Diffusion flame

About: Diffusion flame is a research topic. Over the lifetime, 9266 publications have been published within this topic receiving 233522 citations.

Flame propagation: the measurement of burning velocities of slow flames and the determination of limits of combustion

Abstract: A method of measuring burning velocities of combustible gas/air mixtures near the limits of combustion is developed, using a burner providing a flat disk-shaped flame. The method is applied to methane, propane, n -pentane, n -heptane, ethylene, acetylene and benzene flames of velocities 5 to 10 cm/s. The characteristics of the burner and the flames are discussed; the time during which unburnt gas can be heated by conduction from the flame appears to be insufficient for purely thermal initiation, and the reactions are therefore probably started by diffusion of radicals from the flame front. The burning velocities of these slow flames are mainly dependent on reaction heat which determines the temperature of the flame and the rate of the reactions. The effect of some additives (1/2 % by volume) on the burning velocities in the range investigated and on the lower limits is thermal; no catalytic influence wets found. The flat flame is only stable within a fairly narrow range of velocity; cusped flames are readily formed, particularly with mixtures rather richer in oxygen than upper-limit mixtures. The flat-flame burner is also applied to the determination of limits of combustion. The lower limits are lower when determined in this manner compared with the standard tube method. The limit determinations can be carried out easily over a wide range of mixtures. The effect of argon on the limits is consistent with the change in specific heat of the mixture, but carbon dioxide appears to have a further effect.

Effects of fuel-air mixing on flame structures and NOx emissions in swirling methane jet flames

Abstract: An experimental investigation is performed to study the effects of initial fuel-air mixing on NOx and CO emissions in swirling methane jet flames. The major parameters used to modify the initial fuel-air mixing ahead of the swirling flame are the swirl number, the fuel-air momentum flux ratio, and the fuel injection location. Two characteristic swirling combustion modes, the fuel jet-dominated (type-1) and the strongly recirculating (type-2) flames, are identified from flame visualization and 2-D laser-induced predissociative fluorescence imaging of OH by varying the fuel-air momentum flux ratio. Laser Doppler velocimetry (LDV) measurements show that the shear layer between the edge of the swirling recirculation zone and the external flow is a highly turbulent and rapid mixing region. The maximum mean flame temperature is located at the edge of the recirculation zone, indicating violent combustion and strong mixing of fuel, air, and hot products in this region. Strong and rapid mixing of the strongly recirculating flame, which increases mixture homogeneity and shortens the characteristic time for NOx formation, results in a lower NOx emission index than that in the fuel jet-dominated flame. Excess cold air entrained by the swirling flow may quench the combustion and the hot products, resulting in an increase of CO emission, indicating poor combustion efficiency. By modifying the fuel injection pattern with the annular fuel injector, which changes the fuel-air mixing pattern and properly smooths the rapid mixing leading to a higher flame temperature, the NOx emission level can further be reduced with a significant decrease in CO emission.

Corona‐assisted flame synthesis of ultrafine titania particles

Abstract: Synthesis of ultrafine titania particles is investigated in a diffusion flame aerosol reactor in the presence of a gaseous electric discharge (corona) created by two needle electrodes. The corona wind flattens the flame and reduces the particle residence time at high temperatures, resulting in smaller primary particle sizes and lower level of crystallinity. Increasing the applied potential from 5 to 8 kV reduces the particle size from 50 to 25 nm and the rutile content from 20 to 8 wt %. Coronas provide a clean and simple technique that facilitates gas phase synthesis of nanosized materials with controlled size and crystallinity.