Combined Numerical and Experimental Investigation of a Hobby-Scale Pulsejet

A review of pollutants emissions in various pressure gain combustors

“…This aspiration is also present at the exit end of the pulsejets causing significant backflow into the device during every cycle of operation. Hence, unlike other devices, pulsejets are prone to producing both positive and negative thrust, 25 owing to this resonance-based operation. NOx emissions in pulsejets are lower than most conventional systems due to three main reasons 28 : (i) cooling of hot products by the colder ambient gases due to the backflow part of the cycle, (ii) cooling of the hot combusted products by the colder fresh reactants at the injector end of pulsejets, and (iii) short residence times of the combusted products inside the pulsejets due to the high frequency of operation.…”

“…23 It is generally agreed upon that this coupling is based on a Rayleigh criterion-type combustion process where there is in-phase pressure increase and heat addition. [24][25][26][27] While the exact mechanism of the combustion is not yet deciphered, several possibilities such as conventional turbulent flame ignition, 23 autoignition from the heated wall, 25 and shockless explosion combustion 26 have been proposed. Similarly, there is some contention on the nature of the acoustic oscillations happening inside pulsejets.…”

“…28 Additionally, within a given pulsejet operating cycle, it has been conceded that the device could behave like a half-wave tube owing to the valves being open for a finite time to allow for reactants injection. 25 Despite this class of combustors existing for multiple decades, there are still considerable unknowns regarding its operation, including the issue of emissions. Because of the broad promises of pressure gain combustion technologies, research into pulsejets have increased in recent years, once again, because of their prospective efficiency increase over conventional systems; Yungster et al 29 numerically estimate that pulsejets tend to produce more than a 5% gain in stagnation pressure.…”