Diesel RVs: Re: Fwd: [diesel_mercedes] Doing some R&D need your help

Barry:

A diesel cannot run "too lean". If there is not enough fuel for the engine to run at the speed it is going, it will slow down until combustion (and more importantly, work) can take place. Or, more accurately, the engine will slow down until the fuel balances with the load the engine is under. Please recall that a diesel engine has no throttle valve. So there is no artificial restriction on the amount of air ingested during each intake stroke. Engine speed, or more accurately, output power, is entirely controlled by the amount of fuel injected. At idle, for example, you are taking in just as much air during each intake stroke as at freeway speed. The only difference is the amount of fuel injected. So it is not possible for a diesel engine to "run lean". It will simply slow down if it is "not getting enough fuel".

And as for the bubbles, if you are seeing bubbles then it is not sucking air in, but blowing it out. And the cylinder is under pressure on every stroke but the intake. And on the intake stroke the intake valve is wide open so there is little chance that you are sucking air into the chamber through the "bubbling leak" that you see. Oh yeah, and if your turbo is working then the cylinder is under pressure even during intake.

Diesel engines are not like gasoline engines. Gasoline engines control both the air flow and the fuel. Further, the fuel and air is homogeneously mixed during intake. If you don't balance the fuel and air then it can be too rich or too lean. But in a diesel things work differently. A full charge of air is taken in on each intake stroke regardless of the amount of fuel that will be injected. At idle that is a small amount of fuel. At full speed that is a large amount of fuel. And for the exact same amount of air. So why does it work? Well . . . when the fuel is injected, it starts out in a very dense concentrated cloud or mist that quickly thins out into the pre chamber or cylinder depending on the engine design. There is no air in the center of this fuel cloud to burn. It is too rich in the center of this cloud. But there is air around the edges. So it starts to burn there. That first burning produces heat that helps the cloud of fuel expand and disperse. In our case, as it blows through the pre-chamber holes, a violent turbulence is created that really breaks down and disperses the fuel cloud. In the ideal case every molecule of fuel will eventually find enough oxygen molecules to completely react with. And if there is extra oxygen, hey, it just doesn't get used. This is very different from mixing the gasoline and air beforehand and hoping you get it just right.

At the very least, the guy who told you that your engine is running lean does not know what he is talking about.

Bogy.

--- On Thu, 4/7/11, Barry Edwards <duckn8r@me.com> wrote:

Begin forwarded message:
Thanks I try.
Hay today I was driving my 1979 123 300D Mercedes down the road the car was running great, I stopped and turned off the car.
After ten minutes started back down the road and at between 50 to 60 miles hour It would get
this detonation sound. It was like this light knocking.
A few months ago I had a fuel leak, from the washer on top the fuel filter under the main bolt and air would get in the line,
I could see little bubbles moving in the clear lines,going from the filter to the fuel injection pump and it knock. The mechanic told me that was a knocking from it being to lean. That's what it sounded like today.
I see bubbles coming out around one of my injectors when it is at an idle.
could the piston be sucking air in at that speed causing that knock?

Sent from my iPad

On Apr 6, 2011, at 4:51 PM, Blaise Colasante <supervee03@yahoo.com> wrote:

Barry,

Have you checked fuel filters? My 300D had a similar problem but not so pronounced. I found that I had fungus in my fuel tank that was clogging the fuel filter. The clear filter was looking black and the sending unit in the tank was covered with black slime. Let us know if you discover the same problem. There are corrective measures short of dropping the fuel tank.

Blaise

From: Barry Edwards <duckn8r@me.com>
To: "diesel_mercedes@yahoogroups.com" <diesel_mercedes@yahoogroups.com>
Sent: Tue, April 5, 2011 12:49:34 PM
Subject: Re: [diesel_mercedes] Doing some R&D need your help

Now I don't know what to believe, I'm just trying to make this car drive, right now it slow down to 10 mile an hour driving up a hill if I don't get it up to 50 before I go up it.
I'm just hoping to have a engine that will get forty miles a gallon or better but the motor should have a little better pick up I not trying to make a race car, what do you guy think of that?thanks again for your response, Barry

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