A heat engine is a system that converts heat or thermal energy and chemical energy into mechanical energy which in turn does mechanical work. It allows work to be done by using provided energy in the form of heat and then exhausts the heat that cannot be used to do work. A heat engine generally distinguishes itself from other types of engines because its efficiency is fundamentally limited by Carnot’s Theorem, which states that the efficiency of all reversible engines operating between the same two temperatures is the same, and no irreversible engine operating between these temperatures can have a greater efficiency than this.
A heat engine is constrained by the First and Second Laws of Thermodynamics mentioned above. The conversion of energy to the system is the first law and the second law sets limits on the possible efficiency of the machine and determines the direction of energy flow. The most significant heat engine developed was that of the steam engine. The use of steam to produce a mechanical effect has its origin in the 1st century AD, and is described as a steam wheel which utilized the thrust effect of escaping steam jets. In parallel with the early development of the steam engine, several inventors pursued the idea of an engine in which the combustion of a fuel would take place within a piston-cylinder arrangement.
In 1673 the Dutch scientist demonstrated a piston engine to the French Academie des Sciences. It was an atmospheric-type engine which made use of a small quantity of explosive. It worked by displacing cold air from the cylinder by means of the hot gases from the explosion. When the hot gases remaining in the cylinder cooled and contracted, the cylinder gas pressure was lower than the atmospheric pressure outside the arrangement and, like other atmospheric-type engines, movement of the piston was affected. This invention was unfortunately thwarted by the inability to find a suitable fuel. It was much later that it was found that when coal is heated in a closed vessel a combustible gas (coal gas) is given off, which forms a suitable fuel. In the early 1800’s, Stirling engines used helium and hydrogen. This engine is still used in the present time, owing to their stringent manufacturing requirements, and are confined to special applications, such as submarines and spacecraft.
In 1824, his work on the efficiency of the steam engine created the new science of thermodynamics. The next several years saw designs of gas engines but it was never constructed. The first internal combustion engine that was able to operate reliably was built by inventor Jean Joseph Lenoir. These early internal combustion engines only operated on gas and liquid fuels were not introduced until the late 19th century. In 1883, engineers designed an engine that ran on petrol. It ran faster and performed more efficiently with the capability of producing more power for the given weight of the engine. In 1889, the engine was placed in the first modern motor car.
In 1893, Diesel patented a prototype four-stroke engine. This engine differed from the petrol engine in that ignition of the fuel occurred spontaneously without a spark. The Diesel engine has of course found wide use for both marine and land transport.