Hello everybody.
This has been a nagging thing on my mind for some time now. Every once in a while, I log on to this forum and look over how things are going, and I always seem to find people experiencing extreme frustration with severe engine problems. From head nuts coming loose, to wrist pin bearings falling apart and destroying the entire engine, there is usually one culprit for all of these problems; DETONATION.
For those who are not sure what this is and what causes it, read on.
Detonation is the spontaneous ignition of a portion of the air/fuel mixture.
Normally, the spark plug should initiate combustion, and that flame front will expand until all of the air/fuel mixture is burned. This ideal situation will transmit the most energy to the rear wheel. However, this does not always happen this efficiently. As the flame front expands, pressure in the cylinder increases. As pressure increases, temperature of the air/fuel mixture also increases proportionately. Once pressure and temperature inside the cylinder reaches the critical flash point temperature of the particular type of fuel that is being used, any remaining air/fuel mixture that has not yet been burnt will spontaneously ignite(explode).
These engines we are using are old design, without knock sensors and sophisticated engine management controls. Today's fuels are not of the quality that many of us remember from several decades ago, and in order for us to operate these engines reliably, we must pay careful attention to detonation, as it is causing numerous problems for many motorized bicycle operators.
Extreme cases of detonation will be easily noticeable by the engine sounding loud, usually during extended periods of full throttle operation. However, it is very common to have partial detonation occurring without these noticeable symptoms.
When the rapid pressure spike of detonation occurs, there is little constructive work that can be done, so much of this energy is converted into heat which only aggravates the problem. The pressure spike transmits powerful forces to the piston, often resulting in damage to the bearings and even complete breakage of the crankshaft itself. I still keep a piston on the shelf that has a quarter inch diameter hole right through the center of the crown as a reminder.
What to do about eliminating detonation?
High octane, leaded racing fuel for competition 2 stroke engines is available in 5 gallon pails and works beautifully, however costs about $16.00/gallon.
The stock cylinder heads have limited thermal capacity and are very flimsy and should be replaced with a properly designed head with increased cooling capacity and the right size combustion chamber for the particular engine configuration that you are running.
I will make a short post in swap shop area to deal with the nitty-gritty on combustion chamber sizes, and where to get the right cylinder head for your engine.
-Fred
This has been a nagging thing on my mind for some time now. Every once in a while, I log on to this forum and look over how things are going, and I always seem to find people experiencing extreme frustration with severe engine problems. From head nuts coming loose, to wrist pin bearings falling apart and destroying the entire engine, there is usually one culprit for all of these problems; DETONATION.
For those who are not sure what this is and what causes it, read on.
Detonation is the spontaneous ignition of a portion of the air/fuel mixture.
Normally, the spark plug should initiate combustion, and that flame front will expand until all of the air/fuel mixture is burned. This ideal situation will transmit the most energy to the rear wheel. However, this does not always happen this efficiently. As the flame front expands, pressure in the cylinder increases. As pressure increases, temperature of the air/fuel mixture also increases proportionately. Once pressure and temperature inside the cylinder reaches the critical flash point temperature of the particular type of fuel that is being used, any remaining air/fuel mixture that has not yet been burnt will spontaneously ignite(explode).
These engines we are using are old design, without knock sensors and sophisticated engine management controls. Today's fuels are not of the quality that many of us remember from several decades ago, and in order for us to operate these engines reliably, we must pay careful attention to detonation, as it is causing numerous problems for many motorized bicycle operators.
Extreme cases of detonation will be easily noticeable by the engine sounding loud, usually during extended periods of full throttle operation. However, it is very common to have partial detonation occurring without these noticeable symptoms.
When the rapid pressure spike of detonation occurs, there is little constructive work that can be done, so much of this energy is converted into heat which only aggravates the problem. The pressure spike transmits powerful forces to the piston, often resulting in damage to the bearings and even complete breakage of the crankshaft itself. I still keep a piston on the shelf that has a quarter inch diameter hole right through the center of the crown as a reminder.
What to do about eliminating detonation?
High octane, leaded racing fuel for competition 2 stroke engines is available in 5 gallon pails and works beautifully, however costs about $16.00/gallon.
The stock cylinder heads have limited thermal capacity and are very flimsy and should be replaced with a properly designed head with increased cooling capacity and the right size combustion chamber for the particular engine configuration that you are running.
I will make a short post in swap shop area to deal with the nitty-gritty on combustion chamber sizes, and where to get the right cylinder head for your engine.
-Fred
