http://yetl.yabesh.ir/yetl1/handle/yetl/19033 2026-04-09T02:02:40Z http://yetl.yabesh.ir/yetl1/handle/yetl/4311041 Dynamic Characteristics of Ion Concentration Distribution for Combustion Instability With Different Injection Schemes Du, Minglong; Jia, Xingyu; Feng, Hao; Song, Jun; Li, Jizhen The performance of aerospace vehicles directly depends on the operation of large combustion propulsion devices. Combustion instability has long been an inevitable and challenging problem in the development of large combustion propulsion devices. In this study, the dynamic characteristics of combustion instability under different injection schemes in a Helmholtz pulse combustor were investigated experimentally. The ion concentration signals at different locations in the combustor were acquired to characterize the dynamic process of unsteady combustion with different injection parameters. The flow field characteristics and reactant components distribution of the dual jet flame were simulated numerically. The results indicate that injection schemes with a large fuel injection angle ϕ and nozzle hole spacing are not conducive to combustion stability. A large fuel injection angle ϕ and nozzle-hole spacing L can prevent fuel jet convergence, thus dividing the central flame front into two parts: one is located near the nozzle outlet with fuel-rich combustion, and the other is close to the combustor wall with fuel-lean combustion. The fuel-rich state can more easily stimulate combustion instability than the fuel-lean state. Compared with the original converging jet, the newly established fuel-rich combustion region increases the occurrence of combustion instability. Nevertheless, the excessive fuel injection angle ϕ and nozzle-hole spacing L may result in the peak of the combustion heat release preceding the pressure oscillation, which is not conducive to combustion instability. 2025-01-01T00:00:00Z http://yetl.yabesh.ir/yetl1/handle/yetl/4311008 Method for Predicting the Damping Ratio of Ring Dampers in Radial Standing Waves Du, Chenhong; Wang, Yanrong; Jiang, Xianghua Blisks are utilized by most modern aircraft turbine engines to reduce the weight of rotors and eliminate air leakage between platforms. Ring dampers are widely used to reduce the vibration of blisks and avoid high-cycle fatigue. Two methods are proposed to calculate the damping caused by the radial displacement of the ring damper. First, the analytic method was provided by previous researchers. It is improved to increase the precision on calculating the range of slipping region. Second, a one-dimensional (1D) finite element method with novel iteration process is introduced by us. In this method, the ring damper is modeled using rod elements, and the energy dissipation due to friction is calculated through maximum displacement or time-marching. The damping ratio of the ring damper under arbitrary standing wave modes can be calculated using this novel method. The simulation results show that the 1D finite element method has good mesh independence. Both methods show good agreement in terms of damping ratio and the position of the slipping region. 2025-01-01T00:00:00Z http://yetl.yabesh.ir/yetl1/handle/yetl/4311007 Blade Designs for Improved Multi-Phase Performance in sCO2 Compressors: Optical Diagnostics in sCO2 and Experimental Evaluation With Particle Image Velocimetry Fernandez, Erik; Gabriel-Ohanu, Emmanuel; Vesely, Ladislav; Kapat, Jayanta; Hosangadi, Ashvin; Cooper, Paul This paper presents the second part of a study in which the leading edge and suction surface of a compressor blade was modified to delay onset of phase change for sCO2 compressors operating near the critical point. Using a first-of-its-kind apparatus for the measurement of sCO2 flow fields, Particle Image Velocimetry (PIV) is used for local flow field measurements of two compressor blade geometries: the modified “biased wedge,” and a conventional constant thickness blade. Utilizing the developed hardware, the feasibility of a simple, laser-based diagnostic for qualitatively measuring liquid phase regions, is also presented. The design of the optical diagnostics rig, a discussion of numerous challenges, and necessary considerations involved in performing optical-based measurements like PIV, in sCO2, are discussed. Velocity field measurements for the modified compressor profile show a much lower suction peak compared to a conventional blade. These results validate numerical results at the tested conditions, where the suction side profile of the biased wedge works to minimize the local pressure gradient. 2025-01-01T00:00:00Z http://yetl.yabesh.ir/yetl1/handle/yetl/4311006 Design and Dynamic Analysis of Different Balancing Mechanisms for Development of a Small Direct-Injection Spark-Ignition Optical Engine Velugula, Ravi; Loganathan, Balasubramanian Thiruvallur; Varadhaiyengar, Lakshminarasimhan; Asvathanarayanan, Ramesh; Mittal, Mayank Improving the performance of small engines, which have widespread use in two- and three-wheeled vehicles in several countries, is vital. Recently, direct-injection spark-ignition (DISI) technology, used on moderate- to large-sized engines, offers improved fuel economy, better transient response and reduced emissions. When applied to small-bore engines, DISI, however, further complicates the fuel impingement on in-cylinder surfaces and inhomogeneity in fuel-air mixture formation. Hence there is a growing demand for a comprehensive examination of in-cylinder processes to address these challenges using optical engines. Optical engines, incorporated with elongated piston and a transparent window therein for direct monitoring of in-cylinder events, give rise to increased unbalanced forces and thus lead to increased vibrations. Therefore, it becomes imperative to implement a suitable balancing mechanism to reduce the unbalanced forces within the space constraints of small engines. In the present study, three different balancing mechanisms, i.e., (i) crankshaft with counterweights, (ii) crankshaft with counterweights and primary balancer shaft, and (iii) crankshaft with counterweights and primary and secondary balancer shafts, are designed in solidworks. Subsequently, a dynamic analysis of these mechanisms is conducted using ADAMS/View to investigate the unbalanced forces. The resultant unbalanced forces are compared for different balancing mechanisms. The analysis revealed that the crankshaft with counterweights and primary balancer shaft (i.e., balancing mechanism-II) is suitable for the balancing of the small DISI optical engine (displacement volume of 200 cm3) under investigation. The methodology is helpful in designing and analyzing various balancing mechanisms for optical engines, particularly for small optical engines with space constraints. 2025-01-01T00:00:00Z