Ion current sensing-based lean blowout detection for a pulse combustor

In this paper an ion current sensing method is proposed for early detection of lean blowout (LBO) in a pulse combustor. The method was also compared with the pressure measurement method. Near LBO characteristics in the pulse combustor were inferred from ion current and pressure time domain signals recorded for different operating conditions and initially analyzed using the spectral analysis method. As LBO approached, low frequency (below 20 Hz) components were gradually observed and the spectral energy between 0 and 20 Hz gradually increased while the energy of the working frequency components decreased. The ratio of the working frequency components energy fraction over the low frequency components energy fraction could thus be treated as an indicator of LBO, denoted by stability to instability ratio (SIR). The index SIR remained at a high level under stable conditions and decreased steeply when LBO was approached. Based on the ion current sensing method and the prediction index SIR, the gas supply pressure for stable operation in the pulse combustor was suggested to be more than 15.2 kPa. The result shows that the proposed ion current sensing method and the index SIR can help to estimate the LBO limit of the pulse combustor and avert the unexpected LBO. Compared to pressure sensing, ion current sensing was observed to be more sensitive to LBO events, leaving sufficient time for combustion control.