I was reading my latest MAKE [issue 13, should be up there real soon now] and I came across the article about making an internal combustion engine demo with all parts “available from Home Depot.”
The author insists that the convention IC engine is powered by “explosions, front and center,” not the burning of fuel. Unless things have changed radically since I went through my formative car phase, he has it exactly backwards. The whole notion of engine timing and fuel injection systems (seen a new car with a carburetor lately?) is based on making sure the fuel mixture is introduced and burned at the right (most efficient) time. In fact, incomplete combustion or detonation is the cause of the pinging or knocking you can hear in an engine that is not properly adjusted or has the wrong grade of fuel and is considered to a Bad Thing, for reasons of efficiency and the life of the engine.
It seems to be a commonly held misconception, as some of the Google search results I found refer to an explosion as the result of the spark plug igniting the mixture. But I think that is an oversimplification, given the speed of the reaction: it is called combustion, not explosion or detonation, after all.
Disappointing to learn that this is how 11 year olds are being taught about this (that’s about when I learned it myself from a small plane owner and pilot).
And they recommended I leave a comment with the online version (I elected to make it less peevish):
I was a little surprised at the use of the word “explosions” to describe what happens in the cylinder of an internal combustion engine, and I think it would be good to make it clear that what actually happens is a burn of the fuel/air mixture. Admittedly, it happens extremely quickly, but there is a difference between the two.
An explosion is what you would hear as a knock or ping from an engine, meaning that the timing is off, the fuel is of the wrong grade, or some other adjustment is needed. The result is a loss of power and possibly engine damage, as the parts are not designed to withstand explosions. A bad thing, all around.
The burning (or combustion) is a carefully timed event, computer-controlled on modern cars with ever-more sophisticated fuel injection systems.
Anyway, anything that helps kids understand the workings of the things they use and rely is good stuff, just thought this could be refined. After all, a controlled burn is harder to do than an explosion, which would help explain the increased complexity of modern cars (seen a carburetor on any recent models? How ’bout a choke?).