## Mechanical & Aerospace Engineering Theses & Dissertations

Winter 1991

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

#### Department

Mechanical & Aerospace Engineering

#### Program/Concentration

Mechanical Engineering

#### Committee Director

Sushil K. Chaturvedi

#### Committee Member

Surendra N. Tiwari

#### Committee Member

Albert S. Roberts

Jag J. Singh

#### Abstract

A numerical study has been conducted to analyze a fuel injector with three in-line cylinder geometry that has been adopted as a model for investigating the combustion phenomenon in the 8-Foot High Temperature Tunnel (HTT) combustor at the NASA Langley Research Center. The primary objective here is to analyze the flame lift-off phenomenon in the three cylinder fuel injector geometry in two-dimensions. The fluid mechanics model used in the analysis includes time-averaged Navier-Stokes equations that are employed in conjunction with a two-equation k-$\epsilon$ model for predicting the effects of turbulence. Calculations were performed with three chemistry models, namely fast chemistry, one-step and two-step reaction kinetics. The coupled elliptic, non-linear, partial differential equations are solved by an existing quadratic upwind scheme. Predictions are made for the flame lift-off, injector surface temperature and thermal load resulting from the combustion phenomenon downstream of the fuel injector.

Effects of fuel jet velocity, chemistry model, inlet turbulent intensity and oxygen enrichment on the flame lift-off phenomenon, and the thermal load on the fuel injector are analyzed by considering simultaneously combined convection (outside the cylinders) and conduction (inside the cylinders). Results indicate that as the fuel jet velocity is increased, the flame is transformed from a wrap around configuration to a clearly lifted flame configuration. Of the three chemistry models considered in the present study, only the two-step chemistry model predicts a clearly lifted flame. The results indicate that as the fuel injection velocity is increased the thermal load and peak surface temperature decreases sharply (as the flame gets detached from the injector surface). The effect of oxygen enrichment on the combustion process is very pronounced and causes the establishment of a wrap around flame even at higher injection velocities.

#### DOI

10.25777/34k9-7e62

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