Troels Dyhr Pedersen.indd - Solid Mechanics

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Since the total equivalence ratio did not reach the same level at 1800 RPM as the 1000 RPM case, the BMEP did not reach the same level either. To increase the torque it would be required to increase the amount of DME and balance the combustion timing with methanol. THE EFFECT OF EGR ON COMBUSTION TIMING Figures 10 and 11 shows that the combustion timing was retarded approximately 12 CAD when the EGR ratio was increased from 0 to 65 % for both 1000 and 1800 RPM. There was no notable effect on the heat release rate within this interval. The peak pressure was however reduced 8 bar in the 1000 RPM case and 13 bar in the 1800 RPM case. At 1000 RPM the turbocharger is not active, and hence the pressure reduction is due both to the increase in specific heat capacity resulting from increasing concentrations of water and carbon dioxide, as well as the inlet throttling required to force additional EGR back to the inlet manifold. At 1800 RPM the pressure increase from the turbocharger is reduced when EGR is increased, so the pressure reduction is also due to a decrease in inlet manifold pressure. BMEP is increased with increasing amounts of EGR (figure 3), despite the decrease in peak pressure. This is due to lower heat losses and increased expansion work which are the consequences of later combustion. The BMEP is only slightly higher at 1800 RPM, despite a notable increase in compression pressure at this speed due to the turbocharger. It was not possible to retard the combustion as much as desired. The optimum timing would have been somewhere around 10 CAD after TDC, but the latest timing achieved was a few CAD before TDC. It was noted that the combustion timing became very sensitive to changes in the EGR at the highest ratios used, where the exhaust gas oxygen concentrations were low. Changing the EGR rate from 65 to 70 % caused a delay of 5 CAD, the same result as changing from 0 to 60 %. It is most likely due to the fact that the oxygen concentration is more important for the reaction rate when it is closer to the stoichiometric limit. Page 9 of 22 300 200 100 BMEP [kPa] 1000 RPM 1800 RPM EGR ratio 0 0.0 0.2 0.4 0.6 0.8 Figure 3: BMEP vs. EGR ratio It is also observed that the peak pressure is greatly reduced as the amount of EGR increases. This does however not mean that the power is reduced. Both torque and IMEP increases with increasing EGR percentage. The reason is that the compression work is reduced at a greater rate than the expansion work. A secondary effect is that friction work is also reduced slightly as the cylinder pressure decreases.
With EGR there was a notable change in the engine sound as the exhaust oxygen concentration reached 3-5 %. The engine sound changed to become very quiet, which must be a result of a decreased rate of reaction. As the combustion becomes increasingly sensitive to exhaust gas concentration of oxygen, the EGR valves should possibly be controlled using feedback from an exhaust gas measurement with a broadband lambda sensor. This would ensure that the optimum concentration of oxygen is maintained. PERFORMANCE RELATIVE TO DI CI Table 3 shows the performance at each operating condition, at the highest brake efficiency obtained. The BSFC is given as diesel fuel equivalent. Table 4 shows the performance at similar loads previously recorded for the same engine operating in DI CI mode. The engine was fitted with a jerk-type pump and injection system made for DME and operating at the standard compression ratio of 19 [13]. The data are those achieved at optimum BSFC. It is worth noticing that the BSFC achieved in HCCI operation with methanol is not much higher than those of the same engine in DI CI part load, despite the difference in the compression ratio. Page 10 of 22 Mode HCCI DME+ MEOH HCCI DME+ MEOH HCCI DME+ EGR HCCI DME+ EGR Speed 1000 1800 1000 1800 Torque [Nm] 160 138 95 97 Power [kW] 16.8 26.1 9.9 18.3 BMEP [kPa] 441 380 261 267 e 0.35 0.31 0.29 0.26 Bsfc [g/kWh] 236 266 287 320 Table 3: Performance at highest brake efficiency
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Homogeneous Charge Compression Igni
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- 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
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
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
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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
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
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: Page 8 of 22 0 -5 -10 -15 -20 -25
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
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