The Effect of Swirl Number On Lean Blow Out Limits of Lean Direct Injection Combustors

Yogesh Aradhey, Zackary Stroud, Joseph Meadows
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Abstract

This is the first study where a single variable sweep of swirl number (SN) is conducted to assess its impact on lean blowout limits (LBO) in a liquid fueled Lean Direct Injection (LDI) combustor. This study uses a scaled NASA SV-LDI (Swirl Venturi - Lean Direct Injection) hardware and is concerned with the impact of swirl number on the lean blow out limit of a single element LDI system at atmospheric pressure. The SN was varied from 0.31 to 0.66 using continuously variable active SN control system that was developed in-house. It is shown that the minimum operating equivalence ratio is a linearly increasing function of swirl number. While previous literature agrees with the positive slope for this correlation, past work has insisted that the LBO limit is proportional to the swirler vane angle of swirl cup flame holders which is shown to be untrue for LDI systems. By actively varying the swirl number, it is proven that LBO is proportional to SN, and it is well known that SN is not proportional to swirler vane angle. Increased SN reduces LBO margin because the better-mixed, high swirl cases dilute locally rich pockets of fuel air mixture. In addition to a baseline venturi, which was scaled from NASA's geometry, two other venturis were tested. A low pressure loss venturi with a large throat diameter showed poor blow out performance where as a parabolically profiled venturi improved LBO over the baseline for the same swirl number.
漩涡数对贫油直喷燃烧器吹出极限的影响
这是首次对漩涡数(SN)进行单变量扫描,以评估其对液体燃料精益直喷(LDI)燃烧器中贫油喷出极限(LBO)的影响的研究。这项研究使用了按比例缩放的 NASA SV-LDI(漩涡文丘里-精益直接喷射)硬件,关注的是漩涡数对大气压下单元素 LDI 系统精益喷射极限的影响。使用内部开发的连续可变主动 SN 控制系统,SN 在 0.31 至 0.66 之间变化。结果表明,最小工作当量比是漩涡数的线性增加函数。虽然以前的文献同意这种相关性的正斜率,但过去的工作坚持认为 LBO 限制与漩涡杯火焰座的漩涡叶片角度成正比,这对于 LDI 系统来说是不正确的。通过积极改变漩涡数,可以证明 LBO 与 SN 成正比,而众所周知,SN 与漩涡叶片角度并不成正比。增加 SN 会减少 LBO 余量,因为混合更好的高漩涡会稀释局部富余的燃料空气混合物。除了根据 NASA 的几何尺寸缩放的基准文丘里管外,还测试了另外两个文丘里管。一个喉部直径较大的低压损文丘里管显示出较低的吹出性能,而一个抛物面文丘里管在相同漩涡数的情况下比基准文丘里管改善了 LBO。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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