Troels Dyhr Pedersen.indd - Solid Mechanics

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Page 17 of 21 8 side chambers 3 BTDC 1 ATDC 6 ATDC 1000 3000 5000 f (Hz) 7000 9000 Figure 18: Frequency distribution with the eight side chamber piston 8 cylindrical chambers 6 BTDC 3 BTDC 2 ATDC Sound pressure (Pa) 1000 3000 5000 f (Hz) 7000 9000 Figure 19: Frequency distribution with the eight cylindrical chamber piston 7 hemispherical chambers 8 BTDC 4 BTDC TDC Sound pressure (Pa) 1000 3000 5000 f (Hz) 7000 9000 Figure 20: Frequency distribution with the seven hemispherical chambers Sound pressure (Pa) 1 0.8 0.6 0.4 0.2 0 1 0.8 0.6 0.4 0.2 0 1 0.8 0.6 0.4 0.2 0
Page 18 of 21 diesel type chamber 3 ATDC 1 BTDC 3 BTDC 1000 3000 5000 f (Hz) 7000 9000 Figure 21: Frequency distribution with the diesel bowl chamber piston The common feature of all the FFT analysis result is that the largest contribution to the total SPL is found in the lower part of the frequency band from 1-3 kHz. These frequencies cannot exist inside the cylinder, since the lowest resonance frequency is 5-6 kHz in all cases except for the ring shaped geometry, which has its primary resonance frequency at 4 kHz. The 4 kHz frequency is clearly present in the analysis for this piston crown (fig. 16). Engine block resonance will however occur as a result of higher frequencies being transmitted through the structure. The connection between structure born noise and emitted noise was investigated by Andreae et al [10]. It was found that the general source of noise was not that which was directly transmitted, but that of engine structure resonance being exited by the transmitted noise. A great reduction in the noise level was achieved by moving the chambers away from the cylinder walls and into the piston. The total surface area and therefore heat transfer was however increased. The crevice volume with this and the following pistons was very large since it was not possible to fit piston rings. This resulted in a reduction of combustion efficiency. In terms of noise reduction the performance was similar. The crevice volume was however unchanged, so the combustion efficiency was still reduced Frequency response The frequency response of the engine is here defined by the ratio of the sound pressure measured outside the engine to the sound pressure generated in the cylinder. The response is calculated for the range of frequencies in the FFT. A short term average of 5 ms following the peak heat release was used to allow all established modes of vibration to be included. The response is converted to dB. Since -100 dB corresponds to an attenuation of 100,000, a SP of 100 kPa in the cylinder will result in a SP of 1 Pa outside the engine. Figure 22 is an example of the frequency response of the flat chamber. The response of the other piston crowns was found to follow this pattern. The response of the flat chamber was selected because it produces a wide range of frequencies in the cylinder and thus provides a good signal-to-noise ratio for the response curve. Sound pressure (Pa) 1 0.8 0.6 0.4 0.2 0
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Homogeneous Charge Compression Igni
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- 2 - - Table of contents 1 FOREWOR
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- 4 - - 11.5.3 Filtering of sample
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- 6 - - 1 Foreword The work describ
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3 Résumé - 8 - - This thesis is b
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4 Resumé (dansk) - 10 - - Denne af
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5 Introduction - 12 - - 5.1 About H
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- 14 - - 5.3 Scope of investigation
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6 The basics of HCCI combustion - 1
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- 18 - - the cylinder. In HCCI comb
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7 Combustion of DME - 20 - - 7.1 Co
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- 22 - - 8 Description of experimen
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- 24 - - 8.1.3 Piston modifications
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- 26 - - combustion event is often
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- 28 - - however not possible, sinc
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- 30 - - (excess air ratio 3) of ai
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dQ dt = h ⋅ A ⋅ - 32 - - ( T
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- 34 - - In addition, many reaction
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- 36 - - Arrows in the scheme indic
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- 38 - - formaldehyde (CH2O) and fo
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Figure 12: Termination of the low t
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- 42 - - The non-carbon radical act
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10.7 List of species Radicals of hy
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- 46 - - If a frequency analysis of
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- 48 - - 11.5.3 Filtering of sample
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- 50 - - The SPL of the cylinder pr
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Figure 17: Intensity chart for cyli
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- 54 - - 11.7.3 Axial modes Axial w
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- 56 - - A case was set up to make
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12 Simulation of detonation phenome
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- 60 - - provided more ideal condit
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- 62 - - positive in the x- directi
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3,0 x 10 6 2,5 x 10 6 2,0 x 10 6 1,
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- 66 - - A detailed drawing of the
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- 68 - - In the expressions above,
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( 21) ( 22) - 70 - - The mach numbe
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( 25) - 72 - - Δt v = u ⋅ Δx wh
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- 74 - - Figure 29: Development in
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- 76 - - 12.5 Observations of deton
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- 78 - - On figure 34, the individu
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- 80 - - • The engine load obtain
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- 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
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
Page 104: CONCLUSION • It was possible to a
Page 107 and 108: close to the lean limit. HC is comp
Page 109 and 110: Reactions do however not stop entir
Page 111 and 112: METHANOL TEST PROCEDURE In the firs
Page 113 and 114: Page 8 of 22 0 -5 -10 -15 -20 -25
Page 115 and 116: With EGR there was a notable change
Page 117 and 118: Page 12 of 22 9 8 7 6 5 4 3 2 MEOH
Page 119 and 120: Page 14 of 22 250 200 150 100 50 40
Page 121 and 122: EMISSIONS The emissions in table 6
Page 123 and 124: Page 18 of 22 15 12 9 6 3 0 1000 RP
Page 125 and 126: REFERENCES 1. Mingfa Yao: An Invest
Page 127 and 128: PM: Particulate matter THC: Total H
Page 129 and 130: Coupling of pressure waves and reac
Page 131 and 132: chambers which often have this flat
Page 133 and 134: The two piston crowns with chambers
Page 135 and 136: Page 8 of 21 Figure 10: Steel plate
Page 137 and 138: Page 10 of 21 16.7 kW @ 3000 rpm 17
Page 139 and 140: v v, ref T T ref with T and Tref be
Page 141 and 142: dB higher than the 8 cylindrical ch
Page 143: Page 16 of 21 Flat chamber 7 BTDC 3
Page 147 and 148: CONCLUSION HCCI combustion generate
Page 150: DTU Mechanical Engineering Section
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