Analysis of pressure fluctuation signals in dense gas-solid flow of powder fuel engine using HHT

Fluidized pressure is significant for powder fuel fluidization and conveying characteristics in powder fuel engines. In this work, the effects of fluidized pressure on the powder fluidization characteristics of a piston-driven powder feeding system is experimentally investigated, and the pressure fluctuation signal analysis was carried out by using autocorrelation function and Hilbert–Huang transform (HHT) methods. The experimental results show that the relative pressure drop first decreases sharply and then gradually stabilizes with the increase of initial total fluidized pressure. With the increase of fluidized pressure in the range of 0.5–5.5 MPa, the powder mass flow rate shows an increase from 48 to 97 g/s. Through the autocorrelation analysis, the corresponding frequency band of effective flow characteristics is determined as 0–40 Hz. Three scales, namely micro scale with high-frequency (>100 Hz), meso-scale medium-frequency (1–100 Hz) and macro scale with low-frequency (0–1 Hz), are obtained to represent the dense two-phase flow characteristics by using HHT analysis. The energy fraction distribution corresponding to intrinsic mode functions (IMFs) shows that with the increase of pressure in the range of 0.5–2.3 MPa, the pressure is dominated by powder layer and turbulence fluctuations firstly, but when the fixed powder layer is formed, it becomes completely dominated by turbulent fluctuations. In the range of 2.3–4.3 MPa, the IMFs distribution is consistent with the pressure range of 0.5–2.3 MPa, which shows there is probably a periodic law varying with fluidized pressure for dense gas-solid flow characteristics in powder feeding system.