Fuel Pressure / Why

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by lucky devil, Sep 27, 2016.

  1. Blownalky

    Blownalky Top Sportsman

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    That's what I was thinking. It's not like a carburetor atomizing the fuel in an open plenum manifold where multiple cylinders can draw the fine mist. Using your numbers it would mean the intake is closed 61% of the time but we are still spraying fuel into the port at the same rate as when the valve is open. I don't see how much of that would be atomized. Makes me think it doesn't matter that much but with the boost in the manifold, when the intake opens, it would be like opening a freshly shook up can of soda. That would break up the puddle some.
     
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  2. craig moss

    craig moss Member

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    I would think by the time the fuel is blown around the valve it would be atomized for the most part. Then the heat of compression would help even more????
     
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  3. aj481x

    aj481x Member

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    Remember too that when the intake opens the exhaust valve is still open and a lot of this fuel waiting behind the intake valve shoots right on through and burns in the header, that is one reason blown motors are loud.
     
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  4. TOL

    TOL Active Member

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    My two cents worth on this topic are these....

    If you splat the port methanol fuel against the port walls, it is going to then drizzle into the cylinders in huge drops/globs relative to the air stream, with little or no fuel vapor presence resulting within the cylinder at the time of either IVC or ignition initiation.

    Those drops/globs must then be later vaporized thru compression, in order to be available to be burned with the air.

    The heat of compression in the case of a blown meth motor will attempt to vaporize the drops/globs during compression, but 'ya gotta remember that there is a finite time in which to do so while still being able to turn around and create good peak cylinder combustion pressures at an appropriate crank angle for optimal TQ/HP production. What you want at the time of compression is a good supply of liquid meth so as to continue vaporizing during compression (near constant chamber temperature) and a good supply of vapor. These two need each other hand-in-hand.

    So, if you dump a huge amount of air and liquid methanol into a chamber of a blown meth motor, and if you have little or no vapor at the time of ignition initiation, then you'll likely be hard pressed to make any decent power, and the outcome will appear to be lean-like performance when you look at all of your numbers. Your notes might make you think your engine was rich, when in actual fact it was way lean versus what it actually needed to be in the timeframe (crank time) for making good power.

    The more that you can improve the going in atomization and vaporization state of the methanol fuel (assuming supercharged - NA is different) the more chance you have of initiating a higher mass fraction of charge burned by the time of "X" crankshaft rotation.

    Power production with methanol is all about how much meth and air can a person combust in a given period of time relative to crank time. If combusted late, or not at all, then no useful power is generated from that process at the crank.

    So is going in vaporization and atomization important? Yup.... Is it worth pursuing? Yup.... Does more pressure behind a conventional MFI fan nozzle necessarily mean better atomization/vaporization? Nope.... Would a better spray/target nozzle be beneficial? Yup....

    Hope this stirs some thoughts. Open to thoughts.
     
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    Last edited: Oct 3, 2016
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  5. JustinatAce

    JustinatAce Member

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    So... Lets Math, perfect world type shit. Lets say you've got 13 GPM flowing into a motor at 8000 RPM to keep numbers nice and even. At 8000 RPM, every intake valve opens 33.3 times per second. 13GPM = approx. .216 gal/sec. Split that 8 ways.. .027 Gal/cyl/sec. 1 fl oz. = .008 Gal. 3.375 fl oz/cyl/sec. split that 33 times and you get approx 0.1 fl oz per valve event. That is 1/10th of a shot glass of "puddle". Not to mention all the heat working to evaporate the puddle. And your boost works to spray the fuel around the valve as it opens as well. That's why I don't think you see much difference between running dribbling fuel pressure vs. boiler pressures. There are a lot of kinetics at work moving very fast and warm.

    Until they let us run direct injection, it will always waste fuel.
     
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  6. lucky devil

    lucky devil Member

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    Thank you for all the answers and input so far , keep it coming
     
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  7. Mike Canter

    Mike Canter Top Dragster

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    Boost pushing the atomized fuel around the valve is not a problem. The problem is when the sprayed fuel hits the runner walls and dribbles down. That fuel takes longer to get into the chamber and is not easy to ignite and doesn't burn at the same rate. This messes up your mixture and your final AFR making the AFR leaner than what you planned for the amount of fuel injected thus causing a loss of power. Yes, direct injection would help as would using electric fuel injectors with better designed outlets aimed down the runners. Our current mechanical nozzles just spray a wide fan pattern from runner wall to runner wall.
     
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  8. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    Mike - that was based on a discussion with a fuel system guru several years ago around the time some people were trying 300-400 lb fuel systems. I think the premise is based on if the fuel were still atomized at the time of combustion from the fuel pressure.

    One of my concerns with higher pressure systems is small jet changes can yield much different results than lower pressure systems.
     
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  9. Mike Canter

    Mike Canter Top Dragster

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    That is a good point on small changes having bigger results with higher fuel pressure
     
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  10. rb0804

    rb0804 Member

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    There has to be high atomization nozzles out there that work. Gorr has some listed that are dependent upon nozzle size. Waterman has what they call HVT and I hear Davenport also has a high atomization nozzle. So who's using what and what seems to be working vs the standard enderle stuff?
     
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  11. JustinatAce

    JustinatAce Member

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    Mike, what I meant is the flow of air around the valve when it opens helps disperse the "pooling", within reason of course, but as it hits the top of the valve entering the chamber, the valve acts like the end of the nozzle, fanning the air and fuel out in the chamber. On that same token, I've seen guys run impressively well with the nozzles pointed back into the manifold as well. I think we can overthink mechanical systems until we're blue in the face. Ready for EFI....

    And the AFR is a constant for maximizing potential energy. What changes are the conditions in which the AFR is best mixed for ignition. Different heat levels throughout the process can have major effects on the amount of fuel you can usefully burn.
     
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  12. Mike Canter

    Mike Canter Top Dragster

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    I have tried turning the nozzles up but didn't see any difference. That was the thing to do about ten years ago. It came and went. For myself I have a set fuel pressure at a specific rpm I always try and maintain so I have one less variable to worry about
     
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  13. TOL

    TOL Active Member

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    Rob, think dirt track alky nozzles, with the tip/restriction points way down about 2-3 inches from the backsides of the hot intake valves, direct shot, no impingement on the port walls, just impingement on the valves. Make sure you target the "right" side of the valve (versus the stem) to get the fuel into a proper trajectory going in thru the open intake valve when it is actually open.

    In years gone by, certain Indy Car meth engines have used what was called "Laser Beam" EFI fuel delivery, to their advantage.

    Picture a high velocity tight stream of liquid meth, impinged directly against the backside of the intake valve, from not too far away (about 2-3 inches). This gave great performance while not suffering the setbacks of charge displacement due to early vaporization and fuel misplacement.

    MFI as is currently in drag racing is kinda crude. There's a lot of room for improvement. The improvements do not necessarily require ECU management though, or EFI. Same is true for meth or nitro fuel. EFI gives more precise control, but the mechanical thingy delivering the fuel is way more important.
     
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  14. TOL

    TOL Active Member

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    Agreed in part, and as the world evolves yes.....

    There is not a DI injector on this planet, at this time, which will support the required flow volumes versus time (crank time) for what we do with our fuels of choice (meth, nitro, etc....).

    Likewise, there is not a high pressure fuel pump on this planet that can service the task in terms of volume and pressure.

    Lastly, DI injection into a 50+psig boost application at say 10:1 static compression would be a further hugely daunting task even if such devices were available.

    Thinking out of the box, yes, DI injection or a combination of DI and MPI, would certainly be a benefit. Let's not overlook some basic historical facts though, before we go off trying to put a satellite into space. Past successes could help future blown drag race engines.

    Turbocharged Indy & Road Race engines have routinely made 8'ish Hp per cubic inch in boosted non intercooled race form, with huge reliability. Often higher in qualifying trim. All they had back then was MFI fuel, methanol, and very crude/weak ignition systems. Take a look for example at the turbocharged Offy and Drake engines.

    Today's roots blown MFI drag engines are around 5'sh Hp per cube, and their screw cousins are around 6'ish Hp per cube. Approximations here (rough numbers....).

    Ever stopped to wonder why/how the difference? Their RPM's were about equivalent to what any good screw would turn these days in competition.

    My own personal feeling is that MFI as is known in the drag world needs to evolve, as do the engine designs. Forget ECU control, but rather go back to first and foundational principals and then work from there. Get the basics optimized, and then maybe consider ECU control "if" required.
     
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    Last edited: Oct 7, 2016
  15. JustinatAce

    JustinatAce Member

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    Ahhhh. But the big question is, what volumes do you really need when every last particle is going exactly where it needs to be? At least with Methanol, I'd think there is a lot to be gained. I don't think you'd gain a damn thing doing it with nitro since they're trying to compress it into damn near a solid before they ignite that fuel volume. And nitro is far less dependant on the AFR for optimal power since it has it's own oxygen, at least in the top fuel cars. Good air just helps them with their pre-ignition pressures.

    And as for the injector and pump size... There are diesel engines running on this planet with 8+ cylinders with Pistons and Rods the size of a Tractor/Trailer. How do they get fueled? You can't just dribble diesel.. Not to mention pulling trucks, 2,500+ hp diesel engines fueling into 100-300 psi of boost.

    Today's roots blown MFI drag engines are around 5'sh Hp per cube, and their screw cousins are around 6'ish Hp per cube. Approximations here (rough numbers....).

    D Rotor TAFC's and BAD's with latest and greatest are probably closer to 7hp/cube. C Rotor Outlaw guys and Turbo'd Billet Hemis are pushing 8 hp/cube, maybe more. As for the road race vehicles and Indy cars, they aren't all about the displacement, or at least instant torque. Designed to achieve high horsepower by revving sky high. If you get X work per rev, more revs = more work = more hp. 2 inch stroke x 6 inch bore, rev it to 18,000+ all day. Thing won't make 100 ft-lbs of torque, but will make 1000 hp screeching. And if I can turn 18,000 RPM, I can run a hell of a torque producing gear reduction. Drag racers seem to need more torque. But if I'm only using 280 cu in engines, mathematically it is a lot easier to get your hp/cube up. You need half as much horsepower as a 560 would to accomplish each whole number step.
     
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  16. promodracer

    promodracer Member

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    My understanding is that's why its good to run close to 200 psi. That lower pressures make for difficult tuning. Others have told me it doesn't matter.
     
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  17. Mike Canter

    Mike Canter Top Dragster

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    200 psi when? What rpm? 9000, 10000 or what. So as a reference what is you fuel pressure at 8000 in first gear?
     
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  18. aj481x

    aj481x Member

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    An MFI system using some sort of fuel management that by passes fuel is going to have a pretty broad pressure range. It seems like that if the highest pressure attained, usually at the finish line is around 200 psi this can make a workable combination.
     
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  19. lucky devil

    lucky devil Member

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    Thank you for all the input , some great response and detail
     
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  20. promodracer

    promodracer Member

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    Yes at top end or at 8000 rpm to be exact.
     
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