Pondering about flathead potentials

[peejay]

Anyway, if the ignition propagates faster than a shock wave could, that will spoil the otherwise possible detonation.

That, in a nutshell, is why flathead engines are no longer relevant. You can't get a good fast burn with them because your chamber shape is severely limited.

[peejay]

HCCI is one example of combustion propagation faster than sound. The problems caused by detonation arise from the fact that the flame front is travelling AT the speed of sound. This creates a pressure front/shock wave that grows in slope and magnitude as it travels across the chamber. When it reaches the edge of the chamber it is violent enough to do mechanical damage and equally important - it breaks through the stagnant gas boundary layer and exposes metal to the burning gas.

So flame speed faster than Mach 1 is not as bat as a flame travelling at Mach 1.

Detonation doesn't have a "flame front" - it is spontaneous ignition caused by the flame front compressing and heating the as-yet-unburnt fuel.

[gruntguru]

HCCI is one example of combustion propagation faster than sound.

Where did you get this info? My understanding is that at best HCCI ignites in more than one place simultaneously but at no time does the flame front exceed the local SoS.

Did you mean "at worst"? If it doesn't ignite at more than one place simultaneously it isn't HCCI.

[gruntguru]

HCCI is one example of combustion propagation faster than sound. The problems caused by detonation arise from the fact that the flame front is travelling AT the speed of sound. This creates a pressure front/shock wave that grows in slope and magnitude as it travels across the chamber. When it reaches the edge of the chamber it is violent enough to do mechanical damage and equally important - it breaks through the stagnant gas boundary layer and exposes metal to the burning gas.

So flame speed faster than Mach 1 is not as bat as a flame travelling at Mach 1.

Detonation doesn't have a "flame front" - it is spontaneous ignition caused by the flame front compressing and heating the as-yet-unburnt fuel.

I know its not a "flame front" - you can give it a better name if you know of one, but it does have a finite propagation velocity - i.e. it does not ignite simultaneously.

[vannik]

It ignites in a lot of places simultaneously but none of the individual little flame fronts travel faster than the SoS, the total effect might be similar to supersonic combustion speed but it is not supersonic and in my opinion describing it as such might lead less informed readers to form a false view of it.

[Kevin Johnson]

https://en.wikipedia.org/wiki/Root-mean-square_speed

https://physics.info/kmt/practice.shtml

Hydrogen molecules can easily surpass the locally prevailing speed of sound in a mixture of gases.

[140Air]

https://en.wikipedia.org/wiki/Root-mean-square_speed

https://physics.info/kmt/practice.shtml

Hydrogen molecules can easily surpass the locally prevailing speed of sound in a mixture of gases.

Any individual molecule can reach extremely high speeds when compared to the average in a gas, but the transmission of sound is not a property of an individual molecule. It is a property of a mass of molecules.
Also, check "mean free path" to get an idea of how far a molecule moves on its own compared to the mass movement in sound transmission.

[MichaelThompson]

Hey gang, I’ll admit up front that my interest Flathead potential comes from the perspective of me being a Flathead Ford enthusiast. Followed by the mighty “K” series Kohler and some other kool small side valve engines.

The game for some Ford V8 guys is how to make Henry’s old lump as good as possible. From a drive ability, reliability AND performance standpoint.

I don’t think anyone believes that a side valve engine can compete with a modern engine in performance. In the same a standard rebuilt 350 Chevy from the 70’s can compete with a modern minivan V6 of today.

When Henry Ford gave us the low cost V8 he gave us way more than just an engine.

The whole car was exactly correct for that peppy V8 and nimbleness and handling were just as much part of the equation.

I’m sure certain OHV GM 6’s could be built to our power a Ford V8 but placing one in a lightweight chassis like the early Ford would have killed overall vehicle dynamics.

It’s like those motorcycles with Chevy big blocks in them. I can’t think of a better tire shredder but I’d hate to try to carve up the twistys with one.

Personally I am not on your guy’s level. I’m no engineer nor super accomplished engine builder.

My own personal goal is to unlock as much potential as I can out of a Flathead Ford V8.

I’d like to think that one could approach .75 hp per cubic inch and still be streetable.

That is not to say this is an idea that can use bolt together parts from various aftermarket vendors.

I’m saying that blazing a trail by designing the right cylinder head and combustion chamber with the right piston, the right camshaft combined with reasonable block mods could open up say 200 hp to a whole bunch of like minded people.

What’s available today are mostly street goodies that are “traditional” and sold well back in the day.

Guys like Navarro, Baron and Tattersfield were competing for speed records and were not beholden to popular but limited parts combinations.

All this talk about Flatheads being one on one with OHV’s and OHC’s is moot in my opinion.

All of us performance minded people are locked into traditional ways whether we like to admit it or not.

I just watched the IMSA 12 Hours of Sebring where the cars in all the classes are “equalized” by something called BOP or Balance Of Performance to allow all different configurations to have a shot at being competitive.

Theoretically you could run a Flathead Ford if you had enough concessions to equalize it to the other stuff.

I say while y’all are very correct in pointing out the drawbacks there are also strengths that should be realized.

For one Flathead Fords require much less ignition lead than you would expect. That to me is indicative of good mixing of the intake charge.

When that piston comes up it doesn’t just squeeze it SLAMS the mixture into the valve chamber area fully homogenizing and creating good conditions for quality burns.

As I said in the other thread the U turns and tall intake manifold are just too much to overcome in the pursuit of even higher performance.

When the intake charge flows past the valve seat on a Flathead Ford it wants to go straight up. Unfortunately we’re trying to rip it sideways to get it down the hole.

I think the trade off has to be made, the head needs to be raised to clear the way for the incoming charge.

The only practical ways to regain lost compression in a Flathead Ford are popping the pistons up in the head or hi doming the pistons like Navarro did.

[Kevin Johnson]

https://en.wikipedia.org/wiki/Root-mean-square_speed

https://physics.info/kmt/practice.shtml

Hydrogen molecules can easily surpass the locally prevailing speed of sound in a mixture of gases.

Any individual molecule can reach extremely high speeds when compared to the average in a gas, but the transmission of sound is not a property of an individual molecule. It is a property of a mass of molecules.
Also, check "mean free path" to get an idea of how far a molecule moves on its own compared to the mass movement in sound transmission.

Yes. I will just say we (I) have been over this ground many times on this forum with respect to kinetic gas theory. Now that we know what is possible for a molecule, extrapolate for an atom of hydrogen which has roughly a diameter of 0.5 angstroms (typical gas theory assumes a molecular diameter of 2.0 angstroms). Remember that a mean is an average and must take into account extrema. It is hardly controversial that hydrogen atoms generated in highly complex combustion kinetics could rapidly exit a cell and influence events far outside the boundaries of that cell. It is easy to forget and conflate a calculated average or mean with the idea that every element in the calculation starts at that value.

[hoffman900]

Neels wrote a very cool article on Squish some time ago.

http://home.earthlink.net/~scloughn/id21.html

It's about 2-strokes, but once above the transfer ports, it's the same bag as a 4 stroke.

[Nikolas Ojala]

Here is an interesting plasma ignition patent: https://patents.google.com/patent/US8555867

I think that a flathead engine, more than any other, needs an improved ignition system.

[140Air]

https://en.wikipedia.org/wiki/Root-mean-square_speed

https://physics.info/kmt/practice.shtml

Hydrogen molecules can easily surpass the locally prevailing speed of sound in a mixture of gases.

Any individual molecule can reach extremely high speeds when compared to the average in a gas, but the transmission of sound is not a property of an individual molecule. It is a property of a mass of molecules.
Also, check "mean free path" to get an idea of how far a molecule moves on its own compared to the mass movement in sound transmission.

Yes. I will just say we (I) have been over this ground many times on this forum with respect to kinetic gas theory. Now that we know what is possible for a molecule, extrapolate for an atom of hydrogen which has roughly a diameter of 0.5 angstroms (typical gas theory assumes a molecular diameter of 2.0 angstroms). Remember that a mean is an average and must take into account extrema. It is hardly controversial that hydrogen atoms generated in highly complex combustion kinetics could rapidly exit a cell and influence events far outside the boundaries of that cell. It is easy to forget and conflate a calculated average or mean with the idea that every element in the calculation starts at that value.

Unfortunately, this is rapidly going down a rabbit hole. It reminds me of the discussion about microscopic bubbles. You have to have a feeling for what a phenomenon's effect can be on the big picture. It requires more than just a few facts.

1 The mean free path is measured in millionths of a millimeter.
2 This means any hypersonically fast moving particle will have a hell of a time travelling "far" because of all the collisions sapping its speed and sending it in random directions.
3 This means if it is created in the flame front, it does not really leave the flame front by any measurable amount.
4 The unburned mixture is already being heated from, a) the compression alone, b) the additional compression due to the burn, c) radiant heating from the flame, d) its own "preflame reactions" that cause molecular breakdown, partial reactions and the copious production of ions of its own that would lead to self ignition if given enough time in those conditions.
5 The entrance of "a" or one or a few or a few hoards of fast particles or ions a few tiny fractions of a millimeter ahead of the flame will produce no separate effect. They are within the normal distribution. This is part of the normal propagation.

A hypersonic particle does not spread the flame faster than the speed of sound nor faster than the normal speed of the burn.

[Kevin Johnson]

Unfortunately, this is rapidly going down a rabbit hole. It reminds me of the discussion about microscopic bubbles.

Yes, that was the discussion where I pointed out that microscopic bubble collapse is a known source of ignition.

https://web.anl.gov/PCS/acsfuel/preprin ... 3_0010.pdf

This is research work from approximately 60 years ago; why you refuse to accept it is beyond my ken. See page 10 and the citation list on page 15.

Good grief, the information is still being left up on the web as a public service so people stop blowing themselves up. Instead of trying to insult me about falling down rabbit holes try reading the past research that has been performed and critique that.

...

You have to have a feeling for what a phenomenon's effect can be on the big picture. It requires more than just a few facts.

1 The mean free path is measured in millionths of a millimeter.
2 This means any hypersonically fast moving particle will have a hell of a time travelling "far" because of all the collisions sapping its speed and sending it in random directions.
...

That is a known problem with human cognition -- large and small numbers. Because something involves low probabilities ("hell of a time") does not exclude its occurrence. The very first collision could be a significant distance away. People have trouble understanding countably and uncountably infinite, for pete's sake and that is just the first two alephs.

Yes, I have brought up radiation effects before too. It just gets tiring having to repeat the information over and over.

[Nikolas Ojala]

Here is an interesting plasma ignition patent: https://patents.google.com/patent/US8555867

I think that a flathead engine, more than any other, needs an improved ignition system.

Plasma_ignition_circuit.png

Most components here are quite usual, but the high voltage diode D3 and resistor R1 enable high current pulse through the spark plug SG1.

I used yellow colour to emphasize the circuit loop C1–D2–D3–SG1–C1. That loop area should be made as small as practically possible. No ferromagnetic components should be placed inside that loop.

[Nikolas Ojala]

Sorry about the recent drawing. There was an error. The voltage source may not be the car's battery, because higher voltage is required. In this case approximately 600 volts. I corrected the drawing so that instead of a battery there is a voltage source V1.

Plasma_ignition_circuit.png

Here are few lines from the patent:

In this embodiment, a 4.7 uF capacitor is charged to 650 volts by the power source, which includes a 12 volt to 600-volt DC-DC convertor. The trigger circuit includes a 1,000 volt 35 amp SCR. The step-up transformer has a winds ratio of 1:100. A supplemental path is provided directly connecting the primary discharge side of the capacitor to the spark plug gap, through the high-voltage diode rated at 50,000 volts and one amp with a 50-amp surge.

So the capacitor will be charged to approximately 1 Joule energy.