Troels Dyhr Pedersen.indd - Solid Mechanics

More documents

Recommendations

Info

- 78 - - On figure 34, the individual samples are shown in the knocking part of the cycle. Pressure [MPa] 16 12 8 4 -16 -14 -12 -10 CAD Figure 34: Zoom on pressure trace in knocking combustion First of all it is noted that the oscillation is very far from being harmonic. The pressure increases are rapid, as expected with a shock wave. The strong oscillation following the peaks is most likely due to resonance in either the transducer or the hole connecting it to the cylinder, which is exited by the impact of the shock wave. The first two peaks appear with a spacing of 22 samples and the following with a spacing of 24 samples. A spacing of 22 samples is also found in many of the other cycles in the test. Assuming that the peaks are due to the reflection of a single shock wave in the chamber, the velocity of the shock wave may be calculated: 133000samples / s v = 2 ⋅ 0. 084m ⋅ = 1015 m / s 22samples This velocity must be compared to the sonic velocity of the chamber. According to acoustic theory, the lowest resonant frequency of a closed rectangular box may be calculated in a similar way as: v f = 2 ⋅ L with L being the length of the box, here approx. 84 mm. By making an FFT analysis of the oscillation around TDC where the shock wave appears to have degraded to a harmonic wave, it is found that the frequency is approx. 5 kHz. This corresponds to a velocity of 840 m/s, which is the speed of sound. The temperature corresponding to this speed is approx 1950 K. The difference in temperature between 14 CAD BTDC and TDC is approx. 100 K with adiabatic compression. At 1850 K the speed of sound is 820 m/s. The mach number of the shock wave is therefore approx. 1.24.
13 Summary and conclusion The focus of the project was within the following subjects: - 79 - - • Manipulation of combustion phasing by use of dual fuel and EGR • Reduction of HCCI combustion noise Control of combustion phasing was investigated first by a theoretical study on the reaction kinetics of DME in combination with methanol. This study was made with CHEMKIN II, using primarily the homogeneous batch reactor model to model the HCCI engine. The comprehensive detailed mechanism for combustion of DME developed by Lawrence Livermore was reduced to a simple scheme, which is valid only for lean combustion of DME. The reduced scheme also includes reaction paths for methanol and methane, which are both commonly used in combination with DME to moderate the combustion phasing. The simple reaction mechanism for DME combustion was first developed to obtain a fundamental understanding of the combustion process. The conclusion obtained from this study was: • The low temperature reactions are self terminating due to a shift in balance between chain branching and chain terminating reaction paths • The low temperature reactions of DME are inhibited when methanol is added, due to methanol consuming OH radicals in chain terminating reactions • The timing of the main heat release is delayed when the low temperature reactions are inhibited by addition of methanol • It is possible to operate at higher compression ratios as well as higher equivalence ratios, when methanol is added to the combustion An experimental study on combustion of DME and methanol was carried out as well, on a 4.6 L, 4 cylinder engine at NTSEL in Tokyo. The engine had a compression ratio of 14.5, which enabled both normal DI CI operation and HCCI operation. DME was injected directly with a custom common rail system at an equivalence ratio of 0.25, while methanol was injected at the inlet port. The engine was furthermore equipped with an EGR system capable of recycling and cooling a large fraction of the exhaust gas. This capability was used in another experiment, were EGR gas was used to obtain a delay in combustion phasing. The experiments demonstrated the following: • A DI CI engine with a low compression ratio can be operated in both DI CI and HCCI modes without need for further modifications • Combustion phasing can be retarded with a modest amount of methanol added to the inlet air
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 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 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 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
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 and 146:
Page 18 of 21 diesel type chamber 3
Page 147 and 148:
CONCLUSION HCCI combustion generate
Page 150:
DTU Mechanical Engineering Section
show all

Troels Dyhr Pedersen.indd - Solid Mechanics

Create successful ePaper yourself

Delete template?

Save as template?