David Schaub
Mechanical Engineering Student
Automotive Valve Lift
A valves main goal in an engine is to open and close the air inlet and the exhaust ports in the engine cylinder to complete the compression, power, exhaust and intake stroke. Valves, though introduce geometry which restricts airflow and introduces minor losses into the system. But what is the relationship between minor losses and the lift of the valve? To find the relationship between valve lift and losses induced Finite Element Analysis and experimentation in the water tunnel were used for find the losses induced by the flow and provide visualization of the flow.
Fluids Experiment
Part 1: Flow Visualization and Model Creation
The first question that needs to be asked about the valve and losses is where do the losses come from. Minor losses result from flow separation and vortice formation. Flow visualization is the ideal way to verify where separation and how losses occur with the valve. The two options to model flow is using a clear model of the valve in a water or air tunnel and using Computational Fluid Dynamics to model the system in the computer. Model testing was the first approach used to model flow through a valve.
Model limitations presented unique challenges in designing the scale model. The valve that the project was modeled around was an exhaust valve for a stock set of 906 head from a sixties to early seventies 383/440. The valve was clean and did not need to be purchased. The intake port of the model neccessitated the utilization of a clear material. When looking for a clear material that was cost effect for machining out the port, material is solid block configuration quickly was out of the projects budget. Thus, plastics that could be used for casting were considered. The project ended up utilizing acrylic with a hardener to cast the parts and 3-d printed negative of the port was printed for casting. The intake port was modeled around a typical intake port of the cylinder head with a looser radius and the square to round conversion of shape. The molded acrylic plastic block was machined,fitted and polished along with the valve lapped into the block.
With the valve and the port created, the was placed in the water tunnel. The water tunnel was chosen for model testing due to the ability to use pickline to show the flow and run the fluid at a low velocity for better visualization. The water tunnel was set a velocity of 0.16 miles per hour, the equivalent of 2.31 miles per hour. The valve lift was set at three valve lift heights to view variations in flow characteristerics.
0.150" lift
The lowest lift performed in the water tunnel. Large vortice formation in the intake port and underneath the valve.
0.375" lift
The middle lift performed in the water tunnel. Laminar flow increased. Some separation occured underneath the valve.
0.438" lift
The largest lift performed experimentally in the water tunnel. Laminar flow was similar to the mid-lift value and separation increased at the end of the valve with less turbulent flow underneath the valve.
Part 2: Computational Fluid Dynamics and Numerical Results
With a visuaization of the fluid flow the system was modeled in SolidWorks. Using Flow Simulation in SolidWorks, the model was set up as to act as a steady state system using a constant volumetric flow rate. Volumetric flow rate was calculated using a 440 cubic inch motor at a 700 rpm rotational speed. At 700 rpms,11.67 intake cycles per second occur or 0.0857 seconds per cycle. Using the 440's displacement of 4.32" diameter bore and a 3.75" stroke, each cylinder displacement per cylinder is aproximetely 55 cubic inches per intake stroke. Using displacement and cycle per second, we found that the volumetric flow into the cylinder was 641 cubic inches per second. An assuption was incorrectly made assuming that the intake stroke was a full revolution. Thus all calculation for the intake are at 350 rpm roatationall speed.
Using Computational Fluid Dynamics, the intake was set for a fully developed flow rate of 641 cubic inches per minute and the cylinder at a constant atmospheric pressure. CFD on solidworks required the setup described to run the program. The average pressure at the inlet was measured in CFD for lift values between 0.100" to 0.600" lift.
