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Confinement has direct influence on the dome reference velocity and indirect influence on the combustor’s performance, emissions, operability, liner and dome temperature levels and gradients. Understanding the effects of the confinement is crucial to conventional combustor design. Recently, lean direct injection (LDI) combustor has been popularly employed to reduce nitrogen oxides (NOx) emissions from gas turbine. Compared to conventional combustor, LDI combustor has a much larger amount of air entering into the dome. Therefore, combustion characteristics and confinement effects in LDI combustor are quantitatively or even qualitatively different from those in conventional combustor. As a result, some design criteria for conventional combustor are no longer applicable for LDI combustor and it is essential to investigate the effects of confinement level in LDI combustor. In the literature, several studies have been conducted to understand how the confinement levels affect the characters of swirling non-reactive flow. However, there are few studies on the reactive flow and thereby the effects of confinement on combustion characteristics are not well understood. Due to its important role in combustor design, the confinement effect on spray combustion in LDI mode is systematically investigated in the present study. The experimental setup is established to study the confinement effects. Experimental data on flame characteristics, centerline temperature distribution, and pollutant emissions are obtained. Experiments at five different confinement ratios, 2.8, 6.8, 10.6, 19.5, and 28.5, are conducted. The results show that the confinement level has an important impact on the flame characteristics, centerline temperature, and pollution emissions. The optimal confinement ratio is determined, at which the pollution emissions become the lowest.

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