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Turbulent flame development in a high-pressure\ud combustion vessel

By Matthew P. Ormsby

Abstract

The objective of this work was to extend the range of turbulent burning velocities presented in the literature by performing new measurements at elevated pressures over a range of turbulent velocities, u' (r. m. s. deviation from the mean velocity). The influence of equivalence ratio was investigated for a fixed u'= 2 m/s at 0.5 MPa for methane, a 70 % methane/ 30 % hydrogen mixture, methanol, isooctane\ud and a gasoline (Shell dutch-pura). The mixtures were varied from the lean ignition limit to rich limit up to a maximum equivalence ratio of 2. Further measurements were performed with iso-octane and the effect of r. m. s. turbulent\ud velocity (u' = 0.5,1,2,4,6 m/s), pressure (P = 0.1,0.5,1 MPa) and equivalence ratio (0= 0.8,1.0,1.2 and 1.4) were investigated, to produce a database.\ud \ud Turbulent flames were centrally ignited in isotropic turbulence in the Leeds fan stirred bomb. Flame progress was monitored using high-speed schlieren photography and pressure measurements. The turbulent burning velocity based on the production of burned mass, ur was obtained from both techniques. The burning velocities obtained from schlieren imaging and pressure measurements were in good\ud agreement. The turbulent flames continually accelerated throughout the time that they were monitored. This was the result of turbulent flame development, with the range of turbulent scales wrinkling the flame surface increasing as the flames grew. It was shown that flame development occurred primarily as a result of the kernel radius, rather than the time from ignition.\ud \ud For each turbulent condition, corresponding spherically expanding laminar flames were ignited and imaged with schlieren photography. The measurements were processed to give the stretch free laminar burning velocity and also the\ud Markstein number, a measure of the influence of stretch on the burning velocity. The peak laminar burning velocity was found to be in the range 1>ø>1.2 depending on the fuel. At 0.5 MPa a number of the flames were observed to become\ud cellular, in some cases this occurred from ignition, this has been linked to negative Markstein numbers which were observed with lean methane and rich iso-octane - air\ud mixtures.\ud \ud The peak in the turbulent burning velocity with equivalence ratio varied considerably with the different fuels, and did not correspond to that for the laminar burning velocity. In the case of methane and the 70 % methane/ 30 % hydrogen\ud mixture the peak turbulent burning velocity was lean of stoichiometric. In contrast, for iso-octane and the gasoline, the peak in %, was beyond 0=1.3. It was concluded\ud that the shift in the peak could be explained by comparison with the measured Markstein numbers.\ud \ud In the iso-octane database, pressure was not observed to have a significant influence on the turbulent burning velocity for some conditions, however, when fuel\ud rich higher pressure gave an increase in utr. Turndown of utr, (the burning velocity does not increase as with the turbulent velocity) was observed at high turbulence\ud velocities, although this depended on the equivalence ratio. The measurements were then compared with existing turbulent burning velocity expressions and correlations.\ud In general these expressions were found not to predict the effect of equivalence ratio well.\ud \u

Publisher: School of Mechanical Engineering (Leeds)
Year: 2005
OAI identifier: oai:etheses.whiterose.ac.uk:1183

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  1. (1996). An Introduction to Combustion: Concepts and Applications.
  2. (2000). Aspects of Laminar and Turbulent Burning Velocity Relevant to SI Engines.
  3. (1996). Burning Velocities, Markstein Length, and Flame Quenching for Spherical Methane-Air Flames:
  4. (1991). Burning Velocity and the Influence of Flame Stretch.
  5. (2005). Burning velocity correlation of methane/air turbulent premixed flames at high pressure and high temperature.
  6. (1996). Burning Velocity of Turbulent Premixed Flames in a High Pressure Environment.
  7. (1987). Combustion, Flames and Explosions of Gases.
  8. (1998). Direct Experimental Determination of Laminar Flame speed.
  9. (1992). Distribution of Strain Rate and Temperature in Turbulent Combustion.
  10. (1985). Dynamic Behavior of Premixed Flame Fronts in Laminar and Turbulent Flows.
  11. (1990). Experimental Investigation of the influence on the transient premixed flame propagation inside closed vessels.
  12. (1998). Experimental Study on General Correlation of Turbulent Burning Velocity at High Pressure.
  13. (1955). Experiments with butane-air and methane-air flames.
  14. (2000). Flame Propagation in a Tube: The Legacy of Henri Guenoche.
  15. (1992). Flame Stretch Rate as a Determinant of Turbulent Burning Velocity.
  16. (1998). Fundamental Studies of Premixed combustion.
  17. (1988). Internal Combustion Engine Fundamentals.
  18. (2000). Laminar Burning Velocity and Markstein Length of Methane-Air Mixtures.
  19. (1998). Measured and Predicted Properties of Laminar Premixed Methane/Air Flames at Various Pressures.
  20. (2000). Measurements and Large Eddy Simulations of Turbulent Premixed Flame Kernel Growth.
  21. (1995). Measuring the Laminar Burning Velocity of Methane/Diluent/Air Mixtures within a Constant-Volume Combustion Bomb in a micro-gravity Experiment.
  22. (1994). Measurment and Adiabatic Burning Velocity of Methane/Air Mixtures.
  23. (2005). Molecular transport effects on turbulent flame propagation and structure
  24. (1969). On the Propagation of Turbulent Flames.
  25. (1972). Phase Rep. Research Project, Battelle Columbus Laboratories,
  26. (1997). private communication,
  27. (2002). Problems of predicting turbulent burning rates.
  28. (1996). Study of Turbulence and Combustion Interaction: Measurement and Prediction of the Rate of Turbulent Burning.
  29. (1995). The Importance of High Frequency, Small-Eddy Turbulence in Spark Ignited, Premixed Engine Combustion.
  30. (1997). The Importance of Turbulence Intensity, Eddy Size and Flame Size in Spark Ignited, Premixed Flame Growth.
  31. (1998). The Measurement of Laminar Burning Velocities and Markstein Numbers for Isooctane-Air and Iso-octane-n-Heptane-Air Mixtures at Elevated Temperatures and Pressures in an Explosion bomb.
  32. (1990). The Physics of Fluid Turbulence.
  33. (2003). Turbulent Burning Velocity, Burned Gas Distribution, and Associated Flame Surface Definition.
  34. (1994). Turbulent combustion of premixed flames in closed vessels.
  35. (2000). Turbulent Combustion,
  36. (1986). Turbulent effects on combustion in spark ignition engines.

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