Does a high compression diesel engine need glow plugs be used to start

[sd455dan]

I would have thought for sure it would. More compression = more heat, I would have assumed.

Believe it is the actually opposite due to the injection type

most direct injected diesel engines have around 16-18 to 1 compression while indirect injection ( much lower injection pressure) have higher compression like 22 to 1

the tractor diesels I have owned were direct injected and used thermostart units to light the diesel on fire in the intake (crude but effective)
The diesel engines with glow plugs I have been around all were indirect injected and had the glow plugs and higher compression.

I do like the fact that once either tractor with direct injection has been started 1 time during the day they start with out any other added heat.

 

[Industrial Toys]

I need to study this further, because clearly I don't understand. I thought a diesel engine compressed the air til it was red hot at which time fuel was injected into the top of the cylinder. That sounds like direct injection.

 

[777777]

I appreciate everyone's thoughts on this issue. I am still somewhat confused but now starting to think that the need for glow plugs does not necessarily mean problems.

 

[90cummins]

I appreciate everyone's thoughts on this issue. I am still somewhat confused but now starting to think that the need for glow plugs does not necessarily mean problems.

The need for glow plugs is no indication of problems (unless) something changes which requires the use of the glow plugs where previously they weren't required.
Some engines need them on every start, some only on the first cold start.
Some engines don't have glow plugs (Dodge Cummins) but have an intake grid heater which heats the intake air only.
I have a couple Yanmar air cooled diesels which are direct injection and start using a traditional recoil rope starter.
It's all about the design of the engine and injection system.

90cummins

 

[Texasmark]

This is a mid to mid 60`s International Harvester BD-154 so don`t think direct injection would be an issue.

My first Diesel was a '65 Ford 3000 purchased in roughly '95....one of those "just gotta have it" things since seldom do you find one of those babies for sale. Was April in Texas and seller needed ether to start....fast forward and an engine overhaul later.....you don't need ether, and on mild days or after running you don't need glow plugs.......if your engine compression is what it should be!!!!!!! Compression is what heats the air which is sucked in and compressed to explode the squirt of diesel injected at the firing time in the cycle. Food for thought.

 

[Egon]

I appreciate everyone's thoughts on this issue. I am still somewhat confused but now starting to think that the need for glow plugs does not necessarily mean problems.

Using the glow plugs every time on an indirect injection engine is no problem.

For the direct injection diesel there are different methods for preheat but there will be no glow plug. A Google will have lots of information.

[video]http://www.vias.org/kas/en/diesel_engine.html[/video]

 

[buickanddeere]

I need to study this further, because clearly I don't understand. I thought a diesel engine compressed the air til it was red hot at which time fuel was injected into the top of the cylinder. That sounds like direct injection.

How does the "Carnot Cycle "Otto type design Diesel engine going to work with red hot 1200F combustion chamber temps just prior to ignition ? There has to be a delta T increase between the compression and combustion stages that doesn't have temperatures high enough to melt engine components . Diesel ignites somewhere around 460F iirc.
Thermal efficiency improves when the delta T is wider between compression and combustion . Efficiency also increases the more delta T and thus delta P between ignition and when the exhaust valve opens .

 

[buickanddeere]

Thanks for the tip. That makes sense, but doesn't explain why these little diesels need their plugs.

Direct or indirect makes the difference if glow plugged or not. I have a 4HP Yanmar diesel and a 10HP petter diesel . Both have open combustion chambers with direct injection and therefore no glow plug.

 

[LD1]

I am not gonna debate the differences in diesels, heater types, or direct vs indirect. So my comments will only apply to what the OP is asking about.

And specifically, that is the owner/seller of a mid 1960's international BD-154 tractor is telling the op, 777777, that the engine has SOOOO much compression (in good shape and not wore out), that it needs glow plugs to start even on a hot day.

I am calling BS. The seller is trying to pull a fast one on you. And its my opinion, that the engine, specifically the rings, are showing their age. And that the compression isnt as high as it should be, thus the need for a little help even on a warm day. And the seller is counting on the fact that you dont understand, and think you are buying a tractor with an engine in tip top condition as opposed to nearing a rebuild.

Compression is what generates the heat that ignites the diesel fuel. More compression = more heat. On a cold morning, you are stating with colder air, and a colder engine block. Thus the process of compression just doesnt create enough heat to ignite the fuel. So it needs help. There are several methods of "help". Ether is one option, as it ignites at a lower temp than diesel. So when its too cold to ignite diesel, ether will still ignite. Option 2, glow plugs. Heat the air in the cylinder and create a little hot spot to ignite the fuel. Grid heater....heats the incoming air, so that the act of compression gets the air hot enough to ignite the fuel. Block heaters. Heat the entire engine up, including the air in the cylinders, again, so that the act of compression builds sufficient heat to ignite the fuel.

While using glow plugs, grid heaters, block heaters, etc doesnt necessarily hurt anything to use them on a warm day, they should NOT be required. The seller saying that they are required because the compression is so high.....just a retarded statement and someone who is either an idiot, or someone who is intentionally trying to pull a fast one on you.

I have a ford 5500 backhoe. I knew it was wore out. No glow plugs, but needed ether to start anytime it was below 80 degrees F outside. And lots of blow by out the vent tube. Had it had glow plugs, I would have been using them in lieu of either, but the principal is the same. The engine was wore out, not building enough compression to get that fuel ignited. Now that I have rebuilt the engine (which required 0.030" over to clean up), it will start without assistance, down to 35-40 degrees on the second or third hit.

 

[Sawyer Rob]

Something else that enters into this is, the design of the "injection pump".

Old pumps worked at lower pressure and sprayed in nearly "droplets" of fuel. Newer higher pressure pumps, spray the fuel in at nearly a fog of fuel and that's a lot easier to ignite.

Bottom line is, (as was already said) where you spray the fuel makes the difference! (direct or indirect injection)

Thank the stupid EPA for those dam glow plugs, and everything you have to have because of them!

SR