The four-stroke gasoline engine is comprised of many integral parts: the induction system, the cylinder heads, the engine block, the pistons, the camshaft, the crankshaft, and the flywheel. All these parts are necessary for the four cycles of operation in the Otto cycle, illustrated in.
The first stroke in the Otto cycle is the induction stroke. This process starts with the carburetor or the electronic fuel injection system flowing air into the intake manifold. While the air is passing through the carburetor or electronic fuel injection system, gasoline is added into the air creating a fuel mixture.
As the fuel mixture passes through the intake manifold, it is separated from one collective port to individual ports for each of the cylinders. The fuel mixture then progresses into the cylinder heads where an intake valve opens to allow the incoming mixture to flow to the cylinder chamber, while the cylinder head’s exhaust valve is closed so the mixture cannot escape from the chamber.
During this stroke, the piston starts at the top of the cylinder moving back towards the bottom of the cylinder creating a vacuum which creates a vacuum pulling in the fuel mixture.
Fuel and Air Delivery
The second stroke in the cycle is the Compression stroke. During this cycle, both the intake and exhaust valves are closed, and the piston moves from the bottom of the cylinder chamber to the top, thereby compressing the fuel mixture. The stroke ends when a spark is ignited to initiate the combustion of the fuel mixture.
The expansion stroke is the third stroke of the cycle. During the expansion stroke, the two valves in the cylinder head remain closed thereby containing the expansion of the ignited fuel mixture inside the cylinder chamber. The expanded gas propels the piston from the top to the bottom of the cylinder, providing the torque to drive the connecting mechanism.
The final stroke in the Otto cycle is the exhaust stroke. During this stroke, the combusted fuel mixture is forced from the cylinder chamber through the now open exhaust valve by the piston moving from the bottom to the top of the cylinder 18 chamber. The exhaust gas flows into the cylinder head where it continues until it is discharged from the engine through an exhaust manifold pipe.
The four cycle process is assisted by several components. As the pistons reciprocate, they drive or are driven through connecting rods through the crank shaft, which in turn either drives or is drive by the flywheel.
It is through the momentum generated in the revolving flywheel that the pistons are propelled in the first, second, and forth strokes of the Otto cycle and through the moment of inertia, which allows for smooth operation. Lastly, the camshaft, driven by a linkage connected to the crankshaft, opens and closes the intake and exhaust valves.
Last word
Further additions to the engine, such as fuel additives and forced induction systems can provide further power gains from the engine, thereby improving on Nikolaus August Otto’s innovations.
