Hey Andrew,
Sorry for delay in response, been away from computer for a few days now.
Ill answer what i can right now as i gotta jet, but here is a good start:
This is some info i have copy and pasted form a mini "help" word file i have made for myself in the past (I dont remeber where i got this from):
Quote:
|
Originally Posted by Some Source
Let's say we start with 14 degrees BTDC timing and advance to 16 degrees BTDC. What is happening in the combustion chamber (cylinder)?
Many beginners incorrectly believe that the combustion event occurs instantaneously or "all at once" (say over 1-2 crankshaft degrees). If this were true, the shock to the rotating assembly (piston , rods, rod bearings and crank) would disintegrate it, after several combustion cycles. The events do occur very very quickly in the order of milliseconds (faster than a blink of an eye) but they do not occur instantaneously. There is an order of events that occurs.
Do you know how many crankshaft degrees it takes to start and finish a combustion?
How long (in milliseconds) is a 1 degree turn of the crankshaft?
You have to visualize, in your mind's eye, that a spark jumps across the electrode and a flame is started in the shape of a "kernel" (like a corn kernel) around the spark plug electrode. This flame must then travel from the centrally located spark plug outwards at a distance equivalent to half the cylinder's bore and downwards towards the piston top. Remember, during all this time, the piston is rising towards the spark plug at the top of the combustion chamber and squeezing the air/fuel mix . The piston top is the "floor" of the combustion chamber and like an elevator, it is coming up towards the spark plug at the "roof" of the combustion chamber.
In the combustion chamber, the air-fuel mix sits as a series of layers with different air/fuel ratios. The richest air/fuel ratio layer is closest to the spark plug and the leanest air/fuel ratio layer is at the very bottom of the chamber or the piston top.
The air/fuel mix layers are sequentially lit and the igniting process or combustion event is cascading outwards from the spark plug electrode, like dominoes falling in a row. As the air/fuel mix is lit , the mix combusts or explodes which creates an expanding force outwards. This explosion occurs over several milliseconds or crankshaft degrees. This expanding force of the combustion event also raises the pressure inside the cylinder.
When you "advance" your ignition timing, you are starting the lighting of the air/fuel mix earlier during the compression stroke.
|
I dont have a timing curve in picture format to show you as an example but im sure someone will be able to post it
Ill add more later