Direct vs Indirect Fuel Injection?

[LittleBear]

I have always thought that direct fuel injection was better than indirect fuel injection. However, reading many threads on the Kubota M9000 (has indirect), the words smooth, powerful, and quiet keep coming up to describe the engine. What are the advantages and disadvantages of direct and indirect fuel injection? Is there a difference in reliability or durability?

 

[Ranch_Hand_Supp]

LittleBear, A Direct Fuel Injected engine has no Glow Plugs.

Ronald

 

[RalphVa]

A direct-injection diesel is advertised to be more efficient. There's no room for glow plugs though; so, these could be more difficult to start in really cold weather. Their design is also prone to less heat loss in the combustion chamber in cold weather; so, they'll start without glowing at a lower temperature.

My neighbor's mid 1970ish 820 with direct injection has an ether injection port to start it in really cold weather. At anything above about 40 F, I'm astonished at that machine. It'll sit all winter but will start immediately if the battery will turn the engine at least a 1/2 turn or so. This last winter, a friend was trying to start it though in 30ish weather. Even with ether, it wouldn't go. The main injection pump was a problem then. She's since had it rebuilt.

I've started glow plug engines at -22 F in Vermont, but with an engine heater and with the glow plugs. Started instantly, but stopped a couple miles down the road due to diesel wax up. Let sit; fired up; drove another couple miles. Did same thing again, and it kept going. Fuel filter was mounted up against the engine block. Won't work on engines with fuel filter out all alone. Will need a diesel anti-coagulant.

Ralph

 

[_RaT_]

You might try doing a search as well. It has been discussed considerably in the past.

 

[Egon]

Try this site.

web page

Egon

 

[thcri]

</font><font color="blue" class="small">( You might try doing a search as well. It has been discussed considerably in the past. )</font>

Rat,

Last night around 3 in the morning couldn't sleep and saw this post. My first thought was do a search which I did for indirect injection and only about 5 post came up. Maybe I should have just did injection to get more results.

To me either system is fine. I think they both have their pro's and con's. I would not let it be a determining factor in buying one brand over another.


murph

 

[HuskerInVA]

Direct injection does not mean 'no glow plugs'. My VW TDI and my JD 3520 both have direct injection and glow plugs. My Some DI engines may not have glow plugs, but not all.

 

[rockyridgefarm]

Jeeps new Diesel and the Cummins are both DI. We always hear how superior the system is, and most don't have glow plugs, which is nice. My Yanmar engine is DI, no glow plugs, and self bleeding. It is really nice to live with!

But none of that seems to bother Kubota. Despite all evidence that Indirect engines are less efficent and less reliable there is Kubota. Anyone who tries and tell you Kubota engines aren't fantastic, is crazy or stupid. Smooth efficient and bullet proof.

Really there are lots of great engines available. I am not aware of any major complaints from Shibaura (NH/Case) Daedong (Kioti/CubCadet) either.

 

[SkyPup]

Direct injection has the entire combustion chamber located inside the piston crown, thereby allowing faster more complete combustion with the heat concentrated within that space making it more efficient. Also, since the flame front is more controlled within the piston top combustion chamber, igintion timing is more precise and quicker, allowing higher top rpms and more torque and power. Also, multiple injections can be programmed through the more precisely located injector for even more fuel efficency and power output.

Actually, I am amazed that Kubota has not gone to DI on their smaller diesels primarily to meet emission regulations, the fact that they manage to meet current emission regulations with their IDI designs means that it is an especially good design.

Also, due to the fact that DI engine combustion chamber is ovally located inside the top of the piston, the minimum combustion chamber size that DI will operate in is about 400-500cc, since anything smaller diameter than that will result in raw fuel from the injectors hitting the piston combustion chamber wall prior to TDC and destroying the piston with intense heat from the raw unatomized fuel buring on it.

 

[_RaT_]

Murph, the one fellow that always posted plenty about this was John Miller III. He sure was a sharp guy and resourceful.

 

[Highbeam]

"Cummins are both DI. We always hear how superior the system is, and most don't have glow plugs,"

True, the cummins does not use glow plugs but it does utilize an intake air heater grid powered by electricity. At least in the 5.9 that Dodge uses.

 

[rockyridgefarm]

Most DI's have preheaters... They are much lower maintenence than glow plugs

 

[plaindave]

It's been a few years since I worked for an engine company, but back in my days at Caterpillar we sold both direct injection and precombustion chamber engines. My memory is fuzzy but the precombustion chamber engines offered much lower emissions than DI engines. They were not any where near as fuel efficient, but they were able to burn cleaner. In fact, most engines built for underground mining are of the precombustion chamber type.

The prechamber allowed you to ignite a small, rich fuel mixture which gave you a large flame front to ignite a lean mixture in the main cylinder. Which gave you lower emissions.

But again - my memory on this is fuzzy, I left CAT in 1999.

 

[HGM]

DI vs IDI has nothing to do with glow plugs, although some manufacturers will heat the incoming air instead of the combuston chamber. As far as wich is better, to my knowledge the emissions are better on the DI's, although I dont know that for a fact. The DI's do have more power due to the way fuel is injected into the cylinder, allowing the combustion to hapen in the cylinder rather than be wasted in the pre combustion chamber. The injectors can also be tuned to change efficency, noise and emissions by adding a split shot or pilot injection.Cat also uses the same injection system Ford used on the 7.3L Powerstroke since '94, although they may have used other systems as well. Noise is a big issue now, manufacturers are trying to get the 80"s diesel perception out of the public's mind.