Date of Completion


Embargo Period



Lean Direct Injection Combustion

Major Advisor

Chih-Jen Sung

Associate Advisor

Baki M. Cetegen

Associate Advisor

Xinyu Zhao

Associate Advisor

Bryan W. Weber

Associate Advisor

Francesco Carbone

Field of Study

Mechanical Engineering


Doctor of Philosophy

Open Access

Open Access


To reduce the environmental impact of aviation, lean direct injection (LDI) combustion is being pursued to achieve very low emissions. LDI utilizes multi-point mixers to achieve low NOx emissions and satisfactory combustion stability. Since the performance of LDI directly depends on design parameters of each single LDI mixer, a series of fundamental investigations into lean-dome-relevant pilot combustor devices are conducted herein. A single LDI mixer typically uses swirlers with converging venturi and diverging flare to generate swirling flows, which facilitate mixing in the combustor dome. This dissertation aims to investigate the impact of LDI mixer design parameters, including swirler vane angle, flare, and relative swirling direction between inner and outer swirlers, on single-mixer LDI combustion. The flow fields, flame structures and responses, radical distributions, emissions, and lean blowout (LBO) limits of methane-fueled LDI combustion are investigated with varying mixer design parameters. Experimentally, a test system of single-mixer LDI combustion has been designed and built to investigate mixer designs via advanced optical diagnostics, including particle image velocimetry, broadband flame imaging, chemiluminescence imaging, and OH-planar laser induced florescence. Compared against experimental data, the best practices of meshing and turbulence and combustion modeling have been established for Computational Fluid Dynamics (CFD) simulations of LDI. Reasonable agreement between experimental and CFD result has been achieved for flow characteristics and flame structure/response. Larger swirler vane angle lowers LBO limits but produces higher NOx levels. Removing flare reduces NOx emissions at a cost of worsening operability. Counter-swirling forms a stronger shear layer than the co-swirling case.