Quote:
Originally Posted by ckau
This is some good stuff , Travis. you can definitely de-bunk a lot of myths. rumors and false claims though the use of a dyno. I have a overly simplified version of your dyno where the motor capabilities are measured through the motor's ability to produce hydraulic pressure at specified rpms. I can create a graph illustrating the motor output throughout the rpm range and horsepower is found through a math formula on a calculator. A crude but effective way to illustrate the effects of motor modifications.
You stated It's critical to tightly regulate the hydraulic temperature. I was curious as to why?
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Keeping the hydraulic temperature regulated tightly helps to reduce variation in readings. With viscosity of the fluid changing with temperature, power readings at 150° will be inconsistent from readings at 175° (even if all other variables remain the same). So temperature swings can be a big problem when testing from one engine to the next. Or even on the same run if it lasts for more than a minute or two. I'm planning on some extended torture testing, so we need to be able to balance heat in and heat out.
But accuracy aside, probably more important (safety related) is how fast the temperatures shoot through the roof when under full load. It's scary. Back before I had any cooling at all, I won't say that I ever looked up during a run and had a tank full of smoking oil. Nope, never happened.
There are some other design constraints. The pump's maximum temperature rating is 180F, so I'm considering that our max limit for the system. Right now I'm shooting for an operating range between 150° to 160°, with 155 nominal. This will probably change as I get closer to the point of needing to make a final decision on which fluid (ISO 32 or ISO 22) I'm going to run.
My current working theory is that it is best to keep the viscosity as light as possible to reduce drag in the system (which I believe will rob power at higher flow rates without being measured). The pump's manual specifies an acceptable kinematic viscosity range in centistokes from 200cSt (very thick) to 6cSt. Water is 1cSt for comparison.
So I'm going for a viscosity range of 10cST to 15cST (some margin for safety), and will code the processor to compensate the HP calculation for the small viscosity differences across the 10 degrees of temperature range. Would like to get that down to 5 degrees, but won't know until firing it up and seeing how well the cooling system works. And adding a second radiator if needed.
Thankfully, viscosity changes are (more or less) linear with temperature. I traced over the graph below to show what I'm expecting for our temperature vs viscosity over a 10 degree range.
