Quench pad area ratio?

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BradH
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Quench pad area ratio?

Post by BradH »

Are there quench pad area ratio guidelines for 2-valve inline heads? I'd expect there is a point where the quench pad area becomes a large enough % of the bore's total area that it is detrimental, but haven't been able to find anything on this subject from basic online searches. Thanks - Brad
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MadBill
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Re: Quench pad area ratio?

Post by MadBill »

Member David Redszus has a lot of knowledge on this subject. If he doesn't notice this thread you could PM him.

Also, a 'Search' for Squish/Quench ratio yields 17 hits. (18 counting this one...)
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.
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Re: Quench pad area ratio?

Post by BradH »

Thanks, I'll see what I can find here, too.
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Stan Weiss
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Re: Quench pad area ratio?

Post by Stan Weiss »

Remember in the end it is what is the correct (max) squish velocity for a given combination of parts and usage that counts. Squish bore ratio is just one of a number of specs used to calculate squish velocity and the point (degree BTDC) where it happens.

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Re: Quench pad area ratio?

Post by BradH »

Are there any online calculators for squish velocity, etc. for 4-stroke engines? All I've found in my brief search this morning were for 2-strokes.
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Stan Weiss
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Re: Quench pad area ratio?

Post by Stan Weiss »

Maybe David Redszus will see this and join the discussion.

From the way I look at squish velocity those 2 stroke calculators should work fine for a 4 stroke engine.

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Re: Quench pad area ratio?

Post by David Redszus »

Stan Weiss wrote: Sat Apr 27, 2019 11:41 pm Remember in the end it is what is the correct (max) squish velocity for a given combination of parts and usage that counts. Squish bore ratio is just one of a number of specs used to calculate squish velocity and the point (degree BTDC) where it happens.

Stan
Stan is quite right. Simple squish is complex. :)

Squish velocity (measured as m/s) is a function of;
vertical clearance at each crank angle,
squish area ratio (%),
and piston velocity (m/s).

For most engines the peak squish velocity occurs at about 10 deg BTC and also at about 10 deg ATC. Squish velocities in excess of 40 m/s are rarely seen.

Squish velocity will affect flame speed and must be evaluated along with ignition timing in order to position peak combustion pressure angle correctly. A high squish velocity will allow a delay in ignition timing. A delayed ignition firing angle but faster flame velocity reduces the amount of negative work due to premature combustion pressure rise.

In addition to the squish area ratio, the shape of the squish band has an effect on the direction of the squish flow. A symmetrical squish band produces a flow pattern directed toward the center of the piston and is uniform circumventially. This is the case with most all two stroke engines.

With four stroke engines, the squish area may be offset or even quite irregular (wedge, bathtub, etc) in shape. As such, the squish flow pattern may produce a tangental or rotational swirl flow pattern. It may also blow the flame kernal off the spark plug electrode if excessive and impropely aimed.

The complexities of squish are described very well by Heywood, Principles of Internal Combustion, P 353.
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