Flow bench Calibration using a comparative numerical study over a tangential and a helical intake port.

Aim: To compute the effects of varying valve lift in a tangential and helical intake port by noticing the parametric change in mass flow rate, pressure drop, and fluid (Air) flow velocity. Also establishing the results grid independence by comparing the results for three different levels of grid refinement.

Abstract:

While the development of a new highly efficient internal combustion engine requires a thorough investigation of fluid dynamics processes. The study of engines nowadays has been looked for improvement of efficiencies such as volumetric efficiency, fuel efficiency, and overall exhaust emissions. [1] All of this earlier was carried out using experimental techniques like dynamometric, Static flow tests, and Optical techniques which required a lot of time and money (also the scope of research was limited to low-speed engines). It didn’t even allow access to the entire combustion chamber at one time. With an increase in computation power and employment of 3D CFD techniques, Internal Combustion Engines are designed for improving combustion stages, improve the magnitude of premixed burn, reducing ignition lag, and exhaust efficiency. In this study, identical intake ports (Tangential & Helical) of similar dimensions are studied for parametric changes in mass flow rate, pressure drop, and flow velocity in the cylinder for varying valve lift in both the intake configuration to make a comparative numerical study.

Introduction:

Modern-day engines are required to supply energy demands in a short duration of combustion more frequently than ever. Since burning rates are dependent are influenced by in-cylinder gas velocities, often swirl or tumble motions generated during intake strokes to increase the burning rates at given engine speeds and Energy demands or power extracted from an engine also depends on a volumetric efficiency of the engine `eta_v =` (Actual mass air that is drawn into the engine cylinder)/(Ideal mass of air that can be drawn into the engine cylinder)

However, these two requirements are conflicting or inverse in nature. So, the challenge that a design engineer faces is to a trade-off between according to engine types. Modeling the intake system, predicting both intake flow and the in-cylinder flow field, provides a general guideline for the development of intake ports. So, two identical ports are designed

1. Tangential Port (increases the volumetric efficiency)
2. Helical Port (increases tumble and swirl during induction)

Since the main objective of work is the measurement and CFD simulation comparison of intake valve discharge coefficient, it is important to have a precise valve lift data of the flow bench. The figure below shows Engine valve lift vs crankshaft angle(degrees) [1]

To make results from different experimental conditions comparable, in this study, valve lift and inner valve seat diameter ratio are considered dimensionless values: `frac{L_v}{D_v} =`Valve lift/Valve Diameter.

`C_d`(Discharge coefficient) and `C_f`(flow coefficient) are used to define the fluid dynamic efficiency of the intake system. [1]

Formulas for the `C_d`(Discharge Coefficient) is presented by [2]

`C_d =``frac{Experimentalmass flowrate}{Theoreticalmass flowrate}`

Theoretical mass flow rate = `frac{A_ref *C_d * P_te}{sqrt(R*T_te)`*`frac{P}{P_te}^frac{1}{gamma}`*`{frac{2*gamma}{1-gamma}[1 - (frac{P}{P_te})^frac{gamma - 1}{gamma}]}^0.5`

where `P_te =`Intake port pressure

R = Ideal gas constant

`T_te=`Intake Port temperature

`gamma =`ratio of specific heats

`A_ref =`Reference Area

P = Outside Pressure

There is a different `A_ref` in consideration for `C_d`(discharge coefficient) & `C_f`(flow coefficient).

• `A_ref`for `C_d`(discharge coefficient) is called ‘curtain area’ (a region where the mass flow rate is free to pass & grows with the displacement of the valve) = `pi*D_v*L_v`
• `A_ref`for `C_f`(flow coefficient) = `frac{pi*D_v^2}{4}`

The intake port has been lengthened to guarantee a fully developed fluid flow & avoid errors of calculation.

It is seen that as valve lift increases `C_f`(flow coefficient) increases whereas `C_d`(discharge coefficient) decreases for values of `frac{L_v}{D_v} > 0.15`

Particularly for low valve lift, the flow remains attached to the valve seat & head. (Due to high viscous phenomena). When the curtain area increases or high valve head.

As we have seen, it is difficult to improve flow coefficient & swirl intensity in port simultaneously because of the contradiction between them. However, this can be achieved by reducing pressure loss in port.

In steady flow test, `DeltaP`(pressure drop) between pressure before & after test bench procedure can be divided into three parts:

• Axial Kinetic energy in cylinder = `frac{rho*(V_a)^2}{2}`
• The kinetic energy of swirl = `frac{rho*(V_tau)^2}{2}`
• Flow resistance = `deltaP`

`DeltaP = rho*frac{(V_a)^2+(V_tau)^2}{2} + deltaP` - (i)

If pressure drop before & after test bench procedure is used to create theoretical discharge velocity `V_o`(without any loss), the `DeltaP = frac{rho*(V_o)^2}{2}` – (ii)

Comparing eqn (i) & (ii)

`1 = (frac{(V_a)}{(V_o)})^2 + (frac{(V_tau)}{(V_o)})^2 + (frac{2*deltaP}{rho.(V_o)^2})`

`V_a = frac{A*C_f*V_o}{pi*D*L}`

`V_tau = frac{B*N_r*V_o}{4*D*n}`

Where, B = Bore of the engine cylinder

`C_f` = Flow coefficient

`N_r` = Swirl intensity

`A` = Area of intake valve

`L` = Height of valve lift

`n`= No. of Intake valves

So, it is seen that increasing the turbulence level, the discharge coefficient of inlet valves decreases and so does the engine volumetric efficiency. [3]

· Related Terminologies to Flowbench:

Flowbench - A flow bench is an appliance that produces a difference in air pressure across a bounded path producing air movement through the path. The volume of air that is moving through the bounded path is measured to the differential pressure across the path. [4]

Settling chamber - In a flow bench, a settling chamber is a box inline with airflow that allows the air to expand. When airflow can expand, the air movement slows down. This is useful for measuring static pressure and for introducing air into a measuring orifice. [4]

Discharge port - In a flow bench, a discharge port is the opening, usually in the top of the flow bench, where the test piece is located for flow testing. Air is drawn through the discharge port to create a pressure differential across the test piece, causing airflow through the test piece. [4]

Cylinder Bore Adaptor - For a flow bench, a cylinder bore adaptor simulates the cylinder of an internal combustion engine while flow testing cylinder heads. The cylinder affects the flow of a cylinder head, so it is useful to simulate the effects of the cylinder to the cylinder head while flow testing. Some heads may experience more or less flow with different sized cylinders. You should never assume a larger cylinder will increase flow in a cylinder head, and that a smaller bore will restrict flow. [4]

WC means or Inches of Water Column - Inches of Water Column is a unit of measure for measuring pressure. 1 inch of the water column is the amount of pressure that is required to move a column of water 1 inch. [4]

Turbulence is the only effective way of mixing air and fuel inside the combustion chamber in a direct injection(DI) system. The inlet manifold configuration affects the turbulence of fluid inside the cylinder. There are only two types of turbulence flow recognized:

1. Swirl – Swirl is defined as the large scale vortex in the in-cylinder fluid with the axis of rotation parallel to the piston axis [5]
2. Tumble – It is formed about the circumferential axis near the edge of the clearance volume in the piston crown or in the cylinder head, which is caused by squishing of the in-cylinder volume as the piston reaches near TDC. It is created in the axis of rotation not parallel to the piston axis.

· Objective: To plot a graph of discharged mass flow rate with increasing valve lift in both the tangential intake port and helical intake port. By taking an observational difference in pressure drop, velocity profiles, and flow trajectories. It would concur with the analysis of design and performance differences done on intake ports previously.

Simulation Setup:

• Designing of Tangential Port

1. Sketch an engine cylinder with radius – 100mm, Extrude the body by 80mm
2. Now draw a circle of 10mm from the origin at 25mm distance away with angle 45degrees from the baseline axis.
3. Create a plane perpendicular to the cylinder surface passing through the circle center. Create a perpendicular line on this plane that defines the height of the intake port while now at an inclination of 10 degrees to this line in perpendicular from the parallel axis to the cylinder surface. [3]
4. Create a plane at the runner line to now create the geometry for the intake port diameter of 15mm.
5. Use the Sweep/Boss base to create a solid pipe and now apply the shell tool to the inlet face & cylinder by 1mm to create a hollow pipe.
6. Create an axis of the pipe near the valve opening. Use revolve boss/base to create a geometry of valve with such dimensions shown in the figure.
7. Now your geometry is ready for analysis. Create lids at the inlet of intake port and the discharge end of the cylinder to have a water-tight geometry.
8. Now use the Wizard tool to set up the internal flow simulation, with air being the chosen fluid.
9. Now give Boundary conditions to the inlet of the intake port of total pressure to 1.5 bar pressure and Discharge outlet lid of the engine cylinder with a static pressure of 1 bar.
10. Set Global goals and surface goals of mass flow rate. Now set mesh refinement and local mesh refinements (near the in-pipe flow of valve head and valve seat areas)
11. Now create Pressure Cut Plot, Velocity cut-plots, and Flow trajectories using the planes on the axis plane.
12. Now start a new parametric study using the valve lift dimension as an input variable, setting output goals of all the cut-plots and flow trajectories, and SG mass flow rate.

• • Designing of Helical Port
  1. Sketch an engine cylinder with radius – 100mm, Extrude the body by 80mm
  2. Now pin-point a point from the origin at 25mm distance away with angle 45degrees from the baseline axis.
  3. Create a perpendicular plane to the point such that its perpendicular to the cylinder surface and sketch a runner line of 2mm.
  4. Now create a plane at the endpoint of this runner line such that it is parallel to the cylinder surface.
  5. Sketch a circle on this newly created plane of Diameter – 15mm and use the helix tool to define the angle of start(270 degrees).
  6. Use convert entities tool at the helix curve. Now use this converted entity curve and endpoint of runner line to make them coincident to each other.
  7. Finally, draw a 3D sketch runner line to the endpoint of this converted entity helical curve such that it is at 10 degrees from the cylinder face parallel. Then use the composite curve command to make all three lines and curves into one composite curve.
  8. Create a plane at the endpoint of the runner line in this composite curve.
  9. Sketch a circle of diameter – 15mm and use sweep boss/base command using the circle and composite curve as a guide curve to create a solid pipe.
  10. Now use the shell tool to create a hollow dimension of pipe with 1mm thickness.
  11. Use the fillet tool to get more curves out from the sharp edges.
  12. Create an axis of the pipe near the valve opening. Use revolve boss/base to create a geometry of valve with such dimensions shown in the figure.
  13. Now your geometry is ready for analysis. Create lids at the inlet of intake port and the discharge end of the cylinder to have a water-tight geometry.
  14. Now use the Wizard tool to set up the internal flow simulation, with air being the chosen fluid.
  15. Now give Boundary conditions to the inlet of the intake port of total pressure to 1.5 bar pressure and Discharge outlet lid of the engine cylinder with a static pressure of 1 bar.
  16. Set Global goals and surface goals of mass flow rate. Now set mesh refinement and local mesh refinements(near the in-pipe flow of valve head and valve seat areas)
  17. Now create Pressure Cut Plot, Velocity cut-plots, and Flow trajectories using the planes on the axis plane.
  Now start a new parametric study using the valve lift dimension as an input variable, setting output goals of all the cut-plots and flow trajectories, and SG mass flow rate.

Results & Analysis:

• To establish a grid dependency test, the study has been made to simulate over three different grid refinement levels(3,4, and 5) at a 4mm valve lift in both the intake ports.

Tangential Intake Port

Tangential Intake Port Pressure Cut-Plot at grid refinement level – 3	Tangential Intake Port Velocity Cut-Plot at grid refinement level – 3
Tangential Intake Port Pressure Cut-Plot at grid refinement level – 4	Tangential Intake Port Velocity Cut-Plot at grid refinement level – 4
Tangential Intake Port Pressure Cut-Plot at grid refinement level – 5	Tangential Intake Port Pressure Cut-Plot at grid refinement level – 5

Helical Intake Port

Helical Intake Port Pressure Cut-Plot at grid refinement level – 3	Helical Intake Port Velocity Cut-Plot at grid refinement level – 3
Helical Intake Port Pressure Cut-Plot at grid refinement level – 4	Helical Intake Port Velocity Cut-Plot at grid refinement level – 4
Helical Intake Port Pressure Cut-Plot at grid refinement level – 5	Helical Intake Port Pressure Cut-Plot at grid refinement level – 5

Note: As it is seen from the grid refinement levels that at 5 the accuracy of the Cut-Plots increases but so does the computation time.

• Comparison of Tangential and Helical Port.

• Tangential Intake Port

Case – a When the Valve Lift is 1mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – b When the Valve Lift is 2mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – c When the Valve Lift is 3mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – d When the Valve Lift is 4mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – e When the Valve Lift is 5mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – f When the Valve Lift is 6mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – g When the Valve Lift is 7mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – h When the Valve Lift is 8mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

• Helical Intake Port

Case – a When the Valve Lift is 1mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – b When the Valve Lift is 2mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – c When the Valve Lift is 3mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – d When the Valve Lift is 4mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – e When the Valve Lift is 5mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – f When the Valve Lift is 6mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – g When the Valve Lift is 7mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

Case – h When the Valve Lift is 8mm

Pressure Cut-Plot	Velocity Cut-Plot
Flow Trajectories

• Comparison of Mass Flow rate discharged from both intake system configuration

Mass flow rate discharged in Tangential Intake Port

Mass flow rate discharged in Helical Intake Port

Note: As the charge flows out of the cylinder body, this graph shows a declining negative graph. Otherwise the mass flow rate increases with an increase in valve lift

Conclusion:

It is seen in both the intake port configuration cases that as the valve lift increases it can be deduced from (Pressure Cut-Plot) that pressure decreases(due to the increasing distance between the valve opening and cylinder and it is seen maximum at valve lift – 1mm) and from Velocity Cut-Plot it is seen that the velocity is increasing(which is seen maximum at the valve lift - 8mm). At high pressures, the flow trajectories show that there is a more swirling effect of flow in the cylinder which reduces with an increase in the valve lift.

If the Valve lift increases the values of the coefficient of C_f increase and C_d decreases. This statement holds true for the values of range L_v/D_v > 0.15 [1]. Whereas As the C_f increases it causes effect in-cylinder motion which reduces the combustion stability(increasing turbulence level) which reduces C_d decreases and hence the Engines Volumetric efficiency decreases. [6]

The mass flow rate seems to be drastically be increasing till 5mm of valve lift after that it becomes almost constant with very minute changes in mass flow rate discharged in both the intake ports. This is due to the reduced flow resistance offered by the valve as the valve lift increases causing charge to move freely in the cylinder.

The volumetric efficiency and burn rate of the design can then be determined from mass and angular momentum flux. But due to their inverse nature, its seen from the mass flow rate discharge graph that the Tangential Intake port has more engine volumetric efficiency(more mass flow rate discharged) but Helical Intake Ports have more swirl and tumble in their flow.

References

[1]	R. B. R. d. Costa, R. L. Franco, C. A. G. Júnior, R. d. O. A. Coelho and R. M. Valle, "Experimental Methodology and Numerical Simulation of Intake Valves Discharge Coefficients for a Single Cylinder Research Engine," SAE TECHNICAL PAPER SERIES.
[2]	J. B. Heywood, Internal Combustion Engine Fundamentals(Second edition), McGraw-Hill, 1988.
[3]	Z. Lu, T. Wang, X. Li, L. Li, and G. Zhang, "Parametric Design of the tangential intake port in diesel engines," Journal of Automobile Engineering.
[4]	[Online]. Available: http://www.flowperformance.com/faq.html.
[5]	R. Ramachandra and V. Pandurangadu, "PERFORMANCE OF IC ENGINE BASED ON SWIRL INDUCTION BY USING CFD," International Journal of Engineering Research and Science & Technology, vol. 5, p. No. 3, 2016.
[6]	G. Fontana, E. Galloni, R. Palmaccio, L. Strazzullo, and G. Vittorioso, "Development of a New Intake System for a Small Spark-Ignition Engine. Modeling the Flow Through the Inlet Valve," SAE TECHNICAL PAPER SERIES.
[7]	"Blog - CAESES (Intake Port Design)," [Online]. Available: https://www.caeses.com/blog/2018/intake-port-design/.
[8]	"Wikipedia," [Online]. Available: https://en.wikipedia.org/wiki/Air_flow_bench.