An Experimental Study on the Force Coefficient and the Discharge Coefficient of a Safety Valve in Air-water Mixture Flow

Due to the low number of experimental investigations on the sizing of safety valves in multiphase flow, a novel set of measurement data of an air-water mixture is reported. This paper presents an experimental study on three different geometries of safety valves, a poppet valve with jet angle θ = 120°, and two-disc valves with deflection angles θ = 0° and θ = 90°, respectively. Our test rig comprises a pipeline with 42.5 mm inner diameter, spray nozzles to supply the added water quality (water mass fraction) to the pressurized airflow up to 40 % mass fraction and an inlet pressure up to 6.6 bar(g). The time histories of force, valve lift, and pressures were recorded. We present correlation data for the force coefficient and the discharge coefficient. The widely used omega technique for the Homogenous Equilibrium Model (HEM) is employed to predict the theoretical mass flux. The results show that the poppet valve experiences less momentum force and lower mass flow rates compared to disc valves, while the disc valve with deflection angle θ = 90° presents the highest discharged flow rates among the tested geometries. Our most important finding is that up to 60 % relative valve lift and 40 % mass fraction, neither the force nor the discharge coefficient changes significantly compared to the pure-air case. Finally, we propose a new correlation with a single equation for the resultant force and the discharge coefficient as a function of the relative valve lift for all tested water mass fractions.

Analysis method of the cavitation vibration signals in poppet valve based on EEMD

To study the vibration characteristics of the poppet valve induced by cavitation, the signal analysis method based on the ensemble empirical mode decomposition (EEMD) method was studied experimentally. The component induced by cavitation was separated from the vibration signals through the EEMD method. The results show that the IMF2 component has the largest amplitude and energy of all components. The root mean square (RMS) value, peak value of marginal spectrum, and center frequency of marginal spectrum of the IMF2 component were studied in detail. The RMS value and the peak value of the marginal spectrum decrease with a decrease of cavitation intensity. The center frequency of marginal spectrum is between 12 kHz and 20 kHz, and the center frequency first increases and then decreases with a decrease of cavitation intensity. The change rate of the center frequency also decreases with an increase of inlet pressure.

Conceptual Design and Finite Element Fatigue Life Analysis of a Poppet Valve Spring Compressor

In the overhauling of the internal combustion engine, a lot of tools are used and among them is the poppet valve spring compressor. In Ghana, auto mechanics at the “way-side” garages make use of improvised tools, such as pipes, pliers, and push rods, for compressing valve springs. However, there are some challenges associated with the usage of these tools which include misplacement of cotters, injuries, and sometimes valve bends. In this work, a review of some of the existing designs of the improvised tools was considered. Also, a survey was conducted to seek the opinion of users (auto technicians and/or mechanics) of the tools. A design was made for spring compression by incorporating a magnet with a pull force of 679.78 N to take care of the removal of cotters during valve assembly dismantling. In this research, an efficient and user-friendly poppet valve spring compression tool with a total mass of 0.88 kg was designed. Finite element analysis (FEA) was performed on the upper and lower parts of the tool to examine its response due to the loads that act on it during operation. It was discovered from the analysis that the upper frame of the valve spring compressor experienced the highest von Mises stress of 59.77 MPa at the neck region, whilst the corresponding fatigue analysis showed a maximum fatigue life of 8.355 × 109 cycles.

Numerical study of the effect of split direct injection on the lean-burn combustion characteristics in a poppet-valve two-stroke gasoline engine at high loads

Poppet-valve two-stroke gasoline engines can increase specific power of four-stroke gasoline engines with the same displacement. But knocking combustion may also occur at high loads in two-stroke engines. The application of stratified lean-burn on poppet-valve two-stroke gasoline engines can avoid knocking and increase combustion stability. To investigate the effect of the mixture stratification on lean-burn events at high loads, simulation was conducted in different split direct injection conditions with constant fuel mass when equivalence ratio is 0.625. Results show that most fuel distributes near the center of the cylinder at any second direct injection ratio ( rSOI2). At different rSOI2s, auto-ignition occurs during flame propagation, causing shortened combustion duration. Auto-ignition causes the second peak of the heat release rate. The second peak of the heat release rate first decreases and then increases with increased rSOI2. Indicated mean effective pressure and indicated thermal efficiency increase with increased maximum pressure rise rate. The maximum indicated thermal efficiency of 42% can be reached without knocking combustion at 1500 rpm. The proportion of fuel mass through auto-ignition in the cylinder is an important factor to change the indicated thermal efficiency of a lean-burn engine at high loads.

Simulation of Cavitating Jet Through a Poppet Valve with Special Emphasis on Laminar-Turbulent Transition

One of the major problems in oil-hydraulic poppet valve is the deteriorated performance accompanied by occurrence of cavitation. This is mainly a consequence of lack in understanding of the cavitating jet, which has inhibited the development of sufficiently general and accurate models for prediction of its performance. In the current paper, a two-phase volume of fluid (VOF) methodology combined with Schnerr-Sauer cavitation model is employed to perform quasi-direct transient fully three-dimensional calculations of the cavitating jet inside a poppet valve, with special concern on the laminar-turbulent transition. The numerical results allow separate examination of several distinctive flow characteristics, which show agreeable consistency with experimental observation. The periodic evolution of cavitation structure is related to temporal development of large-scale structure. The potential core indicated by velocity distribution, however, assumes a similar flow pattern regardless of temporal evolution of large-scale eddy. According to the different flow characteristics, the transitional process is divided into several parts, including laminar part, waving fluctuation, cross-linked vortex segments and cloud of cavitating vortexes. A comprehensive discussion on the transition is performed based on the numerical results, with primary concern on the governing mechanisms, including the formation of coherent structure organized as paired vortex, development of instability together with its effects on the coherent structure, and interaction between the vortexes. The streamwise vorticity strength accounts for less than 10% of the total vorticity in the cross-link region. It reveals that the breakdown of paired coherent structure is a result of the successive pairing process generated from combination of longitudinal and circumferential perturbation, instead of the growth of streamwise vortices as in the case of submerged circular jet.

Visual experimental investigation on the stability of pressure regulating poppet valve

The unstable vibration of a poppet valve drastically fluctuates pressure which directly affects the stability, reliability and safety of a hydraulic system. The unstable vibration of the poppet and cavitation is studied using visual experiments. Experimental results show that for a poppet valve, an orifice at the front of the valve cavity, the compressibility of oil in the sensitive cavity will lead poppet to unstable vibrations. For poppet valve without orifice, the instable vibration appears as three states: impact valve seat, transition (impact or non-impact valve seat occurs randomly) and does not impact valve seat. When poppet impacts valve seat, there will be severe cavitation phenomenon at the valve port. Although poppet does not impact valve seat, the cavitation come up is affected by the pressure difference at the port or vibration amplitude of the poppet. In addition, both of the flow pulsation of the hydraulic pump and the coupling between the poppet and pipeline system will lead the poppet to be unstable.

Comparative study on the improvement of the gas exchange process efficiency of a high speed IC engine using swinging valve

Using poppet valves to control the air-fuel mixture entering and leaving the combustion chamber of an engine is just one among many other more flow efficient alternative solution. The geometry of the poppet valve and its valve seat are the main causes of the flow restriction in the internal combustion engines. The engine downsizing concept dictates to obtain more power from a given engine volume, therefore proportionally more air should be drawn into the cylinders to burn more fuel. These criteria best fulfilled with a new Swinging Valve (SwV) solution that enables the unhindered flow of air and exhaust gas through an engine’s cylinder. The filling of a cylinder is improved while the pumping losses are decreased. In this experiment, a Super Flow SF600 flow bench was used to examine a Suzuki SV650 motorcycle engine’s normal poppet valve cylinder head and a Swinging Valve cylinder head was constructed as well. First the flow parameters of the original cylinder head were obtained then the Swinging Valve head was investigated in the same way. The outcomes of the tests show the superiority of the new concept. The results will also be the base of further 0D/1D engine simulations.