Troels Dyhr Pedersen.indd - Solid Mechanics

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The reference sound pressure pressure was set to 1 Pa The reference for the in-cylinder SPL was chosen because it turned out that this made the in-cylinder and the external SPL approximately equal. The ratio between the two references corresponds to 94 dB. No frequency weighting has been used since the noise measured is in the 1 - 5 kHz region where the sensitivity of the ear is quite linear. The acceleration level is defined by the same formula as the SPL: Page 13 of 21 a AL 20log a where aref is the reference acceleration level which is set to 1 m/s 2 . RESULTS Sound pressure level There is a linear relationship between the SPL measured in the cylinder and the SPL measured 1 meter away from the engine. This is seen in figure 12, where the acoustic SPL is plotted against the cylinder SPL. It is obvious that reducing the SPL in the cylinder results in a reduction in the acoustic SPL as well. Acoustic SPL [dB] 103 97 91 85 79 73 rms Ring shaped chamber Flat chamber 4 side chambers 8 side chambers 7 hemispherical chambers 8 cylindrical chambers Diesel bowl chamber 79 85 91 97 103 109 Cylinder SPL [dB] Figure 12: Cylinder vs. acoustic SPL obtained with the piston crowns The lowest acoustic SPL were obtained with the eight cylindrical chamber and the diesel bowl piston crowns. These were both very silent in operation. The subjective evaluation of the sound emitted from the HCCI combustion was that it was considerably more silent than the DI CI combustion occurring in the other cylinder at approximately the same load. The highest acoustic SPL was reached with the ring shaped chamber. The shape of this piston crown is ideal for the circumferential modes, which results in frequencies of 4 and 8 kHz at high amplitudes. In addition, these frequencies are transmitted efficiently to the cylinder liner which is exposed the most with this piston crown. The same problem is apparent with the 4 side-chamber piston crown which also has strong oscillation at 3-4 kHz and an exposed cylinder liner. The SPL of the eight side-chamber piston crown is about 10 dB lower. The piston crown with seven hemispherical chambers has a SPL which is 3-6 dB lower than the flat piston, but 8-12 ref
dB higher than the 8 cylindrical chambers. This indicates that the acoustic modes are not suppressed very efficiently with the 7 hemispherical chambers. Figure 13 shows the SPL as a function of combustion phasing. In general, the acoustic SPL decreases slightly as combustion phasing is delayed. The piston crown which is least successful in reducing noise is the ring shaped chamber, which increases the SPL considerably above that of the flat piston. The crown with four side chambers also increases the noise level higher than the flat piston. The crown with seven hemispherical chambers reduces the noise level with 3-6 dB. The piston with eight side chambers provides a similar reduction. The best results are obtained with the diesel piston and the eight cylindrical chambers. These two are equally silent in operation, as they provide a reduction of 10-15 dB over the flat piston. IMEP Page 14 of 21 Acoustic SPL [dB] 103 97 91 85 79 73 Ring shaped chamber Flat chamber 4 side chambers 8 side chambers 7 hemispherical chambers 8 cylindrical chambers Diesel bowl chamber -9 -6 -3 0 3 6 9 Combustion phasing [CAD] Figure 13: Acoustic SPL as function of combustion phasing In figure 14 the IMEP is plotted against the combustion phasing. The spread in combustion phasing shows the effect of the inlet cooling, as the leftmost point in each series is obtained at +15 °C and the rightmost at -10 °C. The inlet cooling was however insufficient to reach the best possible combustion phasing which would be around 10 CAD ATDC. IMEP [kPa] 550 500 450 400 350 300 Ring shaped chamber Flat chamber 4 side chambers 8 side chambers 7 hemispherical chambers 8 cylindrical chambers Diesel bowl chamber -9 -6 -3 0 3 6 9 Combustion phasing [CAD] Figure 14: IMEP plotted against combustion phasing
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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
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- 28 - - however not possible, sinc
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- 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 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
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12 Simulation of detonation phenome
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- 60 - - provided more ideal condit
Page 64 and 65:
- 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
Page 70 and 71:
- 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
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
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- 84 - - 15 Appendix A: Reduced sch
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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
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: v v, ref T T ref with T and Tref be
Page 143 and 144: Page 16 of 21 Flat chamber 7 BTDC 3
Page 145 and 146: Page 18 of 21 diesel type chamber 3
Page 147 and 148: CONCLUSION HCCI combustion generate
Page 150: DTU Mechanical Engineering Section
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