Author: Publisher: ISBN: Category : Languages : en Pages : 12
Book Description
The Rayleigh scattering technique has been used to investigate the flame structure of unsteady propane/air flames propagating under quiescent and turbulent conditions initiated by three ignition methods: (1) conventional spark plug (2) pulse jet combustion (PJC) and (3) Pre-Chamber ignition (PCI). The Rayleigh signal obtained for the laminar cases are all characterized by a sharp transition associated with the large density change which occurs as leading flame front of the expanding flame kernel crosses the measurement point. This indicates that the local flame structures are independent of the ignition source and may be characterized as flamelets. The maximum burning rates deduced from the pressure records show that PJC and PCI increases the burning rate from two to three times above that of conventional spark ignition. The Rayleigh scattering signal obtained for the turbulent cases are also characterized by sharp transition. The wrinkled laminar flamelet model, therefore, provides a valid description of the flame structures for all these unsteady flames. For a given equivalence ratio, the maximum turbulent burning rate deduced for the three turbulent cases with different ignition sources are similar. This suggests that while PJC and PCI enhances burning rate when conditions in the chamber are quiescent, the enhancement is not significant when turbulence fluctuations are present. The PJC and PCI, however, are capable of igniting leaner conditions than the spark plug. This may be due to the injection process which initially disperses ignition sites to a larger volume at a faster rate.
Author: Publisher: ISBN: Category : Languages : en Pages : 22
Book Description
A methodology for investigating premixed turbulent flames propagating in intense isotropic turbulence has been developed. The burner uses a turbulence generator developed by Videto and Santavicca and the flame is stabilized by weak-swirl generated by air injectors. This set-up produces stable premixed turbulent flames under a wide range of mixture conditions and turbulence intensities. The experiments are designed to investigate systematically the changes in flame structures for conditions which can be classified as wrinkled laminar flames, corrugated flames and flames with distributed reaction zones. Laser Doppler anemometry and Rayleigh scattering techniques are used to determine the turbulence and scalar statistics. In the intense turbulence, the flames are found to produce very little changes in the mean and rams velocities. Their flame speed increase linearly with turbulence intensity as for wrinkled laminar flames. The Rayleigh scattering pdfs for flames within the distributed reaction zone regime are distinctly bimodal. The probabilities of the reacting states (i.e. contributions from within the reaction zone) is not higher than those of wrinkled laminar flame. These results show that there is no drastic changes in flame structures at Karlovitz number close to unity. This suggest that the Klimov-Williams criterion under-predicts the resilience of wrinkled flamelets to intense turbulence.
Author: Norbert Peters Publisher: Vieweg+teubner Verlag ISBN: Category : Mathematics Languages : en Pages : 218
Book Description
This volume collects the results of a workshop held at Aachen, West-Germany, Oct. 12 - Oct. 14, 1981. The purpose in bringing together scientists actively working in the field of numerical methods in flame propagation was two-fold: 1. To confront them with recent results obtained by large ac tivation-energy asymptotics and to check these numerically. 2. To compare different numerical codes and different trans port models for flat flame calculations with complex che mistry. Two test problems were formulated by the editors to meet these objectives. Test problem A was an unsteady propagating flat flame with one-step chemistry and Lewis number different from unity while test problem B was the steady, stoichiometric hy drogen-air flame with prescribed complex chemistry. The parti cipants were asked to solve one or both test problems and to present recent work of their own choice at the meeting. The results of the numerical calculations of test problem A are challenging just as much for scientists employing numerical me thods as for those devoted to large activation-energy asympto tics: Satisfactory agreement between the five different groups were obtained only for two out of six cases, those with Lewis number Le equal to one. The very strong oscillations that oc cur at Le = 2 and a nondimensional activation energy of 20 were accurately resolved only by one group. This case is par ticular interesting because the asymptotic theory so far pre dicts instability but not oscillations.
Author: L. Talbot Publisher: ISBN: Category : Languages : en Pages : 7
Book Description
Studies of premixed turbulent flame propagation have been carried out using laser tomography, two-point Rayleigh scattering, and combined Rayleigh-LDV single point measurements. Probability density functions of intermediate states, correlation coefficients and correlation length scales within the reaction zone have been measured. A theoretical model has been developed which predicts these quantities, and very good agreement between theory and experiment is obtained.
Author: North Atlantic Treaty Organization. Advisory Group for Aeronautical Research and Development Publisher: Pergamon ISBN: Category : Technology & Engineering Languages : en Pages : 348
Author: 
Author: Ray E. Bolz
Author: HANS RALPH MENKES
Author: 
Author: Norbert Peters
Author: L. Talbot
Author: Jayavant P. Gore
Author: Vahid Vaezi
Author: Stanislav Kostka
Author: North Atlantic Treaty Organization. Advisory Group for Aeronautical Research and Development