Lets talk detonation again

There seems to be some misinformation going around again.

Detonation is caused by explosions along the boundary between rich and lean areas, caused by improper mixing, or over fueling. You cannot have detonation on a lean homogeneous mixture. We see this in the big turbo charged natural gas engines when they are lugged too much, or the turbo is not producing enough boost on the two cycles. A good way to think of this is when you lug an engine down too much starting out and it knocks before picking up, this is caused by over fueling trying to produce the torque, called spark knock by my dad.

Pre-ignition is caused by flakes of carbon that ignite a mixture, by timing that is too advanced for the speed of the flame front, or by a mixture that is above the autoignition temperature. This ignition pushes back on the piston before it has a chance to get the correct angle on the crankshaft to utilize the push. Retarding the timing will help if there are fuel related issues. We re now seeing this issue on the natural gas engines because they are getting more ethane out of the shale gas and it has a lower autoignition temperature.

Sorry RLP, you are just wrong.

You will also get detonation on a Diesel if one cylinder is over fueling.

You can get detonation on the running cylinders if others are missing, because they will be over fueled trying to make up for the lost torque caused by the missing cylinders. This can be caused by lean mixtures in the missing cylinders, making people mistakingly assume that the lean is causing the detonation.

The Ethane also burns faster, so makes a faster flame front requiring less advance.

We run a chromatograph on the fuel gas so we can analyze the fuel in real time and adjust timing if needed for the quality.

so is the auditable noise the piston rattling in the bore?

It is the shock wave from the explosion going through all the metal, bad stuff.

Pre ignition and detonation are both bad, just different things.

While I am ranting.

It is also important that there is no unburned fuel on top of the piston when the flame front reaches it, this will cause detonation. This is where timing comes in, the front will move at different speeds depending on fuel quality, compression and a real lean mixture will move faster.

Might be better worded as constantly fueling. Ie, the injector is not closing. The diesel detonates because there is fuel in the cylinder too early. Extra fuel at the right time won't cause detonation in a diesel.

Here is an interesting read:

Flame Acceleration and Transition to Detonation in High-Speed
Turbulent Combustion

http://www.dtic.mil/dtic/tr/fulltext/u2/1024642.pdf
Poke Here

. All diesels detonate to some degree . Detonation is temperature dependent. When the air/fuel mixture reaches the ignition temperature and ignites , that is detonation .
If detonation is occurring due to low airflow then the airfuel mixture is too hot. because it has not had enough cool air added to lower the air/fuel temperature below the auto ignition temperature .

Absolutely right! A stuck open injector will allow fuel in too early, and it will knock loudly when that happens. Overfueling might make the "diesel knock" a bit louder, it won't sound at all like a stuck open injector will. The sound can be different on the injection pump type used too, constant beginning-variable end of injection like most inline pumps and some rotary pumps are, or variable beginning-constant end of injection pumps like Stanadyne and Delphi rotary pumps. Inline pumps can be built with plunger helix cut that way too, but seldom are.

I would agree on Diesels Detonating to some degree due to the total amount of fuel added at once, this would cause barriers. I would guess the common rail injections that inject multiple times would reduce this dramatically, they are also much higher pressure which would disperse better.

Well you are wrong. A lean mixture is one cause of detonation, among others. It doesn't matter if it's on big engines or little engines. See number 5 in the link. I could reference other sources but I wonder if it would do any good.
http://www.onallcylinders.com/2015/09/24/detonation elimination 9 ways to prevent engine detonation/

David,
Will this shirt help you explain your point?

OK I will put my 50 cents in the discussion. (inflation from 2 cents). Detonation is a full or partial oxidation (burning) of a volume of material at once. It is not a flame front, the combustion occurs throughout the mixture volume at a pace that is more related to pressure related temp rise from thermal radiation and pressure related temp rise than the temp rise of a flame front only. Pour a trail of gasoline for about 50 feet into bare soil and put a match to one end. Woooofff. from the match to the beginning it has a noticeable travel time. If that same combustible mixture was heated with magnetic radiation and compression rapidly there would be a detonation. Detonation is importantly never allowed in a firearm, the powder is burned with flame front based rate of propagation. If not, massive over pressure would be splitting the chamber. The modern knock sensors are designed to keep an engine just barely into the initiation of spark knock. This "edge" provides peak pressure at a crank position a few degrees after TDC. A sweet spot that gives maximum energy transfer to the crankshaft. Is there a rise in pressure in the cylinder when ignited before TDC pushing backward on the engine? Sure, but that is what the flywheel is for. Jim

You left out about five causes of detonation. One thing for sure if you let it persist it will ruin your motor.

I assume several of you folks who post here on these subjects are mechanical engineers. (or maybe physicists?) I'm an electrical engineer and I did have required ME courses, but your posts here are way over my head to understand.