Effect of fuel injection parameters on performance characteristics and emissions of a thermoacoustic system

Abstract

The present study experimentally investigates the effects of different fuel injection parameters on performance characteristics and emissions of a thermoacoustic pulse combustor. Several fuel nozzles were designed to enable various injection schemes. Pressure, photoelectric and radical spectra signals were measured for different fuel nozzles under the same fuel supply pressure; evaluation indexes, to describe the running performance of the pulse combustor, were introduced based on the pressure signal. Preliminary analysis of the pressure signals and evaluation indexes showed that the fuel nozzle with a small top angle was beneficial to the operation performance of the pulse combustor, and there exist an optimal spacing of nozzle holes to enhance the combustor performance most effectively. To further study the influence mechanism, a detailed analysis of the cyclic behaviors of pressure and photoelectric signals was then conducted. Several crests were observed in the cyclic photoelectric signal, all showed different characteristics for different fuel nozzle parameters. It was found that these crests influenced heat release distribution, and therefore, the thermoacoustic behavior and operation performance of the pulse combustor. Rayleigh's efficiency was calculated to quantitatively analyze the effect of various crests on the thermoacoustic coupling in the combustor. In addition to operation performance, radical emissions for different fuel nozzle parameters were also investigated. The obtained radical signals have five spectra peaks (309.35 nm, 430.48 nm, 516.19 nm, 766.19 nm and 927.12 nm) for liquefied petroleum gas. The larger spectra peaks of the free radicals generally indicated higher combustion chemical reaction intensity. Results showed that the fuel nozzle with the small top angle has large spectra peak values and an optimal spacing of nozzle holes that maximized the combustion intensity. This study benefits the optimal design of the nozzle and the improvement of performance as well as efficiency of the combustor.