Why Indirect Injection?

[TurboDiverArt]

Hi All,

Something I have always wondered about. Why did GM use indirect injection? I believe the Cummings and Power Stroke engines are direct injection. I have a few guesses but they are just that, guesses on my part.

Possible reasons from my thinking are:
Cold start up using a glow plug in a smaller pre-chamber would better heat the air fuel vs. doing it in the larger volume main combustion chamber.

Maybe something to do with higher compression engines. Not sure why a higher compression engine would be better served with a pre-chamber. I think higher compression would have better cold starting properties.

Indirect Injection is probably easier on the piston surface as fuel is not ignited directly on top of the piston but starts in the pre-chamber. This would especially be important with a higher compression engine

What I don't have ideas about is if it has anything to do with fuel economy. I assume having a pre-chamber would probably reduce power. I'd also think that having the combustion start in a pre-chamber might also increase noise.

Anyone have any corrections, confirmation or things to add?

Another question would be how big is the pre-combustion chamber (cup?). I've never seen a diesel head so I'm trying to visualize it. I'm wondering how big the pre-chamber is and how big is the hole connecting the pre-chamber to the actual head dome?

Thanks for any information.
Art.

[AndyL]

Only my Guess:

1. The technology didn't yet exist, or exist economically for the pressures required for Direct Injection, 20,000 PSI+.

2. The Prechamber design improved emissions and noise levels for the available designes, something in the 2000 PSI range.

3. The prechamber design also improved fuel economy.

[eracers999]

Pre cup is old technology, cat got away from it when it had the 3406a and went to the B. That being said there are a few people on this board that have led the way to making everything else around the pre cup up to current technology. With all the upgrades you can get good fuel mpg, my problem is im always tempted to use more power if iv'e got it. A 1/2 ton pick up with a 6.5 that gets somwhere in the 20's for mpg is darn good, considering a truck like that really isnt light and is a areodynamic disaster. I think that if you can get somone to tell you the truth about mpg you would find the ole 6.5 is a pretty good horse.
Kent

[rjschoolcraft]

The indirect injection was used primarily for noise considerations. Indirect injection is quieter... just park next to an idling Power Stroke (Pre 2003). :D

[Jim P]

I just want to add my 2 cents here.

The technology for direct injection definitely existed when the 6.2 and 6.5 were built. John Deere tractors used direct injection clear back in the 60's. Not the type that is used on the duramax but it was still direct injection. The injector sprayed the fuel right in on top of the piston which had a dish in the top with a cone sitting right in the middle that looked like a hersheys kiss. These John deeres did not have much higher injection pressures than what we have on our 6.5s.

I have read that direct injection engines require a much stronger engine because the fuel burns instantly where an indirect engine drags out the burning a little longer. This instant burning of the fuel also makes a lot of noise by way of diesel knock.

So I feel that gm used the indirect to cut down on noise and also because the engine is just not built near as heavy as a cummins or John Deere and would never hold up to direct injection.

[eracers999]

My only neighbor has the new 6.0 ford and what a noisy rattly thing that is, ish.
Kent

[Marty Lau]

Originally posted by ronniejoe:
The indirect injection was used primarily for noise considerations. Indirect injection is quieter... just park next to an idling Power Stroke (Pre 2003). :D And don't forget Cummings converting fuel into noise! tongue.gif

[triggerman]

IDI engines are typicaly about 15 to 20 percent less efficent and dirtier than DI engines when ALL considerations are equal. ALL manufactures have gone to DI engines due to emmissions. The 6.5 is not built "weaker" due to its IDI heads. Don't forget the 6.5 handles a 21 plus pounds of compression and DI is only 16 or so. Clearly, GM did IDI for easy cold weather starts AND noise period! The GM designed L-20 6.5 engine would have been built with double overhead cams and DI if it wasn't for Issuzu stepin in. I e-mailed AM general's tech staff once asking if they had any plans on making DI heads or DI 6.5 engines in the future. I recieved no reply. I feel the benifits of going DI for the 6.5 would have been great. Just think 35 lbs boost with out the head cracking temps! Of course the factory LAME fuel rate would have to go as well. AM general has improved the bottom end enough to do wonderfull things with a DI 6.5. A factory Cummins block can be safely taken to over 700 HP and 1600 lb ft of torqe. It would have been reeeal interesting !

[MJEasly]

DI heads for the 6.5 sounds like a great aftermarket opportunity. Lotta cracked heads out there and I am guessing that most would upgrade if given the choice (and the cost was reasonable over a direct replacement, and most stock head parts were reuseable). I wonder how difficult the conversion would be and what new/modified parts would be required. Would you even have to modify the fuel rates and other ECU parameters?

Just thinking out loud.

[G. Gearloose]

GM wanted a multifuel engine for the M100x line that didn't sound like a tank, and could maintain some vehicle heat in cold weather, like Germany, hence, indirect injection.

I'd be surprised if direct injection would work well with those pistons.

[More Power]

The Ricardo Comet V precombustion chamber used in the 6.2/6.5 has a spherical chamber which mixes the air and fuel by air swirl. This assists in promoting turbulence, which produces a rapid combustion. This design has a broad efficient operating range, and provides lower diesel combustion noise and a more effective emissions control using the available fuel injection systems.

Downsides include a need for an effective glow system operation and a higher compression ratio to aid in cold starting.

MP

[grape]

personally I've thought about contacting some of our aluminum head sources and changing the injector location. However, I think one of the most difficult and costly parts of the equation would be gearing up and making the precision fuel supply lines. Getting a set of heads cast is no big deal, but when you start changing stuff, it's a big can of worms.

[tom.mcinerney]

C.J. Baker wrote an illuminating article relating to these issues, his definition of 'modern diesel engines'. The article is about a year old, it's accesible at the Banks web site:
http://www.bankspower.com/tech_dieselevolution.cfm

[triggerman]

Tom,
Thanks for the good read.

[BuffaloGuy]

Ditto.