Detonation, want to know what it means ?

Chris@CCM

Member +
Detonation
Detonation is said to occur when the air and fuel mixture in your engines cylinders explodes, or detonates, rather than burning smoothly. This exploding mixture can cause serious engine damage e.g. damaged spark plugs, melted pistons and melted valves. So it's definitely something that must be stopped. Below is a brief explanation of detonation - it's not meant to be a full in depth article, just a guide.

Detonation can be caused by a large number of things, but they can be put into 2 classes:

Pre-ignition of the air+fuel mixture
Excessive peak cylinder pressure for the fuel used
Pre-ignition can be caused by hot spots in the combustion chamber - this can be the spark plug tip, glowing carbon deposits or other hot spots. This cause of detonation isn't very common in modern engine as they run fairly clean, with minimal deposits. Spark plugs are often changed to a lower heat grade - this helps conduct heat away from the plug tip which reduces the chance of pre-ignition.

Excessive cylinder pressure for a given fuel can cause detonation. Excessive peak cylinder pressure can be caused by:

Ignition timing too advanced - peak cylinder pressure occurs too early in the engine cycle and causes detonation
Air + fuel mixture too lean - a lean mixture burns faster than a richer mixture, this can also cause peak cylinder pressure to occur too early
Effective compression ratio (CR) too high - if the static CR is too high, or you are running too much boost, detonation can occur.
Fuel plays a big part in detonation. Different fuels have different resistance to detonation. This resistance to detonation is measured and a fuel is given a RON or MON rating. A fuel with a higher RON or MON rating will be more resistant to detonation. Normal unleaded has a rating of 95 RON (Research octane number), super unleaded is 97 RON and Optimax is about 98 RON. Tesco Have just started to sell 99 RON fuel - I've used this and it seems to be more resistant to detonation than Optimax, and usually cheaper.



i took this from a site i did not write this my self
 

dark_knight

Member +
Does this mean that V-Power (Shell) burns slower than standard gasoline..? I always thought it was the other way around..? Please confirm this.. :)
 

AdamB

Member +
The higher the octane the more resistant it is to burn. So 99 RON is more resistant to burn than 95 RON.
Hope this helps.
 

dark_knight

Member +
Gotcha. So turbocharged engines are best run on higher RON to prevent this as compression introduces it's own complications to the 4-stroke cycle :)
Repped..
 

AdamB

Member +
You can still use 99 RON in a N/A engine to still give better performance over 95 RON. But due to the properties of 99 RON's resistant to burn, it doesn't lead to detonation or pre-ignition as easy as a lower octane rating.

As to yor question, an N/A engine will have a higher compression ratio than that of a turbocharged engine, so I assume it is more suited to a higher octane rating otherwise it will lead to pre-ignition due to the high compression, much like a diesel engine. It is much easier to burn petrol than it is to burn diesel :)
 
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GP82

Member +
Actually octane rating is not a measurement of the fuels burn rate. Higher octane fuel does not neccessarily burn slower then low octane fuel, but rather a measurement of the fuels resistance to detonate; higher fuel octane has greater stability at higher temperatures and pressures than low octane fuel.

The increase in power is more likely due to the fact that the structure of the hydro carbons content that may not vaporize like for example at 400 degrees. Where as the higher octane fuel hydro carbons content vaporizes at a lower 275 degrees.

In a street application that see's low rpm, the pump fuel has plenty of time to heat, vaporize and burn, but in our 4E's and 5E's, there is not time at 7200rpm for the pump fuel to totally vaporize.

As a result, the engine cannot take full advantage of the fuel's available energy at higher rpm. With the higher octane fuel vaporizing more quickly at lower temps, it's possible to burn more fuel at higher engine speed's which equals more power.
 

GP82

Member +
YES it DOES!

The performance difference from a change in fuel type is often common to a presumed change in the burn rate of the fuel as a result of the octane rating.

The octane rating is not a measurement of the burn rate! Higher octane does not necessarily burn slower than low octane.

It is the oil content within the fuel mix that determines the burn rate of the fuel, not the octane rating.
 

Paul_JJ

Member +
The performance difference from a change in fuel type is often common to a presumed change in the burn rate of the fuel as a result of the octane rating.

The octane rating is not a measurement of the burn rate! Higher octane does not necessarily burn slower than low octane.

It is the oil content within the fuel mix that determines the burn rate of the fuel, not the octane rating.

Give them a call and say that they don't know anything about petrol!

http://www.state.mn.us/mn/externalDo...ctaneFacts.pdf

" High octane gasoline burns slower than low octane gasoline. The slow burn prevents engine knock when cylinder pressures are high"

The Minnesota Department of Commerce, Weights and Measures Division regularly checks the quality,
safety and labeling of motor fuels, heating fuels and gasoline sold in Minnesota.
The Division also ensures the accuracy of all commercial transactions in the state involving products that are
weighed ore measured. These products include grain, produce, livestock and gasoline.
For more information on these services, contact the Minnesota Department of Commerce, Weights and
Measures Division, 2277 Highway36, St. Paul, MN 55113-3800, Phone: 651-215-5821
 
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