Navigation menuFigure 1. 4-stroke internal combustion engine. 1:fuel injection, 2:ignition, 3:expansion(work is done), 4:exhaust.[1] The four-stroke engine is the most common types of internal combustion engines and is used in various automobiles (that specifically use gasoline as fuel) like cars, trucks, and some motorbikes (many motorbikes use a two stroke engine). A four stroke engine delivers one power stroke for every two cycles of the piston (or four piston strokes). There is an animation to the right (Figure 1) of a four-stroke engine and further explanation of the process below.
The Otto CycleFigure 2.The real otto cycle process that occurs in a four stroke engine.[3] Figure 3. The ideal Otto Cycle.[4] The pressure volume diagram (PV diagram) that models the changes the fuel-air mixture undergoes in pressure and volume in a four stroke engine is called the Otto cycle. The changes in these will create heat, and use this heat to move the vehicle or machine (hence why it's a type of heat engine). The Otto cycle can be seen in Figure 2 (real Otto Cycle) and Figure 3 (ideal Otto Cycle). The component in any engine that uses this cycle will have a piston to change the volume and pressure of the fuel-air mixture (as seen in Figure 1). The piston gains motion from combusting the fuel (where this happens is explained below), and an electric boost at the start up of the engine. The following describes what occurs during each step on the PV diagram, in which the combustion of the working fluid—gasoline and air (oxygen), and sometimes electricity, changes the motion in the piston: Real cycle-step 0 to 1 (ideal cycle-green line): Referred to as the intake phase, the piston is drawn down to the bottom to allow the volume in the chamber to increase so it can "intake" a fuel-air mixture. In terms of thermodynamics, this is referred to as an isobaric process.
Process 3 to 4: The thermal energy in the chamber as a result of combustion is used to do work on the piston—which pushes the piston down—increasing the volume of the chamber. This is also known as the power stoke because it is when the thermal energy is turned into motion to power the machine or vehicle.
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