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Modelling NOx-Formation in Combustion Processes

ISSN 0280-5316 ISRN LUTFD2/TFRT--5769--SE Modelling NOx-Formation in Combustion Processes Christian Schwerdt Department of Automatic Control Lund University June 2006 Document name MASTER THESIS Date of issue June 2006 Department of Automatic Control Lund Institute of Technology Box 118 SE-221 00 Lund Sweden Document Number ISRN LUTFD/TFRT--5769--SE Supervisor Hubertus Tummescheit at Modelon Lund, Sweden Anders Rantzer Automatic Control Lund, Swden Author(s) Christian Schwerdt Sponsoring organization Title and subtitle Modeling NOx-Formation in Combustion Processes (Modellering av NOx-Formation vid f rbr nning) Abstract As the regulations of pollutant emission is getting more and more strict, models of pollutant formation , as a part of system level models for control design, are needed.

ISSN 0280-5316 ISRN LUTFD2/TFRT--5769--SE Modelling NOx-Formation in Combustion Processes Christian Schwerdt Department of Automatic Control Lund University

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Transcription of Modelling NOx-Formation in Combustion Processes

1 ISSN 0280-5316 ISRN LUTFD2/TFRT--5769--SE Modelling NOx-Formation in Combustion Processes Christian Schwerdt Department of Automatic Control Lund University June 2006 Document name MASTER THESIS Date of issue June 2006 Department of Automatic Control Lund Institute of Technology Box 118 SE-221 00 Lund Sweden Document Number ISRN LUTFD/TFRT--5769--SE Supervisor Hubertus Tummescheit at Modelon Lund, Sweden Anders Rantzer Automatic Control Lund, Swden Author(s) Christian Schwerdt Sponsoring organization Title and subtitle Modeling NOx-Formation in Combustion Processes (Modellering av NOx-Formation vid f rbr nning) Abstract As the regulations of pollutant emission is getting more and more strict, models of pollutant formation , as a part of system level models for control design, are needed.

2 In this thesis NOx (nitrogen oxides) formation is modeled. A method is developed to mix equilibrium and non-equilibrium reaction equations to model NOx formation in Combustion Processes . This algorithm reduces high-index DAE systems by introducing ``reaction invariants''. Two models are built with help of this algorithm which describe NOx formation during Combustion in a cylinder in a spark ignition car engine and in a gas turbine (for more information about the Combustion models see [4] and [7]). The models use both equilibrium and non-equilibrium/dynamical reaction equations. A rough verification of the cylinder model is also done.

3 Keywords Classification system and/or index terms (if any) Supplementary bibliographical information ISSN and key title 0280-5316 ISBN Language English Number of pages 45 Security classification Recipient s notes The report may be ordered from the Department of Automatic Control or borrowed through:University Library, Box 3, SE-221 00 Lund, Sweden Fax +46 46 222 42 43 Contents1 Background .. About Modelon AB .. Objectives .. Outline .. 52 Combustion .. Molar Gibbs free energy .. Equilibrium and non-equilibrium/dynamic reactions.. Stoichiometry .. Stoichiometric coefficient matrix.

4 Equivalence ratio .. Premixed and non-premixed/diffusion flame .. NOx formation .. Thermal NOx formation .. Fuel NOx formation .. Prompt NOx formation .. Modeling NOx formation .. Algorithm to model reactions containing both equilibrium anddynamic reactions .. 153 Modelica and Dymola .. Model of a cylinder in a spark ignition car engine .. Model of Gas Turbine .. 2814 SIMULATIONS and Verification of Cylinder model .. Simulation results from the Gas turbine model .. Conclusion .. 392 PrefaceThis thesis is a required part for the degree of Master of Science in Engi-neering Physics at Lund Institute of Technology (LTH), and constitutes of20 weeks full time university studies.

5 The thesis has been written in coop-eration with Modelon AB in Lund and the work has been performed duringwinter and spring would like to thank my supervisor at Modelon AB, Hubertus Tummescheit,for always having time to meet and talk about the work. He spent many hoursdiscussing the work and his ideas and solution suggestions helped me get thework done. During this time I ve learned very much about Combustion temperature in Kelvin (K)PPressure in Pascal (Pa)PoutDownstream pressure (Pa)VVolume inm3if not specified otherwise (m3)MiNumber of moles of substance iMTTotal number of moles of all substancesFinMolar rate inflow (moles)FoutMolar rate outflow (moles)

6 Stoichiometric coefficient matrix EQStoichiometric coefficient matrix only including equilibrium reaction equations MReaction invariantsxiMole fraction of substance iRUniversal gas constantKEquilibrium constantrReaction rate inmolem3 s Equivalence ratio Null vector to EQnTotal number of equationsyTotal number of substanceskNumber of equilibrium reactionszNumber of null vectors to EQ Density (kgm3) Thermal layer thickness (m)PrPrandt numbercpHeat capacity (JKg K) Viscosity (kgm s)utTurbulent intensity (ms)hSpecific enthalpy (JKg)sSpecific entropy (JKg K) hMolar enthalpy (JM ole) sMolar entropy (JM ole K) gMolar Gibbs free energy (Jmole)HTotal enthalpy (J)QHeat (J)MMX Molar mass (Kgmole)mMass (Kg)UTotal internal energy (J)uSpecific internal energy (JKg)4 Chapter BackgroundWe learn more and more about the effects of pollutants like nitrogen oxides(NOx).

7 In the case of NOx it poses as a risk both to the environment aswell as to human health. NOx reacts with moisture and other compoundsto form dangerous particles when inhaled and NOx emission also contributesto the formation of ozone smog. Acid rain can also be traced back to NOxemission as well as the weakening of the ozone layer to some extent andmany other negative effects. The biggest source of NOx emission comes fromthe fossil fuel driven part of the transportation sector, where NOx is formedin the engines during Combustion . As a result more regulations concerningemission of NOx are made. These stricter rules require system level modelsfor control design in order to decrease NOx About Modelon ABThis thesis was written in cooperation with Modelon AB in Lund.

8 ModelonAB offer their customers model-based engineering is mainlydone by either deliver reusable model libraries for in-house use or custommodels. The model services are done using theModelica languageand arewell integrated with the Modelica standard libraries. Their biggest customergroup is from the car industry where Modelon AB offer servicesin air condi-tioning, motor cooling and vehicle dynamics. The company isalso buildingup libraries in the power sector such as libraries for turbines or a whole ObjectivesThe aim with this thesis is to develop a method to model NOx formation withboth equilibrium and non-equilibrium reaction method willbe used to build two models.

9 The first model is simulating NOx formationin a cylinder in a spark ignition car engine. The second modelis simulatingNOx formation in a gas turbine using the same model classes used in the firstcylinder model. The purpose of these two models is that they,in the future,will be a part of system level models, models of Flue Gas Recirculation(FGR), for control design. For this reason the models must not be toocomputational demanding and have to be robust, flexible and cylinder model developed will also be roughly validatedto see if it givesreasonable OutlineThis report is divided into four chapters. The first chapter dealt with theintroduction to the subject.

10 The second chapter deals with the theory usedin the thesis. It contains some fundamental theory of Combustion in internalengines and NOx formation . This chapter ends with a section elaborating analgorithm used in the models. The third chapter gives a briefintroductionto the programming languageModelica, in which the models are written,and the programDymolawhich was used to simulate the models. The twodeveloped models, describing Combustion in a cylinder in a spark ignition carengine and a gas turbine, are then explained. The fourth and last chapteranalysis the final models and discusses simulation results from 2 THEORYIn this chapter the basic theory used in the thesis will be introduced andshortly described.


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