Impact of Equivalence Ratio on the Macrostructure of Premixed Swirling CH4/Air and CH4/O2/CO2 Flames

Premixed CH[subscript 4]/O[subscript 2]/CO[subscript 2] flames (oxy-flames) and CH[subscript 4]/air flames (air-flames) were experimentally studied in a swirl-stabilized combustor. For comparing oxy and air flames, the same equivalence ratio and adiabatic flame temperature were used. CO[subscript 2] dilution was adjusted to attain the same adiabatic temperature for the oxy-flame and the corresponding air-flame while keeping the equivalence ratio and Reynolds number (=20,000) the same. For high equivalence ratios, we observed flames stabilized along the inner and outer shear layers of the swirling flow and sudden expansion, respectively, in both flames. However, one notable difference between the two flames appears as the equivalence ratio reaches 0.60. At this point, the outer shear layer flame disappears in the air-flame while it persists in the oxy-flame, despite the lower burning velocity of the oxy-flame. Prior PIV measurements (Ref. 9) showed that the strains along the outer shear layer are higher than along the inner shear layer. Therefore, the extinction strain rates in both flames were calculated using a counter-flow premixed twin flame configuration. Calculations at the equivalence ratio of 0.60 show that the extinction strain rate is higher in the oxy than in the air flame, which help explain why it persists on the outer shear layer with higher strain rate. It is likely that extinction strain rates contribute to the oxy-flame stabilization when air flame extinguish in the outer shear layer. However, the trend reverses at higher equivalence ratio, and the cross point of the extinction strain rate appears at equivalence ratio of 0.64.King Abdullah University of Science and Technology (Grant KUS- 110-010-01

Using internet search data as economic indicators

Data on the volume of online searches can be used as indicators of economic activity. This article examines the use of these data for labour and housing markets in the United Kingdom. These data provide some additional information relative to existing surveys. And with further development, internet search data could become an important tool for economic analysis.

Impact of fuel composition on the recirculation zone structure and its role in lean premixed flame anchoring

We investigate the dependence of the recirculation zone (RZ) size and structure on the fuel composition using high-speed particle image velocimetry (PIV) and chemiluminescence measurements for C[subscript 3]H[subscript 8]/H[subscript 2]/air lean premixed flames stabilized in a backward-facing step combustor. Results show an intricate coupling between the flame anchoring and the RZ structure and length. For a fixed fuel composition, at relatively low equivalence ratios, the time-averaged RZ is comprised of two counter rotating eddies: a primary eddy (PE) between the shear layer and the bottom wall; and a secondary eddy (SE) between the vertical step wall and the PE. The flame stabilizes downstream of the saddle point of the dividing streamline between the two eddies. As equivalence ratio is raised, the flame moves upstream, pushing the saddle point with it and reducing the size of the SE. Higher temperature of the products reduces the velocity gradient in the shear layer and thus the reattachment length. As equivalence ratio approaches a critical value, the saddle point reaches the step and the SE collapses while the flame starts to exhibit periodic flapping motions, suggesting a correlation between the RZ structure and flame anchoring. The overall trend in the flow field is the same as we add hydrogen to the fuel at a fixed equivalence ratio, demonstrating the impact of fuel composition on the flow field. We show that the reattachment lengths (L[subscript R]), which are shown to encapsulate the mean RZ structure, measured over a range of fuel composition and equivalence ratio collapse if plotted against the strained consumption speed (S[subscript c]). Results indicate that for the flame to remain anchored, the RZ structure should satisfy [L[subscript R,isothermal] over L[subscript R,reacting]] · [S[subscript c] over U[subscript ∞]] ~ 0.1. If this criterion cannot be met, the flame blows off, flashes back or becomes thermoacoustically unstable, suggesting a Damkohler-like criterion for aerodynamic flame stabilization in backward-facing step flows.King Abdullah University of Science and Technology (Grant KUS-110-010-01

Validation study of large-eddy simulations of wake stabilized reacting flows using artificial flame thickening approaches

Wake flows are the preferred mode of flame stabilization in lean premixed combustion in gas turbine engines, low NOx burners, afterburners etc. These flows exhibit inherent unsteadiness and for their numerical modeling and simulations, large eddy simulation (LES) techniques with an appropriate combustion model and reaction mechanism afford a balance between computational complexity and predictive accuracy. Before using them in practical systems, these techniques must be validated against experimental measurements in a number of canonical cases. In this work, results from LES of non-reacting and reacting flows are compared to data from a number of experiments, corresponding to the following configurations: a triangular bluff body in a rectangular duct, a backward facing step, and a cylindrical sudden expansion with swirl. The artificial flame thickening approach is applied for modeling turbulence-combustion interactions at small scales. Algebraic and equationbased efficiency function models are implemented, along with an appropriate reduced chemistry mechanism. A novel dynamic formulation for the efficiency function based on the flame-wrinkling equation that explicitly incorporates the influence of strain and time-history effects is proposed, and a detailed combustion chemistry mechanism is also used. Results show that the approaches are effective in simulating turbulent premixed combustion

The embryonic and early larval development of Gonodactylus falcatus (Forsskal) (Crustacea : Stomatopoda) from India

The embryology and early larval development of Gonodactylus falcatus (Forsskal) were studied, based on eggs reared and hatched in the laboratory. The larval development was followed up to the fourth larval stage when all the larvae died. Observations on the behaviour of larvae, their feeding habits and moulting periodicity were also made. Differences in the larval characters between the present series and the ones described earlier have been discussed

Descriptions of Stomatopod larvae from the Arabian Sea with a list of Stomatopod larvae and adults from the Indian Ocean and a key for their identification Part 2

Studies on stomatopods from seas around India have brought to light the need for an assessment of stomatopod fauna known from the Indian Ocean. No recent work fulfils this need and so an attempt has been made in the present paper to list all the known species of adults which are at present 115 from the Indian Ocean proper and to provide identification keys for them

Stomatopods as a potential resource

The stomatopods are consumed by people as food in some countries like the Philippines and Japan in the Indo-Pacific region. In the south west coast of India stomatopods are landed in fairly large quantities by the shrimp trawlers. The catch mainly constitutes a single species, namely,[Oratosquilla nepa. It forms nearly 10 to 20 % of the catch in a shrimp trawler. At present they are used only as manure. The present price value of stomatopods caught by a single shrimp trawler in a day varies from Rs. 5 to Rs. 50 depending on the catch. The flesh content in stomatopods is little but it could be consumed as food or could very well be converted into fish meal. There is considerable scope for the development of this potential resource

Three new records of Stomatopoda (Crustacea) from the seas around India

Our knowledge of stomatopods from the seas around India is fairly extensive. The monograph of Kemp (1913) is a landmark in the history of the group from the region. Subsequent contributions by Kemp and Chopra (1921), Chopra (1934), Chopra (1939) and Alikunhi (1967) have enriched our knowledge of the group. While making collections for a detailed study of the group, the following three species which are new records to the seas around India Lysiosquilla tredecimdentata Holthuis (Family Lysiosquillidae) and Alima hyalina Leach, and CarinosquUla lirata (Kemp and Chopra) (Family Squillidae)were collected. The diagnostic characters of each species and detailed measurements of some specimens are given. Attention is also drawn to differences observed from earlier descriptions. Data on the total length (TL) measured from the tip of the rostrum to the tip of the submedian spines of the telson; the carapace length (CL) exclusive of rostrum ; the abdominal width measured at the 5th somite and the corneal index (CI) obtained by dividing the carapace length by the corneal width and multiplying it by 100 are given

A new species of Heterosquilla (Crustacea : Stomatopoda) from Indian seas

For a detailed study of stomatopods from Indian Seas, collections were made from various localities along the coasts. This interesting Heterosquilla was identified amongst the crustacean specimens from the Minicoy Island (Laccadives) from the collections of Dr. S. Jones. Although two species namely H. insignis and H. spinosa of this genus have been recorded from Indian waters so far, the present material exhibited striking differences from these and had more similarities with H, mccullochae (Schmitt, 1940) which is known from Gulf of California