A gunpowder engine, also known as an explosion engine or Huygens' engine, is a type of internal combustion engine using gunpowder as its fuel. The concept was first explored during the 1600s, most notably by famous Dutch polymath Christiaan Huygens. George Cayley also experimented with the design in the early 1800s as an aircraft engine, and claims to have made models that worked for a short time. There is also a persistent claim that conventional carboretted gasoline engine can be run on gunpowder, but no examples of a successful conversion can be documented.
Earliest mentions
The gunpowder engine is based on many previous ideas and scientific discoveries, developed by multiple people independently.
Early devices just aimed at lifting and/or holding weight (usually to study and demonstrate the physics), while engines aim at doing work continuously (usually with the intention of doing something useful).
Vacuum devices to lift/hold weight
Leonardo da Vinci described in 1508 a device to "lift heavy weight with fire" using a cannon barrel and gunpowder.
Galileo Galilei made thorough experiments about lifting weight using vacuum. Otto von Guericke researched vacuum practically, but used pumps to create the vacuum.
Robert Hooke did hide a phrase that translates to The ‘vacuum’ left by fire lifts a weight. in his 1676 book Description of Helioscopes and Other Instruments.
Early engines
The earliest references to a gunpowder engine appear to be those of Samuel Morland in 1661. This consists solely of a letter of patent written by King Charles the Second that was received at Whitehall on 11 December 1661. No other information about this "engine" remains, but the description involves the use of vacuum and powder to draw water.
The next known reference is by Jean de Hautefeuille in 1678, suggested as a solution to the problem of raising water from the Seine to supply Versailles. He presented two ideas, one using the vacuum like Morland's idea, and a second that used a U-shaped tube with water in one side and air in the other. When the gunpowder was lit in the air-filled side, the rise in pressure would drive the water up the other side.
Like early steam engine designs, these engines used the air or vacuum created by gunpowder to directly lift the water. There were no mechanical parts in the manner of modern engines, which translate the power in the gas pressure into any needed mechanical form.
Huygens and Papin
In 1671, Denis Papin was given a job at the Academy of the Royal Library in Paris, where he worked under the Curator of Experiments, Christiaan Huygens. Huygens set Papin to the task of carrying out a research effort on air and vacuum, at that time a matter of widespread international study. As part of the experiments, Papin measured the force of a small amount of gunpowder lit in small iron and copper vessels. Papin published an account of all of these experiments in 1674 in New experiments on the vacuum, with a description of the machines used for making them.
Papin moved to London shortly after publication, and from then on was more involved in the development of steam. Although his developments pointed the way towards the early steam engine, Papin himself became more interested in the latent heat of steam and developed the "steam digester", the first pressure cooker. He also conceived of a number of devices using air pressure as a working fluid, include a series of fountains, pumps, and similar devices.
In spite of there being no further examples of particle work on the part of Papin, he did carry on a continued correspondence with Gottfried Wilhelm Leibniz on this and other topics. Leibniz tried to interest Papin in further development throughout, at one point noting "Yet I would well counsel [you], Monsieur, to undertake more considerable things which would force everyone to give their approbation and would truly change the state of things. The two items of binding together the pneumatic machine and gunpowder and applying the force of fire to vehicles would truly be of this nature". Papin replied that he had constructed a small model of a paddle-wheel boat, but the type of engine is not stated.