Large-scale rotating detonation experiments with a 500 mm outer diameter combustor are carried out in this study. The experiment used aviation kerosene (RP-3) as fuel and hot air as oxidant. Detonation is successfully initiated between the equivalent ratio of 0.85 and 1.20. The engine works steadily for 2 s and 3 s. The detonation wave modes are two-wave collision. The average speed of detonation wave is between 920 m/s and 980 m/s. The detonation wave velocity increases with the increase in equivalence ratio, and when the equivalence ratio exceeds 1.0, the increasing trend of detonation wave slows down. Through sampling and analysis of detonation gas, it is found that the uneven distribution of fuel supply pressure in large-scale rotating detonation experiment results in inconsistent local equivalent ratio and uneven combustion. The complete combustion rate based on carbon atoms is used to evaluate the combustion completeness of detonation. With the increase in equivalent ratio, the combustion changes from deflagration to detonation, and the detonation combustion completeness gets better. The combustion completeness of detonation wave is the best near the appropriate chemical equivalent ratio. Once the equivalent ratio exceeds 1.0, then oil-rich combustion occurs and the strength of the detonation wave becomes weaker.
In this study, the effects of three injection parameters on the propagation and instabilities of rotating detonation waves (RDWs) in a kerosene/air rotating detonation engine (RDE) with an S-shaped isolator are experimentally evaluated. The dimensionless parameter momentum flux ratio is considered a pivotal factor, and the influence of the injection geometry factors is analyzed. An empirical formula concerning the characteristic factor of oxidizer-fuel blending is derived to facilitate the RDE injection configuration design. The research reveals a significant correlation among the injection parameters, kerosene-air momentum flux ratios, and instability of RDWs. High dimensionless injection parameters do not necessarily result in a stable RDW phenomenon. Stable RDWs and unstable detonations are discussed under various injection parameters and momentum flux ratios. Additionally, a statistical analysis of the detonation instability is conducted, revealing two distinct cyclic categories: ignition-extinguishment-ignition and attenuation-recovery-attenuation. Two pathways of RDW instability propagation are identified to summarize the evolutionary processes of these variations and elucidate their mechanisms. Changes in the injection parameters cause the RDW to develop in two unstable orientations, resulting in the extinguishing and re-generating phenomenon of the RDW.
In this study, the effects of channel widths on the characteristics of the rotating detonation wave (RDW) were investigated. Pre-combustion cracked kerosene and 50% oxygen-enriched air were taken as the propellant. Keeping the outer diameter ( D = 150mm) constant, the channel widths ( W) of the combustor range from 15 mm to 50 mm in the experiments. The results indicate that the time for the formation of a stable RDW is longer under the wider channel, while the velocity of the RDW increases significantly with a wider channel. Increasing the ER has a positive effect on the wave velocity and the flow rate has little effect on wave velocity. The wave pressure increases under the higher ER and flow rate. Under the same flow rate and ER, the RDW pressure tends to reach the maximum value when the channel width is 25 mm, and the pressure range is 2 bar to 6 bar. Five kinds of the RDW modes were observed in the experiments, namely the failure “pop-out”, single-wave mode, two-counter rotating waves mode, and two-co rotating waves mode. The two-counter rotating waves mode seems to be an intermediate mode of single-wave mode and two-co rotating waves mode in the conducted experiments, and the multi-wave mode is more likely to occur under the narrower channel and the higher oxygen content.
Relighting of jet engines at high altitudes is very difficult because of the high velocity, low pressure, and low temperature of the inlet airflow. Successful ignition needs sufficient ignition energy to generate a spark kernel to induce a so-called critical flame initiation radius. However, at high altitudes with high-speed inlet airflow, the critical flame initiation radius becomes larger; therefore, traditional ignition technologies such as a semiconductor igniter (SI) become infeasible for use in high-altitude relighting of jet engines. In this study, to generate a large spark kernel to achieve successful ignition with high-speed inlet airflow, a new type of multichannel plasma igniter (MCPI) is proposed. Experiments on the electrical characteristics of the MCPI and SI were conducted under normal and sub-atmospheric pressures (P = 10–100 kPa). Ignition experiments for the MCPI and SI with a kerosene/air mixture in a triple-swirler combustor under different velocities of inlet airflow (60–110 m/s), with a temperature of 473 K at standard atmospheric pressure, were investigated. Results show that the MCPI generates much more arc discharge energy than the SI under a constant pressure; for example, the MCPI generated 6.93% and 16.05% more arc discharge energy than that of the SI at 30 kPa and 50 kPa, respectively. Compared to the SI, the MCPI generates a larger area and height of plasma heating zone, and induces a much larger initial spark kernel. Furthermore, the lean ignition limit of the MCPI and SI decreases with an increase in the velocity of the inlet airflow, and the maximum velocity of inlet airflow where the SI and MCPI can achieve successful and reliable ignition is 88.7 m/s and 102.2 m/s, respectively. Therefore, the MCPI has the advantage of achieving successful ignition with high-speed inlet airflow and extends the average ignition speed boundary of the kerosene/air mixture by 15.2%.
To reduce the requirement of rotating detonation related to the temperature of the incoming air, this study develops a rotating detonation combustor with precombustion cracking. Stable detonation was carried out without an oxygen supplement at a temperature of the incoming air of 419 K, and the technical advantage of using precombustion cracking to activate kerosene was verified. Cross-correlation analysis and high-speed image diagnosis were then used to analyze the mode of the detonation wave. The results show that the mode was a double-wave collision, and the speed of propagation of two opposing waves was different such that it led to the movement of the points of collision. The results of the cross-correlation analysis were used to determine the trajectory of these points. High-speed image-based mode recognition was used to directly observe the processes of conversion of the single-wave and double-wave modes of collision, where the velocity of the wave was 900 m/s as determined by the time–space diagram. The effect of the number of injection holes on the boundary of detonation was also examined. We found that the boundary of detonation shifted to lean with a decreasing number of injection holes.
◎ Excited by 397 nm UV light CET (x=0.15) CELT(x=0.15) ◎ Excited by Blue LED ◎ Excited by Blue LED CET (x=0.15) CELT (x=0.15) Com. YAG Com. YAG + CELT(x=0.15) Yun-Fang Wu a, Yung-Tang Nien b, Yi-Jhang Wang a, In-Gann Chen a, b* a Department of Materials Science and Engineering, National Cheng Kung University, Tainan 70101, Taiwan b Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan 70101, Taiwan
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