Short Communication Analysis of Gaseous Fuel and Air Mixing

Brasoveanu, Dan; Gupta, Ashwani K.

doi:10.1080/00102209908924185

Cited by 4 publications

(6 citation statements)

References 5 publications

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“…(18). These results are in agreement with previous studies, 15 which showed that the rate of mixing is enhanced by reducing the initial pressure or increasing the rate of pressure.…”

Section: Resultssupporting

confidence: 95%

“…These results are in agreement with previous studies 15 that showed a reduction in the rate of mixing at high temperatures and increase in the rate of mixing at high rates of temperature. 15 Rates of temperature of less than 1,000 K/s provide mixing times in excess of 0.3 s. Figure 6 shows the affect of temperature on maximum fuel-lean mixing time. A constant density of 1.2 kg/m 3 and two initial temperatures of 293 and 1465 K, respectively, are considered here.…”

Section: Resultsmentioning

confidence: 97%

“…15 The model predictionsare compared here with the available experimental results. The methane-air mixing times are also determined.…”

Section: Theoretical Approachmentioning

confidence: 97%

“…Assuming an ideal gas mixture containing n f moles of fuel and n a moles of air, 15 the number of moles of fuel and air can be calculated from…”

Section: Theoretical Approachmentioning

confidence: 99%

“…Two mixing mechanisms that can be distinguishedare the penetration of air into the fuel ow and the dispersion of fuel into the surrounding air. 15 Each mixing mechanism can be characterized by the time required to yield a ammable mixture. The time associated with the rst mechanism, i.e., the time required to reduce the local equivalence ratio from in nity to the upper ammability limit, 6 is de ned as t r .…”

Section: Theoretical Approachmentioning

confidence: 99%

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Maximum Mixing Times of Methane and Air

Brasoveanu

Gupta

2000

Journal of Propulsion and Power

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The combined effect of the distribution of fuel, air, temperature, pressure, and velocity in a combustor on methane-air mixing times is examined using a uni ed mixing model. The model is designed to study mixing under both nonreacting and reacting conditions up to the ame front at low pressures. The degree and rate of mixing is quanti ed using the local equivalence ratio and its total derivative with respect to time, respectively. Results show that velocity divergence, and rates of pressure and temperature affects mixing. The model is validated using available experimental results. Two mixing mechanisms that can be distinguished are air penetration into the fuel ow and fuel dispersion into the surrounding air. Algorithms to calculate the rates of mixing and mixing times for both these mechanisms are presented. Results show that under both reacting and nonreacting conditions, the maximum mixing time is directly proportional to the initial pressure and temperature of mixture and inversely proportional to rates of pressure and temperature, and to velocity divergence. Mixing through fuel dispersion into the surrounding air is shown to be faster than via air penetration into the fuel ow. The range of conditions for the distributions of pressure, temperature, and velocity have been chosen to represent characteristic conditions encountered in most low-pressure combustors. Rates of pressure of less than one atm/s acting alone provide a mixing time in excess of one second, which is unacceptably long for many applications, in particular gas turbine combustion. Rates of temperature that act alone may provide mixing times of 0.001 s or less. Mixing times of the order of a few milliseconds, required for ef cient combustion and low emission, require high velocity gradient at the fuel-air boundary. Results show that enhanced mixing is achieved by combining temperature and velocity gradients. This analysis of mixing time assists in providing design guidelines for the development of high intensity, high ef ciency, and low emission combustors. Nomenclature dP / dt = rate of pressure, atm/s (dP / dt ) max = maximum rate of pressure, atm/s (dP / dt ) min = minimum rate of pressure, atm/s dT / dt = rate of temperature, K/s (dT / dt ) max = maximum of rate of temperature, K/s (dT / dt ) min = minimum rate of temperature, K/s div U = velocity divergence, 1/s div U max = maximum velocity divergence, 1/s div U min = minimum velocity divergence, 1/s e 1 , e 2 , e 3 = unit vectors along the x, y, z axes M = molecular weight of mixture, kg/kmol M(0) = initial molecular weight of mixture, kg/kmol M a = molecular weight of air, kg/kmol M f = molecular weight of fuel, kg/kmol m a = mass of air, kg m f = mass of fuel, kg (m a / m f ) st = stoichiometric mass ratio of fuel and air P = pressure, atm R = universal gas constant/atmospheric pressure, m 3 /Kmol-K R n = fuel nozzle radius, m r e = rate of equivalence ratio, 1/s r (exp) e = experimental rate of equivalence ratio, 1/s r (max) e = maximum rate of equivalence ratio, 1/s r (min) e = minimu...

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“…(18). These results are in agreement with previous studies, 15 which showed that the rate of mixing is enhanced by reducing the initial pressure or increasing the rate of pressure.…”

Section: Resultssupporting

confidence: 95%

Section: Resultsmentioning

confidence: 97%

“…15 The model predictionsare compared here with the available experimental results. The methane-air mixing times are also determined.…”

Section: Theoretical Approachmentioning

confidence: 97%

“…Assuming an ideal gas mixture containing n f moles of fuel and n a moles of air, 15 the number of moles of fuel and air can be calculated from…”

Section: Theoretical Approachmentioning

confidence: 99%

Section: Theoretical Approachmentioning

confidence: 99%

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Maximum Mixing Times of Methane and Air

Brasoveanu

Gupta

2000

Journal of Propulsion and Power

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Methane and air mixing times under nonreacting and reacting conditions

Brasoveanu

Gupta²

IECEC 96. Proceedings of the 31st Intersociety Energy Conversion Engineering Conference

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Determination of Propane and Air Maximum Mixing Times

Brasoveanu

Gupta

2000

Journal of Engineering for Gas Turbines and Power

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The model of gaseous fuel and air mixing, developed by the authors, is applied here to calculate maximum mixing times of propane and air. The degree of mixing is determined using the mass fraction of fuel while the rate of mixing is determined from the rate of this mass fraction. The values of both these parameters are local, i.e., measured within an infinitesimal element of fluid. A Eulerian representation is used. The model is based on the assumption that both fuel and air behave as a single chemical species. It is further assumed that pressure is low and only fuel and air are present within the fluid element. Under nonreacting conditions, the model is valid anywhere in the combustor. Under reacting conditions, the model is valid within those combustor regions where the fuel–air mixture is not flammable. The results of this analysis show that mixing times of propane and air are most reduced by high gradients of temperature and velocity, as long as these gradients provide in phase contribution. To a lesser degree, high gradients of pressure also help reduce mixing times. High initial pressure and temperature increase mixing time. Mixing with air penetration into the fuel flow is slower than with propane dispersion into the surrounding air. In general, the exact mixing time has to be determined numerically. Nevertheless, the analytical solutions included here provide maximum mixing times of propane and air under most conditions. These results provide important guidelines for the development of high intensity, high efficiency, and low emission combustors.

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Short Communication Analysis of Gaseous Fuel and Air Mixing

Cited by 4 publications

References 5 publications

Maximum Mixing Times of Methane and Air

Maximum Mixing Times of Methane and Air

Methane and air mixing times under nonreacting and reacting conditions

Determination of Propane and Air Maximum Mixing Times

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