Estimation of combustion efficiency range and pressure fluctuation at low working condition

The exact data of combustion efficiency are rare in the open literature near the ignition and at sub-idle, especially at the state close to the lean blowout limit, due to the complexity of combustion characteristics and inconvenience of measurement in these situations. At low working condition, in order to pursue low emission, the well-premixed combustion is expected to be used as much as possible even when it is close to the low limit combustion state. Consequently, this makes the devices easier to suffer from the sharp increase of pressure fluctuation, which results in pressure oscillation and even resonance. In this paper, a model combustor with an adjustable premix of fuel and air for low working condition is used. The problem of pressure oscillation under well-premixed and low working condition is pointed out through a comparison test. A simplified estimation method of combustion efficiency range is proposed and compared with the experiment. The experimental data confirm the applicability of the simplification algorithm of the combustion efficiency range. On the other hand, it is also pointed out that the reduction in premixing degree may be able to make the combustion efficiency less than 30%, and the CO2 content is a more important criterion for the efficiency range judgment near lean blowout state. This paper will provide a reference for the further study of combustion efficiency and pressure fluctuation under low limit combustion conditions.