Guest Anonymous Posted January 11, 2003 Share Posted January 11, 2003 Thought I new what it was til I did some reading. Now need more data. I thought detonation is misfire ie fuel releases energy with no control spark like dieseling when ignition off and engine hot. Now I am thinking detonation is not that abrupt in some cases like with fuel injection when you use lower than required octane. Detonation causes damage which I guess is too high a heat in combustion chamber ( burns valve/seats), or non control energy release 'might brake stuff'. Also, I guess ECU's retard spark with lower octane fuel usage. Quote Link to comment Share on other sites More sharing options...
Mudge Posted January 12, 2003 Share Posted January 12, 2003 ECU should retard spark with lower octane fuel if knock is present, however reaction time is another thing altogether. Usually knock retard is also more than is needed, because once it starts, it can get bad fast, so any knock is not good for power or the engine. Detonation is not really extra heat, heat = power in the internal combustion engine, detonation is firing at the wrong time, due to a spark plug or sharp area or exaust valve holding too much heat and pre-igniting/deiseling the mixture. If you fire prematurely, the piston could have enough upwards travel left in the compression stroke that you end up fighting the piston face/ringlands, and can blow something up. This can force extra compression to a point, but again if its happening before you want it too you are basically sending two fast moving objects on a collision course and something is going to break. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted January 15, 2003 Share Posted January 15, 2003 Some (relevant?) info from the aviation world. Going through school to get my A&P we were taught that detonation and pre-ignition are two seperate events. Detonation is the rapid burning of the fuel air mix, causes are many, most common (in aviation) were high combustion chamber heat, (high ambient temps) lower than needed octane rating, and elevated compression ratios (seen in turbo/supercharged engines). Pre-ignition is when a hot spot in the combustion chamber lights the f.a.m. before the firing of the spark plug, this could be the feathered valve, (lead) deposits, etc... Pre-ignition will sometimes cause backfires (through the carb/induction), and will usually lead to detonation. Hope this info helps. Quote Link to comment Share on other sites More sharing options...
Mudge Posted January 15, 2003 Share Posted January 15, 2003 Good info, that helps clear it up. Since I'm not an engine builder, you got me with my pants down Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted January 15, 2003 Share Posted January 15, 2003 Originally posted by theflyingcloud:Some (relevant?) info from the aviation world. Going through school to get my A&P we were taught that detonation and pre-ignition are two seperate events. Detonation is the rapid burning of the fuel air mix, causes are many, most common (in aviation) were high combustion chamber heat, (high ambient temps) lower than needed octane rating, and elevated compression ratios (seen in turbo/supercharged engines). Pre-ignition is when a hot spot in the combustion chamber lights the f.a.m. before the firing of the spark plug, this could be the feathered valve, (lead) deposits, etc... Pre-ignition will sometimes cause backfires (through the carb/induction), and will usually lead to detonation. Hope this info helps. I'll add this, to hopefully make the point more clear...in super/turbo charged engines, it's not compression ratio that causes detonation, it's an improperly cooled intake charge. A lean fuel mixture will also be more prone to detonation. Quote Link to comment Share on other sites More sharing options...
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