Increase In Back Pressure Research Articles

Performance and analysis of a retrofit electrostatic precipitator before a diesel particulate filter to reduce particulate matter in diesel exhaust system

ABSTRACT In this work, an electrostatic precipitator is used in a diesel particulate filter to reduce the particulate matter (PM) emission and lead emissions. As evident by the USEPA (United States Environmental Protection Agency), the trucks and buses account for one-fourth of PM and one-third of lead suspended in the atmosphere. The diesel particulate filter, as an individual, has its own limitation, that is, only ultra-low sulphur diesel must be used (15 ppm); otherwise, the particulate filter clogs and engine exhaust back pressure increases leading to engine failure. Electrostatic precipitator is found to have some drawback from the research: it cannot precipitate the low resistive diesel PM in its collection plates. The concurrent use of these two helps in overcoming the above-mentioned problems. Other than this, the use of this set-up has decreased in the rate of increase in back pressure at the exhaust system. The particle number density is 98% less when compared to a system of diesel particulate filter only. It increases the collection efficiency of PM and engine efficiency.

Numerical Simulation on Interfacial Characteristics in Supersonic Steam–water Injector Using Particle Model Method

Steam–water injectors have been widely applied in various industrial fields because of their compact and passive features. Despite its straightforward mechanical design, the internal two-phase condensing flow phenomena are extremely complicated. In present study, a numerical model has been developed to simulate steam–water interfacial characteristics in the injectors based on Eulerian–Eulerian multiphase model in ANSYS CFX software. A particle model is available for the interphase transfer between steam and water, in which a thermal phase change model was inserted into the model as a CFX Expression Language (CEL) to calculate interphase heat and mass transfer. The developed model is validated against a test case under a typical operating condition. The numerical results are consistent with experimental data both in terms of axial pressure and temperature profiles, which preliminarily demonstrates the feasibility and accuracy of particle model on simulation of gas–liquid interfacial characteristics in the mixing chamber of injector. Based on the dynamic equilibrium of steam supply and its condensation, interfacial characteristics including the variation of steam plume penetration length and steam–water interface have been discussed under different operating conditions. The numerical results show that steam plume expands with steam inlet mass flow rate and water inlet temperature increasing, while it contracts with the increase of water inlet mass flow rate and backpressure. Besides this, the condensation shock position moves upstream with the backpressure increasing.

Ejector based CO2 transcritical combined cooling and power system utilizing waste heat recovery: A thermoeconomic assessment

To reduce the fossil fuels consumption and their environmental impact, improve the waste heat efficiency, an enhanced transcritical CO2 ejector based combined cooling and power system is proposed using recovered waste heat. This system can employ in vehicles and make them run more environmentally friendly. The new proposed system includes a power generation part and a transcritical ejector based refrigeration system. A thermodynamical model is developed to evaluate the enhanced proposed system. A comprehensive parametric investigation and thermoeconomic analysis are presented to study the effects of key parameters on the thermoeconomic performance of the system. The results show that back pressure of ejector (gas cooler pressure) plays the main role to improve the system performance. A 10 bar increase in ejector back-pressure of ejector leads to an increase of 16.4% in energy efficiency while the exergy efficiency decreases of 9.2%. From exergy analysis, it is found that the biggest irreversibility in the system belongs to the internal heat exchanger used between pump and turbine outflows. For the cooling capacity of 10 kW, a multi-objective optimization is carried out and the optimal values of energy and exergy efficiencies obtained from the Pareto frontier results are 27.42% and 24.21%, respectively, while it leads to the net power output of 7.55 kW. In this case, the net present value and the simple payback period of the proposed system are equal to 0.3419 M$ and about 4 years and 6 months, respectively.

Investigation on the Dynamic Characteristics of Port Valves in a Diaphragm Pump for Exhaust Gas Treatment System by FSI Modeling

The motions of port valves are a primary aspect to consider in achieving superior reliability and performance of a diaphragm pump, and it is necessary to perform detailed analyses to stabilize the motions of port valves. A transient 3D fluid-structure interaction (FSI) model was proposed to simulate a complete working process of a diaphragm pump and the motions of port valves. The dynamic mesh technique was used, and the deformation of the diaphragm was considered. Detailed descriptions of the FSI model creation development and the simulation methodology for the diaphragm pump were provided. Based on the FSI model, the influences of the back pressure and pump speed on the dynamic characteristics of port valves were analyzed, and the flow rate of the prototype was tested under different conditions on a test rig. The simulation results indicate that an increase in the back pressure and pump speed can lead to a reduction in the flow rate. The motions of the port valves are dependent on the back pressure and pump speed, and the deformation of the diaphragm is only dependent on the back pressure. The opening lag angles of the port valves increase significantly as the back pressure increases, but they are independent of the pump speed. In addition, the opening velocities of the port valves increase with increasing back pressure and pump speed. Finally, the simulation results also show agreement with the experimental data, and the FSI simulation method can predict the dynamic characteristics of port valves in a diaphragm pump.

Experimental study on the spray and mixing characteristics for equilateral triangular and circular nozzles with diesel and biodiesel under high injection pressures

The present research work presented an experimental comparison of the fuel-air mixing quality and macro spray behaviors for the equilateral triangular and circular sprays between diesel and biodiesel, through Mie-scattering method based on a laser beam system, at different high injection pressures (120 MPa, 140 MPa, 160 MPa) and backpressures (1 MPa, 3 MPa). The results indicated that the biodiesel spray had longer spray tip penetration than the diesel spray, and also the spray tip penetration of the circular one was consistently longer than that of the equilateral triangular spray for both fuels and injection conditions. The spray tip velocity of biodiesel was higher than that of the diesel fuel, and the spray tip velocity decreases with increasing backpressure. The biodiesel spray cone angles were always smaller than the diesel spray in both major and minor planes. The spray cone angle of the circular orifice was consistently smaller than that of the equilateral triangular spray. Besides, the equilateral triangular spray discharging axis-switching phenomenon for both fuels even under the high injection pressure conditions. The increase of backpressure will decrease the number of interactions of spray cone angles in major and minor planes, while the increase of injection pressure will increase the number of interactions. Moreover, the spray axis-switching occurred earlier at the higher injection pressure, which illustrated the increase of the injection pressure was helpful to increase the equilateral triangular spray instability and deformation. The biodiesel spray was more difficult to undergo the spray axis-switching as compared to the diesel spray. Furthermore, the biodiesel spray projection area was smaller than the diesel spray in all view planes. The spray projection area of equilateral triangular spray was higher than that of the circular spray for both fuels. Meanwhile, the diesel spray had more mass of the entrained air than the biodiesel spray. The mass of the entrained air of equilateral triangular spray was higher than that of the circular spray. The combination of high injection pressure and using an equilateral triangular nozzle can mitigate the poor spray quality of biodiesel significantly.

The effects of ash inside a platinum-based catalyst diesel particulate filter on particle emissions, gaseous emissions, and unregulated emissions.

Ash deposited in the DPF cannot be burnt, which will affect the service life of DPF. However, previous works focused on the effect of ash on the engine exhaust emissions are limited. Therefore, the influence of ash on the emissions was studied in this work. The particle emissions, the gaseous emissions, and the unregulated emissions (carbonyl compounds and volatile organic compounds) were measured by an AMA4000 gaseous analyzer, ELPI, HPLC, and GC-MS, respectively. Research results indicate that the filtration efficiency decreases by 0.57-4.49% for accumulation mode particle of particulate matter, while it has very little effects on the other type and the particle number in the presence of ash. For regular gaseous pollutions, ash has no influence on CO2 and NOx emission, while CO and THC increase by 68.2% and 91.0%, respectively. For unregulated emissions, overall, carbonyl compounds increase by 41-150% and the BTEX decreases by 8.6-23.6% after ash formed. The change is mainly caused by the increase in the exhaust backpressure that plays a key role.

Coupled CFD–DEM method for undrained biaxial shear test of methane hydrate bearing sediments

Methane hydrate (MH), a potential source of future energy, is extensively deposited in marine sediments. It is essential to understand the mechanical properties of methane hydrate bearing sediments (MHBS) for applications relevant to mining and geotechnical engineering. This study aims to investigate the undrained shear strength of MHBS through coupled computational fluid dynamics and discrete element method (CFD–DEM) numerical approach. The Tait’s fluid state equation is implemented into the Navier–Stokes equation-based CFD, while the DEM is used to model granular particle system of MHBS. The CFD–DEM tool is first verified by two typical geomechanics problems where analytical solutions are available. The simulations show that the stress–strain behavior of MHBS depends on temperature, back pressure and MH saturation, as observed in reported experimental results. The presence of MH alters the hardening response of clean sand into softening response due to the bonding effects of MH. The friction angles and cohesions described by total stress and effective stress both increase as the back pressure and MH saturation increase or the temperature drops. There is significant localization in MH bond breakage events but no localization effect is observed in fluid flow and excess pore pressure distribution. This is because fluid is mostly controlled by the boundary conditions instead of specific fluid–particle interactions locally in the simulated quasi-static loading.

An investigation on the characteristics of and influence factors for NO2 formation in diesel/methanol dual fuel engine

It had been found in previous experimental studies that the compression ignition engine with Diesel/Methanol Compound Combustion (DMCC) could significantly increase nitrogen dioxide (NO2) emission, compared with conventional diesel mode. However, the detailed formation process and influence factors of NO2 in Diesel/Methanol Dual Fuel (DMDF) engine have not been reported previously. In order to investigate the mechanism of increased NO2 and effect factors of NO2 emission, following works were conducted: Firstly, in light of the literature researches, a hypothesis concerning the NO2 formation procession in DMDF engine was presented, whose demonstration was realized by using numerical simulation; Secondly, the experiments about the effect of methanol substitute proportion (MSP), exhaust gas recirculation (EGR) and exhaust backpressure on the NO2 emission were conducted, whose results were analyzed by using the proved hypothesis. The results of simulation justified that compared with diesel case, the existence of methanol premixed region in DMDF mode was the main cause of increased NO2, and the impact of temperature on the NO2 emission mainly lay in that of temperature on hydroperoxyl (HO2) radicals. The experiments showed that along with the increase of MSP, NO2 emission increased firstly and then decreases. The addition of EGR could lead to the reduction of NO2, while the slight increase of exhaust backpressure would increase total nitrogen oxides (NOX) emission.

Analysis on integrity of cement sheath in the vertical section of wells during hydraulic fracturing

The sustained casing pressure (SCP) problems occur mainly in intermediate casing that might affect the safety and efficiency of shale gas production. Cement sheath is the main barrier against leakage and migration of gas from the pay zone to the shallow zones. Since the production casing is cemented all the way up to the intermediate casing in the vertical section of the well, the in-situ stress can only act on the intermediate casing and not directly on production casing. Based on this situation, an analytical model considering the well completion steps is established to study the integrity of cement sheath as a two-layer casing-cement system. The effect of mechanical and geometrical parameters of casing and cement are further investigated through a sensitivity analysis. The results show that the tensile failure more likely occurs at the inner face of the cement sheath in the intermediate casing. The casing thickness is in favor of decreasing the tensile stress in the cement sheath. But on the contrary, increasing the thickness and elastic modulus of the cement sheath may increase the risk of tensile failure in the cement sheath while reducing the costs. However, an appropriate increase of back pressure in the annulus during cementing is beneficial to reduce the tensile stress in the cement sheath.

Large eddy simulation of unsteady flow in gas–liquid separator applied in thorium molten salt reactor

Axial gas–liquid separators have been adopted in fission gas removal systems for the development of thorium molten salt reactors. In our previous study, we observed an unsteady flow phenomenon in which the flow pattern is directly dependent on the backpressure in a gas–liquid separator; however, the underlying flow mechanism is still unknown. In order to move a step further in clarifying how the flow pattern evolves with a variation in backpressure, a large eddy simulation (LES) was adopted to study the flow field evolution. In the simulation, an artificial boundary was applied at the separator outlet under the assumption that the backpressure increases linearly. The numerical results indicate that the unsteady flow feature is captured by the LES approach, and the flow transition is mainly due to the axial velocity profile redistribution induced by the backpressure variation. With the increase in backpressure, the axial velocity near the downstream orifice transits from negative to positive. This change in the axial velocity sign forces the unstable spiral vortex to become a stable rectilinear vortex.

Experimental study on the spray characteristics discharging from elliptical diesel nozzle at typical diesel engine conditions

The elliptical orifice diesel nozzle has potential beneficial for improving spray and air-fuel mixing quality, which has great impact on combustion and emission performances for diesel engine. This paper presents experimental studies on the macro spray characteristics and the mechanism of axis-switching for elliptical and circular orifice diesel nozzles with same cross section area, with biodiesel fuel by using shadowgraph technique, under various injection pressures (50 MPa, 70 MPa, 90 MPa) and backpressures (1MPa, 2 MPa, 3 MPa). Two CCD cameras were adopted to acquire the macro spray images at the minor and major view planessimultaneously. Macroscopic spray characteristics from different view planes of spray were processed by MATLAB. The results indicated that the spray width of the elliptical spray was greater than that of the circular spray in all the view planes. Elliptical orifice spray exhibited axis-switching phenomenon during the injection process even at high injection pressure and backpressure. The increasing of backpressure enhances the aerodynamic effects, resulting in suppressing axis-switching of elliptical spray. However, increasing the injection pressure is beneficial for improving the axis-switching frequency, because the higher spray inertia resulting from higher injection pressure can cause greater spray surface-instabilities, which are conductive to enhance the axis-switching. Moreover, the spray width at the downstream increases as the backpressure increases, and for all geometrical orifices exhibited greater spray width under the higher injection pressure. In addition, the spray tip penetration of circular orifice was longer than that of elliptical orifice during the whole injection process. This is due to the larger spray surface of elliptical spray resulting in larger aerodynamic drag. Furthermore, the spray cone angle of the circular orifice is consistently smaller than that of elliptical orifice under typical diesel engine conditions. Because the axis-switching phenomenon of elliptical spray is helpful to improve the air entrainment ratio and thus resulting in larger spray cone angle. Finally, the present experiment results indicate that elliptical sprays are conductive to increase air entrainment ratio and air–fuel mixing quality as compared to circular sprays, due to the axis-switching phenomenon, larger spray cone angle and width.

When allocation “back out” agreements can become “lose out” agreements

When a newly developed third party field is tied back to existing infrastructure, such as a pipeline system, there is the potential for the new field’s production to cause an increase in back pressure and reduce the flow of the incumbent fields already producing through the system. This is termed “back out” and in effect defers some of the incumbent fields’ production.Back out agreements are sometimes put in place, within the allocation system, to compensate the incumbent fields for the reduction in flow they experience. This may take the form of a transfer from the third party of hydrocarbons to the incumbent fields so that in effect they do not experience deferment and suffer resultant economic lossAs the production matures the situation reverses and the incumbent fields back out the third party field, the transfer then proceeding in the opposite direction. The assumption often made is that eventually the transfers will cancel one another and over their lifetime, all fields’ cumulative allocation will equal their cumulative productionThis paper presents the concept of how back out calculations typically work and presents a simplified mathematical model of a system where an incumbent field is backed out by a new field introduced into a pipeline. This simplified model is used to illustrate potential problems with the concept of back out, particularly in the repayment period and shows that there is the very real potential for “back out” to become “lose out” for the new field.Finally the paper discusses methods to overcome the pitfalls exposed by the analysis.

Shock Train Unsteadiness Characteristics, Oblique-to-Normal Transition, and Three-Dimensional Leading Shock Structure

The structure and unsteadiness characteristics of a shock train in a constant-area ducted flow are studied experimentally as a function of duct back pressure, which is mechanically controlled by a valve. Increasing the back pressure pushes the shock train upstream where the approach conditions (including Mach number and boundary-layer momentum thickness) are different, as these quantities vary along the duct length. Despite nominally constant boundary conditions during a run, the shock train fluctuates about its time-averaged position. Schlieren imaging reveals that the unsteadiness characteristics, including the fluctuation amplitude and frequency content, are independent of back pressure. However, changes in the Mach stem length and shock angles demonstrate that the leading shock structure transitions from oblique to normal as back pressure increases. Time-averaged pressure profiles show that the shock train length decreases and the pressure rise across the shock train increases during this process, but these quantities are nominally constant when normalized by the approach conditions. Finally, stereo particle image velocimetry is used to study the three-dimensional structure of a normal leading shock. The velocity fields show a large separation region on the side-wall of the duct and a degree of axisymmetry that indicates a nominally conical shock structure.

Effect of back pressure and freestream dynamic pressure on a typical Ramjet engine duct under realistic supersonic inlet condition

ABSTRACTThe present study investigates the behaviour of the shock train in a typical Ramjet engine under the influence of shock and expansion waves at the entry of a low aspect ratio (1:0.75) rectangular duct/isolator at supersonic Mach number (M = 1.7). The start/unstart characteristics are investigated through steady/unsteady pressure measurements under different back and dynamic pressures while the shock train dynamics are captured through instantaneous Schlieren flow visualisation. Two parameters, namely pressure recovery and the pressure gradient, is derived to assess the duct/isolator performance. For a given back pressure, with maximum blockage (9% above nominal), the duct/isolator flow is established when the dynamic pressure is increased by 23.5%. The unsteady pressure measurements indicate different scales of eddies above 80 Hz (with and without flap deflection). Under the no flap deflection (no back pressure) condition, the maximum fluctuating pressure component is 0.01% and 0.1% of the stagnation pressure at X/L = 0.03 (close to the entry of the duct) and X/L = 0.53 (middle of the duct), respectively. Once the flap is deflected (δ = 8°), decay in eddies by one order is noticed. Further increase in back pressure (δ ≥ 11°) leads the flow to unstart where eddies are observed to be disappeared.

A novel fiber length measurement technique for discontinuous fiber‐reinforced composites: A comparative study with existing methods

The residual fiber length in a molded part is one of the most important microstructural properties of discontinuous fiber‐reinforced composites. While there have been several research studies characterizing the process‐induced fiber length reduction, the measurement procedures vary substantially, calling into question the comparability of reported results. This article introduces a newly developed measurement procedure that aims to provide accurate, repeatable, robust, and time efficient fiber length analyses. A comprehensive study of measurement techniques was performed comparing commercially available systems and the conventional approach of measuring the fiber length manually. The results emphasize the need for a standardized procedure to characterize the fiber length distribution and the risk of generating inadequate results through improper sample preparation. The developed measurement technique was tested and compared for an experimental study of fiber breakage in injection molding. For a simple plaque geometry, the residual fiber length along the flow path was obtained for a long glass fiber‐reinforced polypropylene at 30 and 40%wt for varying process conditions. The new measurement technique showed accurate and repeatable results. The results of the injection molding study showed that screw speed and back pressure are important factors that drive fiber breakage. An increase in back pressure from 13 to 50 bar and screw speed from 27 to 35 rpm reduces the weight‐average fiber length by 37.5%. POLYM. COMPOS., 39:4058–4070, 2018. © 2017 Society of Plastics Engineers

Numerical Investigation on the Performance of Different Primary Nozzle Structures in the Supersonic Ejector

Computational fluid dynamics (CFD) technique is employed to investigate the effect of primary nozzle structures on the supersonic ejector performance. The performance of the supersonic ejectors with three different nozzle structures, including conical nozzle, petalage nozzle and crenation nozzle, have been compared under the same conditions. Compared with the ejector equipped with the conical nozzle, the entrainment ratio of petalage nozzle is slightly smaller, while the critical back pressure increases by 5.2%. Just the opposite, the entrainment ratio of crenation nozzle is slightly higher, and the critical back pressure would decrease by 2.1%. In addition, the effects of primary/induced fluid pressure on the flow field (pressure and Mach number along the ejector centerline) are observed and analyzed to explain the mixing process occurring inside the ejector. It finds out that the shape of the mixing layer in the supersonic ejector with different nozzles is different.

Influence of the energy regeneration unit on pressure characteristics for a proportional relief valve

Overflow loss through the relief valves is universal in hydraulic systems. To explore the feasibility to regenerate the overflow loss, an energy regeneration unit is connected to the outlet of the proportional pilot relief valve which can reduce the pressure difference and the overflow loss accordingly. The added energy regeneration unit may affect the performance of the proportional pilot relief valve. The mathematical model of the proportional pilot relief valve with the energy regeneration unit is established. And AMESim is employed to develop the simulation model of the proportional pilot relief valve to obtain the characteristics of the proportional pilot relief valve which is affected by the energy regeneration unit. The experiment is carried out to test the influence of the energy regeneration unit on the performance of the proportional pilot relief valve. The experimental results show that the inlet pressure of the proportional pilot relief valve decreases gradually with the increase in back pressure of the energy regeneration unit. The maximum pressure drop of the inlet pressure of the proportional pilot relief valve is about 0.63 MPa. Compared to the fluctuation caused by the flow rate, which is 10%–30%, the fluctuation caused by the energy regeneration unit is only 2.8% and can be neglected. This indicates that the feasibility and effectiveness to regenerate the overflow loss of the proportional pilot relief valve through connecting an energy regeneration unit to the outlet of the proportional pilot relief valve.

Experimental characteristics of oblique shock train upstream propagation

The structure and dynamics of an oblique shock train in a duct model are investigated experimentally in a hypersonic wind tunnel. Measurements of the pressure distribution in front of and across the oblique shock train have been taken and the dynamics of upstream propagation of the oblique shock train have been analyzed from the synchronized schlieren imaging with the dynamic pressure measurements. The formation and propagation of the oblique shock train are initiated by the throttling device at the downstream end of the duct model. Multiple reflected shocks, expansion fans and separated flow bubbles exist in the unthrottled flow, causing three adverse-pressure-gradient phases and three favorable-pressure-gradient phases upstream the oblique shock train. The leading edge of the oblique shock train propagates upstream, and translates to be asymmetric with the increase of backpressure. The upstream propagation rate of the oblique shock train increases rapidly when the leading edge of the oblique shock train encounters the separation bubble near the shock reflection point and the adverse-pressure-gradient phase, while the oblique shock train slow movement when the leading edge of the oblique shock train is in the favorable-pressure-gradient phase for unthrottled flow. The asymmetric flow pattern and oscillatory nature of the oblique shock train are observed throughout the whole upstream propagation process.

Emission reduction through internal and low-pressure loop exhaust gas recirculation configuration with negative valve overlap and late intake valve closing strategy in a compression ignition engine

An investigation was carried out to examine the feasibility of replacing the conventional high-pressure loop/low-pressure loop exhaust gas recirculation with a combination of internal and low-pressure loop exhaust gas recirculation. The main objective of this alternative exhaust gas recirculation path configuration is to extend the limits of the late intake valve closing strategy, without the concern of backpressure caused by the high-pressure loop exhaust gas recirculation. The late intake valve closing strategy improved the conventional trade-off relation between nitrogen oxides and smoke emissions. The gross indicated mean effective pressure was maintained at a similar level, as long as the intake boosting pressure kept changing with respect to the intake valve closing timing. Applying the high-pressure loop exhaust gas recirculation in the boosted conditions yielded concern of the exhaust backpressure increase. The presence of high-pressure loop exhaust gas recirculation limited further intake valve closing retardation when the negative effect of increased pumping work cancelled out the positive effect of improving the emissions’ trade-off. Replacing high-pressure loop exhaust gas recirculation with internal exhaust gas recirculation reduced the burden of such exhaust backpressure and the pumping loss. However, a simple feasibility analysis indicated that a high-efficiency turbocharger was required to make the pumping work close to zero. The internal exhaust gas recirculation strategy was able to control the nitrogen oxides emissions at a low level with much lower O2 concentration, even though the initial in-cylinder temperature was high due to hot residual gas. Retardation of intake valve closing timing and intake boosting contributed to increasing the charge density; therefore, the smoke emission reduced due to the higher air–fuel ratio value exceeding 25. The combination of internal and low pressure loop loop exhaust gas recirculation with late intake valve closing strategy exhibited an improvement on the trade-off relation between nitrogen oxides and smoke emissions, while maintaining the gross indicated mean effective pressure at a comparable level with that of the high-pressure loop exhaust gas recirculation configuration.

Effect of Pore Structure on Soot Deposition in Diesel Particulate Filter

Nowadays, in the after-treatment of diesel exhaust gas, a diesel particulate filter (DPF) has been used to trap nano-particles of the diesel soot. However, as there are more particles inside the filter, the pressure which corresponds to the filter backpressure increases, which worsens the fuel consumption rate, together with the abatement of the available torque. Thus, a filter with lower backpressure would be needed. To achieve this, it is necessary to utilize the information on the phenomena including both the soot transport and its removal inside the DPF, and optimize the filter substrate structure. In this paper, to obtain useful information for optimization of the filter structure, we tested seven filters with different porosities and pore sizes. The porosity and pore size were changed systematically. To consider the soot filtration, the particle-laden flow was simulated by a lattice Boltzmann method (LBM). Then, the flow field and the pressure change were discussed during the filtration process.