The purpose of the engine is to provide power to move your car down the road. In order to do this, it turns gasoline into energy that can be used to move that machine. The gasoline engine has been around for over a century and has made significant progress, especially in the last 10 to 20 years, and has evolved into what we have today.
With exhaust emission and air quality regulations imposed on car manufacturers, and the cost of fuel continuing to go up, manufacturers have made great strides making your plunger engine more powerful and efficient. One might be able to argue that without government intervention, this evolution would not have been so rapid.
The engine in your car is technically known as an internal combustion, spark ignition, 4-stroke engine. We call it internal combustion because the combustion event happens inside the cylinders. And for 4-stroke, it is because it takes four strokes of the piston to accomplish one Power stroke. These four strokes require two revolutions of the delivery valve crankshaft, which the pistons are attached to. A 4-stroke engine can be anything from one single cylinder to a V-8 or V-12 engine.
The piston starts at the top of the intake stroke in the cylinder bore. As the piston travels down it creates negative pressure in the cylinder. The intake valve opens allowing a very carefully metered mixture of fuel and air that fills the cylinder.
The combination of intense heat combined with spark plug ignition causes a controlled explosion within the cylinder, expanding the gases and forcing the piston down rapidly. With all of the available energy extracted from the air/fuel mixture, the piston now starts its way up the cylinder for the fourth stroke. The exhaust valve opens and the spent gases are now forced out of the nozzle cylinder and through the exhaust system of the vehicle. Once finished, the very next stroke, or down-travel, of the piston is the succeeding intake stroke.