I was reading a thread on TT. Net about high compression engines and turbo and the last post had a link to an article about detonation and pre ignition which I honestly I feel is misleading. I couldn't finish reading it cause I didn't feel like putting on my boots to walk through that bs, so do these sound right to you?
1. He labels pre ignition and detonation as an unknown phenomenon?? Whaaa? What really had me scratching my head is how he claims detonation only happens atdc which if that was the case I don't see how it could even happen if the cylinder has already passed it's peak compression point and the a/f mixture has already been ignited and the exhaust valve open.2. Octane is nothing magical? What is this guy smoking? Leaded, unleaded, alcohol, ethanol all burn different. I was taught octane is anti knock. Higher octane is a slower more controlled burn. 86, 88, and 91 ignite quickly like a bomb, boom, and expells all of it's energy at the time of combustion. E85 ignites and the flame front not only pushs, but follows, and fills the entire combustion chamber which is what makes it was safer inmo, in other words leaded unleaded ignite quickly almost punching the piston, E85 burns so slow it literally pushs the piston down the entire way burning all if the charge which q16 doesn't due. I believe pre ignition and detonation both happen before the spark plug fires, and are essentially a result of poor poor tuning, uneducated mods and it an Improper functioning engine. Pre ignition is simple. It's when the combustion of air and fuel is initiated by something other than the spark plugs or cylinder pressure i.e. Pieces of hot carbon or a sharp metal edge in the compression chamber. Detonation is combustion caused by excessive cylinder pressure, this is happening constantly in a diesel truck. They don't have spark plugs so how do they ignite there af mixture. Cylinder pressure. There are a couple things that cause this to happen. One of the fearures of our Z's help prevent this is vtc adding more overlap. Overlap is when the intake and exhaust valve are open at the same time allowing the scavenge affect to clear the cylinder of the previously combusted gas's. This scavenging only happens at the top of the combustion chamber between the valves wear the spark plug is and should pull all if the previous charge out of the chamber. If all the gas's don't escape due to poor scavaging during overlap due to various reasons now there is an large area of the combustion chamber already occupied by a possibly ignitable charge, and we just force more combustible air eventually ignited before the spark plug due to excessive cylinder pressure, and we put more fuel ontop of that which means the spark plug can't efficiently burn everything, poor scavenging doesn't clear the chamber the excessive pressure causes gas's build up and pressure ignites part of the charge before the spark plug can. Then the plug fires igniting the second charge so it's two kabooms which is where the idea flame fronts crashing. So detonation is essentially two kabooms real quick. The first combustion untimed uncontrolled and ignited by pressure
when the piston is traveling upward causing the engine to want to stop in place, and this is one crush rod bearings and this is where the term two flame fronts crashing comes from. The second by the spark plug and this is usually what cracks the rings.
So in a way detonation can be a type pre ignition, that would cause crazy cracking of parts forming edges, that would eventually get hot from a lean inefficient engine, start glowing orange like a glow plug and igniting the charge before the plug.
High compression TT solves it all
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12:54:00 03/17/14
