Emission Characterization of a CAT3410 Engine using CONVERGE

Objective:

1. To generate a sector geometry of the combustion chamber of the CAT3140 Engine for the Open W and Omega Pistion configurations.
2. To run a simulation of both these generated sector profiles using same parameters.
3. To analyse 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 fo rthe same.

Introduction:

The CAT3410 is an Industrial Engine by Caterpillar. It operates with diesel as the fuel. In diesel engines, fuel is put into the combustion chamber using injection througha nozzle. The fuel spray is subjected to break up and atomisation before being mixed with air and experiencing combustion in the chamber. A diesel engine combustion chamber with different piston haed will affect the combustion process and eventually affect the diesel engine performance.

The mixing of air and fuel in the combustion chamber happen 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:

The geometry profiles are generated using the Make Engine surface Tool available in Converge. For the Open W piston the surface profile is extracted and the sector is then generated from the bowl profile.

For the Omega piston, the sector is generated 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 anlysed in this project. Hence the sector angle is 60 degrees.

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 sector generated for the Open W piston can be seen in the figure below followed by the sector generated for the Omega piston.

Case Setup:

Materials

Gas simulation is chosen with Diesel2 as the parcel for spray modelling.

The reaction mechanism file is also setup along with the species file.

Simulation Parameters:

Simulation Start: -147 degrees

Simulation End: 135 degrees

Boundary Conditions:

The periodic boundary condition is set up as the sector geometry is only a part of a 360 degree cylinder.

Initial Conditions:

The current simulation there is only one region present

Physical Models:

Spray Model:

The fuel is modeled in the form of Lagrangian spray parcels with the parcels clustered towards the centre of the cone.

The O'Rourke model is chosen for turbulent dissipation.

The Frossling model is used for evaporation along with all the fuel getting evaporated into its pure vapour form.

To calculate the penetration length of the spray, the three conditions that must be satisfied are as follows:

The fraction of liquid mass 0.97

The bin size:0.001m

The minimum vapour mass fraction per cell:0.001

The Ntc collision Model is chosen with post collision outcomes.

Drop drag model:Dynamic Drop Drag

Spray wall Interaction:Droplets Rebound or slide

Injector Details:

Start of Injection:9 degrees

Injection Duration:21 degrees

Temperature:341K

Injected mass:2.7016e-5

The rate shape can be seen in the plot below

The Kelvin Helmoltz model and the Rayleigh Taylor model are used.

Combustion Model:

SAGE detailed chemistry solver with CVODES

For emissions: Extended Zeldovich NOx model and Hiroyasu Soot model

Turbulence Model:

RNG K epsilon model

Meshing:

Base Grid Size: 0.0014 in x, y z directions

Fixed Embedding:

AMR:

The timing map for the entire case setup can be seen below:

Results:

The simulation is carried out and the mesh generated can be observed in the animation clip below:

The fuel spraying that is modelling as lagrangian parcels is seen in the clip below followed by the velocity profiles generated in both the configuration of pistons.

Here it can be observed that the spraying of the fuel occurs when the piston is in the Top dead centre of the cylinder.

The velocity profiles of the combustion chamber obtained indicate that when the fuel is sprayed, atomisation of the fuel causes mixing with the compressed ait in the combustion chamber. This air and fuel mixture then starts to flow in the radial direction causing a swirl.

The following plot shows a omparison between the volumes in both configurations of pistons:

The volume curves of both configurations are coinciding as the compression ratios of both are selected to be same.

The following plot shows the comparison in the pressure in both the types of pistons followed by mean temperatures.

It can be seen that the mean pressure and temperature attained in the omega piston are higher than those on a Open W Piston.

The following animation shows the propogation of flame and the temperature distribution in both the configurations.

The temperature profiles of the combustion chamber show that when the piston moves towards the TDC, the air in the combustion chamber slowly gets compressed and this causes the temperature to slowly rise. When the fuel is sprayed into this high temeprature high pressure air, the resulting mixture ignites causing the observed increase in temperature in the combustion chamber before the volume of the mixture starts to increase.

The follwing plot shows the comparison between the Integrated Heat Release Rates of both configurations:

The IHRR of the omega piston can be observed to be higher and as the same fuel is used in both the configurations with the same amount of injected mass, an inference can be drawn that the combustion efficiency of the omega piston is higher.

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

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

Power and Torque Calculations:

The time per cycle can be calculated as follows:

`=60/(360timesRPM)=60/(360 times 1600)=0.000104 sec/ (deg`

As the duration is 270.156 degrees

`270.156 times0.000104=0.02814 sec/(cyc`

The power is calculated by

`P=W/(time)`

`P=(2piNT)/60`

Hence Torque is calculated as:

`T=(60P)/(2piN)`

For the Open W piston:

`P=3028.53/0.02814=107623W`

`T=(60 times107623)/(2 pi times 1600)=642.65Nm`

For the omega Piston Configuration

`P=3409.28/0.02814=121154W`

`T=(60 times 121154)/(2 pi times 1600)=723.45 Nm`

The Power and Torque generated by the Omega Piston configuration are greater than that of the open W configuration

The PV Diagram or 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 dne by the engine. Here from the comparison of the PV diagrams of the two piston configurations, the area under the omega piston P-V curve is higher indicating higher work done which corroborates with the values of work done obtained by the Engine Performance calculator Tool.

Emissions:

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

The quantity of Unburnt Hydrocarbons is higher in the Open W piston. The formation of Unburnt Hydrocarbons id dure 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 hydrocarbins produced.

Soot and Carbon monoxide are formed due to improper mixing of air and fuel. In the open W piston, the Higher fuel impingement could be the cause for the improper mixingof the fuel an air resulting in Higher Soot in the Open W pistion configuration.

The Nox emissions for a Omega Piston configuratiosnare way higher when compared to that of the Open W configurations. However the cueent environmental requirements are that the NOx emissions be reduced.Thus the usage of the omega piston to that of the Open W piston may be hindered.

Conclusion:

The simulation is carried out for two configurations of the piston in the CAT3410 Engine. The Work and, Power and Torque produced by the omega piston configuration is found to be higher that the Open W configuration.The IMEP of the omega piston is also higher indicating that the Omega piston configuration is better in terms of performance.

The Emissions produced by both the piston configurations are characterised, and it can be concluded that the soot, Co and unburnt hydrocarbons produced in the Open W piston are higher, however the NOx emissionsof the Omega Piston configuration are five times higher than that produced by the Open W configuration.