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4-Stroke SI Engine Mechanical Movement
Above, you should be able to see a more complex animation of the mechanical process which all EFI piston-based internal combustion engines perform. For reference:
– The blue particles represent the intake charge.
– The yellow particles represent the fuel sprayed from the fuel injector.
– The red particles represent the exhaust gases.
Stroke 1) The intake stroke in which the intake valves are pushed open by the intake camshaft lobe, allowing the air/fuel mixture to be sucked into the cylinder sleeve from the intake manifold and head assembly. Take note that th intake valve is also proportionally larger than the exhaust valve, this is a common design feature of modern IC engines.
Stroke 2) The compression stroke in which the intake and exhaust valves are both seated. The piston compresses the combustion gases (air/fuel) in order to make them more volatile so they can release more energy when ignited. Notice how the ignition event occurs before the piston reaches TDC on the compression stroke, this is why the timing of a motor is referred to as ignition advance.
Stroke 3) The combustion stroke occurs after the ignition event which releases a pressure wave forcing the piston down, thus turning the crankshaft creating torque. NOTE: the output of an engine should always be measured in torque!
Stroke 4) The exhaust stroke in which the exhaust valves are pushed open by the exhaust camshaft lobe, allowing the spent combustion gases to be pumped into the exhaust manifold. The exhaust stroke cleans out the cylinder sleeve and prepares it for the next intake stroke.
