Week 10: Project 1 - FULL HYDRO case set up (PFI)
AIM:
To simulate a full hydrodynamic case for a PFI IC engine.
1. To calculate the compression ratio.
2. Why do we need a wall heat transfer model? Why can't we predict the wall temperature from the CFD simulation?
3. To calculate the combustion efficiency.
4. To calculate power and torque.
5. To explain the significance of ca10 ca50 and ca90.
PROCEDURE:
A fully designed and boundary flagged PFI engine is examined on a no hydro case and now a full hydrodynamic case is to be setup.
This model is properly dignised and all the errors are minimized and boundaries are assigned as per the requirement.
Case setup has to be done carefully for spray and parcel which are highly necessary for a fuel injection case.
Case setup:
- Application type:
Crank angle based IC engine simulation
- Materials
Gas simulation - upload therm.dat form the files provided.
Parcel simulation - We just have to add a predefined liquid or fuel which is IC8H18 in our case. This will eventually auto populate all the required physical properties.
Global transport properties - default
Reaction Mechanism - upload the mech.dat file.
Species - Go to the parcels tab and add IC8H18.
- Simulation Parameters
Run parameters - Transient solver with full hydro solver simulation mode.
Simulation time parameters -
start time: -520 deg
end time: 120 deg
Solver parameters - default
- Boundary Conditions
Piston - region - combustion region
type - wall
wall motion - Translating
Surface movement - moving
Piston motion check.
Temperature - law of wall - 450k
Cylinder - region - combustion region
Type - wall
Velocity - motion type: stationary - surface movement - fixed
Temperature - law of wall - 450k
Cylindr head - region - combustion region
type - wall
Velocity - motion type: stationary - surface movement - fixed
Temperature - law of wall - 450k
Outlet - region - exhaust region
Type - outflow
pressure - specified value - 101325pa
Species backflow - co2(0.192304), H2O(0.088559),N2(0.719137) These are derived from stoichimetry equation of combustion by finding the total mass of species and dividing individual mass by total mass to get the percentage.
Inlet - region - inlert port 2
Type - Inflow
Pressure - specified value - 1bar
Temperature - specified value - 300k
Species BC - Air
Inlet port 1 - region - inlet port 1
Type - wall
Velocity - motion type: stationary - surface movement - fixed
Temperature - law of wall - 425k
Exhaust port - region - exhaust region
Type - wall
Velocity - motion type: stationary - surface movement - fixed
Temperature - law of wall - 500k
Inlet port 2 - region - inlet port 2
Type - wall
Velocity - motion type: stationary - surface movement - fixed
Temperature - law of wall - 425k
Inlet valve bottom - region - combustion region
Velocity - motion type: Translating - Surface movement - moving - Profile: Intake_lift.in
Temperature - law of wall - 480k
Exhaust valve bottom - region - combustion region
Type - wall
Velocity - motion type: Translating - Surface movement - moving - Profile: exhaust_lift.in
Temperature - laww of wall - 525k
Inlet valve angle - region - inlet port 1
Type - wall
Velocity - motion type: Translating - Surface movement - moving - Profile: Intake_lift.in
Temperature - law of wall - 480K
Inlet valve top - region - inlet port 1
Type - wall
Velocity - motion type: Translating - Surface movement - moving - Profile: Intake_lift.in
Temperature - law of wall - 480k
Exhaust valve top - region - Exhaust region
Type - wall
Velocity - motion type: Translating - Surface movement - moving - Profile: exhaust_lift.in
Temperature - law of wall - 525K
Exhaust valve angle - region - exhaust region
Type - wall
Velocity - motion type: Translating - Surface movement - moving - Profile: Exhaust_lift.in
Temperature - law of wall - 525K
Spark plug - region - combustion region
Type - wall
Velocity - motion type: stationary - surface movement - fixed
Temperature - law of wall - 550K
Spark ignitor - region - combustion region
Type - wall
Velocity - motion type: stationary - surface movement - fixed
Temperature - law of wall - 600K
Here its the end of boundary conditions.
- Initial Conditions and Events
Regions and initialization:
Combustion region - Temp: 1360k - Pressure: 185731Pa
Species - pull from boundary - outlet
Inlet_port_1(close to combustion region) - Temp: 390K - Pressure: 1bar
Species
IC8H18 - 0.025508
O2 - 0.020157
N2 - 0.77292
Inlet_port_2 (away from combustion region) - Temp: 370K - Pressure: 1bar
Species - Air
Exhaust_region - Temp:300K - Pressure: 1 bar
Species - pull from boundary - outlet
Events:
Cyclic - 1. events by regions - regionA(inlet_port_1) - region B(combustion region) - event valve
2. events by regions - regionA(exhaust_region) - region B(combustion region) - event valve
Permanent - event by regions - Region A(inlet_port_1) - RegionB(inlet_port_2) - event open.
6. Physical Models
Spray modeling -
General - Turbulent dispersion: O'Rourke model
Use evaporation model - species: IC8H18
Injectors - add an injector and click on edit
Injected species - IC8H18
Models - Kelvin-Helmholtz model, Rayleigh-Taylor model, Discharge coefficient model.
Time/temp/tke/eps/mass/size - Injection temporial type: cyclic
cyclic period: 720 deg
start of injection: -480deg
Injection duration: 191.2deg
Mass: 3e-5kg
Nozzles - create 4 nozzles and their location are
Nozzle 0
center 0.0823357 0.00100001 0.07019
Align Vector -0.732501 0.210489 -0.647408
Nozzle 1
center 0.0823357 -0.00099999 0.07019
Align Vector -0.732501 -0.210489 -0.647408
Nozzle 2
center 0.0823357 -0.0004 0.07019
Align Vector -0.5 -0.2 -0.647408
Nozzle 3
center 0.0823357 0.0003 0.07019
Align Vector -0.5 0.2 -0.647408
Combustion modeling -
Model: SAGE
General: Fuel - IC8H18
Temporal output - cyclic
Cyclic period - 720 deg
star time - -482 deg
end time - 131.3 deg
Turbulence modeling - RNG k-e
Source/Sink modeling - create 2 energy sources both with max temperature of 50000k and start time of -15deg. end time for one source is -14.5deg and for the other one it is -5deg. Both have a same energy value of 0.02J.
7. Grid control
Base grid - 0.004m
Adaptive Mesh Refinement - maximum cells 1500000
Make cylinder and intake system2 active.
Use velocity and temperature AMR with 1m/s SGC and 2.5 SGC respectively.
Fixed embedding - 1. type: boundary - ID: exhaust_valve_angle - mode: permanent - scale:3 - embed layers: 1
2.type: boundary - ID: intake_angle - mode: permanent - scale:3 - embed layers: 1
3.type: sphere - mode: cyclic - scale:4 - Period: 720 deg - start time: -16deg - end time: 0 deg. - coordinates: -0.0034 0 0.0091 radius 0.003.
4.type: sphere - mode: cyclic - scale:5 - Period: 720 deg - start time: -16deg - end time: 0 deg. - coordinates: -0.0034 0 0.0091 radius 0.001
5. type: injector - mode: cyclic - period: 720deg - start time: -485deg - end time: -265deg - injector ID: Inhector 0 - radius 1: 0.002 - radius 2: 0.004 - length: 0.015m
6. Type: cylinder - mode: permanent - scale:2 - coordinates:(0,0,0.1)(0,0,-0.2) radius: 0.06m
8. Output/Post-Processing
Post variable selection - default
Output files - default
end of case setup.
Compression ratio calculation:
C.R = displacement volume/clearance volume
The values can be found from volume graph
Vd+Vc = 0.000574219 m^3
Vc = 5.7035e-5 m^3
Compression ratio = 10.067
Why do we need a wall heat tranfer model?
The efficiency of an IC engine plays a major role and heat loss through the walls due to high temperature when spark is ignited reduces the engine performance. It is likely to utilize that heat or energy from the combustion to improve engine efficiency which is where the wall heat transfer model coms into play. The heat loss calculation is tough which makes it difficult to predict the loss of energy which should be given to crankshaft but is been unused. This also affects the amount of pollutants in the exhaust because the loss of heat results in the improper combustion which leads to formation of NOx.
It is applicable to take the data from a CFD solution when the walls are perfectly adiabatic but in real situation it is not the case. The temperature of the fuel inside the chamber varies in less than a second while the surface of the walls take time so here the walls are not adiabatic. In some cases we can say that the fluid when undergoes mesh generation the walls of the mesh have to provide the boundary conditions which make it feasible and practicle because the heat loss is non uniform through out the engine hence predicting the heat transfer from a wall through a CFD simulation is not a right solution.
Combustion efficiency:
combustion efficiency is calculated from heat released, mass of fuel injected and calorific value of fuel.
HR = 1241.09 J
m = 3e-5 kg
Qhv = 44400KJ/Kg
η = 1241.09/(3e-5 * 44400 *10^(3))
=> η = 0.9317 = 93.17%
The combustion efficiency of this PFI engine is 93.17%
Power and torque calculations:
we require engine performance charaters
Work: 468.646 Nm
Duration: 240.199 Deg
RPS: 50
Therfore time = 0.01334 secs
Hence,
Power = work/time = 468.646/0.01334 = 35.13 KW
P = (2*π*N*T)/60
=> T = 60*P/(2*π*N)
=> T = (60*35.13*10^(3))/(2*3.14*3000)
=> T = 111.8789 N.m
Significance of ca10, ca50 and ca90?
This providdes us the information to know how much fuel is being burnt at different crank angles, which eventually makes us clear if we are left with extra fuel inside the chamber which is being unburnt.
From the above data
at 6.837 deg of crank angle 10% fuel is burnt
at 18.4623 deg of crank angle 50% of fuel is burnt
at 31.701 deg of crank angle 90% of fuel is burnt
RESULTS:
Mesh:
Link of animation: https://youtu.be/xSLQoH2NcTE
Cell count:
The adaptive mesh refinement and fixed embedding keep changing the amount of cell density for a precise results. we can see that the cell count after zero degree is rising at a high rate due to combustion process.
Pressure:
The pressure is very high when the compression stoke takes place which is visible here.
Mass injection:
link: https://youtu.be/Iy1gIs5VK1s
Pollutants:
Mean temperature:
temperature link: https://youtu.be/RuSmQubu2rY
PV diagram:
CONCLUSION:
The full hydro case is being setup and engine performance parameters are obtained. The required parameters like torque power efficiency are calculated. We can also see the fuel film in the intake port which can be reduced by reducing the end time for the injectors which will reduce the fuel left in the ports.