Emission Characterization on a CAT-3410 Engine with W open profile and Omega profile

OBJECTIVE: To run the simulation close cycle of CAT3410 Diesel engine with two different pistions W_piston and Omega_based_pistion.And run simulations with both these pistons and characterize the emissions (Soot, Nox and UHC) and showing cut plane animation of these emissions.

INTODUCTION: Now-a-days the raising competition in engine industry and emission restrictions due tothe environmental concerns, manufacturers are forced to evaluate engine performance using different combustion chamber geometries.

In this project, we introduced two different types of pistons to simulate using converge CFD package, to evaluate engine efficiency, power, torque ,combustion efficiency and emissions(Soot,Nox,UHC).

METHODOLOGY:

PISTON PROFILE GENERATION: The image below shows a 360 degree combustion chamber which has closed combustion chamber. We need to run simulation of entire combustion chamber is computationally expensive and require more time. Thus, a sector of the geometry extracted which would be the objectives of the project. A tool we can use to make engine sector surface to accomplish this task.

FIG 1.1: Engine 360 degree bowl surface

FIG 1.2: Make engine sector surface

Step-1: To extract profile from \"surface.dat\". This generates forward profile, reverse profile, head profile and bowl profile of the combustion chamber.

Step-2: Entering the geometric parameters namely bore, stroke, connecting rod length and combustion ratio.

Step-3: To specify the periodic angle of piston and use bowl profile option to export bowl surface file which is a graphical representation of piston and click the make surface. It will generate 3D geometry of two different types of pistons which contain fully boundary flagging and surface finishing.

FIG 1.3: Open W Profile piston

FIG 1.4: Omega Profile piston

Case Setup:

1.Materials:

In this process, firstly we are providing the C7H16 diesel fuel and \"thermo.dat\"file which contain types of species being used in this simulation.

In this step, we define type of parcels(C7H16) being used in this simulation which contain physical properties with respect to temperature and provide reaction mechanism file(mec.dat) which instructs how the combustion process takes place in engine.

In species, we define type of parcel spray into the cylinder and passive(Hiryo soot, NOX) which defines emissions (user specified) after combustion takes place.

2. Simulation parameters:

In this process, we are defining engine parameters where simulation start and end time and defining run parameters what kind of simulation takes place in engine.

3. Boundary conditions and regions:

The sector engine has only one region which is in cylinder region. The temperature of this region is 335K and pressure is 197000pa. The diesel fuel C7H16 reacts with air inside the combustion chamber to undergo stoichiometric reaction to give carbon dioxide and water as the products. Converge takes in species concentration of this molecules as inputs for this purpose mass fraction of the products were calculated.

Defining the boundary conditions wall type and periodic type boundary condition.

3.1. Periodic type boundary condition:

This type of boundary to generate the simulation results one portion of thge domain that can be reflected to other domain. Its better to reduce the simulation time.

3.2. Wall type boundary:

This boundary condition defines the turbalent flow at a certain point is proportional tothe logerthemic distance from the wall or boundary fluid region.

There are 3 types of wall boundary conditions:

1)Law of the wall

2)Slip

3)No slip

4. Spray modelling:

Converge is well euip for fuel injectors and spray to solve. It is well suited for spray wide varities of fuel injector options. Primarily, combustion process can be depends how fuel spray injection, cell size, velocity. Fuel injection is of two types:

1)Solid

2)Hollow

Converge uses lagrangian spray model when we are using liquid spray.You can generate accurate fuel mass flow through the nossle head. Converge can also simulate the mixing and evapouration of multi-fuel fuel sprays. The fuel spray has different physical properties. These are 1)Primary breakup

2)Secondary breakup

3)Drop drag

4)Collision and coansense

5)Turbalent dispersion

6)Evapouration

FIG 1.5: Spray modelling

4.1. Parcel distribution:

For solid cone spray converge assume conical. In that there is two types of spray

1)Cluster parcel near cone centre

2)Cluster parcel through out cone centre

4.2 Evapouration model:

For evapouration modelling converge provides two models.

1)Frossling

2)Chiang

For this setup frossling model is used. Next, we define evapouration sources which specifies how to converge simulates multi-component liquid species will be evapourated into the base species as no composite files has been provided.

1)Source specified species

Parcels evapourate to user specified species.

2)Source all composite parcel species

If composites are defined multi-component liquid species evapourate into composite species.

If composites are not specified multi-composite liquid species evapourate into base species.

3)Source all base parcel species

Multi-component liquid species evapourate into the base species.

4.3 Maximum radius for ODE droplets heating:

After this defined parameters for controlling the model performance where we defined the maximum radius for ODE droplet heating which controls if the dropping temperature is uniform or rapidly varying if the drop radius exceed the maximum value define then converge will assume rapidly varying temperature and solve heat equation.But, if the drop radius does not exceed the maximum limit that converge will assume uniform temperature distribution.

4.4 Penetration:

When fuel is injected into the cylinder some of the fuel has been evapourated by ambient temperature.

Liquid penetration(LPL):

When you have injected the fuel spray into the cylinder that has been contatin fuel mass fraction is equals to the user specified value, where it has located the distance from injection is called \"LPL\".

Vapour penetration(VPL):

Firstly, we define the value of parcel contain vapour and that is not exceed the bin size. The parcel contains vapour from user specified value, if not that is not consider vapour penetration length.

4.5 Collision/coalesense:

This model parcels collision with another parcel, which can be lead to grid sensitivity.Drop let collisions have proven very difficult to calculate. In addition to the complex physics, droplet colllision has presented several numerical difficulties.These difficulties include high competetional cost and large numerical errors. In light ofthe large roll that droplet collisions can have in determining drop size. This situation is most unfortunate. In response to the need for faster and more accuratecollision calculation. A new algorithm has been developed for calculating the incidence of droplet collision. The mostly used two methods:

1)Orouke

2)NTC(No Time Counter)

Orouke algorithm is consistent with the stochastic nature of spray simulations, where only sub sample of droplets is tracked.The tracked drops represent parcels of varying numbers of drops. The size number and velocities of parcels determine the probability of colliding with other parcels. Schmidt and Rutland showed that this approach is second order accurate in space, but fails dramatically with typical mesh-resolution. The problems of mesh dependency are particularly severe when using catitian mesh so, the problem of mesh dependency .

A faster more accurate replacement for existing collision algorithm has been developed the method called \"NTC algorithm\". It is not grid dependent and is much faster than older algorithms.

4.6 Drop drag model:

When parcels enter through the gas phase, they counter drop drag whoose affects can be introduced in the simulation. Dynamic drop drag model is selected which calculates drag coefficient by taking into account the influence of velocity and drop shape. There are 2 types.

1)Spherical drop drag

2)Dynamic drop drag

4.7 Spray wall model interaction:

1)Rebound/Slide

2)Wall flim

3)Vanish

Under spray wall interaction model rebound/slide was selected. Here, the drop rebounds or slide along the wall after impingement.

4.8 Time/Temp/Mass/Size:

Although injection does not continuously takes place inside an IC engine. It can be lumped into fuel mass/cycle.

1)Total number of injected parcels per nossles = 50000

2)Injection start time = -9

3)Injection duration = 21

4)Fuel temperature = 341

5)Total injected mass = 2.70167e-0.5 kgs

4.9 Injectors/Nozzle:

Injectors contain a set of nozzle and spary parcels along injector axis.

Nozzle diameter= 0.000259 M

Circular injection radius = Nozzle Radius

Spray cone Angle=9

Nozzle Radial Position = 0.00097

5. Combustion Modelling:

Combution is basicaly produces the heat energy from chemical energy during chemical reaction in engine.Combution processes are being used detailed chemistry solver using principle of chemical kinetics.In convege we are using different types of combution models has been used and its takes lot of time to simulate because in each cell to simulated by detailed chemistry solver its contain large ODE equestion.while simulation it takes lot of time, so accelerates the simulation time we had activate the jacobian,re clycle temperature and Multizone.Coverge provide different combution models Mainly pre mixed and non premixed

1)SAGE(simulation and atomization on grid environment)

2)CTC (characterstic time combustion).

3)G_equation

4)RIF(Representive interactive flamelet)

5)CEQ(chemical equilibrium)

6)ECFM(Extended Characterstic Flame Model)

5.1 SAGE:

Simulation and atomization on grid environment this model is to simulate using local condition to calculate the chemical reaction by principle of chemical kinetics,This model uses to predict the ignition delay and combution.Chemical kinetics is defined the rate of species concentration using Arrhenius Law.In that we are providing Mechanism file (Mech.dat) it has contain physical properties and instructions of chemical reaction.When we are solving ODE we will get Source term that will put in transport equation, This is called coupled transport equation.

FIG 1.6 Combuction model

Chemistry solver produces large ODE that can be solved by CVODES. In this model start time and end time is most expansive because chemistry solver sove ODE at each cell,In that provide cell temperature and provide HC species mole fraction 1e-8, that is specified the cell undergo combution, if not that is not consider combution.Combution processes is too slow 3 times lesser than transport. so we need to accelerate.

5.2 Emmision:

Detailed chemistry solve simulate the hirroy soot and NOX emmision.

1)NOX can simulate by converge has Zeldovich Model

2)Soot can simulate by converge has Hiroy emphirical model.

6. Turbulence Modeling:

The mostly Flow is turbulent in IC engines its very hard to calculate because flow is unsteady and choatic. The flow high fluctvating with respect to time so its its hard predict the velocity and physical properties.At the wall flow is contineuosly increasing due to high viscous forces.So we were using two methos

1)RANS (Reynolds Averaged Nevier Stoke Equastion)

2)LES(Large eddy simulation)

In this simulation we were used RANS turbulent Modelto calculating the velocities and physical properties of fluid,LES model is used only Large eddies and Contineously flow ,its eliminate small edies the effect of resolved flow is linear flow+large eddies and it is refer for lagrgian purporse and research laburities.

6.1 RANS:

It is focous on mean flow and mean flow properties,it is decomposition processes .It has decomposition the NE into Averaged mean time and Fluctvation.

`u=u^_ + u^\'`

When we were going to solve NE using RANS turblent model we will ge un solved stresses there are call by reynolds stress. Reynolds stress contains Molecular stress and turbulent stress.These stresses solved by different turbulent models 1)k-e model

2)RNG k-e model

3)standed k-e model

4)k-w model

Using this models will be solve unkown stresses that will define log-law model,law of the wall define the average velocities in turbulent flow at certain point is proportional to the logerthemic distance from the wall.When we use law of the wall boundary condition its automatically enable Turbulent Model.The velocity define using y+ value its define behavier of flow field in viscous sub layer if we will get y+ value below 30 then it is laminer and the flow in viscous sub layer ,30<y+<100 then it is turbulent flow and have high reynolds number.

7. Grid controls:

A base meshof 1.4 mm was provided. Sequential embeddingof scale 1 was enabled at the pistion and cylinder head between -20 and 180 when the combution occurs. Nozzle embedding of Factor 2 was providedto accuretle capture fuel spray .apart from this velocity and temperature adapative mesh refinmentwas also used

W_type_piston Omega_type _pistion

FIG 1.7 Meshing

Animation:1

Results:

Integrated Heat release rate:

• The total integrated heat release plot for Open_W_profile is 7109.07 J
• The total integrated heat release rate for Omega _profile is 7244.34 J

Power and work calculation:

• work done by open_w_profile (w)= 2984.87 NM
• work done by Omega_profile (w) = 3420.07 NM

1)Open_w_profile engine Power=w/t = (work)/(time)

Time per degree=`60/(360*RPM)`

Engine RPM=1600

Time per degree = `60/(360*1600)`

time per degree = `1.0147 * 10^(-4) sec/(degree)`

Time per 270.189 degree = time per one degree * 270.189

Time per 270.189 degree = 0.2814 sec/cycle.

Power= Work/Time = `2984.87/0.2814`

Power = 106.07KW

2)Open_Omega_profile engine Power=w/t = (work)/(time)

Time per degree=`60/(360*RPM)`

time per degree = `1.0147 * 10^(-4) sec/(degree)`

Time per 270.189 degree = time per one degree * 270.189

Time per 270.189 degree = 0.2814 sec/cycle.

Power= Work/Time = `3420.07/0.2814`

Power = 121.53 KW

Calculate Torque:

1)Open_w_profile

P=`(2*pi*N*T)/60`

T=`(P*60)/(2*pi*N)`

T=`(106.07*60)/(2*pi*1600)`

T=633.38 NM

2)Base line_Omega profile

P=`(2*pi*N*T)/60`

T=`(P*60)/(2*pi*N)`

T`=`(121.53*60)/(2*pi*1600)`

T=725.67 NM

Pressure:

Mean Temprature:

The engine with omega piston produces more heat as a result of better combustion of air and fuel mixture inside the chamber. From the animation video we can see some amount of spray parcels in open omega profile engine do not combust. This can be attributed to a delay in combustion process, which is reflected in the plot below. The spray parcels does not combust completely, becuase of it has low pressure than omega profile engine.

Animation 1:

Heat Release Rate:

Emmisions Result compare between Two pistons:

Hiroy Soot:

The major pollutant emitted in the combustion of diesel in an internal combustion engine. It is deep black substance which consists of mainly amorphous carbon produced by the incomplete burning of fuel. The formation of soot is described by the hiroy empherical soot model. Since, omega profile engine combust faster than open omega.

Animation 2 :

NOX:

It is produced from the reaction of nitrogen and oxygen gases during combustion especially at high temperatures.

Animation 3:

UHC:

It results from hydo carbon present in the fuel escaping combustion. From the above parcel animation it was found the open W piston does not thoroughly combust the air and fuel mixture becuase of it has lower mean temperature inside the cylinder.

Conclusion:

As we seen above results of different pistons profiles in that Omega profile is better than open_W_profile both interms of power ,torque, emissions.As we seen engine profiles Omega piston bowl have sharp edges its help to increase pressure at the wall so temperature and pressure has increases,thats why omega piston produce high temperature and pressure.Omega piston have good emission results compare to Open w profile,but Nox emission Omega piston has high because it has high temperature in cylinder.Through out the W piston profile animation video we seeen unburn fuel spray particles because of Low temperature in cylinder than Higher production Hiroy soot,UBC and Co