Troels Dyhr Pedersen.indd - Solid Mechanics

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- 34 - - In addition, many reactions which may be relatively important at low temperatures and pressures have insignificant reaction rates when temperature and pressure are elevated. In order to apply the reaction scheme in CFD models the scheme needs to be simplified without loosing its accuracy. The target was that the reaction mechanism should be reduced considerably without affecting the ignition delay, low temperature reaction paths, heat release rate, sensitivity to radical concentrations and composition of products. There are some commercial tools available that performs automated reduction of reaction schemes. A software called ASRT (automatic scheme reduction tool) was developed by Yamauchi et al [22] and used specifically for DME. These reduction tools can eliminate elementary reactions from the main paths, which further simplifies the total scheme. The application of such tools was however beyond the scope and purpose of the study, in particular since a major benefit of reducing the scheme is that it creates a fundamental understanding of the reaction paths. The process of reducing the scheme began by setting up and running a CHEMKIN simulation with the full reaction scheme. CHEMKIN is a program developed for simulation of chemical reactions. The software analyses the mechanism and other data that is supplied by the user and solves the stiff ordinary differential equation system that constitute the problem. To simplify the detailed reaction scheme, a set of well known operating parameters were chosen from the functional experimental setup. An excess air ratio of 4, a compression ratio of 10 and an engine speed of 1000 rpm were used. The results from this simulation run were used as the basis for reducing the scheme. The operating parameters are sufficient for obtaining a model that functions well within the operational limits of HCCI combustion. Changes to equivalence ratio are limited due to the narrow temperature interval within which HCCI can be realized. Variation to engine speed should not affect the outcome either due to the short timescale of the reactions compared to the engine speed. Finally, changes to the compression ratio will only affect the temperature history and hence the timing of the combustion process. The method used to reduce the scheme was to select only the dominating paths from the fuel molecule to complete combustion products. The dominating carbon containing species were picked out initially, and the paths leading to the formation and destruction of these species were identified. Besides fuel species the scheme has a number of non-carbon radical reactions. These reactions are between the species: O, H, O2, H2, OH, H2O, HO2 and H2O2. The dominating reactions were selected based mainly on the species rate-of-production. Although concentrations of highly reactive species may be low, their rate of production is often very high. By choosing only those reactions with high rates of production, the scheme for non-carbon radicals may be simplified greatly.
- 35 - - The result from this process was a new scheme with 29 species and 55 reactions. Figure 8 was constructed to illustrate the reaction paths in the reduced scheme. The scheme itself is listed in appendix A in the CHEMKIN format. A list of the species names is given in the end of this chapter. 287 + O2 CH3OCH2O2 293 + O2 + OH + OH CH2OCH2O2H 295 50 % @ LTR 294 O2CH2OCH 2O2H 296 HO2CH2OCHO 297 298 + CH2O CHO2 + HO2 331 + O2 90 % @ LTR, 10 % @ HTR + OH OCH2OCHO 50 % 303 50 % 40 % @ LTR 100 % @ HTR (2 x CH2O) CH2O2 HOCH2OCO + CO + OH + H2O + H + OH + H + O + HO2 + O2 274 90 % 275 276 10 % 277 280 + H2O + H2 + OH + H2O2 + HO2 + CHO + CH3 38 307 304 60 % @ LTR HOCH2O 333 334 + OH + OH + H 308 100 % @ HTR 7 + H +OH + H2O + OH + OH + H CO2 + OH 78 + H2O CO CH3OCH3 CH3OCH2 CH4 + H2O + H2 12 100 % @ HTR CHO + M + O2 46 CH2O 45 40 32 33 54 +H + M + HO2 + HO2 + OH CH3OH + O 18 + OH 23 CH2OH + O2 83 + HO2 + O2 + HO2 + OH 16 + OH 110 + H2O Figure 8: Reduced reaction scheme for lean combustion of DME + M + HO2 + H2O2 CH3O 3 4 22 + OH + H2O CH3 + HO2 + OH 269 + O + OH + O2 282 10 % @ LTR, 90 % @ HTR + H + M + OH + CH3
Page 1: Homogeneous Charge Compression Igni
Page 4 and 5: - 2 - - Table of contents 1 FOREWOR
Page 6 and 7: - 4 - - 11.5.3 Filtering of sample
Page 8 and 9: - 6 - - 1 Foreword The work describ
Page 10 and 11: 3 Résumé - 8 - - This thesis is b
Page 12 and 13: 4 Resumé (dansk) - 10 - - Denne af
Page 14 and 15: 5 Introduction - 12 - - 5.1 About H
Page 16 and 17: - 14 - - 5.3 Scope of investigation
Page 18 and 19: 6 The basics of HCCI combustion - 1
Page 20 and 21: - 18 - - the cylinder. In HCCI comb
Page 22 and 23: 7 Combustion of DME - 20 - - 7.1 Co
Page 24 and 25: - 22 - - 8 Description of experimen
Page 26 and 27: - 24 - - 8.1.3 Piston modifications
Page 28 and 29: - 26 - - combustion event is often
Page 30 and 31: - 28 - - however not possible, sinc
Page 32 and 33: - 30 - - (excess air ratio 3) of ai
Page 34 and 35: dQ dt = h ⋅ A ⋅ - 32 - - ( T
Page 38 and 39: - 36 - - Arrows in the scheme indic
Page 40 and 41: - 38 - - formaldehyde (CH2O) and fo
Page 42 and 43: Figure 12: Termination of the low t
Page 44 and 45: - 42 - - The non-carbon radical act
Page 46 and 47: 10.7 List of species Radicals of hy
Page 48 and 49: - 46 - - If a frequency analysis of
Page 50 and 51: - 48 - - 11.5.3 Filtering of sample
Page 52 and 53: - 50 - - The SPL of the cylinder pr
Page 54 and 55: Figure 17: Intensity chart for cyli
Page 56 and 57: - 54 - - 11.7.3 Axial modes Axial w
Page 58 and 59: - 56 - - A case was set up to make
Page 60 and 61: 12 Simulation of detonation phenome
Page 62 and 63: - 60 - - provided more ideal condit
Page 64 and 65: - 62 - - positive in the x- directi
Page 66 and 67: 3,0 x 10 6 2,5 x 10 6 2,0 x 10 6 1,
Page 68 and 69: - 66 - - A detailed drawing of the
Page 70 and 71: - 68 - - In the expressions above,
Page 72 and 73: ( 21) ( 22) - 70 - - The mach numbe
Page 74 and 75: ( 25) - 72 - - Δt v = u ⋅ Δx wh
Page 76 and 77: - 74 - - Figure 29: Development in
Page 78 and 79: - 76 - - 12.5 Observations of deton
Page 80 and 81: - 78 - - On figure 34, the individu
Page 82 and 83: - 80 - - • The engine load obtain
Page 84 and 85: - 82 - - 15. Takayugi Tsuchiya, Yos
Page 86 and 87:
- 84 - - 15 Appendix A: Reduced sch
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16 Appendix B: Detonation model in
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- 88 - - 17 Paper I: The Effect of
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- 90 - - 19 Paper III: Reducing HCC
Page 94 and 95:
DESCRIPTION OF THE EXPERIMENT OBJEC
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Engine modification To obtain a low
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Pressure [Mpa] 6 5 4 3 2 1 lambda 2
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Pressure [Mpa] 6 5 4 3 2 1 lambda 4
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At lambda 4, IMEP peaks at a compre
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CONCLUSION • It was possible to a
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close to the lean limit. HC is comp
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Reactions do however not stop entir
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METHANOL TEST PROCEDURE In the firs
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Page 8 of 22 0 -5 -10 -15 -20 -25
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With EGR there was a notable change
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Page 12 of 22 9 8 7 6 5 4 3 2 MEOH
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Page 14 of 22 250 200 150 100 50 40
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EMISSIONS The emissions in table 6
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Page 18 of 22 15 12 9 6 3 0 1000 RP
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REFERENCES 1. Mingfa Yao: An Invest
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PM: Particulate matter THC: Total H
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Coupling of pressure waves and reac
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chambers which often have this flat
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The two piston crowns with chambers
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Page 8 of 21 Figure 10: Steel plate
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Page 10 of 21 16.7 kW @ 3000 rpm 17
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v v, ref T T ref with T and Tref be
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dB higher than the 8 cylindrical ch
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Page 16 of 21 Flat chamber 7 BTDC 3
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Page 18 of 21 diesel type chamber 3
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CONCLUSION HCCI combustion generate
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DTU Mechanical Engineering Section
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Troels Dyhr Pedersen.indd - Solid Mechanics

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