question re fluid pressures and flow rates...

[zharzhay]

hello all,
I'm trying to figure out some approximate numbers, for an alternative fuel prototype. I want to use engine oil to heat my fuel. In order to engineer a heat-transfer system, I need to know the rate of flow for engine oil (I can figure out flow rate for fuel, based on mpg) and the psi of both fuel and engine oil in the lines.
Could somebody give me a ballpark number on the following?
- psi in fuel line *up to* injector?
- psi in engine oil line, downstream of oil pump?
- flow rate of engine oil?

Thank you!
Erik

[ivymike1031]

Originally Posted by zharzhay

hello all,
I'm trying to figure out some approximate numbers, for an alternative fuel prototype. I want to use engine oil to heat my fuel. In order to engineer a heat-transfer system, I need to know the rate of flow for engine oil (I can figure out flow rate for fuel, based on mpg) and the psi of both fuel and engine oil in the lines.
Could somebody give me a ballpark number on the following?
- psi in fuel line *up to* injector?
- psi in engine oil line, downstream of oil pump?
- flow rate of engine oil?
Thank you!
Erik

rough answers to your questions, assuming you're using a gasoline-fueled engine (in which case its my guess that you're wasting your time anyway):
* My guess is that you would want to know fuel pressure so that you could be sure that you're not boiling the fuel in the lines when you heat it. 30-60psi is probably going to be in the right neighborhood, but you want to be conservative vs boiling, so figure 20psi.
* I'm not sure why you care what the oil pressure is, unless you're worried about rupturing the hx tubes. Pressure downstream of the oil pump is commonly regulated by a spring-loaded valve, its worst-case peak is in the neighborhood of 5 bar for many engines (3.5 bar for lower noise engines), but you might want to pull a spec for your specific engine
* Volume flow rate of oil will depend on the engine size and oil pump size, and a host of other factors about the application. Oil flow can be roughly estimated as 6.6 cc/rev for every liter of engine displacement, but it varies significantly based on application. For a naturally aspirated gasoline engine operating at rated speed with 140hp power output, the oil flow rate out of the pump will likely be approximately 40 L/min.

[MustangRoadRacer]

the fuel pressure depends on the car.
EFI has much higher pressures than carbureted.
EFI is usually 60-70, Carb is under 10.
Oil pressure is dependant on RPM.
Idle is around 20, full throttle is 60-70, depending on the application.
Flow rate can be determined with the following formula.
flow rate = areaXvelocity.
so the size of your tubing is important.
and because pressure decreases as velocity increases, you can determine the velocity if you know the perssure.
Since Pressure = Energy/Volume, the volume is the length of the line X circumference. and Energy is what you want to determine (flow rate).
so without actually measureing your oil lines it's hard to say!
normally though, to make matters simple, the flow rate can be found by contacting the manufacturer of your pump (oil, fuel, etc)
I hope that helps, let me know if you need to know more.

[ivymike1031]

Originally Posted by MustangRoadRacer

the fuel pressure depends on the car.
Flow rate can be determined with the following formula.
flow rate = areaXvelocity.
so the size of your tubing is important.
and because pressure decreases as velocity increases, you can determine the velocity if you know the perssure.
Since Pressure = Energy/Volume, the volume is the length of the line X circumference. and Energy is what you want to determine (flow rate).
so without actually measureing your oil lines it's hard to say!
normally though, to make matters simple, the flow rate can be found by contacting the manufacturer of your pump (oil, fuel, etc)
I hope that helps, let me know if you need to know more.

ah yes, I'm sure that was quite helpful.

[MustangRoadRacer]

well I could have gone into fluid dynamics.
bernoulli equation etc.
I gave a blanket answer, for simplicities sake.

[ivymike1031]

Originally Posted by MustangRoadRacer

well I could have gone into fluid dynamics.
bernoulli equation etc.
I gave a blanket answer, for simplicities sake.

hmmm... second-year engineering student?

how about a couple of example calcs then -
- if the pressure was "70" (psi), and the cross-sectional area of the tube was 78.5mm^2, what would the fluid velocity be? (since "you can determine velocity if you know the pressure" it should be an easy one, right?)

- if the tube was round, and the circumference was 25mm, and the length was 10mm, what would the volume be?

[MustangRoadRacer]

1. velocity of fuel? which has a fluid density of 42.4,
and a viscosity of 4.95?
well, Q=VA, and leaving out velocity loss to friction, we can figure the velocity based on the pressure and length of pipe I will use 1m.
the velocity would be just about 500cm/sec
I only have the windows calculator here!

2. vol = areaX length
area = pi/4Xd^2
so, D=C/pi
C=25mm/3.14... = 7.96mm = D
63cm^3 would be the volume

[ivymike1031]

Originally Posted by MustangRoadRacer

1. velocity of fuel? which has a fluid density of 42.4,
and a viscosity of 4.95?
well, Q=VA, and leaving out velocity loss to friction, we can figure the velocity based on the pressure and length of pipe I will use 1m.
the velocity would be just about 500cm/sec
I only have the windows calculator here!

The velocity problem is indeterminate. The velocity could be zero, or 1 cm/sec, or 10cm/sec, or just about any other value for that matter. I'm not exactly sure what calculation you were performing, but it's not the right one. If you don't believe me, calculate the velocity of a fluid in a pipe with a closed end, with the pressure and area conditions I specified - it's zero. Now put a pinhole in the end of the pipe, and hold pressure constant - velocity increases, but isn't much, right? Now make the pinhole bigger, and hold pressure constant - velocity increases again, and you still haven't changed area or pressure. I could see you doing a velocity calculation given a pipe ID, length, and pressure at the inlet, dumping to atmosphere at the outlet, along with fluid properties, by calculating velocity along the pipe to give pressure drop equal to p_inlet - p_atm, but in this case you didn't have a pipe length, and you didn't seem to assume one either. What calculation were you doing?

The correct way to calculate flow at the pump outlet based on the pressure at the pump outlet, for steady-state operation, ignoring pumping effects due to rotating components, with no relief valves, ignoring changes in fluid properties (temp, visc, density, etc) within the system, is outlined thus:
* calculate a total resistance based on the flow network downstream of the point where your pressure is given (you have a branching system with many different restrictions and lots of different pipe diameters along the way)
* use your favorite pipe flow equation to calculate a flow rate based on pressure drop (given pressure - crankcase pressure) and the equivalent restriction of your flow network

It's certainly not a simple matter to model the flow network, even if you leave out heat transfer, the effects of journal bearings, etc. Normally one would use a program such as Flowmaster or Matlab to construct a model of the system, then run simulations over various rpm and engine load conditions to determine what the required pump output would be. An oil pump usually gives flow that is roughly proportional to rpm, with very little regard for pressure drop. To keep the pressure down to acceptable levels, excess pressure is vented through relief valves just downstream of the pump. The pump is sized to provide enough flow at idle.

The flow numbers I gave earlier were based on general design guidelines for gasoline engines.

Originally Posted by MustangRoadRacer

2. vol = areaX length
area = pi/4Xd^2
so, D=C/pi
C=25mm/3.14... = 7.96mm = D
63cm^3 would be the volume

That's probably right (I won't bother checking the numbers) - I was waiting for you to use the equation you mentioned earlier - you said volume was length x circumference, not length x area.

[zharzhay]

Hi you guys,
Your equation slinging looks fun, but as you would probably guess, it's a bit beyond me...
Perhaps you could consider a bit about my project:
6L turbo-diesel EFI (International)
I'm not an engineer, but I'm trying to find a way to heat an alternative fuel (vegetable oil) as hot as possible before sending it through the fuel filter and on to the injectors. Because engine oil runs about 220-240F, it would be an ideal source of heat. I am thinking about using a heat exchanger to transfer this heat from the engine oil to the fuel. I would like to put a heat exchanger in the oil line where the oil exits the engine and is theoretically hottest. The alternative fuel will run through this heat exchanger.
In order to figure out what sort of heat exchanger to use (coil or brazed plate, size, etc), I need to know the pressures and flow rates that will be involved. The reason I asked about the pressure just downstream of the pump is that I figured this will be the max pressure in the system, and I need to be sure that whatever heat exchanger I install will be able to handle the pressure.
ivymike, your note about boiling the fuel lines is something I hadn't quite thought about yet... can you recommend a hose for fuel at up to 250F? Also as I noted above, this heated fuel will pass through the fuel filter. I know other veggie-fuel users have no problems running the heated fuel through ordinary diesel filters at about 170-200F... do you think that 240F would be too hot for the filter?
I know these figures will vary with RPM and hose/pipe size, but I just need some rough figures. If this info gives you guys any ideas, I'd love to hear them.
Thanks again!
Erik

[ivymike1031]

Originally Posted by zharzhay

Hi you guys,
Your equation slinging looks fun, but as you would probably guess, it's a bit beyond me...
Perhaps you could consider a bit about my project:
6L turbo-diesel EFI (International)
I'm not an engineer, but I'm trying to find a way to heat an alternative fuel (vegetable oil) as hot as possible before sending it through the fuel filter and on to the injectors. Because engine oil runs about 220-240F, it would be an ideal source of heat. I am thinking about using a heat exchanger to transfer this heat from the engine oil to the fuel. I would like to put a heat exchanger in the oil line where the oil exits the engine and is theoretically hottest. The alternative fuel will run through this heat exchanger.
In order to figure out what sort of heat exchanger to use (coil or brazed plate, size, etc), I need to know the pressures and flow rates that will be involved. The reason I asked about the pressure just downstream of the pump is that I figured this will be the max pressure in the system, and I need to be sure that whatever heat exchanger I install will be able to handle the pressure.
ivymike, your note about boiling the fuel lines is something I hadn't quite thought about yet... can you recommend a hose for fuel at up to 250F? Also as I noted above, this heated fuel will pass through the fuel filter. I know other veggie-fuel users have no problems running the heated fuel through ordinary diesel filters at about 170-200F... do you think that 240F would be too hot for the filter?
I know these figures will vary with RPM and hose/pipe size, but I just need some rough figures. If this info gives you guys any ideas, I'd love to hear them.
Thanks again!
Erik

I was wondering whether this was a diesel or gasoline engine - some people try to heat their gasoline in the belief that it makes it burn better...

Since it's a diesel, the fuel pressure numbers I provided are probably WAY off! Is it a powerstroke that you're dealing with, or another Int'l engine?

[ivymike1031]

Originally Posted by ivymike1031

Since it's a diesel, the fuel pressure numbers I provided are probably WAY off! Is it a powerstroke that you're dealing with, or another Int'l engine?

if it is a powerstroke, the fuel pressure is probably 55-80 psi, based on a quick internet search.

Oil flow rates will be higher than I stated, because the turbo requires cooling oil (naturally aspirated engine doesn't have a turbo, of course).

[MustangRoadRacer]

Ivy mike, since you didn't mention anything about pressure drop in your equation "use your favorite pipe flow equation to calculate a flow rate based on pressure drop " the outlet pressure I used was the atmosphere, at 25 deg. celcius. 760 torr.
Of course the velocity of a pipe with a closed end would be zero, so why ask that question?
I calculated the velocity of fuel with the given pressure and given pipe area at 100 degress celcius, and a pipe length of 1m to answer your question "in this case you didn't have a pipe length, and you didn't seem to assume one either".

I am not an engineer or an engineering student, and I suppose I should have stated in the earlier posts that you need more info to go on in order to determine what he was asking, but I wasn't thinking about specifics.