Powertrip wrote: ↑Mon Apr 15, 2019 1:22 pm
The Toyota paper discussed a directed squish, not a tapered quench if I'm reading that paper correctly.
On page 5 in the Toyota paper, Development of Toyota 1ZZ-FE Engine (
https://drive.google.com/file/d/1hMznDx ... share_link), the authors describe the combustion chamber as a “TAPER SQUISH COMBUSTION CHAMBER – The squish area formed by the piston top and cylinder head bottom surface has been tapered by being inclined along the cylinder head combustion chamber wall (Fig. 10).”
Figure 10. Taper Squish Combustion Chamber.png
Working with the definition that taper means to reduce the thickness from one end to the other, I find it confusing when the authors say “tapered by being inclined,” because I don’t understand how angling something leads to it being tapered. Therefore, I can only assume that the squish area is tapered. To be certain, I would need to disassemble one of these engines and measure the angle of those two surfaces.
I hope that their squish area is tapered, and that the angle is deliberately selected to direct the squish towards the spark plug, because those are the two attributes of squish that hold the most promise with sidevalve engine chamber design.
Piston TDC.png
This sketch shows the piston at TDC. At 5000 rpm, with the squish area equal to 37% of the piston area, the maximum squish velocity (calculated) is about 40 m/s and occurs 8 degrees BTDC.
The squish direction is towards the valves rather than the spark plug. Changing the squish direction is not easy since it requires redesigning the head and piston.
I agree with Vannik (
memberlist.php?mode=viewprofile&u=11007), a ST forum member, that “a 1 degree taper usually leads to better results as a parallel clearance can lead to trapped end gas with piston rocking, leading to trapped end gas and more pre-ignition / detonation.” Angling the squish zone of this sidevalve chamber by one degree reduces squish velocity by about 10 percent. The reduced velocity can be made up by reducing the quench height or by increasing the squish area.
Creating turbulence in the chamber (the goal of squish) requires work. That work comes from the squished A/F mixture in the form of kinetic energy. I don’t know how much is required to achieve the desired level of turbulence. Nor do I know the desired level of turbulence. However, I am convinced that a sidevalve chamber, because of it length, requires more energy than an OHV chamber to get the job done.
Kinetic energy includes the effect of squish clearance and squish area. A tight squish (less than 0.020”) may sound impressive but the velocity stream may not have the necessary energy if the area is not considered as part of the design. Large squish areas on sidevalve engines is easy to achieve because the piston is not over the valves.
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