Emission characterization on a CAT3410 engine

            Emission Characterization on a CAT3410 Engine

 

Aim:  To run the simulation for emission characterization on a CAT3410 Engine.

Objective:

• To run the simulation  for emission characterization on a CAT3410 engine for two different piston profiles (i.e. Open-w, Omega).
• To characterize the emissions (Soot,Nox and UHC) and comparing them for both type of pistons.
• To compare the imep and Power Values.

Description:

Diesel engine is an internal combustion engine in which air is compressed to be sufficiently high temperature to ignite diesel fuel injected into the cylinder, where combustion and expansion actuate a piston.It converts the chemical energy stored in the fuel into mechanical energy. The diesel engine gains its energy by burning fuel injected or sprayed into the compressed hot air charge with in the cylinder. In a diesel engine, fuel is introduced as the piston approaches the top dead centre of its stroke. The fuel is introduced under high pressure either into precombustion chamber or directly into the picton cylinder combustion chamber. Diesel engines fuel injection systems are typically designed to provide injection pressure in range of 7 to 70 megapascals. Engine work is obtained during the power stroke. The power stroke includes both constant-pressure process during combustion and the expansion of the hot products of combustionafter the fuel injection ceases. The principle drawback of diesel engines is their emission of air pollutants. These engines discharge high levels of particulate matter i.e.soot, reactive nitrogen compounds i.e.NOx.

 

Procedure:

Creating Open-W Piston

Generating Piston profile from the given data. Here we need to import  the provided file i.e. (open_w_piston_360.dat) in converge. For this go to File > select  import > import surface file. Here select the .dat file and click on import, to import the geometry.

           

In order to create various profiles like bowl_profile, forward_profile, head_profile etc  we need to go to Tools > select Make engine sector surface. After selecting, set the values as shown and check for the bowl profile. 

 

To generate an engine sector surface, firstly add a working directory where we want to save the profiles. Then click on "Extract profiles from surface.dat". Extract profiles from surface.dat tab opens and now direct to the folder where there is surface.dat file is located. 

Click on Extract to generate various profiles and surfaces of the geometry.

 

Now after generating the profiles and surface files, enter the specifications of engine i.e. Bore, Stroke, connecting rod length, and set the compression ratio as shown below. As we require a bowl profile, select Use Bowl Profile. Then we can see that Bowl Profile is activated, here import the file 'bowl_profile' from the generated files. After importing we can see the profile generated. Also set the sector angle as 60deg.

Check if all the parameters are entered and then click on "Make Surface". On clicking this it will generate a new Surface.

Now the geometry for the Open-W piston is ready. Save the generated surface.

Now immediately, go to Diagnosis and click on Find to check if there are any errors i.e. intersections, open edges, etc. If we find any errors, we need to clear them before setting up the case setup. Check multiple times such that there are no errors.

In order to do the Case setup, go to File > select 'Import Case Setup' and navigate to the directory where we saved the "baseline_input_files". This folder contains necessary parameters which are required for setting up the case.

Now the complete CaseSetup is ready.

 

 

Creating Omega Piston

For Omega Piston we are directly provided with the bowl profile and hence no need of extracting bowl profile from the .dat file. 

Here go  Tools > select "Make Engine Sector Surface".

 

Enter the specifications of engine i.e. Bore, Stroke, connecting rod length, and set the compression ratio as shown below. As we require a bowl profile, select 'Use Bowl Profile'. Then we can see that Bowl Profile is activated, here import the file 'bowl_profile' that is provided for Omega Piston. After importing we can see the profile generated. Also set the sector angle as 60deg.

Check if all the parameters are entered and then click on "Make Surface". On clicking this it will generate a new Surface.

The geometry for the Omega piston is ready. Save the generated surface.

Now immediately, go to Diagnosis and click on 'Find' to check if there are any errors i.e. intersections, open edges, etc. If we find any errors, we need to clear them before setting up the case setup. Check multiple times such that there are no errors.

In order to do the Case setup, go to File > select 'Import Case Setup' and navigate to the directory where we saved the "baseline_input_files". This folder contains necessary parameters which are required for setting up the case. After doing this, the complete CaseSetup is ready.

Before directly exporting the input data we need to check complete case-setup, so that the data provided is accurate for both the cases. As we are characterizing the emissions for two different pistons the case setup remains the same for both of them.

Case Setup for Open-W Piston :-

Here as we are doing engine related simulations we should select Crank Angle-based IC engine.

The main parameters of the engine are specified as per our required inputs or follow the engine specifications if provided.

Spray Modeling:-

The spray & turbulence modelling  is not easy to predict diesel engine and gasoline combustion simulations. To obtain correct results we have to use various spray and turbulence modeling options. Generally in Converge both Reynolds-Averaged Navier Stokes and Large Eddy Simulations turbulence models. For spray, the Converge contains various options to simulate the injection, breakup, vaporization and various spray related parameters. The liquid penetration length and the vapour penetration length characterize a spray.In order to find the liquid penetration length, software calculates the total mass pf the liquid parcels from the nozzleand later multiplies this mass by the liquid penetration fraction to obtained the penetrated spray mass. In converge it writes the corresponding  iquid penetration length to spray.out file.

Here we use Forssling Model and should enter the Sourced species that we are taking i.e. C7H16.

Specify the details of liquid fuell mass fraction for calculating the spray penetration, bin size for calculating the vapour penetrationand and also the standard fuel vapour mass fraction for finding the vapour penetration. In this case to find Turbulent Dispersion we use O'Rourke Model.

Based on the fuel parameters tghe Mass diffussivity constants are also set accordingly.

Here scaling the coefficients is standard throught.

Along with setting of spray characteristics, it is very important to set the injector specifications.

Here we set the nozzle orientation i.e the nozzle location and orientation is set in order to obtain good engine efficiency and obtained less emissions. This helps to have effecting spray in the cylinder.

In this step the spray  rate is being calculated i.e. basic parameters are provider to check the spray rate of the injector specified. Mainly Speed , injection duration, total injected mass and temperature is provided to calculate the various parameters like Peak injection pressure, Peak injection velocity etc.

Combustion Modeling- 

Converge provides various chemical solvers to calculate the various reaction rates based on the principles of chemical kinetics. This is linked to the flow solvers where as the flow solvers and the chemistry solvers are indipendent to each other which speeds the simulation in faster phase. The SAGE solver predicts a wide range of cases like how the fuels are mixed (premixed , partially mixed), emission modeling is also part of this. With high accuracy we can predict the modeling. SAGE is a detailed chemistry solver.In this case Fuel species = C7H16. 

Emission Modeling- 

Here all the parameters for NOX are being set accordingly. Initiall we select the thermal NOx model and select the Equilibrium assumption is considered for O/OH models for the thermal NOx. Parameters for Soot model is also set as shown below.

To predict the formations species we need to select Use total hydrocarbonds for the formation of species.

Turbulence Modeling- 

Turbulence modeling is the construction /use of mathematical model to predict the effects of the turbulence. For most of the turbulent flows , CFD simulations use turbulent modelsto predict the evolution of turbulence. These turbulence models are simplified constitutive equations that predict the statistical evolution of the turbulent flows. Here we use Reynolds Averaged Navier Stokes to solve and turbulent model used in this case is RNG K-$\epsilon$.

Adaptive Mesh Refinement (AMR)-

It is a method of adapting the accuracy of a solution within certain turbulent regions of the simulation, dynamically and during the time of solution is calculated. AMR  automatically adjusts the grid at each time step, adding cells in areas where it requires and eliminates cells that are not needed to yield accurate results. This kind of refinement ensures that the software can resolve flame fronts and the high velocity flows while minimizing the overall cell count.

Sub Grid Scale (SGS)-

The sub Grid Scale parameter is bascially used for fine grain control of the AMR algorithm sensitivity. It refers to the representation of important small scale physical process that occur at length scales that cannot be adequately resolved on a computational mesh. In large Eddy  Simulation of turbulence , SGS modeling is used to represent the effects of unresolved small-scale fluid motions.

Refined Mesh Grid Size= (Base Grid Mesh Size)/(2^embeded level)

Fixed Embedding-

Here it is generally used to refine the grid size at the specified locations to increase the accuracy  of the solutions. If there are any speific areas where we need results more accurate then we should use this that means at that point the mesh is refined and rest of the places the mesh remains coarse. This helps to save the simulation time. In our case we use fixed embedding for the selected boundaries and the nozzle. 

With this setting up of the case is complete and now go to Files > Export > click on Export Input Files. Select the destination folder (test) to save the data. 

After exporting the data, from programe files copy 'mpiexec.exe' file and paste in the test folder.

 

Now, in Cygwin direct to the folder where the data is saved. Using the below command, run the simulation

Once the simulation is complete, go converge and convert the output files so that they can be imported in ParaView. ".VTM File " from the Output is used to open the geometry file in Paraview. Hence Contours are generated and animations are created. The same output files are used in converge to generate various plots.

 

Results:

 

Meshing for Open-W and Omega Pistons-

 

Spray-Wall Interaction-

When the fuel is injected i.e. the fuel entering the domain we can clearly observe that Open-W piston the spray is imping on the piston, where as we can see that there is significant amount of penetration length for Omega piston. This is the main drawback for Open-W piston and hence majority of fuel is not getting vaporized. As it is not getting vaporized quickly, large amount of liquid fuel is leftover. This requires more time i.e. due to high temperatures it slowly gets evaporated. In this case we cannot conclude that the Open W piston is not suitable but on changing the penetration characteristics the efficiency of the piston may increase little bit. Hence the Omega Pistons undergoes good vaporization as it has proper and effective penetration characteristics. 

 

Temperature-

Animation-

 

Pressure-

From the plot, it is observed that the peak pressure for Open-W piston is 11.7MPa and for Omega piston the peak pressure is 11.6MPa. Hence we can conclude that Open-W piston has little higher compared to the omega piston. This slight difference is due to the geometry of the piston as the pressure is inversely praportional to the area.

 

Mean Temperature-

From the plot it clear that the peak temperature for Open-W piston is significantly lower when compared to Omega piston. As the temperature is too low for open-w piston, it conveys that the fuel didnot burnt properly. Whereas the Omega piston has higher temperature. In some cases having low temperatures is also fine as it produces less amount of NOx. Generally NOx is produced at high temperatures. In case of Open-W piston, the effect of liquid spray infringment i.e. the combustion process is delayed causing lower performance.

 

Heat Release Rate-

This plot clearly explains how the heat is released during the process.Here, the omega piston releases more amount of heat compared to the open-w piston that means omega piston has higher heat release rate.This also helps to understand why the temperature is higher for omega piston.

 

Integrated Heat Release-

Integrated Heat Release rate is nothing but the integral form of Heat release rate. This plot indicates how much energy is released from combustion at a a particular moment. It is observed that for open-w it is burning slow. At the end we are injecting same amount of fuel but total energy output is comparatively small. It is observed that some amount of heat energy is unburnt in the engine.

 

Gaseous Fuel (C7H16)-

It is observed that in the omega piston there is some amount of gaseous fuel. That means we can confirm that we have some amount a vapour in the chamber which is burnt latelyandd hence temperature increase is also low.

 

NOx-

The NOx emission from the Open-W piston are low when compared to the omega piston. If our main objective is to lower NOx then open-w piston is the best choice to select, but when we are considering all the aspects of engineit is reasonable/valid to inspect all the emission profiles to have a good selective conclusions. 

 Animation:

 

Hiroy Soot-

Here, in the combustion the fuel leads to formation of the black smoke which is reffered as soot at generally consists of carbon content in it. It is clearly observed that for open-w piston the formation of soot is high.This is due to lower cylinder temperature in open-w piston and hence leads to incomplete combustion of fuel. 

Animation-

 

HC plot-

The unburnt Hydro-Carbons results from the Hydro-Carbons present in the fuel escaping from the combustion. The above shown animations clearly say that Open-W piston does not completely combust the air and fuel mixture because of the lower mean temperature inside the cylinder and also the geometry of the piston effects the process.This plot shows for Open-W piston the UHC is higher when compared to omega pistons. In order to achieve more good combustion process higher cylinder temperature aswell as perfect piston design is essential.

 

Co plot-

Generally the formation of carbon monoxide is because of incomplete combustion and the improper mixing of air and fuel.Here cylinder with open-w piston has improper mixing of fuel-air mixture which decreases the reaction rate. Hence the lower temperature is observed in open-w piston. Because of this lower temperature the flame propagation is not achieved and this leads to incomplete combustion of fuel.Hence large amount of carbon monoxide is formed.Even with higher values during combustion, the overall output values have decreased drastically for the Omega Piston.

 Animation-

 

Calculating Engine Performance:-

Open-W Piston-

Work done= 3028.53 N-m

Combustion Duration= 270.156 deg

Crank Speed= 1600rpm i.e. 26.66 rps

Degress per scond= 26.66*360 = 9597.6 deg per sec

Time for one degree = 1/9597.6 = 0.000104 sec per deg

Time for Combustion= 270.156*0.000104

                              = 0.028 sec

Therefore, 

  Power = Workdone/Time for Combustion

            = 3028.53/0.02814 

            = 107.62 KW

Hence, Power= 107.62 KW

 

Omega Piston-

 

Work done= 3409.28 N-m

Combustion Duration= 270.171 deg

Crank Speed= 1600rpm i.e. 26.66 rps

Degress per scond= 26.66*360 = 9597.6 deg per sec

Time for one degree = 1/9597.6 = 0.000104 sec per deg

Time for Combustion= 270.171*0.000104

                              = 0.0281 sec

Therefore, 

  Power = Workdone/Time for Combustion

            = 3409.28/0.0281 

            = 121.33 KW

Hence, Power= 121.33 KW 

 

 Power comparision between Open-W piston  and Omega Piston:-

 

IMEP comparision between Open-W piston and Omega Piston:-

 

Comparig IMEP and Power values  for Open-W piston and Omega Piston:-

From the above three comparisions it is observd that the power generated  from the Omega piston is higher when compared to the Open-W piston. This is mainly because the engine with Omega piston produces more heat energy and hence the maximum i.e. the heighest combustion temperature is obtained. Here the bowl geometry also plays a major role i.e. it helps to generate improved swirl which provide proper mixing of the fuel air mixture which later decreases the amount of unburnt fuel in the cylinder. 

 

Conclusion:

The combustion simulation is performed on the CAT3410 Engine with two different pistons i.e. Open-W piston and Omega piston as they have different bowl geometries. Simulations are carried out with these two different pistons various plots and animations are generated to characteriz the emissions.Comparing all the necessary parameters, it can be concluded that Omega Piston performs more efficiently when compared to Open-W piston. As we can observe from the above calculations, we can say that Omega piston produces more power than Open-W piston. In this case we can say the penetration of Air-fuel mixture into the chamber i.e penetration characteristics helped Omega piston to achieve more efficiency compared to Open-W piston.

Hence it can be concluded that, Omega piston profile is more efficient than the Open-W pisiton profile. It is recorded that Omega piston produce more power than Open-W piston and produce low amount of Hiroy_Soot,UHCand CO. But from the results the NOx concentration is higher in Omega piston as it has higher cylinder temperature during combustion process. As we have various techniques to reduce NOx like nozzle modification, varying compression ratio, EGR(Exhaust Gas Recirculation), SCR(Selective Catalytic Reduction) etc.