Why do some diesels require glow plugs and others don't?

[Ken]

Art I agree a lot of different type of engines.
Many years ago forget the H-P of a Witte diesel. To start there was a compressipon release lever then remove crank from wall and get the flywheels spinning replace the crank on wall close compression lever and engine would start running. forget to hang up the crank the first pop of engine would slap the crank up along side of head and make you stagger. Ran 24/7 for 5 years then shut down and replace rings. bearings and redid the valves then restart.. Burned about 1000 gal of diesel a year. had a 50 gal drum of oil to add should need during when it was checked. provided power to Micro-wave tower in the Mountains.

Then as kid my job was to use a blow torch to warm a brass rod built in a kerosene water pump engine. when rod was about red could crank and engine would start. Have looked every since for type never found another.
I like the new what ever type of engine that only takes 30/45 sec. to start on cold days.
ken

 

[Raspy]

I've found it quite interesting to read all the comments here. Following the tractors and engines for most of my life and working with gas as well as diesels.


To get a diesel to run you need heat, this is caused from compressing the fuel, might it not be easier to heat a smaller area such as a pre-cup vs the whole cylinder?



It's not the fuel that gets compressed, but the air. This works better in a larger area because the center of the hot compressed gas volume is farther from a cold surface. It can get warmer and stay warmer long enough to ignite the fuel when it arrives. Pre-combustion engines are harder to start than direct injection engines because of this

 

[Richard]

Compression ratio and RPM are significant factors in starting DI diesels in the cold, of course not counting the actual temperature.

I'm no expert but I'd agree. I've got a Perkins 4 cylinder inside my industrial JCB. (I have no idea what model the Perkins is)

Using only my ear as a reference, it seems this machine will start up in maybe 3/4 of a revolution of the crank WHEN it has a strong battery. (I have continual weak battery issues because I don't use this too much anymore)

Even during the winter, if the battery is charged it will light off in what might seem to be 1 1/2 revolutions instead of 3/4.

Those comments on revolutions are merely guesses by me. Main point being made is this thing lights off "right now" if it has a good battery on it that can throw the crank around with some authority.

With a weak battery, the crank will whirr....whirrrrrrrrrr and whirrrrrrr, just barely getting around.... then all the sudden BAM, it's as though a single cylinder ignites and the engine is running. If it doesn't catch like that then I know the battery is too weak to crank and I get out the jumper cables

My experience with this machine is it's all tied to how strong the crank is turning, almost regardless of weather (but not totally)

 

[PILOON]

I had a deere (510) that had a device in the dash to screw in a can of either.
A button would allow U to squirt a few shots at start up.

That deere was a large 3 cylinder german built engine of about 50 hp.
Never did find the cans that fitted the dash device so I sprayed into the air cleaner and ran back to the cab to start.

Darn cab door was opposite side of the air cleaner and I hit the FEL most times rushing to the start button. (around the back was just as bad due to the snowblower.)

 

[Wis Bang]

I used to transport an old D8 CAT dozer [50's non hydraulic] that started via the gas pony engine. At least ours had an electric starter on the pony engine, never had to use the crank...

Once the gas engine was running you would pull a lever to make the main engine turn and watch the oil pressure gauge. As soon as you had good oil pressure, closing the compression release got the diesel started.

De-clutching the pony engine and shutting down made the pony exhaust flapper suck shut as the pony engine exhausted out the far end of the diesel's intake manifold...how's that for a pre-heater!

 

[art]

I've found it quite interesting to read all the comments here. Following the tractors and engines for most of my life and working with gas as well as diesels.


To get a diesel to run you need heat, this is caused from compressing the fuel, might it not be easier to heat a smaller area such as a pre-cup vs the whole cylinder?



It's not the fuel that gets compressed, but the air. This works better in a larger area because the center of the hot compressed gas volume is farther from a cold surface. It can get warmer and stay warmer long enough to ignite the fuel when it arrives. Pre-combustion engines are harder to start than direct injection engines because of this

I haven't seen to many direct injection systems that could out start a indirect injection system. The indirect seem to clean up the smoke faster on starts then the direct injection. They also seemed to be a bit ahead of the industry as far as modifications needed to meet the new standards. When I say this I'm not counting on twenty or thirty year old engines but even the new engines. To say new I've yet to see the tier four work yet although I believe they will be better then the tier three.

You are correct it is the air that gets compressed not the fuel as you can't compress liquids. Hopefully the injector has put a fine mist that works well with the compression to have a good explosion.

 

[art]

Maybe I am being a bonehead here. I hope not. So we go to the tractor showroom and I look at a 1964 MF135 diesel. The dealer tells me it will start, sitting outside, in -10 degree weather with out glow plugs. We then look at a 2006 Kubota. The dealer tells me the Kubota will not start, with out warming up the glow plugs, sitting in a garage while it's 90 degrees outside.

I'd start the Kubota on a ninety degree day any time without the glow plugs. Would it crank less with the glow plugs being activated, yes! We regularly start Kubotas here at -10 as well as -20 where other tractors won't start at all without being plugged in to warm the engine. I'm not going to say that I haven't seen some direct injection engines that would also start at those temps.

On many older engines who might have rebuilt them might make a big difference on how well they start when it's cold. Many shops don't spend the extra time to make them right. With the diesels cranking speed and compression is key to starting!

 

[picker77]

The JD 4020 diesel I ran for a while had a fitting right on the instrument panel to press in a can of starter fluid (ether). This worked well, too, even at temps around zero up in Wyoming. My previous tractor, an '82 Kubota L295DT, insisted on at least 30 seconds of glow plug heat even if only below room temperature (45 seconds if it was in the 30's or colder). In contrast, my JD 3032E has dire warnings of damage and disaster in the manual to NEVER using starter fluid of any kind. So far it starts instantly, but then it and my Duramax truck get babied by being parked in a heated shop that's kept at a miniumum of 55 degrees in the winter. Guess that's the difference in modern injection systems.

 

[Chilly807]

As far as Kubotas in general not starting without glow plugs, I can shed some light on that myth. Mine lights up just fine without using them above 40 F, however it does take a few more turns than if I used the glow plugs. Once we're down near 40 F, I'll give it maybe 5-7 seconds of glow, then it's off and running after the first turn of the crank.

I do know some of the older VW non-turbo diesels refused to start without glow plugs even when the engine was warm. Second-hand info, one of the gentlemen I worked with used to curse his VW every time he got in it because of that.

Sean

 

[jonyyuma]

It seems the pre-chambers came about for Smog control and unburned fuel. Most the old tractors you are talking about smoke like tar-kettles, especially when cranking. Glow plugs heat red hot and the fuel sprays directly on top of them in the prechambers. I have had 4 diesels all with prechambers.We should all be breathing better air if the fuel injectors or nozzels are clean and in good shape. I hate being behind cement trucks and dump trucks, they seem to cinder or smoke you down,like an old coal train... just 2 Cents. Jy.