Detonation and Pre ignition
Thread Starter
Melting Slicks
Joined: Apr 2002
Posts: 2,337
Likes: 14
From: Norfolk VA
Detonation and Pre ignition
What does it sound like and do they occur under load, upon acceleration from a stop, etc. I am aware they are different but do they sound the same? BTW The archives section seems to be down......yet again.
Burning Brakes
Joined: Dec 2003
Posts: 1,004
Likes: 7
From: Adelaide South Australia
I've always considerred them as being just as destructive...
Is there a difference? Both result in premature explosion whilst piston still travelling up during compression stroke..... results in HUGE load on rods, bearings, piston crown etc.
Under load you'll hear what sounds like marbles rattling underneath the bonnet.
In mild cases, you might only hear it going up hills in a higher gear... still bad.
In severe cases, it will occur at any time you accellerate.
And contrary to what the pump bowser states, some operators are shonky!
On my way home after a longer cruise, I filled up with BP fuel (Ultimate 98 RON) and noticed immediately I had a "ping" whilst accelerating in 2nd gear. Drove home real easy.....
Drained all fuel, refilled with Mobil Synergy 8000 (98 ron) from my local station, and problem disappeared immediately.
Now I keep a bottle of octane booster in the car if travelling out in the country.
(note Australian 98 ron is ~= US 93 octane )
Is there a difference? Both result in premature explosion whilst piston still travelling up during compression stroke..... results in HUGE load on rods, bearings, piston crown etc.
Under load you'll hear what sounds like marbles rattling underneath the bonnet.
In mild cases, you might only hear it going up hills in a higher gear... still bad.
In severe cases, it will occur at any time you accellerate.
And contrary to what the pump bowser states, some operators are shonky!
On my way home after a longer cruise, I filled up with BP fuel (Ultimate 98 RON) and noticed immediately I had a "ping" whilst accelerating in 2nd gear. Drove home real easy.....
Drained all fuel, refilled with Mobil Synergy 8000 (98 ron) from my local station, and problem disappeared immediately.
Now I keep a bottle of octane booster in the car if travelling out in the country.
(note Australian 98 ron is ~= US 93 octane )
Racer
Joined: Mar 2006
Posts: 366
Likes: 1
From: Houston Texas
As my simple mind understands it:
Detonation is any ignition of the gas/air charge in the cylinder not caused by the spark plug firing. Pre-ignition is detonation that happens before the plug fires.
Detonation can happen after the plug fires but before the entire gas/air charge is burned which causes two (or more I suppose) burning wave fronts to collide which causes the distinctive sound described as a ping or knock. If the detonation happens first, the plug firing creates the second wave front. Over advanced timing creates a deformed wave front by igniting the mixture before optimum compression is reached and the mixture is not to a homogeneous density.
Detonation is caused by 'hot spot(s)' in the cylinder due to an edge or rough surface, carbon buildup, insufficient cylinder cooling, etc. It is most commonly associated to some load factor on the engine (acceleration, climbing a hill, passing) where the gas/air charge mixture changes and produces more force and heat for the burn.
Octanes change the gas/air ignition properties to eliminate the hot spots and their actions so that only the plugs spark ignites the fuel charge and results in a single wavefront burn.
Detonation is any ignition of the gas/air charge in the cylinder not caused by the spark plug firing. Pre-ignition is detonation that happens before the plug fires.
Detonation can happen after the plug fires but before the entire gas/air charge is burned which causes two (or more I suppose) burning wave fronts to collide which causes the distinctive sound described as a ping or knock. If the detonation happens first, the plug firing creates the second wave front. Over advanced timing creates a deformed wave front by igniting the mixture before optimum compression is reached and the mixture is not to a homogeneous density.
Detonation is caused by 'hot spot(s)' in the cylinder due to an edge or rough surface, carbon buildup, insufficient cylinder cooling, etc. It is most commonly associated to some load factor on the engine (acceleration, climbing a hill, passing) where the gas/air charge mixture changes and produces more force and heat for the burn.
Octanes change the gas/air ignition properties to eliminate the hot spots and their actions so that only the plugs spark ignites the fuel charge and results in a single wavefront burn.
Last edited by justanotherdoe; Feb 10, 2009 at 10:54 AM.
