Methane equivalence ratio

From these results, it is clear that sll hydrate formation decreases the propane to methane equivalent ratio. This change becomes detectable from 5 bbl/MMscf. The main advantage of this device is that it can measure equivalent concentration of both methane and propane imlike the SoS device which could only detect the overall change in composition. 

Fig. 3. Quenching distance as function of equivalence ratio for hydrocarbon mixtures with air (1), where x = methane, = propane, A = propylene, and...

If the substitute fuel is of the same general type, eg, propane for methane, the problem reduces to control of the primary equivalence ratio. For nonaspiring burners, ie, those in which the air and fuel suppHes are essentially independent, it is further reduced to control of the fuel dow, since the air dow usually constitutes most of the mass dow and this is fixed. For a given fuel supply pressure and fixed dow resistance of the feed system, the volume dow rate of the fuel is inversely proportional to. ypJ. The same total heat input rate or enthalpy dow to the dame simply requires satisfactory reproduction of the product of the lower heating value of the fuel and its dow rate, so that WI = l- / remains the same. WI is the Wobbe Index of the fuel gas, and... 

Relationship between minimum ignition energy and equivalence ratio for hydrogen-air and methane-air mixtures. 

This system produces a steady laminar flow with a flat velocity profile at the burner exit for mean flow velocities up to 5m/s. Velocity fluctuations at the burner outlet are reduced to low levels as v /v< 0.01 on the central axis for free jet injection conditions. The burner is fed with a mixture of methane and air. Experiments-described in what follows are carried out at fixed equivalence ratios. Flow perturbations are produced by the loudspeaker driven by an amplifier, which is fed by a sinusoidal signal s)mthesizer. Velocity perturbations measured by laser doppler velocimetry (LDV) on the burner symmetry axis above the nozzle exit plane are also purely sinusoidal and their spectral... 

Dynamics of a methane-air conical flame submitted to a convective wave of equivalence ratio perturbations,/= 175 Hz, and = 0.1. The mass fraction perturbation is shown on the color scale. The flame is represented by temperature isocontours. Two cycles of modulation are displayed. 

It is presumed that the global-quenching criteria of premixed flames can be characterized by turbulent shaining (effect of Ka), equivalence ratio (effect of 4>), and heat-loss effects. Based on these aforemenhoned data, it is obvious that the lean methane flames (Le < 1) are much more difficult to be quenched globally by turbulence than the rich methane flames (Le > 1). This may be explained by the premixed flame shucture proposed by Peters [13], for which the premixed flame consisted of a chemically inert preheat zone, a chemically reacting inner layer, and an oxidation layer. Rich methane flames have only the inert preheat layer and the inner layer without the oxidation layers, while the lean methane flames have all the three layers. Since the behavior of the inner layer is responsible for the fuel consumption that... 

It is also well known that there exist different extinction modes in the presence of radiative heat loss (RHL) from the stretched premixed flame (e.g.. Refs. [8-13]). When RHL is included, the radiative flames can behave differently from the adiabatic ones, both qualitatively and quantitatively. Figure 6.3.1 shows the computed maximum flame temperature as a function of the stretch rate xfor lean counterflow methane/air flames of equivalence ratio (j) = 0.455, with and without RHL. The stretch rate in this case is defined as the negative maximum of the local axial-velocity gradient ahead of the thermal mixing layer. For the lean methane/air flames,... 

Variations of extinction stretch rate and extinction temperature of methane/air mixtures with equivalence ratio for the five different cases as in Figure 6.3.4. 

Transient computations of methane, ethane, and propane gas-jet diffusion flames in Ig and Oy have been performed using the numerical code developed by Katta [30,46], with a detailed reaction mechanism [47,48] (33 species and 112 elementary steps) for these fuels and a simple radiation heat-loss model [49], for the high fuel-flow condition. The results for methane and ethane can be obtained from earlier studies [44,45]. For propane. Figure 8.1.5 shows the calculated flame structure in Ig and Og. The variables on the right half include, velocity vectors (v), isotherms (T), total heat-release rate ( j), and the local equivalence ratio (( locai) while on the left half the total molar flux vectors of atomic hydrogen (M ), oxygen mole fraction oxygen consumption rate... 

Many detailed reaction mechanisms are available from the Internet. GRI-Mech (www.me.berkeley.edu/gri-mech/) is an optimized detailed chemical reaction mechanism developed for describing methane and natural gas flames and ignition. The last release is GRI-Mech 3.0, which was preceded by versions 1.2 and 2.11. The conditions for which GRI-Mech was optimized are roughly 1000-2500K, lOTorr to lOatm, and equivalence ratios from 0.1 to 5 for premixed systems. 

The experimental setup for diode-laser sensing of combustion gases using extractive sampling techniques is shown in Fig. 24.8. The measurements were performed in the post-flame region of laminar methane-air flames at atmospheric conditions. A premixed, water-cooled, ducted flat-flame burner with a 6-centimeter diameter served as the combustion test-bed. Methane and air flows were metered with calibrated rotameters, premixed, and injected into the burner. The stoichiometry was varied between equivalence ratios of = 0.67 to... 

However, the combustion process for methane requires no fewer than 325 individual mechanistic steps (elementary reactions) to be accurately described, rather than the one-step route shown above. As such, incomplete combustion is a common occurrence and ROS are pervasive byproducts of that phenomenon, affecting an engine s fuel efficiency and producing atmospherically detrimental emissions. Moreover, combustion varies with system temperature, as different oxidative pathways become accessible, as well as fuel/oxidizer ratio (equivalence ratio). By examining the representative cases of methane oxidation at high and low temperatures, this phenomenon becomes clearer. 

Use laminar premixed free-flame calculations with a detailed reaction mechanism for hydrocarbon oxidation (e.g., GRI-Mech (GRIM30. mec)) to estimate the lean flammability limit for this gas composition in air, assuming that the mixture is flammable if the predicted flame speed is equal to or above 5 cm/s. For comparison, the lean flammability limits for methane and ethane are fuel-air equivalence ratios of 0.46 and 0.50, respectively. 

Fig. 17.23 Sampling-probe measurements of CO2 mole fractions in a stagnation-flow boundary layer above a hexaluminate-based catalyst. In all cases the equivalence ratio of methane in air is 4> — 0.3, while the surface temperature varies from 880°C to 1110°C. In all cases the inlet flow that issues though the contraction nozzle is Tin = 400°C and the inlet velocity is U n = 70 cm/s. The separation distance between the nozzle exit and the stagnation surface is /. = 1.65 cm.

A mass-spectrometer sampling probe is used to measure major species profiles for a variety of surface temperatures. For all cases shown in Fig. 17.23 the inlet mixture is lean methane air at an equivalence ratio of

[Pg.734]

Two flat flame burners have been employed, a 4 cm 10 cm burner with a ceramic-lined chimney for NO measurements (4) and a 2.6 cm x 8.6 cm open-faced burner with a nitrogen shroud flow for CO measurements. Both burners operate at atmospheric pressure with laminar, premixed methane-air mixtures. These burners work satisfactorily over a broad range of fuel-air equivalence ratios, but both have cold boundary regions which cause non-uniform conditions along the optical axis that can be important in the data analysis (4). 

Four flat, disc-shaped laminar flow flames were probed and analyzed using standard microprobing techniques. The flames were composed primarily of CO, H2, 02> and Ar with small amounts of CH4 or natural gas added to simulate intermediate Btu gas mixtures. Gas compositions used in the probings are presented in Table 1. Flames A and B contained excess air, air/fuel equivalence ratio = 1.13 Flames C and D were slightly fuel rich, air/fuel equivalence ratio = 0.93. Each of the mixtures had a CO/H2/X (X = methane or natural gas) mole ratio of 1/1/0.22. 

Figure 7.3. The combustion time (the time needed to reach the maximum pressure in a closed vessel) for a methane/air flame with and without turbulence, plotted as a function of the proportion of CH4 in the reactant mixture, corresponding to the equivalence ratio (j> (stoichiometric proportions correspond to about 10 % of methane). Time units correspond to 10-2 seconds ([377 307]).

In order to evaluate the flame structure of characteristic fuels, this procedure was applied to propane-, methane-, and hydrogen-air flames at the stoichiometric equivalence ratio and unbumed gas conditions of 298.1 K and 1 atm. Hie fuels were chosen because of their different kinetic characteristics. Propane is characteristic of most of the higher-order hydrocarbons. As discussed in the previous... 

Fig. 8 Laminar premixed flames of methane. (A) Slightly fuel rich (B) fuel-rich and sooting and (C) diffusion flame. Note increased luminosity with increasing equivalence ratio.

Although higher flame temperatures are desirable for improved waste/fuel destruction, there are also drawbacks. Most significantly, the reactions leading to NO formation increase with increasing temperature. This is shown in Fig. 12, where equilibrium NO levels are shown to increase with increasing temperature and decreasing fuel equivalence ratio in methane-air... 

In Fig. 15, the sooting limits of chlorinated methanes/ methane/air mixtures are presented in terms of critical equivalence ratios and as a function of the chlorinated methane/methane molar ratio (7 ). As the chlorine content of the mixture was increased, sooting occurred at lower equivalence ratios. 

Fig. 15 Critical equivalence ratios (onset of soot formation) of premixed methane and chlorinated methane flames. (From Ref...

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