Week 11: Project 2 - Emission characterization on a CAT3410 engine
1. Title – Emission characterization on a CAT3410 engine.
2. Objective –
- To import the CAD model of the engine in converge Software and check for errors.
- To make sector for both omega piston and w piston, with make engine sector surface.
- To solve the case using a suitable solver and convert the result for Paraview software.
- To import output files in Paraview and generate required contours and plots.
3. Introduction –
A heat engine is a device that transforms the chemical energy of a fuel into thermal energy and uses it to produce work. Mainly, a Heat engine is classified into two categories External combustion engine and internal combustion engine. when the products of combustion of air and fuel transfer heat to a second fluid which is the working fluid of the cycle, then the engine is called an external combustion engine, and when the combustion of air and fuels take place inside the cylinder and are used as the direct motive force then the engine is called as an internal combustion engine.
Internal combustion engines can be classified further, according to the type of fuel like a petrol engine, diesel engine, and gas engine. The diesel engine works on the diesel cycle which was proposed by Rudolf diesel in 1892. In a Diesel engine, First, the air is allowed into the cylinder and the piston compresses it—but much more than in a gasoline engine. In a gasoline engine, the fuel-air mixture is compressed to about a tenth of its original volume. But in a diesel engine, the air is compressed by anything from 14 to 25 times. Air will become hotter and the injection of fuel results in an explosion, which pushes a piston, Simply, it generated mechanical energy. Diesel engines are up to twice as efficient as gasoline engines—around 40–45 percent efficient at best.
4. Theory
Simulating internal combustion (IC) engines is challenging due to the complexity of the geometry, spatially and temporally varying conditions, and complex combustion chemistry in the engine. Converge software provides a special feature to simulate IC engine. in this study, we are going to simulate the emission characteristics of the CAT 3410 engine.
One of the biggest advancements in piston technology is the use of different piston tops or crowns, the part that enters the combustion chamber and is subjected to combustion. While older piston tops were mostly flat, many now feature bowls on top that have different effects on the combustion process. The piston bowl is primarily used in the diesel engine. Diesel doesn't have an ignition phase, so the piston crown itself may form the combustion chamber. The shape of the piston bowl controls the movement of air and fuel as the piston comes up for the compression stroke and it contributes to expelling exhaust gases during the exhaust stroke as well. So, piston shape can increase combustion efficiency. In this study we are going with two different piston configurations one is omega and the second is w. we will look at how the piston shape affects the heat rate, pressure, and temperature by plot and we will look at some animation as well.
5. Procedure –
IC engine is always going to be tricky due to its complex nature. To generate the desired result it is very important to choose the right physical model with a perfect solver. In these of simulations, it is advisable to grab the right initial conditions, boundary conditions, physical models, etc. because it will take a lot of time to solve. In this study we simulated the emission characteristic of the CAT3410 engine, for it, the procedure was as followed –
1. First, we imported the model and ran the diagnosis tool to find errors. We found no errors.
2. We went with the creation of the sector and considered closed-loop analysis. The piston body is divided into sectors to save simulation time.
3. In the case setup we started with a crank angles-based IC engine as the application type. In the crank angle-based menu some parameters were defined as shown in the following image.
4. In gas simulation parameter therm.dat file was imported which contains gas thermodynamic data specifically related to IC engine.
5. From the materials option parcel was enabled. In parcel simulation fuel Diesel2 was selected, which imported all the properties of the fuel. Converge employs discrete Lagrangian parcels to simulate a special type of liquid in conjunction with spray modeling. In converge the Parcel simulation dialog box is for configuring properties of Lagrangian liquid parcels (such as for spray simulations).
6. In the reaction mechanism windows properties were checked to see the available species, which were imported by the therm.dat file.
7. Diesel2 was defined in the parcel option of species. SOOT and NOX were defined in internal passives.
8. In the run parameter transient was chosen as the solver type with hydrodynamic simulation mode to simulate the effect of liquid and gases. In temporal type crank, angle-based engine simulation was chosen, because we wanted to run the simulation on crank angles.
9. In the simulation time parameter start and end time were specified in degrees, these were crank angles. Other parameters were defined in the following image. Solver parameters were left as defaults.
10. There were 5 boundaries created in flagging process. Boundary conditions were given as the following images –
11. One region was defined, which was in the cylinder. Since we were analyzing the emission characteristics of engine, so one region was enough. Species and their mass fraction were defined as follows.
12. From the physical model’s menu spray and combustion with emission were enabled.
13. The Spray modeling dialog box is used to configure nozzles, injectors, boundary injections, and injection rate shapes, set various spray-related constants, and choose from several injections and drop models. We started with choosing the drop evaporation option with frossling model, it determines how the radius of the drop changes with time.
Converge contains the widely used O’Rourke and NTC collision models. These models are designed to estimate the number of droplet collisions and their outcomes in a relatively computationally efficient manner. We went with the NTC model since it is faster and more accurate than the O’Rourke model.
In the wall interaction dialog box when defining how liquid interacts with the walls and its parameter. wall film model is used for modeling the interaction of liquid drops with solid surfaces and it comes with a wall splashing option also. To determine the splash O’Rourke model is used and the spray wall interaction wall film model was used.
Converge offers two categories of liquid injection mechanisms: injectors and nozzles. An injector is a group of nozzles that have some of the same characteristics. Each injector can have any number of nozzles, each with its own hole size, cone angle, position, and orientation. We went with one nozzle with Kelvin-Helmholtz and Rayleigh-Taylor models. These models were responsible for the prediction of liquid atomization and drop breakup. Time of injection, temperature, species, and nozzle parameters was given as shown in the following image.
14. Combustion model is responsible for the chemical reactions and kinetics during combustion. We chose the SAGE model, which solves for chemical reaction mechanism and its related parameters. In the general setting, the time of combustion was defined in form of crank angles means combustion will take place between crank angles -10 to 135degrees.
15. Converge provides many models to simulate NOx and SOOT production. Species of interest such as CO, CO2, and unburned hydrocarbons are always calculated or interpolated in CONVERGE, provided they are included in the reaction mechanism file and are a part of the combustion model used by the simulation.
There are two NOx models one is thermal NOx and another one is prompt NOx. The prompt NOx model predicts the formation of NO at low temperature fuel-rich conditions and it is suitable for gas turbines. So, we chose the thermal NOx model.
The soot models in converging describe the complex soot formation and oxidation process using several global steps, including soot inception, surface growth, coagulation, and oxidation. Phenomenological and detailed soot models are computationally expensive. So we went with the empirical model.
16. We chose the k-epsilon turbulent model and the base grid was chosen as 0.004m since we would enable fixed embedding and AMR the global grid size won’t be a big problem.
17. Adaptive mesh refinement option was enabled to get the finer mesh. This option is very important because you cannot deploy the same-sized mesh on the whole model. Velocity and temperature were two criteria chosen for AMR. In the velocity criteria, sub-grid criteria were 2m/s means above it, the cell will become finer by a factor of 2^n, where n is the embedded level, in our case, it is 2 and mesh will get finer by 4 times. Similarly, when the sub-grid temperature goes beyond 5K mesh will get finer by a factor of 4.
18. Fixed embedding option was enabled from the grid control menu. Fixed embedding makes finer mesh on the basis of time or on the basis of crack angles. It is different from AMR because the AMR option was dependent on the particular cell property. Fixed embedded was applied around the nozzle, piston, and around the boundary of the cylinder. The parameter can be seen in the following images.
19. Time interval for writing 3D output data files was set to 2second for writing text output it was 0.1 seconds, and other parameters of output files were left as default.
6. Results –
Geometry -
Omega piston -
w piston -
Useful plots and animations were generated to compare the piston profiles. It's very difficult to choose one of them, because they have their own advantages. Animations were created to see spray wall interaction and piston movement.
1. We if look at the pressure plot, we can see we are getting higher pressure by the omega piston, but we cannot declare it best only on this criteria.
2. Now, look at the mean temperature plot. For w piston mean temperature is low, we can assume there might be some fuel that is unburn, but we have to see further criteria to validate it. Low temperature gives us a lower amount of NOx as well.
3. Now come to heat rate and integrated heat rate plots. The omega piston has a higher heat release rate, that why it has a higher temperature compared to the omega piston. The integrated heat release rate is the accumulation of heat released during the whole cycle. IHR is higher for omega piston.
4. If we look at the following plot, we can say the omega piston has higher gas fuel, which is being burned lately, it can be verified from the IHR plot also.
5. With omega piston there is lower NOx and it can be selected, if it someone targets lower NOx.
6. Open w piston has larger amount of carbon mono oxide, so we can say there is a lot of unburn fuel.
7. Omega piston produces lower soot, again, someone can choose it, if he is targeting lower Soot.
Omega piston -
Spray wall interaction -
https://drive.google.com/file/d/13Zks3PFVGZHjphbr2dX3JTTh2qKo72V0/view?usp=sharing
NOx formation -
https://drive.google.com/file/d/1IOcOEd7XoaqFSRh1sZzJZE7vNfnL3FWl/view?usp=sharing
Unburned hydrocarbon -
https://drive.google.com/file/d/1y8H-_y1f2uIt5yu9anlN0l90jEBJTO8A/view?usp=sharing
w piston -
Spray wall interaction -
https://drive.google.com/file/d/1CQYuH1M8OJx-itrbgRdu9whZ-_xMR_gP/view?usp=sharing
NOx formation -
https://drive.google.com/file/d/1U4YLfbEDKWLLaYSzzF7vAQYVVXfA-LA8/view?usp=sharing
Unburned hydrocarbon -
https://drive.google.com/file/d/1y65JDNGrza6VYl-vL0X-1R5eg1mGt6hu/view?usp=sharing
We can conclude that the omega piston is best if someone wants to lower the NOx and SOOT, basically pollutants, it has a higher penetration length also.