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

[soulasphil]

It doesn't get very cold here, yet temperatures fall under 0°C and we have a nice snow cover these days. I used to run a 1960 MF 135. It was very difficult to start the indirect injection engine in cold weather. You had to warm up the glow plug in the air intake then squirt fuel on it from a tank on the right side of the engine with a small manual pump on the dashboard. Seldom worked on the first try.
I now run a JD 3520 with a turbo compressed direct injection engine. It has an intake air heater but I have never used it yet. The yanmar starts as soon as you turn the key. I gather turbos start more easily ? I am surprised nobody mentioned the subject.

 

[JDGreenGrass]

My JD770 is a 1992. When I turn the engine off the throttle is at 1200rpm. I start it at 1200rpm.

At what rpm do you guys start your tractors.?? Just curious to know.

 

[dcyrilc]

When I start mine, it usually ends up being around 2K RPM. As soon as it starts, I back it down to 1000-1200 RPMs to let it warm up. I don't try for 2K, it just always seems to be there. I shoot for 1200-1500.

 

[Chilly807]

Good question. Next time I start 'er up I'll have an answer to it, but it gets started with the throttle fully shut, in the low idle position. 900 rpm comes to mind, but it may be slightly higher.

The reason is that the less turns the engine makes before it gets full oil pressure the better. Once it's running for a minute or so I will often bump the throttle up to about 1200 rpm to give a faster warm-up.

Incidentally, a diesel during a start doesn't get any more fuel with the throttle wide open than it does at the low idle setting. The governor is in an "under-speed" condition with the engine stopped, so it is calling for maximum fuel to get the speed it needs. As soon as it starts and reaches the set speed the governor immediately reduces the fuel setting to maintain the set speed. Turbo-charged engines may be slightly different, in that if they have a fuel limiter it will be active until the boost comes up under load, so they will typically be limited to ~60% of maximum fuel delivery with zero manifold pressure.

The usual puff of grey/black smoke on start up is the result of a momentary over-fuel condition. Once the governor corrects the fuel delivery rate for idle, the smoke should mostly go away. Grey is because of low cylinder temps not being able to properly burn the injected fuel.

Sean

 

[Raspy]

I had one of those Perkins (4-108) on my last boat (45 foot sailboat). That engine was reluctant to start regardless of the weather. I used to shoot WD40 into the intake and light that with the pre-heater. It would fill up the cabin with smoke and cough about 6 times then finally get running. I'm glad my Kubota is a bit easier!

Wow, does that sound familiar!

I had a Perkins 4-107 in mine (a 42' Cascade Ketch). It would start immediately in the summer, and think about it in the winter. All right here in the water in the Bay Area. Down in Mexico it was always ready to go, like me! :laughing:

 

[whistlepig]

90 degrees is an exaggeration isnt it? :confused2: Our BX starts to need it somewhere around 40 ... altho I havent checked it closely.
larry

No, it's not an exaggeration. It won't start cold in the mornings on a 90 degree day for the first start of the day with out glow plugs for about 15 seconds. After the initial start in the morning it will start all day long with just a bump from the starter.

 

[picker77]

No, it's not an exaggeration. It won't start cold in the mornings on a 90 degree day for the first start of the day with out glow plugs for about 15 seconds. After the initial start in the morning it will start all day long with just a bump from the starter.

Ditto. My L295DT was a very reliable cold starter as long as I used the glow plugs every time, with glow plug activation time directly related to ambient temp. After warmup, it would start instantly without glow, but let it sit a couple of hours, even in the summer, and it took at least a short shot of glow to fire up again. Great little tractor, if I could have put a loader on it for a reasonable cost I'd still have it. Unfortunately the cost of a third party loader was about equal to the worth of the tractor itself, so selling it was a no brainer.

 

[Mickey_Fx]

Quite an active thread and numerous opinions being offered.

Have been a long time since I did any reading on diesel designs. Combustion chamber design is the big factor on ease of starting. At the time there were 5 distinct combustion chamber designs in use and each had its own operating characteristics. Pre-combustion chambers were new and was the answer for smaller high speed diesels. Many diesels have their combustion chamber built in to the top of the piston and not in the head.

MF has received a fair amount of comments and how easy they start and without the use of glow plugs. That is one of the characteristics of the combustion chamber design used in those engines and their CR was one of the lower ones around. The engine in my 165 was 15:1 quite low for a diesel and not that much higher than found in muscle cars of the day.

My current Yanmar has glow plugs but rarely need to use them until temps get down in to the 30's. Don't know which combustion chamber design it uses.

Do a search for "diesel combustion chamber design" and you'll get a number of hits.

 

[ModMech]

^^^ No arguememt with that, except for 15:1 being "low".

CC design, piston bowl design, injector pattern, injection pressure, CR, cranking speed, injection timing ALL are important factors.

Turbo or not is really not a factor *except* that the same engine with or without a turbo will almost always have a lower CR WITH a turbo than without. Therefore, speaking about the same engine only comparing a change in CR, the turbo'd engine will often not start quite as well in the cold. The, dare I say it, 8.2L DD is a prime example of this as it was available both turbo'd and NA. The (lower CR) turbos were cold blooded at 60*F while the (higher CR) NA engines would start decent to about 45*F. There was a difference of 15.5:1 vs 16.5:1 in the respective CRs.

As for Kubota, ours mimmicks those of others, at 60*F no GP = no start, or at best a LOT of smoke and long cranking. A *little* GP use, and it starts immediately, increase the GP time and there is no problem with starting at all even to 20*F - starts like it's 80*F.

What RPM? Idle, I start it and shut it down at idle, I think that is per the OM.

 

[MMH]

The combustion chamber type (i.e. Direct Injection (DI) vs. Indirect Injection (IDI)) is a design decision that is made at the beginning of the design process. This decision is based on many things, and not just starting. DI engines can have larger injectors, and the injectors spray straight down (in the center of the piston). The IDI engines have more complicated cylinder heads (due to precombustion chamber) and limit injector size.

DI engines used to be MUCH louder than IDI engines. This is because until the late 90's diesel injection pumps were purely mechanical devices. With mechanical injection pumps, when the injection pump would squirt the fuel, the all of the fuel would instantly ignite & thus the loud BANG (remember how loud the old diesel over the road trucks used to be?). With a IDI engine, the fuel pre-combusts in the pre-combustion chamber (and thus the reason it is called indirect injection), then this burning fuel continues to spray out of the pre-combustion chamber to the main combustion chamber (i.e. the cylinder). This results in a more progressive burn instead of a big bang.

Modern diesels with electronically controlled injection can control the big bang by modulating the fuel volume & pressure in a way that mechanical injection systems could not. Catapillar started this w/ their HEUI system, International Harvester used 'split-shot' injectors, and then came along common rail, which is most common today. I'm not sure if this is the most common on tractors, but it certainly is on pickups, marine/industrial engines, etc.

Neither a DI or IDI engine will start in cold weather without some type of assist. Both DI and IDI can utilize glow plugs or intake grid heaters for this assist.