Emission characterization on a CAT3410 engine

Emission characterization on a CAT3410 engine

OBJECTIVE:-

To run a 3D 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.

GEOMETRY:-

A tool called Make engine sector surface is used to create the engine the engine sector model and to perform the closed cycle analysis. The reason behind generating engine sectors is that the geometry is symmetric about its axis and by using periodic boundary condition at the forward and backward face; the entire combustion chamber can be simulated using a sector, thereby saving lot of computational resource.

For Diesel engine, the fuel injector is mounted exactly at the centre of cylinder head and it will have multiple nozzles. In this case, the spray will be symmetrical. Hence to increase the computational efficiency, one sector of the engine is taken and combustion is simulated with it. It will lead to faster run times. This is called sector modelling and it is carried out as shown below.

Different Bowl Profiles Open-W type Omega type

The geometry available with us has six nozzles with engine specifications:-
1.Bore = 0.13716 m
2.Stroke = 0.1651 m
3.Connecting rod = 0.263 m and Speed = 1600 rpm
4.Compression ratio = 17.5 : 1
5.Sector angle = 60 degrees (No. of Nozzles = 6 ; Sector angle = 360/60 = 60 degrees) i.e. each injector with one nozzle.

SETUP:-
Converge studio provides us a separate application for IC engine flow.

2. Materials:-

1.Gas simulation and Reaction mechanism are selected and thermodynamic properties are imported for the equation to be solved.

2.Parcels are used to simulate a special type of liquid that is used in conjunction with spray modelling. Setting up a parcel simulation is identical to setting up a liquid simulation.

3.DIESEL2 species is selected under parcel simulation as this has very close properties to diesel.

3. SIMULATION PARAMETERS:-

1.Transient simulation is selected and Full hydro case is run. Running a no hydro simulation ignores transport equation, spray and combustion thus greatly reducing computational time.
2.Running the simulation in this mode is an efficient way to check for errors in surface motion and mesh creation.
3.We have previously run this and checked for mesh simulation earlier.

4. BOUNDARY CONDITIONS:-

The following boundaries each with different colours.

The boundary conditions are shown with numeric values assigned.

Piston

Front Face:

Back Face

Cylinder wall

Cylinder head

5. REGIONS AND INITIALIZATION:-
Here we create region id to assign temperature and pressure to each region and initialize species, passives and turbulence in each region. By doing this we can highlight and isolate all boundaries associated to a region.

Region0 : In Cylinder Region
Temperature = 355K
Pressure = 197000 Pa
Species:
O2 = 0.23029
N2 = 0.76765
CO2 = 0.0014304
H2O = 0.0006296

6. SPRAY MODELLING:

The Kelvin-Helmholtz model and Rayleigh-Taylor model are used for spray modelling. An injector with a nozzle is used to spray the fuel.
Converge offers injector mechanism that consists of „n‟ number of nozzle each with different size, orientation, cone angle etc.

• Parcel Species : DIESEL2
• Start of Injection: -9.0 deg
• Injection Duration: 21.0 deg
• Total Injection Mass : 2.70167e-05 Kg
• Fuel Temperature: 341.0 K

Injector with one nozzle as 6 nozzles are divided into 6 parts i.e. 60 degree sector angle Rate shape profile

7. COMBUSTION MODELLING:-

• The SAGE detailed chemical kinetics solver is used for the combustion modelling.
• CONVERGE uses the multi-zone model which accelerates the chemistry calculations by grouping together similar computational cells and then invoking the chemistry solver once per group rather than once per cell.
• On the other hand generally less computationally expensive and less predictive. This may be used if we want to use global parameters correctly or just find out the maximum combustion temperature
• Start time: -10 deg
• End time : 135 deg
• Turbulence Model: RNG K-ε

8. GEOMETRY MESH & EMBEDDING:-

• Base mesh size of 1.4 mm was provided in the x, y, z directions

• Sequential embedding of factor 1 was defined at the piston and cylinder head boundaries between the crank angles -20 deg to 180 deg when the combustion is said to occur.
• In addition to this, a nozzle embedding of factor 2 was provided at the injector to capture the fuel sprays
• Along with mesh embeddings, velocity and temperature adaptive mesh refinement was also enabled.

Adaptive mesh Refinement :-

• It eliminates the need to mesh the whole model finely. Adaptive mesh refinement provides such a dynamic programming environment for adapting the precision of the numerical computation based on the requirements of a computation problem in specific areas which need precision while leaving the other regions at lower levels of precision and resolution.

VI LINE PLOTS :-
The variation of pressure, mean temperature, heat released rate, integrated heat release for both the piston bowl profiles were plotted and analysed.
Pressure Plot :

• From the plot, it can be seen that, peak pressure for Open W piston type 11.5 MPa is a bit mhigher than the peak pressure of Omega piston type 11.2 MPa. The difference being about 0.3 MPa which is due to difference in combustion chamber geometries/shape of piston as pressure is inversely proportional to area. Nevertheless, in case of pressure comparison both piston types has the same amount of credibility.

Mean Temperature Plot :

• Omega piston tend to produce higher mean temperatures due to better mixing of air-fuel mixture inside the combustion chamber leading to higher heat release rates. Whereas, in the case of Open W piston, due to the effect of liquid spray infringement, the combustion process is delayed leading to lower performance ratings.

Integrated Heat release plot :

• From the above integrated heat release plot, it can be noticed that for the same amount of fuel injected, the energy outputs have some deviations about 64 J for both the piston types. Hence, there are discrepancies in the total heat released due to combustion differences between the two piston bowls for the same quatity of fuel injected. The reason being that the fuel which has been impringed upon the Open W piston bowl doesnot get vaporized in time for combustion to occur even though all the fuel vaporizes due to high cylinder temperatures.

Heat Release Rate Plot :

• From the plot below, one can infer that heat release rate for Omega piston type is more than that of Open W piston type. This is due mixing of air-fuel mixture inside the combustion chamber leading to higher heat release rates. The plot is smoother for Omega type than Open W type and it indicates that there waves forming leading to knocking/detonation phenomenon.

Emission Plots :

• IC engines generate undesirable emissions during the combustion process. The major causes of these emissions are non-stoichiometric combustion, dissociation of nitrogen, and impurities in the fuel and air.

Hydro Carbons :

• These consist of small non equilibrium molecules formed when large fuel molecules break up i.e. thermal cracking during combustion reaction. In general CI engines has combustion efficiency of 98%. This means only about 2% of HC fuel being emitted. This may be due to wall deposit absorption, crevice volume etc.

Carbon monoxide:

• Carbon monoxide is a colorless and odorless but a poisonous gas generated when operated with fuel-rich equivalence ratio. When there is not enough oxygen to convert all carbon to CO2 some carbon ends up as CO.

Oxides of Nitrogen:

• Diesel engines operate at a higher temperature and pressure than petrol engines. These conditions favour the production of NOx gases. The quantity depends on the volume and duration of the hottest part of the flame. NOx is created mostly from nitrogen in air, especially at high temperatures. Most of these will be NO and NO2 and produced due to energy limitations, oxygen and nitrogen do not react at ambient temperatures. But at high temperatures, they undergo an endothermic reaction producing various oxides of nitrogen. As NOx are produced during the combustion process when nitrogen and oxygen are present at elevated temperatures, Open W tend to produce lesser NOx emissions compared to Omega piston due to the fact that lower
  cylinder temperatures are maintained in Open-W compared to Omega piston.

Soot emission:

• Internal combustion engines produce soot as a result of incomplete fuel combustion. Ideally, complete combustion in a cylinder would only produce carbon dioxide and water, but no engine is completely efficient. Because of the way that fuel is injected and ignited, soot formation occurs more commonly in diesel than in gasoline engines. Unlike gasoline engines where the fuel/air mixture is ignited with a spark, fuel and air entering the diesel cylinder ignite spontaneously from the high pressure in the combustion chamber. The fueland air mixture in diesel engines typically do not mix as thoroughly as they do in gasoline engines. This creates fuel-dense pockets that produce soot when ignited. While the majority of soot easily escapes through the exhaust, some gets past the piston rings and ends up in the oil.

Carbon dioxide:
Carbon dioxide is a green house gas which should be considered for its reduction in emission. CO2 is a result of complete combustion.

VI PERFORMANCE CALCULATIONS :-
Performance Evaluation (Open-W type) :

i) Power (P) :

• Power (P) = Work done / Time taken
• Work done = 3028.53 N-m (From engine performance calculator)
• Time per degree = 60 / (360*1600)
• Hence time for 270.156 degrees = (270.156 * 60) / (360*1600) = 0.02814125 sec/deg
• Power (P) = 3028.53 / 0.02814125
• Power (P) = 107.62 KW

ii) IMEP :

• IMEP = 1.24076 E6 Pa (or) 12.4076 Bar (From below calculator)

• Work done can also be calculated under the area of P-V graph.

Open-W type piston

Performance Evaluation (Omega type) :

i) Power (P) :

• Power (P) = Work done / Time taken
• Work done = 3409.28 N-m (From engine performance calculator)
• Time per degree = 60 / (360*1600)
• Hence time for 270.171 degrees = (270.171 * 60) / (360*1600) = 0.02814281 sec/deg
• Power (P) = 3409.28 / 0.02814281
• Power (P) = 121.14 KW

ii) IMEP :

• IMEP = 1.39878 E6 Pa (or) 13.9878 Bar (From below calculator)

• Work done can also be calculated under the area of P-V graph.

Omega- type piston

• Hence we can say that Omega Piston is 11.16 % more efficient than Open-W piston.

IMEP v/s POWER

IMEP v/s POWER

• The above graph compare IMEP vs POWER graphically where blue line indicate Open-W type and red indicates the Omega type piston

CONCLUSION :-

• The simulation of sector model is done i.e. Open-W type piston and Omega type of CAT 3410 diesel engine and their parameter plots and performance parameters are compared. The Omega type piston outperforms Open-W type in many critical factors and is 11.16% more efficient than the latter with lesser concentrations of Hiroy soot, UHC, CO were generated in the former one. The NOx concentration was higher in the Omega piston due to the higher cylinder temperatures. NOx emission can be reduced by primary methods such as retard injection, fuel nozzle modification, change of compression ratio, water direct injection, water emulsification, exhaust gas recirculation (EGR) and secondary method such as selective catalytic reduction (SCR).
  
  

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