An experim ental and num erical investigation of the flow generated by anewly designed low NOₓ producing burner is presented. The burner is comprised of 14 jets (7 fuel and 7 air), arranged in acircle around acentral pilot flame, which fire directly (no quarl) into the refractory lined research furnace atthe Centre for Advanced Gas Com bustion Technology. T he heat release of the burner is on the order of 350 kW. The angles and diam eters for the air and gas nozzles are 10° and 15°, and 19.5 mm (0.75”) and 6.4 mm (0.25”) respectively. This gives an inlet natu ral gas mass flux is 6.75 g/s (43 m/s), and the air mass flux is 128 g/s (100 m/s), for the operating stoichio etry of 15% excess air and an air to fuel axial momentum flux ratio of 47.

The furnace laboratory is aright-parallelepiped (dimensions:​ 3 x 4.5 x 1 m) with the CGRI burner firing 785 mmalong, and half way up, one of the 4.5 mvertical walls. Testing is done for two furnace tem peratures, with mean refractory tem peratures of 800°C and 900°C and exhaust gas tem peratures are 975°C and 1075°C respectively.

The objectives of the research are to gain an in depth understanding of the structure of the flow generated by this burner and to determ ine the source of the NOx it produces.

The study is unique in three major ways. First, the burner studied is of anovel design for which apatent is soon expected to be obtained. The multijet design and large open com bustion zone for this burner are responsible for the very small am ount of pollutants it produces during operation. Second, the research laboratory allows realistic sim ulation of industrial operation of the burner in awell instrumented facility. The research shows the im portance of furnace cross flow, which is not present in typical labs with atunnel furnace design, but is present in most industrial furnaces. Third, the near field probing mechanism allows for very detailed measurem ents close to the burner outlet since the system allows free probe movement in any direction.

Probing of the near field is facilitated using atraversing system which allows movement of probes in three directions throughout the near field of the burner. Measurem ents are taken using gas sam pling, therm ocouples of high response time (𝜏 ~ 20 — 60 ms), and atwo com ponent laser Doppler velocimeter. These experim ents give detailed descriptions of mole concentrations of O₂, CO₂, CO, CH₄, NOₓ and unburnt hydrocarbons:​ two components (axial x. and vertical z) of velocity (mean, and Reynolds stresses):​ and the mean and RMS tem peratures (com pensation is applied for transient and radiative effects);​ in a 1.5 m³ volume near the burner face. The experim ents are supplem ented by wall refractory tem peratures and floor heat fluxes in the furnace.

Numerical modelling of this flow is perform ed using the commercial software package TASCflow. This is done on aC artesian grid of 1.5 x 10⁵ nodes for which grid em bedding is used to make efficient use of available com puter memory. Turbulence modelling is handled using the k — ϵ model and com bustion is modelled with asimple 2 step eddy diffusivity com bustion model. Thermal radiation is modelled assum ing optically dense gas. The coupled multi-grid solver is generally able to bring residuals down four orders of magnitude, to amean norm alized level of ~ 10⁵.

The velocity field in the furnace is dominated by the high momentum inlet air jets and two large circulation zones they generate. The furnace gases which are entrained into the air jets pull the fuel jets into the centre of th ering of air jets. Com bustion very close to the jet inlets is lim ited by the delayed mixing due to the air and fuel delivery. This means that com bustion takes place over arelatively large volume.

The Reynolds norm al stresses indicate isotropic turbulence in the flow outside the inlet jets, and anisotropy favouring the axial (x) direction in the inlet je ts and in the combined flow region dow nstream ;​ the degree of the anisotropy (the ratio of the Reynolds normal stresses) is som ew hat higher than reported in the literature for cold free jets. The Reynolds shear stresses clearly describe the vertical turbulent transport of axial momentum in the flow.

Further dow nstream (x > 0.45 m), the air jet ring is broken up by the cross flow from the larger recirculation flow, transform ing into acrescent shape, and then to asingle oval jet. At 1.25 mdow nstream from the burner, the majority of the reactants are fully mixed, but the high dilution with furnace gas slows th ecombustion of th erem aining reactants. Mass and mom entum flux calculations at 1.25 mfrom the burner indicate less than half the fuel is consum ed. The rem aining fuel burns outside the range of the near field measurements;​ the highest refractory tem peratures are observed where the com bined jet flow impinges with the opposing wall.

For the furnace tem peratures studied in the current work, NOₓ emissions are very low (3-8 ppm NOx in dry samples of the stack gases). This is largely due to the low furnace tem peratures tested for. The flux measurements also indicate that most of the NOₓ is produced outside the near field and that some of the NOₓ from the furnace gases is reduced when they are entrained into the combined jet flow.