If you are talking about pre-ignition pinging, it will occur is the fuel mixture is ignited before the piston reaches its design position relative to top dead center. It will usually cause a bucking. However, if the fuel explodes it can damage the engine. It can throw a rod or bread a piston. The energy of an explosion is greater than the energy of a controlled burn even a pre-ignition. The difference between burn and explode is extremely important. The chemistry is quite mature and I think available on the net. If not it is in most chemistry books. Burn and explode related to the IC engine is the same as Burn and explode in a propane stove. When you cook, the oxidation rate of the propane should be burn and not explode. The flame on an acetylene torch can be made hotter or less hot according to the oxygen mixture adjustment. Rapid oxidation is involved in explosives. An explosion will occur if the oxidation rate increases to the specific explosion point of whatever molecular structure is involved. In chemical or pharmaceutical plants as well as in mining there is a need to determine the Least Explosive Level (LEL). A company by the name (I think) is Mine Safety Equipment makes such detection instrument. ----- Original Message ----- From: "Gerhard Fiedler" To: Sent: Thursday, June 28, 2007 9:42 AM Subject: Re: [EE] Simple fuel-saver, so they say lean mixture > Lee Jones wrote: > >>> I don't know the difference between burn fast and explode. Does fuel >>> burn fast and if the engine flies apart then the fuel was "exploding" ? >> >> Modern engines have a knock sensor. The computer controller leans the >> air-fuel mixture as much as possible, usually based on an O2 sensor in >> the exhaust system. When it senses the fuel exploding via the knock >> sensor, it enrichens the mixture "enough" to stop it. > > I don't think the "knocking" is fuel exploding. AFAIK it is fuel expanding > before the piston reached its end position. IIRC, you can make any engine > knock without changing the mixture, just by moving the ignition point > forward. And you can make it stop knocking by moving the point back. Since > the time between the spark and the mixture expanding depends on many > factors, and you want the mixture to start expanding right after the > piston > reached the dead point but not before, they control the ignition point now > with knock sensors. > > Gerhard > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist