#4 Properties of air...
Anyone that has followed the first 3 write ups should have a decent idea of how the mechanical aspects of an internal combustion 4 cylinder engine operates...with one very complex issue left aside; camshafts...which will need a write up all of their own...but before that, there are some...very annoying...properties of our atmosphere that need addressed...
1st is the make up of whats hugging this planet...and to keep it simple, this is the 'troposhere', or the layer of gas that sustains terrestrial life (us, animals, plants, etc.)...and more importantly...our engines...
the layer touching the surface of earth is made of roughly 78% nitrogen, 21% oxygen, 1% (variable by climate) water vapor, and a small amount of trace gases (one of which, surprisingly, is C02...which if you listen to the news, you'd think it made up most of the gas surrounding earth)...
for our engine purposes...we only need to really be concerned with 2 of them...the most important is obviously Oxygen...the oxygen molecules are very willing to react and combine with the hydrocarbon chains that make up gasoline...and reaction results in an exhaust accumulation of water and carbon dioxide, but more on that later...Nitrogen is also deemed 'important', as it acts as a stabilzer for that reaction...this, too, will be discussed in a future 'whatever you want to call these essays'...
Aside from the chemical make-up, there are a couple of properties related to ambient air that directly effect our engines...most of which are annoying, hard to understand, hard to predict, and annoying...
First is pressure. At sea level air surrounds everything with about 14.7 psi of pressure...the higher you go up from sea level, the more that pressure drops, and the less available air you have to burn in your engine...thats pretty straight forward, and without getting heavily into density, volume, and temperature...i'll just leave it at that...
the other quality though...is the hard one...Air is very elastic, mostly due to the fact that at only 14.7 psi...its not held or 'squeezed' together with that much force...and therefor isn't very dense...the elasticity of air is pretty much the single hardest thing to overcome understanding when building a naturally aspirated engine...as from the get go...you're forced to only use this ambient pressure to get air into the engine, and its not exactly easy...
for me at least; the best way to think of a charge of air...from the filter of the intake system...all the way to the intake valves of the cylinder head...is that its kind of like an invisible slinky...its filling the intake system...but pushing on one end, or pulling on the other...doesn't make the entire 'spring' move in any uniform motion...part of it will do what you want, part of it will fight and not move anywhere...and even worse...part of it will go the other direction...then start coming back, start squishing on other parts of the spring, then move forward again...and it just goes on and on...
So this property makes an absolute mess out of an engine...its why its so damn hard to make an engine have a lot of low end torque, but still make a lot of power up high...piston speeds at one location will suck in air and get volume moving perfectly...but at other locations will cause air to slam into itself and just jam up in there...
These simple 'facts' are much easier to understand than the complex systems engineers have come up with to address them...The next write up is going to be about my most disliked parts of an engine...the camshafts (i've always disliked them; not because recently mine are giving me trouble...)...and i'll address why i think they're archaic, and should've been replaced with systems that make a whole lot more sense (NOT VTEC, cams entirely should be gone)...given the atmosphere we're stuck with...