How does a car get air in order to run the engine?
In: 5
When the spark ignition engine (typically gasoline burning, your normal engine) is running, the intake valves open relative to the pistons in such a way that a vacuum (negative pressure relative to atmospheric pressure) is created in the intake manifold. (A differential in pressure is what creates flow in a certain direction. The air will always want to travel away from high pressure to a lower pressure.) A flowrate control valve (throttle body) is installed at the entrance to the intake manifold. If it closed fully, the engine could not pull any air into the intake manifold and would stall/shutoff. In modern engines, the throttle body is controlled to open a small amount at idle, just so that enough air can pass through to keep the engine operating at 500-800 RPM. When you push down on the gas pedal, you are opening the throttle body, which in turn decreases the restriction on airflow into the engine and allows for it to increase speed and perform work (accelerate from a stop). Keep in mind, the air going through the air filter, passing through the throttle body, through the intake manifold, and then I to the engine to be combusted with fuel is being pulled into the engine. Note, there is additional tube from the inlet of the throttle body to your intake air filter housing. This is to ensure all of the air that is pulled into your engine is clean.
Disclaimer:
1. If you do not understand how an engine operates, it would be beneficial to look on YouTube for a diagrammatic explanation of a simple spark ignition engine. This will explain how the crankshaft is connected to pistons via rods, the crankshaft rotation is fixed relative to the camshafts in the head. The camshafts rotate and open intake and exhaust valves in the head to allow air/fuel into the combustion chamber and exhaust gasses out of the combustion chamber. The intake valves open when a piston is in downward motion, motion which creates more volume and as such, a negative pressure. Before the piston stops moving downward, the intake valve is closed. As this piston begins to move back upward, another piston is beginning to move downward and the cycle continues, maintaining negative pressure in the intake manifold.
2. Air cannot be pulled, however for an ELI5 it makes more sense to explain it this way. So you physicists can get off your high horse for this one…
3. A turbocharger, supercharger, or any form of ‘forced induction’ system is different from this ‘naturally aspirated’ engine described above.
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