Abstract：[Objective] To solve the problem of excessive NOx emissions of the existing natural gas radially staged combustor, the design principle of parameter matching between multiple nozzles at the head of the combustion chamber is explored, and an optimized prediction formula for NOx emission performance of the combustor is obtained. [Methods] This study adopts numerical simulation and experimental data analysis methods. The different loads and diameters of the dilution holes of the combustor are numerically simulated. Through the numerical analysis of the nonuniformity of the premix and the equivalent ratio of the original design, a structural improvement strategy and an optimization scheme to reduce the dilution holes' diameter were proposed. The influence of the improvement in the dilution holes' diameter on NOx emissions and that of the modification scheme on the total pressure loss and other performance parameters were investigated. The relationship between parameter matching of multiple nozzles and NOx emission under different combustion modes was investigated. Because of the deficiency of the current NOx emission prediction formula, based on the experimental and numerical data, the prediction formula of NOx emission under partial load is improved. [Results] Results showed that the original low-emission design of the combustor was unreasonable, and the NOx emission value was six times that of the limit value of 41 mg/Nm3 at 15% O2. The standard scheme of changing the dilution holes' diameter was reasonable and feasible, and the dilution holes' diameter Djet=44.45 mm can ensure that the standard of NOx was determined and verified by the experiment. The resulting changed in the total pressure loss and other performance parameters were within the acceptable range. In the proposed dilution holes' diameter modification scheme, the change in the dilution holes' area from large to small was 33.1%, 47.1%, and 59.5%, which exceeded 30% of the original design, and the head structure was not redesigned. A warning that the combustor may face the risk of wall overtemperature during long-term operation was proposed. The equivalence ratio and nonuniformity of the premix, two key parameters used to characterize lean premix, were sufficient and necessary conditions to effectively control the NOx emission. The central nozzle was the main factor in determining the emission level. Because the central area was in the high equivalent ratio area, the fuel amount of a single nozzle was high, premix uniformity was poor, and diffusion combustion of heavy-duty fuel occurred. Notably, the low-emission design criterion of the multi-nozzle matching relationship in the natural gas radially staged combustor investigated in this study was that the fuel amount of the single annular nozzle was equal to the fuel amount of the central area in combustion mode 2. [Conclusions] Based on the experimental and numerical data in this study, an improved NOx emission prediction formula that can accurately reflect the partial load behavior of this type of combustor is proposed. Compared with the test data of the two combustors, the prediction formula has sufficient accuracy, and the maximum relative error is 8.73%. This research provides a theoretical basis for the subsequent test debugging and design improvement of the combustor.
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