This is of practical significnance for the prediction of noise generation by turbomachinery, since rotating blade rows can produce significant mean swirl downstream. We demonstrate that the presence of swirl can significantly reduce the amplitude of acoustic modes in the pipe. At O(1) we determine local wave numbers according to the parallel-flow theory of Atassi, while at O(É›) a secularity condition yields the variaition of the modal amplitudes along the axis. WKB analysis is applied using É›, the mean axial gradient of the cylinder walls, as the small parameter. We consider the practically important case in which the swirl Mach numbers are comparable to those of the steady axial flow. The coupling leads to separate families of modes, driven by compressibility or by the swirl, which must be treated separately.
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The unsteady flow is decomposed into vortical and irrotational components, and the steady vorticity means that unlike in standard rapid distortion theory these components are coupled, as in recent work by Atassi, Tam and co-workers. We consider the propagation of small-amplitude waves through swirling steady flow conveyed by a circular pipe whose cross-sectional area varies slowly in the axial direction. Zeng, Wei Sjöberg, Magnus Reuss, David L.Īcoustics of swirling flow in a variable area pipe Conversely, swirl flow always convects the spark plasma towards one 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 combustionmore » 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. Zeng, Wei Sjöberg, Magnus Reuss, David L. The role of spray-enhanced swirl flow for combustion stabilization in a stratified-charge DISI engine The results revealed that the intake swirl has great influence on engine performance. The maximum brake power of 9 HP was achieved for modified cylinder head. For same operating conditions, the brake power and brake specific fuel consumption was improved by 6% and 7% respectively with modified cylinder head compared to old cylinder head. In addition, the performance of engine was compared for both modified and old cylinder head. Later, the overall performance of 435 CC DI diesel engine was measured using modified cylinder head.
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The intake swirl intensities of modified cylinder head were measured in swirl test rig at different valve lifts. Modifications in inlet manifold geometry have been suggested to achieve optimized swirl for the better mixing of fuel with air. In the present work, the effect of inlet manifold geometry and swirl intensity on the direct injection (DI) diesel engine performance was investigated experimentally. Sharma, Vinod Kumar Mohan, Man Mouli, Chandra Effect of intake swirl on the performance of single cylinder direct injection diesel engine