Peak Pressure Values Research Articles

A study on raise blasting and blast-induced vibrations in highly stressed rock masses

In deep underground mining, the damage evolution and vibration response mechanisms of rock caused by cut blasting are different from those of shallow rock. It is essential to understand the mechanisms for underground engineering safety. In this study, field raise blasting with vertically parallel and dense bunch longholes was designed and performed at the Shaxi underground mine in China. The raise contour and the blasting vibration were measured in the field, and regression analyses of the peak particle acceleration (PPA) were performed. Then, a numerical model considering the effect of in situ stress was developed and calibrated to simulate raise blasting excavation. The damage contours show that the in-situ stress can reduce the radial fractures outside the raise, but has little influence on the crater. The vibration analyses indicate that the PPA and the average frequency (AF) decrease with an increasing in-situ stress. The confinement effect of in-situ stress on vibration characteristics is discussed, and blast loading relative pressure curves are presented for a demonstration. It is determined that the relative pressure peak value decreases, and the rising time and duration time increase with an increasing the in-situ stress; as a result, the blast-induced vibration is lower in amplitude and AF. In terms of the frequency, the vibration from a higher in-situ stress is more harmful to structures. A short-delay blasting model was conducted, and the results show that it can effectively reduce the structural vibration damage caused by cut blasting.

Development of novel customized pressure distribution surface for reduction of pressure ulcers using additive manufacturing technology

PurposeThis research aims to focus on developing a customized support surface using additive manufacturing (AM) for effective pressure relief for patients who are in bed or wheelchair suffering from pressure ulcers (PU).Design/methodology/approachA novel customized support surface is developed using AM technology incorporated with magnetic levitation and ball and socket mechanisms. Magnetic levitation provides cushioning effect for the developed cushion to users who are sitting in a wheelchair and increases the rate of healing. The ball and socket mechanism provides the user body's self-adaptive mechanism and reduces shear and friction forces between the surfaces of the additive manufactured cushion and the human buttocks.FindingsFrom the results of ISO 16480-6 biomechanical standardized tests, the additive manufactured support surface performed better than, or on par with, the most widely available commercial cushions. It is evident that the developed cushion’s peak pressure values are lower when compared with other cushions. The overall efficiency of the developed cushion was qualitatively reported; 67% of people felt it was excellent and 22% of people responded as good and 11% were satisfactory. Henceforth, the overall effectiveness of the developed support surface provides a better experience to the end-user in the view of PU reduction.Originality/valueA developed additive manufactured customized support surface will be an alternative approach for the reduction of PU, and it overcomes the drawbacks faced by the currently available cushions.

Kinematics and kinetics comparison of ultra-congruent versus medial-pivot designs for total knee arthroplasty by multibody analysis

Nowadays, several configurations of total knee arthroplasty (TKA) implants are commercially available whose designs resulted from clinical and biomechanical considerations. Previous research activities led to the development of the so-called medial-pivot (MP) design. However, the actual benefits of the MP, with respect to other prosthesis designs, are still not well understood. The present work compares the impact of two insert geometries, namely the ultra-congruent (UC) and medial-pivot (MP), on the biomechanical behaviour of a bicondylar total knee endoprosthesis. For this purpose, a multibody model of a lower limb was created alternatively integrating the two implants having the insert geometry discretized. Joint dynamics and contact pressure distributions were evaluated by simulating a squat motion. Results showed a similar tibial internal rotation range of about 3.5°, but an early rotation occurs for the MP design. Furthermore, the discretization of the insert geometry allowed to efficiently derive the contact pressure distributions, directly within the multibody simulation framework, reporting peak pressure values of 33 MPa and 20 MPa for the UC and MP, respectively. Clinically, the presented findings confirm the possibility, through a MP design, to achieve a more natural joint kinematics, consequently improving the post-operative patient satisfaction and potentially reducing the occurrence of phenomena leading to the insert loosening.

Analysis of the Deformation Law of Deep and Large Foundation Pits in Soft Soil Areas

Taking a deep excavation in Suzhou soft soils adopting three support schemes as the background, the excavation performance metrics, including the heave and lateral deformation of diaphragm walls, surface vertical deformation, vertical deformation of surrounding buildings, and earth pressure, are thoroughly investigated based on 15 excavation cases collected in the soft soil area of Suzhou. Based on the analysis of monitoring data, some findings were achieved: the foundation pit deformation is greatly affected by the spatial effect. The existing station can constrain the foundation pit deformation. Benefiting from the combination of various support solutions, the average maximum deflection of the diaphragm wall is 0.10% He. The maximum lateral movement depth of the diaphragm wall (δhm) is mainly located at (He-7, He+12.5). The vertical deformation of the wall top is greatly affected by the excavation exposure time and soil conditions. The heave range of the wall top is (−0.08∼0.26%) He. Under the action of the displacement of the diaphragm wall to outside the pit and the upward displacement of the wall top, the ground surface is uplifted, and the maximum uplift is (0.02∼0.14%) He, ranging from 0.12δhm to 1.13δhm. The maximum surface settlement is (−0.01% ∼ −0.15%) He, ranging from −0.22δhm to −3.11δhm. The form of building heave is mainly affected by the surface heave and the distance from the diaphragm wall (d). When d is within a certain range, there is a heave settlement difference between the adjacent side and the opposite side of the excavation, and the adjacent side undergoes mostly subsidence, while the opposite side undergoes mostly uplift. The peak value of the apparent earth pressure (AEP) envelope is 0.59γHe, which falls within (0.47∼0.78) He. The calculation scheme proposed by Kim can be used to predict the AEP for multiple soil types.

Numerical investigation on the water entry of a 3D circular cylinder based on a GPU-accelerated SPH method

As a typical fluid–structure interaction (FSI) problem, water entry involves violent fluid flows and changing free surfaces, which presents great challenges for numerical modeling. Smoothed Particle Hydrodynamics (SPH) is a Lagrangian particle method that has natural advantages in modeling free surfaces and moving interfaces. However, SPH is computationally expensive due to the search of particle–particle interactions, and it causes great difficulties for performing large-scale simulations of 3D FSI problems. In this work, we present an accelerated SPH framework based on the Graphics Processing Unit (GPU) techniques to study water entry problems. The multi-threading programmed by Compute Unified Device Architecture (CUDA) is applied to enhance the computational performance in terms of efficiency and scale. Compared to the Single-CPU-based strategy, the newly presented GPU-accelerated SPH method is computationally more efficient with a speedup over hundreds times and enables a larger memory available for large-scale simulations of around ten million particles for three-dimensional cases. With the GPU-accelerated SPH method, the 3D water entry of a circular cylinder is investigated with some kinematic and dynamic characteristics explained. The results demonstrate that the rotational characteristic of a 3D cylinder in water entry is related to the dimensionless number γ defined as the ratio of the initial inclination angle to the initial velocity angle. The rotation of a cylinder changes from anticlockwise to clockwise with the increase in γ. A transition value of γ exists between the anticlockwise to clockwise rotation, which focuses on the range from 1.0 to 6.0. Meanwhile, the water entry of a 3D circular cylinder leads to a violent impact on the bottom of the cylinder, which causes a peak value of pressure being a maximum value at the early stage of the water entry. It is also indicated that the selection of the initial inclination angle has a great effect on the maximum pressure.

Thermodynamic effects on single cavitation bubble dynamics under various ambient temperature conditions

Thermodynamic characteristics and their effects on single cavitation bubble dynamics are important to elucidate the physical behaviors of cavitation phenomena. In this study, experimental and numerical methods were utilized to explore the thermodynamic effects on single cavitation bubble dynamics under various ambient temperature conditions. A series of experiments was performed to generate a single cavitation bubble at ambient temperatures between 20 and 80 °C using a laser-induced method and a high-speed camera to observe the dynamic behaviors of bubbles. By increasing the ambient temperature, a nonspherical bubble shape with a jet flow at the bubble rebound stage was observed. Next, the numerical simulation results in terms of the bubble radius and bubble shape were validated with the corresponding experimental data. Generally, the results exhibited reasonable agreement, particularly at the later collapse and rebound stages. Critical hydrodynamic and thermodynamic mechanisms over multiple oscillation stages at different ambient temperatures were analyzed. The bubble behaviors and their intensities were numerically quantified with respect to the bubble radius, collapsing time, internal pressure, internal temperature, and phase transition rate parameters. The results showed that the maximum bubble radius, first minimum bubble radius, and collapsing time increased with an increase in the ambient temperature. Nevertheless, the peak values of the internal pressure and internal temperature decreased with an increase in the ambient temperature. Generally, the bubble collapsed less violently at high temperatures than at low temperatures.

Evaluation on Distribution Characteristics of Pore Water Pressure within Saturated Pavement Structure Based on the Proposed Tire-Fluid-Pavement Coupling Model

To investigate the flow characteristics of pore water in asphalt pavement and the variation law of the pore water pressure under vehicle loading, a novel method based on BA network and quartet structure generation set method was proposed to reconstruct the three-dimensional (3D) pavement model with pores. The permeability coefficient and the gradation curve were adopted to evaluate the reliability and stability of the random growth pavement model. Then, the tire-fluid-pavement coupling model was established with FLUENT 3D based on the fluid Mie–Gruneisen state equation. According to the built fluid-solid coupling model, the pressure-velocity coupled finite volume algorithm was applied to study the distribution of the pore water pressure in asphalt pavement. Results show that the pore water pressure in asphalt pavement decays periodically with time under vehicle loading. For different types of asphalt pavement, the pore water pressure in open-graded friction course (OGFC) pavement is the smallest during the whole process. Moreover, the peak values of the pore water pressure decrease in the order of asphalt concrete (AC) pavement, stone mastic asphalt (SMA) pavement, and OGFC pavement. The maximum negative value of the pore water pressure is generally less than 0.3 times the maximum positive values. As for saturated pavement pores, the pore water pressure is hardly affected by the water film thickness. The positive peak value of the pore water pressure increases on an approximate parabolic curve as the vehicle speed improves gradually, while the negative one remains largely unchanged. The results are expected to help reduce tire hydroplaning risk and provide guidance for the selection of asphalt mixtures of drainage asphalt pavement.

Nanoparticle Components and Number-Size Distribution of Waste Cooking Oil-Based Biodiesel Exhaust Gas from a Diesel Particulate Filter-Equipped Engine.

An experimental study of the particulate matter (PM)-related emissions from the combustion of waste cooking oil (WCO)-based biodiesel-blended (0%, 30%, and 100% v/v) fuels in a four-cylinder diesel particulate filter (DPF)-equipped engine was carried out. A laboratory-scale DPF under the controlled conditions was installed into an aftertreatment system, and the PM mass and number characteristics were investigated. The combustion analysis based on in-cylinder pressure shows that the added WCO shortened the ignition delay, advanced the combustion ignition, and increased peak pressure values compared to conventional diesel fuel. The WCO increase in specific fuel consumption led to a slight reduction in brake thermal efficiency. The WCO-fueled engine showed reduced PM and total unburned hydrocarbon but increased nitric oxide emission. The nucleation and accumulation were characterized for nanoparticle number and size distribution. The particle number (PN) concentration in total was declined to smaller values when fueling with WCO. In the thermogravimetric analysis, the PM of WCO oxidized to a greater level than that of diesel fuel, which was observed by the weight loss rates during the specified heating program. WCO lowered the elemental carbon (EC) part of PM than diesel fuel. When equipping an exhaust system with DPF, the EC and the total PN drastically reduced while the particle size slightly increased. The use of DPF with the WCO biodiesel mitigated both EC and organic carbon components of the captured particles of the released PM.

Research on the influence of different heating zone lengths on pressure waves and a newly designed method of pressure wave mitigation in railway tunnels

In this paper, through experimental and numerical simulation methods, the influence of the tunnel heating zone length on the pressure wave peak and temperature field changes is investigated in tunnels with different heating zone lengths. The accuracy of the applied simulation algorithm is verified against experimental data from moving model tests. Via numerical simulations, the changes in the pressure wave peak value and temperature field are explored with five heating zone lengths. For the compression wave, this research revealed that when LH (length of the heating zone) < LT (length of the train) and that with an increase in LH, the peak value of the initial compression wave notably decreases. When LH > LT, the compression wave peak value remains basically stable. In regard to the expansion wave at tunnel measurement points, for L (from tunnel entrance) ⩽ 110 m, the initial expansion wave peak exhibits small fluctuations. At L > 110 m, with an increase in the heating zone length, the peak value of the expansion wave peak gradually decreases. In addition, the dynamic temperature field changes. The obtained research results provide a new idea to reduce the peak pressure value in a tunnel. In addition, this study provides a method for pressure wave mitigation during tunnel design and guidance for passenger comfort improvement in future city railway tunnels.

Simulation study on in-cylinder combustion and pollutant generation characteristics of PODE/methanol blends

In order to cooperative control particulate matter (PM) and nitrogen oxides (NOx) emissions from compression ignition engines, the coal-based oxygenated fuels polyoxymethylene dimethyl ethers (PODE) and methanol are selected as diesel alternative fuels. The numerical model of in-cylinder combustion is established by CFD simulation platform coupling PODE/methanol chemical reaction mechanism and then in-cylinder combustion and pollutant generation of PODE/methanol blends under various methanol ratios, fuel injection parameters and intake pressures conditions are calculated and analyzed. Results show that compared with pure PODE, the maximum combustion pressures of the blends with 30% methanol increases by 3.7%, the combustion duration is shortened by 1.2°CA, and NOx emissions decrease by 16.1%. Soot emission of the blends decreases with the increase of methanol ratio. Both the advance of injection timing and the increase of injection pressure lead to the increased peak values of in-cylinder pressure and temperature of the blends, the advance of combustion heat release starting point, the reduction of combustion duration and the increase of NOx emissions. However, soot emission shows an overall downward trend. The increment in intake pressure significantly reduces the in-cylinder temperature and the emissions of NOx and soot, which effectively alleviates the trade-off relationship between NOx and soot.

Effects of Minimalist Footwear and Foot Strike Pattern on Plantar Pressure during a Prolonged Running

The use of minimalist shoes (MS) in running involves changes in running mechanics compared to conventional shoes (CS), but there is still little research analysing the effects of this footwear on plantar pressure, which could help to understand some risk injury factors. Moreover, there are no studies examining the effects of a prolonged running and foot strike patterns on baropodometric variables in MS. Therefore, the aim of this study was to analyse the changes produced using MS on plantar pressure during a prolonged running, as well as its interaction with the time and foot strike pattern. Twenty-one experienced minimalist runners (age 38 ± 10 years, MS running experience 2 ± 1 years) ran with MS and CS for 30 min at 80% of their maximal aerobic speed, and mean pressure, peak pressure, contact time, centre of pressure velocity, relative force and contact area were analysed using a pressure platform. Foot strike pattern and time were also considered as factors. The multivariable linear regression mixed models showed that the use of MS induced, at the end of a prolonged running, higher peak pressure (p = 0.008), lower contact time (p = 0.004) and lower contact area (p &lt; 0.001) than using CS. Also, runners with forefoot strike pattern using MS, compared to midfoot and rearfoot patterns, showed higher mean and peak pressure (p &lt; 0.001) and lower contact time and area (p &lt; 0.05). These results should be considered when planning training for runners using MS, as higher peak pressure values when using this type of footwear could be a risk factor for the development of some foot injuries.

The transition to turbulence in rarefaction-driven Rayleigh–Taylor mixing: Effects of diffuse interface

Effects of interface diffusion on the transition to turbulence in rarefaction-driven flows are numerically investigated via Implicit Large-Eddy simulation. Three-dimensional, multimode perturbations are imposed on the diffuse interface between Air and SF6, with various diffusion layer thicknesses. A non-constant acceleration ranging from 103g0 to 104g0, where g0 is the acceleration due to gravity, is generated by the interaction between the interface and a rarefaction wave. Evolution of first- and second-order statistics, instantaneous flow structures, and the power spectrum of turbulent kinetic energy as well as spatial distributions of energy budget are evaluated, in order to confirm the accuracy and robustness of the mixed mass transition criterion proposed here. Meanwhile, it turns out that transitional behaviors are mainly governed by Reynolds normal stresses in the plane perpendicular to the streamwise direction. Furthermore, as interface diffuses, the decrease in peak values of pressure and advection components dominated in the laminar regimes, particularly at the bubble tips, eventually leads to transition delay.

Pressure field in the reservoir and well, taking into account the dynamic level during the selection and subsequent shutdown

An analytical solution of the non-stationary filtration problem is presented, taking into account the change in the dynamic level of the fluid in the well during extraction with a variable flow rate, which made it possible to construct calculation formulas for the pressure field in the well when operating at a constant pump performance and subsequent shutdown. The problem contains the equation of piezoconductivity for non-stationary plane-radial filtration in a formation surrounded by an impermeable bottom and tire. It also includes an integro-differential condition connecting the pressure fields in the well and the reservoir, the condition of equality of pressures at the outlet from the reservoir to the well, the absence of disturbances at the initial time and in remote sections of the reservoir. When constructing an exact analytical solution of the problem in dimensionless variables, the Laplace — Carson integral transformation with respect to time was used. The originals of the solution are also obtained analytically and contain the Bessel functions of the zeroth and first orders. The general analytical solution for the pressure during extraction with a constant flow rate and subsequent shutdown is written using the Heaviside function. Based on the solution found, computational experiments were performed in which the reservoir parameters of the oil-saturated reservoir are varied, and pump stops are performed at various stages of well operation: relaxation, transitional and stabilization. It has been established that the main influence on the dynamics of the pressure field is exerted by the permeability of the reservoir. Reducing the displacement capacity of the reservoir by an order of magnitude leads to an increase in the amplitude of the pressure perturbation by 25-35%. However, the influence of this parameter does not exceed the contribution of permeability. The contribution of the reservoir porosity is less than 6% of the peak pressure values in the stabilization mode. The viscosity of the sampled fluid has a significant impact on the pressure field recorded in the well.

Improvement and evaluation of ATWS Protective Signal and mitigation system for ACPR1000 nuclear power plant

At the event of Loss of Normal Feed Water-An Anticipated Transient without Scram (LOFW-ATWS) in ACPR1000 unit, there exists the primary overpressure risk probability when the regulation function of temperature regulation (R) rods and power regulation (G) rods cannot work timely or lost. In order to reduce primary pressure and avoid the overpressure risk in this transient process, this paper proposes the improvement scheme of ATWS protective signal and mitigation measure which adds shutting-down action of coolant pumps, and then adopts THEMIS program to analyze ATWS transient to verify this scheme. The verification results indicate that the improvement scheme can effectively reduce the peak value of primary pressure and eliminate the overpressure risk in LOFW-ATWS event. This improvement scheme has been adopted in the design of Yang Jiang Nuclear Power Plant (NPP) 5&6 units in China.

Influences of High-Speed Train Speed on Tunnel Aerodynamic Pressures

To comprehensively investigate the characteristics of aerodynamic pressures on a tunnel caused by the whole tunnel passage of a high-speed train at different speeds, we conduct a series of three-dimensional numerical simulations. Based on the field test results obtained by other researchers, the input parameters of our numerical simulation are determined. The process of a high-speed train travelling through a railway tunnel is divided into three stages according to the spatial relationship between the train and tunnel. Stage I: before train nose enters the entrance; Stage II: while the train body runs inside the tunnel; Stage III: after the train tail leaves the exit. The influences of high-speed train speed on the tunnel aerodynamic pressures of these three stages are systematically investigated. The results show that the maximum peak pressure value decreases with increasing distance from the entrance and increases with increasing train speed in Stage I. There is an approximately linear relationship between the three types of maximum peak pressure (positive peak, negative peak, and peak-to-peak pressures) and the power of the train speed in Stage II. These three types of maximum peak pressure values of the points near tunnel portals increase with increasing train speed in Stage III. Moreover, these three types of maximum peak pressure in the tunnel’s middle section at different train speeds are more complex than those near the tunnel portals, and there is one or more turning points due to the superimposed effects of different pressure waves.

The Effect of Postmenopausal Osteoporosis on Middle Ear Resonance Frequency.

Background: The effect of postmenopausal osteoporosis on the middle ear mechano-acoustic system is unknown. The aim of this study is to investigate whether or not middle ear resonance frequency is affected in females with postmenopausal osteoporosis.Methods:The study included postmenopausal women aged 45-60 years, separated into 2 groups as females with postmenopausal osteoporosis and healthy postmenopausal females (control group). A detailed anamnesis was taken from all subjects and then the ear, nose, and throat examinations were done followed by pure tone audiometry, tympanometry, and multifrequency tympanometry tests. The groups were compared in respect of pure tone average, bone conduction threshold, RF, static admittance, and tympanometric peak pressure values.Results: The mean age of the patients was 59.2 ± 4.53 years (range, 48-65 years) in the postmenopausal osteoporosis group and 57.11 ± 4.27 years (range, 48-65 years) in the control group (P > .05). The mean resonance frequency values for the postmenopausal osteoporosis and control group were 954.41 ± 127.47 and 935.29 ± 126.39 Hz (P > .05 ). The mean static admittance values for the postmenopausal osteoporosis and control group were 0.82 ± 0.33 and 0.85 ± 0.3 mmho, and mean tympanometric peak pressure values were −7.35 ± 18.52 and −6.94 ± 19.52 daPa (P > .05 for both static admittance and tympanometric peak pressure). The mean pure tone averagevalues for the postmenopausal osteoporosis and control group were 20.96 ± 6.82 and 15.60 ± 7.81 dB, and mean bone conduction threshold values were 17.57 ± 6.03 and 12.10 ± 6.52 dB (P < .05 for both pure tone average and bone conduction threshold).Conclusions: The results showed that the middle ear resonance frequency values were not affected in postmenopausal osteoporosis patients, but there was seen to be greater sensorineural hearing loss in females with postmenopausal osteoporosis compared to healthy postmenopausal females.

Effect of a novel shrinkage-reducing polycarboxylate superplasticiser on plastic shrinkage cracking of mortars

Plastic shrinkage cracking propagating at early ages inevitably impairs the performance of concrete structures. To mitigate this, using a recently developed shrinkage-reducing polycarboxylate superplasticiser (SR-PCA) with outstanding shrinkage-reducing and water-reducing effectiveness can be a promising approach. The present work aims to investigate the effect of SR-PCA on plastic shrinkage cracking and to clarify the underlying mechanisms. For comparison, a traditional polyether type shrinkage reducing admixture (SRA) and a polycarboxylate superplasticiser (PCA) were also used. Based on the investigations on horizontal shrinkage, settlement, bleeding, evaporation mass loss, cement hydration, surface tension of pore fluid and capillary pressure, the underlying working mechanisms of SR-PCA were identified. The results indicate that SR-PCA is able to reduce the crack area, maximum crack width and average crack width by up to 55, 48 and 50%, respectively. Furthermore, prolonging the bleeding duration and initial time of capillary pressure build-up caused by retarding the cement hydration, lowering the evaporation mass loss, and a lower development rate of capillary stresses and capillary pressure peak value induced by decreasing the surface tension of pore fluid are responsible for preventing the plastic shrinkage cracking of mortars containing SR-PCA.

A comparative study on the turbulent explosion characteristics of syngas between CO-enriched and H2-enriched

Syngas, containing mostly CO and H2, has variant explosion properties for the specific contents. For a further understanding, a comparative study on the turbulent explosion characteristics of syngas between CO-enriched (the mole ratio of CO was 70%) and H2-enriched (the mole ratio of H2 was 70%) were conducted at different equivalence ratios (φ, from 0.4 to 3.0) and turbulent intensities (u'rms, from 0 to 1.309 m/s). The peak value of maximum explosion pressure (pmax) was attained in the stoichiometric explosion of H2-enriched syngas but in fuel-rich explosion of the CO-enriched, the growth extents of pmax seemed more sensitive to u'rms for H2-enriched syngas compared to CO-enriched syngas. The lowest values of explosion duration (tc) was attained in fuel-rich explosions for both CO-enriched and H2-enriched syngas but different corresponding φ to the lowest tc, the phenomena were analyzed from the aspects of ignition delay time, laminar burning velocity, intrinsic instabilities, and flame/turbulence interaction. Finally, the pressure rising was comparatively observed, the maximum pressure rise rate ((dp/dt)max) expressed more similar variation regulations to tc rather than pmax, which meant flame propagation speed plays a more important role on the evolution of pressure rising.

On the effects of the number of baffles in sloshing dynamics

ABSTRACT This study examines the effect of the number of perforated baffles in sloshing phenomenon in a partially filled tank. The natural frequencies in one-, two- and no-baffle cases are experimentally obtained; change in natural frequencies and reduction in sloshing impacts due to baffles are reported. It is observed that adding the second baffle has a minor effect in damping the sloshing loads at non-resonance frequencies in comparison to ones obtained in one-baffle sloshing tests. Although the natural frequency is significantly increased and pressure distribution profile is altered at higher oscillation frequencies in two-baffle case, the significant reduction in peak pressure values is observed at the frequencies near the natural frequency in one-baffle case. The results indicate that the number of the baffles should be optimised considering the natural frequency of the carrier and external excitation frequencies for the purpose of weight minimisation, fast loading and unloading of the tanks.

Experimental study on the high load extension of PODE/methanol RCCI combustion mode with optimized injection strategy

The polyoxymethylene dimethyl ethers (PODE)/methanol reactivity controlled compression ignition (RCCI) mode was realized by direct injection of PODE as high-reactivity fuel to ignite pre-mixed methanol as low-reactivity fuel in a high-pressure common-rail diesel engine. The effects of load extension ratio (LER) on in-cylinder combustion, emission characteristics and fuel economy of RCCI engine were investigated, and the influences of PODE injection strategy on the high-load extension of PODE/methanol RCCI mode were also systematically studied, including the start of main-injection (SOImain), start of pilot-injection (SOIpilot) and pilot-injection quantity (PIQ). The results show that with the increase of LER, the peak values of in-cylinder pressure and heat release rate of RCCI mode increase, the brake thermal efficiency (BTE) and the hydrocarbons (HC), carbon monoxide (CO) and unregulated emissions also increase, but the increase of the ringing intensity (RI), the coefficient of variation of IMEP (COVIMEP) and nitrogen oxides (NOx) limit the further increase of LER. The delay of SOImain can effectively reduce RI, but it will lead to the deterioration of CO and HC emissions and fuel economy. The pilot-injection strategy can weaken the trade-off relationship between NOx and soot emissions and improve combustion stability. With the advance of SOIpilot, the RCCI combustion process evolves from two-stage heat release to single-stage heat release, and the emissions of HC, CO, NOx and soot are reduced. With the increase of PIQ, the combustion phase of PODE/methanol RCCI mode advances, and the RI, COVIMEP and IMEP increase. At 59.5 mg/cycle condition, when PIQ is increased from 2 mg to 10 mg, CO and HC emissions decrease by 19.57% and 6.97% respectively, while NOx emissions increase by 7.93%. With the appropriate LER combined with the optimized PODE injection strategy, the BTE of PODE/methanol RCCI engine reaches 48.68%, and the IMEP is extended from 0.77 MPa to 1.08 MPa.