# Calculating engine air intake per minute

Hi guys i tried to calculate the amount of air liters per minute that an engine consume , so the engine is a V8 diesel 15L max rpm 3000. The 15L displacement is the total size so
15/8 = 1.875 L/minute
Considering that each crankshaft turn only one piston conbust so
3000×1.875 = 5625 L/minute
is my calculation correct?

Edit:

• 4 stroke engine.
• turbocharger.
• commun rail direct injection.

The way you're attacking the problem will be extremely difficult to pull off, because there are quite a few variables, and you need to chart them in real time. You'll need a multi-channel data logger.

However, there's a much easier way to get a coarse value.

Diesels don't have throttle plates, so they ingest nominally their nameplate displacement volume of air every 2 revolutions. (Every 1 revolution for 2-stroke).

Figure out how many revolutions the engine has turned in the testing period. Divide by 2. Multiply by the engine's displacement.

Now if you need more than a coarse arm-wave, you'll need to adjust for the fact that the intake ducts are not perfect, and do create some restriction to airflow. Or, you may at high altitude. Conversely, superchargers may be boosting. Look at pressure at the intake valve in atmospheres (0=vacuum, 1=sea level atmosphere at 14.7 PSI) and multiply the above by that fraction.

• Harper the firing of a 4 stroke engine is simultaneous so i guess this mean one firing each revolution . Commented May 11 at 9:21
• @Tintin - Simultaneous on a 4-stroke engine? No, it's not. There is a "firing order" ... for old school Chevrolet engines, it's: 1-8-4-3-6-5-7-2. A cylinder fires every 90° of crankshaft travel. Commented May 11 at 11:21
• @Tintin in the 4 stroke cycle, 2 strokes do not involve air movement through the engine. So they don't count. A perfect 302 cubic inch Chevy small block engine will move 302 cubic inches of air through it in two complete revolutions. Commented May 13 at 0:01
• @Harper-ReinstateMonica so let say ~ 2 812,5L/minute. Commented May 13 at 11:59

No, it is not correct. This is because you don't have (or aren't giving) enough information.

One bit of information you don't have is: What is the volumetric efficiency of the engine? Volumetric efficiency is how much is a cylinder filled during the intake process. Most naturally aspirated engines don't fill 100%. Those engines with turbo or superchargers will fill over 100%.

Another bit of information you need is: Is this a 2-stroke or a 4-stroke engine? If a 2-stroke, each cylinder fires once per revolution of the crankshaft. If a 4-stroke, it fires once every two revolutions of the crankshaft. If it's a 4-stroke V8, you have to figure 1/2 of the cylinders, not 1/8.

And yet another bit of information you need is: What's the air density at the time of the test? If you're at sea level, the air density will be higher than if you're at 7000 feet above sea level. If the air is 90°F, it will be less dense than if its at 50°F.

Without this information, you can't really get a good idea of how much air is being consumed by an engine at any given engine speed. Note, these are just some of the factors off the top of my head. I'm thinking there may be others.

• Paul were you in the air force hhh i hear my brother here talking. About my question its a 4 stroke, what i know in an engine is the cycle is syncronous i mean a piston fires once every two revolutions but the pistons next of them are at a different step and that what gives the engine its smoothess thats why i said at each rpm one combustion. About volumetric effeciency let say 100% . Commented May 11 at 9:11
• @Tintin - Saying "at each rpm" is just plain wrong, because unless it's a 2-cylinder, 4-stroke engine, it doesn't happen like that. Also, real world, the vast majority of naturally aspirated engines will not be at 100% VE, so using it as a constant doesn't work. Commented May 11 at 11:29
• @Tintin Not enough information. Turbocharged engines operate under "boost", that is, the air pressure in the manifold is, typically, 0.05-2 bar above atmospheric pressure. Boost can only be calculated by knowing turbocharger parameters, state (RPM), and actuator positions (wastegate, VGT position). Commented May 12 at 18:19