Why is it that colder air is less likely to cause detonation... I know it that this is true, but not sure as to really why... Something to do with the dense air or is it totally temperature?
I think it has to do with the cooler air being harder to light off. Since detonation is two flame fronts hitting each other. With the cooler air a hot spot will have a harder time lighting everything off.
I have taken quite a bit of physics, but I don't think it is that complicated. I think it comes down to simply cooling the intake air thus not allowing the temperature inside the cylinder to reach it flash point. So w/out the help of the spark, there would be no fire. If you think about it this way. A diesel needs no electricity to run, in fact many of the fuel pumps (used to be anyways) are mechanical so they don't even need electricity to run. A lot of people think that glow plugs in a diesel combust the gas or the engine needs them to run. The only thing a glow plug is for is to warm the cylinder when it is cold out because of the cooler temperature the fuel would not combust. Once the engine is running the cylinder temperature is warm enough to run it self. If you have ever driven an old tractor you see this better. You turn the key off , all the electrical things go off, but the tractor stays running. You pull a switch wh/ is connected to the fuel pump and kills fuel to the engine, the engine stops. Deisel engines are very basic, if it doesn't run, you don't have one of three things: Air, Fuel, or Pressure, that is it. Sorry for the long thread but I hope this helps you better understand why cooler air prevent detonation. By lowering it 20deg, it takes more pressure to raise the temperature enough in the short time it has in a cylinder to combust by itself.
I believe it to be the density ,due to (edit) temperature.
The molecules are bonded more closely, with little energy initially. thats what cold is, lack of energy. When something is cold, the molecules are very still (never totally still). It will therefore take more heat (energy) to ignite and destroy the bond between these molecules.
Hotter air will combust quicker, because it already has a significant amount of energy inside these molecules.
you guys aren't bringing in enough info. If you have a motor with a blower on it and you are driving around in really dense air, lets say its 40 degrees out side, you will see detonation because you do not have enough fuel to compensate for how dense the air is. Bringing air temperature down helps in the combustion of the gases.
remember detonation has a lot more to do with lack of fuel and timing.
you guys aren't bringing in enough info. If you have a motor with a blower on it and you are driving around in really dense air, lets say its 40 degrees out side, you will see detonation because you do not have enough fuel to compensate for how dense the air is. Bringing air temperature down helps in the combustion of the gases.
remember detonation has a lot more to do with lack of fuel and timing.
mrpositraction nailed it right on the head. Pre-ignition is the temp with in the cylender exceeding the fuel's flash point thereby cuasing the fuel to self ingnite before the timing of the spark.
Interesting short story: I owned a '91 volks diesel, 100% mechanical motor. One day late at night my alternator went, drove home 25 miles by fading parking lights only but the car ran without skipping a beat. The fuel was fed mechanically through a belt driven injection pump. So once the starter started the motor, it would continue to run as long as it had fuel and enough RPM (500-700) to keep it moving, even with a dead alternator.
mrpositraction nailed it right on the head. Pre-ignition is the temp with in the cylender exceeding the fuel's flash point thereby cuasing the fuel to self ingnite before the timing of the spark.
Interesting short story: I owned a '91 volks diesel, 100% mechanical motor. One day late at night my alternator went, drove home 25 miles by fading parking lights only but the car ran without skipping a beat. The fuel was fed mechanically through a belt driven injection pump. So once the starter started the motor, it would continue to run as long as it had fuel and enough RPM (500-700) to keep it moving, even with a dead alternator.