EMISSION CHARACTERIZATION OF CAT 3410 ENGINE

OBJECTIVE:

                 The objective is to run simulations with both the open-w and omega piston

                 Characterize the emissions (Soot, Nox and UHC).

                 Create cut-plan animations showing Soot, Nox and UHC and compare them between the omega and the open-w pistons. 

                 Compare the IMEP and power values of both pistons graphically.

INTRODUCTION:

                  The CAT3410 Engine is a heavy duty diesel engine used in industrial applications. 

                  The simulation is performed in closed-cycle, this means all the valves are closed. Thus there will be only two strokes - combustion and compression.

                  To Characterize the Emissions and compare the performance of this Engine with two different piston profiles. 

MAKE ENGINE SECTOR SURFACE:

                   

  This is 360 degree view of combustion chamber which has closed valves. Running simulation in the  entire combustion chamber is computationally expensive. Thus a sector of this geometry is extracted and by using a tool Make Engine Sector Surface piston profile is generated.

 BORE - It is the diameter of each cylinder in the engine.

 STROKE -  A phase of the engine's cycle (e.g. compression stroke, exhaust stroke), during which the piston travels from top to bottom or vice versa. 

CONNECTING ROD - A connecting rod is the part of a piston engine which connects the piston to the crankshaft.

WRIST PIN OFFSET - The wrist pin is a little offset to one side of the piston therefore the rod is not straight up and down when the piston is at TDC or BDC. This in turn allows the crank to rotate with much less resistance giving the engine more power and speed.

COMPRESSION RATIO -  The compression ratio is the ratio of the volume of the cylinder and the combustion chamber when the piston is at the bottom, and the volume of the combustion chamber when the piston is at the top.

SQUISH HEIGHT - It is used to specify the distance between the cylinder head and piston, when the piston is at TDC. Instead of compression ratio, squish height is used.

SECTOR ANGLE - It is used to specify the the number of nozzles present in fuel injector. Injector is placed in the centre of cylinder in diesel engine. The spray parcles are evenly distributed in 360 degrees. In this the nozzles are 45 degrees each totally 8 nozzles.

BOWL PROFILE - The bowl profile is imported thus graphically data are represented. Thus two different shaped bowl profile is created. Left side is omega pistion profile and right side is open-w piston.

                        

                 Omega piston                            Open-W piston

REGIONS AND INITIALIZATION:

                           There is only one region namely Incylinder region in which 355K temperature and 197000 pascal pressure is maintained. In this the diesel fuel(C7H16) reacts with air inside the combustion chamber and produces a stoichiometric reaction and CO2, water. Converge takes species concentration of these molecules as input for these purpose mass fractions of the product is calculated.

   

BOUNDARY CONDITIONS:

                  PISTON - Wall motion type - Translating; Surface movement - Moving; Temperature - 553K

                  CYLINDER_HEAD - Wall motion type - Stationary; Law of wall; Temperature - 523K

                  CYLINDER_WALL - Wall motion type - Stationary; Law of wall; Temperature - 433K 

                  FRONT_FACE -  Periodic type - Stationary; Periodic shape - Sector;Sector angle- 45 degree

                  BACK_FACE - Matched boundary

SPRAY MODELLING:

                   

 

Parcel distribution - For solid cone sprays, Converge assumes the injection is conical. For gasoline engines, 'Parcels evenly throughout the cone' is better than the 'cluster parcel near cone centre'.

            

Turbulent dispersion - O'Rourke model is better in diesel engine than the tke preserving model and No turbulent dispersion.

EVAPORATION MODEL - It defines the rate at which radius of drop shrinks and rate at which mass is being transferred. Frossling model is used here.

EVAPORATION SOURCE - "Source all base parcel species" is used which means, C7H16 liquid fuel is converted into C7H16 gaseous fuel. We are converting it into gas phase because gas phase chemistry are captured accurately with this species

                                          'Source specified species' evaporates according to specified species. 

                                          'Source all composite parcel species' is used when there is two species involved.                              

RADIUS ABOVE WHICH 1D HEAT DIFFUSION WILL BE SOLVED - It will control the drop temperature wheather it varies uniform or radially. Maximum value is maintained in order to maintain uniform temperature distribution. If the value is maximum Converge will automatically consider as Uniform distribution and if the value is minimum then it wil consider as radially varying temperature distribution.

 

LIQUID MASS FRACTION FOR CALCULATING SPRAY PENETRATION - When fuel injection takes place some of the fuel may vapourize if the ambient temperature is high. The fuel will penetrate into the combustion chamber upto certain length due to the high temperature in it. This length is known as Liquid Penetration Length. Converge calculates the penetrated spray mass by multiplying the mass fraction by total liquid mass in the domain. Liquid penetration length is not calculated based on the spray axis of the nozzle, it is calculated based on the injector axis. In this example, the mass fraction of the liquid fuel is 0.98 left side bar indicates the LPL.

 

BIN SIZE FOR CALCULATING VAPOR PENETRATION & FUEL VAPOR MASS FRACTION FOR CALCULATING VAPOR PENETRATION - Converge calculates vapor penetration length for each nozzle. The recommended bin size is to be twicethe size of cells in spray cone. Converge calculates the fuel vapor mass fraction in each cell inside the spray cone. It calculates the distance from the centre of nozzle to centre of cell. The fuel vapor mass fraction exceeds the user specified fuel vapor mass fraction.

 

USE COLLISION MESH - In a typical spray simulation, parcles can collide only with parcels in same cell which lead to grid sensitivity. Using collision mesh will lead parcel to collide across grid cells, this feature is independent of gas phase grid and used only for collision calculations.

DROP DRAG MODEL - Dynamic drag model is the advanced method because the drop coefficient calculation accounts for variation in the drop shape. This model invokes the TAB model to determine the drop distortion. This model is mostly preferred.

COMBUSTION MODELLING:

                      Combustion facilitates the energy transfer in an engine. Converge contains a detailed chemistry solver and simplified combustion models. SAGE detailed chemistry solver is most predictive and accurate way to model combustion. It also accurately model ignition and laminar flame propagation. Simplified combustion models are generally less computationally expensive and predictive than SAGE. It may provide acceptable results for specific applications.

 

COMBUSTION TEMPERATURE CUTOFF & MINIMUM HC SPECIES MOLE FRACTION - Increase in the cell temperature and minimum hydrocarbon species mole fraction to reduce the number of cells to perform combustion. If enough hydrocarbons are not present in the cell incomplete combustion can take place.

START TIME & END TIME - The combustion starts certain angle before the spark begins and  the end time is when the exhaust valve opens.

 

EMISSION MODELLING:

   

The modelling of Nox which is also known as thermic oxide is described by extended Zeldovich mechanism. This mechanism involves the reaction of N2 with oxygen atoms, Nitrogen molecules  and hydoxide atom to form nitric oxide.

  

The above equations are solved by assuming nitrogen has steady state population and assuming the below equation as equillibrium.

 

The soot formation is modeled by a two step formation and oxidation model known as Hiroyasu Soot model. The rate of change of soot mass is equal to

 - Soot Formation;  - Soot Oxidation

 

Advantages of SECTOR Simulation:

                        The computational efficiency is higher since we simulate only for one sector. This simuation can be run only during closed cycle analysis. In sector simulation only a part of combustion chamber is simulated so the number of cells captured is also less so computational time is less. 

When will the sector approach not work:

                       The sector simulation does not takes place in open cycle analysis. In open cycle analysis the intake and exhaust valves are kept to be open and the position of these valves must be varied according to time. The sector simuation will not capture the valve movement with respect to time. If the injector is not symmetric about the centre axis of the engine then sector simulation does not work. 

MESH GRID:

             Base mesh of 0.004m is used. Sequential embedding of scale 1 was enabled at the piston and cylinder head between -20 degree to 180 degree when the combustion occurs. Nozzle embedding of scale 2 was provided to accuratley calculate fuel spray. Also, velocity and temperature adaptive mesh refinement is also used.

  Mesh Generation           

ENGINE PERFORMANCE:

OMEGA PISTON:

 OPEN-W PISTON:

              

 POWER = WORK/TIME

 Engine, RPM = 1600

 Time per degree = 60/360*1600 = 1.0417. 10^-4 sec/deg

 For OMEGA PISTON

  Time per 282.018 degree = `282.018*(1.0417*10^-4)`

                            TIME   =  0.0293 sec/cycle

                             WORK = 3409.28 Nm

                            POWER = 3409.28/0.0293

                           POWER = 116357.679 W

                           POWER = 116.35 kW

                            TORQUE = P * 60/(2*pi*N)

                                           = 116.35*60/(2*3.14*1600)

                            TORQUE = 694.765 Nm                           

  For OPEN-W PISTON

   Time per 282.003 degree = `280.003*(1.0417*10^-4)`

                               TIME = 0.02916 sec/cycle

                                WORK = 3028.53 Nm

                                POWER = 3028.53/0.02916

                               POWER = 103859.053 W

                               POWER = 103.85 kW

                               TORQUE = P * 60/(2*pi*N)

                                             = 103.85*60/(2*3.14*1600)

                              TORQUE  = 620.123 Nm 

        The power and torque produced from Omega piston profile is greater than the open-W piston profile.                         

PRESSURE:

              The pressure in Open-W piston is 11.5 MPa whereas the pressure in Omega piston is 11 MPa.   

Indicated mean effective pressure (IMEP) is a measure of the work output for the swept volume of the engine, The result is a fundamental parameter for determining engine efficiency as it is independent of speed, number of cylinders, and displacement of the engine.

        For Omega piston, the  IMEP = 1.38679e+06 Pa

        For Open-W piston, the  IMEP = 1.2308e+06 Pa

MEAN TEMPERATURE:

 

                     The mean temperature of omega piston profile is 1767K whereas the temperature of open W piston profile is 1464K. Thus, there is higher temperature in Omega piston it means that most of the fuels are burnt and that is the reason for high temperature heat release in the combustion chamber of Omega piston. Low tmperature in the Open-W piston shows that there might be not all the fuels burnt so there is less temperature heat release. 

Temperature flow in both the piston

    

          The total heat release in Omega piston is 7279.4606  J   

          The total heat release in Open-W piston is 7212.0672 J       

          Calorific value of C7H16 = 48.06 MJ/kg

          Amount of fuel injected per cycle = 2.70167e-05 Kg

          Total Heat content of the fuel = Amount of fuel * Calorific value * no.of injector = 10387.38082 J

          For Omega piston, Combustion Efficiency = Total heat release/Total heat content of the fuel 

                                                                      = 7279.4606/10387.38082

      Combustion Efficiency of Omega piston = 70.09%

         For Open-W piston, Combustion Efficiency = Total heat release/Total heat content of the fuel 

                                                                      = 7212.0672/10387.38082

     Combustion Efficiency of Open-W piston = 69.43%     

The heat released in Omega piston is higher this clearly shows that combustion efficiency is higher in Omega piston than Open-W piston.

 SUMMARY:

PARAMETER	DIFFERNCE BETWEEN BOTH THE PISTON PROFILE
Work done	The workdone in omega piston is higher than open-W piston.
Power	The power in omega piston is higher than open-W piston.
Torque	The torque produced in omega piston is higher than open-W piston
IMEP	The IMEP value in omega piston is higher than open-W piston
Mean Temperature	Mean temperature in Omega piston is higher than open-W piston
Integrated Heat Release	The total heat release in Omega piston is higher than Open-W piston
Combustion Efficiency	The Combustion efficiency of Omega piston is slightly higher than Open-W piston

EMISSION CHARACTERISTICS OF OMEGA AND OPEN-W PISTON:

            The major pollutants emitted in diesel engine are Soot, Nox, Carbonmonoxide and unburnt hydro carbons.

SOOT:

           Hiroy soot is mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons.

              The soot produced from open-W piston profile engine is 1.7467e-06 kg whereas the soot produced from omega piston profile engine is 1.5155e-06 kg. Thus lower soot is produced in Omega piston profile than open W piston.

Hiroy-soot Emission

NOx:

         In the exhaust of IC Engines, NOx refers to a class of compounds called nitrogen oxides.

              The Nox produced in open-W piston profile engine is 2.0884e-06 kg whereas the engine with omega piston produces 1.0645e-05 kg. Thus lower concentration of NOx is produced in open W piston profile than omega piston profile. The Nox emission is less in Open-W piston because there is less temperature in the combustion chamber and Nox is generally produced when the temperature is high.

 Nox Emissions

UNBURNT HYDRO CARBON:

       Hydrocarbons are a class of burned or partially burned fuel, hydrocarbons are toxins.

           The concentration of UHC released in open W piston profile is 6.2411e-05 kg whereas the UHC released in omega piston profile is 3.1292e-05 kg. Thus open-W piston profile releases higher UHC than omega piston profile. This clearly shows that air-fuel mixture is not well combusted in open-W piston profile due to its geometry and lower mean temperature inside this cylinder.

UHC Emissions

 SUMMARY:

EMISSIONS	DIFFERENCE BETWEEN BOTH PISTON PROFILE
Hiroy-soot	Omega piston profile produces lower soot than open W piston.
Nox	Omega piston produces higher concentration of NOx than open W piston profile.
UHC	Omega piston profile produces lower UHC released  than the open-W piston profile.