<img src="/forums/images/graemlins/lol.gif" alt="" /> Jeepete, this has been fun, and thanks for the timely definitions!

BigJim, I'm sorry your grandson was burned so badly; what a terrible thing to have happen! My best wishes to your family and especially to your grandson for a speedy and complete healing.

Sunder, I understand your hang-up about using the word explosion to describe what happens in the combustion chamber. All explosions occur just as you describe; at some point in the gas-air mixture volume, a molecule, not all at the same time, has sufficient heat to cause the carbon to carbon and carbon to hydrogen chemicals bonds to "break", explosively releasing the chemical energy as heat, light, sound, etc., and the hot gases of CO2 and H2O; and then, cause your chain reaction throughout the gas-air mixture volume as you have described. The igniting of the gas-air mixture is done after the gas-air mixture is compressed by the piston to allow the exploding molecules' gaseous by-products at high pressure to effectively force the piston down the combustion chamber to turn the crankshaft. Burning is a word that describes the combustion of materials as seen by the eye. At the molecular level, the release of enegy from chemical bonds is explosive.