Question on engine oil passages...
Is anyone familiar with modeling the effects of changes in oil passage geometry and its effect of pump/filter sizing and adequate delivery to critical surfaces (bearings, cylinder linings, etc.)?
Yes, you want a flow network modeling tool. Do you have specific questions?
First, you need to get all the specs on the oil you are going to be using. Thermal properties of the oil, viscosity, molecular weight, density ect.
You would also need to know the operating temperature range of the engine. You would need to know the antcipated oil pressure throughout the rpm range, and the temperature curve thoughout the rpm range. The volume of oil retained in the passages when the engine is off is a consideration, as well as any gravitational forces that may enhance or inhibit flow from an engine off state to an engine on state.
Tribology is the science of lubrication and bearings. Lots of texts available.
Byrds book "Transport Phenomena" has a formula for just about everything, elasticity and viscoelasticity ect..as well as formula for curved tubes ect..Pick the applicible formulas and plug into your model. Segment your model into straight pipes and curved pipes and other geometric structures and assemble them into a contigous form. Plug in the thermodymanics and temperature and pressure gradients, add anticipated hydraulic effects and vapor phase effects to your model.
Any book on fluid mechanics would help, Fundamentals of Fluid Mechanics, Munson & Young.
http://epubl.luth.se/1402-1617/2007/187/LTU-EX-07187-SE.pdf an actual model
Vacuums created by flow must be considered, as well as momentum of the oil itself. If you have more than one passage, one could act as an eductor and create a vacuum. Other hydraulic effects may be present.
A centrifugal oil filter can work at 30 to 80 psi, and spins at 6000 rpm.
If you have a working protoype, you can fill it with water to get the volume, or if its a computer model you should have the volume. The pump could be mechanical or centrifugal. The filter could be conventional, or centrifugal.
Cavitation may or may not be a consideration.
The fluid in an engine is not in a static state. There may be G forces due to vehicular movement. Buoyancy may be a consideration.
Cold oil gets very thick.
Cold weather starting is a crucial consideration.
Oil coolers are a consideration. Fuel type must be taken into account. Diesels run a little hotter.
You may encounter some multiphase flow due to combustion residual gases. There may be a small amount of superheated steam.
Another consideration is the texture of the internal walls of the pump. In a custom made pump or a very small production run you can have a finely polished machined wall. However, in a mass production setting, it will be a steel casting with the texture of casting sand on the walls and machined surfaces only where required due to the cost of machining. If you can design with no machine work, that is optimal for cost reduction.
The hard part is constructing a CAD model. Mathematical input of formulas into the CFD program is the easy part.
I would start with the physical 3d dimensions, set up forumulas for those, then add flow. Then if possible add other factors, such as G loading from acceleration, braking, multiphase complications, cavitation prevention, hydraulic effects, surface wall roughness, thermodynamic effects, viscosity, types of metals involved ect.
At rest, the machine should retain eneough oil in the journals to prevent a dry, high friction stat up. You may be able to use gravitation and the weight of the oil itself to accomplish this, with a column of oil in a ready state for applied pressure and priming. I would look at oil pump patents for ideas. What worked in the past? What were the successful designs? Freepatents online..google patents. Resevoir placement and size must be considered as well.
Thanks for all that information! :o
We will be using a standard media filter for the oil and not centrifigal force.
But I will definitely take a look at the links you provided...
Thanks again to Andy for taking the time to provide all that information - apparently someone in one of my LinkedIn groups noticed his efforts as well - Bravo!
But, earlier this afternoon, I received an email from a former associate (who now works for a CFD software firm), who turned me onto a webinar related to my line of questions. I just thought I'd share it in case anyone was interested:
I will circle back to the board and let folks know if there was anything that directly addressed my project. I may even have additional questions after watching it. Thanks again!
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