Engine/Transmission (1998.5 - 2002) I feel almost dumb for asking this

[tajensen]

I was talking with one of my buddies yesterday and we ran into a disagreement. I was under the assumption that the function of glow plugs are to head the cylinder head to facilitate combustion. My friend was "sure" that glow plugs = spark plugs. Do glow plugs have a function after the Wait To Start light goes off? I'd sure love to tell him that he's wrong, but I need to know for sure first.

 

[Gizmo 007]

you're correct... glow plugs are there to help the engine fire when cold (ie. first started). After that, they shut off and not used again until the key is cycled. They do not act as spark plugs! Don't you love it when you're right



Thank God our Cummins don't have them!

 

[dresslered]

First off, I am by no means an expert either, but the glow plugs are electricly heated until the compression gains enough heat for the engine to ignite its own fuel. You are aware, however, that your Cummins doesn't use them, aren't you?

 

[duaneparks]

Glow plugs DO NOT EQUAL spark plugs... diesels are "compression ignition" engines. This means that the compressed air/fuel mixture is ignited by the temperature created by the compression of the mix itself as opposed to the introduction of a spark to the mix.



Does that help? The glow plugs, as I understand it, are for heat and serve the same function as our grid heaters. Once the engine is up to operating temp (or a pre-determined time period has expired) the glow plugs quit functioning.



I do believe they are in a location similar to a spark plug, though, which could lead to some confusion.



HTH, Duane

 

[parcher]

On our trucks there are no glow plugs, this function is performed by the intake air heaters or "grid" heaters. The intake air heater is the reason we NEVER use either to start our trucks.

 

[BV]

Some glow plugs are designed to pre-heat the cylinder to start that compression-ignition process then they turn off but continue to help ignite the fuel like a spark plug.



These glow plugs heat up with electricity then remain hot through the normal compression-ignition cycles.



They is a new system that will Pre-Heat and Post-Heat with electricity to improve cold starting and lower emissions. Here is the web site to BERU if your interested. They supply DC with ISS's (instant start system) for the Mercedes.

 

[tajensen]

So let me get this straight:



I many diesels, glow plugs heat the cylinder to facilitate combustion ONLY when the engine is cold. In our diesels (24V Cummins), however, we have a grid heater on the air intake instead of glow plugs. Do Ford, GM, or other Cummins generations have glow plugs?

 

[CstlEng]

Depends on the engine model, many do, many don't. Our big cummins and detroits in our work boats don't have glows. We have a detroit driven generator with glows. The cat in our dozer does, the cat in the loader does not. Our little fords in our ambulances at the firehouse have glows.



BTW... the glows in the ford ambulances are a real PITA. you know how we are supposed to wait to start, but if we don't it isn't a big deal. Well, if you don't wait the entire time for the light to go out in the ford and you turn it over before the heating cycle finishes, you burn up the plugs... not the best thing for multible drivers who are often eager to get out on the road and turn the siren and lights on quickly. We $pent lots on plugs for that truck over the last couple years. Intake heaters are the way to go, if they can't make the engine otherwise easy enough to start without help.

 

[Mschevey]

Long engineering responce

As said before a diesel engine ignites the fuel from the heat generated by compression. During compression heat is generated that is more than sufficient to ignite the fuel when it is sprayed in at the top of the stroke. However when the engine is cold a lot of the heat generated by compression is lost to the cold cast iron around the cylinder. Therefore the temperature of the air is not high enough to guarantee fast, complete ignition. Large diesels can tolerate the loss and still start well because of the large volume of air. Smaller diesels need a way to keep the temperature of the air high at the time fuel is injected. Our engine uses a grid heater. This pre-heats the air before it is compressed. The result, if no heat was lost would be much higher temperatures after compression. Even with the lost heat the temperature is still high enough. With lower compression engines, or engines with lower cylinder volume (V-8's) the amount of heat lost to the engine block is more. Therefore they make use of a pre-combustion chamber. The air is compressed into this chamber and this is where the fuel is injected. (Indirect injection) This is the chamber where the glow-plug is located in these engines. The glow-plug tip extends far enough into the chamber that it is sprayed by the injected fuel. When voltage is applied to the glow pug the end will 'glow' bright red. The drawback to this design is that the pressure generated by the burning fuel does not press directly on the piston. It must pass out of the pre-combustion chamber and into the area above the piston. Also the cast iron walls of this chamber is often subject to failure.



End of class, Sorry I got carried away. Mike Schevey

 

[tajensen]

Mike. Perfect. Thanks.

 

[kaffine krazed]

Glow plugs are used on direct injected diesels as well.

 

[Royk]

tajensen,



Why don't you just ask your buddy how your Cummins manages to run considering it doesn't have any glowplugs? I think we'd all like to hear his answer!



Roy

 

[tajensen]

He should be coming over tonight, so I'll be sure to mess with him.

 

[rashwor]

Hmmmm....

Just don't let him work on your Dodge... he is only qualified to work on his pukestroke!



Sorry! It is Friday and I could not resist. Oo.

 

[Gary - K7GLD]

I'm pretty sure NONE of the Power Stroke engines are indirect injection - that's fairly old technology in diesels as we use them - goes back a few years to pre-PS years...