Emission characterization on a CAT3410 engine

AIM:

To perform 3-D simulation on the CAT3410 Diesel engine with two different piston bowl profiles using Converge3.0 to understand the effect of piston bowl geometry on the performance and emission characteristics of the engine and to post-process the results using ParaView.

Procedure:

A typical Diesel engine consists of a piston, cylinder wall, cylinder head. The simulation is done under closed conditions that mean without the usage of valves. We will be taking the sector of geometry for performing the simulations to reduce the computational cost. The injector is mounted on the cylinder head with multiple valves. The geomentry of the closed diesel engine should be created. With the help of the Make Engine Sector Surface tool, we should extract the geomentry profile. With the help of this profile data, we can create a closed engine sector with varying sizes.

The geomentry is created with the boundary flagging of Cylinder Head, Cylinder Wall, Piston, Front, and Back faces. For the present simulation, two individual piston profiles are used as shown below.

The sector angel we are using is: 45

The figure of the Bowl-Piston.

The figure of the open W-piston

These are the physical parameters of the two pistons.

Case Setup:

1) The Crank-angle based I.C engine is selected in the application tool.

2) MATERIALS

a) The therm.dat and gas.dat files are loaded under the Gas simulation.

b) The Diesel2 or n-heptane fuel is used and the liquid properties are loaded as shown below.

c) Form therm.dat file the number of species are loaded in the reaction mechanism.

d) The fuel spray enters into the cylinder in the form of Parcels this is condition is given in the Species module.

3) SIMULATION PARAMETERS

a)The Transient solver used in this simulation. For a gas flow and liquid flow solver, the compressible and incompressible conditions are given respectively.

b) The simulation time parameters are given as shown below.

4) BOUNDARY CONDITIONS

a)Piston

Boundary type: Wall

Wall type motion: Translating

Temperature: 553K

b)Front face

Boundary type: Periodic

Periodic type: stationary

Periodic shape: Rotational

c)Backface

Boundary type: Periodic

d)Cylinder Wall

Boundary type: Wall

Wall type motion: Stationary

Temperature: 433K

e)Cylinder Head

Boundary type: Wall

Wall type motion: Stationary

Temperature: 523K

5) The Initialization of the region is done as shown below.

6)PHYSICAL MODEL

a)In the spray model, the start of injection is given at -9deg crank angle and the duration of the spray is 21deg crank angle. The injection profile is given as shown below.

b)The sage combustion model is used which starts at -10deg crank angle and ends at a 135deg crank angle.

c) For calculating the NOx emissions the Zeldovich model is used and Hiroyasu model is used for getting soot emissions.

7) GRID CONTROL

a) The base grid size:0.004mm

b) The adaptive mesh refinement is done as shown below.

c) The fixed embedding is done for the nozzle, Piston, and Cylinder head. The below video links shows the working of Adaptive mesh refinement and Fixed embedding.

The mesh generation video link for bowl-piston: https://www.youtube.com/watch?v=E4-GhzQFQqg

The mesh generation video link for w-piston: https://www.youtube.com/watch?v=q1wBoa6flSo

RESULTS and DISCUSSION:

1) Ignition Delay: The Physical properties of the fuel such as viscosity, cetane number, and Flash properties will affect the Ignition Delay of the fuel. Another parameter that affects the Ignition delay depends on the in-cylinder surroundings i'e for ignition the fuel it needs to be vaporized and the temperature of the local region should be greater than the critical temperature so that it catches the flame and the combustion is started.

Ignition delay in bowl piston: 3.5deg crank angle

Ignition delay in W-Piston: 2.8deg crank angle

Spray injection video for bowl piston: https://www.youtube.com/watch?v=eO0R-3HiaI8

Spray injection video for w piston: https://www.youtube.com/watch?v=C3RoYwr6rk4

The same fuel is using in both cases so the variation in ignition delay is due to in-cylinder regions. If we observe the spray injection videos for both cases it can be noticed that in w-piston the contact of fuel and piston happening in a few crank angles only because of this fuel on contacting with hot piston is getting vaporized quickly when compared to bowl-piston this is the reason for less Ignition delay in w-piston.

2) Heat Release Rate :

The above graph is the comparison of the Integrated Heat Release Rate for two pistons.

The above graph is the comparison of the Heat Release Rate for two pistons.

• We can observe that the bowl piston is releasing the high amount of energy when compared to the w-piston this is because the Ignition delay of the bowl piston is high so that the more amount of fuel is accumulated within the cylinder at the time of combustion because of this more amount of energy is released when compared to w-piston.
• The peak heat release rate of the w-piston is occurring before bowl-piston this is because in w-piston the early combustion has occurred when compared to bowl-piston.
• Due to late combustion bowl-piston, the maximum temperatures are maintained at the time of the controlled combustion phase because of this the heat release rate is more in bowl-piston when compared to w-piston.

3) maximum Pressure:

The above graph is the comparison of the pressure Rate for two pistons.

The peak pressure is more in bowl-piston Due to the high heat release rate and more combustion of fuel in the bowl piston when compared to w-piston

Due to the above-specified regions, the IMEP of the bowl-piston is greater than the w-piston.

The Temperature contour video link for the bowl-piston: https://www.youtube.com/watch?v=0iTTDuMmrRI

The Temperature contour video link for the W-piston: https://www.youtube.com/watch?v=w8T09iaEepM

The pressure contour for video link the bowl-piston: https://www.youtube.com/watch?v=TcYb5vr5Zo8

The pressure contour for video link the w-piston: https://www.youtube.com/watch?v=JAHoh84x8js

EMISSIONS:

NOx Emissions:

The above figure shows the comparison of NOx emission for both cases.

The main reason for the formation of NOx emissions is due to the High temperature within the engine. From the HRR and IHR graphs, it is clear that the usage of bowl-piston leads to higher temperatures so this will gives the high NOx emissions. In this case, the W-piston gives good results.

The video for the formation of NOx in bowl-piston: https://www.youtube.com/watch?v=EwCrP-WAkPM

The video for the formation of NOx in W-piston: https://www.youtube.com/watch?v=aC17zYkYxSc

Carbon monoxide emissions:

The above figure shows the comparison of CO emission for both cases.

In general, the CO emissions are formed due to the incomplete combustion of a fuel-air mixture this may be due to the insufficient temperature or time. In this case, the CO emissions are more in W-piston is due to the insufficient temperatures within the cylinder.

The video for the formation of CO in bowl-piston: https://www.youtube.com/watch?v=iOHL8nsAKVY

The video for the formation of CO in W-piston: https://www.youtube.com/watch?v=IjWnKw8EKaY

Unburnt Hydro-Carbon emissions:

The above figure shows the comparison of UHC emission for both cases.

The unburnt hydrocarbon emissions are the direct result of incomplete combustion due to incomplete mixing of air and fuel. If we observe in the spray modeling videos for both cases it can be noticed that in the W-piston the time needed for vapourization of spray parcels is more when compared to bowl-piston this is the main reason for the formation of more UHC in W-piston.

Soot Emissions:

The above figure shows the comparison of Soot emission for both cases.

The main reason for the formation of soot emissions is insufficient mixing of air and fuel, low temperatures, late vaporization of the fuel. The w-piston contains low-temperature and late vaporization of fuel so this is the reason for more soot emissions when compared to bowl-piston.

CO2 Emission:

The above figure shows the comparison of CO2 emission for both cases.

The CO2 emissions are the results of complete oxidation of the fuel within the cylinder. On comparing the results of the two pistons it is clear that more amount of Oxidation of fuel is done in the bowl-piston when compared to W-piston so the usage of bowl-piston yields good results.

The above figure shows the engine performance data for the bowl-piston.

The above figure shows the engine performance data for the w-piston.

The indicated mean effective pressure for w-piston: 168738 pa

The indicated mean effective pressure for bowl-piston:197475 pa

The indicated mean effective pressure bar graphs for the two pistons

The Gross work done in W-piston: 411.867 N*m

The Gross work done in bowl-piston: 482.012 N*m

Power = Work/time

Time = 270.226 deg crank angle

Speed = 1600 Rpm = 1600*360/60 dps = 9600 dps

Time in seconds = 270.226/9600 = 0.02814sec

The power produced in W-piston = Work/time = 411.867/0.02814 = 14.636 KW

The power produced in bowl-piston = Work/time = 482.012/0.02814 = 17.129 KW

The power produced by the W-piston is 14.5% less than the bowl-piston.

The power produced bar graphs for the two pistons

Conclusion:

• Form the above performance and emission analysis it is found that bowl-piston is more efficient in both performance and fewer emissions when compared to W-piston.
• The Formation of NOx is high in bowl-piston this is due to high in-cylinder temperature maintained in the engine. The UHC, CO and soot emissions are lower in bowl-piston.
• The efficient mixing of fuel and air is done in bowl-piston, but in W-piston due to fuel impingement on piston surface mixing doesn't take efficiently so the performance of the engine reduces that leads to increase in the emissions.

This project will prove that the piston geomentry also plays a major role in engine performance and emission characteristics.