2012 Prius 120k miles diesel sound when slowly accelerating

The key to preventing preignition is to ignition the mixture before it occurs. The earlier the spark is initiated before top dead center; the less power the stroke generated. Early ignition works against the momentum of the piston and creates loss of energy, until the piston passes top dead center.

How is igniting the remainder of the fuel air mixture after it has been pre-ignited going to help with an increase in power? Please explain.

 

Yes but.....
The problem here is......that what you said in this previous post makes no sense.

Pre-ignition happens BEFORE the desired ignition point. What is or is not left over after the ignition is an entirely different condition.
What is left over AFTER the ignition can't have any impact on what occurs BEFORE the desired ignition point.

 

(A) Pre-ignition means it happens too soon, too far before TDC. You don't solve that by making it happen even sooner.

(B) This is true ONLY when the mixture ignites sooner or faster than the design calls for. Ignition timing advance, which means before TDC, is done on purpose, up to a point, so that the fuel burn is reaching it's peak expansion pressure as the piston passes TDC.

(C) I never said any such thing. When the fuel ignites early due to temperature/pressure or a carbon "hot spot", then the spark does NOTHING.

 

Another important point is that preignition does not occur at the same timing point in the piston's position for each cylinder as it does in spark plug ignition. The random ignition thus throws off the balance of the engine.

 

You guys are arguing technicalities. The pre-ignition is adjusted for when sensed by the knock sensor. Exactly how, ask the engineer(s) who designed it, or someone who studied their design.

The valves have variable valve “timing”, so yes “timing” is retarded. The mechanism is beyond me, but has something to do with delaying the closing of the valves I suspect, decreasing the effective compression ratio, (I guess).

 

whatever..........

 

Not exactly. The octane rating of gasoline is the percentage of pure iso-octane (= 2-2-4 trimethylpentane) in a test mixture which would have equal tendency to knock when mixed with pure normal heptane. There are two versions of the test, called Research method and Motor method. The numbers posted on US pumps are an average of those two methods.