Conceptual wrote:Jersey Tom wrote:Conceptual wrote:I think that with some work, you could get 140hp from a 20mm restrictor...
Based on what data? There is a limit to the amount of air mass that you can pull through any sized orifice when it achieves choked flow at Mach 1. Since generally power is a function of mass flow, there is a hard limit to power you can generate.
It's been a while since I've run the numbers, and I was only a junior at the time, but I believe when I worked it out... the maximum isentropic flow rate possible through a 20mm restrictor would have been good for about 80-85hp or so.
There are FSAE teams that claim to be well into the 100+ hp range, though obviously you can generate just about whatever number you want off a dyno based on the corrections... and it's possible I didn't work it out right.
The cold output side of a medium sized vortex tube is 20mm, so I just figured that you could use a turbo charger to pressurize the tube, and shoot -30C air into the engine. I understand your math, but it the air was much colder, and more dense, wouldn't it produce more power? And since the work to compress the charge is directly related to the temperature of the charge, you may lose some parasitic loss that way as well.
I would look at the 650CC Freedom Rotary motor. It produces 75hp stock, and has a 3/4 inch air intake. Hooking the turbo/vortex tube to that should be a quick way to determine if it is a workable proposition.
Actually, I may email them to ask if they will try it themselves...
Vortex tube? Could you explain a bit further? With what power would you compress your air?
Assuming an ambient temperature of about 20C, a 20mm restrictor should be able to sustain about 9.9 lbm/min (0.71 kg/min). An efficient engine tuned well can produce about 10 HP per lbm/min of air consumed. This metric is dependent upon many variables, but from what I've seen, it's about right.
Dyno's vary wildy and results always need to be evaluated comparatively...
I've seen dyno plots of both N/A and F/I FSAE cars that produced in excess of 115 HP. I guess it would be possible to run an extremely high compression ratio to bump the 10 HP/lbm/min up a bit to achieve these sort of numbers.
The vast majority of FSAE cars make somewhere in the range of 60-70 HP, possibly due to unhealthy engines or poorly designed intake and exhaust systems.
I ran a bunch of CFD tests to revisit restrictor designs and confirmed the max mass flow rate numbers.
