Do some diesels not have glow plugs?

[wrexham]

someone told me this today and i just assumed they all did??

 

[knackerdecobre]

Yes, a diesel engine NEEDs glow plugs, like saying some petrols don't have spark plugs

 

[Mr White]

All diesels have glow plugs that im aware of. They don't need them once the engine has started though. Diesel ignties under pressure (and heat) so the glow plugs are really only used cold starting i.e. in the morning when theres no pressure in the engine.

 

[Neo]

On modern diesels they are rarely used, but as far as I`m aware they all have them.

 

[Modelmakerman]

Nope, not all Diesels need Glow plugs. Large direct injection diesel engines, like in heavy construction equipment and locomotives, do not need glow plugs. Their cylinders are large enough that the air in the middle of the cylinder is not in contact with the cold walls of the cylinder, so it retains enough heat to allow ignition.

On some engines without glowplugs in the cylinders there is one glowplug in the intake manifold together with an injector. While the starter is operated this glowplug and injector are energised. This set up supplies the engine with some preheated diesel in the intake and helps the engine to start. You will find this on some tractors.

 

[jdesousa]

Nope, not all Diesels need Glow plugs. Large direct injection diesel engines, like in heavy construction equipment and locomotives, do not need glow plugs. Their cylinders are large enough that the air in the middle of the cylinder is not in contact with the cold walls of the cylinder, so it retains enough heat to allow ignition.

On some engines without glowplugs in the cylinders there is one glowplug in the intake manifold together with an injector. While the starter is operated this glowplug and injector are energised. This set up supplies the engine with some preheated diesel in the intake and helps the engine to start. You will find this on some tractors.

Very interesting. Never new that. Never to old to learn hey!!!

 

[Slimy]

I was also under the mistaken impression that glow plugs are used like spark plugs, IE an engine won't run without them. But my friend explained to me that as long as the engine could get the diesel hot enough to burn then the engine will run.

On the other hand, I do find it odd that SEAT diesels will complain about a faulty glow plug, even though they're not actually being used 99% of the time.

 

[Modelmakerman]

Diesel engines are compression ignition, basically the cyinders run at a very high compression ratio (compared to petrol engines) and the act of compressing the fuel/air mix generates enough heat to cause combustion. Because of this a diesel engine will continue to run as long as there is a supply of fuel and air.

Modern diesels have a fuel cut off solenoid to stop the engine (some older engines you had to purposely stall when you wanted to stop the engine!) where as on a petrol engine the ignition is switched off (supply of power to the coil/distributor/spark plugs) and the fuel supply remains open. In some cases diesel engines can be severely damaged when oil leaks into the intake (usually due to catastrophic turbo seal failure) and the engine starts burning the oil as fuel and revs run away even if you operate the fuel cut off! The only way to stop a diesel engine run away whilst burning oil is to stall it or block the supply of air the the intake.

Glow plugs are purely to help first ignition when the cylinders are cold. Generally most diesel engines would eventually start without glow plugs after being cranked a few times as the cranking will be compressing the air/fuel mix and warming up the cylinders anyway.

 

[leontdi130]

early transit vans didn't have glow plugs i'm lead to believe.

 

[Neo]

Nope, not all Diesels need Glow plugs. Large direct injection diesel engines, like in heavy construction equipment and locomotives, do not need glow plugs. Their cylinders are large enough that the air in the middle of the cylinder is not in contact with the cold walls of the cylinder, so it retains enough heat to allow ignition.

Never heard of a car without though. Nice WIKI paste by the way!

 

[sssstew]

some spot on information from modelmakerman. +1

In VAG TDIs there is a temperature trigger point which they are used at, i think from memory its anything below 5 degrees, but its been a few years now.

 

[James_R]

Some people maybe mistaken that the 2.0tdi doesnt have them as they're buried within the head next to the injectors.

 

[Muttley]

Just to pick a nit, the glowplugs heat the cylilnder head itself and the air inside the cylinder, not the diesel fuel. The cold metal of the engine block is the biggest factor in cold-starting diesels.

 

[alibali45]

I was also under the mistaken impression that glow plugs are used like spark plugs, IE an engine won't run without them. But my friend explained to me that as long as the engine could get the diesel hot enough to burn then the engine will run.

On the other hand, I do find it odd that SEAT diesels will complain about a faulty glow plug, even though they're not actually being used 99% of the time.

Yeah dealerships will usually pick up and notify customers on that, cause if they don't come winter time the customer will come in complaining of rough running at cold starting or prolonged cranking periods.