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==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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| + | ;From [http://www.corvetteonline.com/tech-stories/engine/ultimate-guide-to-budget-bbc-cylinder-heads-under-2000/ corvetteonline.com]: | ||
| + | <blockquote> | ||
| + | While the terms “quench” and “squish” are often used interchangeably by many manufacturers, quench and squish are not the same thing, nor are they produced by the same set of conditions. The [http://www.sae.org/ Society of Automotive Engineers] (SAE) has defined squish as the gases trapped between the piston dome and head that are ejected across the combustion chamber at high speed by the near-collision of the piston dome and head, causing turbulence and mixture homogenization. For our purposes, if the squish area is too close, there is a pumping loss and if the area is too far apart there will be lower squish velocity and less turbulence. | ||
| + | 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. | ||
| + | </blockquote> | ||
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. | 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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