Skoltech scientists theoretically predicted the synchronization effect, a role of self-sorting, in detonation waves. This discovery may help curb inherent chaotic processes and thus stabilize the combustion of rotating knock engines, an experimental setup that can save a lot of fuel than traditional rocket and ship engines.
This research published in the famous Journal of Fluid Mechanics and was recognized as the best theoretical work of the year at a meeting of the Institute of Chemical Physics, Russian Academy of Sciences. Detonation engines are being developed to save fuel due to more efficient combustion modes. When detonated, the combustion products propagate at supersonic speed, which theoretically improves efficiency by 25%.
"In a rotating knock engine, smaller cylinders are located in larger cylinders, and the combustible mixture is periodically injected into the cavity between them, and its combustion occurs in a continuous knocking manner: waves are circle after circle around small cylinders. Cylinders.
But due to the chaotic nature of the process, detonation waves in general do not behave so predictable and cycle regularly after a cycle. In particular, the speed of wave propagation fluctuates violently and unpredictably over time, making the engine unstable," explained Aslan Kasimov, associate professor at Skoltech, the head of the study. Skoltech found a way to suppress explosive waves by simplifying its vibration. To this end, scientists have demonstrated for the first time the synchronization effect of the knock region.
synchronization was first discovered by Christian Huygens in the 17th century. He observed a pair of pendulum clocks hanging from the same beam, and it turned out that due to this delicate connection, the oscillations of the pendulum synchronize over time—they start to move in phase or inverse phase. Since then, synchronization has appeared not only in mechanics, but also in various fields of chemistry, medicine, biology and even sociology.
"For example, some fireflies flash at a certain frequency. When many of these fireflies gather in one place, they start to flash synchronously because of their very weak connections: each beetle can only see its nearest neighbor," said Andre Golding, a doctoral student at Skoltech and first author of the paper, and gave some examples from different fields.
Therefore, experiments show that each person's natural biological rhythm can have a frequency different from 24 hours - this can be seen if the experimenter is placed in an artificial environment without day and night. In fact, under the influence of periodic external influences (sunrise, noon, sunset), the internal rhythm adaptation of humans and animals is also synchronized.
pacemaker is also a similar periodic external influence that simplifies internal vibration of the heart—it can neutralize arrhythmia . From a synchronization perspective, it can be considered that the rotation of the moon and the earth are always on the same side, and even the number of victims of serial killers depends on the date. In their new work, scientists from Skoltech demonstrated the synchronization of detonation waves for the first time. The essence of
detonation is that even in a completely uniform medium, detonation waves will propagate at "rapid", that is, at variable speeds. This means that the wave itself is an oscillator, just like the arrhythmic heart in the pacemaker example. It is related to arrhythmia, because the oscillation of this wave is very unpredictable – we remember that this is what disturbs the operation of the knock engine.
"It turns out that fluctuations in the velocity of the detonation wave can be sorted by external periodic effects, but this is not an effect in the usual sense, but rather a regular inhomogeneity of the medium. The waves propagate in a combustible mixture, which in the case of the engine is injected into the annular cavity between the two cylinders in the form of a jet.
Kasimov explained that in this case, the inhomogeneity of the medium can be imagined as a series of areas more or less saturated by fuel (one air, one fuel, etc.)."So, by changing the design of the engine, for example, the distance between adjacent injectors , the characteristic scale of the medium inhomogeneity encountered by the knock wave can be changed."
As the researchers found, the complex internal oscillations of the detonation wave can be ordered due to synchronization with the "oscillation" of the medium (periodic inhomogeneity). If we consider a set of characteristic scales of media inhomogeneity, we find that the fluctuations of detonation waves are known to be regularized over the entire continuous range of these scales, that is, it continues to propagate "jump", but these assholes become very easy to predict. Due to the special shape of the figures, the collection of these ranges is called Arnold's tongues—they are described for the first time in the realm of detonation. The timing of the knock wave and the discovery of Arnold's tongue laid the foundation for further research. In the future, the question of which engine design will suppress the knock wave by controlling its speed should be answered. So far, scientists have performed one-dimensional calculations; in the engine, the process immediately occurs in three.
