spark plug, as in a diesel engine.

Sources

1. other
   Nicolaus August Otto and the four-stroke engine
   Technik Museen Sinsheim Speyer (online story), 10 Jun 2022. Accessed 22 Oct 2026.
2. patent
   Working procedures and design for combustion engines (DE67207C)
   Google Patents (German patent record), 23 Feb 1893. Accessed 22 Oct 2026.
3. company announcement
   1886-1905: From first workshop to factory
   Robert Bosch (company history), 22 Oct 2026. Accessed 22 Oct 2026.
4. company announcement
   Bosch Japan history article: first high-voltage magneto ignition with spark plug
   Robert Bosch (Japan), company history, 24 Sept 2014. Accessed 22 Oct 2026.
5. company announcement
   Birth of an idea: Etienne Lenoir and the internal combustion engine
   Jean Francois Tissot. Accelleron (Charge magazine), 29 Oct 2020. Accessed 22 Oct 2026.
6. other
   Wilhelm Maybach
   Wikipedia, 22 Oct 2026. Accessed 22 Oct 2026.

Revision history

3 changes since this profile was created.