High Intake Air Temperature Leading to Knock

"High intake air temperatures will also result in a higher combustion temperature, and again this may lead to knock." The higher the temperature, the lower the oxygen it contains that is available for combustion. Does the amount of oxygen for combustion not related to the combustion temperature?

The amount of oxygen in combustion chamber is definitely related to the combustion temperature. However the intake charge temperature is more important in terms of knock threshold. The higher initial intake temperature is the hotter the compressed air-fuel mixture gets and it results in higher pressure. That combination of higher temperature and higher pressure affects on stability of hydrocarbon molecules in case the octane rating of fuel in use in not high enough. That unstable mixture is prone to knock when more pressure and temperature applied during combustion process. That's how you get knock with high intake charge temperature.

The thermodynamics formula explaining the raise in temperature after compression is t2=t1(v1/v2)^gamma-1 which basically tells us that the final temperature of compressed air will be the initial temperature times (the initial cylinder volume devided by the cylinder volume when piston is at TDC) in power of 0.4. So, since it is in power the higher the initial number is the bigger will be the final difference resulting in higher temperature and pressure leading to knock if fuel octane rating doesn't support such conditions.

Seems to be some confusion there.

It's important to realise that while the amount of oxygen is always going to be around 19% in air, the mass, or amount, of the actual air may vary.

This is because of the temperature, pressure, volume relationship - you may be better to read up on those in Filipino/Tagalog - and how they affect density, which is the amount of air per unit volume.

With higher temperatures, for the same volume and pressure (how 'full' the cylinder is under that boost pressure), there is less physical air to oxidise/burn the fuel.

From Greg's Banish book:

"Fuels with a higher octane number have a stronger concentrations of these more robust molecules versus the more easily broken longer chains. Thus, they require more energy to break these bonds,, and have more resistance to knock. An interesting side note is that the energy required to break these bonds comes in the form of heat during combustion. Heat transfer from one molecule to the next requires a small amount of time. Even though this is a very small amount of time, more total transfer means more time for it to happen. Adding more heat to the molecules in order to separate their ions means more time is required. This means that the burn rate is slightly slower for high octane fuels. This becomes important later when we choose spark advance timing."

Sir Gord, the question is not addressed in your response, and the answers you provided are redundant from my statement. Thanks anyway. Sir Shota gave answers with thorough explanation as how my question should be responded. Sir Shota’s expertise on the matter offered clarity, allowing myself to move forward with a better understanding of the topic at hand. I appreciate it!

Your query was unclear, but if Shota helped, all's good.

Cristian, I'm glad we could clarify it for you. I would also pay attention to what Gord explained as it's directly related to the topic and it's very important information to be mindful of...