Project 2 - Emission characterization on a CAT3410 engine

OBJECTIVE:

To compare the emissions such as NOx, Soot and Unburnt Hydrocarbons as well as key performance parameters for an Open W Piston vs an Omega Piston in Diesel Engines.

PROCEDURE:-

1.1 INTRODUCTION:

A typical diesel engine consists of a piston, liner and a cylinder head. The type of simulation we are going to run is a closed cycle analysis which doesn\'t make use of valves. We will be removing only a sector for performing combustion simulations to improve computational efficiency. Injector is mounted on entire cylinder head and has multiple nozzles. The geometry for a closed diesel engine is shown below:

1.2 GEOMETRY:

Based on the data provided we can extract the head, bowl, forward and reverse profiles. Once we extract our profiles we import only the bowl profile and provide useful data to create an engine sector using the tool \"Make Engine Sector Surface\". The picture below shows us the tool bar where we make the sector surface:

The four individual boundaries flagged are Cylinder Wall, Cylinder Head, Piston, Front and Back Faces. These are done respectively for the two individual Piston profiles and they are shown in the figure given below:

We are only concerned with having one injector and one nozzle when considering the sector geometry for both the profiles depicted in the image above. Also the parameters for the engine geometry are given in the picture below:

Once we are done with providing suitable physical parameters for our engine we have to provide the suitable boundary conditions for each and every individual boundary for the two piston bowls. This is described in the table below:

Boundary	Temperature (K)	Boundary Condition
Cylinder Head	433	Wall-Stationery-Translating-Law of Wall
Cylinder Wall	523	Wall-Stationery-Translating-Law of Wall
Piston	553	Wall-Moving-Translating-Law of Wall
Front Face	No Value	Peroidic
Back Face	No Value	Peroidic

We then group all the individual boundaries into one region and provide values for the mass fraction for gases and emissions. The entire region is assumed to be at a particular temperature and pressure. All these are described in the picture given below:

The grid size is 1.4mm and we activate the AMR for both the velocity and temperature. Also Embedding is provided for our nozzle, cylinder head and piston. RNG k-ε model is used as our standard turbulence model. For combustion we are implementing the SAGE solver.

The meshing for both of our pistons is visualized below:

2. SPRAY MODELLING:

Spray Models make use of simplified mathematical models to capture the physics of the entire spray process. Our Lagrangian Spray usually C7H16 for diesel sprays is made up of a bunch of parcels. The collection of the entire parcels in the spray domain will make up our fuel spray. For our simulation the schematic shown below is followed:

The following procedure is then followed step by step as given in the image below:

• Turbulent dispersion refers to fluctuating velocity in the gas phase which is responsible for affecting the gas drop characteristics.
• Evaporation models describe the rate at which the radius of the drop shrinks and it also the rate at which mass is being transferred.
• The physical properties of fuel are captured well by Hydrocarbons. Liquid Heptane is converted into its gaseous form.
• We are keeping a maximum radius for our droplets as anything above that radius is solved by our ODE and anything below is not solved by our ODE.

• From injector up to the point of injection we can count the mass of fuel injected which accounts to 97% of total mass, which is the value for Liquid Penetration Length.
• The cell with vapor has a minimum amount of vapor present and that is characterised by 0.001.
• Distance from nozzle to the particular cell center with minimum vapor.i.e.Vapor Penetration Length.

• Collision models tell us how the individual parcels interact with one another.
• Dynamic Drop Drag model calculates the drag coefficient(Cd) based on the effect it has on the velocity and drag it has on the drop shape.

• When the drop comes in contact with the walls of the surface we want it to Rebound/Slide making use of O\'Rourke Models.

3. INJECTORS:

• We are using Diesel as the parcel species with a mass fraction of 1. The rate shape value is indicated by the profile shown in the image above.

• Next step we setup the models for our simulation. All of them have constants which control how the parcels breakup. A particular equation known as the Dispersion Relation will tell us how long it is going to take for the disturbance for a particular parcel to go unstable. Size constants occur are important because they increase or decrease the time taken for the break up to occur and also increase or decrease the size of the child droplets. All these values are given in the above

• The picture above depicts the data provided for the duration of time required for the spray injection to happen in our diesel engines.

• We have a solid cone for our nozzle spray and all the essential data are specified in the picture above.

• The important parameters for injectors are then calculated by making use of spray rate calculator in the tool box.

Spray Visualization in both our Piston profiles is shown below:

4. PLOTS AND DISCUSSIONS:-

Performance Parameters:

4.1. Power and Torque:

For the Open W piston making use of the engine performance calculator the following parameters are obtained for our engine. This is shown in the picture below:

RPM of Engine	1600
Time Per Degree	60/[360*1600]
Time Taken for moving 270.156deg	270.156*{60/[360*1600]}

Power = Work Done/Time Taken = 3028.53/0.02823 = 107280.55W (107.28KW)

The value of power is also given by the formula, P=[2*π*N(RPM)*T]/60

From the above formula we can calculate the value for Torque(T) = 640.6 N-m.

Similiar way we are going to obtain the values for the Power and Torque in the Omega Piston. Let us take a look at our Performance Parameters for our Omega Engine as shown in the figure below:

The value for the Power(P) and Torque(T) obtained are 121154.23W(121.15KW) and 723.45 N-m respectively.

From the results obtained we can conclude that Omega Piston operates at a power which is 11.45% higher than Open W piston.

4.2. Peak Pressure (P):

• The peak pressure of an Open W piston is higher compared to an Omega piston. However we can\'t conclude that Open W piston is better for our diesel engine based on a single parameter alone.

4.3. Mean Temperature (T):

• We can see that a low temperature for our Open W piston is beneficial if we are supposed to lower our NOx emissions. But there is a problem of fuel not being burned properly which needs to be verified by looking at other essential parameters.

4.4 Heat Release Rate:

• A higher heat release rate in Omega piston explains the high temperature and a low heat release in Open W piston with sudden dips in the curve tells us about the noise inside the engine.

• We can see that the total heat energy released from the combustion process alone in the Omega Piston i.e. 7279.46 J. While in the Open W piston the energy released is i.e. 7211.74 J. There is a discrepancy of close to 63 J/cycle. Also the rate at which the fuel burns in Open W piston is much slower when compared to Omega Piston.
• Open W has a low temperature and the combustion efficiency of the engine is also low.

4.5. Fuel Mixture:

• From the graph we see that the gaseous fuel vapor is burned lately in a Open W piston when compared to the Omega piston and that is why the temperature increase is also low.

4.6. Emissions:

• The NOx emission from the Open W piston are low to that of the omega piston. If our objective is to lower NOx then the Open W piston is a good choice. But if we are looking at the overall aspects of an engine it is quite reasonable to look at other emission profiles before jumping to any conclusions.

• Lowering Nox at the expense of other major pollutants is not feasible. This can be clearly seen in the graphs above for Soot,HC,CO etc as the Open W piston contributes for higher emissions when compared to Omega piston. Also if we analyse the hydrocarbon plot we see that a lot of unburned fuel is responsible for less NOx emissions.

The various emissions are visualized below:

CONCLUSION:

• By analysing the major parameters we can conclude that the Omega Piston performs better when compared to Open W piston if we take into account all the important parameters that are necessary for the engine to perform efficiently.
• Majority of fuel not vaporised quickly which is why there is a lot of unburned fuel in Open W engines. If we can allow fuel to vaporise properly by mixing it with air, by changing the angle at which the fuel sprayed from nozzle comes in contact with the piston, we can come up with better results.