In contrast, operation without swirl displays higher variability of flame-spread patterns, occasionally causing the appearance of partial-burn cycles.
Broadband flame imaging demonstrates that with swirl, the flame consistently propagates in multiple directions to consume fuel–air mixtures within the piston bowl. The swirl decreases local RMS velocity, consistent with an observed reduction of early-burn variability. Conversely, swirl flow always convects the spark plasma towards one spray plume, causing a more repeatable ignition. Without swirl, the plasma is randomly stretched towards either side of the spark plug, causing variability in the ignition of the two spray plumes that are straddling the spark plug. They demonstrate that the spark-plasma motion is highly correlated with the direction of the gas flow in the vicinity of the spark-plug gap. PIV results for fired operation are consistent with the measurements made of motored flow. Here, PIV measurements and flame imaging are applied to fired operation for studying how the swirl flow affects variability of ignition and subsequent combustion phases. This paper is an extension of the previous work. The engine operation with high swirl was found to have significant improvement in cycle-to-cycle variations of both flow pattern and flow momentum. It was found that the sprays of the multi-hole injector redistribute the intake-generated swirl flow momentum, thereby creating a better-centered higher angular-momentum vortex with reduced variability. The fluid dynamics of swirl/spray interaction was previously demonstrated using high-speed PIV measurements of in-cylinder motored flow. Thermodynamic analysis and optical diagnostics are used here to clarify why swirl improves the combustion more » repeatability from cycle to cycle. Moreover, cycles can experience burning-rate regression during later combustion stages and may or may not recover before the end of the cycle. In-cylinder pressure-based heat-release analysis reveals that the appearance of poor-burn cycles is not solely dependent on the variability of early flame-kernel growth. Engine-performance tests demonstrate that increasing engine speed induces combustion instability, but this deterioration can be prevented by generating swirling flow during the intake stroke. Implementing spray-guided stratified-charge direct-injection spark-ignited (DISI) engines is inhibited by the occurrence of misfire and partial burns. This paper discusses design, evaluation, and application practice enhancements for the use of swirl/vortex technologies as part of a combined sewer overflow and storm-water pollution control system. Simultaneous flow-rate measurement synchronized to sampling times is also necessary. Reliable determination of performance depends principally upon accurate sampling techniques, suspended solids and other pollutant analyses, and settling-velocity distribution of the influent and effluent. When correctly installed with other controls of the combined-sewerage or separately sewered storm-water system, swirl/vortex devices can play an important role more » in combined sewer overflow and storm-water discharge pollution control. Performance of swirl/vortex devices depends on the settling characteristics of the suspended solids and the fraction of dissolved solids in the storm flow. A variety of opinions have developed regarding the application of these technologies, which vary from overwhelming support to reservations of their effectiveness. While different forms of swirl and vortex technologies have been developed during the last thirty years, their major function has been the dual purpose of flow regulation and settleable-solids concentration for combined sewer overflows. New generations of this technology emerged after the EPA versions were developed including the Fluidsep,
These projects resulted in the EPA swirl and helical-bend flow regulators/settleable-solids concentrators and the swirl degritter.
Swirl design series#
Environmental Protection Agency (EPA) conducted a series of projects to develop and demonstrate swirl flow regulator/settleable-solids concentrator (swirl) technology. Swirl and vortex technologies have been with us for over thirty years now, ever since Bernard Smisson incorporated a cylindrical vortex-type combined sewer overflow (CSO) regulator/settleable-solids concentrator into the Bristol, England sewerage system back in the early 1960`s.