In a study published on January 18, 2024 within the journal Physics of Fluids, researchers from Tohoku University theoretically linked ignition and deflagration in a combustion system, unlocking latest configurations for stable, efficient combustion engines attributable to the possible existence of any variety of steady-state solutions.
“This research directly tackles the challenge of reducing carbon dioxide emissions by enhancing the efficiency of combustion engines, a major source of those emissions,” said Youhi Morii from the Institute of Fluid Science at Tohoku University.
“A greater understanding of combustion dynamics may even support the event of safer, more sustainable engineering solutions,” said Kaoru Maruta, also from the Institute of Fluid Science.
Combustion dynamics involves complex coupled fluid and chemical reactions. Researchers use computational fluid dynamics to assist them higher understand and control the method.
If a system that operates stably in a gradual state and has a certain tolerance range for small perturbations might be utilized, it will simplify the structure and control of combustors, and increase the feasibility of commercializing latest combustor designs.
To explore this idea, the Tohoku University researchers considered a straightforward, one-dimensional reactive flow system, where unburned premixed gas enters a combustion chamber from the left inlet boundary, while burned gas, or deflagration wave, exits from the proper outlet boundary.
The working theory up up to now held that a steady-state solution exists only when the inlet velocity matches either the rate of the deflagration wave (which travels at subsonic speeds) or the rate of the detonation wave — a shock response where the exiting flames travel at supersonic speeds.
Nonetheless, this conventional wisdom relies on the idea that chemical reactions within the preheating zone are negligible. Recent studies emphasize the importance of what is called “autoignition-assisted flames,” wherein a deflagration propagating in a hot unburned premixed gas mixture has a faster propagation speed with the assistance of chemical reactions in front of the flame. This implies that there are any variety of steady-state solutions, which affect the quantity of residence time gas stays in front of the deflagration.
Constructing on these findings, the Tohoku University researchers designed a theory that successfully bridged the gap between ignition and deflagration waves, revealing the existence of additional steady-state solutions which can be possible once they considered the “autoignitive response wave” — a wave that’s affected by ignition within the preheat zone but behaves like a deflagration wave.
“Contrary to the prevailing view that only a single steady-state solution exists for deflagration waves in subsonic one-dimensional systems, our approach posits an infinite variety of such solutions as autoignitive response waves, asserting that ignition and flame are intrinsically linked,” Morii said.
Which means that steady-state solutions exist not merely on the two points where the inlet velocity matches the velocities of the deflagration or detonation waves, but additionally in a broader region if autoignitive conditions are considered.
The team further prolonged the speculation to scenarios involving supersonic inlet velocities. Within the supersonic regime, the standard understanding is that a steady-state solution is feasible only when the inlet velocity matches the detonation wave velocity. Nonetheless, provided that the autoignitive response wave originates from zero-dimensional ignition, the researchers argued that it needs to be independent of the inlet velocity.
“We propose that an infinite variety of steady-state solutions exist for the autoignitive response wave, even in supersonic conditions,” Morii said.
By theoretically linking ignition and flame, the engine can now be considered from a brand new perspective. Accounting for ignition phenomena offers the potential of more stable combustion, resulting in the thought of a brand new concept of engine that’s more efficient than the standard one.
“This work on stabilizing autoignitive response waves marks a fundamental breakthrough, potentially revolutionizing the design of combustion systems, especially within the realm of supersonic combustion,” Morii said.
While theoretical and numerical results have provided a brand new engine concept, it has not yet been experimentally verified. The team, due to this fact, plans to use the research findings to an actual engine through further experimental verification through joint research.
