Effect of Fuel Injection and Mixing Characteristics on Pulse-Combustor Performance at High-Pressure

Abstract

Recent calculations of pulse-combustors operating at high-pressure conditions produced pressure gains significantly lower than those observed experimentally and computationally at atmospheric conditions. The factors limiting the pressure-gain at high-pressure conditions are identified, and the effects of fuel injection and air mixing characteristics on performance are investigated. New pulse-combustor configurations were developed, and the results show that by suitable changes to the combustor geometry, fuel injection scheme and valve dynamics the performance of the pulse-combustor operating at high-pressure conditions can be increased to levels comparable to those observed at atmospheric conditions. In addition, the new configurations can significantly reduce the levels of NOx emissions. One particular configuration resulted in extremely low levels of NO, producing an emission index much less than one, although at a lower pressure-gain. Calculations at representative cruise conditions demonstrated that pulse-combustors can achieve a high level of performance at such conditions. Nomenclature EI= emission index (grams of NO per kilogram of fuel) f = pulse combustor operating frequency Lpc = pulse combustor length mT = total massflow rate p = pressure p0 = inlet total pressure pavg = average combustor pressure pinj = fuel injection pressure pmax = peak combustor pressure T = temperature T0 = inlet total temperature t = t i m e tefi = end of fuel injection time tsfi = start of fuel injection time tsvc = start of valve closing time tsvo = start of valve opening time tvfc = valve fully closed time tvfo = valve fully open time x = axial coordinate Φ = equivalence ratio

Parametric Study of Pulse-Combustor-Driven Ejectors at High-Pressure

“…The results obtained in Ref. 5 further revealed that two counter-rotating vortices were formed in the pulsecombustor, and that the fuel was being split between these two vortices. The combustion occurring in the secondary vortex, located further away from the combustor head-end, was not being confined as efficiently as the combustion occurring in the primary vortex, potentially affecting negatively the pressure gain in the combustor.…”

“…Preliminary calculations of pulse-combustors-ejector configurations operating at high-pressure conditions (10 bar) produced pressure gains significantly lower than those observed experimentally and computationally at atmospheric conditions 4 . A recent study 5 identified the factors limiting the pressure-gain at highpressure conditions and investigated the effects of fuel injection and air mixing characteristics on performance. New pulse-combustor configurations were developed in Ref.…”

“…The study presented in Ref. 5 only considered the pulse-combustor by itself (i.e., without an ejector). However, the pulse-combustor by itself is not suitable to replace a conventional combustor in a gas turbine engine.…”

A review of pollutants emissions in various pressure gain combustors

“…Pulsejet combustors are prone to being highly sensitive to the mixing inside; in some scenarios, significantly more so than traditional combustors. Yungster et al 34 have shown that depending on the nature of coupling between the vortex formation after the valves and the combusting region (combustion occurring on the inner Pekkan and Nalim (2003). 22 region of the vortex vs. that occurring outside the vortex, near the wall, which can produce hotspots) there could be a factor of two increase in the observed NOx emissions index.…”

“…Hence, a novel method was used to sample a PDC, wherein a type of pseudo-averaging of emissions is performed by aggregating the produced gases from four consecutive tests into a container, and then sampling the stored gases in it. 45 Tests were run for about 2.5 s, whereas sampling started 34 and ended a seventh of a second after ignition and before shutoff, respectively. A wall-mounted probe at the end of the PDC tube was fitted with the sampling probe.…”