"Inventing" a "New Multi-Fuel Engine"

[Hammer]

Was not the original hypercycle design of the multifuel a German design, by the predecessor to the current MANN line of engines?

Yeah, but they did a lot of work to make the engine quiet(er). It just happened to be able to run on other fuels as well.
Nice fringe benefit there if you ask me...

 

[jesusgatos]

No, what I was getting at is that I'm having a hard time understanding what the concerns are regarding raising the compression ratio in engines that are already being subjected to massive amounts of boost. Was just wondering why they're hold up to one and not the other.

 

[Wolfen]

I will Definitely watch this Topic.

 

[Hammer]

No, what I was getting at is that I'm having a hard time understanding what the concerns are regarding raising the compression ratio in engines that are already being subjected to massive amounts of boost. Was just wondering why they're hold up to one and not the other.

Ah, that lies in how you can design the cam profile.
Also, to a point, how close your tolerances have to be for a higher CR engine compared to the lower CR + boost.
But, to a point, you are right. They are being built a lot stronger, and withstand a LOT of boost = cylinder pressure.

 

[jesusgatos]

Thanks, but just so I'm clear, can you please explain to me in a little more detail how they're different? Think I've got an idea, but want to make sure I'm not misunderstanding anything.

 

[QuickSilver]

This table is for a Dodge 408 stroker engine, but the concept still applies. You'll notice as you look at it that you can almost draw a diagonal line across as you lower the compression and raise the boost, or visa versa, and the PSI in the cylinder stays almost the same. So yes, you can use boost or compression to reach similar levels of pressure. After a certain point however, forced induction, weather turbo or supercharger, can radically speed up the process of getting the air into the engine. You can only "drag" so much air into an engine so fast before the vacuum is going to start slowing you down.

Engine Compression Ratio VS Boost Pressure

Edit: I changed this table to a link as the copy and paste method didn't turn out too well on the forum.

 

[jesusgatos]

Thanks. So then it doesn't matter whether the cylinder pressure is generated by high-compression pistons or a high-boost turbo, if an engine can tolerate one it should be able to take the other equally well? In that case it sounds like the compression wouldn't be much of an issue, but figuring out the delivery and combustion of air/fuel might take a while to get sorted out, huh?

 

[motomacguyver]

There is more to it then that.
I have been thinking a LOT about this exact topic for quite some time now.
I figured two setups would be nice to have.
I would like to base one off of the GM 6.2 setup (indirect injection diesels already have a high compression ratio, stupid easy setup, and already have a low pressure setup for the injection.)
And a much smaller engine, like a small VW, or maybe older benz. Thinking here is that they would make EXCELLENT power plants for house hold sized generators.
Think of that, a 5k to 10k (or up to 30k really) that runs on ANYTHING!

The truly hard part is designing a new head. I don't know of ANY other head that is close enough to how our multi-fuel heads are in design.

If one doesn't know.
Stupid simple terms of how our multifuel engines work.
Fuel is SQUIRTED into the cup in the top of the piston. Note the cup even has a cut in it to help the fuel squirt in without atomizing any of the fuel, yet.
Second, and the hardest part, the head is designed so that all incoming air is swirling just right, so that when it enters the cylinder, it is swirling directly into the cup in the top of the piston. The swirling air is what atomizes the fuel, which is obviously a technical feat to do this close to top of the compression stroke.
The high compression ratio is required to ignite the fuel when it is being atomized in this form.
Newer diesels use higher fuel pressure, smaller holes in the injectors, etc. to help precisely atomize the fuel.

So, designing the pistons is easy. Copy what we already have. Then try and find an engine with a head design that closely matches that of our MFs as well.
Also, having an engine that already has a high compression ratio solves a lot of other issues.

If we went with a variable timing, variable pulse injection system, Mechanicaly controled from the cab, we could compensate for various fuel densities. Then with a variable psi turbo system, the compression ratio could be "altered". Back all of this up with exaust gas gauging to see where were at.

I know it’s a lot of variables but it would be easier and cheaper than designing our own head.

 

[Hammer]

Thanks. So then it doesn't matter whether the cylinder pressure is generated by high-compression pistons or a high-boost turbo, if an engine can tolerate one it should be able to take the other equally well? In that case it sounds like the compression wouldn't be much of an issue, but figuring out the delivery and combustion of air/fuel might take a while to get sorted out, huh?

To a point, remember, to ignite a lot of the fuels we would like to use, we will still need a fairly high static CR. It needs to be able to START easily, and then run at idle, where we are not generating boost levels.
Unless you did like the detroits and run a turbo on top of the super charger.

 

[jesusgatos]

Oh yeah, I understand that part Ed. Wasn't trying to suggest that boost is equal to high compression pistons as a substitute, just seemed like if an engine holds up to one it will hold up to the other. That's all I wanted to clarify.

 

[Hammer]

Figured you did, but wanted to make it clear for anyone who didn't.

Actually, an engine has some other dynamics that can play into this even more.
Like the 2nd upward travel of the piston. Leaving enough volume to compress will help soften the 'snap' that the rod/pin/piston sees. Granted, this is mainly an issue at higher rpm, but it does affect longevity on any engine.

We really would want the lowest compression possible that would be able to start and idle with assorted fuels.
But seeing as a lot of people have run a lot of stuff through their trucks, and at some cold temperatures as well, it would seem that the CR of the MF is probably fairly close to where we would actually want it.
Fyi, a lot of indirect injection diesels are between 18:1 and 23:1 for the CR. So, there should be a good number out there that already have a start on the compression side, and having internals that are designed to handle the higher compression.
Problem lies in the head and piston design for those engines. Not exactly a good match up to actually copying our MF design into.
Of course, those same engines already run darn well on a lot of the heavier fuels we put in them. Just stay away from too much gas, etc....

 

[jesusgatos]

...and the only thing to be gained by reworking the head/s injectors would be the ability to burn gasoline? Bah. Personally would rather just optimize the fuel system to burn the alternative fuels that they seem to already tolerate fairly well.

 

[Hammer]

Well, we happen to like to 'thin' our heavy oils with gas. So having the engine burn it as well is a safety issue as well as a multi fuel issue.

 

[Hammer]

You are right though, it would only take so much reworking on the existing engines to make them more 'tolerant' of other fuels.

 

[dozer1]

Would the computer controlled engines do a better job of efficiently burning sayyyy 50/50 diesel / filtered WMO or the older mechanical diesel be the better bet? (I bet a guy could get away with that in a moderately warm climate with little or no mods)

 

[budman67]

Still being new to this,I would rather see a reliable flow
of new parts to keep these multi fuels going than trying
to re invent the wheel. Maybe improve a way to cut down
on the smoke?

 

[Hammer]

Cut down on smoke and run smoother.
Easy, swap on a newer turbo with a waste gate. Don't try and make a ton of boost, just make the boost come in a lot sooner, and let the wastegate bleed off the extra at the higher rpms.
Or just turn down your fueling a little

As for 50/50, they can run more then that. But that ratio is done quite a bit already in the CUCV setups we already have.
Honestly, when it comes to the heavier fuels we use, a LOT of diesels that are mechanical can run them just fine. They start a little harder, and you can't let any of these things get cold and sludge up the filters, injectors, etc.

 

[Hammer]

Check this out!
New technology turns petrol engines into low compression diesel!
Different idea to get the same affect that we are after.
Now, put that piston in a simple engine like the 6.2 and have fun!

 

[dozer1]

Thats pretty darn interesting! SONEX RESEARCH I wonder what engines they have these available for. If it says, I missed it. If for the small block chev (SBC) just about anything else you could ever possibly need is available...Making it a good off the shelf find...I need to read more about this.

 

[4trans]

"The short duration of SCAI combustion as validated by the rate of heat release supports the
goal of reaching 400 Hp at high rpm with an engine displacing 3.2 liters." Quoted from one of their PDF's. Thats enought to power a Duece, and at 3.2L you could mount two of them together and put them in tractor trailers. Dang.