Do the glow plugs work as spark plugs do in gas engines or are they only used to start engine initially. If say you lived in a warm climate that never got below 75 degrees, would glow plugs be used? Thanks.

 

The glow plug (GPs) cycle on/off based on cylinder wall temp and outside temp, IIRC. Minimum starting temperature is somewhere around 850*C for the cylinders. GPs are used every time the cylinder temperature is below this value.

They do not ignite the air/fuel mixture like spark plugs. Diesel fuel is ignited by the heat caused by the compressed air in the cylinder. When diesel fuel is injected into the cylinder under these conditions, the friction caused by the injected fuel into the compressed air is what ignites the fuel.

 

All they do is preheat the cylinders to help get the engine running. They are not used in the combustion cycle; diesel fuel is self-ignited in the cylinder by temperature and pressure. When the engine is cold, you need glow plugs to help with the temperature part of that combination. Once the engine is started, it will run without them.

75 degrees is dead cold to an engine. You will still need glow plugs.

It is possible to start a truck without glow plugs, but it is certainly harder to do.

 

Where did you get that idea?

The diesel is ignited because it is above it's flash point for the given temperature and pressure. Air to fuel friction... that's like replacing muffler bearings.

 

 

I live in Louisiana and I disconnect my GP's durning the summer and do not hook them back up till temps start getting below 60*

 

What's an "exoast volve"?

I'm not even sure what accent that is.

 

It's called, "compression ignition." The compressed air is denser and hotter than atmospheric pressure because of the compression force from the piston. Fuel is injected into this compressed air. When two or more substances are forced together, friction is applied to those substances. Are you saying there is no friction between the air and fuel?

Your first sentence validates my claim. The friction between the air and fuel is what raises the fuel above its flashpoint.

Edit
According to:
Definition of Compression Ignition - What is Compression Ignition

Definition: The concept behind compression ignition involves using the latent heat built up by highly compressing air inside a combustion chamber as the means for igniting fuel.

The process involves compressing a charge of air inside the combustion chamber to a ratio of approximately 21:1 (compared to about 9:1 for a spark ignition system). This high level of compression builds tremendous heat and pressure inside the combustion chamber just as fuel is primed for delivery. An injection nozzle plumbed into the combustion chamber sprays a mist of precisely metered fuel into the hot compressed air where upon it bursts into a controlled explosion that turns the rotating mass inside the engine.

Examples:
Diesel engines use compression ignition.

 

The heat that ignites the fuel does not come from friction. It ignites purely from the heat generated when the air is compressed. The diesel vapor hits the hot air and burns.

Edit: To the OP's original question, if its never below 75°F you don't really need glow plugs.

 

http://www.beru.com/download/produkte/TI04_en.pdf

 

No, they don't. Not even close. The glow plugs cycle ONCE. The run time is determined by the engine oil temp (EOT) at startup.

As said, they are not used to ignite the fuel. But they are used for some time after startup to raise the chamber temperature for a more complete burn. This is why they're timed to stay on after engine startup, up to two minutes.

 

Our engines do not monitor cylinder wall temperature. IIRC, GP cycle time is based on EOT, but I might be wrong on that. I'm also not sure that the GPs ever come back on after they initially shut off.

 

You beat me too it, lol.

 

I am saying that if you pour a spoon full of diesel fuel into a controlled chamber, and then pressurize and heat it up to the conditions seen inside a diesel combustion chamber, that the fuel will combust. The reason the fuel is injected is 100% atomization. Atomization increases the surface area of the fuel and allows it to be combusted more completely, faster, and more uniform within the cylinder.

Friction, although present, has a negligible contribution to the cycle.

 

I stand corrected. My understanding is friction causes heat. I imposed this on the compression-ignition process.

By not stating "continually" I thought it was understood that the GPs turn on then off once, not continually. I did not mean to imply, nor did I state, that the GPs cycle on/off in a continuous fashion. Apologies for the confusion.

Again, I stand corrected. As stated above, my understanding is friction causes heat. I imposed this on the compression-ignition process.

I learned something new today. I thank you all.