Emission characterization on a CAT-3410 Diesel engine using Converge studio

Objective :

1. The CAT3140 engine for open-W and omega piston models generates a sector geometry of the combustion chambers.

2. To simulate the two-sector profiles with the same parameters.

3. To analyze and compare the different operative conditions of both configurations and compare their performance parameters.

4. To study the emissions for both the configurations and draw suitable conclusions for the same.

Introduction :

The CAT3410 is a caterpillar commercial engine. It acts as a substitute for diesel. In diesel engines, fuel is put into the combustion chamber using injection through a nozzle. the fuel spray is subjected to break up and atomization before being mixed with air and experiencing combustion in the chamber.

A diesel engine combustion chamber with different piston head will affect the combustion process and eventually affect the diesel engine performance.

The mixing of air and fuel in the combustion chamber happens when the piston is in the TDC. thus there is a combined flow in the swirl, the flow in the radial direction from the piston crown. This flow of air and fuel is closely related to the shape of the piston head.

Geometry Profiles :

Based on the data provided we can extract the head, bowl, forward, and reverse profiles. Once we extract our profiles we import only the bowl profile and provide useful data to create an engine sector using the tool "Make Engine sector surface". The picture below shows us the toolbar where we make the sector surface.

For the Omega profile :

For the Open W profile :

The four individual boundaries flagged are cylinder wall, cylinder head Piston front, and back faces these are done respectively for the two individual piston profiles and they are shown in the figure given below:

The geometrical details of the engine are as follows:

Bore = 0.13716m

Stroke = 0.1651m

Rod length = 0.263m

RPM = 1600

Compression Ratio = 17.5

For the Open W piston, the sector is generated by using the bowl profile.

We are only concerned with having one injector and one nozzle he considering the sector geometry for both the profiles depicted in the images. Also, the parameters for the engine geometry are given in the picture below

The geometrical details of the engine are as follows:

Bore = 0.13716m

Stroke = 0.1651m

Rod length = 0.263m

RPM = 1600

Compression Ratio = 17.5

For the Omega piston, the sector is generated by using the bowl profile.

As the Engine has a 6 nozzle configuration and the geometry is axisymmetric a cut section with a single is generated for each nozzle and one of the sections is analyzed in this project. Hence the sector angle is 60 degrees.

Application Type :

Crank angle based for IC Engine

Once we are done with providing suitable physical parameters for our engine we have to provide suitable boundary conditions for every individual boundary for the two-piston bowls.

Gas simulation :

The gas simulation properties were set as following

Parcel simulation :

The fuel chosen was Diesel-2 and the spray parcel properties were taken from the data files.

The transport parameters were set as default values. The reaction mechanism was set based on the data files and for Diesel-2 combustion.

Global transport parameters :

The global transport parameters are considered to as shown below

Reaction mechanism :

The transport parameters were set as default values. The reaction mechanism was set based on the data files and for Diesel-2 combustion.

Species :

The parcel elements are set as the Diesel-2 liquid and the passive elements are kept as the Hiroy soot and NOx.

Run Parameter :

The simulation type was set for the full hydrodynamic state and the solver was used to be the transient state for the simulation.

Simulation time parameters :

The simulation was run with a start time of -147 and the end time was 135 with the initial time step being with 5e-07 seconds and the final time step being 2.5e-05 seconds.

Solver parameters :

The solver parameters have been set for the Navier-Stokes solver and the PISO scheme was used for the Navier strokes solver and the solver type used was Density-based.

Boundary Conditions :

The piston boundary was set at a temperature of 533 k and the motion type was set a translating with a moving surface. The velocity and temperature boundary conditions were set as the law of the wall and the species, passive and the turbulent kinetic energy was set as the Neumann boundary conditions and the turbulent dissipation was set to wall model(law of the wall).

The front face boundary was set with a boundary type of periodic and with a periodic type of stationary and then with a periodic shape of the rotational angle of 60 degrees. The matching boundary was set to be the back-face.

The back face boundary was set with a boundary type of periodic and with a periodic type of stationary and then with a periodic shape of the rotational angle of 60 degrees. The matching boundary was set to be the front-face.

The Cylinder Wall boundary was set at a temperature of 433 k and the motion type was set a stationary with a fixed surface. The velocity and temperature boundary conditions were set as the law of the wall and the species, passive and the turbulent kinetic energy was set as the Neumann boundary conditions and the turbulent dissipation was set to wall model (law of the wall).

The Cylinder head boundary was set at a temperature of 523 k and the motion type was set a stationary with a fixed surface. The velocity and temperature boundary conditions were set as the law of the wall and the species, passive and the turbulent kinetic energy was set as the Neumann boundary conditions and the turbulent dissipation was set to wall model(law of the wall).

Regions and initialization :

All the individual boundaries are grouped into a single region and provide values for the mass fraction for gases and emissions. The entire region is assumed to be at a particular temperature and pressure. All these are described in the picture given below

Spray modeling :

Spray model makes use of the simplified mathematical model to capture the physics of the entire spray process. Our Lagrangian Spray usually C7H16 for diesel sprays is made up of a bunch of parcels. The collection of the entire parcels in the spray domain will make up our fuel spray.

• Turbulent dispersion refers to the fluctuating velocity in the gas phase which is responsible for affecting the gas drop characteristics
• Evaporation models describe the rate at which the radius of the drop shrinks and it also the rate at which mass is being transferred.
• The physical properties of the fuel are captured well by hydrocarbons.
• Liquid Heptane is converted into its gaseous form.

• Collision models tell us how the individual parcels interact with one another
• Dynamic Drop Drag model calculates the drag coefficient based on the effect it has on the velocity and drags it has on the drop shape.

Wall-Interaction :

• when the drop comes in contact with the wall of the surface we want it to Rebound/Slide making use of O'Rourke Models.

Rate Shape value :

• We are using diesel as the parcel species with a mass fraction of 1. The rate shape value is indicated by the profiles shown in the image above.

• Next step we set up the models for our simulation. All of them have constants that control how the parcels breakup. A particular equation known as the Dispersion Relation will tell us how long it is going to take for the disturbance for a particular parcel to go unstable.
• Size constants occur are important because they increase or decrease the time taken for the break up to occur and also increase or decrease the size of the child droplets. All these values are given above.

• The picture above depicts the data provided for the duration of time required for the spray injection to happen in our diesel engines.

• We have a solid cone for our nozzle sprays and all the essential data are specified in the picture above

Combustion modeling :

A SAGE model was used to model the combustion process in this simulation the start time was specified as -10 CAD and the end time as 135 CAD.

A SAGE model was used to model the combustion process in this simulation. The SAGE model was assumed to be region independent for simplicity.

Turbulence modeling :

An RNG k-epsilon turbulence model with default parameter was under for turbulence modeling

Base grid :

The baseline mesh was set around 0.0014

And the Cell Count estimated to be around 117839 cells.

Animation for the mesh Generation :

The animation for the mesh generation for the Omega and Open W-Type piston is shown above.

Adaptive mesh refinement :

AMR was used for the In-cylinder-Regions to improve accuracy. Embedding level set as 2 and subgrid criterion of 5 and 2 were used.

A Velocity AMR is provided with the Embedding level set as 2 and the subgrid criterion of 5 was used.

A Temperature AMR is provided with the Embedding level set as 2 and the subgrid criterion of 2 was used.

Fixed embedding :

A Sequential embedding for the injector was used as embedding needs to be active only when the fuel is sprayed.

The Nozzle arrangement was given an embedding at 1 level on a scale of 2. And the start time was at -12 CAD and the end time was 15 CAD.

The boundary embedding was provided for the Piston arrangement was given an embedding at 1 level on a scale of 1.

The boundary embedding was provided for the Cylinder head arrangement was given an embedding at 1 level on a scale of 1.

Results and Discussions.

PV Diagram:

The PV Diagram of the indicator diagram of both piston configurations is seen in the plot below

The area under the PV diagram of an engine indicates the work done by the engine. Here from the comparison of the PV diagram of the two-piston configurations, the area under the Omega piston P-V curve is higher indicating higher work is done which endorse with the values of work done by the engine Performance calculator tool.

Compression Ratio :

The geometrical details of the engine are as follows:

Bore = 0.13716m

Stroke = 0.1651m

Rod length = 0.263m

RPM = 1600

Compression Ratio = 17.5

The bore, stroke and compression ratio are the same for both the pistons. Hence the parameters are calculated as follows.

For getting the diameter

For finding the Displacement Volume :

For finding the Clearance Volume :

Compression Ratio :

Power and IP calculation:

Omega Piston :

Engine calculator details for the Omega piston

Power calculation :

IP calculation :

The Open W-Type engine.

Engine calculator details for the Open W type piston

IP calculation :

Plots and Discussions.

Total cell count :

Initially, the simulation starts with a cell count of approx.180,000 at -130 CAD. and after the combustion completed we can see that the total cell count is nearly 820,000 for the omega piston and for the Open W-Type piston we can see a total cell count of 745,664.

Peak Pressure(P) :

• The peak pressure of an Open W piston is higher compared to an Omega piston. However, we can't conclude that Open W piston is better for our diesel engine based on a single parameter alone.

Animation for the Pressure for the Omega and Open W-Type Pistons

The Pressure formation in the omega and the Open W-type Pistons are provided in the animation above.

Mean Temperature(T) :

• we can see that low temperature for an Open W piston is beneficial if we are supposed to lower our NOx emissions. But there is a problem of fuel not being burned properly which needs to be verified by looking at other essential parameters.

Animation for the temperature for the Omega and Open W-Type Piston.

The Temperature formation in the omega and the Open W-type Pistons are provided in the animation above.

Heat Release rate :

A higher heat release rate in Omega piston explains the high temperature and a low heat release in Open W piston with sudden dips in the curve tells us about the noise inside the engine.

• We can see that the total heat energy released from the combustion process alone in the Omega piston i.e 7279.46 J. While in the Open W piston the energy released is i.e 7211.74J there is a discrepancy of close to 63 J/Cycle.
• Also, the rate at which the fuel burns in Open W piston is much slower when compared to Omega Piston
• Open W has a low temperature and the combustion efficiency of the engine is also low.

Emissions:

HC :

The quantity of Unburnt Hydrocarbons is higher in the Open-W-piston. The formation of Unburnt hydrocarbons is due to the improper combustion of the fuel. As inferred earlier from the Heat Release Rates of both piston heads, the combustion efficiency would be higher for the Omega piston, thus explaining the higher quantity of unburnt hydrocarbons produced.

Animation for the H2O and H2 for the Omega and Open W-Type Pistons

The H2O and H2 formation in the omega and the Open W-type Pistons are provided in the animation above.

CO :

The CO production, even though the peak is higher for the omega piston, the quantity immediately drops.

Animation for the CO for the Omega and Open W-Type Piston.

The CO formation in the omega and the Open W-type Pistons are provided in the animation above.

Hiroy_soot :

Lowering NOx at the expense of other major pollutants is not feasible. This can be seen in the graph above for Hiroy_soot as the Open W piston contributes to higher emissions when compared to Omega piston. Also if we analyze the hydrocarbon plot we see that a lot of unburned fuel is responsible for fewer NOx emissions.

Animation for the Hiroy-soot for the Omega and Open W-Type Pistons

The Hiroy-soot formation in the omega and the Open W-type Pistons are provided in the animation above.

NOx :

The NOx emission from the Open W piston is low to that of the omega piston. If our objective is to lower NOx then the Open W piston is a good choice. But if we are looking at the overall aspects of an engine it is quite reasonable to look at other emission profiles before jumping to any conclusions.

Animation for the NOx for the Omega and Open W-Type Pistons

The NOx formation in the omega and the Open W-type Pistons are provided in the animation above.

Comparing the IMEP and power values

The Omega Piston :

The performance parameters for both the configurations are calculated using the performance calculator tool in converge

Engine calculator details for the Omega piston

The Open W-Type engine.

Engine calculator details for the Open W type piston

From the above table, the work done by the omega piston is higher and the IMEP is also higher for the Omega piston. From the crank angles, it is seen that 90% of the fuel combust at 53.02 degrees for the open W type piston and at 27.52 degrees for the omega piston. This shows that the combustion is faster in the Omega piston

Comparing the IMEP and power values

Hence we can say that Omega piston is 11.16% more efficient than Open W piston

The comparison of graphical representation for the IMEP and power is shown above in the bar graph.

Conclusion :

Simulation is performed for the CAT3410 Engine for two-piston configurations. The work and power and torque produced by the omega piston configuration are found to be higher than the Open W piston configuration. The omega-piston IMEP is also higher, indicating the better performance of the omega piston configuration.

The configurations for Omega and Open W pistons are characterized by emissions and it can be concluded the soot, CO and unburnt hydrocarbons produced in the Open W piston are higher. However, the NOx emissions of the Omega piston model are five times greater than that of the Open W model.