Emission Characteristics on a CAT 3410 Engine
Emission Characteristics on a CAT 3410 Engine
by Ashraya Band
OBJECTIVE
To run a simulation of a CAT3410 diesel engine using two different piston bowl profiles and to understand the effect of Piston bowl geometry on the performance and emission characteristics of the engine .
INTRODUCTION
Internal Combustion Engine is the primary source of Input for any fuel operated machine. It is the Prime mover for small to large machines. The invention of IC Engine dates back to decades of year past and since then efforts has been made to increase the efficiency of the Engine.
Various Engines have been designed with focus on how to get the controlled combustion at its optimum efficiency which emphasizes the importance of parameters such as pressure, temperature velocity etc. which has to be optimized at the value where we get controlled efficient combustion.
After the design we must make analysis of the flow in the engine which is done via CFD simulation soft wares that enables us to visualize and obtain the flow parameters from which we can determine the engine efficiency.
In this Project we shall simulate and understand the effect of Piston Bowl Profiles and evaluate the emission characteristics with the data obtained after completing the simulation.
We shall use Open W Piston and Omega Profiles for the same engine. We have to do the analysis by means of Sector creation , a sector can be determined with reference to the number of nozzles on the injector . A sector of 60 degree means there are 6 Nozzles in the injector. The results from one sector gives the idea about the whole Piston.
GEOMETRY SET UP
Sector Creation
Sector can be created through means of a tool called make Engine Sector where we have to first extract profiles from surface.dat file.
Later details as follows must be entered:
Bore : 0.13716 m
Stroke : 0.1651 m
Length of connecting rod : 0.263 m
Since our analysis is about the Bowl Profile, we shall import the profile of the bowl and create surface as follows:
Open W Piston & Omega Piston
CASE SET UP
Spray Modelling
In Gasoline Injected Engine the quality of Air Fuel Mixture is highly affected by the injection and ambient conditions, including fuel type and injection pressure .With the help of Spray modelling we can replicate the exact flow but that shall require more computational time therefore we shall approximate to get a just model.
A model is type of mathematical approximation that has been done to capture a particular type of physics .
Parcels are distributed evenly throughout the cone , Frossling model is used as Evaporation Model and the source as composite species . Maximum radius of ODE droplet heating which shall control if the drop temperature is uniform or radially varying.
In a typical spray simulation parcels can collide only with parcels in the same cell which can lead to grid sensitivity .With the collision mesh parcels can collide across the grid cells , with the collision mesh spray parcels are obtained properly . When the parcels enter the gas phase it encounters the drag
Combustion Modelling
Combustion models for CFD refers to combustion models for computational fluid dynamics. Combustion is defined as a chemical reaction in which a hydrocarbon fuel reacts with an oxidant to form products, accompanied with the release of energy in the form of heat.
Combustion facilitates the energy transfer in an engine .
The SAGE detailed chemistry solver uses local conditions to calculate reaction rates based on principles of chemical kinetics
Turbulence Modelling
The Reynolds-averaged Navier–Stokes equations (or RANS equations) are time-averaged equations of motion for Fluid flow. The idea behind the equations is Reynolds decomposition, whereby an instantaneous quantity is decomposed into its time-averaged and fluctuating quantities. The RANS equations are primarily used to describe Turbulent flows. These equations can be used with approximations based on knowledge of the properties of flow Turbulence to give approximate time-averaged solutions to the Navier Stokes Equation.
Timing Map
The timing map gives us an overall timely information as what we have specified for our Engine .
Graphs and Discussions
Pressure
p-V Diagram
As it can be observed that the pressure for Omega Piston is less than the Open W Piston from the both the graphs above , this is not a distinctive factor to distinguish between the two profiles . It can be said that the Piston performance is good in terms of Pressure .
Area under the p-V curve represents the work done , from the graph the Omega type profile Piston produces more work as compared to the W type piston .
Temperature
The temperature is significantly high for Omega Piston as compared to the Open W Piston which might suggest that the combustion has not happened properly , there is some unburnt fuel etc.
Temperature Contour
Liquid Spray
C7H16 (Gaseous)
The gaseous C7H16 is more in terms of Omega Piston that means there is vapor which burns later .
Heat Release Rate
Integrated Heat Release Rate
As it can be inferred from the diagram that the heat release for the Omega type profile is more than the Open W Piston and that is due to the fact that the spray penetration and Turbulent Kinetic Energy is more in the Omega profile (ref. tke & Spray penetration graphs) .
This leads to proper combustion and hence more heat release .
Performance
Power and Torque of the Engine
Power defines as the maximum power the engine can produce whereas Torque is the turning power of the Engine which is due to the Piston movement.
Power
Power = Work / Time
Torque
Torque = `(60*Power)/(2*Pi*RPM)`
Data obtained from Engine Performance Calculator for Two Profiles :
Open W Bowl Profile Piston
RPM = 1600
Work = 3028.53 Nm
Duration: 270.156 deg
Time per Duration = `((60)/(360*1600))*270.156 = 0.02814125 s/(deg)`
Power = 3028.53/0.02814125 = 107.62 KW
Torque = (60*107.62*10^3)/(2*pi*1600) = 642.64 Nm
Omega Bowl Profile Piston
RPM = 1600
Work = 3409.28 Nm
Duration: 270.171 deg
Time per Duration = `((60)/(360*1600))*270.171 = 0.02814281 s/(deg)`
Power = 3409.28 /0.02814281 = 121.14 KW
Torque = (60*121.14*10^3)/(2*pi*1600) = 723.38 Nm
Performance Wise The Omega Bowl Profile Piston is better than the Open W type Bowl Profile Piston.
Spray Penetration
Mesh Contour
What we see at the in the Time step 71 and 75 is that in case of Open W type piston we have liquid impingement i.e. Spray is directly impinging on to the surface whereas in the Omega profile we have spray penetration length . The phenomenon in the W piston is the reason why majority of fuel is not getting vaporized and large amount of fuel is unburnt, not getting vaporized is low air fuel mixture that leads to improper combustion.
For this case the spray angle can be modified so that vaporization can occur properly.
Turbulent Kinetic Energy
The TKE graph describes the way turbulent kinetics is in the two different profile. For the Omega type profile the turbulent kinetic energy is more which is good as it supports combustion to happen in an efficient way.
The motion that occurs within the cylinder is quite important to speed the evaporation of the fuel, this enhances the mixing of air and fuel and thus increases combustion speed and efficiency.
That is why more heat is liberated in the Omega type due to higher mean kinetic energy per unit mass.
Turbulent Kinetic Energy Contour
Emissions
Hiroy Soot
The above plots is the representation of soot produced calculated via Hiroyasu Model , the soot produced is greater in the W type piston , that is because of higher level of Spray wall impingement in the W Type piston .
Hiroy Soot Contour
Hydro Carbon
The amount of Hydro Carbon Produced in the W type Profile is more and that is due to incomplete combustion and the end of the cycle the amount is reduced to zero as it gets eventually burned later .
Carbon Monoxide
The Carbon Monoxide is at higher amount in Omega Piston than W type during combustion Phase and eventually becomes zero at the end of the combustion phase indicating god combustion . Whereas in the W type profile the CO stays after combustion also and later is forced outside in the exhaust stroke indicating improper combustion .
Carbon Monoxide Contour
Nitrogen Oxides
The Nitrogen Oxide is less produced in the W type Piston than the Omega Piston which contributes to the fact that the NOx formation is primarily dependent upon the temperature in the combustion process , since the temperature was at higher side in the Omega type profile therefore there is more NOx formation .
Nitrous Oxide Contour
Summary of Emission
Open W Bowl Profile Piston
Omega Bowl Profile Piston
The graphs shows a summary of emissions for two different types of Bowl profile , as we observe the CO 'Carbon Monoxide' forms at a greater extent in the Omega Piston , and the Hiroy Soot and Hydrocarbon forms more in W Piston due to incomplete combustion .
The NOx formation is at higher rate in Omega Piston due to more heat formation in this profile and as we know heat acts as catalyst for formation of NOx .
it is alos deduced that CO & HC stays for a longer period and is forced out as exhaust during exhaust stroke .
Conclusion:
After Simulating and analyzing the results for two different kind of Bowl profiles we can say that the Omega type Piston has a better performance at the cost of more emissions (NOx in specific) which is prominently due to high temperature in the Combustion chamber , The Open W piston performance is less but the NOx obtained is less due to less heat in the Combustion Chamber .
Efforts to reduce emissions have been made and methods like Exhaust Gas Recirculation and Catalytic Converters are significant at reducing the emissions .
Also apart from the modification in the Engine , the emissions also depends upon the quality of fuel , since every region has varying quality therefore it is observed that manufacturers make different kinds of engines specific to the regions considering the Hydrocarbon and Sulphur content.