Why Do The Heat Ranges Of Spark Plugs Have So Much Ability To Damage An Aluminum Piston When Plug Is So Small

There are 3 Answers

1. tirespoke . says:

   this is overcompensated by the SHAPE of the combustion chamber which helps to quench the explosion. less quench, more heat is produced in the combustion chamber which requires a lower heat range to prevent plug blowout and detonation.

   more quench requires a higher heat range to keep the plug hotter and in its effective operating range for proper combustion of the air/fuel mixture.

   you are looking at the picture on a whole, you have to remember that an engine operates at least at 500rpm. thats 500 times that cylinder is firing per minute…and thats only under no load idle.

   you put a load on it and as the engine accelerates, the timing changes accordingly and you have to have a spark plug that can accurately function in the engine parameters.

   this is about the broadest way I can explain this without getting into thermal dynamics…much less forced induction engines, where plug heat range is MUCH MUCH more important to prevent detonation or high exhaust temps which is when you start burning holes in pistons but this is also affected by air/fuel ratios.

   not to mention…spark plugs do NOT protrude that far into the combustion chamber. pretty much all threading is in the thread wall of the cylinder head. you want the plug thread flush with the combustion chamber and only the electrodes protruding into the combustion chamber to prevent the plug thread wall itself from becoming a hot spot which will lead to detonation.

   not only this but obviously if the plug protrudes too far and either contacts the piston @ whatever rpm it is metal on metal SLAMMING into each other. something will break. usually the plug itself which then bounces around in the piston as the pieces cant escape the valve opening and thus it just tears stuff up.

   think about coins in a blender or garbage disposal. that is havok on a massive scale.
2. vrrJT3 says:

   It’s because the center electrode can get hot enough to cause pre-ignition (like super advanced timing), resulting in detonation.

   So it’s not the spark plug that puts the hole in the piston. It’s the detonation of the fuel that causes the damage. But the spark plug was glowing and caused the pre-ignition.
3. Mr. KnowItAll says:

   The engine fires on the compression stroke.
   Therefor it only fires 250 times @ 500 RPM.
   So, the first answerer is mistaken.

   That being said, understanding the “heat range” of a spark plug is primarily to extend the life of the spark plug it’s self and not to control the temperature of ignitied gas/ fuel mixture.

   The insulator nose length is the distance from the firing tip of the insulator to the point where insulator meets the metal shell. Since the insulator tip is the hottest part of the spark plug, the tip temperature is a primary factor in pre-ignition and fouling. Whether the spark plugs are fitted in a lawnmower, boat, or a race car, the spark plug tip temperature must remain between 500C-850°C. If the tip temperature is lower than 500°C, the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. These accumulated deposits can result in spark plug fouling leading to misfire. If the tip temperature is higher than 850°C the spark plug will overheat which may cause the ceramic around the center electrode to blister and the electrodes to melt. This may lead to pre-ignition/detonation and expensive engine damage. In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber. A projected style spark plug firing tip temperature is increased by 10°C to 20°C.

   http://www.ngksparkplugs.com/techinfo/spark_plugs/overviewp2.asp?nav=31000&country=