Interesting air volume requirements

[Sharecropper]

Today while doodling around on my calculator I began to think about how much fresh air is required for our original 6.2 naturally-aspirated engines to operate (or any engine for that matter). I was reminded from my early high school engine class that all engines (non-turbo) must suck in the air it requires for combustion, and this sucking occurs when the pistons are going down immediately before the compression stroke. Because the pistons must suck in the air to fill the chamber through a small orfice around the intake valve, it requires energy (horsepower) to achieve this. This is one reason a turbo'd engine is more powerful, because when the intake valve open the air above the valve is pressurized from the turbo and therefore it fills the combustion chamber without requiring any energy (horsepower). This is also why a fresh air supply to a naturally-aspirated engine will improve the performance, albiet slightly.

Our 6.2 diesel engines have just that - 6.2 liters of displacement. Converted, 6.2 liters equals 379 cubic inches. Which means that, with every revolution of the engine, 379 cubic inches of air is required for combustion. If the engine is rolling down the highway at 2000 RPMs, the engine will need 758,000 cubic inches of air per minute to operate (379 x 2000). Since there are 1728 cubic inches in 1 cubic foot (12 x 12 x 12), the engine will require 438 cubic feet of air per minute for normal combustion (758,000 divided by 1720). At 2500 RPM, the air requirement increases to 548 cubic feet of air per minute.

Interesting. Very interesting. But not funny.

For those of you who do not plan to turbo your engine, at least get a fresh air supply to the air cleaner. Hope this stimulates thought.

 

[Sharecropper]

Correction - because there is always one engine revolution of each piston on the compression/combustion stroke which does not require outside air, my calculations were exactly double what is actually needed. At 2000 RPM therefore a volume requirement of air would be almost 220 CFM. This makes it more believeable, but still quite amazing, when you think about it.

 

[SCSG-G4]

Figure out what the larger truck engines need. There was a thread around 2011 talking about driving through volcanic ash and what it would take to keep the driver and the truck going, and how big an air filter would be needed. If I remember correctly about half the cargo area of a deuce would have been 'lost' to the filter required to move 30 miles in those conditions.