Week 11: Project 2 - Emission characterization on a CAT3410 engine

AIM: To simulate, analyze and compare the significance of both omega and open-w pistons.

DESCRIPTION:

In this project we demonstrate the diesel engine simulation and the characteristic difference between open-w type piston and omega type piston.

The simulation will be a close sector analysis with a 60 degree angle and this includes on fuel injector nozzle.

STEPS FOR SIMULATION OF CAT3410 ENGINE:

We will illustrate the step by step procedure to construct a complete setup to begin and analyze the simulation.

GEOMETRY:

In this analysis we perform simulation on close sector surface/ geometry.

To make the sector surface we need the geometry file. By using the 'Make engine sector surface' tool we can create a surface file.

To extract the sector files we import the surface file in as below-shown dialog box and click and extract.

A set of files are generated in the directory as shown in the second image.

Next we open the same toolbox to extract the geomtry, enter the dimensions of the bore, stroke and connecting rod. These values are provided in the forum.

Check the use bowl profile, the compression ratio value is known 17.5. The sector angle is set to 60 degrees with one nozzle in it.

After checking the 'use bowl profile' option the bowl profile dialog box activated, import the bowl profile file using the import option situated within the bowl profile box, and click on extract to create sector surface.

By using the above mentioned process we have developed both open-w and omega pistons.

CASE SET-UP:

We select the crank angle based IC Engine setup.The values of this setup are provided in the challenge section.

In the reference field initialy, the IDs are not available we should flag the boundaries and name them in order to get the paths in the reference section.

We have flagged the boundaries prior to setting up or feeding the values into the application dialog box.

For open_w

For omega piston

CASE SET-UP:

We set up crank based IC Engine

MATERIALS:

There are couple of options enabled in this section

Parcel simulation, Reaction mechanism and Species

After enabling the above parameters we start setting up the simulation furthur.

GAS SIMULATION & GLOBAL TRANSPORT PARAMETERS

We use the default options for this parameter. However we will be using atmospheric air and fuel.

REACTION MECHANISM:

It is always advisable to set up a reaction mechanism before setting up the parcel simulation. As we may not find the option we should enable it prior.

In the reaction mechanism, upload the mech.dat file and check properties. Initially this will show some error because the mechanical files that contain the species in the mech.dat are incomplete without thermodynamic properties.

So, there will be another file called therm.dat. we need to upload the input file by File>import>Import input file and here upload the desired file.

Now check the properties, this time the reaction mechanism shown zero errors.

SPECIES:

In the species anable the parcel option and add 'Diesel2" species as shown in the below image

To introduce a new species click on the '+' icon on the right side and enter the tile. With this the material set-up is complete.

SIMULATION PARAMETERS-RUN PARAMETERS:

In the run parameters, we use a transient based solver with full hydrodynamic mode.

SIMULATION TIME PARAMETERS:

The starting and ending time is -147 degrees and 135 degrees respectively.

For other values, we have followed the information provided on the challenge page.

SOLVER PARAMETERS:

In solver parameters use the density based Navier-strokes solver.

BOUNDARY FLAGGING:

There are few boundaries in this geometry compared to IC engine simulation.

For the Piston boundary conditions, check the piston motion option.

INITIALIZE CONDITIONS AND EVENTS:

In this simulation, as this is a close sector analysis we have only one region.

SPRAY MODELLING:

• Parcel distribution is set to 'cluster parcels near center', this model injects the fuel to the center of the cone.
• This type of model is suitable for compression ignition engines.
• Fuel after entering into the combustion chamber is affected due to the turbulence characteristics. O'Rourke model given better performance in solving the turbulence modeling.
• Collision: To calculate the collisions in the lagrangian spray simulation NTC model is used. In general, when the fuel enters the droplets per parcel is not the same all the time the number varies. So, the NTC (no time counter) is several orders of magnitude fatser and slightly more accurate than other methods.
• Wall interactions, we have enables the spray wall interaction model to wall film. This helps in reflecting or splashing the droplet when it hits the wall. The film model is set to the O'Rourke method.
• Injector, we have included the fuel that we are using for simulation i.e diesel 2.
• We have also provided a profile for rate shape to a trapezoid. Converge utilizes this profile to inject the total mass according to the given time that we have provided.
• Kelvin-Helmholtz and Rayleigh-Tailor models are the industrial standard models for fuel injection with standard values. These values describe the parcel break up and time taken for a parcel to get unstable.
• For Nozzles, in this simulation we are using a compression ignition engine the injector is situated at the center of the cylinder.
• On the other hand we can also locate the center by using the measure option.
• The final part of the nozzles is the injection pressure. The injection pressure is automatically solved by the converge by using the initial conditions such as RPM, injection duraction, total mass injected, discharge coefficient.

The Spray model has several fields to be filled.

In general set-up, the parcel distribution is set to distribute parcels evenly through out the cone.

Turbulent dispersion is set to O'Rourke model.

Collision model to NTC collision.

Collision outcomes to post-collision outcomes.

In this simulation we have used only one nozzle.

The Injector model used is the Kelvin-Helmholtz model. To set up the values for the field we can use the recommended values options on the bottom left side of the dialog box.

It is important to determine the start of injection, duration of injection and total mass of injection. These values are also provided on the challenge page.

Finally, as mentioned in the above line regarding the four nozzle injections, we introduce nozzles by selecting the add nozzle option and use the values for each nozzle flow direction or nozzle angle that are provided.

We use the input file to generate the rate shape. This input file is experimental data provided in the forum.

COMBUSTION MODELLING:

In this combustion modelling we have used the SAGE model by using the values provided in the challenge

• SAGE type of combustion model is used and multi zone model to speed up the combustion calculations.
• Firstly, the type of fuel used for combustion is mentioned. Next the start time, end time and the cyclic period is given.
• For the start time the combustion model is set to start a few degress before the spark takes place so as to initiate the combustion calculation.
• The end time is same as the exhaust valve closing time.

EMISSION MODEL:

We set up the model as follows

TURBULENCE MODELLING:

We set up the turbulence model as follows

BASE GRID:

The rough cell count is estimated for the open-w piston to be 6073 cells.

The rough cell count is estimated for Omega piston is 6736.38 cells.

ADAPTIVE MESH REFINEMENT:

We have used AMR for temperature and velocity for intake ports 1&2 and cylinder head.

• In numerical analysis, AMR method is used for adapting the accuracy of the solution witin certain sensitive turbulent regions of simulation, dynamically and during the time the solution is being calculated.
• When the solutions are calculated numerically, they are often limited to pre-determined quantified grids as in the cartisean plane which constitutes the computational grid or mesh.
• Many problems in numerical analysis, however do not need a uniform precision in the numerical grids used for plotting or computational simulation and would be bteer suited if specific areas of graphs need precision. AMR provides such a dynamic programming environment for adapting the precision of the numerical computational based on the requirements of computational problem in specified locations.
• Sub-grid criteria (SGS) is an integral part of AMR. As AMR is used for different parameters like temperature, velocity, pressure and species etc.
• The SGS is provided witth a predefined value. If the parameter exceeds the specified value the SGS, the AMR automatically enables.

FIXED EMBEDDING:

We have implemented the fixed embedding in the nozzle region.

• Fixed embedding is a smart feature. It heps in adding extra mesh in specified locations.
• This offers numerous benefits including the ability to apply more cells near a wall and get an increase in accuracy and running a fast coarse mesh without distorting the geometric representation.
• The following regions and boundaries included in fixed embedding including intake valves, exhaust valves, cylinder regions, nozzles and spark plugs.
• The fixed embedding acta as an additional refinement in that areas.

OUTPUT & POST-PROCESSING:

The values provided in the post variables and output files by default are correct and we can proceed using these values.

OPEN-W PISTION ENGINE PERFORMANCE:

Power `P = (2*pi*N*T)/(60)`

Power = work/time

Work = 481.93 N-m

Time = duration(degrees)/degrees per second = 240.199/18000 = 0.0133sec

Power = 481.931/0.0133 = 36235KJ or 36.235KW

N = 3000 RPM

`T = (P*60)/(2*pi*N)`

T = 36235x60/2x3.14x3000 = 115 N-m

OMEGA PISTION ENGINE PERFORMANCE:

Power `P = (2*pi*N*T)/(60)`

Power = work/time

Work =548 N-m

Time = duration(degrees)/degrees per second = 240.199/18000 = 0.013 sec

Power = 548/0.013 = 41225 KJ or 41.225 KW

N = 3000 RPM

`T = (P*60)/(2*pi*N)`

T = 41225x60/2x3.14x3000 = 131N-m

RESULTS:

The pressure plot is as follows

The temperature plot is as follows

The integrated heat release plot is

The heat release plot is

The Soot plot is

The NOx plot is

The CO emission plot is

The CO2 emission plot is

The HC emission plot is

RESULTS FOR OPEN-W PISTON COMPRESSION IGNITION PRESSURE AND TEMPERATURE CONTOUR ARE

For the pressure is

For the temperature is

For the velocity is

RESULTS FOR OMEGA PISTON COMPRESSION IGNITION PRESSURE AND TEMPERATURE CONTOUR ARE

For the pressure is

For the temperature is

For the velocity is

CONCLUSIONS:

• In this simulation we have performed a close sector surface analysis. In this type of analysis, the inlet ports, the exhaust ports, inlet valves, exhaust valves are ignored for the simulation and performed the calculation of piston.
• The 'make engine sector surface' tool develops a part of piston with specified angle.
• In the toolbox, the sector angle is specified to be 60 degrees that mean the injector has six nozzles inside the combustion chamber i.e 360/60 =6.
• The benefits of close sector surface are it reduces the computational cost, by eradicating the ports and valves, the simulation time decreses and this also helps in concentrating the characteristic changed inside the combustion chamber.
• For the above plots it is observed that the pressure and temperature inside the 'omega' type piston are greater than the 'open-w' type piston.
• There is not much difference in pressure value but there is considerable difference between omega and open-w piston temperature gradients.
• The peak pressure attained by the omega piston and the open-w piston is closer to 12MPa. The peak temperature attained by both the pistons are omega = 1.7e+3 K and open-w 1.5e+3K.
• The heat released or generated by omegs piston is also greater than the open-w piston.
• The soot production i.e incomplete burned particles that contained a large amount of amorphous carbon is very high in the open-w piston. On the other hand, the NOx i.e nitrogen oxide produced by the open-w piston is lesser than omega piston.
• The Carbon emissions from omega pistons are also greater than the open-w pistons (CO and HC), despite it emits fewer carbondioxides.
• The above animations represent the pressure and temperature inside the pistons. After referring to the animations we conclude that higher pressure and temperature inside the omega piston is due to its design advantage. The omega bowl has more volume than the open-w piston which increase the pressure and temperature.
• If the pressure and temperature are higher inside and fuel burns completely and helps to reduce the soot formation.
• From the engine performance caluclations the omega puston has more torque than compared to the open-w piston.
• Due to environmental restrictions and concerns, omega piston may not be suitable for current scenarios.
• The omega piston could be used for logistic and transportation purposes because of its design advantages, high power and torque.