| Higher combustibility associated with hydrogen fuel has received increased attention as an additive to other traditional hydrocarbon fuels for extending the lean combustion flammability limits of hydrocarbon and achieving more stable combustion. Alternative fuels such as SNG and biomass syngas are getting more and more attention recently. These fuels typically contain a significant fraction of hydrogen. And the composition of the fuels are not keep constant. So we need to develop the fuel flexibility gas turbine and understand the role of hydrogen in the hybrid fuel.In this paper, the combustion characteristic of hydrogen/natural gas hybrid fuel of lean-premixed swirl is investigated by numerical simulation and experiment. Firstly the combustion property data of hydrogen/natural gas hybrid fuel was calculated by CHEMKEN. And analysis the effects of hydrogen content on the combustion property. Secondly, the influence of hydrogen content and pilot fuel content in cool flow field and hot flow field were investigated by numerical simulation. Finally, in order to study the multi-factors’effect on the NOx emission and the temperature of wall, experiments were scheduled by design of experiment (DoE). And the trend of NOx emission and the temperature of wall affected by multi-factors were obtained by this method. Though traditional experimental method the influence of preheat temperature, mass flow rate, equivalence ratio, pilot fuel and hydrogen content in combustion instability was investigated. The main conclusions are as follows:1. Combustion characteristic analysis of hydrogen/natural gas hybrid fuelWith increasing of hydrogen content the laminar flame speed will be increase. Depending on the hydrogen content, there are three different regimes in the hybrid flame propagation: methane-dominated combustion (low hydrogen contents), transition regime (intermediated hydrogen content), methane-inhibited hydrogen combustion. In addition to, the flame thickness, chemical characteristic time, auto ignition delay time decrease with the increase of hydrogen content.2. Numerical analysis of hydrogen/natural gas hybrid fuel of lean-premixed swirl flameIn the cool state, the change of hydrogen content have no obvious effect on flow field, the shape and strength of back flow have no obvious change. In the hot state, because fuel composition change make the temperature of reaction zone changed. The flow field have obvious change. The diameter of back flow decrease with the increase of hydrogen content, and the strength of the back flow becomes weak. In addition to, the length of the flame becomes shorter and shorter with the increase of hydrogen content, and the NOx emission increase.When the pilot fuel increase, the premix fuel decrease, and the diameter of the back flow becomes bigger. Around the pilot injector, there is a fuel enriched zone. This zone will become a high temperature reaction zone in the hot state, and is the main reason for high emission of NO.3. Experimental analysis of hydrogen/natural gas hybrid fuel of lean-premixed swirl flameBy the DoE analysis, the influence of multi-factors on NOx are listed in descending order as preheat temperature, pilot fuel, equivalence ratio, mass flow rate and hydrogen content. As the increase preheat temperature, pilot fuel and equivalence ratio the NOx increase. And the preheat temperature and pilot fuel are highly significant factors, equivalence ratio is significant factor. The hydrogen content has little effect on NOx emission. The NOx emission and temperature of wall will increase when the factors that make the adiabatic flame temperature rise.The intensity of oscillation would be stronger with increase of the preheat temperature, mass flow rate, equivalence ratio and hydrogen content. Keep the air inlet condition unchanged when changing the equivalence ratio and hydrogen content, but the intensity of oscillation of air passage become stronger and stronger with the increase of equivalence ratio and hydrogen content. Maybe is influenced by the intensity of oscillation of chamber,fchamber and fair almost the same and slight increase when the equivalence ratio increasing. When the preheat temperature is relatively low, the fchamber and fair are different, when the preheat temperature reach a certain value, they are almost the same. The pilot fuel make the intensity of oscillation become weaker.All in all, the influence of hydrogen content on characteristic of lean-premixed swirl flame is analysis by numerical simulation and experiment. And getting the influence of preheat temperature, mass flow rate, equivalence ratio, hydrogen content and pilot fuel on NOx emission and thermoacoustic oscillation. |
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