Air staged double swirl low NOx LPG burner

Paper from the AFRC 2015 conference titled Air staged double swirl low NOx LPG burner

Due to the environmental concern and the realization of the harmful effects of pollutants emerging from combustion systems burning fossil fuels, new strategies have been developed in the design of combustion equipment. These strategies must take into account reduction of the levels of NOx, CO and UHC while maintaining high combustion efficiency, wider stability limits and safety. The present work aims at providing a comprehensive experimental study of the flame characteristics of a staged double swirl low NOx gaseous burner. This burner configuration is a replacement of the traditional coaxial burner having a central fuel jet with a single coaxial swirler. The proposed configuration allows for better control of the degree of mixing and charge stratification by varying the swirl angles, inlet momentum ratio and equivalence ratio of the annular and outer streams. The scope of this experimental program is divided into three distinct stages, namely; the flame stability (stage 1), exhaust emissions (stage 2) and in-flame measurements (stage 3).

Air staged double swirl low NOx LPG burner * A.M. Elbaz*,** and W.L. Roberts* Clean Combustion Research Center, King Abdullah University of Science and Technology, Saudi Arabia ** Faculty of Engineering Materia, Helwan University, Cairo, Egypt. [e-mail] Abstract The present work aims at providing a comprehensive experimental study of the flame characteristics of a staged double swirl low NOx gaseous burner. The proposed configuration allows for better control of the degree of mixing and charge stratification by varying the swirl angles, inlet momentum ratio and equivalence ratio of the annular and outer streams. The scope of the work is divided into three distinct stages, namely; the flame stability mapping, exhaust emissions and in-flame measurments (temperature, species concentration, and ion current). Comprehensive mapping of lean blowout equivalence ratio of the annular and central streams together with the overall lean blowout equivalence ratio and the exhaust gaseous emissions at varying geometrical and operating parameters are executed. The stability data show that, the annular fuel admitting improve the flame stability than the outer stream admitting, while the central fuel admittance gives extra improvement to the flame stability. The higher the momentum ratio, the largest the annular swirl angle, the uniform mixture strength together with the smallest outer swirl angle, the lowest NO emission. The inflame measurments showed that the largest NO concentration was limited to the internal recirculation zone, so the residence time, mixture strength and temperature at the boundaries of IRZ are the controlling parameter for NO emissions. The largest the annular swirl angle together with small outer swirl angle has a great effect in reducing the overall temperature of the flame and lowest residence time. This in turn gives low NO concentrations. 1. Introduction Over the past two decades, increasingly stringent regulations reducing allowable NOx emissions from combustion sources have been implemented. In response to these regulations, a variety of technologies for control of NOx emissions from combustion sources have been developed. Swirl burners are the most common type of devise in a wide range of combustion applications, including utility boilers, industrial furnaces and boilers or gas turbine combustors. Detailed information on this type of burners and the corresponding flames can be found, for example, in [1-3]. The flow and mixing patterns generated by swirling flow afford excellent flame stability, which confers a notable versatility on this type of burners. In particular, many of the so-called ‘low NOx burners' developed during the last decades are based on swirlstabilized flames. These burners accomplish a low NOx emission by means of a suitable design of the burner flame aerodynamics and mixing. The basic low NOx techniques based on combustion modification and mixing control are fuel staging and air staging [4-7], in these techniques NOx formation is controlled by staging or delaying, respectively, the admission of a fraction of fuel and air into the flame. Air staged flames are studied in this work, in which the air staged was achieved through using coaxial double swirl burner (annular and outer swirls), and this to investigate the effects of swirl levels, air momentum ratio, the degree of the segregation of the mixture strength between the annular and outer swirling jets on flame stability and NOx emissions. NOx reduction is achieved by creating two staged combustion, the detailed analysis of NO chemistry in the two stages are provided in [8, 9]. By using compensated thermocouple technique, the characteristic of co-swirling double swirl flames were investigated [10], although the data provided insight into local turbulent flame structure, the measurments were insufficient to visualize the global flame behavior. One of the difficulty in designing low NOx burners is to ensure good flame stability, which can be hindered precisely by those effects that help in reducing NOx formation: delaying mixing, highly off-stoichiometric conditions and/or low flame temperatures. However, no detailed study on the stability characteristics, emissions, and flame structure of air staged flames with different degree of segregation has been found in the open literature. In view of providing wider stability AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah limits and/or minimizing NO-emissions the stability, emission and flame structure induced from double swirlers concentric with a central multi holes axial nozzle will be investigated in this work. 2. Experimental setup and methodology The tests have been performed in a horizontal water-cooled combustor as shown in Fig.1-a, equipped with a gas air staged burner. The burner includes double concentric swirlers (annular and outer) with a central nozzle. Three separate air supply lines are used (Fig. 1-b), two for the outer and annular premixed mixtures of equivalence ratios Φout and Φan respectively. The third one for the central premixed mixture of equivalence ratio Φcen. Both the annular and outer air flow rate were controlled and metered using a differential pressure flow meters. The outer and annular fuel streams were supplied from Liquefied Petroleum Gas (LPG, 70% C4H10 and 30 % C3H8) bottles. The fuel flow rate was controlled and measured by calibrated Rotameters (FL-1347-C, Omega). The gaseous fuel for the annular and outer streams were injected into their air streams before the burner head, (see Fig. 1.b). The central premixed mixture flows through the central pipe to the exit nozzle. The central nozzle has a 6 axial holes each of inner diameter 1 mm distributed at a circular of 8 mm diameter. The annular and outer swirlers have cascaded guide vanes that are being placed axially inside the annular and outer tubes of 56 mm and 104 mm, respectively. As shown in Table 1, three values of guide vanes swirl angle were chosen for the annual and outer swirl, in addition, the corresponding swirl number were defined according Beer and Chigier [11] formula. The combustor is a horizontal cylindrical water cooled flame tube of 200 mm inner diameter and 2 meter length and is segmented to a 14 adjacent segments. The first segment of the combustor is 220 mm length and has 11 measuring tabs of 12 mm diameter, however the for each rest of the segments has only one middle measuring tab. The rear side of the combustor is opened to the atmosphere under the hood of the laboratory air ventilation system. Table 1: swirl angle and the corresponding swirl number Outer swirl Annular swirl Swirl location Swirl angle No. of blades S 30o 45o 60o 30o 45o 60o 8 8 6 16 12 10 0.43 0.74 1.29 0.48 0.83 1.44 Local temperatures were measured by a platinum/ platinum 13 % Rhodium thermocouple of 75 µm wire diameter. All the temperature data presented in this work are uncorrected for radiation error because of its relatively small magnitude [12]. Gas composition was determine using Lancom series II gas analyzer for O2, CO, NO, HC (unburned hydrocarbon). A water cooled gas sampling probe of 5 mm outer tube diameter was used to obtain the spatial distribution of those species inside the flame and in the exhaust gaseous (on dry basis). The electrostatic (Longmuir probe) was employed to detect the local variations of the positive ions within the flame zone. The design of this probe include a 300 µm (platinum-13 % Rhodium) single wire inserted in a 1 mm single bore ceramic tube with a sensor tip of 2 mm length, which in turn placed inside a stainless steel tube with a water cooled jacket. A 16-bit card (PCI 6014) at 12 KHz sampling rate was used to acquire the ion signal, the high frequency noise was eliminated digitally at a critical frequency fc of 5 KHz. The experimental program is divided into three consecutive stages. In the first stage the stability map was investigated. The flame was extinguished via gradually decreases the fuel admittance to the annular mixture at zero central jet equivalence ratio (Φcen = 0). Another set of stability map was achieved via gradually decreases the fuel admitted to the central nozzle mixture at zero annular equivalence ratio (Φan AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah = 0). The effects of momentum ratio (Mr: defined as, the ratio of the inlet axial momentum of the annual air stream to the axial momentum of the outer air stream), the outer/annular swirl angles and the outer mixture equivalence ratio on the lean stability limit were investigated in this stage. The effects of the previous mentioned parameters on the exhaust emission were investigated in the second stage (exhaust emission). In the third stage, in-flame measurments were conducted on some selected flames. The list of the flames for the three stages are indicated in Table2. Table 2: experimental program Stage I: stability mapping Mr =0.8, =2.2, =4.9, Φout 0.4,0.6, 0.8 an/out 45o/30o 45o/45o 45o/60o out/an Mr = 0.55 Φcen =10 o =0.8 Stage 2: Exhaust emission o 30 /45 45o/45o 60o/45o = 0.4.9 Φcen =10 Φout 0.7, 0.6, 0.5, 0.4 0.7, 0.6, 0.5, 0.4 an/out Stage3: in-flame measurments Mr Φout an/out out/an 0.55 0.4, 45o/30o 60o/30o,45o,60o 0.7 45o/30o (30o , 45o , 60o /30o) (30o , 45o , 60o /45o) (30o , 45o , 60o /60o) 30o, 45o, 60o /30o 4.9 0.4 3. Results and discussion 3.1 Flame appearance It seems appropriate before proceeding to the presentation and discussion to portray the varaiations in the flame appearance with the progressive changes of the geometrical and flow parameters for some selected flames. Figure 2.a shows the flame appearance under the following conditions, an/out = 30o/30o, and Φan = 1, Φout = 0.4, Φov = 0.73 and Mr = 2.2. The flame photo indicates short, nonluminous flame, proving the fast and proper mixing. A yellow central core was observed, and this is mainly due to the rich fuel central mixture. The frontal view shows eight radially spreading bluish flame sheets corresponding to the annular swirl blades. As shown in Fig. 2.b, the increase of Mr to 4.9 leads to decrease the width of the flame, where the higher annular momentum increases the strain rate associated with the annular stream, pushing the reaction zone axially downstream. 3.2 Flame stability 3.2.1 Flame extinction via leaning out the annular stream equivalence ratio Figure 3 represents the effect of increasing the outer equivalence ratio Φout from 0.4 to 0.8 on the annular blow off equivalence ratio and the corresponding overall equivalence ratio Φan,bo and Φov,bo respectively, under fixed Mr and swirling angles, (an = 45o, out= 30o, 45o, 60o). For the three momentum Ratios Mr= 0.8, 2.2, and 4.9, the results indicate that, the annular stream Φan,bo is almost linearly decreased substantially with increasing Φout. This proves that there is entrainment from the outer mixture toward the annular stream through the mixing shear layer between the two streams. The observed decrease in Φan,bo with increasing Φout generally did not imply a lower overall equivalence ratio, but in the contrary for the three momentum ratios, the overall equivalence ratio at blow off, Φov,bo, is increased with increasing Φout. This indicates that the portion of the outer fuel that was not entrained to the annular region, does not play a role in the flame stabilization mechanism. The amount of the outer fuel stream that was entrained to the annular stream is controlled by both the degree of mixing between the two streams and the mixture strength of the outer stream. The evaluation of the degree of mixing between the two streams, may be performed by introducing the effective equivalence ratio (Φeff), and it is expressed as: Φeff = αΦout + (1-α) Φan AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah Where the parameter α indicates the degree of mixing. At α = 0; only the annular flow exist, and, at α = 1; only the outer stream exist. For a fixed annular/outer mixture momentum ratio, and, for a fixed burner geometry, the effective equivalence ratio at blow-off can be taken a constant. The previous equation could be solved for the mixing parameter as: α = [1/ (1- (dΦout/dΦan))] In the present work dΦout/dΦan could be calculated from the slope of the straight line that fits the data shown in Fig. 3, and the values of α for different momentum ratio are given in Table 3. The data show that higher values of the mixing parameter α as the momentum ratio Mr is decreased. Also, the data in Fig. 3 shows that for annular swirl angle an = 45o, increasing the outer swirl angle an by (30o, 45o, 60o) causes a decrease in both Φan,bo and Φov,bo. Increasing the outer swirl angle reduces the axial velocity of the outer swirling jet, which in turn reduces the quenching effect of the annular flame envelop and delay the mixing between the annual and outer swirling jet further down streams. Also with increasing the outer swirl angle reduces the strain rate at the vicinity of the flame envelop. Table 3: mixing parameter α at Mr Mr 0.8 2.2 4.9 α 0.57 0.44 0.35 Figure 4 shows the effects of the momentum ratio Mr, on both Φan,bo and Φov,bo. The data consistent with the previous argument of the mixing parameter, at Mr = 0.8 the mixing parameter has a higher value, and hence the effect of the outer stream mixture strength on the reaction zone has a relatively high effect. So it is consider as a destabilizing factor in the case of leaner outer mixture strength, Φout= 0.4. However, with increasing the momentum ratio, the mixing parameter is decreased, consequently, it reduces the effect of the outer stream on the flame envelop and leads to a higher Φan,bo at the leanest Φout and a lower value as the outer streams becomes more strength. On the other side, the annular swirl angle, an has no influence on both Φan, bo and Φov, bo. This can be seen from the overlap of the curves of Φan, bo and Φov, bo on one curve for the three annular swirl angles (an =30o, 45o, 60o) at Mr = 0.8 and outer swirl angle of 45o, see Fig. 5. This indicates that even with low Mr (which means higher mixing parameter) changing the annular swirl angle was not able to change the degree of mixing between the lower annular momentum and the higher outer momentum. 3.2.2 Flame extinction via leaning out the central stream equivalence ratio. In this part, we will discuss the flame extinction via leaning out the central stream equivalence ratio, Φcen,bo, and this at Φan= 0.0. Figure 6 shows the effects of increasing the outer equivalence ratio Φout on the central stream equivalence ratio at blow off (Φcen,bo) and the corresponding overall equivalence ratio (Φov,bo) for a fixed annular swirl angle an =45o. For the momentum Mr = 0.8, the results show a steeper decrease of Φcen,bo with a progressive increase in the corresponding value of Φov,bo, with increasing the outer stream equivalence ratio. This indicates that, the outer stream fuel was entrained to the reaction zone, through the mixing shear layers. With increasing Φout the entrained fuel is increased and this can be deduced from the decreasing Φcen,bo. The remaining quantity of the outer stream fuel stream does not take a role of the stabilization mechanism, and this quantity is increased with increasing Φout, and hence increases Φov,bo. The lower value of the central mixture equivalence ratio is considered a destabilization factor, as a result of moving the forward stagnation point at further downstream location, where the flow field has a higher axial velocity. This reduces the effect of the stagnation point to act like an attachment point. AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah From Fig. 6, the effects of the outer swirl angle on the flame stability could also be discussed. For Φout= 0.4 and 0.6., increasing the outer swirl angle leads to a gradual reduction of both Φcen,bo and Φov,bo, where increases the outer swirl angle reduces the strain rate and quenching effect at the reaction zone and keeping the mixture at the boundary of the reversed region at the flammable mixture strength. For Φout = 0.8, the outer swirl angle has no effect of both Φcen,bo and Φov,bo. In this case two opposing effects are found, increasing the outer swirl angle improve the flame stability as discussed before for Φout= 0.4 and 0.6. The opposing factor, increasing the outer swirl angle pushes the outer stream radially outward, while it has a higher equivalence ratio, reduces the contribution of the outer fuel to the reaction zone. Figure 7, illustrates effect of the annular swirl angle on the flame stability limit. The data show that increasing the annular swirl angle leads to an increase in both Φcen,bo and Φov,bo, and this effect diminishes with increasing Φout. This may be explained by increasing the annular swirl angle increases the recirculated mass toward the central vortex, which leads to higher quenching and dilution effects to the flame root (Φan = 0), however this effect is reduced at Φout = 0.8, because the recirculated mass has a higher mixture strength. 3.3 Exhaust emission results In this stage, comprehensive mapping of the dry exhaust gas analysis at different operating conditions that cover the effect of momentum ratio (Mr), the annular and outer swirl angles (an and out) are conducted, see Table 2. In all cases the overall equivalence ratio is kept constant at a lean value of 0.73. This means, during each series of results, with the progressive lowered the value of Φout, the progressive increase of Φan such that Φov = 0.73. The entire exhaust emission results is conducted at constant Φcen = 10. The exhaust gas analysis indicates a zero concentration of HC, CO species, and nearly 6.2 % O 2 by volume, while variable NO Concentration. Consequently, the effect of the different operating parameters on only NO concentration in the exhaust gases and the exhaust mean temperature will be discussed. Figures 8-9 reveal the effect of Φout on NO emission and mean gas temperature T for Mr = 0.55 and 4.9 respectively. For Mr = 0.55, the effect of increasing Φout from 0.4 to 0.7 at the expense of reducing Φout from 1.3 to 0.7 are presented in Fig. 8.a, for out= 30o. The results exhibit a steeper reduction in the NO concentration with a slight reduction in the exhaust temperature with increasing Φout. This is attributed to the progressive change in the mixture equivalence ratio at the vicinity of the recirculation boundaries leading to uniformity, (Φout and Φan are approaching each other of lean mixture). Thus, both the thermal and prompt NO are reduced. The former is due to the lean combustion and to eliminate of the high temperature spots caused by the local stoichiometric fuel/air ratio, while the latter is attributed to the reduction of the HC radical within the reaction zone. This means that the thermal non uniformity is significantly high with the relative higher difference in the equivalence ratio. For example, at Φout = 0.4, the annular stream mixture has a rich equivalence ratio of Φan = 1.3. This means a rich mixture at the vicinity of high temperature near the boundaries of the recirculation zone. This will provide a sufficient residence time pyrolysis. This conditions initiate the reactions of hydrocarbon radicals, present in and near the reaction zone, with molecular of nitrogen to form HCN species. Within the shear layer between the annular and outer streams, the concentration of the oxygen radical is high enough to react with HCN species and hence NO formation, (the Fenimore prompt NO mechanism). For Mr = 4.9, Fig. 9, the set of results show a qualitative similarities with those previously examined for Mr = 0.55. But the level of NO emissions is decreased with increasing the Mr. Increasing Mr is not the direct cause of this reduction of the NO emissions. Increasing the momentum ratio at the same Φout, leads to a lower annular stream equivalence ratio, to keep the overall equivalence ratio constant at 0.73. Also the effects of the outer swirling angle on the NO emission could be understood by investigation the results in Figs. 8-9. For Mr =0.55, at Φout =0.4 increasing the outer swirl angle out leads to increasing the AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah NO emissions. While this effect is decreased with increasing both an and Φout. Increasing out pushes the outer stream toward the combustor wall at the early combustion region. Consequently, the mixing between the annular and the outer streams is delayed some distance downstream the burner exit. So the quenching and the dilution effects of the outer stream to the reaction zone are decreased and hence higher NO emissions. On the other hand with increasing the outer stream equivalence ratio, the degree of segregation between the two streams is decreased and hence lower NO emission is recorded. On the other hand at the higher annular swirl angle an = 60o combined with lower out = 30o, it gives minimum NO emission. This configuration leads to the highest mixing degree and hence more mixture uniformity and lowest NO emission. As indicated in Fig. 10 for Mr = 0.55 under a fixed outer swirl angle, increasing the annular swirl angle an, results in a steeper decrease in the NO emissions. With increasing Φout, the effect of the annular swirl angle in decreasing the No emissions, is changing from a steeper decrease to a gradually and slightly decrease. This is attributed to the increase of the recirculation zone with increasing an, which enhanced the recirculated mass and hence fast mixing, lower residence time, and diluting the mixture strength at the vicinity of the reaction zone. Accordingly, low exhaust gas temperature, and NO emission. 3.4 In flame measurments Results 3.4.1 Effect of the outer stream equivalence ratio Φout In this part, the measurments are conducted on a macroscopic level to yield the mean gas temperature and the dry volumetric analysis of the gaseous (CO, NO, HC, O2) throughout the flow regimes. The measurement is also extended to cover the ionization measurments on microscopic level. To evaluate the effect of partial premixing on the flame structure, the stream equivalence ratio, Φout, is increased from 0.4 to 0.7 under fixed Mr = 0.55 and swirling angles an/out = 45o/30o. Figs. 11-12 illustrate the radial profiles for temperature and species concentrations at different axial locations (x/d, where d is the inner diameter of the combustor) for Φout = 0.4 and 0.7, respectively. For the case of Φout = 0.4, the temperature distributions close to the burner exit (at x/d = 0.13, 0.23, 0.33) indicate the existence of a recirculation zone; where the temperature levels are almost uniform, indicating a well-mixed zone of the hot combustion products. The maximum temperature occur just outside the reversed zone in the mixing region, increased up at axial distances 0.33 and then decayed further downstream indicating a depletion of the fuel. Also, the radial location of the peak temperature is gradually shifted to outward direction indicating the increasing width of the reversed region. The temperature profile showed a steep temperature decline at radial location 0.7 < r/R < 0.7, due the flame quenching of the annular stream jet. Near to the combustor walls, the temperature increases, this is may be again due to the outer stream flame. Further downstream axial locations (0.73 < x/d < 5.9), the temperature distribution takes a flat profile across almost the whole combustor diameter. For NO profiles, at early axial distance x/d = 0.13; the nitrogen oxide concentration indicates the relatively high NO concentration and it is limited to the RZ. The profile exhibits a sharply decay with the steeper temperature decreasing at the boundaries of the RZ. At X/d =0.23, and, 0.3, the NO concentration within the reversed region are rapidly dropped to a lower level, while the temperature profile at these distances are still increasing. These conditions indicate that, the prompt NO mechanism is dominating at these early axial distances. Further downstream x/d > 0.33, a highly drop in NO concentration, and this is due to rapid temperature decay caused by rapid mixing at the early region with the outer lean stream, in addition to the dilution due to the reversed exhaust gas within the recirculation zone, RZ. The CO profiles reveal a maximum CO concentration at the steeper decline in the flame temperature, and this under the extremely rich fuel annular stream. Further downstream X/d =0.23, 0.33, the CO concentration is decreased, and is radially spreading following the decline in the temperature profile. With more axial distances. CO concentration is reduced, and this is attributed to the fuel depletion. HC concentration profiles at x/d = 0.13 showed a slightly small HC concentration inside RZ due to the central fuel stream of rich mixture, and the entrained AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah fuel from the annular mixture. HC concentration exhbits a more appreciable level at the boundaries of the RZ. With increasing the axial distances, HC concentration is gradually reduces with a radial peak shift outward. The O2 concentration show a nearly uniform and a low value within the reversed region. While at 0.2 ≤ r/R ≤ 0.4, the O2 concentrations show a steeper increase in the concentrations at x/d = 0.13, and this steeper increase is changed to gradually increase further downstream. The radial temperature profile for Φout = 0.7 shown in Fig. 12, the sets of the temperature profiles show qualitative similarities with those discussed above for Φout = 0.4. These are featured in the presence of internal recirculation zone having a flat temperature profile, a rapid decay in temperature within the reaction zone envelope. But for Φout = 0.7, the peak temperature noticed before disappeared and it showed a lower temperature level and this is due to reducing the annular equivalence ratio. Leaning the annular mixture to the extent that both the annular and outer mixture have the same equivalence ratio, namely 0.7, leads to a uniform mixture and this eliminates the peak temperature within the flame zone. The radial profiles of NO concentration for this flame are seen to possess qualitatively the same trends with those examined for Φout = 0.4, but with a quantitative attenuation in NO concentration. This is due to increasing the outer stream equivalence ratio and the corresponding decreasing of the annular equivalence ratio, leads to decreasing in the HC concentration near the reaction zone, see Figs. 11-d, 12-d, and hence reduces the contribution of the prompt NO mechanism. In addition to the lower temperature profiles within the reaction zone with the increase of Φout. As the outer stream equivalence ratio is increased at the expense of reducing the annular equivalence ratio as the CO concentration is decreased. This indicates fast combustion process with the premixed mixture than the case of rich annular equivalence ratio (rich at Φout = 0.4) needs a longer time for mixing and hence gradual mixing, which in turn leads to increasing the residence time for NO formation. The HC concentration within the early axial distances showed a gradually attention with increasing Φout to 0.7 in respect to Φout = 0.4. 3.4.2 Effect of the annular swirl angle Figures 13, 14, and 15 illustrate the effect of progressive increasing the annular swirl angle θan by 30o, 45o, 60o on the flame structure respectively, for Mr= 4.9 and θout = 30o. The radial profiles of mean temperature and species concentrations possess qualitative similarities with those previously examined for the effect of the partial premixing at Φout=0.4, Mr=0.55, Fig. 11. However, increasing θan leads to a wider flat temperature region within the reversed flow zone with the shift of the peak temperature toward the outer stream. This indicates a larger RZ and the higher the recirculated mass, which means a short residence time. With increasing θan leads to fast mixing and hence reduces the HC concentration within the vicinity of the reaction zone, and this reduces the environment for prompt NO formation. Also, the steeper temperature decay at the immediate outer region of the reaction zone, is decreased with increasing the annular swirl angle, where this steep decay is totally disappeared at θan = 60o. Consequently, the more thermal flame uniformity and hence lower NO concentration. In a summary increasing the annular swirl angle together with higher axial momentum ratio can be considered as an effective tool to guide the annular stream to mix with the outer stream region. 3.4.3 Effect of the outer swirl angle Figures 16, 17, and 18 show the effect of increasing the outer swirl angle θout by 30o, 45o, 60o, for fixed annular swirl angle θan=60o, Mr=0.55. Increasing the outer swirl angle reduces the shear between the outer and annular streams, indicated by the gradually disappearance of the steeper temperature decay at early axial distances (see Figs. 16-17). The peak flame temperature at the reaction boundary is increased with more widely the flat temperature region. These circumstances leads to a slightly increase. Also, with increasing θout, the NO concentration is following the radial temperature profile, even at the early axial distance. This indicates that with higher annular swirl angle, associate with higher mixing, the HC AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah consumption is high at early axial distance together with short residence time controlling the prompt NO mechanism. 3.4.4 Presentation and discussion of Ionization measurments Figure 19-a shows the radial distribution of mean ion current at several axial distances and the corssponding mean gas temperature for flame running conditions of [Φout = 0.4, Mr = 0.55, an = 45o, out = 30o]. The results indicate that, although the recirculation zone exhibits high value of the mean temperature, the ion current signal within it, showed diminished levels, see Fig. 19-b, which shows the row ion signal at different radial locations in the flame zone. The ionization level shows rapidly rise at the inner side of the flame sheet reaching a peak value and it shows a gradual decline at the outer direction. These findings suggest that the recirculation zone is occupied with hot recirculated gases interspersed with small percentages of reactants which occasional react. Figure. 20 illustrates the distributions of the pdf of the ion current at the axial location of x/d=0.13 which have the maximum reaction intensity within the flame front for Mr=0.55, θan=45o, θout=30o at different Φout. Five regions having different pdf shapes are seen to characterize the flame zone as follows: (a) Within the recirculation zone, as shown in Fig.20, panel (a ), single peaked Pdf associated with the rather low levels of ion current appear. The most probable value nearly coincides with the mean value of Ĭ, (zero value on abscissa), and very low probabilities of occurrence at higher levels of I, (positive side on abscissa), are also observed. This proves that the recirculation zone is not always filled with fully burnt gas but reaction may take place intermittently in accordance with the engulfment of unburned mixture into the recirculation zone. (b) At the immediate inner boundaries of the flame front, Fig. 20, panel (b), shows a higher levels of reaction rates which evidently proved by both the probabilities shown at the R.H.S., and the positive skeweness of the pdf''s signal. The former indicates that the absolute level of the ion current at which the most probable value occurs is lower than the mean value of the ion current. This suggests that the unburned or burned gases of very low reactedness exist as well. While the later suggests the existence of a fine eddies of various reactedness. (c) Within the flame front, Higher reaction rates are evidently proved by the higher values of the probabilities at R.H.S of the profile this suggests the existence of fine eddies of various reactedness, also higher values of probability at L.H.S of the profile suggest that unburned or burnet gases of very low reactedness exist as well, see panel (c). (d) At the immediate outer boundaries of the flame front, the pdf profile in Fig. 20, panel (d), are generally characterized by the existence of two peaks. The first peak located in the L.H.S of the profile corresponding to the presence of the main reaction zone and the second at the R.H.S of the profile, corresponding to the existence of the unburned mixture. (e) At the outer boundaries of the flame front, panel (e), the percentage of the surrounding outer mixture stream (lean) increases, but the reacting eddies still exist as evidenced by the smeared profiles on the R.H.S, the probabilities would be a near Gaussian and a Dirac delta for the two parts respectively. The observed profiles are a combination of these two distributions. Summary and conclusions The present work aims at providing a comprehensive experimental study on the flame characteristics of staged double swirl low NOx gaseous burner. This burner configuration is a replacement of the traditional coaxial burner having a central fuel jet with a single coaxial swirler. The proposed configuration allows for better control of the degree of mixing and charge stratification by varying the swirl angles, the inlet momentum ratio and equivalence ratio of the annular and outer streams.The Experiments are executed in a horizontal water-cooled flame tube. The burner assembly is coaxially mounted onto a flange being fitted to the entry section of the tube. The scope of the experimental program is divided into three distinct stages namely; the flame stability (stage1), exhaust emissions (stage2) and in-flame measurements (stage3). Complete mapping of the value of the lean blowout equivalence ratio at different operating conditions are conducted. Also a comprehensive mapping of the dry exhaust gas analysis at different operating conditions that cover the effect of momentum ratio (Mr), the annular and outer swirler angle (θan and θout), the outer stream equivalence ratio (Φout ) are conducted. The overall equivalence ratio is kept constant at AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah a lean value of 0.73. The entire measurements are conducted at constant central stream equivalence ratio namely, Φcen=10. The experimental program include also studies of the in-flame structure associated with varying the local equivalence ratio (Φout, Φan) and swirling angles (annular and outer) at different momentum ratios between the annular and outer streams. The measurements are conducted on a macroscopic level to yield the mean gas temperature and the dry volumetric analysis of the gaseous species (CO, NO, HC, O2) throughout the flame regions. The measurements are also extended to cover the ionization measurements on the microscopic level. The results of the flame stability showed that as the fuel is admitted near the boundary of the recirculation zone, as the flame stability is improved. The annular fuel admittance gives better flame stability than the outer admittance, while the central fuel admittance gives extra improvement to the flame stability through the creation of the forward stagnation point. The effect of the momentum ratio on the annular lean stability limit depends on the mixture strength of the outer stream. With a relatively higher outer stream equivalence ratio increasing the momentum ratio results in increasing both the annular stream equivalence ratio and the overall equivalence ratio at lean blow off limits. On the contrary, with the lean outer stream equivalence ratio the effect of increasing the momentum ratio is to lower the annular equivalence ratio and increases the overall equivalence ratio. The annular swirl angle has no effect on flame stability for low momentum ratio and very lean outer stream equivalence ratio. On the contrary, it has a great effect on the central equivalence ratio at blow off, where increasing the annular swirl angle results in increasing the central equivalence ratio and the overall equivalence ratio. Stage2 of the experimental program indicates that the higher momentum ratio, higher annular swirl angle, uniform mixture strength together with low outer swirl angle are considered the best conditions low NO emissions. The in-flame measurements stage show that at the immediate vicinity of the burner exit, the flame structure can be divided into three distinct regions, the reversed region, the reaction region, and the outer flame region. NO concentration was limited to the internal recirculation zone which also, has a higher temperature at its reaction zone envelop. Increasing the annular swirl angle together with small outer swirl angle increase the width of the recirculation zone and has a great effect in reducing the overall temperature of the flame as due to the higher mass recirculated toward the flame root. This in turn gives low NO concentration. References [1] J.M. Bee´r, N.A. Chigier, Combustion Aerodynamics, Krieger Pub Co., 1983. [2] A.K. Gupta, D.G. Lilley, N. Syred, Swirl Flows, Abacus Press, 1984. [3] A.H. Lefebvre, Gas Turbine Combustion, second ed., Taylor & Francis, 1999. [4] A.K. Gupta, M.S. Ramavajjala, J. Chomiak, N. Marchionna, , AIAA J. Propulsion 7 (2) (1991) 473-480. [5] J. Ballester, C. Dopazo, N. Fueyo, M. Herna´ndez, P. Vidal, Fuel 76 (5) (1997) 435-446. [6] T.-C.A. Hsieh, W.J.A. Dahm, J.F. Driscoll, Combust. Flame 114 (1998) 54-80. [7] J.M. Bee´r,M.A. Toqan, J.M. Haynes, R.W. Borio, J. Eng. Gas Turb. Power 126 (2004) 248-253. [8] S.C. Li, F.A. Williams, Combust. Flame 118 (1999) 399-414. [9] S. Naha, S.K. Aggarwal, Combust. Flame 139 (2004) 90-105. [10] Marshall. A.W, Gupta. A.K., Combustion Science and Technology, 176 (2004) 437-451. [11] Beér, J.M. and Chigier, N.A. (1972), Applied Science Publishers, London. [12] Lockwood, F.C. and Moneib, H.A., Combustion and Flame, 47, (1982) 291-314. AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah Outer mixture (Фout) Central nozzle Annular mixture (Фan) (a) Combustor Central mixture (Фcen) Annular swirler swirler Outer swirler 1 Burner head Central mixture from mixing chamber ( Фcen) Combustor Фan (b) LPG for outer mixture LPG for annular mixture Air for annular mixture Air for outer mixture Фout Controlling valve Air for annular Flow meter mixture Settling Chamber Flow meter Settling Chamber Air for outer mixture 1 Fig. 1. Experimental set up, (a) double swirl burner, (b) layout of the experimental setup, burner, combustor, and air supply lines (a) (b) Fig. 2. Flame appearance, (a) flame at an/out = 30o/30o, Φan = 1, Φout = 0.4, Φout = 0.73, and Mr =2.2, and (b) flame at an/out = 30o/30o, Φan = 1, Φout = 0.4, Φout = 0.73, and Mr =4.9. AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah out=30o out=45o out=60o (a) 0.80 flame 0.50 an,bo ov,bo 0.60 0.50 0.40 0.40 0.80 0.6 out 0.8 0.4 0.80 (c) 0.70 0.70 out=30o, OUT=0.4 0.60 OUT=0.8 0.60 0.50 0.50 0.40 0.40 0.6 out (d) 0.8 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 Mr Mr Mr=2.2 (c) 0.80 (d) 0.80 out=45o, OUT=0.4 OUT=0.6 0.70 0.60 0.50 0.50 0.40 0.40 0.4 0.80 0.6 out 0.8 0.4 0.70 0.50 0.40 0.40 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 Mr Mr 0.80 0.80 (e) 0.70 an,bo ov,bo 0.60 0.50 0.8 0.70 0.60 0.60 Mr=4.9 (f) 0.80 (e) 0.6 out 0.60 0.60 0.50 0.50 0.40 0.40 0.40 0.40 0.6 0.8 0.4 0.6 out 0.8 Fig. 3. Effect of outer stream equivalence ratio (Φout) on the annular and overall blow off limits (Φan,bo)& (Φov,bo) at different Mr of 0.8, 2.2, 4.9, Φcen=0, an=45o 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 Mr Mr 0.70 0.70 ov,bo an,bo Mr=0.8 0.80 0.50 0.40 0.40 0.6 0.8 an=30o an=45o an=60o 0.60 0.50 out OUT=0.8 Fig. 4. Effect momentum ratio Mr on the annular and overall blow off limits (Φan,bo)& (Φov,bo) at different Mr of 0.8, 2.2, 4.9, Φcen=0, an/an =45o/30o, 45o/45o, 45o/60o 0.80 0.4 OUT=0.4 OUT=0.6 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 cen=0,out=45o 0.60 out=60o, 0.60 0.50 out (f) 0.70 0.50 0.4 OUT=0.8 0.70 ov,bo 0.60 0.70 an,bo ov,bo an,bo 0.70 (b) flame extinction flame extinction 0.4 0.80 ov,bo an,bo 0.60 0.80 OUT=0.6 flame 0.70  cen=0, an=45o (a) 0.80 0.70 an,bo Mr=0.8 (b) ov,bo cen=0, an=45o 0.4 0.6 out 0.8 Fig. 5. Effect of outer swirl angle an on the annular and overall blow off limits (Φan,bo)& (Φov,bo) at out = 45o and Mr = 0.8 AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah an=0, an=45o 90 (a) 80 60 ov,bo cen,bo 70 50 40 30 20 10 0.4 (c) 0.6 out 60 ov,bo cen,bo 70 50 40 30 20 10 90 0.6 Mr=0.8 out=30o out=45o out=60o 0.4 80 out (b) 0.8 90 0.4 0.54 0.52 0.5 0.48 0.46 0.44 0.42 0.4 0.38 0.36 0.34 0.32 0.6 (d) 0.54 0.52 0.5 0.48 0.46 0.44 0.42 0.4 0.38 0.36 0.34 0.32 Mr=2.2 out=30o out=45o out=60o 0.8 0.4 0.6 0.8 out (f) 0.54 (e) 0.8 out 0.52 80 0.48 60 0.46 ov,bo cen,bo 0.5 70 50 Mr=4.9 0.44 out=30o 0.42 out=45o 40 0.4 0.38 out=60o 30 0.36 20 0.34 10 0.32 0.4 0.6 out 0.8 0.4 0.6 0.8 out Fig. 6. Effect of Φout on Φcen,bo and Φov,bo at different Mr , an = 45o Mr=0.8 an=30o (a) an=0, out=45o 90 80 60 ov,bo cen,bo 70 50 40 30 20 10 0.4 0.6 out 0.8 an=45o an=60o 0.54 0.52 0.5 0.48 0.46 0.44 0.42 0.4 0.38 0.36 0.34 0.32 0.4 0.6 out 0.8 Fig. 7. Effect of annular swirl angle on the central blow off limit and the overall blow off equivalence ratio at Mr = 0.8. AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah (a) an=45o,out=30o 35 an=60o,out=30o 25 20 15 700 10 650 600 550 750 20 Mr=4.9 an=30o,out=30o 15 an=60o,out=30o 700 Temperature (Co) an=30o,out=30o 40 (b) 25 NO ppm (at 15% O2) 45 30 (a) (b) 750 Mr=0.55 Temperature (Co) NO ppm (at 15% O2) 50 an=45o,out=30o 10 5 650 600 550 500 500 5 0.5 out 0.6 0.4 0.7 (c) 50 40 an=45o,out=45o 35 an=60o,out=45o 30 25 20 15 10 650 600 550 0.5 out 0.6 0.7 0.4 (c) 25 700 Temperature (Co) an=30o,out=45o out 450 0.4 0.7 0.6 (d) 750 Mr=0.55 45 0.5 NO ppm (at 15% O2) 0.4 20 an=45o,out=45o 15 0.5 an=60o,out=45o 10 out 0.6 0.7 0.6 0.7 0.6 0.7 (d) 750 Mr=4.9 an=30o,out=45o 700 Temperature (Co) 450 0 NO ppm (at 15% O2) 0 5 650 600 550 500 500 5 (e) 50 out 0.6 0.4 0.7 an=45o,out=60o an=60o,out=60o 30 25 20 15 25 700 Temperature (Co) 40 450 0.4 0.7 0.6 0.5 out 0.6 0.7 0.4 10 650 600 550 500 ann=30 ,out=60 20 o ann=60o,out=60o 10 5 out (f) 700 o ann=45o,out=60o 15 0.5 750 (e) Mr=4.9 an=30o,out=60o 35 out (f) 750 Mr=0.55 45 0.5 Temperature (Co) 0.5 NO ppm (at 15% O2) 0.4 NO ppm (at 15% O2) 0 450 0 650 600 550 500 5 0 450 0 0.4 0.5 out 0.6 0.4 0.7 0.5 out Fig. 8. Effect of the local equivalence ratio on the NO emission and men temperature at different an and Mr = 0.55 45 NO ppm ( at 15 %O2) 40 out=30o 30 25 20 15 10 0.6 0.7 0.4 0.5 out=45o 45 40 35 30 25 20 15 10 5 0 out (b) 50 out=0.4, an=1.3 out=0.5, an=1.1 out=0.6, an=0.9 out=0.7, an=0.7 35 0.5 5 30 45 an 60 0 30 45 an 60 (c) 50 out=60o 45 NO ppm ( at 15 %O2) 40 35 30 25 20 15 10 5 0 30 45 an out Fig. 9. Effect of the local equivalence ratio on the NO emission and men temperature at different an and Mr = 4.9 NO ppm ( at 15 %O2) (a) 50 450 0.4 0.7 0.6 60 Fig. 10. Effect of the annular swirl angle on the NO emission and men temperature at fixed out and Mr = 0.55 AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah out=0.4 600 1000 800 600 400 400 200 200 0.2 0.4 0.8 1 0.2 0.4 NO (ppm at 15% O2) (b) 15 10 5 0 0.2 0.4 0.6 0.8 0.8 800 600 400 200 0 0.2 0.4 15 10 5 0.6 0.8 1 0 r/R 25 20 0 0.2 0.4 0.6 0.8 1 0.2 (b) 20 15 10 5 0.4 0.6 0.8 1 r/R 25 0 r/R 5000 (g) 20 15 10 5 0 0 (c) 12500 4000 0.2 0.4 0.6 0.8 1 0 r/R 15000 (h) 12500 3000 7500 2500 1000 5000 0 0 2500 0 0.2 0.4 0.6 0.8 1 0 r/R 0.2 0.4 0.6 0.2 0.4 0.6 12000 0.8 1 4000 5000 0 0.2 0.4 0.6 0.8 0 1 r/R 20 0.2 0.4 0.6 0.8 1 20000 15000 12 16 8 12 4 4 0 0 0 0.2 0.4 0.6 r/R 0.8 1 0 0.2 0.4 8000 0 0.6 0.8 0.2 0.4 1 r/R 0.6 0.8 0.2 0.4 0.6 0.8 1 r/R 20 (j) (e) 16 8 4 12 8 4 0 0 0 0.2 0.4 0.6 0.8 r/R Fig. 11. Radial profiles of species concentrations and temperature, an/out = 45o/30o, and Mr = 0.55, Φout = 0.4 0 1 r/R O2 % 8 (i) 4000 20 (j) O2 % O2% 12 1 12000 0 16 0.8 5000 0 (e) 16 0.6 r/R 16000 25000 r/R 20 0.4 (d) 10000 0 0.2 20000 30000 8000 0 0 r/R HC ppm 10000 2000 0 0 40000 HC ppm HC ppm 15000 (h) 1000 35000 20000 1 1 (i) 16000 25000 0.8 3000 0 (d) 30000 0.8 r/R 20000 35000 0.6 r/R 4000 CO ppm 2000 5000 40000 0.4 10000 CO ppm CO ppm 7500 0.2 5000 (c) 10000 O2% 1000 200 1 (g) 1 r/R 15000 CO ppm 600 x/d=0.73 x/d=2.4 x/d=5.9 0 0 HC ppm 800 r/R 25 20 0.6 (f) 1200 400 0 r/R 25 NO (ppm at 15% O2) 0.6 1000 NO (ppm at 15% O2) 0 1200 1400 Temperature (Co) 800 1200 1600 x/d=0.13 x/d=0.23 x/d=0.33 1400 Temperature (Co) 1000 Temperature (Co) 1200 further downstream axial distances (a) 1600 x/d=0.73 x/d=2.4 x/d=5.9 1400 out=0.7 at early axial distances (f) 1600 x/d=0.13 x/d=0.23 x/d=0.33 1400 Temperature (Co) at further downstream axial distances (a) 1600 NO (ppm at 15% O2) at early axial distances close to the burner exit 1 0 0.2 0.4 0.6 0.8 1 r/R Fig. 12. Radial profiles of species concentrations and temperature, an/out = 45o/30o, and Mr = 0.55, Φout = 0.7 AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah 800 600 400 400 200 200 0.2 0.4 0.8 1 0 0.2 (b) 12 8 4 0.4 0.6 0.8 1 0.2 0.4 0.6 0.8 4 0 r/R 15000 0.2 0.4 0.6 0.8 1 0 0.2 0.4 (b) 8 4 0.6 (h) 0.8 1 r/R (g) 12 8 4 0 0.2 0.4 0.6 0.8 1 0 r/R 0.2 0.4 0.6 12500 0.8 1 r/R 5000 (c) (h) 4000 10000 3000 CO ppm CO ppm 0.8 16 12 0 10000 2000 5000 7500 3000 2000 5000 1000 2500 1000 2500 0 0 0 0.2 0.4 0.6 0.8 1 0 r/R 40000 0.2 0.4 0.6 0 0 0.2 0.4 (i) 0.6 0.8 1 0 r/R 40000 16000 30000 0 1 r/R 20000 (d) 35000 0.8 10000 8000 25000 HC ppm 15000 12000 HC ppm HC ppm 20000 20000 15000 10000 4000 5000 0.4 0.6 0.8 1 r/R (i) 16000 30000 25000 0.2 20000 (d) 35000 12000 8000 4000 5000 0 0 0.2 0.4 0.6 0.8 0 1 r/R 20 0.2 0.4 (e) O2% 8 0 1 0 (j) 8 4 0 0.2 0.4 0.6 0.8 1 0.6 (d)0.8 0 r/R 0.2 r/R 0.4 0.6 0.8 1 0.2 0.4 (e) 0.6 8 1 (j) 16 12 0.8 r/R 20 12 8 4 0 0 0 1 4 0 0 0.4 16 12 4 0.2 20 16 12 0.8 r/R 20 16 0.6 O2% 0 O2% CO ppm 0.6 r/R 15000 4000 7500 0.4 0 1 r/R 5000 (c) 12500 600 200 0.2 16 8 1 800 400 0 12 x/d=0.73 x/d=2.4 x/d=5.9 1000 200 0 0 HC ppm 600 (g) 0 O2% 800 r/R (f) 1200 400 16 NO (ppm at 15% O2) NO (ppm at 15% O2) 0.6 r/R 1000 NO (ppm at 15% O2) 0 1200 1400 Temperature (Co) 600 further downstream axial distances 1600 x/d=0.13 x/d=0.23 x/d=0.33 1400 NO (ppm at 15% O2) 800 1000 (a) 1600 Temperature (Co) 1000 1200 an=45o at early axial distances x/d=0.73 x/d=2.4 x/d=5.9 1400 Temperature (Co) 1200 16 (f) 1600 x/d=0.13 x/d=0.23 x/d=0.33 1400 Temperature (Co) further downstream axial distances (a) CO ppm an=30o at early axial distances 1600 0 0 0.2 r/R 0.4 0.6 0.8 1 r/R 0 0.2 0.4 0.6 0.8 1 r/R Fig. 13. Radial profiles of species concentrations and Fig. 14. Radial profiles of species concentrations and temperature, out =30o, an =45o and Mr = 4.9, Φout = 0.4 temperature, out =30o, an =30o and Mr = 4.9, Φout = 0.4 an=60o (a) x/d=0.13 x/d=0.23 x/d=0.33 Temperature (Co) 1400 1200 1000 800 600 further downstream axial distances x/d=0.73 x/d=2.4 x/d=5.9 1400 1200 1000 800 600 400 400 200 200 0 0.2 0.4 0.6 0.8 1 0 r/R 0.2 0.4 (b) 12 8 4 0 0.6 0.8 1 r/R 16 NO (ppm at 15% O2) 16 NO (ppm at 15% O2) (f) 1600 Temperature (Co) at early axial distances 1600 (g) 12 8 4 0 0 0.2 0.4 0.6 0.8 1 0 r/R 15000 0.2 0.4 0.6 12500 0.8 1 r/R 5000 (c) (h) 4000 CO ppm CO ppm 10000 7500 3000 2000 5000 1000 2500 0 0 0 0.2 0.4 0.6 0.8 1 0 r/R 40000 35000 0.4 0.6 HC ppm 25000 20000 15000 10000 0.8 1 r/R (i) 16000 30000 HC ppm 0.2 20000 (d) 12000 8000 4000 5000 0 0 0 0.2 0.4 0.6 0.8 r/R 20 0.2 0.4 (e) 8 4 0.8 16 O2% 12 0.6 1 r/R 20 16 O2% 0 1 (j) 12 8 4 0 0 0 0.2 0.4 0.6 r/R 0.8 1 0 0.2 0.4 0.6 0.8 1 r/R Fig. 15. Radial profiles of species concentrations and temperature, out =60o, an =60o and Mr = 4.9, Φout = 0.4 AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah 1000 800 600 400 400 200 200 0 0.2 0.4 0.8 0 (b) 8 4 0 0 0.2 0.4 0.2 0.4 0.6 0.8 0.6 0.8 1 12 8 4 0 0.2 0.4 0.6 0.8 0.6 0.8 1 0 r/R (b) 8 4 0.4 0.6 1 (g) 12 8 4 0.2 0.4 0.6 0.8 1 0 r/R 0.2 0.4 0.6 12500 0.8 1 r/R 5000 (c) (h) 0.8 r/R 0 0 15000 4000 0.2 16 12 1 r/R (h) 4000 CO ppm 3000 2000 7500 2500 1000 2500 0 0 0 0 0.2 0.4 0.6 0.8 1 0 r/R 40000 0.2 0.4 0.6 15000 0.6 0.8 1 0 r/R 8000 0.4 0.6 20000 15000 1 (i) 16000 25000 0.8 r/R (d) 10000 4000 0.2 20000 30000 12000 10000 0 0.4 35000 HC ppm HC ppm 20000 1 (i) 16000 25000 0.8 0.2 40000 (d) 30000 2000 1000 0 r/R 20000 35000 3000 5000 5000 HC ppm CO ppm 7500 CO ppm 10000 10000 12000 8000 4000 5000 5000 0.2 0.4 0.6 0.8 0 1 r/R 20 0.2 0.4 0.8 0 1 r/R 20 O 2% 12 8 r/R 16 12 12 8 8 0 1 0 0.2 0.4 r/R 0.6 0.8 1 0.4 0.6 0.8 1 1200 1000 800 600 x/d=0.73 x/d=2.4 x/d=5.9 1400 1200 1000 800 600 400 400 200 200 0 0.2 0.4 0.6 0.8 1 0 r/R 0.2 0.4 (b) 12 8 4 0 0.6 0.8 1 r/R 16 NO (ppm at 15% O2) 16 NO (ppm at 15% O2) (f) 1600 Temperature (Co) Temperature (Co) further downstream axial distances x/d=0.13 x/d=0.23 x/d=0.33 1400 (g) 12 8 4 0 0 0.2 0.4 0.6 0.8 1 0 r/R 0.2 0.4 0.6 0.8 1 r/R 5000 (c) 15000 (h) 4000 CO ppm CO ppm 12500 10000 7500 3000 2000 5000 1000 2500 0 0 0 0.2 0.4 0.6 0.8 1 0 r/R 40000 0.4 0.6 HC ppm 25000 20000 15000 10000 1 (i) 16000 30000 0.8 r/R (d) 35000 HC ppm 0.2 20000 12000 8000 4000 5000 0 0 0 0.2 0.4 r/R 20 0.8 0 1 0.2 0.4 16 16 12 12 8 4 0.6 r/R 20 (e) O2% O2% 0.6 0.8 1 (j) 8 4 0 0 0 0.2 0.4 0.6 r/R 0.8 1 0 0.2 0.4 0.6 0.8 1 0.8 (j) 8 0 0.2 0.4 0.6 0.8 1 r/R Fig. 17. Radial profiles of species concentrations and temperature, an =60o, out =45o and Mr = 0.55, Φout = 0.4 out=60o 1600 0.6 r/R 0 0.2 r/R Fig. 16. Radial profiles of species concentrations and temperature, an =60o, out =30o and Mr = 0.55, Φout = 0.4 (a) 0.4 4 0 r/R at early axial distances 0.2 20 16 0 0.8 0 1 12 0 0.6 0.8 16 4 0.4 0.6 (e) 4 0.2 0.4 20 4 0 0.2 (j) (e) 16 0.6 O2% 0 0 0 0 0 O 2% 0.4 0 5000 12500 600 200 0.2 16 (g) 1 r/R 800 400 0 r/R (c) CO ppm 600 0 15000 HC ppm 800 x/d=0.73 x/d=2.4 x/d=5.9 1000 200 16 12 1000 400 1 (f) 1200 O2% NO (ppm at 15% O2) 0.6 r/R 16 1200 1400 Temperature (Co) 600 Temperature (Co) 800 1200 further downstream axial distances 1600 x/d=0.13 x/d=0.23 x/d=0.33 1400 NO (ppm at 15% O2) 1000 Temperature (Co) 1200 x/d=0.73 x/d=2.4 x/d=5.9 1400 NO (ppm at 15% O2) Temperature (Co) 1400 out=45o (a) 1600 (f) 1600 x/d=0.13 x/d=0.23 x/d=0.33 at early axial distances further downstream axial distances (a) NO (ppm at 15% O2) out=30o at early axial distances 1600 1 r/R Fig. 18. Radial profiles of species concentrations and temperature, an =60o, out =60o and Mr = 4.9, Φout = 0.4 AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah Mr=0.55 1600 1200 x/d=0.13 x/d=0.23 1.6 I ( Temperature (Co) (a) out=0.4 2 (a) 800 1.2 0.8 400 0.4 0 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 r/R r/R within the flame sheet 5 I( 4 Mr=0.55, out=0.4 an=45o, out=30o 3 2 x/d=0.13 1 0 0 at the immediate inner boundaies of the flame front 0.2 0.4 0.6 0.8 1 1.2 1.4 Time in (sec) 4 2 1.6 2 I ( I( 3 1 (b) 1.2 0.8 0 0 0.2 0.4 0.6 0.8 1 1.2 0.4 1.4 Time in (sec) 0 0 0.2 0.4 0.6 0.8 1 r/R at the immediate outerboundaies of the flame front 2.5 2 2 1.5 1.5 I( I( within the recirculation zone 2.5 1 1 0.5 0.5 0 0 0 0.2 0.4 0.6 0.8 Time in (sec) 1 1.2 1.4 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Time in (sec) Fig. 19. (a) Radial distribution of the ion current at different axial locations at Mr = 0.5 and Φout = 0.4, (b) row ion current signal at different radial location in the flame zone. AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah panel (a): within therecirculation zone 10 10 out=0.4 10 out=0.5 8 6 6 6 Pdf 4 4 4 2 2 2 0 0 0 -4 -2 panel 0 2 4 6 -4 -2 0 2 4 6 -4 10 out=0.4 8 4 2 2 2 0 4 6 4 6 4 6 4 6 4 6 out=0.7 Pdf Pdf Pdf 4 2 4 6 4 0 2 8 6 0 0 (I-Imean)/ 10 out=0.5 8 6 -2 -2 (I-Imean)/ (I-Imean)/ (b): at the immediate inner boundaries of the flame front 10 -4 out=0.7 Pdf 8 Pdf 8 6 0 -4 -2 (I-Imean)/ 0 2 4 6 -4 -2 (I-Imean)/ 0 2 (I-Imean)/ panel (c): within the flame front 10 10 out=0.4 8 10 out=0.7 out=0.5 8 8 Pdf Pdf 6 Pdf 6 6 4 4 4 2 2 2 0 0 -4 -2 0 2 4 6 0 -4 -2 0 2 4 6 -4 (I-Imean)/ (I-Imean)/ panel (d): at the immediate outer boundaries of the flame front 10 10 out=0.4 8 out=0.5 8 10 4 2 2 2 0 -2 0 2 4 6 0 -4 -2 (I-Imean)/ 0 2 4 6 -4 30 Pdf 20 Pdf Pdf 20 10 10 0 10 0 -2 0 2 (I-Imean)/ 4 6 2 out=0.7 out=0.5 20 0 (I-Imean)/ 30 out=0.4 -4 -2 (I-Imean)/ panel (e): at the outer boundaries of the flame front 30 out=0.7 Pdf Pdf 4 -4 2 6 4 0 0 (I-Imean)/ 8 6 Pdf 6 -2 0 -4 -2 0 2 4 (I-Imean)/ 6 -4 -2 0 2 (I-Imean)/ Fig.(4.43) Selected distribution of the probability density function,at different Fig. 20. Selected distribution of the probability density function, at different radial locations with diffrent outer equivelane ratio, fixed ov=0.73, x/d=0.13, axial locations with different equivalence ratio, an/out = 45o/30o, Mr = 0.55 Mr=0.55, an=45o,out=30o AFCR 2015 Industrial Combustion Symposium, September 9-11, University of Utah, Utah