Can squish clearance and boost hydraulic an engine?
Can squish clearance and boost hydraulic an engine?
(OP)
Hello everyone,
I am new to the forum although I have been lurking by finding lots of answers here through Google.
In A. Graham Bell's "Forced Induction Performance Tuning" Bell notes that reduced squish clearance can cause an engine to hydraulic.
I have reviewed my basic thermo books but can't figure out how to calculate when a fuel/air/water mixture will be "solid."
Specifically, I would like to determine at what boost and CR this could occur.
Dan
I am new to the forum although I have been lurking by finding lots of answers here through Google.
In A. Graham Bell's "Forced Induction Performance Tuning" Bell notes that reduced squish clearance can cause an engine to hydraulic.
I have reviewed my basic thermo books but can't figure out how to calculate when a fuel/air/water mixture will be "solid."
Specifically, I would like to determine at what boost and CR this could occur.
Dan





RE: Can squish clearance and boost hydraulic an engine?
From the stoichiometric air/fuel ratio and the (known) densities, you can figure out how much space the fuel takes up when it is in liquid state. For gasoline, the fuel in liquid state takes up approx 1/10,000 the volume of the air at normal atmospheric conditions. If the compression ratio is 10:1 then the fuel in liquid state takes up 1/1000 the volume of the air. No "reasonable" supercharging pressure and "reasonable" compression ratio and "reasonable" air/fuel ratio could ever cause a gasoline/air mixture to hydraulic-lock an engine.
That's not necessarily true of all fuels, though. I believe the statement could be true of nitromethane in drag-racing applications. Drag racing engines are heavily supercharged and the air/fuel ratio is extreme because nitromethane carries along a lot of its own oxygen.
If the fuel takes up a substantial amount of the compression space, keep in mind that even though it might not actually be compressed "solid", the pressure may go high enough that, from the point of view of bending con-rods and blowing head-gaskets, it might as well be solid.
RE: Can squish clearance and boost hydraulic an engine?
Now, those 200+psi boost tractor pulling Diesels that run hefty amounts of water injection may be candidates for hydraulic lock...
RE: Can squish clearance and boost hydraulic an engine?
I never heard of a top alcohol engine locking though. You need a fair swag of nitro in it to risk locking it.
It cannot see how itwill not lock because of squish unless you do something real stupid with piston or deck surface shape.
The whole idea of squish is to squeeze almost all the gas out. It does this progressively as the piston comes up and the gas over the piston can escape due to any pressure difference. If dynamic effect caused a temporary pressure spike over the piston, the gas would flow faster well before the air solidified.
Also pistons rock in the bore so the tightest side would slope toward the chamber due to rock. This would assist any liquid out of that space.
Also a problem can only occur at very near TDC and at this point the piston is travelling real slow, relatively that is.
Regards
Pat
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RE: Can squish clearance and boost hydraulic an engine?
It makes a lot more sense that the cylinder pressure could be too high than the mixture locking up.
There must be a tipping point where boost pressure and compression overcome the force of the crank.
Do you know any calculators that determine the cylinder pressure generated on the compression stroke?
The intake air charge temp must play a big factor.
Dan
RE: Can squish clearance and boost hydraulic an engine?
As to the big drag engines? I have so little experience in anything approaching 'modern' that I can only give the one example that I believe to be true... Test of a Keith Black engine, I am told by the dyno operator that it hydrauliced a cylinder and then blew the blower off when the throttle was inadvertently opened full and abruptly closed. That's second hand, but I trust his statement to be true.
Rod
RE: Can squish clearance and boost hydraulic an engine?
I posted late at night got a bit lost and phrased some of it poorly and some of my post is not what I meant to say.
Below is a fix.
Brackets () indicate what should be removed and all additions are in caps to indicate changes, not to yell
Regards
Pat
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RE: Can squish clearance and boost hydraulic an engine?
Regards
Pat
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RE: Can squish clearance and boost hydraulic an engine?
- Steve
RE: Can squish clearance and boost hydraulic an engine?
BTW, liquids above their critical temps. do become gases, but their density can be the same as the liquid--they ain't gonna compress like a gas at any non-explosive pressures.
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Can squish clearance and boost hydraulic an engine?
By the way, squish is just what the proletariat refers to the quench area. I'll not say squish again. Also, it's hard for non race engine oriented engineers to "see" a 0.010" stretch in a rod/piston assembly...brother, it happens. Often a lot more, too.
I also dislike reference to a Panhard rod as a 'track bar', too. Plus a few more but that probably belongs in the
engineering language forum.
RE: Can squish clearance and boost hydraulic an engine?
I always thought of squish as the piston getting close enough to the head to squish out virtually all the charge from the area and set up swirl or more likely tumble in the chamber to spread the flame kernel.
I presumed the confusion came from both functions resulting from tight piston to head clearance in the areas a long way from the plug.
This is supposition on my part rather than a study of credible sources.
Regards
Pat
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RE: Can squish clearance and boost hydraulic an engine?
I can get good power with no detonation with my wedge head at over 16:1 CR whereas I can only get about 13:1 CR on the hemi to work on the available (to me) 110 octane fuel. I mean work to optimum power for the displacement.
Rod
RE: Can squish clearance and boost hydraulic an engine?
I have had witness marks on engines with 0.038" piston to head. Some of that 0.038" may have been due to differential expanion as the piston is aluminium and athe piston, rod and crank are all hotter than the block, butsome was surely due to slack in clearances being pushed in the same direction and due to stretch and piston rocking.
Regards
Pat
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RE: Can squish clearance and boost hydraulic an engine?
The most common form is on restricted turbo charged engines. When particular rich fuel mixtures are run it seems possible that the fuel droplets do not actually atomise and can lead to hydraulicing between the piston and the head area, resulting in bent connecting rods. From this i have seen a 300hp restricted wrc type engine destroy (bend) conrods that are fine in 1000hp drag cars.
The matter is made worse if water injection is also used.
If you find build specs for WRC engines, or high output hill climb type turbo engines, alot most of them will have either no squish area at all, or the piston will be about 2mm away from the squish pads.
RE: Can squish clearance and boost hydraulic an engine?
Rod
RE: Can squish clearance and boost hydraulic an engine?
Or even if it really did hydraulic is it possible to know it wasn't a mechanical failure like an injector sticking open or something?
The theory about high ratio fuels like Nitro sounds possibly plausible but I find it hard to believe in most situations.
I have known many people and groups running high boost and making big power, many using water and alcohol injection and have never heard of this being suspected for an engine failure.
RE: Can squish clearance and boost hydraulic an engine?
I certainly have seen hydraulic lock with water injection when things go wrong, like it siphons a cylinder full of water when parked or the pump switch fails in the on position.
Regards
Pat
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