Ok, i am sorry, still learning....

Detonation? I hear that term all the time.... what the heck is that and what does it come from?

 

Ok,

Go for a ride, roll your windows up, stereo off. Make a pass, listen for ANY type of rattleing sound... Thats Detonation or PINGING!!

 

which comes from..............?

 

... Dumbass tuners who assume that everybody lives in 80 degree weather and has access to 106 octane gas everyday.

 

MOP,

LOL thats funny man.




It comes from to much timing usually giving a bad Air/Fuel Ratio...

 

lol, he's just bein' a jerk ;-)

Basically: your engine has 4 cycles... (actually, kinda 5)
intake: the induction of gas/air to the cylinders of your engine
compression: the compression of the two as the pistons move up.
ignition: the point RIGHT before top dead center (TDC) of the cylinders.
explosion: bang, the gas/air is compressed to a point where it just can't take anymore
exhaust: all the yucky stuff leaves the cylinders.

so basically, all this stuff run on the precision of a needle. pre-detonation is when the explosion in the cylinder happens BEFORE top dead center.

I think that kinda explains, if anyone else cares to add to make it a little more simpler, please do

 

Um yeah, what he said...

He is right on with it!!

 

Gas/air can start burning by "spontaneous combustion" like in a diesel motor from the combination of pressure and temperature. The more pressure or temperature the easier this is to have happen.

Detonation is the un-controled lighting of the gas/air mixture by something other than the ignition spark in the spark plug gap. This can happen from any hot (glowing) thing in the combustion chamber.

Examples of things that cause this are:

A spark plug that is too hot and that is not getting rid of the heat from the center. (this is a function of plug heat range)

A spark plug that is glowing on the ground lug. (this is not a function of plug heat range) note: Split Fires have more corners and no more ability to get rid of the heat.

A hot corner on the piston.

A hot piece of carbon on the piston.

A hot corner on a head.....


Once this starts to happen. The heat and pressure just keeps getting worse in a hurry.

The sound you hear is the flame front (coming from where ever it started accidentally) hitting the flame front coming from the spark plug when it finally did spark. The result is a sonic boom just like comes from the old jet airplanes at over the speed of sound. You have to be in your mid 40's to remember these. HEHE

All this is very bad! When you own 3 race two stroke motors all this is far more expensive and far faster.


Hope this helps

 

I am a little suprised in the "no comments" on my explanation

 

Well, everything you've read is correct. One of the causes of pre detonation CAN be a low octane fuel. High octane fuel DOES NOT ignite as spontaneously as low octane. In other words, it needs a spark to make it happen. Soooooo, when burning a high octane fuel, generally speaking, you can advance the timing to expand the power (or ignition) range.

 

Volatility

The key gasoline characteristic for good driveability is volatility — the gasoline's tendency to vaporize. Volatility is important because liquids and solids don't burn; only vapors burn. When a liquid appears to be burning, actually it is the invisible vapor above the surface that is burning. This rule holds true in the combustion chamber of an engine; gasoline must be vaporized before it can burn. In cold weather, gasoline is blended to vaporize easily. This allows an engine to start quickly and run smoothly until it is warm. In warm weather, gasoline is blended to vaporize less easily to prevent vapor lock and minimize evaporation, which contributes to air pollution.

Three properties are used to measure gasoline volatility: vapor pressure, distillation profile and vapor-liquid ratio. A fourth property, driveability index, is calculated from the distillation profile.

Vapor Pressure

Vapor pressure is the single most important property for cold-start and warmup driveability. (Cold-start means that the engine is at ambient temperature, not that the ambient temperature is cold.) When the gasoline's vapor pressure is low, the engine may have to be cranked a long time before it starts. When it is extremely low, the engine may not start at all.

Distillation Profile

Gasoline is a mixture of hundreds of hydrocarbons, many of which have different boiling points. Thus gasoline boils or distills over a range of temperatures, unlike a pure compound, water for instance, that boils at a single temperature. A gasoline's distillation profile is the set of increasing temperatures at which it evaporates for a fixed series of increasing volume percentages — 5%, 10%, 20%, 30%, etc. — under specific conditions. (Alternatively, it may be the set of increasing evaporation volume percents for a fixed series of increasing temperatures.)

Various ranges of a distillation profile have been correlated with specific aspects of gasoline performance.

Front-end volatility is adjusted to provide:

• easy cold starting
• easy hot starting
• freedom from vapor lock
• low evaporation and running-loss emissions

Midrange volatility is adjusted to provide:

• rapid warmup and smooth running
• good short-trip fuel economy
• good power and acceleration
• protection against carburetor icing and hot stalling

Tail-end volatility is adjusted to provide:

• good fuel economy after engine warmup
• freedom from engine deposits
• minimal fuel dilution of crankcase oil
• minimal hydrocarbon exhaust emissions

Vapor-Liquid Ratio

The vapor locking tendency of a gasoline is influenced both by the temperatures at the front end of its distillation profile and by its vapor pressure. But the property that correlates best with vapor lock is the temperature at which the gasoline forms a vapor-liquid ratio of twenty (V/L=20) — the temperature at which it exists as twenty volumes of vapor in equilibrium with one volume of liquid at atmospheric pressure. This correlation was developed for vehicles with suction-type fuel pumps and carburetors. How well it applies to later-model fuel-injected cars with pressurized fuel systems is not known.

Driveability Index

While each range of the distillation profile is important, the gasoline represented by the entire profile is what the engine must distribute, vaporize and burn. To predict cold start and warmup driveability, a driveability index (DI) has been developed using the temperatures for the evaporated percentages of 10% (T10), 50% (T50) and 90% (T90):

DI= 1.5(T10) + 3.0(T50) + (T90)

The DI varies with gasoline grade and season; the normal range is 850 to 1300. Lower values of DI generally result in better cold-start and warmup performance, but once good driveability is achieved, there is no benefit to further lowering the DI.

Volatility Specifications

The gasoline specification, ASTM D 4814 controls the volatility of gasoline by setting limits for the vapor pressure, distillation profile and vapor-liquid ratio properties. The specification employs six vapor pressure/distillation profile classes and six vapor-liquid ratio classes. The specification assigns one vapor pressure/distillation profile class and one vapor-liquid ratio class each month to each geographical area (state or portion of a state) in the United States based on altitude and the expected ambient temperature range.

Gasoline volatility not only affects a vehicle's driveability, but also its hydrocarbon emissions — both evaporative and exhaust emissions. Because of this relationship, the federal government and some states limit gasoline volatility to control the aspect of air quality affected by hydrocarbon emissions. ASTM incorporates federal volatility regulations into the gasoline specification as they are promulgated.

Fluctuating volatility requirements make gasoline manufacture and distribution a complex process. A refiner producing gasoline for a multi-state area may have to make gasolines with several different volatilities and change the volatility from month-to-month. And each gasoline has to be kept separate while it is shipped to the appropriate location.

Antiknock Performance

Knock-free engine performance is as important as good driveability. Octane number is a measure of a gasoline's antiknock performance - its ability to resist knocking as it burns in the combustion chamber. There are two laboratory test methods to measure the octane number of a gasoline. One yields the Research octane number (RON), the other, the Motor octane number (MON). RON correlates best with low speed, mild-knocking conditions; MON correlates best with high-speed and high-temperature knocking conditions and with part-throttle operation. For a given gasoline, RON is always greater than MON. The difference between the two is called the sensitivity of the gasoline.

Because RON and MON are measured in a single cylinder laboratory engine, they do not completely predict antiknock performance in multicylinder engines. There is a procedure to measure the antiknock performance of a gasoline in vehicles. The resulting value is called Road octane number (RdON). Since vehicle testing is more involved than laboratory testing, there have been a number of attempts to predict RdON from RON and MON. The equations take the form:

RdON = a(RON) + b(MON) + c

A good approximation for RdON sets a=b=0.5 and c=0, yielding (RON + MON)/2, commonly abbreviated (R+M)/2. This is called the Antiknock Index (AKI).The Federal Trade Commission requires dispensing pumps to be labeled (posted) with the gasoline's AKI. (The gasoline being dispensed must have an antiknock index equal to or greater than the posted value.) Owner's manuals also must indicate the octane requirement of vehicles by AKI. (Older owner's manuals of some foreign cars specify RON; some more recent ones specify both RON and AKI.)

Neither the AKI nor the several other single-value indices that have been developed work for all vehicles. The performance of some vehicles correlates better with RON or MON alone than with a combination of the two. And for a given vehicle, the correlation can vary with driving conditions.

As the formula indicates, gasolines with the same AKI can have different RONs and MONs. This may explain why a vehicle knocks with some fill ups of the same brand but not with others; or why it knocks with one brand of gasoline but not with another. Of course, for a comparison to be valid, the vehicle must be operated under identical conditions, which is not easy for the typical driver.

Generally, three grades of unleaded gasoline with different AKIs are available in the United States — regular, midgrade and premium. At sea level, the posted AKI for regular-grade is usually 87 and for midgrade, 89. The AKI of premium-grade varies more, ranging from 91 to 94.

The posted AKIs gasoline are lower in the Rocky Mountain states. These altitude gasolines historically provided the same antiknock performance as higher-AKI gasolines at sea level. The octane requirement of older-model engines decreases as air pressure (barometric pressure) decreases the barometric pressure is lower at higher elevations.

Since 1984, vehicles have been equipped with more sophisticated control systems, including sensors to measure, and engine management computers to adjust for, changes in air temperature and barometric pressure. These vehicles are designed to have the same AKI requirement at all elevations and the owner's manuals specify the same AKI gasoline at all elevations.

It is difficult for a driver to know whether a gasoline has the antiknock performance the engine requires when the engine is equipped with a knock sensor system. These systems, which temporarily retard spark timing to eliminate knocking, are installed on many late-model engines. Retarding the spark reduces power and acceleration. The knock sensor responds so quickly that the driver never notices the knock. Loss of power and acceleration will be the only clues that the antiknock quality of the gasoline does not meet the vehicle's octane requirement.

Using gasoline with an antiknock rating higher than that required to prevent knock or to prevent spark retardation by the knock sensor will not improve a vehicle's performance.

Power

The power an engine develops depends on its design. In general, the more air an engine can process, the more power it can produce. Major design considerations for power are the displacement of the engine, the compression ratio, and the presence of a supercharger or turbocharger. Other factors affecting power are the number of valves per cylinder, valve timing, and spark timing. Because different grades of gasoline have essentially the same heating value, they all provide the same power as long as their antiknock performance meets the engine's requirement.

 

This was posted here before but its good.
WHAT IS DETONATION?
The octane number of a gasoline is a measure of its resistance to detonation. Detonation occurs when the octane number is too low for the engine and its operating conditions. When the spark plug fires, the flame moves through the air/fuel mixture, burning it very rapidly. Detonation occurs if a portion of the unburned air/fuel mixture gets raised to a temperature and pressure it cannot tolerate and ignites before the flame front gets to it. Detonation causes the maximum pressure in the combustion chamber to be reached before the piston reaches top dead center and pushes down the piston before it has reaches the top of its travel. Much of the gasoline's energy is wasted in trying to move the piston up while the high-pressure gasses are trying to push it down. The extreme temperature and pressure developed can cause broken rings, rod-bearing damage, piston overheating, and erosion of the aluminum. Pistons sometimes end up with holes in their tops from the high temperatures and high pressures.

 

and no flames, comments ?

Ahh, now I know, I am finally treated with ...respect.

No, that's not the word,.. it'll come to me.... ignorance.

 

BlackLight, nice cut and paste =/

http://www.chevron.com/prodserv/fuel...gas/ch1a.shtml

 

Hey, give me some credit, I had to erase some to fit the caracter limit per post...