喷嘴射流速度对富氢燃料平行射流燃烧器燃烧特性影响的实验和数值研究

Experimental and Numerical Investigation of Nozzle Jet Velocity Effects on Parallel Jet Combustor Characteristics of Hydrogen Enriched Fuel

关键词:  柔和燃烧  富氢燃料  NOx排放  抬升高度  Da数

Key words:  MILD combustion  Hydrogen enriched fuel  NOx emissions  Lift-off height  Damköhler number

摘要:

针对燃气轮机燃烧，天然气掺氢是减少碳排放的可行策略。柔和燃烧（Moderate or Intense Low Oxygen Dilution）具备解决高绝热火焰温度下NOx排放过高的潜力。本文通过实验和数值模拟相结合的方式，研究了喷嘴射流速度对富氢燃料平行射流燃烧器燃烧特性的影响。实验燃料由Vol.50%甲烷和Vol.50%氢气构成。喷嘴的射流速度为90~150m/s。基于实验工况，利用化学反应网络模型计算了富氢燃料在不同绝热火焰温度下实现柔和燃烧的临界回流比。当量比小于0.6时，临界回流比随着氢气含量的增加而降低。实验结果表明，喷嘴射流速度的增加，NOx排放略有下降，CO排放和反应区抬升高度增加。喷嘴喷射速度由90m/s增加到150m/s，数值模拟结果显示，平行喷射燃烧器内的烟气回流比例保持不变。Da数（Damko?hler number）的分布可作为判定柔和燃烧的因素，其直观显示喷嘴射流速度对柔和燃烧的影响。喷嘴射流速度增加，流场内Da>1的区域呈现降低趋势，这意味着慢速反应区域增加。对于富氢燃料，提高喷嘴射流速度有利于建立柔和燃烧，达到低NOx排放。

Abstract:

Adding hydrogen into natural gas fuelled for gas turbines is a feasible strategy for reducing carbon emissions. Moderate or Intense Low Oxygen Dilution （MILD） combustion has potential to solve the problem of high NOx emissions for high adiabatic flame temperature. The effects of jet velocity on the characteristics of parallel jet combustor were studied through experimental investigations and numerical simulations. The fuel is consisted of 50% methane and 50% hydrogen by volume. The jet velocity ranged from 90m/s to 150m/s. Based on a simplified chemical reactor network model， the threshold recirculation ratio for MILD combustion of hydrogen enriched fuel under different adiabatic flame temperatures was calculated according to the experimental conditions. When the equivalent ratio is less than 0.6， the threshold recirculation ratio decreases with the increase in the hydrogen fraction. The experimental results show that NOx emissions decrease slightly， and CO emissions and the lift-off height of reaction zone increase as the jet velocity increases. When the nozzle jet velocity changes from 90m/s to 150m/s， the numerical simulation results show that the proportion of flue gas recirculation in the parallel jet combustor remains unchanged. However， the region with Da>1 decreases to visualise the effect of jet velocity of MILD combustion of hydrogen enriched fuel， which means that the region of slow-chemistry reaction increases. For hydrogen enriched fuel， increasing the jet velocity is conducive to establishing MILD combustion and meeting the requirement of low NOx emissions.