Troels Dyhr Pedersen.indd - Solid Mechanics

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Page 19 of 21 Frequency response [dB] -60 -80 -100 -120 -140 -160 -180 0 5000 10000 15000 20000 Frequency Figure 22: Frequency response of engine to internal sound pressure As indicated by the figure, lower frequencies are more efficiently transmitted to the surroundings. This may be part of the explanation why the diesel chamber is very silent compared to the other geometries. The diesel chamber resonance frequency was measured to be approx. 10 kHz, and this frequency is attenuated 10 dB more than frequencies around 5 kHz. The piston crowns producing lower frequencies than 5 kHz were also found to result in more noise, which is also part due to the frequency response of the engine. In figure 22, the rise in frequency response from 0-3 kHz is primarily due to this region being the engine’s resonance frequency. This frequency band is exited shortly after the combustion although the cylinder does not emit any vibrations at frequencies lower than the first mode, which is approx. 5.8 kHz. The frequency band from 3 kHz and above indicates a somewhat linear decrease in response at increasing frequencies. Engine acceleration level The coherence between the cylinder SPL and the engine acceleration level is illustrated in figure 23. The figure is a plot of the acceleration level and the acoustic and cylinder SPL for one complete cycle of the engine in knocking combustion with the ring shaped chamber. The increased acoustic SPL and acceleration levels after - 360 CAD are caused by the diesel combustion event. The HCCI combustion occurs at -10 CAD and causes a rapid increase in cylinder and acoustic SPL as well as the acceleration level. This is due to acoustic energy from the cylinder being transmitted directly to the surface during combustion [11]. The SPL and the AL decrease at the same rate, while the acoustic SPL decreases at a slower rate due to the engine resonance which is not measured by the accelerometer. SPL and AL [dB] 160 120 80 Acceleration level 40 Cylinder SPL Acoustic SPL 0 -360 -270 -180 -90 0 CAD 90 180 270 360 Figure 23: Cylinder SPL, acoustic SPL and acceleration level
CONCLUSION HCCI combustion generated noise is primarily reduced by limiting exposure of the cylinder liner to the combustion. A diesel type piston is most effective in achieving this reduction. A flat piston type, as commonly used in SI combustion, results in large amplitude pressure waves in the combustion chamber. The exterior noise level is therefore high with this kind of chamber. A diesel type piston provided the largest reduction in the combustion noise of all tested piston crown geometries. It is believed that the smaller diameter of the bowl in which the combustion takes place is the reason that the combustion does not generate strong pressure waves. The exposure of the cylinder liner is also minimized with this kind of piston, which helps to reduce the noise further. Two pistons with the compression volume split into 4 and 8 volumes respectively placed in their perimeter were tested. The latter was found capable of reducing the noise, but not the indicated efficiency which suffered from increased heat losses to piston and cylinder liner. The first piston crown increased combustion noise due to Helmholtz resonance between the volumes. Two pistons with combustion chambers placed as cavities in the top of the piston were tested. One of them had 8 cylindrical cavities and was found capable of similar noise reduction capability as the diesel type piston. The large surface area, crevice volume and possibly the squish region as well however resulted in a lower indicated efficiency. The second piston had hemispherical chambers in order to reduce the heat transfer and the squish region, but as a result of a more open geometry, combustion noise increased to a level comparable to the flat piston. The diesel type piston is possibly the best option for obtaining a silent combustion. It may however not be the best option with respect to indicated efficiency, in which case the flat piston design is the best solution. REFERENCES 1. Chris Morley, Derek Bradley, X. J. Gu, D. R. Emerson: Amplified Pressure Waves During Auto Ignition: Relevance to Cai Engines. SAE 2002-01-2868. 2002 2. Ge-Qun Shu, Jingsi Wei, Hai-qiao Wei, Xinwei Chen. Research on Couple Mechanism of Heat Release and Acoustic Characteristics during Combustion of Butane in Close Chamber. SAE 2007-01-2175. 2007 3. B. Stiebels, M. Schreiber and A. Sadat Sakak. Development of a New Measurement Technique for the Investigation of End-Gas Auto Ignition and Engine Knock. SAE 960827. 1996 4. J. Pan and C.G.W. Sheppard. A Theoretical and Experimental Study of the Modes of End Gas Auto Ignition Leading to Knock in S.I. Engines. SAE 942060. 1994 5. Tadashi Tsurushima, Yasuo Asaumi, Yuzo Aoyagi: The Effect of Knock on Heat Loss in Homogeneous Charge Compression Ignition Engines. SAE 2002-01-0108. 2002 6. David Scholl, Craig Davis, Stephen Russ, Terry Barash. The Volume Acoustic Modes of Spark-ignited Internal Combustion Chambers. SAE 980893. 1998. 7. Eng, J.A.; Characterization of Pressure Waves in HCCI combustion. SAE 2002-01-2859. 2002 8. Andreas Vressner; Andreas Lundin; Magnus Christensen; Per Tunestål; Bengt Johansson. Pressure Oscillations During Rapid HCCI Combustion. SAE 2003-01-3217. 2003 9. A. Broatch, X. Margot, A. Gil, J. C. Donayre: A CFD Approach to Diesel Engine Combustion Chamber Resonance. SAE 2007-24-0043. 2007 Page 20 of 21
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
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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
Page 16 and 17:
- 14 - - 5.3 Scope of investigation
Page 18 and 19:
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
Page 38 and 39:
- 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
Page 50 and 51:
- 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
Page 56 and 57:
- 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
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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 and 144: Page 16 of 21 Flat chamber 7 BTDC 3
Page 145: Page 18 of 21 diesel type chamber 3
Page 150: DTU Mechanical Engineering Section
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