In order to reduce NO_x emissions, modern gas turbines are often equipped with lean-burn combustion systems, where the high-velocity fuel-lean conditions that limit NO_x formation in combustors also inhibit the ability of ignition, high altitude relight, and lean combustion stability. To face these issues, internally staged scheme of fuel injection is proposed. Primary and main fuel staging enable fuel distribution control, and multi-injections of main fuel lead to a fast and efficient mixing. A fuel-staged low emission combustor in the framework of lean-burn combustion is developed in the present study, i.e., the central pilot stage for low power conditions is swirl-cup prefilming atomization, the main stage is jet-in-crossflow multi-injection, and a combination of primary and main stage injection is provided for higher power output conditions. In lean-burn combustors, the swirling main air naturally tends to entrain the pilot flame and quench it at low power conditions, which is adverse to the operability specifications, such as ignition, lean blow-out (LBO), and high-altitude relight. In order to investigate the effects of the main swirl angle on combustion performances, the ignition and LBO performances were evaluated in a single dome rectangular combustor. Furthermore, the spray patterns and flow field are characterized by kerosene-planar laser induced fluorescence and particle image velocimetry (PIV) to provide insight into spray and combustion performances. Flow–flow interactions between pilot and main air streams, spray–flow interactions between pilot spray and main air streams, and flame–flow interactions between pilot flame and main air streams are comprehensively analyzed. The entrainment of recirculating main air streams on pilot air streams enhances with the increase of main swirl angle, because of the upward motion and increasing width of main recirculation zone. A small part of droplets are entrained by the recirculating main air streams at periphery of combustor and a majority of droplets concentrate near the centerline of combustor, making that entrainment of recirculating main air streams on pilot spray and quenching effects of recirculating main air streams on pilot flame are slight, and the extinguishing effects can be ignored. The contributions of main swirl strength to improvement of ignition and LBO performances are due to enhancement of air/fuel mixing by strengthening turbulence level in pilot zone.

Lean staged combustion can reduce the NOx emissions by prevaporizing and premixing fuel with air, which is considered the state-of-the-art solution strategy in achieving low emission in aeronautical combustors. However, lean premixed combustion is subjected to combustion stability problems, which restrict the ground and altitude operation limits of the commercial engine. In this work, the effect of the swirl intensity of pilot inner swirler on combustion stability of a lean staged injector is experimentally and numerically studied. The lean staged injector is piloted by a dual swirler prefilm atomizer. The swirl intensity of the pilot inner swirler is varied by parameterizing the vane angle as +20 deg, −20 deg, and −35 deg, with −20 deg selected as the baseline with a counterswirling design. A single sector model combustor is designed, and the nonreacting flow field and fuel concentration distributions are measured by particle image velocimetry (PIV) and kerosene planar laser induced fluorescence (kerosene-PLIF) techniques. The alteration of swirl direction from counterswirling to coswirling induces a negligible effect on flow structures, but the spray distribution changes from a solid pattern to a hollow pattern. The increase in the pilot inner swirl intensity causes a shrunk cyclone recirculation zone (CRZ) and a reduction of kerosene concentration in the central region. The influences of the pilot inner swirler angle on combustion stability are evaluated. The ignition and lean blow-out (LBO) results show that the baseline injector exhibits excellent combustion stability, while the coswirling design holds the highest ignition and LBO fuel–air ratio (FAR). In order to find out the physical mechanisms dominating the ignition and LBO processes, nonreacting numerical simulations are conducted to provide information regarding the flow structures and kerosene concentrations at ignition limits. Moreover, the ignition sequences are redefined as the radial flame propagation phase, the axial flame propagation phase, and the flame stabilization phase. The comparison of kerosene concentration along the radial and axial propagation routes concludes that the fuel enrichment in the two processes improves the ignition performance. On the other hand, the Karlovitz number of flame anchoring points in the flame rooting region is calculated to evaluate the flame stabilization characteristics. The results indicate that promoting the number of flame anchoring points and their radial range benefits the LBO performance.

High-altitude relight is a critical challenge for aero-engines, directly impacting the safety and emergency response capabilities of aircraft. This paper systematically reviews the physical mechanisms, key factors, and relevant prediction models of high-altitude relight, highlighting the detrimental effects of extreme conditions such as low pressure and temperature on fuel evaporation rates, flame propagation speeds, and turbulent combustion processes. A comprehensive overview of the current state of high-altitude relight research is presented, alongside recommendations for enhancing the ignition performance of aero-engines under extreme conditions. This paper focuses on the development of ignition prediction models, including early empirical and semi-empirical models, as well as physics-based models for turbulent flame propagation and flame kernel tracking, assessing their applicability in high-altitude relight scenarios. Although flame kernel tracking has shown satisfactory performance in predicting ignition probability, it still overly relies on manually set parameters and lacks precise descriptions of the physical processes of flame kernel generation. Future studies on some topics, including refining flame kernel modeling, strengthening the integration of experimental data and numerical simulations, and exploring the incorporation of new ignition technologies, are needed, to further improve model reliability and predictive capability.

Based on directed relation graph with error propagation methods, 39 species and 231 reactions skeletal mechanism were obtained from Mech_56.54 (113 species and 710 reactions) mechanism of methane. The ignition delay times, laminar flame propagation speed, and important species were calculated using the simplified mechanism at different pressures and equivalence ratios. The simulation results were in good agreement with that of detailed mechanisms and experimental data. The numerical simulation of the Bunsen burner jet flame was carried out using the simplified methane mechanism, and the simulation results well reproduced the temperature, flow fields and distribution of important species at flame zone. The compact methane reduced mechanism can not only correctly respond to its dynamic characteristics, but also can be well used for numerical simulation, which is of great significance in engineering applications.