Inflating Balloons With An Exhaust - How Much Air Do Cars Use?

Опубликовано 1 марта 2017, 15:00

How Much Air Does A Car Engine Use? Exhaust Balloons
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In this video we’re determining how much air an engine consumes, and as a visual aid to demonstrate this, I’ve attached two balloons to the exhaust of my Honda S2000, to show how much air is passing through the engine.

The balloon has slightly higher than atmospheric pressure inside of it. That’s all it takes for it to inflate. If you think about it, you can inflate this balloon with your lungs, so to me it seems silly to think that a 240 HP air compressor couldn’t do the same, very easily, and with no ill effects. Now I’m not saying I’d recommend anyone try this, but the back pressure caused by the balloon is extremely minimal, and it’s a great visual aid to show us the volume of air an engine spits out while running.

Calculating the amount of air an engine consumes at wide open throttle is fairly straight forward, with a few basic assumptions. We’re going to assume the engine has a volumetric efficiency of 100%, meaning that at wide open throttle, the engine is able to completely fill the cylinder with atmospheric air.

Let’s use this Honda S2000 as an example, which has a 2.0L engine and a rev limiter at 9,000 RPM. Since this is a four stroke engine, we know that for every two crankshaft revolutions there will be one intake stroke for each cylinder. So for our engine at the rev limiter at wide open throttle, we can calculate the flow rate of air through the engine as 2 Liters, multiplied by 9000 RPM, divided by 2. This gives us 9,000 liters per minute, or 9 cubic meters per minute. If we have a two car garage, six meters wide by six meters deep, by three meters high, this would give us a volume of 108 cubic meters. 108 cubic meters divided by our volumetric flow rate of 9 meters per minute, would mean it would take 12 minutes for all of the air in a garage of this size to pass through the Honda, assuming it were at wide open throttle at the rev-limit.

Compare this to the latest and greatest, the new Bugatti Chiron with it’s 8 liter 16-cylinder engine will ingest as much as 60,000 liters per minute at full tilt. In other words, it could swallow up your entire garage in less than two minutes.

Now judging by the rate at which these balloons are inflating, you can see that the air flow rate is much slower than at wide open throttle. With the throttle closed, there’s a vacuum within the cylinder, so the volumetric efficiency is much less than 100%.

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