Quench
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==Introduction== | ==Introduction== | ||
[[File:Squishband.jpg|thumb|350px||]] | [[File:Squishband.jpg|thumb|350px||]] | ||
| + | For this discussion, we will be using the term "'''''quench'''''" to denote the distance between the cylinder head deck and the piston deck at TDC, as well as for the overall action/effect of the combination of squish and quench. | ||
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Quench (or squish, or "squench") is sometimes referred to as ''mechanical octane''. It decreases the need for octane by promoting a more homogeneous air/fuel charge in the combustion chamber and it also helps promote flame travel. | Quench (or squish, or "squench") is sometimes referred to as ''mechanical octane''. It decreases the need for octane by promoting a more homogeneous air/fuel charge in the combustion chamber and it also helps promote flame travel. | ||
==Quench vs. squish== | ==Quench vs. squish== | ||
The terms ''quench'' and ''squish'' are often used interchangeably. But they actually have different technical meanings. Quench also refers to the passing of heat from the combustion chamber into the surrounding metal, some of which finds its way into the cooling system. The more quench that is in effect, the more heat passes into the cooling system and vise versa. On one hand, having a quench-type combustion chamber and piston shape and tight quench distance may be looked at as a detriment to power production (heat IS energy, after all). But in the case of the IC engines we are working with, the loss of heat energy is more than offset by the decrease in the tendency to encounter detonation- which will kill power at a much greater rate and amount than the loss of some combustion chamber heat to the quench effect. | The terms ''quench'' and ''squish'' are often used interchangeably. But they actually have different technical meanings. Quench also refers to the passing of heat from the combustion chamber into the surrounding metal, some of which finds its way into the cooling system. The more quench that is in effect, the more heat passes into the cooling system and vise versa. On one hand, having a quench-type combustion chamber and piston shape and tight quench distance may be looked at as a detriment to power production (heat IS energy, after all). But in the case of the IC engines we are working with, the loss of heat energy is more than offset by the decrease in the tendency to encounter detonation- which will kill power at a much greater rate and amount than the loss of some combustion chamber heat to the quench effect. | ||
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| + | ==What is squish?== | ||
| + | Squish is the name given to the turbulent mixing of the air/fuel mixture caused by the close proximity of the piston to the quench pad(s) of the cylinder head. As the piston approaches top dead center (TDC), the clearance between the crown of the piston and the quench pad of the cylinder head diminishes to about 0.040" (steel rods, aluminum rods require more distance). This squeezes or "squishes" the air/fuel mixture from the area where the piston and head are closest, to the area where the combustion chamber is located. This action creates turbulence to achieve a more homogeneous mixing of the air/fuel mixture. A quench distance of ~0.040" will allow a high performance engine to run without detonation using less octane than would otherwise be needed. Of course this is providing that all the other important areas are also covered, like the static and dynamic compression ratios, correct air/fuel ratio, correct plug heat range, good ring and valve guide seal, etc. | ||
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;From [http://www.corvetteonline.com/tech-stories/engine/ultimate-guide-to-budget-bbc-cylinder-heads-under-2000/ corvetteonline.com]: | ;From [http://www.corvetteonline.com/tech-stories/engine/ultimate-guide-to-budget-bbc-cylinder-heads-under-2000/ corvetteonline.com]: | ||
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Quench on the other hand, is the ability to lower temperature of the end gases trapped between the piston dome and head by conduction. This prevents a second flame front from igniting the air/fuel mix prematurely. Members of the SAE acknowledge that for motors with 3.5” to 4.5” cylinder bores, a quench distance of 0.035” to 0.040” work well and result in near zero clearance due to thermal expansion, rod stretch and piston rock-over. | Quench on the other hand, is the ability to lower temperature of the end gases trapped between the piston dome and head by conduction. This prevents a second flame front from igniting the air/fuel mix prematurely. Members of the SAE acknowledge that for motors with 3.5” to 4.5” cylinder bores, a quench distance of 0.035” to 0.040” work well and result in near zero clearance due to thermal expansion, rod stretch and piston rock-over. | ||
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==How to arrive at the target quench figure== | ==How to arrive at the target quench figure== | ||
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