Diesel V12 Meteor Conversion -02

Pistons,
Classic gasoline = Aluminum
Diesel = 1) Aluminum with steel ring lands
2) Steel
My engine is a slow turner ~2500-3000rpm so I am tempted to machine new steel pistons instead of trying to deal with steel inserts for alum. pistons.

Question#1 Opinions?

Also, most if not all OEM diesel designs have the fuel injector located in the center of the cyliner bore (please correct me if I'm wrong on that). From the information I've gathered so far about the R/R conversion, they replaced the 2 spark plugs with 1 glow plug and 1 fuel injector. That puts the injector over on the side of the chamber. Whey I machine the valley into the new pistons I'll try to design a heart shape or something to get the fuel down into the bowl during the initial bang. However, once the piston begins to travel down the bore, I'll have the fuel injecting from the side of the head and therefore one side of the chamber walls would probably get hotter than the other side.

Question #2: Does anyone have any ideas on how to protect that side of the cylinder bore? coatings/ coolant rate/ could I direct the fuel jet off axis from the injector, more toward the C.L. of the bore/ etc.?

Question #3: The classic Diesel thermodynamic cycle had a constant pressure combustion stage, where the fuel was injected/ignited at the same speed as the piston descended, offsetting the increasing volume of the chamber. The "hybrid-diesel" allows for some initial increase in pressure, by beginning the comustion before the piston reaches TDC. Was this for smog or fuel efficiency or power or computer processing or what? How prevailant is it with today's diesels and how effective is it? What pressure does the chamber get up to? I can't seem to google the answer to that real well.

Thanks

You might try putting this in engine tech

Nobody's chimed in on this one since January, huh? LOL

The idea of converting an odd-ball gas engine to a Diesel engine is a helluva concept, almost one that is guaranteed not to turn out well if you have to ask questions about it. But if you're looking for brainstorming, I never shy from brainstorming on somebody else's crazy irrational project.

1) 2500-3000 RPM isn't slow by Diesel standards, especially if you're going to be using custom-machined steel pistons, because I imagine that custom machined steel pistons are going to be much heavier than the stock aluminum ones. Steel is a great option, but if you can't keep the weight down then you're better off with aluminum, or else you'll be picking perfectly good steel pistons out of your crankcase.

2) Having the injector centered in the combustion chamber is far from a primary design consideration; many engines, including the venerable 12 valve Cummins B-series, have offset injectors. I'd steal a 12 valve piston and copy the bowl design as closely as possible.

Which if you've ever seen a combustion bowl, isn't going to be that easy. The shape of the bowl is very important, and the combustion ratio is determined by the bowl volume. Trying to spitball out a functional piston strikes me as something that'd be highly difficult to say the least. What's the stock compression ratio? You're going to want it from 16-20, which opens up the question of whether the headgaskets and bottom end parts are going to last. And then even harder, you have to spitball out a matching injector nozzle. I'd measure the angle of entrance of the spark plugs and pray that you can find an existing Diesel engine that has an injector enter from the same angle.

I wouldn't worry about glow plugs. You can always add giant grid heaters as an afterthought if you find that you need them.

3) More important than theoretical questions about the thermodynamic cycle is figuring out how you're going to drive an injection system, and what injection system you're going to use. Any injection system you pick and manage to install on the engine can work, provided that the piston geometry isn't totally off and the engine doesn't blow to bits due to the added pressure required.

On a high-speed Diesel, over 1000 RPM, you're always going to be injecting fuel before TDC. It doesn't start burning well until a few moments after injection; it's critical to start before TDC for any kind of worthwhile performance. Depending on the injection system, you might be able to get, what, 30-50 degrees of fuel delivery? Maybe a bit more, where it starts to flow is the point of most concern, where it stops flowing is important but something you have less control over on a mechanical injection system.

^^ Nice post Beg, ive been curious about this project every since this thread came about.

Any updates?

I stumbled across another thread on it somwhere cant find it back right now though. edit scroll on down a few