Ph.D. Proposal

Samuel E. Wonfor

(Advisors: Prof. Adam Steinberg and Prof. Jerry Seitzman)

"Effects of Reactant Inhomogeneity on Lean-Premixed-Prevaporized Gas Turbine Combustor Operation"

Wednesday, July 10

10:00 a.m.

Montgomery Knight Building 317

Abstract 

With the shift towards lean-burn combustors for aviation gas turbine engines, further understanding of the connections between combustor stability and pollutant emissions is required to achieve reliable and sustainable combustor designs. One promising lean-burn combustor architecture is lean-premixed-prevaporized (LPP) combustion. In LPP combustion, fuel is injected, vaporized, and mixed before entering the combustor. In theory, this leads to the burning of a homogeneous lean mixture that greatly lowers flame temperatures, mitigating pollutant production and extending liner lifetime. In practice, this leads to challenges with flashback, blowoff, and autoignition. Understanding the tradeoffs between pollutant production and combustor stability is required to bring LPP technology to the readiness levels required for aircraft engine operation.

An important parameter that remains to be systematically studied regarding LPP combustion is the level of fuel prevaporization and premixedness, further termed as reactant inhomogeneity. Reactant inhomogeneity is generally considered to be due to partial premixedness or stratification phenomena. These phenomena have been shown to enhance both the stability and emissions of laminar and turbulent combustion in several ways. Previous studies have been conducted on benchtop burners with simple geometries, operating at atmospheric pressures. This work aims to explore when and how reactant inhomogeneity affects LPP combustor operation at flight relevant conditions.

Future work entails two test campaigns, each with a distinct goal that build towards a better understanding of reactant inhomogeneity in LPP combustion. The first campaign will focus on mapping the operability of the combustor, while recording trends in lean blowoff (LBO) limits and pollutant emissions with respect to reactant inhomogeneity. Quantification of reactant composition will be achieved through joint planar laser induced fluorescence (PLIF) and filtered Rayliegh scattering (FRS) measurements of vaporized fuel. An extractive emissions sampling system will be used to obtain measurements of both gaseous and particulate emissions. This data will be compiled and used to establish trends in combustor stability and emissions with respect to reactant inhomogeneity. These trends will be useful in understanding the effects of reactant inhomogeneity on LPP combustion.

The second campaign will focus on measuring the turbulent flame structure within the LPP combustor, and its variation due to changes in reactant inhomogeneity. Fuel PLIF and FRS will again be used to characterize the reactant composition, while several other PLIF techniques will be considered for measuring flame structure. These methods include OH PLIF, Overlap Layer (OL) imaging with simultaneous OH-CH2O PLIF, CH PLIF, and again fuel PLIF. Each technique has its own advantages and

challenges when implemented in a high pressure, LPP combustor, and further development of these diagnostics to obtain high quality data in such environments will be made. Measurements from each technique will be used to calculate several turbulent flame parameters, including turbulent progress variable, flame brush thickness, and 2D flame surface density. The effect of reactant inhomogeneity on these parameters will allow further understanding of the mechanisms that cause reactant inhomogeneity to manifest in practical combustion systems.

Collectively, this experimental study will inform the combustion community on the influence of reactant inhomogeneity on LPP combustion stability and emissions, identify the mechanisms by which reactant inhomogeneity manifests in such a combustor, and develop existing laser diagnostic techniques to make measurements of reactant composition and flame structure in LPP combustors.

Committee

· Prof. Adam Steinberg – School of Aerospace Engineering (advisor)

· Prof. Jerry Seitzman – School of Aerospace Engineering (advisor)

· Prof. Wenting Sun – School of Aerospace Engineering

· Prof. Ellen Yi Chen Mazumdar – School of Mechanical Engineering