Pressure Rise Ratio Research Articles

Research on the effect of different gas release conditions on the explosive boiling of overheated water containing NaCl

High-pressure storage tanks are widely used for transportation due to their convenience. However, sometimes the tanks themselves or the stored medium may become contaminated with impurities. NaCl is one of the most commonly encountered impurities. The pressure response curves of 1.0 mol/L NaCl solution and pure water within a 17L square stainless steel vertical storage tank are being investigated. The experimental results indicate that the pressure rebound is most pronounced when the medium inside the tank releases gas phase. Unlike pure water, NaCl solution still exhibits pressure rebound during pure liquid phase release. High-speed imaging reveals that the addition of NaCl impurities reduces the nucleation radius of bubbles, sharply increases their quantity, and exacerbates boiling phenomena. As the rupture area increases, the remaining liquid level of 1.0 mol/L NaCl is much lower compared to pure water. At the 70 % leakage position, the pressure recovery ratio of both liquids is the highest. After adding NaCl impurities, under all operating conditions, the pressure recovery ratio and pressure rise ratio exceed those observed under pure water conditions. This indicates that the presence of NaCl exacerbates the boiling of superheated liquids and increases the possibility of tank rupture.

Effects of PODE substitution rate and fuel injection timing on combustion, emission characteristic and energy balance in PODE-gasoline dual direct-injection engine

Dual direct injection (DDI) mode allows two kinds of different reactivity fuels to be flexibly injected into the cylinders and offers lower pressure rise rate (PRR), CO and HC emissions than Reactivity Controlled Compression Ignition (RCCI) mode. Thus, a single-cylinder engine was modified to adopt two direct-injection systems to inject PODE and gasoline respectively in this paper. Due to high oxygen content and high cetane number, PODE was selected as a high reactivity fuel to replace diesel in the experiments. The effects of different PODE substitution rates(PSR), PODE injection timing(injP) and gasoline injection timing(injG) on the combustion, emission characteristics and energy balance were studied. The results concluded the using PODE-gasoline mode could increase the indicated thermal efficiency(ITE) and reduce exhaust losses compared to the diesel-gasoline mode. As PSR increased, it led to the increased ITE and effective power, decreased CO, HC emissions. Compared to the PODE late injection mode, the effective power and ITE were higher, and CO, HC emissions were lower in the PODE early injection mode. The coefficient of variation of IMEP(COVIMEP) for the DDI combustion was also in an acceptable range. Furthermore, an early injG could lead to higher ITE, lower COVIMEP, CO and HC.

Study on Dust Explosion of Wheat Starch Inerted by NaHCO3

With the aim of researching the inerting effect of NaHCO3 upon the wheat starch dust explosion, the test of explosion pressure was implemented by 20L spherical explosion test system. The results showed that as NaHCO3 mass fraction increased, the maximal explosion pressure and the maximal explosion pressure rise ratio of wheat starch dust decreased gradually. When 70wt% NaHCO3 was added, the maximal explosion pressure and the maximal explosion pressure rise ratio of wheat starch dust lessened by 73.82% as well as 93.88%, separately. The deflagration flame propagation experiment of NaHCO3 inerting wheat starch was implemented inside a device of the improved Hartmann tube. These consequences showed that velocity and length of the deflagration flame propagation of wheat starch decreased gradually as NaHCO3 mass fraction increased. When 15wt% NaHCO3 was added, peak velocity and average velocity of deflagration flame of wheat starch decreased by 95.30% and 89.69%, respectively. When 20wt% NaHCO3 was added, the deflagration of wheat starch could be completely inerted.

Numerical Simulation and Wind Tunnel Test of a Variable Geometry Auxiliary Inlet for a Wide-Body Aircraft Environmental Control System

A variable geometry auxiliary inlet for a wide-body aircraft environmental control system with moveable deflectors operating in a large mass flow rate range is studied through numerical simulation and wind tunnel tests, which yields a design method for the variable geometry auxiliary inlet with high performance. The characteristics of the flow field are studied by numerical simulation. The results show that the favorable pressure gradient and the roll-up vortices are the major impetus that inhales the incoming flow into the inlet. The law of regulation and the performance variation under different conditions are obtained by wind tunnel test. The flow coefficient increases first but then decreases with the increase in the inlet opening, and the pressure rise ratio and total pressure recovery coefficient increase first and then decrease with the increase in the mass flow rate. In general, under the condition of a high Mach number (Ma > 0.4), the inlet opening of this test configuration should not exceed 50%. The deflectors can maintain the normal work of the environmental control system by moving properly to control the mass flow rate of the auxiliary inlet.

Experimental Investigation of Terminal Shock/Boundary-Layer Interaction with and without Upstream Lateral Confinement

A generic external-compression inlet test model is designed and fabricated to investigate the flow characteristics of terminal shock/boundary-layer interaction for inlet applications with and without upstream lateral confinement. When the leading edge of the sidewall is positioned 150 mm upstream of the duct entrance, the bifurcation height of the shock, the centerline separation length, and the pressure rise ratio at are close to reported values in the literature, although the corner separation herein is minor as compared with previous experiments with thick sidewall boundary layers. However, when the leading edge of the sidewall is aligned with the duct entrance, an obvious increase in the bifurcation point height can be observed, and an increase in centerline separation can be inferred from schlieren photographs. The significantly intensified separation is verified directly by surface oil flow visualization. In addition, the focus previously present in the corner region is replaced by a reattachment node located near the junction region of the bottom plate and sidewall leading edge. The intensification of the separation is attributed to a local high-pressure region caused by the impingement of the postshock subsonic flow onto the sidewalls.

Shock characteristics evolution of detonation waves forward impacting on the solid wall

The forward reflection of detonation waves on the solid wall will lead to a high pressure rise. The research systematically introduced the theoretical, numerical, and experimental exploration on the shock propagation characteristics of detonation waves forward impacting on a solid wall in the present work. The one-dimensional shock theory was carried out to solve the pressure rise ratio in this process. The exact solution and its variation law of a positive increase with filling pressure were expressed. One-dimensional simulations based on the space-time conservation element and solution element method were utilized to reveal the pressure decrease and velocity increase laws for the reflected shock wave. The blockage, oscillation, and attenuation phenomena of detonation waves and reflected shock waves under the effect of the tube–wall reflection were demonstrated in two-dimensional works. Experimental results from the detonation tube pressure test system showed a larger amplitude and duration of the reflected shock wave than the detonation wave. Pressure evolution and the formation of pressure plateaus were consistent with the simulation results. In addition, the time required for the pressure plateaus to decay to 0.5 times the Chapman-Jouget (C–J) detonation pressure is relatively constant under different filling conditions.

Boundary-layer viscous correction method for hypersonic forebody/inlet integration

The aerodynamic shape of the hypersonic forebody/inlet integrated vehicle is usually designed according to the inviscid flow. However, due to the effect of air viscosity, there is a boundary layer flow near the wall surface. In order to get the actual flow characteristics and performance parameters of the inviscid design vehicle close to the inviscid design values, the inviscid design surface must be corrected by considering the viscous boundary layer. In this paper, the theory and method of the boundary-layer viscous correction (BLVC) for the forebody/inlet integrated configuration are studied. Firstly, two modification schemes of the BLVC for the forebody/inlet integrated configuration are proposed. The calculation method of boundary-layer displacement thickness (BLDT) based on the momentum integral equation of steady two-dimensional (2D) axisymmetric compressible flow is described in detail, and two calculation methods of the BLDT are compared and analyzed. Secondly, the numerical simulation method used in this paper and its validation are introduced. Thirdly, an axisymmetric configuration of the forebody/inlet integration is selected as the first case, and two modification schemes of BLVC are studied and analyzed by numerical simulation. The effects of the two modification schemes of BLVC on the internal and external flow characteristics and aerodynamic performance of the axisymmetric configuration of the forebody/inlet integration are compared and analyzed. Finally, a full-waverider configuration of the forebody/inlet integration is selected as the second case, and the second modification scheme of the BLVC is used to modify the full-waverider configuration. The shock wave characteristics and inlet performance parameters of the modified full-waverider configuration are studied by both the numerical simulation and the wind tunnel experiment. The obtained results prove that the calculation method of the BLDT by a numerical integration method to solve the momentum integral equation of the steady 2D axisymmetric compressible flow is correct and the BLVC method and scheme for the forebody/inlet integrated configuration are effective. The modification scheme 1 of the BLVC can only improve the characteristics of forebody shock wave incident on the inlet lip under viscous conditions, that is, to improve the performance of inlet to capture precompressed air flow, while the modification scheme 2 of the BLVC can simultaneously improve the characteristics of forebody shock wave incident on the inlet lip and the characteristics of the lip shock wave cancelled on the shoulder of the inlet under viscous conditions, and make the air flow capture performance of the inlet and the pressure rise ratio at the inlet exit close to those of the inviscid design state.

Physical property effects of the compression process with supercritical carbon dioxide as working fluid

The compressor is one of the key components in the closed supercritical carbon dioxide (S-CO2) Brayton cycle, but its design method is far from mature. It is naturally expected that the well-established design method of the air compressor can provide favorable guidelines, on the basis of further understanding the effects of the physical property on the compressor flow field. Considering that isentropic compression is one of the core physical processes in the compressor, the physical property effects on this process were mainly investigated in this work. Similarity criterion was considered, and the change rate discrepancy of the main variables in this process between S-CO2 and the ideal air was fully analyzed. Results show that S-CO2 is compressed faster than the ideal air in most cases, along with generating smaller Mach number and larger pressure rise ratio. It is noted the important parameter of the static pressure coefficient distribution with S-CO2 in the compression process is almost the same as that with the ideal air at low Mach number, which is conductive to the extension of the air compressor research experience, but it is quite different at high Mach number. The simulation cases about compressor cascade are further applied and prove the suitability of the revealed physical property effects in the compressor passage. Understanding these effects on the compression process is helpful to improve the design method of the S-CO2 compressor.

Two Dimensional Hypersonic Body-Intake Multi-Object Optimization with NSGA-II Algorithm

The forebody/inlet shape of the scramjet engine is significant to airplane performance. A multi-object optimization of hypersonic body-intake configuration is reported in the present work. The optimization system consists of geometry parameterization, mesh deformation, aerodynamic performance evaluation via computational fluid dynamics (CFD) and the top level driving optimization algorithm. In the present work, geometry parameterization is accomplished through B-Spline based free form deformation (FFD) method, volume mesh deformation is computed via inverse distance weight (IDW) method. Aerodynamic performance is evaluated with shear stress transportation model closed Reynolds averaged Navier-Stokes equations. At the top level, optimization is driven by the non-dominated sorting genetic algorithm II (NSGA-II) algorithm. Finally, the present optimization system is applied to a two dimensional hypersonic combined forebody-intake configuration. Numerical result shows that optimization gained improvement of 5% thrust, 9% pressure rise ratio and 7% total mass flow rate, which approved the effectiveness of the present optimization methodology.

Research on performance optimization and fuel-saving mechanism of an Atkinson cycle gasoline engine at low speed and part load

The Atkinson cycle engine plays a key role in the development of hybrid electronic vehicle (HEV) because of greater fuel economy than Otto cycle engine. The thermodynamic analysis shows Atkinson cycle has the significant advantage of cycle efficiency and the ratio of expansion ratio to effective compression ratio and pressure rise ratio have great influence on efficiency. A performance optimization strategy for the Atkinson cycle engine is proposed through analysis of compression ratio range according to cycle efficiency at small pressure rise ratio and optimization of the high compression ratio and the late intake valve closure (LIVC) under the compression pressure constraint. The experimental results show significant improvements in pumping losses and fuel economy are achieved, thus verifying verifies the effectiveness of the optimization strategy and brake specific fuel consumption (BSFC) of is improved by 9% at 2000 rpm@2 bar and 8% at 3000 rpm@3 bar, respectively. The fuel-saving mechanism is investigated in depth. The increase of mechanical efficiency due to the reduction in pumping mean effective pressure (PMEP) is the main reason for the fuel economy improvement at low and medium load, while the increase of indicated thermal efficiency is the main reason at high load. The increase in intake pressure is the main reason for the decrease in PMEP. The Atkinson cycle engine can achieve more obvious constant volume combustion and the combustion quality has been greatly improved. These findings can be used as guidelines for the development of new Atkinson cycle engines.

Effects of the aerothermoelastic deformation on the performance of the three-dimensional hypersonic inlet

The hypersonic inlet is more prone to deform when simultaneously subjected to aerodynamic load and harsh aerothermodynamic load. Moreover, the flow field of the hypersonic inlet is sensitive to configuration. Therefore, it is necessary to investigate the effects of the aerothermoelastic deformation on the flow structure and the performance of the hypersonic inlet. This study develops a loose coupling static aerothermoelastic analysis framework based on the CFD/CSD coupling method, and the one-way and the two-way aerothermal-aeroelastic coupling are both used in the analysis. Furthermore, the effects of the aerothermoelastic deformation on the flow structure and the performance of a three-dimensional hypersonic inlet are studied in detail. The reliabilities of the CFD method and the CFD/CSD coupling method are verified by the validation cases of DLR hypersonic inlet experimental model and the HIRENASD experimental model. The results obtained by the coupling methods are similar. However, the aerothermoelastic deformation obtained through the two-way coupling method is relatively larger, and the effects of the deformation on the inlet performance are more obvious. The maximum of the aerothermoelastic deformation exists at the leading edge of the inlet lip. The deformation changes the shock wave structure near the lip, strengthens the shock wave intensity inside the inlet, increases the length of the separated region and the temperature of the external wall, and changes the flow field of the exit. The aerothermoelastic deformation will lead to the increasing of the mass flow coefficient and the pressure rise ratio; however, it will decrease the total pressure recovery coefficient.

Effects of aeroelasticity on the performance of hypersonic inlet

Effects of the aeroelasticity on the performance of the hypersonic inlet have been investigated numerically in this study. The aeroelasticity has been simulated using the coupled computational fluid dynamics/computational structural dynamics method, which is solved by the in-house code. The unsteady Reynolds-averaged Navier–Stokes equations have been solved in the computational fluid dynamics simulation, and the modal method has been adopted in the computational structural dynamics simulation. Two cases have been utilized to validate the numerical method. Finally, the aeroelasticity has been simulated for inlet plate with different thicknesses. The effects of aeroelasticity on performance parameters and flow structure have been discussed in detail. The results show that the generalized displacements present the “beat” phenomenon in the time domain. The power spectral density of the generalized displacements implies that the aeroelastic instability is mainly caused by the coupling between the fourth- and fifth-order modes. The time-average flow rate coefficient and pressure rise ratio increase relative to the initial value, while the total pressure recovery coefficient decreases. The fluctuation amplitude of the flow rate coefficient is small, while that of the total pressure recovery coefficient and pressure rise ratio are relatively large. Besides, the phases of the three performance parameters are greatly different. Furthermore, the aeroelasticity has significant effect on the shock wave structure especially at the exit of the inlet.

Computational research on load extension route of diesel homogeneous charge compression ignition engine

A quasi-dimension combustion that considers fuel film evaporation is built to simulate rate of heat release of diesel HCCI combustion. The calculation results are in good qualitative and quantitative agreement with the experiment results. Load extension route of HCCI engine is studied based on the validated simulation model. In the process of load extension, the maximum combustion temperature and pressure rise ratio are the single limitation condition in low and high intake pressure respectively. The transformation boundary of single limitation condition is at intake pressure about 1.4 bar. The matching relation between intake pressure and excessive air ratio indicates that excessive air ratio can be taken as feedback signal to control load extension route. Along the ultimate load extension route, load of HCCI engine (IMEP) can be extended to 0.889 MPa by single supercharging mean and be further extended from 0.889 MPa to 1.029 MPa by combined supercharging and LIVC means.

Numerical investigation of impeller trimming effect on performance of an axial flow fan

To study the performance variations of an axial fan after impeller trimming, numerical simulations are executed under the following conditions: trimming quantity of 5%, 10%, and 15% of blade height, with tip clearance changed and unchanged. The effects of trimming quantity and tip clearance on flow field and performance of the axial fan are investigated, and formulae are presented for total pressure rise and flow rate ratio versus impeller diameter ratio and for operating points before and after impeller trimming. The simulated results show that the performance curves after impeller trimming tend to decline. Near the design flow rate, the performance of the fan with unchanged tip clearance is aerodynamically superior to that with changed tip clearance; the former deteriorates at a large flow rate. The margin of parameters provided by design units exceeding the actual operation requires the fan to normally operate to the left of the rated load, therefore, axial fans with tip clearance unchanged after impeller trimming have been found to maintain better performance. The equations, denoting total pressure rise ratio and flow rate ratio versus impeller diameter ratio are available to determine the trimming quantity according to actual requirements of operating points after impeller trimming.

Analysis of Combustion Characteristics and Influencing Factors of Space Dispersed Double-Wall-Jet Combustion System

Based on the ideas of wall-guiding-spray and spatial dispersion, A new type of diesel engine double-wall-jet combustion system is designed. The effect of speed, load and injection condition on the double-wall-jet combustion system is researched by testing, on the double-wall-jet combustion system, the combustion modes for whole working condition is analyzed, the comparison of combustion and performance between the original machine with the new one is carried out. The results showed that: Instantaneous heat release rate of double-wall-jet combustion system shows a single peak. As the speed increases, the corresponding crank angle of ignition retards, the peak outbreak pressure increases and then decreases, the peak instantaneous heat release rate, the peak average temperature, the peak cylinder pressure rise ratio, and the cumulative heat release per unit mass of working gas is reduced. As the load increases, the corresponding crank angles of peak cylinder pressure and gravity center of heat release rate are postponed. With the load increasing, the ignition crank angle corresponds early at low speed, and the ignition point does not change significantly with the load at high speed. The effect of the injector hole diameter/number on the cylinder pressure and instantaneous heat release rate curve is not significant at high speed and large loads, but at low speed and large loads is significant. Cylinder pressure of 6-Φ21 injector is higher than 5-Φ25, the instantaneous heat release rate of 6-Φ21 injector has a trend of a single peak, the instantaneous heat release rate of 5-Φ25 injector has a trend of a double peak and the focus of the heat release rate postponed. With the advancing of injection timing, the ignition crank angle and combustion phase advances, the peak cylinder pressure increases. Injection pressure has little effect on the combustion characteristics. By comparison with the original machine, while maintaining the power performance of the same circumstances, the cylinder pressure and NOx emissions of double-wall-jet engine are reduced in degree, fuel consumption rate is not almost changed, and the same plane rather, smoke intensity is improved at low speed, smoke intensity at high speed smoke high-speed only deteriorates of 0.2-0.3 BSU.

Distinction between the upper explosion limit and the lower cool flame limit in determination of flammability limit at elevated conditions

Previous research showed that at certain conditions, close to the flammability range exists a regime where cool flame may develop either due to elevated temperature or it may be initiated by an ignition source. Propagation of the cool flame in a closed test vessel may double the initial pressure. Such pressure increase exceeds recommended ignition criteria for explosion limit determination that are based on 5 or 7% of pressure rise leading to inaccurate classification of the oxidation phenomena, i.e. cool flame propagation may be classified as hot flame propagation. Two mixtures were tested: n-butane-oxygen (extensively) and C1–C2–oxygen (in limited range), which represent a typical composition in ethylene oxide production, at elevated conditions at their upper explosion limits. Flame development was analysed by flame emission spectroscopy and the post-oxidation mixture was analysed by gas chromatography (GC) to characterise the oxidation mechanism of the flame. Additionally explosion pressure rise, flame temperature, and maximum rate of pressure rise were measured. In all experiments with the pressure rise ratio below two the low temperature oxidation mechanism assisted the flame propagation.

Analysis of additional leakage resulting from the feeding motion of a vacuum-compatible air bearing stage

A rise in pressure is generated when a vacuum-compatible air bearing stage moves in a vacuum condition. This study analyzed this pressure rise phenomenon theoretically and verified it experimentally. Results indicate that the pressure rise was caused by additional leakage resulting from stage velocity, along with adsorption and outgassing of gas molecules from the guide rail surface. Tilting of the stage had a negligible effect because the tilting time was very short. Additional leakage caused by stage velocity was inevitable if the stage incorporated mechanical movements, but rises in pressure caused by adsorption and outgassing could be suppressed by coating the guide rail surface with titanium nitride, to which gas molecules are less likely to adhere. The results also indicate that the pressure rise ratio increased when the air bearing stage operated under high-vacuum conditions.

Characteristic Experiment of Swashplate Type Axial Piston Motor (I)

The purpose of this study is to construct a testing equipment with which several characteristics of the domestically developed swashplate type axial piston motor can be tested and to develop a software with which the data from experiment can be stored and can be applied. The results of the study are as follows; 1) The leakage flow and the torque of the motor being stopped is propotional to supply pressure and their relation can be showed by linear equations. 2) The motor movement is not smooth below 50 rpm but it moves smoothly up 170 rpm. 3) When the motor starts or stops, the pressure rise ratio effects decisively to the max. torque.