Experimental study on combustion instability of lean premixed swirl flame was conducted for methane-hydrogen mixtures, and the influence mechanism of hydrogen content (0%, 10%, 20%, and 40%) on the combustion instability under different acoustic frequencies (110–240 Hz) was investigated. A forced acoustic field created by a loud speaker was to simulate the complex and variable acoustic environment of unstable combustion. The flame transfer function was used to characterize the combustion instability. The morphologies of the flame, the evolution of vortex in the flame flow field, intensity of OH^* chemiluminescence of flame front structure, and the degree of local thermo-acoustic oscillation of flame were also investigated to facilitate this study. The results show that the increase in hydrogen content weakens the combustion instability of lean premixed swirl flame in the acoustic frequency ranges of 170–240 Hz, while the combustion instability is enhanced for the acoustic frequency ranges of 110–160 Hz. The main reason for this phenomenon is the increase in the hydrogen content changes development of the vortex in the flame flow field, the evolution of the flame surface and the intensity of OH^* chemiluminescence of flame front structure. This study provides an important reference for mastering the mechanism of the combustion instability of mixed gas flames and for developing technologies to inhibit combustion instability.

Few experiments have been performed to investigate the hydraulic performance in a chevron brazed plate heat exchanger (BPHE) with the narrow channel at lower Reynolds number. The hydraulic characteristics of seven types of chevron BPHEs were investigated experimentally and numerical simulation revealed the effects of structural parameters on hydraulic performances. The correlations between friction factor f and Re were fitted out based on more than 500 sets of pressure drop data. The research results show that there is a power-law between f and Re; which has a similar trend but a different amplitude for different plates, and the exponent of the power-law could be approximate to a constant. Numerical results show that the pressure drop Δp is positively correlated with the corrugated angle and spacing, however, negatively correlated with the corrugated height. Research on the hydraulic performance is significant for the optimal design of BPHE.

The effects of acoustic frequency (f)/0–400 Hz and amplitude (A)/0–1400 Pa on nitrogen oxides (NOx) emissions of a partially premixed flame were investigated experimentally. The mechanism of NOx emissions was analyzed by the evolution of the vortex, which was shown by particle image velocimetry (PIV). From the relationship of NOx emission index (EINOx) and acoustic parameters, it was concluded that a critical frequency (f_c) from 170 Hz to 190 Hz appeared. When the frequency was less than f_c, EINOx decreased linearly with an increase in amplitude. The flame length became shorter, which led to a decrease in the global residence time, and hence, a reduction in reaction time for NOx. However, a direct proportional relationship between EINOx and amplitude was not found when the frequency was larger than f_c. Based on PIV particle scattering images, with an increase of the acoustic frequency, the effects of the acoustic field on the flame base became less significant, but the flame length and reaction space of NOx were gradually increased.