Troels Dyhr Pedersen.indd - Solid Mechanics

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- 30 - - (excess air ratio 3) of air and ethanol, for the corresponding burned mixture and an average of burned and unburned. All components are assumed to be ideal gasses. Specific heat ratio 1,40 1,38 1,36 1,34 1,32 1,30 1,28 1,26 1,24 1,22 250 700 1150 1600 2050 2500 T [K] γmodel γmodel γair γair γburned γburned γunburned γunburned γaverage γaverage Figure 7: The specific heat ratio calculated for dry air, for a burned and unburned charge and the average of burned and unburned charge. The linear relation is for the model expression. As can be seen from the figure, simply assuming a linear relationship will result in a great deviation at elevated temperatures, when compared to the values calculated from the tabulated properties. For motoring conditions with pure air, the curve for pure air will provide a better estimate on the specific heat ratio than the linear expression. For operating conditions, the specific heat ratio is less depending on whether the gas is burned or not, than it is on temperature. The error of using the average value is les than one percent and hence acceptable for calculations of heat release. The calculation of gamma may be performed with a third order polynomial fit. The equations in table 3 are very close approximations to the curves above, at temperatures higher than 400 K Table 3: Polynomial fits of specific heat ratios Air −4 −8 2 γ = 1. 45 − 1. 62 ⋅10 T + 5. 49 ⋅10 T −11 − 1. 26 ⋅10 T Unburned −4 −8 2 γ = 1. 44 − 2. 22 ⋅10 T + 9. 39 ⋅10 T −11 − 1. 26 ⋅10 T Burned −4 −8 2 γ = 1. 44 − 1. 18 ⋅10 T + 6. 96 ⋅10 T −12 − 9. 51⋅ 10 T Average −4 −8 2 γ = 1. 44 − 2. 03⋅ 10 T + 8. 18 ⋅10 T −11 − 1. 11⋅ 10 T 3 3 3 3
- 31 - - The calculations do not take into account that the effects of dissociation or presence of other intermediate species. It is however not very important, since the amount of dissociation at 2000 K is insignificant. For HCCI combustion these approximations will therefore be acceptable. 9.4 Temperature estimate Assuming ideal gas behavior and no mass loss, the temperature may be estimated from the ideal gas law: pV T = mRmass Rmass is the mass based gas constant, 287 J/kg-K. This value is only valid for dry air. The gas constant valid for the unburned and burned charges is calculated as: Rmolar R mass = ; M mixture = xi M i M mixture where Rmolar is the universal gas constant, Mmixture is the molar weight of the mixture, xi the mass fraction of species i and Mi the molar weight of species i. Table 4: Molar masses and gas constants calculated for air, burned and unburned charge. Mixture Components Molar mass Gas constant Air N2: 0.78, O2: 0.21, Ar: 0.01 28.97 287.0 Unburned N2: 0.739, O2: 0.225, DME: 0.036 29.55 281.4 Burned N2: 0.739, O2: 0.15, CO2: 0.069, H2O: 0.042 29.28 283.9 Average Based on burned and unburned 29.42 282.6 The change in the mass based gas constant before and after combustion is insignificant. An average value of 283 is sufficient to improve accuracy in the temperature calculation with both burned and unburned mixtures. Since pressure and volume are known with good precision, the most critical is the determination of the cylinder mass, m. The amount of air entering the engine may be estimated from the volumetric efficiency and the intake conditions which are well known parameters for a diesel engine, while the amount of residual gas may be estimated from the exhaust temperature and cylinder pressure at EVC. A more precise evaluation of the trapped mass may be made by measuring the air flow with a laminar flow meter, if the valve overlap does not result in air flowing through the engine. 9.5 Heat losses The preferred method of calculating heat transfer is by the Woschni Correlation. The heat transfer between a gas and a surface of area A is given by:
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 34 and 35: dQ dt = h ⋅ A ⋅ - 32 - - ( T
Page 36 and 37: - 34 - - In addition, many reaction
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
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- 80 - - • The engine load obtain
Page 84 and 85:
- 82 - - 15. Takayugi Tsuchiya, Yos
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- 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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