Effects of oxygen partial premixing on soot formation in ethylene counterflow flames with oscillating strain rates

Effects of Ammonia Addition on the Sooting Characteristics of Ethylene Counterflow Diffusion Flames with Oscillating Strain Rates

“…This implies that the soot formation (represented by the SVF) has limited time to respond effectively to the imposed oscillations, thus resulting in smaller oscillation amplitudes at higher frequencies or at a larger Stokes number. Such a trend is also observed in previous neat C 2 H 4 counterflow diffusion and C 2 H 4 partially premixed flame …”

“…To ensure that the fuel stream oscillates identically to the oxidizer in terms of oscillation phases and amplitudes, two independent speaker control signals are used to separately tune the two streams based on the reference velocity measured at the nozzle exits. It should be noted that our preliminary experiments have shown that using only one speaker signal makes it difficult to achieve precise synchronization between the fuel and oxidizer stream velocities . This difficulty may be attributed to minor differences between the two speakers (despite being of the same model) and differences in the physical properties of the fuel and oxidizer streams.…”

“…Flames. The present measurements were conducted based on a newly designed unsteady counterflow burner 61 (see Figure 1), which is an upgrade from a previous steady counterflow burner 62 by introducing additional loudspeakers to generate controllable acoustic forcing. For that reason, we provide only a brief description here.…”

“…Each loudspeaker has a membrane with a diameter of 12 cm, a resistance of 8 Ω, and a frequency ranging from 40 to 4000 Hz, following the setup used in our previous study. 61 By driving the loudspeakers with an amplified sinusoidal voltage waveform, we can establish a controlled sinusoidal oscillation for the exit flow fields of the oxidizer and fuel. To ensure that the fuel stream oscillates identically to the oxidizer in terms of oscillation phases and amplitudes, two independent speaker control signals are used to separately tune the two streams based on the reference velocity measured at the nozzle exits.…”

“…To overcome this limitation, a phase-locking method was employed to measure the SVFs over multiple oscillation cycles, taking advantage of the periodic nature of the unsteady flames. As documented in our previous study, 61 a sinusoidal voltage waveform was utilized to drive the speaker, serving as the master time reference. A TTL signal (referred to as TTL-A) was defined once the sinusoidal voltage crossed the 0 potential on the rising edge.…”