OCR Text |
Show processes and, hence, comparable. Furthermore, the jet-flame geometry offers the advantage over the counterflow that NO emission indices are easily measured, since all of the fuel burns in the jet, unlike the opposed-flow flame where much of the fuel escapes. Apparatus and Procedures The laminar jet-flame burner used in the experiments is illustrated in Fig. 8. A laminar fuel jet issues from a 10.9-mm Ld. tube into a uniform low-velocity coannular air flow to produce stable conical flames. A I05-mm Ld., 230-mm long duct surrounds the flame to prevent any room drafts from influencing the flame. The products of combustion are mixed by a series of baffle plates at the top of the glass duct before being sampled at the outlet of a contracting section. Calibrated rotameters were used to measure the mass flowrates of the air, fuel, and diluent (N2) at room temperature before the gases were heated. The Cf4 fuel (technical grade, 98% purity) and its diluent was heated, when desired, by heating tapes, while the air stream and any diluent was heated by a 950 W process heater. Exhaust gas samples were withdrawn through a stainless-steel, water-cooled sample probe for analysis. NO and NOx concentration measurements were made with a chemiluminescent analyzer (TECO Model IO-A) equipped with a stainless-steel N02-to-NO converter. Carbon dioxide concentrations were measured using either a long- or a short-path nondispersive infrared analyzer (Horiba PIR-2000). A gas-filter correlation analyzer (TECO Model 48) was used to measure CO emissions. Temperature distributions within the flame were measured using a fine-wire Pt - PtIRh 10% thermocouple. The thermocouple bead, coated with alumina to eliminate catalytic reactions, had a diameter of approximately 240 Jlm. Temperature measurements were corrected for radiative heat losses. A three-dimensional traversing system was used to provide accurate positioning of the thermocouple in the flame. Radial temperature profiles were acquired by translating the burner with the probe rigidly mounted. A more detailed description of the apparatus and procedures is found in Ref. [12]. Two basic flame conditions were studied: one with unheated reactants, and one with the reactants heated to nominally 400 K. Tests were conducted, starting at the baseline condition 10 |