Air pressure explained
Air absolutely has mass and weight because it's made of molecules (like nitrogen, oxygen, water vapor) that take up space and are pulled down by gravity, even though it seems weightless because it's so spread out (low density), but you can prove it by weighing a deflated balloon versus an inflated one, or a container with and without air. The total mass of Earth's atmosphere is enormous, around 5.15 quadrillion tonnes, demonstrating air's significant mass.
Matter: Air is matter, meaning it has mass and occupies volume.
Composition: It's a mixture of gases, primarily nitrogen (78%) and oxygen (21%), all made of molecules with mass.
Density: Air has low density (about 1.29 kg/m³ at sea level), making its mass hard to notice, but it's still there.
Proof: An inflated balloon weighs more than a deflated one, and a vacuum chamber shows a measurable weight difference when air is removed, proving air has mass.
Atmospheric Pressure: Because air has mass, gravity pulls it down, creating atmospheric pressure that pushes on everything.
For engine builders we use PSI pounds per square inch 14.7 psi, we also work with Bar which is 14.5 psi
What I am trying to get across how air has body and can travel at very high speeds, but as we think we cant feel it or weigh it we tend to overlook the power of air.
The two most common units for measuring air pressure are Millibars (mb) used heavily in meteorology, and Kilopascals (kpa) the standard SI unit, often alongside inches of mercury (inhg) U.S. weather reports, with atmospheres (atm) and pounds per square inch (psi) also frequently seen, especially for general or technical
An American university did a experiment, take a meter long tube place a ping pong ball in the tube box tape both ends then suck out the air, the prick the end and the ball comes out the other end at 375 MPH, that is the power of air.
When a compressor explodes, if you use high speed recording the tank doest destroy its self when it bursts, its after the air has been expelled the air then fills the vacuum at 343 m/s that destroys the tank.
So how does it all work
Its laws of physics in a simple explanation
Air travels into a vacuum at 343 m/s or 1234 kilometres per hour into a vacuum, so air is not sucked into a engine its pushed in as it has to fill the vacuum.
A piston descending in a cylinder creates a vacuum and as the piston is only travelling at 25 meters per second the air has more than enough time to charge the cylinder, it only when the piston speed + volume does it stop and then relies on suction.
We can work out the RPM of that cylinder which is determined by piston cubic capacity, lets say your cubic capacity is 300cc per cylinder.
To work out maximum RPM a engine we will only need to look at one cylinder and at 11,500rpm
My avenger is 326cc which will rev to 10,500 before it has to suck in air, which can be done and my car-calc program will tell you a % in loss of power over max revs over the law of physics but it can still rev to 12,000rpm with its max power at 10,500rpm
The fact air will find its way into the cylinder you can start playing around with valve size, inlet size and exhaust size. By fitting a smaller inlet valve means the air speed over the valve has to be faster to fill the cylinder in the given time, but this means much better air to fuel atomization giving more power at lower revs but will still reach the max rpm.
This is where things get complicated
The leading edge (pressure wave) the front edge of rushing air - the pressure wave- traveles exactly at the speed of sound.
The absolute maximum velocity: while the bulk flow is limited by the speed of sound, a small fraction 0f individual gas molecules like lightweight nitrogen and oxygen will defuse into the vacuum at higher speeds due to their natural motion. under certain physics model air molecules can travel up to 650m/s at 60,000rpm
The absolute maximum velocity: while the bulk of flow is limited by speed of sound,a small fraction of individual gas molecules (like light weight Nitrogen and oxygen)
Will defuse into the vacuumat higher speeds due to there thernl motion. Under certain phyisics models, the front of the exspanding gas can reach around 500m/sto 1,700m/s depending on the temperature and the properties of the gas, that says it can fill a cylinder up
One of the best engines to exploit this was the 60s GT40 when they enlarged the cubic capacity they reduced the valve size, this gave the car more torque but still revved to its max which was much less than a Ferrari V12 revving to 12,000rpm but little torque, as a driver i would rather have torque in a 24 hour race, a winner every time in my book.
So to design your engine you only need to develop one cylinder, say 300cc reving to 11,500rpm once you have developed it to its max BHP then you can add on cylinders depending on what overall cubic capacity you want, 4 cylinders = 1200cc 8 cylinders = 2,4000cc and 12 cylinders = 3,600cc and all will rev to 11,500rpm.
What does this tell us, dont have the inlet valve opening before TDC, dont have direct injection as you are not using the speed of air for better atomisation.
if you like this article the next one will tell you how to build a engine using phyisics, or if you understand this article you should have enough information to work it out yourself.
I do have Robertson air shutters that works with the throttle opening and air restriction to increase air speed at lower revs up to max RPM. these have 12 moving parts and cost £500 per unit but with bulk orders the price should reduce per unit as they are made on a 5 axis CNC machine patent pending
The reason it works is a Professor Bill Ray told me in 1976 it would work and i believed him, and worked on it until it did what he said, so its all about belief.