I looked for a thread, and could not find one. This may seem like a dumb question. In a Diesel engine, the glow plug heats the chamber (cylinder), the piston compresses the hot air on compression stroke and the fuel is squirted into the chamber then creates a fire (or explosion). So I got that part. I was told that once the engine heats up to operating temp, that the glow plugs actually stop working, because the heat is so intense and with the super high compression, all that is done, is fuel is injected into the cylinder to fire the piston. So is it true that the glows plugs are only to start the engine, and remain on until the engine is at operating temp? Is this why it's bad to run a Diesel for short periods of time, i.e. get in, start engine, drive 5 minutes to store, shut off engine before complete warm up?

I do understand the operation of a gas engine, on the compression stroke, the fuel is injected, then the spark ignights the fuel/air mixture. I never really understood the oil burner, though I have had one for six months. Thanks guy's.

 

The piston sucks air in, then compresses it a whole bunch on the compression stroke. When you compress air, its temperature rises, in this case above the (relatively high) combustion point of diesel fuel. The fuel is sprayed in at the top of the compression stroke, hits the hot air, ignites, explodes, which provides the power stroke. So it's not a gas/air mixture that ignites like in a gasoline engine. And the same amount of air is sucked in on every stroke; the power is varied by how much fuel is injected. (To accelerate, inject more fuel.)

With a really really cold engine block and really really cold air, the temperature rise from the compression still doesn't get you above the combustion point of the fuel, thus the need for glow plugs in the first couple of minutes of starting a cold diesel on a cold day. If they aren't there or working, you get white smoke out the tailpipe which is just atomized unburned diesel fuel.

Because of the high compression which requires a lot of energy to overcome with the starter, and because of the high current draw of the glow plugs, a diesel takes a whomping amount of battery capacity to get going, even more so on a cold day with thick oil. Our trucks have two batteries to help provide a ready reserve of power for this, but if you only run it a minute and shut it down again, you haven't rcharged the batteries to make up for what you just spent getting it started. Do that enough and you'll end up with dead batteries.

Duncan

 

http://auto.howstuffworks.com/diesel.htm

Howstuffworks.com is a good source of starter info on a great many topics.

You can also google diesel with a few extra keywords and be in business in a second

 

I had this same question, and I found the answer on the howstuffworks website. I would post a link, but apparently we are not able to anymore?!?

I also learned how 4X4, turbo/superchargers, and limited slip differentials work on that site too.

They explain just about anything your looking for.

 

dang DH, beat me to it!

 

Daryl, great info there, Thanks Daryl and to the rest of you!