What is the role of Valves in Engine Operation?

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Engine Operation:

Four stoke or four-cycle burning engines make use of two primary styles of valves – the intake valve and the exhaust valve. Intake valves are opened to permit the flow of an air/fuel mixture into the engine’s cylinders before compression and ignition, while exhaust valves receptive permit the expulsion of exhaust gases from the combustion process after ignition has occurred.

In normal operation, a crankshaft in the engine to which the pistons are attached is tied to a camshaft as a part of a valve train arrangement for the engine. The movement of the crankshaft transfers motion to the camshaft through a timing chain, timing belt, or other geared mechanism. The timing and alignment between the position of the crankshaft (which establishes the position of the piston in the cylinder) and also the position of the camshaft (which determines the position of the valves for the cylinder) are critical not just for peak engine performance but also to preclude interference between pistons and valves in high compression engines.


Intake Cycle:

In the intake cycle, the intake cylinder piston cycles downwards because the valve opens. The piston movement creates negative pressure that helps draw the air/fuel mixture into the cylinder. Just after the piston reaches the lowest position in the cylinder (known as bottom dead center), the valve closes. Inside the compression cycle, the valve is closed to seal off the cylinder because the piston rises within the cylinder to the very best position (known as top dead center), which compresses the air/fuel mixture to a tiny low volume.

This compression action serves to supply the next pressure against the piston when the fuel is ignited moreover as pre-heating the mixture to help with an efficient burning of the fuel. In the power cycle, the air/fuel mixture is ignited which creates an explosion that forces the piston backtrack to the lowest position and transfers the energy released by burning the air/fuel mixture into the rotational motion of the crankshaft. The exhausting cycle has the piston again rising upward in the cylinder while the valve remains closed.



The pressure created by the piston helps force the exhaust gases out of the cylinder through the valve and into the manifold. Connected to the manifold are the system, a collection of pipes that features a muffler to scale back acoustical noise, and a converter system to manage emissions from the engine combustion. Once the piston reaches the highest of the cylinder in the exhaust cycle, the valve begins to shut and the intake valve starts to open, beginning the process over again. Note that the cylinder pressure on the intake helps to stay the valve opened and therefore the high pressure in the compression cycle helps to stay both valves closed.

In engines that have multiple cylinders, the identical four cycles repeat in each of the cylinders but sequenced in an order that the engine proves smooth power and minimizes noise and vibration. The sequencing of piston movement, valve movement, and ignition is accomplished through the precise mechanical design and electrical timing of ignition signals to the spark plugs that ignite the air/fuel mixture.

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