The power of fossil fuels, mankind relies on it every day. One way of harnessing this kind of power is through the use of a combustion engine.The first four-stroke engine was developed in 1860 by Jean Joseph Etienne Lenoir. This was an 18 litre displacement engine. While massive in size, this engine produced a mere 2 horsepower at a 4% efficiency. So many others sought for ways to increase efficiency and decrease size.In 1876, Gottlieb Daimler and Eugen Langer managed to achieve far higher efficiencies because they compressed the gases before combustion instead of not compressing them like in the Lenoir engine preceding it.So in 1876 the first four-stroke engine with an acceptable efficiency was created known as the Otto four stroke engine. The exact efficiency is not knownNowadays four stroke type engines are still only able to produce 30-40% efficiency.Two types of efficiency are also recognised. The first is the energy efficiency. How much chemical energy goes into the engine compared to how much is useful energy produced by the engine. The other type of efficiency is called volumetric efficiency and shows how much air-fuel mixture is sucked into the cylinder compared to the amount of air- fuel mixture that would be in the cylinder at standard pressure or ambient pressure. So the higher the pressure before compression in the cylinder, the higher the volumetric efficiency will be.Turbo- or supercharged cars will have a volumetric efficiency of more than 100%, because the air fuel mixture is pressurized before entering the cylinder. Volumetric efficiency also has an influence on energy efficiency, because higher pressures will be achieved after compression, causing the efficiency to increase.For this extended essay, we would like to encounter the problems and engineering complications with building our own engine out a an old water pumping unit. Many different cycle iterations have been developed through the years in order to improve upon this volumetric or energy efficiency. These will be elaborated upon later.