Diesel Conversion

[John_Forbush]

Ok, I have an 11hp briggs and Stratton engine I converted to diesel, as of right now it's carbureted, I was wondering if it would be possible to take a low pressure injector from a late 80's Mercedes diesel and a fuel pump and making a manifold so I could make it a direct injection engine?

[Skywatcher]

Hi John

Did you say you have converted or have plans to convert? If the engine is still carburetor fed, then it's not a true diesel. A true diesel works on compression ignition not spark ignition. (that being said, some model airplane engines were carburetor fed diesels but were really fussy to start and needed a special nitromethane blended fuel) I'd be very surprised if a B&S engine would hold up to the pressures required in a diesel. We used to figure minimum compression for a diesel at cranking speed was 350 to 400 psi. Is this going to be a direct or indirect injection design.

Have you installed a new piston with the toroidal dome for direct injection or piston the cloverleaf recess and a pre combustion chamber in the head for indirect. Also, how do you intend to drive the injection pump once installed? bearing in mind the injection pump has to be driven at camshaft speed and timed perfectly to the crankshaft for correct start of injection. I'd be interested to know how you make out with this project. All the best,

Sky

[KE4AVB]

Here is an article that might be of interest on this subject from the smokstak forum.
http://www.smokstak.com/library/technical-information-7/running-kerosene-in-a-gasoline-engine-23/

[bobodu]

You will like end up with a pile of scrap metal. That engine isn't strong enough to take the beating for long.
" The air is then compressed with a compression ratio typically between 15:1 and 22:1 resulting in 40-bar (4.0 MPa; 580 psi) pressure compared to 8 to 14 bars (0.80 to 1.4 MPa; 120 to 200 psi) in the petrol engine. " From wiki..
After reading the thread again..it looks like you still plan to keep the ignition..So what's the point with the price being so much higher for fuel?

[KE4AVB]

Maybe he is using home brew diesel fuel (bio-diesel). There is sure enough used cooking oil to make it from at least during Thanksgiving time frame. Obtaining the lye to do it can be a problem or at least in my area because of the meth problem.

If he is using the carburetor feed version the compression ratio is less than most thinks. According to the article I reference to there is a need to use two head gaskets stack to lower it.

From what I gather he is asking if can use direct injection on this set-up and the answer is no as the fuel needs to vaporize instead of being heated by the compression. There is simply not enough compression on a standard gasoline engine to produce the required heating of the cold compressed diesel fuel for it to self ignite.

This engine would more like the kerosene versions that I have read about, for me I haven't physically seen one.

[bgsengine]

Obtaining the lye to do it can be a problem .

Who needs to obtain it? All you need is wood ash and water.

[John_Forbush]

It's already converted, it's carbureted and runs in the summer on just compression ignition and in the winter I UN an e3 spark plug, if I make it fuel injected it'll be indirect injection, I'm thinking about using a Mercedes injector. And thanks for the advice.

[John_Forbush]

And to time the pump I was thinking of maybe setting up a crank trigger.

[bgsengine]

Fascinating. Can you explain how the conversion was done, what exactly has to be done to convert it?
It would be an excellent education for the rest of us here!

[John_Forbush]

As of right now the head is milled about .20 and it just runs on diesel.