(abstract of PhD thesis)
SCIENTIFIC COORDINATOR: PhD candidate:
PhD. Engineer Paul BOC Ă NETE Mahran Dawwa
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List of Contents
Abbreviations …………….…………………………………………………...........….…………..v
List of Symbols and indexes………..…….…………………………….……………….………...vi
List of table……….……………………………………………………………………....….….....x
List of figures………………………………………………………………………….……….….xi
Chapter 1. Introduction ...………………………………………………....………...…………..1
1.1.The importance and actuality of the subject ………………………...…….............…..1
1.2.Objectives ……..…………………...………………………………………………….1
1.3. Study contents.…...……………………………..…………..……………..………….2
Chapter 2. DIESEL ENGINE OVERVIEW ……………………..………….………..........…..4
2.1. Diesel engines ………………………………...………………………………………4
2.2. Marine diesel engines classification ………………………………………….....……4
2.3. Thermodynamics of marine diesel engines ………………....…………………….….5
2.3.1. Air standard diesel cycle ……………………………….…………………...5
2.3.2. Actual cycle of four stroke diesel engines…………….…………………….5
2.4. Diesel engine emissions…………………………...…………………………………..6
2.4.1. The effects of NOx emission on environment…………………..…….….....9
2.4.2. The methods and systems for controlling NOx emissions…………….…..10
Chapter 3. OVERVIEW ON THE COMBUSTION AND NOX FORMATION IN
DIESEL ENGINES
……………...…………………………………………………….………...12
3.1. Combustion phases……………………………………….………………………….12
3.2. NOx formation……………………………………………...………………………..13
3.2.1. NOx formation mechanisms…………………………………………….....13
3.2.2. NOx formation models…………………………………………………….15
3.2.3 NOx previous studies…………………………….…………………………15
Chapter 4. THERMODYNAMIC MODEL FOR THE PREDICTION OF NOX
EMISSIONS IN DIESEL ENGINES .………………………………………………...……..…18
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4.1. Single-Zone Thermodynamic Model for the prediction of thermal NO…...………...29
4.1.1. Cylinder volume and area modeling…………………………………….…21
4.1.2. Intake stroke……………………………………………………………….23
4.1.3. Compression stroke…………………………………………………………..……24
4.1.4. Modeling of combustion characteristics and NOx formation……......…….27
4.1.4.1. Ignition delay and heat release models in diesel engines………..27
4.1.4.2. Heat transfer models in diesel engines…………………….….…34
4.1.4.3. Engine mechanical work and internal energy……………………37
4.1.4.4. Diesel fuel combustion ………………………...….………….....39
4.2. Prediction of NOx emissions based on two-zone model………………..…………...43
4.3. Chemical equilibrium and reaction rate in burned gases…………………...………..47
Chapter 5. COMBUSTION SIMULATION AND NOX PREDICTION IN DIESEL
ENGINES BASED ON CFD………………………………………………………………… …50
5.1. Introduction …………………………………………………….…………...……….50
5.2. Simulation steps……………………………………………….……………..………51
5.2.1. ICE step……………………………………………….……………………52
5.2.2. Geometry step ……………………………………………………….…….52
5.2.3. Mesh step…………………………………………….…………………….57
5.2.4. ICE solver setup step………………………………………………….…...60
5.2.5. Setup step ……………………………………………………….…………60
5.2.6. Solution step ………………………………………………………………61
5.2.7. Result step …………………………………………………………………62
5.3. Simulation of flows inside the cylinder of diesel engines during the compression stroke……………………………………………………………………………………………..62
5.3.1. The type of flows inside engine cylinder…………………………………..62
5.3.2. Simulation of turbulence inside engine cylinder………………………......63
5.3.3. Boundary conditions……………………………………………………….65
5.3.4. Simulation results discussion………………………………………………66
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5.4. Simulation of temperature inside the cylinder of diesel engines during the compression stroke………………………...…………………………………………………......71
5.5. Simulation of the injection process in diesel engines………………………………..79
5.5.1. The theory of fuel atomization and evaporation………………………...…79
5.5.2. Diesel fuel spray model……………………………………………..……..80
5.5.3. The effect of diesel injection and evaporation on NOx formation……..….82
5.5.4. Results discussion……………………………………………………….....82
5.6. Combustion simulation in diesel engines based on CFD……………………..….….88
5.6.1. Simulation of combustion process in diesel engines based on eddydissipation model ………………...…………………………………………………………..…..88
5.6.2. Simulation of combustion process in diesel engines based on laminar finiterate model…………………………………...…………………………………………………....92
5.6.3. Simulation of combustion process in diesel engines based on finiterate/eddy-dissipation model……………………………….……………………….……………..95
5.7. Simulation of NOx emissions …………………………………...……….………….97
Chapter 6. EXPERIMENTAL SECTION
…………………………………………...………..98
Chapter 7. DISCUSSION AND VALIDATION OF PREDICTED NOX EMISSIONS BY
USING THERMODYNAMIC MODEL ……………………..……………………………...104
7.1. Validation and discussion of thermodynamic model……………………………….104
7.1.1. Validation of thermodynamic model……………………………….…...104
7.1.2. Optimizing the accuracy of the thermodynamic model…………………..108
7.1.3. The model sensitivity……………………………………………….…….112
7.1.3.1. The effect of wall temperature…………….…………………....112
7.1.3.2. The effect of changing air temperature coefficient……….…….114
7.1.3.3. The effect of residual gases temperature………….……………115
7.1.3.4. The effect of heat transfer model…………………………….…115
7.1.3.5. The effect of parameter m1 and m2………………………….…117
7.1.3.6. The effect of parameter A
 ………………………………...……119
7.2. Discussion and validation of predicted NOx emissions by using CFD model…......120
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7.2.1. Comparison the results of CFD models………………………………..…120
7.2.2. The validation of CFD models………………………………….………...122
7.3. Conclusion…………………………………………...……………………………..123
Chapter 8. SIMULATION STUDYS ON CONTROLLING NOX EMISSIONS IN DIESEL
ENGINES
…………………………………………………………………..………..………...125
8.1. Effect of injection angle on NOx emissions…………………………...……...……125
8.2. Effect of injection timing on NOx emissions…………………………………........129
8.3. Effect of Cone angle on NOx emissions……………………………………………134
8.4. Effect of load on NOx emissions…………………………………………………...140
8.5. Effect of EGR on NOx formation………………………………………………..…143
8.6. Effect of different reduction strategies on the formation of NOx…………………..148
8.6.1. The first strategy of NOx reduction………………………………………148
8.6.2. The second strategy of NOx reduction………………...…..……………..151
Chapter 9. CONCLUSION
………...………………………………………..………………...156
9.1. Summary…………………………………….……………………………...…...….156
9.2. Personal contributions ……………………………………………….………...…...158
9.3. Future work…………………………………………….…...……………………....159
References …………………...…………………….………………………………..………….160
Appendix 1 Coefficients for the molar enthalpy of gases……………………………...…….…172
Appendix 2 Equilibrium Constants……………………………………………………………..173
Appendix 3 NOx prediction program ………………………………………….……………….175
Appendix 4 NOx Calculation time by the use of MATLAB program…………….……………201
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Thesis Summary
Chapter 1 explains the importance, the objectives, and the content of the thesis.
Chapter 2 is an introduction which explains the principles of diesel engines, the applications of diesel engines in marine sector, and diesel engines exhaust emissions and their impacts on the environment.
Chapter 3 a thermodynamic model based on two-zone model was performed to predict
NOx emissions from diesel engine at different engine operating regimes. Al the phenomenon such as heat release, heat transfer, and ignition delay which take place into combustion chamber were explained and modeled. an improvement was introduced in order to enhance the accuracy of the model by modifying two vibe function by using a third function, which resulted in improving the flexibility of two vibe function in describing the heat release phenomenon in diesel engines at different engine operating regimes
Chapter 4 In this chapter, a CFD model was performed to predict NOx emissions from diesel engines. For this purpose a combustion chamber geometry was created by using
SOLIDWORKS program, then the geometry was imported, decomposed, and meshed by using
ANSYS ICE program. For the sake of predicting NOx emissions, different physical processes were simulated, such as the injection process, the flow inside the engine cylinder, and combustion process. The simulation process was carried out by the use of KH-RT model for simulating injection process, K-epsilon model for simulating the turbulence inside the combustion chamber, three different combustion models laminar finite-rate model, eddy-dissipation model, and finiterate/ eddy-dissipation model. NOx emissions modeling was performed based on resolving the transport equation for nitrogen monoxide NO
Chapter 5 is the experimental section, engine test stand and all sensors which were used for measuring the different parameters were illustrated in this chapter.
Chapter 6 NOx emissions where predicted at different engine operating regimes by using a thermodynamic model based on two-zone thermodynamic model and other sub-models such as heat release model, and heat transfer model. The program that was created on MATLAB program shows that it is able to predicted NOx emissions at different engine regimes with a satisfied accuracy. The results were very satisfied in terms of accuracy when they were compared and validated with the experimental measurements.
The results show that CRI-MECH 3.0 equation is more accurate in predicting NOx emissions than Heywood and Baulch et al. equations.
Introducing a correlation coefficient is the second enhancement which improved the accuracy of thermodynamic model at low and high loads, and maintained a good accuracy at medium loads.
Sensitivity analysis showed the influence of different parameters such as the temperature of residual gases, vibe function parameters, and the parameter of burned zone temperature on the model sensitivity.
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The results of simulation study show that eddy-dissipation model is more accurate in predicting NOx emissions from diesel engines than laminar finite rate model. The results of simulation study by using eddy-dissipation model show that eddy-dissipation model is able to predict NOx emissions from diesel engines at different engine operating regimes with a good and satisfied accuracy.
CFD model is able to predict thermal NO and prompt NO. The contribution of thermal NO and prompt NO in the total predicted NO was illustrated and explained, while thermodynamic model is just able to predict thermal NO, All simulated, modeled, and experimental results confirmed that the formed NOx are linked with engine operating regimes.
Increasing the engine load at the same engine speed leads to increase the formed NOx, while increasing the engine speed at same engine loads leads to reduce the formed NOx emissions.
Chapter 7 After the validation of the results of CFD model at different engine operating regimes, the CFD model was used in simulation studies for simulating the effect of injection timing, cone angle, injection angle, and EGR on the formation of NOx emissions. Every simulation case was compared with the base case that validated with the experimental measurements. Simulation study was performed to show the effect of the combined use of EGR and retarded injection timing on the formation of NOx emissions, this study used two different
EGR rates and two different injection timing. The results of simulation study confirmed that NOx emissions can be reduced by using EGR technology.
The results of simulation study confirmed that NOx emissions can be reduced by retarding the injection timing. The simulation study showed that by the combined use of EGR and retarded injection timing, NOx emissions were reduced. Two different strategies of the combined use of EGR and retarded injection timing were discussed and illustrated . The results of simulation study show that injection angle and cone angle are an important factors that influence the formation of NOx emissions in diesel engines.
Personal contribution
The main personal contributions can be listed as follows:
Building a specialized program on MATALB which is able to predict NOx emissions from diesel engines at different engine operating regimes.
Introducing a correlation coefficient for improving the accuracy of the thermodynamic model in NOx prediction.
Detailed description of the designing steps of combustion chamber geometry, and the steps of preparing the geometry to be used in simulation study.
Simulating thermal NO and prompt NO by using three different combustion model and by the use of ANSYS program.
Simulation study of the effect of EGR technology on the NOx formation in diesel engine
Simulation study of the effect of injection parameters such as injection timing, cone angle and injection angle on the NOx formation in diesel engines.
Simulation study of the effect of two different strategies that combine EGR and retarded injection timing on the NOx formation in diesel engines.
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Publications
Dawwa M., CFD Simulation of Injected Fuel Spray in Marine Diesel Engines,
International Journal of Scientific Research,Vol.4, Issue 7, pp.124-127, 2015.
Dawwa M., Simulation of Combustion Process in Diesel Engines Based on Eddy
Dissipation Model, Proceedings of the International Conference of Mechanical
Engineering ICOME2015, Craiova, Romania, October 8th -9th , 2015.
Dawwa M., Baboiu I.L., Simulation and Modeling of Compression Stroke in Diesel
Engines, Proceedings of the International Conference of Mechanical Engineering
ICOME2015, Craiova, Romania, October 8th -9th , 2015.
Dawwa M., Bocanete P., A CFD study on the effect of injection parameters on the formation of NOx emissions in diesel engines, Journal of Marine Technology
&Environment, Vol.1, pp.29-32, 2016.
Dawwa M., Bocanete P., The preduction of NOx emissions from diesel engines based on two-zone thermodynamic model, Journal of Marine Technology &Environment, Vol.1, pp.33-36, 2016.
Dawwa M., Bocanete P, CFD study on the reduction of NOx emissions from marine diesel engines, Constanta Maritime University Annals, Vol.24, pp.63-66, 2015.
Dawwa M., Bocanete P., Prediction of NOx emissions from marine diesel engines based on eddy dissipation model, Constanta Maritime University Annals, Vol.24, pp.67-70,
2015.
Dawwa M., Zakria Y., Predicting the Fluid Flow Shape in the Combustion Chamber of an
Internal Combustion Engine by Using CFD Simulation, Journal of Ecomomics and
Technology Knowledge, Vol.1, No.3, pp.67-72, 2015.
Future studies
NOx emissions are considered one of the main challenged issues that face diesel engine companies and developers especially after implementing a new regulations of NOx emissions from marine diesel engines. Reducing the emitted NOx with maintaining fuel consumption without any increase will be the focus point on the future study. The main two directions that can be followed are:
The combination of different reduction technologies such as the combination between
EGR and pilot injection.
Studying the possibilities of reduction the NOx emissions by modifying the combustion chamber shape.
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