Quote:
Originally Posted by Ecky
I'd like to add that mean piston speed, peak piston speed, and piston speed during the first few dozen degrees after TDC (probably most important to us), will all vary based on engine geometry. An engine with a larger rod ratio (reduces sideloading and friction) will increase the dwell time at TDC (possibly good for thermal efficiency?), after which the piston will accelerate downward at a greater rate, compared with another engine that has the same bore and stroke but shorter rods.
I've never really tried to wrap my head around all of the variables at once.
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What's really fun is playing with Quench Velocity calculators and seeing how increases in quench velocity increase the turbulent burn speed and reduce the ignition timing advance required. -Quench really is "free octane booster in every tank" and the opportunity for free MPG gains, if planned for.
Right now I like the idea of being able to push the limits of cylinder pressure, both for power and fuel economy by using things like quench and tight control over air and coolant temps to eke out more power and fuel economy for more of the RPM band, anyway. (My engine has a strange aftermarket VERY long-runner version of a TPI intake and detonation around the torque peak becomes an issue, but lots of small tweaks and advanced electronic strategies can help push the peak torque and MPG a bit further.)
-I'm learning why the OEMs with DI have a huge advantage being able to use 100% of the cooling capacity of the fuel to cool the chamber- AND they can time it perfectly and stratify the charge to make for ultra lean AFRs... I'm jealous of the control they have, but I'm stuck trying to make my port injection behave as much like DI as I can.
Adam