OCR Text |
Show ignition, as long as the firing rate remained within 120% of the nominal value. The high velocities and temperatures of the flame jets near the calorimeter surface provide intense convective heat transfer to the calorimeter. The high flame jet velocities prevent flashback and ensure intense internal combustion product recirculation and mixing, uniform furnace and load temperature, and complete fuel burnout within the furnace. Tests were carried out to investigate the perfonnance of the high velocity multi-flame DFI approach over the following operating ranges: • Equivalence ratio of the gas-air mixture -- 1.0 to 1.04 2 • Specific gas flow rate per unit calorimeter surface area -- 0.013 to 0.042 kg/m sec (0.0026 to 0.0086 lb/fesec) • Heat input per unit calorimeter surface area -- 0.64 to 2.07 MW/m2 (203,000 to 656,000 Btulft2·h) • Velocity range at nozzles exit -- 60 to 200 m/s (200 to 660 fils) for ambient air and 130 to 340 mls (430 to 1100 fils) for preheated air (up to 700 K; or 800 F). • Furnace temperature -- 1500 to 1900 K (2240 to 2960 F). During the tests, the calorimeter's surface temperature remained in the range 420 to 460 K (300 to 370 F). The dynamic pressure along the flame's axis was measured using specially designed thin quartz probes with a diameter of 0.5 mm (0.02 in.). The probes were calibrated to provide accurate data for high velocity jet flows. The local velocities were determined from the measured dynamic pressure profiles. The local flame temperatures within the high velocity flame jets were measured using thermocouple probes made from 0.1 mm (0.004 in.) diameter platinum wire, which was covered with a 0.01 mm (0.0004 in.) thick silicon film to prevent surface temperature rise due to catalytic combustion. The local gas temperatures in low velocity regions in the furnace were measured using a suction pyrometer. Gas species (CO, CO2, CH4, H2, and O2 ) concentrations (mU were measured with a chromatograph. All measured species were normalized using the calorific value of methane Qrn to estimate the weighted average fuel concentration: mg=sum (mjxQi ) IQm , where Qj is the species calorific value and mj is its mass fraction. The overall heat flux to the calorimeter was calculated from the heat absorbed by the cooling water. Temperatures of the furnace walls as well as the exhaust gases were recorded. The experimental values of convective heat transfer coefficients were calculated using the following expression: a = (qt - CIt)/(T g - T w) where qt is total heat flux, CIt is radiant heat flux, and T g and T w are the gas phase and the calorimeter surface temperatures, respectively. 5 |