Learn how a four Stroke Engine Moves Millions of Vehicles Worldwide
Thecombustion engineis the energy source that moves the majority of the vehicles you see on the road. Although most of these engines use gasoline or diesel to run, their operating principles remain the same. They are made up of several systems, assemblies and parts. Thus, knowing about their main components and how they interact with each other can help you understand how the combustion engine works.The main components of the combustion engineBasically, you can say that an engine is divided into two major sections: The block-or lower section-and the cylinder head-or upper section. These two sections hold the main parts, assemblies and components that make the combustion engine what it is: A power plant.The engine blockIf you were to lift the cylinder head off the engine, you'll be able to see the main section of theengine block. This block consists of a series of cylinders-four or more, depending on engine size-that serve as guide to the pistons that live inside the cylinders. Each piston connects to the crankshaft underneath through a connecting rod. The reciprocal-up and down-movement of each piston, helps rotate the crankshaft, which in turns helps rotate the vehicle driving wheels through the transmission to get the car moving.The cylinder headThecylinder headserves as a cap to each cylinder to form the combustion chamber. However, besides forming the top of the combustion chamber, the cylinder head is also the housing for the camshaft, the intake and exhaust valves, and the spark plugs.It is the camshaft that helps the intake and exhaust valves in each cylinder to open and close, providing the way for fuel to enter and combustion gases to leave. The camshaft accomplishes this through a series of lifters, rockers and springs.However, for the combustion process to take place, both the crankshaft and camshaft must work in unison. Therefore, they connect through a timing belt or chain that travels around a sprocket or sprockets at the front end of each shaft. It is this belt or chain that allows both shafts to rotate synchronously (or in time) so that each phase of the pistons' and valves' movement occur at the right time during the combustion process.The combustion process and the four-stroke cycleThe engine uses afour-stroke cyclefor the combustion process. So the key to understand this process is to look at each of these four strokes. These strokes consist of piston down and up movements called intake, compression, power and exhaust stroke.The intake strokeThe intake stroke represents the first part of the cycle. During this part, the piston moves down in the combustion chamber or cylinder. At the same time, the intake valve in the chamber opens. The piston's downward movement creates a vacuum in the chamber, which draws in-through the intake valve opening-a mixture of fuel and air that has been injected into the intake manifold. Once the piston reaches its bottom position, the intake valve closes and the next part of the cycle begins.The compression strokeAt this point, the piston begins to slide up through the cylinder, compressing the air/fuel mixture that has entered the chamber while both the intake and exhaust valves remain closed. As the piston nears its top position, the spark plug produces an electric arc that ignites the compressed air fuel mixture.The power strokeBy the time the piston has reached its top position again, the mixture has burned and exploded, initiating the power stroke of the cycle. The explosion creates enough heat to expand the gases produced by the burning mixture and propels the piston down with great force.The exhaust strokeWhen the piston reaches its lowest position again, it begins its fourth and last part of the cycle: The exhaust stroke. As the piston begins to travel up once more, the exhaust valve begins to open, letting the gases out of the chamber and into the *exhaust system. When the piston reaches the top position, the exhaust valve closes, the combustion process ends, and a new cycle begins.Each cylinder in the engine goes through its own four-stroke cycle in an alternating way-with a mere difference of degrees-in rapid succession and in an orderly sequence. A common vehicle combustion engine may have three, four, six, eight and even ten cylinders. Thus, more cylinders means more power strokes and more power to the engine. In this is a simplified overview, you've learned how the combustion engine works. In reality, though, many systems, assemblies and components work together to make the combustion process possible.
