Week 10: Project 1 - FULL HYDRO case set up (PFI)

Aim:

• To study the port fuel injection engine performance characteristics by setting up the combustion and spray modeling and post process the results.

Port fuel Injection:

An internal combustion engine (ICE) is a heat engine where the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is applied typically to pistons,turbine blades, rotor or a nozzle. This force moves the component over a distance, transforming chemical energy into useful mechanical energy.

With gasoline port fuel injection, the air-fuel mixture is prepared in the intake manifold and fed to the cylinder for combustion. Fuel injectors are essential for the mixture generation because they prepare the fuel for combustion in the engine. The fuel injectors mounted on the fuel rail continuously dose the required fuel quantity into the intake manifold according to the spray pattern and with highest precision.

Gasoline engines require an ignition spark in order to burn the air-fuel mixture in the engine cylinder. This spark is produced by the spark plug. The required high voltage is provided by the ignition coil. To do so, it transforms the electrical energy from the battery into an ignition voltage and provides this voltage to the spark plug at the ignition point

Spray Setup:

CONVERGE has two types of liquid injection parameters: nozzles and injectors. An injector is a group of nozzles. In CONVERGE you can set up local coordinate systems, which help you intuitively configure and manipulate the geometry of the nozzles within an injector. In applications such as internal combustion engines, the fuel spray initiates, propagates, and dissipates very quickly and on a very small spatial scale. To dynamically capture the important physics of the injection process, you need a high-density grid around the spray. However, you do not need high resolution far from the spray or before fuel is injected. Our automated Adaptive Mesh Refinement (AMR) technology provides the resolution you need exactly when and where you need it: in spray cases, near the injector and along the path of the spray. The combination of AMR and powerful spray models makes converge uniquely suited to helping you achieve grid convergent results in a timely manner.

Fuel injection:

The combustion process can be strongly affected by the exact nature of the fuel spray: droplet velocity, size, distribution, and physical attributes. CONVERGE allows you to tailor the degree of accuracy of the fuel injection simulation to the needs of your particular study. You can analyse the injection of liquid fuel via physical models for blob injection, injection distribution, variable rate-shape, discharge coefficient, and hollow cone and solid cone sprays. You can generate an accurate prediction of fuel mass flow through the nozzle head with appropriate use of these models. CONVERGE can also simulate the mixing and evaporation of multi-component fuel sprays.

Ring Triangles:

• The ring triangles are created to make sure the only values are moved not the deformation of inflow manifold.

Disconnect Triangles:

• In an actual engine, periodically the port and valves are in contact which prevents the flow between these parts of the engine. To control the flow while avoiding the intersecting triangles converge adds or removes virtual triangles (Disconnect Triangles).
• In an IC engine CONVERGE uses the Concentric cycle disconnection to control the flow between the cylinder and the port regions.
• When the disconnected triangles are created correctly, then you will not have any intersection errors.

Procedure:

Import the geometry into the converge studio workbench and run the diagnosis tool we can find a lot of errors like open edges, Intersections, Normal orientation and Non manifold edges. In the below image you can observe the errors what we get

• After done all the repairs in the geometry and then run the diagnosis tool then we can find no errors i.e. we sort out all the errors in the geometry and ready for the simulations done on this. In the below image we can see that the error free dialogue box

Boundary Flagging:

• In this geometry there are various parts and we can name and arrange the all parts in the sequential manner. The below image shows the all parts for the geometry and also shows the boundary flagging for the geometry.

Case Setup:

• Application Type: Crank angle based IC engine

• Go to materials and Enable the Gas simulation, parcel simulation and the Reaction mechanism
• Make the defaults valves in the gas simulation and in the parcel simulation add the liquid parcel as a IC8H18 and click ok
• Global transport parameters keep the default values.
• Reaction mechanism add the file of mech.in and then we get all the species that are required for the simulation.

• In the Species add in the parcel simulation as IC8H18 and also the passive intake, cylinder, exhaust, Soot and NOX and the Schmidt number for all is 0.7800

Simulation Parameters:

• In run Parameters the solver we used is Transient and type as Crank angle based engine simulation and then remaining should be default values.
• In simulation time Parameters the start time = -520 degrees, end time=120 degrees, initial time step=5e-07 sec, minimum time step=1e-08 sec, maximum time step=2.5e-05 sec and collision grid time step multiple 1e+28 and put the remaining values default.
• In solver parameters the solver should be Density based solver

Boundary Conditions for the geometry:

Regions and initialization:

Events:

• CONVERGE uses events to active or deactivate the disconnect triangles, which control when and where flow between regions is allowed. An OPEN event deactivates the disconnect triangles and thus allow flow between the specified regions. A CLOSE event activates the disconnect triangles and thus prohibits flow between the specified regions. When disconnect triangles are activated, they act as a SYMMETRY boundary condition.
• The Events must be CYCLIC, SEQUENTIAL, PERMANENT, or NO_DIS_TRIANGLES
• In this we used the Event as Cyclic which is shown below

Physical models:

• In the physical models enable the Spray Modeling, Combustion Modeling, Turbulence Modeling and Source/Sink Modeling

Spray Modeling:

Accurate spray and turbulence modelling is critical for predictive diesel and gasoline combustion simulations. In order to obtain results that are the realistic as possible, converge contains a wide variety of spray and turbulence modeling options. Converge includes both Reynolds-Averaged Navier Stokes (RANS) and large Eddy Simulation(LES)turbulence models. For spray, converge contains a host of options to simulate injection, breakup, vaporization and other spray related processes. All of the spray and turbulence models in Converge are well validated and powerful.

The liquid and vapor penetration lengths (LPL and VPL) are two of the properties that characterize a spray. CONVERGE calculates both quantities for each nozzle at each timestep.
To measure the LPL, CONVERGE first calculates the total mass of the liquid parcels from the nozzle and then multiplies this mass by the liquid penetration fraction to yield the
penetrated spray mass. Starting from the center of the nozzle hole, CONVERGE sums the mass of the liquid parcels until it reaches the penetrated spray mass. This distance is the
LPL. CONVERGE reports the LPL for penetration fractions of 0.90, 0.95, 0.97, and 0.99 in spray_ecn.out. Additionally, you specify a liquid penetration fraction, penet_frac, in spray.in.
CONVERGE writes the corresponding LPL to spray.out.
Figure shows a schematic of the LPL with penet_frac set to 0.98.

To measure the VPL, CONVERGE requires two parameters in spray.in: the vapor penetration fraction, vapor_penet_frac, and the penetration bin size, penet_bin_size. For
each cell inside the spray cone, if the mass fraction of fuel vapor in the cell exceeds the vapor_penet_frac and if the cell size does not exceed the penet_bin_size, CONVERGE
calculates the distance from the center of the nozzle hole to the center of the cell. The largest of these distances is the VPL, which CONVERGE writes to spray_ecn.out. We
recommend a penet_bin_size of at least twice the size of the cells in the spray cone.

Combustion Modeling:

CONVERGE’s SAGE detailed chemistry solver uses local conditions to calculate reaction rates based on the principles of chemical kinetics. This solver is fully coupled to the flow solver, but the chemistry and flow solvers parallelize independently of one another, which speeds up the simulation. With the appropriate mechanism, the SAGE solver can predict a wide range of cases (e.g., a variety of fuels [premixed, non-premixed, partially premixed, multiple fuels], emissions modeling, and unique phenomena such as end-gas auto-ignition). With its accuracy and robustness, Converge can perform predictive modeling instead of merely confirming experimental results.

• In combustion modeling the general the fuel species name=IC8H18 and under relaxation for steady state combustion is =0.25
• Temporal type=Cyclic
• Cyclic period=720 degrees
• Start time=-482.0 degrees
• End time=131.3 degrees
• Region =Not region independent
• Combustion temperature cut off =600
• Minimum HC species mole fraction=1e-10

Turbulence Modeling:

Source/Sink Modeling:

• Two energy sources i.e. Spark plug and its terminal. This the source energy in the equation responsible for the increase of the temperature pf species.
• The dimensions of the sphere are (X=-0.003,Y=0,Z=0.0091) along with the sphere radius is 0.0005 m

Grid Control:

• The base grid mesh we used in the simulations as dx=dy=dz=0.004 m

Adaptive mesh refinement (AMR):

• In numerical analysis, adaptive mesh refinement(AMR) is a method of adapting the accuracy of a solution within certain sensitive or turbulent regions of simulation, dynamically and during the time the solution is being calculated. When solutions are calculated numerically, they are often limited to pre-determined quantified grids as in the Cartesian plane which constitute the computational grid, or 'mesh'. Many problems in numerical analysis, however, do not require a uniform precision in the numerical grids used for graph plotting or computational simulation, and would be better suited if specific areas of graphs which needed precision could be refined in quantification only in the regions requiring the added precision. Adaptive mesh refinement provides such a dynamic programming environment for adapting the precision of the numerical computation based on the requirements of a computation problem in specific areas of multi-dimensional graphs which need precision while leaving the other regions of the multi-dimensional graphs at lower levels of precision and resolution.
• In our simulation we used the velocity and temperature based sub grid criterion of three embedding level and the sub grid criterion as 1 and 2.5 in cylinder region and Intake port 2 region. So Converge checks the temperature and velocity property provided in the AMR and refines the mesh of the both property between the consecutive grid is more than the defined SGS valve.
• The formula used by the AMR to refine the mesh

Fixed embedding:

• Embedding is provided to refine the grid mesh size at the specified locations to improve the accuracy of the solutions. An embedding is given for the spark plug in the combustion chamber which enables the combustion process.
• Use fixed embedding to refine the grid at specific locations in the domain where a finer resolution is critical to the accuracy of the solution. For example, when simulating sprays, you can add an area of fixed embedding by the nozzle to resolve the complex flow behaviour. Fixed embedding allows the rest of the grid to remain coarse to minimize simulation time

Sphere Embedding:

Use the SPHERE keyword to specify a spherical area of fixed embedding and mode should be cyclic for a period of 720 degrees with the scale of 4, the start time and end time should be the -16.0 and 0.0. The sphere is defined by its centre (-0.0034,0,0.0091) and radius 0.003

Use the SPHERE keyword to specify a spherical area of fixed embedding and mode should be cyclic for a period of 720 degrees with the scale of 5, the start time and end time should be the -16.0 and 0.0. The sphere is defined by its centre (-0.0034,0,0.0091) and radius 0.001

Cylinder Embedding:

Use the CYLINDER keyword to specify a cylindrical or truncated conical area of fixed embedding mode is permanent and scale of 2. The cylinder is defined by the centre (0,0,0.1) and radius of one base of the cylinder is 0.06 m, followed by the centre (0,0,-0.2)and radius of the other base (0.06 m)

Output and Post Processing:

• Time interval for writing 3d output data files=1 degree
• Time interval for writing text output =0.0001 degrees
• Time interval for writing restarting output =10 degrees
• Maximum number of restart files saved=10

Results:

Pressure Plot:

• Here the pressure was low at the expansion stroke and constant for some time and suddenly increases the pressure in compression process and pressure reaches the peak point at that time and slowly reduced the pressure after that and comes constant.

Volume Plot:

Temperature Plot:

• The mean temperature during the compression stage reaches the maximum temperature i.e.2500 k

Integrated Heat Release plot:

Emissions of HydroCarbons:

Emissions of NOX:

Emissions of CO:

Emissions of CO2:

Emissions of Hiroy_Soot:

• The above plots shows the different emissions of the fuel which are unburnt during the process takes place at different angles.It can be observed that the enigne produces the emissions such as carbonmonoxide,Carbondioxide,Hydrocarbons,Nox,Soot

• Liquid spray drops represents the number of lagrangian parcels in the domain.These are formed due to the vapourization and after the combustion takes place,the graph shows the unburnt hydrocarbons amount left over.

Mesh Body:

Animation for the Hydro of the Port fuel injection:

What is the significance of Ca10, Ca50 and Ca90??

• Ca10 (Degrees in crank angle for 10% Cumulative heat release)
• Ca50 (Degrees in crank angle for 50% Cumulative heat release)
• Ca90 (Degrees in crank angle for 90% Cumulative heat release)

CA 10 is considered as the combustion chamber duration from the ignition of the spark to a small measurable fraction of charge i.e 10% burned. This is helpful in finding the ignition delay of the engine.Its valve for the PFI engine is 6.83717

CA 50 is considered as the crank angle required to burn the bulk of the charge i.e 50%.This is the stage where the flame propagates throughout the charge. If CA 50 is high, then the flame velocity is low which leads to the low thermal efficiency as we always need a high pressure exactly at the top TDC.Its valve for the PFI engine is 18.4623

CA 90 is considered as the crank angel required to burn the 90% of charge burned. This gives the overall burning process. Lower the CA 90 the higher output of the engine as the piston expands at the considerably high pressure.Its valve for the PFI engine is 31.701.

What is the compression ratio of this engine?

• It is the ratio of the total Cylinder volume when the piston is at the top dead centre to the Clearance volume. It is designated by the letter r.

• From the plot the maximum volume is 0.000574214 m^3
• From the plot the minimum volume is 5.71064e-5 m^3
• Compression ratio=maximum volume/Minimum volume

=0.000574214/5.71064e-5

=10.05 :1

Why do we need a wall heat transfer model? Why can't we predict the wall temperature from the CFD simulation?

The broader goal of our research is to develop predictive models for modern-day heavy duty engines (both compression-ignition CI and spark-ignition SI). Such engines strive towards lesser pollutant emissions and higher efficiency. One way of improving the overall engine efficiency is reducing wall heat losses. These losses occur due to the high temperature gradient across the chamber walls which are maintained at moderate temperatures (about 500K) by a cooling fluid while combustion inside the chamber causes very high instantaneous temperatures (almost 2000K). If such losses could be reduced through better design, it would imply that a greater percent of the fuel (chemical) energy can go into generating power. In order to reduce wall heat losses, it is important to understand the mechanism of heat transfer at the walls.

The physical processes in the boundary layers of IC engines have great implications on heat exchange and combustion phasing. Hence these are modeled using wall-functions, which can be derived from the thin boundary layer equations (reduced Navier Stokes equations in boundary layers) after making the following assumption

• Flow is parallel to the chamber walls with negligible flow normal to the walls
• Quasi-steady flow with negligible transients
• Constant density and transport properties in the boundary layer
• High Reynolds number flow, very thin laminar shear layer
• Zero pressure gradients along the flow
• No combustion and chemically inert mixture
• The model which results from these assumptions is called the equilibrium wall-function model for the flow and the corresponding model (by analogy from low Mach number assumption) for temperature is known as the thermal wall-function model.

We cannot predict the wall temperature from the CFD Simulation because we are simulating only the fluid flow domain and we are not Computating any solid part.so we need the wall heat transfer model in order to acquire the wall temperature properly.

Calculate the combustion efficiency of this engine?

• Combustion efficiency is a measurement of how well the fuel being burned is being utilized in the combustion process.
• Combustion efficiency, defined as the ratio of heat released by the fuel to the heat input by the fuel.

• From the integrated heat release graph, the total heat release from the combustion is 1241.13 Joules.
• The heat input by the fuel is the product of mass of the fuel * Calorific value of the fuel.
• Mass of the fuel=30 microns’ kg=30 X 10^-6 kg.
• Calorific value of the fuel =44.8 MJ/kg

use the engine performance calculator, to determine the power and torque for this engine?

• The engine performance calculator is a very useful tool in finding some parameters. Here we add the thermos_region0.out is added for the cylinder and then the bore and stoke values are entered that gives the necessary following parameters.

• Power is defined as the ratio of doing work done per unit time.

Power= work done/time

• Work done=468.646 N*m
• Rotations per minute =3000
• Rotations per second=50
• Degrees per second=50*360=18000
• Hence time per degree =1/degree per second

=1/18000=5.55e-5 sec/degrees

• Hence time moving for the 240.199 degrees is =240.199 X 5.55 e-5

  = 0.013330545 sec

  Power=work done/time=468.646/0.013330545=35155.809 watts

  =35.15 Kilowatts

Conclusions:

• Successfult completed the full hydro simulation using the port fuel injection system.
• Various efficiences of the engine are calculated.