EMISSION CHARACTERIZATION ON A CAT3410 ENGINE

EMISSION CHARACTERIZATION ON A CAT3410 ENGINE

Introduction:

• The diesel engine is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to the mechanical compression.
• Diesel engines work by compressing only the air. This increases the air temperature inside the cylinder to such a high degree that atomised diesel fuel injected into the combustion chamber ignites spontaneously.

Diesel Cycle:

• The Diesel cycle is a combustion process of a reciprocating internal combustion engine. In it, fuel is ignited by heat generated during the compression of air in the combustion chamber, into which fuel is then injected.

Process:

• 1→2 : isentropic compression of the fluid
• 2→3 : reversible constant pressure heating
• 3→4 : isentropic expansion
• 4→1 : reversible constant volume cooling

Importance of Piston Bowl Design:

• A piston bowl is a recess in the piston crown primarily used in (direct injection) Diesel engines, where it basically forms the combustion chamber. The design and shape of the piston bowl influences the movement of air and fuel during the compression stroke, thereby affecting the air/fuel mixture.
• A good mixture leads to a more efficient combustion, resulting in more power or better fuel economy. Additionally, using an effective piston bowl shape can reduce the in-cylinder emissions (like NOx and soot) and the cost for after-treatment.

Objective:

• Is to run simulations for two types of pistons and characterize the emissions (Soot, Nox and UHC).
• And to create cut-plan animations showing Soot, Nox and UHC and compare them between the omega and the open-w pistons.
• And also compare the imep and power values graphically.

Piston Profile Generation:

• For generating the W-type piston surface, Initially we have to extract the profile from the given .dat file and then by using the bowl profile we can make the engine sector surface. In this case we have used the sector angle as 45 degree.

• For generating the omega piston the bowl, They have already provided the bowl profile, We just want to import the bowl profile and provide the required inputs.

Case Setup:

Application: IC Engine (crank-angle based)

Materials:

• The material and its thermodynamic properties are imported using the given file.
• Parcel species: DIESEL2
• Passive species: Hiroy-soot & NOx

Simulation Parameters:

• Simulation mode: Hydrodynamic solver
• Start time: -147 deg
• End time: 135 deg

Boundary Conditions:

• For the piston the translating wall condition is used with the piston motion.
• For the front & back face the periodic type boundary condition is used.
• And for the cylinder wall & head the stationary wall boundary condition is used.

Regions & Initialization:

Physical Models:

Spray modelling:

• For the spray modelling we are using the parcel distribution as cluster parcel near cone center and the O\'Rourke model turbulent dispersion is used.

Injectors:

• Different shapes of injection rate profile should be investigated. Modelling results demonstrate that injection rate shape can have obvious influence on heat release process and heat release traces which causes different combustion process and emission. Here we are using the user defined rate-shape profile.

Combustion Modelling:

• Here we are using the SAGE combustion model. The SAGE detailed chemistry solver evaluates the chemical source term in each cell at each time-step. The detailed chemistry solver can be computationally expensive, and so this study includes adaptive zoning, which accelerates the simulation by grouping similar cells into zones and then performing detailed chemistry calculations once per zone rather than once per cell.

Turbulence Modelling: RNG K-Epsilon

Grid Control:

Base Grid:

• dx=dy=dz=0.002

Adaptive Mesh Refinement:

Fixed Embedding:

• In this case we are using both fixed embedding and adaptive mesh refinement for getting more finer mesh and for accurate results.

Simulation Results:

• The pressure starts to increase during the combustion cycle and reaches the peak pressure during the combustion and starts to decrease as the expansion take place. The pressure in the omega piston is slightly higher than the W-type piston.

• The temperature starts to rise slowly when the incylinder pressure starts to increase and during combustion cylinder reaches the peak temperature. By visualizing the graph we can understand that the omega piston has higher temperature than the W-type piston.
• On one side the lower temperature reduces the NOx pollution but in this case we can see in the animation there is some unburned fuel in the W-type piston, Which increases the hydro-carbon emission and also reduces the efficiency of the engine.

• The heat release rate plot gives as the understanding on how much heat has been released per seconds during the combustion process and the integrated heat release plot is the amount of heat released during the combustion alone.
• By seeing the integrated heat release plot we can say that the heat release rate of omega piston is significantly higher than the W-type piston, This is beacuse the fuel is completely vapourised in the omega piston whereas the W-type piston has some amount of unburned fuel.

• In the velocity animation we can clearly visualize that the fuel is impinging the piston at the start itself in the w-type piston, Whereas in the omega piston the penetration length of fuel is high when compared to the w-type piston. As the penetration length is low in the w-type piston the fuel is not geting vapourised, As a result the heat release rate is low when compared to the omega piston.

• By seeing the plot we can say that there is a large amount of gaseous fuel hittng the piston in the omega piston and burned, Whereas in case of the W-type piston by seeing the animation & plot we can say that there is some amount of gaseous fuel left in combustion chamber because of that the temperature is also low.

• NOx is produced from the reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures.
• By seeing the plot we can understand that the NOx emission is significantly higher in the omega piston when compared to the W-type piston.
• The NOx emission is caused due to the higher temperature(i.e. Higher the temperature greater the NOx). But in case of the W-type piston we can say that the temperature is low because there is some amount of gaseous fuel left which is burned lately due to that the temperature is low.
• So we can\'t say that W-type piston has lower NOx because there is some amount of fuel is unburned.

• The soot is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbon. We can see that the soot is higher in W-type than in omega type piston, this again confirms that there is some amount of gaseous fuel left in the combustion chamber due to that the soot emission is higher in W-type piston.

• Carbon monoxide (CO) is a colorless, odorless, tasteless, and toxic air pollutant is produced because of the incomplete combustion of carbon-containing fuels.
• As we can see that the W-type piston is higher in the carbon-monoxide emission than the omega piston this is because of incomplete combustion.

• We can see that the W-type piston is higher in the carbon-dioxide emission than the omega piston.

• Hydrocarbon emissions are simply unburned fuel being pumped raw into the exhaust system. It is mainly caused due to misfiring or due to decrease in compression. As we see that the W-type piston has the higher HC emission.

• By visualizing the plot we can understand that initially the cell count is low but during the combustion the temperature and velocity inside the cylinder increases, As we are using velocity & temperature AMR during combustion the cell count starts to rise when the temperature & velocity increases.

Significance of CA10, CA50 & CA90:

• The CA10, CA50 & CA90 are defined as the position of the crank angle (deg) at which the cumulative heat release reaches at 10%, 50% & 90% respectively.
• The physical significance of CA10 is that it is used to identify the start of ignition and the CA50 indicates the end of premixed combustion and the start of diffusion combustion of fuel and the CA90 where the propagating flame burns the unburnt fuel.

From the engine performance calculator:

W-type Omega

• CA10(deg) = -0.198 0.501
• CA50(deg) = 13.12 12.63
• CA90(deg) = 73.72 47.15

Indicated Mean Effective Pressure:

From the engine performance calculator:

• IMEP for open w-type piston = 1.44593e+6 Pa
• IMEP for omega piston = 1.73992e+6 Pa

Power Calculation:

• The power and torque of the engine is calculated with the below formula

Power, P = 2*Pi*N*T/60

Where,

P = Work/Time

Time = Time per degree*Duration

Time per degree = 60/(360*RPM)

From the engine performance calculator:

• Work done for open w-type piston = 3529.32 Nm
• Work done for omega piston = 4246.93 Nm
• Duration for open w-type piston = 270.213 deg
• Duration for omega piston = 270.156 deg

• Time per degree = 1.041e-4
• Time for open w-type piston = 0.02813
• Time for omega piston = 0.02812

• Power of open w-type piston = 125.46 Kw
• Power of omega piston = 151.02 Kw

Torque = 60*P/2*Pi*N

• Torque of open w-type piston = 748.78 Nm
• Torque of omega piston = 901.33 Nm

Conclusion:

• The simulations for two types of pistons is carried out and the emissions (Soot, Nox and UHC) are characterized. By comparing both the piston the NOx is higher in omega piston but the soot, CO2, HC, CO emission are low when compared to the open w-type piston. The reason because the NOx emission is low in the open w-type piston is that it has some amount of unburned fuel. So by comparing both the pistons the omega piston is lower in emission and also has the higher performance figures.