TY - CONF
T1 - Effects of thermal and fuel stratifications and turbulence transport on knocking formation for dimethyl ether/air mixtures
AU - Zhang, Tianhan
AU - Sun, Weiqi
AU - Wang, Liang
AU - Ju, Yiguang
N1 - Funding Information:
Figure 5 The pressure and temperature distributions along the centerline for Case 1, Case 2, Case 3 and Case 4. For Case 1 and Case 2: 1: 385μs, 2:386μs, 3: 387μs, 4: 388μs. For Case 3 and Case 4. 1:384.5μs, 2:385.5μs, 3: 386.5μs, 4:387.5μs. Case 3 and Case 4 have the same turbulence length scales(1mm) and timescales(83μs), but with different ignition kernel sizes 3mm and 2mm, respectively. The temperature on the left boundary are 905K and the upstream temperature is 920K. The resulting ξT=4.5, 6.8 for Case 3 and Case 4 respectively. Case 3 which has a larger ignition kernel size results in a higher detonation pressure than Case 4, which has smaller ignition kernel size. Therefore, at the given turbulence length scale and timescale, the detonation with a smaller ignition kernel will be more weakened by turbulent mixing. This is because turbulence dissipation will reduce the temperature or concentration gradient quicker for a smaller ignition kernel. 4. Conclusion The effects of thermal and fuel stratification and turbulent transport on knocking formation are numerically modeled in the negative temperature coefficient region using dimethyl ether/air mixtures with a detailed chemistry. The critical conditions of detonation formation with thermal and fuel concentration gradients are examined. The effects of turbulence timescales, length scale, and Reynolds number on knocking development and knocking strength are explored. The results show that either a thermal gradient, concentration gradient, or combine gradients can initiate knocking. A unified criterion and diagram for detonation formation including both thermal and fuel concentration gradients as well as the normalized length scale of gradient fields is demonstrated. The results show that turbulence transport can delay knocking/detonation transition and dramatically reduce detonation strength due to turbulent mixing. It is found that when turbulence time scale is much shorter than the ignition delay time of the gradient field, the knocking formation will be modified. With a given turbulence time scale, a larger the turbulence length scale will induce a broader mixing in the preheated zone in front of detonation wave, and thus reduces the knocking strength. Moreover, knocking formation in a smaller gradient kernel is more affected and weakened by turbulence transport. The present research provides important insights of knocking formation and control of knocking using stratifications and turbulence in the real engines. 5. Acknowledgement The authors would like to thank the grant support from the Army Research Office with grant number W911NF-16-1-0076.
Publisher Copyright:
© 2018 Eastern States Section of the Combustion Institute. All rights reserved.
PY - 2018
Y1 - 2018
N2 - The effects of thermal and fuel stratification and turbulent transport on knocking formation are numerically modeled in the negative temperature coefficient region using dimethyl ether/air mixtures with a detailed chemistry. The critical conditions of knocking formation with thermal and fuel concentration gradients are examined. The effects of turbulence timescales, length scale, and Reynolds number on knocking development and knocking strength are explored. The results show that either a thermal gradient, concentration gradient, or combine gradients can initiate knocking. A unified criterion and diagram for knocking formation including both thermal and fuel concentration gradients as well as the normalized length scale of gradient fields is demonstrated. The results show that turbulence transport can delay knocking/detonation transition and dramatically reduce detonation strength due to turbulent mixing. It is found that when turbulence time scale is much shorter than the ignition delay time of the gradient field, the knocking formation will be modified. With a given turbulence time scale, a larger the turbulence length scale will induce a broader mixing in the preheated zone in front of detonation wave, and thus reduces the knocking strength. Moreover, knocking formation in a smaller gradient kernel is more affected and weakened by turbulence transport. The present research provides important insights of knocking formation and control of knocking using stratifications and turbulence in the real engines.
AB - The effects of thermal and fuel stratification and turbulent transport on knocking formation are numerically modeled in the negative temperature coefficient region using dimethyl ether/air mixtures with a detailed chemistry. The critical conditions of knocking formation with thermal and fuel concentration gradients are examined. The effects of turbulence timescales, length scale, and Reynolds number on knocking development and knocking strength are explored. The results show that either a thermal gradient, concentration gradient, or combine gradients can initiate knocking. A unified criterion and diagram for knocking formation including both thermal and fuel concentration gradients as well as the normalized length scale of gradient fields is demonstrated. The results show that turbulence transport can delay knocking/detonation transition and dramatically reduce detonation strength due to turbulent mixing. It is found that when turbulence time scale is much shorter than the ignition delay time of the gradient field, the knocking formation will be modified. With a given turbulence time scale, a larger the turbulence length scale will induce a broader mixing in the preheated zone in front of detonation wave, and thus reduces the knocking strength. Moreover, knocking formation in a smaller gradient kernel is more affected and weakened by turbulence transport. The present research provides important insights of knocking formation and control of knocking using stratifications and turbulence in the real engines.
KW - Concentration gradient
KW - Knocking and Detonation
KW - Temperature gradient
KW - Turbulent transport
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M3 - Paper
AN - SCOPUS:85049199456
T2 - 2018 Spring Technical Meeting of the Eastern States Section of the Combustion Institute, ESSCI 2018
Y2 - 4 March 2018 through 7 March 2018
ER -