Quantification of the transient mass flow rate in a simplex swirl injector

Abstract

When a heat release and acoustic pressure fluctuations are generated in a combustor by irregular and local combustions, these fluctuations affect the mass flow rate of the propellants injected through the injectors. In addition, variations of the mass flow rate caused by these fluctuations bring about irregular combustion, which is associated with combustion instability, so it is very important to identify a mass variation through the pressure fluctuation on the injector and to investigate its transfer function. Therefore, quantification of the variation of the mass flow rate generated in a simplex swirl injector via the injection pressure fluctuation was the subject of an initial study. To acquire the transient mass flow rate in the orifice with time, the axial velocity of flows and the liquid film thickness in the orifice were measured. The axial velocity was acquired through a theoretical approach after measuring the pressure in the orifice. In an effort to understand the flow area in the orifice, the liquid film thickness was measured by an electric conductance method. In the results, the mass flow rate calculated from the axial velocity and the liquid film thickness measured by the electric conductance method in the orifice was in good agreement with the mass flow rate acquired by the direct measuring method in a small error range within 1% in the steady state and within 4% for the average mass flow rate in a pulsated state. Also, the amplitude (gain) of the mass flow rate acquired by the proposed direct measuring method was confirmed using the PLLIF technique in the low pressure fluctuation frequency ranges with an error under 6%. This study shows that our proposed method can be used to measure the mass flow rate not only in the steady state but also in the unsteady state (or the pulsated state). Moreover, this method shows very high accuracy based on the experimental results.

Geometrical Effects on the Fluid Dynamics of an Open-End Swirl Injector

“…With respect to the signal processing circuit, it is reported that an alternating current (AC) power supply is preferred to a direct current power supply because the current does not flow well if polarization occurs [7]; therefore, in this study, AC excitation of 20 kHz was adopted. Although the form of the electrodes is similar to many other researchers' [5,7,8,10,13], the measurement circuit is unique in the present study. Because the pulsation of liquid film is very small, and always accompanied by considerable noise, the lock-in amplifier was used in the signal processing circuit; because of its ability to suppress noise, it is widely used to detect weak signals.…”

“…When heat release and acoustic pressure fluctuations are generated in a combustor, these fluctuations affect the flow rate of the propellants injected through the injectors. In addition, variations of the flow rate caused by these fluctuations bring about irregular combustion, which is associated with combustion instability, so it is very important to determine whether a flow rate variation is caused by pressure fluctuation in the injector and to investigate its transfer function [8]. The aim of an investigation of injector dynamics is to understand the response of the volume flow of the injector to the pressure fluctuations [9].…”

Experimental Study on Simplex Swirl Injector Dynamics with Varying Geometry

“…The pressure in the orifice and liquid film thickness were measured during the experiment and mass flow rate through the orifice was calculated using DPMM with the data obtained above (Khil et al, 2009). …”

“…The discharge coefficient μ, which plays a dominant role in determining the mass flow rate, was calculated as follows (Borodin et al, 1967;Kulagin and Moroshkin, 1966). (n: number of tagnential entries)…”

“…Additionally, DPMM was developed to acquire the output data. Experiments on a simplex swirl injector were conducted followed by results analysis (Khil et al, 2009). …”