Troels Dyhr Pedersen.indd - Solid Mechanics

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Figure 17: Intensity chart for cylinder pressure oscillation Figure 18: Intensity chart for engine acceleration Figure 19: Intensity chart for engine acoustic noise - 52 - - The intensity spectrograms (fig. 17-19) are created from data collected with the ring shaped chamber geometry. The plots reveal that the same frequencies are present in the cylinder and the surface. The acoustic noise show some indications of the strong 8 kHz tone in the cylinder, but the 4 kHz tone appears to be transmitted better. The frequencies below 4 kHz in the acoustic noise are the engine resonance frequencies. These are seen to be quite strong compared to the directly transmitted frequencies.
- 53 - - 11.7 Theory of cylinder acoustics Cylinder pressure oscillations are initiated by the strong pressure gradients formed when the combustion proceeds unevenly in the chamber. The pressure gradient may be created by a confined explosion in the charge due to spatial variation in fuel or temperature distribution, or a developing detonation, which are discussed in the next chapter. Once a pressure difference is introduced, the pressure will drive the gas towards the low pressure area. The momentum of the gas means that the gas will continue into the low pressure region even after pressure equalization, thereby increasing the pressure to that of the former high pressure region. The pressure distribution is now reversed and the gas will be forced back to its origin. This behavior is known as resonance. Established resonance modes in the cylindrical geometry fall in to three categories: circumferential modes, radial modes and axial modes. These are explained in the following subsections. The modes may appear simultaneously by the principle of superposition as shown in table 5. 11.7.1 Circumferential modes If the charge is pushed from one side of the cylinder wall it will oscillate across the chamber in a transverse motion. This situation is equivalent to pushing a glass of water, which forces the water into moving from side to side. The first mode has one node which runs through the diameter of the cylinder. All of the fluid moves from the low pressure to the high pressure zone across the chamber. This mode is therefore the most powerful in terms of momentum transport. The second mode has two nodes that are orthogonal and hence two high pressure zones that must be opposite. The gas does not move across the two symmetry lines. The gas movement takes places from the sides of the high pressure zones to the sides of the low pressure zones. In this case the gas movement is split into four directions. This means that less energy is transported across the chamber and hence less energy is transferred to the walls by momentum and heat transfer. So, despite being measurable in the chamber, this mode is less important in terms of energy losses and transmitted sound. 11.7.2 Radial modes If the pressure rises in the center (or throughout the entire perimeter simultaneously) it will create a radial wave moving from the center towards the cylinder liner. This corresponds to the familiar rings that form when a drop of water hits the surface of a water pool. Like in a glass of water, the wave is reflected back towards the center. The first mode of vibration has a high and low pressure zone and a circular node. The higher nodes that may be formed have more pressure zones in the same ring pattern. As with the transverse waves, only the lowest mode carries enough momentum to be important.
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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 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 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
Page 88 and 89: 16 Appendix B: Detonation model in
Page 90 and 91: - 88 - - 17 Paper I: The Effect of
Page 92 and 93: - 90 - - 19 Paper III: Reducing HCC
Page 94 and 95: DESCRIPTION OF THE EXPERIMENT OBJEC
Page 96 and 97: Engine modification To obtain a low
Page 98 and 99: Pressure [Mpa] 6 5 4 3 2 1 lambda 2
Page 100 and 101: Pressure [Mpa] 6 5 4 3 2 1 lambda 4
Page 102 and 103: 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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