Increase In Back Pressure Research Articles

Impact of chamber back pressure on the ignition dynamics of hydrogen enriched premixed flames

The impact of chamber back pressure and H2-enrichment on flashback of premixed CH4−H2-Air flames triggered by ignition dynamics is investigated. Different back pressures are imposed by varying the exhaust flow blockage with perforated plates of different porosities. Experiments measuring the ignition transient, from kernel formation to stable flames and flashback, with increasing levels of H2-enrichment covering a wide range of operating conditions are conducted. Time-series of pressure, velocity and heat release rate are examined to characterise the ignition process. It is shown that the final state of the flame is highly modified by the over pressure caused by the volumetric expansion of the hot gases. Three different scenarios are identified: Soft ignition with direct stabilisation, transient flashback and permanent flashback. The magnitude of the over pressure generated at ignition is significantly amplified by small increases in mean back pressure which, in turn, modifies the flowrate through the injector thereby promoting flashback. In addition to its role as a pressure amplifier, increasing the combustor back pressure also affects the time lag between the over pressure and the peak in heat release rate just after ignition. The impact of H2-enrichment on flashback is investigated by keeping both the bulk injection velocity Ub and laminar burning velocity Sl0 constant for flames with 0% to 100%H2-content. It is shown that the magnitude of the over pressure approximately scales with Ub/Sl0 and is independent of the total thermal power and H2 enrichment. Although the mean flow conditions and over pressures are kept constant, the stabilisation mode directly depends on H2-content. This shows that flashback triggered by the ignition dynamics cannot be fully described by classical kinematic arguments and a new mechanism is presented.

Effect of back pressure on the separation performance of a hydrocyclone

In industrial process applications, to shorten the process flow and use the residual energy of hydrocyclone overflow, the overflow outlet is often directly connected to the subsequent equipment, and the back pressure of the subsequent equipment inevitably affects the normal operation of the front-end hydrocyclone. Therefore, this paper uses numerical simulation to study the effect of overflow back pressure on the internal flow field and separation performance of hydrocyclones. The results show that increasing the overflow back pressure increases the total pressure drop of the hydrocyclone, has no significant effect on the internal radial pressure gradient, and only increases the energy consumption of the hydrocyclone. With the increase in the overflow back pressure, the solid phase yield of the underflow increases, the content of fine particles gradually increases, the content of coarse particles decreases, and the separation accuracy of the hydrocyclone decreases. • The effects of back pressure on the flow field were investigated. • The influences of back pressure on the separation performance were studied. • The particle size distribution of the products were analysed.

Distributed Fluidic Control Method for Alleviating Rapid Movement of Shock Train

The phenomenon of a shock train experiencing rapid forward movement when climbing upstream in a conventional rectangular isolator with incident shocks has recently been investigated. Although several studies have concentrated on the modeling of this phenomenon, few works have focused on methods to alleviate the problems caused by it. Therefore, a distributed fluidic control method is proposed herein, which combines distributed slot injections at the isolator walls and boundary-layer suctions at the corners of the downstream part of the isolator through return pipes. The control effect of the concept is verified by experiments in a Mach 3 test section. First, a rectangular isolator with incident shocks is tested to reproduce the phenomenon of a shock train accelerating suddenly when surmounting a reflection point in the background waves. Then, different fluidic control methods are proposed to demonstrate that the rapid movement of the shock train in a rectangular isolator can be effectively controlled through distributed slot injections, employing a closed flow cycle built by return pipes. According to the experimental results, when the shock train forms and climbs upstream in the isolator, the secondary flows are ejected toward the core flow from the distributed slots at the upstream part of the shock train, which increases the boundary-layer momentum and decreases the pressure gradient of the shock train head. The distributed injections induced compression similar to that induced at a compression surface. The shape of the slip line changes gradually as the backpressure increases. Moreover, the maximum sustainable backpressure is less affected.

Pressure-drop characteristics of CO2 boiling flow in the regenerative-cooling channel of an Mg/CO2 powder rocket engine for Mars missions

To solve the problem of the thermal protection of Mg/CO2 powder rocket engines, how different working conditions in the regenerative-cooling channel influence the pressure drop of CO2 coolant is investigated. It is found that the proportion of two-phase acceleration pressure drop increases with increasing CO2 mass flux, inlet temperature, and heat flux and decreases with increasing backpressure. The ratio of acceleration pressure drop to total pressure drop is ∼0.3. With increasing mass flux, incoming flow temperature, and heat flux, the two-phase frictional pressure drop increases, and the increase of backpressure decreases the two-phase frictional pressure gradient. The factor flp is introduced to correct for the local pressure drop of the experimental system, and flp = 1.9819 when the two-phase coolant Reynolds number is between 20 000 and 50 000. For the unidirectionally heated cooling channel, the coolant is heated unevenly therein, so the heat-transfer mode has an important influence on the frictional pressure gradient of the coolant. It is found that μl can be used to predict the frictional pressure drop of μtp, but the deviation is still more than 20%. Based on experimental data, a new correlation for predicting the two-phase frictional pressure gradient is proposed. The relative deviation of the predicted data is only −7.02%, and 96.12% of the predicted data fall within the ±15% deviation band, so the prediction accuracy is greatly improved. The present research provides a theoretical basis for designing a regenerative-cooling scheme for an Mg/CO2 powder rocket engine.

Fuel economy benefits in internal combustion engines due to soot restructuring in the particulate filter by water injection

Wall-flow particulate filters are key elements to control particulate matter emissions. The stricter emission standards also for non-road mobility machinery makes this device essential to improve the air quality in the short to medium term. However, their high filtration efficiency brings with it an increase in backpressure. This effect becomes more damaging as particles get accumulated in the filter and in hybrid vehicles where exhaust temperature are lower due to more frequent cold starts. Pre-filter water injection is a proven method to reduce the impact of soot load on the pressure drop avoiding the fuel consumption increase. In this paper, the effect of pre-filter water injections is analysed in engine and flow test rig environments. After verifying the impact of consecutive injection events on fuel consumption, the filter was loaded and divided into quarters. These were studied one at a time in flow test rig to separate soot mal-distribution from water drag effects. A wide range of conditions were tested to assess the change in pressure drop generated by a single injection. With this reference, the soot restructuring pattern was analysed employing optical techniques. These provided evidences of the way the soot fragments got released from the particulate layer and moved towards the inlet channels rear end. Additionally, a closer look into the porous wall micro-structure provided insights explaining the lack of effect on filtration efficiency. These results provide a basis for synergistic removal of vehicle condensates for use in fuel consumption reduction.

Experimental and Simulation Analysis on Spray Characteristics of Hydrous Ethanol–Gasoline Blends

Abstract Hydrous ethanol application in engines can not only improve combustion and reduce emissions but also save energy consumption in the production process, which is a potential alternative fuel for engines. However, little research has been conducted on the influences of hydrous ethanol, gasoline, and hydrous ethanol–gasoline blends on spray characteristics, especially the phenomenon of flash boiling. In this investigation, the spray characteristics of hydrous ethanol and gasoline have been conducted using a constant volume chamber system, and the spray characteristics of hydrous ethanol–gasoline blends have been simulated using validated models. The results show that hydrous ethanol fuel is more likely to enter a flash-boiling state in comparison with gasoline. In addition, the spray penetration of hydrous ethanol is higher than that of gasoline, which increases by 10% approximately under the same temperature. Moreover, the spray cone angle of test fuels is between 32 deg and 43 deg and decreases with the increase of back pressure in trend. Besides, the spray projection area of hydrous ethanol and gasoline decreases significantly with the increase of back pressure. In terms of simulation, the spray penetration of E10w, E20w, E50w, and E85w fuels decreases with the increase of back pressure.

Oscillation of the shock train under synchronous variation of incoming Mach number and backpressure

Experiments were conducted to characterize shock train oscillation under the simultaneous variation of the incoming Mach number and backpressure. Under steady and low-frequency oscillatory backpressure (2 Hz), the incoming Mach number varied from 1.8 to 2.4. According to the intersection of downgoing background wave with bottom front leg, Mach stem, and top front leg of the normal shock train leading edge, the normal shock train/background wave interaction can be divided into three types. Two types of oblique shock train/background wave interaction exist. The downgoing (upgoing) background wave upstream of the oblique shock train can cause the upgoing (downgoing) shock in the shock train leading edge to become the dominated shock. Two modes of shock train oscillation were found: oscillation mode 1, in which the shock train oscillated in the favorable gradient region of the relaxing boundary layer, and oscillation mode 2, where the shock train enters the adverse pressure gradient region caused by the impingement of background wave. Compared with mode 1, mode 2 leads to a larger upstream movement of the shock train and more intense pressure fluctuation. The oscillation of the shock train is caused by instability in the separation region behind the shock train leading edge. The oscillatory backpressure only affected the motion of shock train during each oscillation period. The overall movement trend of shock train is determined by the incoming Mach number and the mean value of backpressure. The increase of incoming Mach number and backpressure can lead to the enhancement of shock train oscillation.

Simulation study on transient performance of a marine engine matched with high-pressure SCR system

The high-pressure SCR system is suitable for low-speed marine engines that burn high-sulfur fuel, but it will cause the increase of the exhaust back pressure of main engine, which will affect the main engine’s performance and fuel consumption. At the same time, due to the large weight and size of the SCR reactor, the overall heat storage performance of the SCR reactor is large, which makes the temperature difference between the front and back of the turbine in the start-up and shutdown of the main engine and transient conditions, affecting the transient response performance of the turbine. In this paper, 6S46ME marine low-speed diesel engine and its high-pressure SCR system are taken as the research object, the co-simulation model is constructed by using GT-Suite coupled with a programming software, and the accuracy of the test model is verified. The influence of high-pressure SCR system on the performance of main engine is analyzed, and it finds that the fuel consumption of the main engine at low load increases significantly greater than that at high load, and the exhaust temperature of the main engine changes differently at different loads. On this basis, the co-simulation model was used to analyze the matching performance of high-pressure SCR system under the transient conditions such as the main engine Tier II/Tier III mode switching process, fast-loading, normal-loading and fast-unloading. The results show that the slow cut-in/cut-out of SCR reactor is beneficial to the stable operation of the main engine system, and the cut-in/cut-out time of high-pressure SCR system greatly affects the transient fuel consumption of the main engine, and the maximum increase of fuel consumption is about 3.6 g/kW·h; In addition, the thermal inertia of the reactor has a greater impact on the performance of the main engine at low load, but not at high load.

Non-Dimensional Analysis of Diffusion Characteristics in Polymer Electrolyte Membrane Fuel Cells with Mismatched Anodic and Cathodic Flow Channels

Polymer electrolyte membrane fuel cells were analyzed to investigate changes in the structure of the flow field and operating conditions. The cell performance, which was controlled by adjusting the width of the cathodic channel, improved as the backpressure increases. With the anodic and cathodic flow channels mismatched, the maximum power densities at 3.0 bar for a narrow cathodic channel were 1115 and 1024 mW/cm2, and those for a wide cathodic channel were 959 and 868 mW/cm2, respectively. The diffusion characteristics were investigated using the non-dimensional numbers Re (Reynolds), Sc (Schmidt), and Sh (Sherwood) to confirm the improvement of mass transport. The narrower the channel or the higher the operating pressure, the larger Re was and the smaller Sc and Sh became. In particular, the wider the anodic channel, the larger the value of Sh.

Novel analytic method of membrane electrode assembly parameters for fuel cell consistency evaluation by micro-current excitation

Consistency evaluation and degradation diagnosis of membrane electrode assemblies (MEAs) in a large-scale fuel cell stack remain critical problems despite the accelerated commercialization. In this paper, a novel analytic method of MEA parameters is proposed with high accuracy and stability, which does not require high sampling frequency and data filtering of voltage signals anymore. By means of micro-current excitation, regardless of whether it is galvanostatic or not, four key parameters of each MEA can be calculated simultaneously based on complete excitation model, including hydrogen crossover current density, electrochemical surface area (ECSA), double-layer capacitance, and short-circuit resistance. The universality of the method is demonstrated by the high consistency between galvanostatic and non-constant current excitation results. Effects of condition parameters, including operating temperature, relative humidity, and back pressure, on MEA parameters are further investigated. Low temperature, high relative humidity, and high back pressure make high ECSA. Elevated temperature and back pressure increase hydrogen crossover. Relative humidity is proved to determine the hydrogen crossover by affecting both anodic hydrogen partial pressure and membrane water content. Finally, the method is applied to evaluate the MEA consistency of a long-time-stored seven-cell stack and recognizes part of the membranes ineffective. This method shows a promising prospect in consistency-based MEA screening, aging evaluation of MEAs in a stack, and recombination of old and broken stacks.

Exergo-economic analysis and optimization of a combined solar collector with steam and Organic Rankine Cycle using particle swarm optimization (PSO) algorithm

With the diminution of fossil fuel sources and the substantial importance of CO 2 and other greenhouse gasses emission, the usage of enhanced thermal power plants coupled with renewable energies, such as solar, becomes more vital and promising. This paper proposes a novel configuration of the power generation system, featuring a solar collector to supply the heat for a two-stage steam turbine with inter heating and an Organic Rankine cycle as bottoming cycle of the steam turbine. The proposed system has been simulated and optimized using the particle swarm optimization algorithm. A heat storage system with NaNO 3 and KNO 3 in 3:2 ratios is used to store the extra heat in daylight to extend the operation at nighttime. For achieving the best working conditions for the proposed hybrid system, we employed a multi-objective optimization to maximizing the exergy efficiency while minimizing the levelized cost of electricity production. The simulation was performed using the Engineering Equation Solver (EES), and MATLAB software which is used for receiving the simulation results from EES and optimizing the key design parameters of the system using the PSO algorithm to select the best design variables. The optimization showed that at the optimum point, the exergy efficiency of the system and the levelized cost of electricity production reach to be 63.89% and 0.1529 USD/kWh, respectively. Results also showed that in the proposed system, the solar collector is the most important source of exergy destruction, in which more than 59% of the total destructed exergy happens in it. Sensitivity analysis also revealed that decreasing the turbine's inlet temperature will increase the production cost of electricity due to lower efficiency. Also, any changes (deviation from design point) in the back pressure of the low-pressure turbine will decrease the efficiency; while the production cost of electricity increases if this back pressure increases and vice versa. • Combining steam and organic Rankine power cycles with a solar collector. • Optimizing combined cycle in three scenarios. • Two-objective optimization with exergy and levelized cost of electricity.

Characteristics analysis of an exhaust thermoelectric generator system with heat transfer fluid circulation

Low heat transfer performance in the exhaust channel limits the thermoelectric conversion efficiency of the internal combustion engine exhaust thermoelectric generator. Enhanced heat transfer of exhaust channel improves the thermoelectric performance of the generator, though with an increase in exhaust back pressure. A new type of thermoelectric generator with heat transfer fluid circulation is proposed. A heat transfer fluid replaces the exhaust after heat exchange with the exhaust into the generator. It is possible to improve the thermoelectric performance of the system, counting on the high heat transfer coefficient of the heat transfer fluid in the generator without changing the exhaust channel. A mathematical model of the novel system is constructed, considering the system structure, resistance power consumption, temperature dependence of the physical properties of the module. The influence of structural parameters and heat transfer fluid parameters on thermoelectric performance are analyzed using this model. It is found that the peak net output power of the new generator can be increased by 77.5 % compared with the traditional generator, while the number of modules can be reduced by 83.2%. Therefore, an optimal exhaust heat exchanger configuration is obtained to maximize the net output of the system. In addition, as the heat transfer fluid flow rate increases, the net output power goes up and then down, an optimal heat transfer fluid flow rate can be obtained. The results also give technical guidance on the design and operation criteria of the thermoelectric generator.

Control of shock‐induced separation inside air intake by vortex generators

AbstractThe present investigation is aimed towards the effect of passive methods on the performance of supersonic air intake along with the control of shock wave boundary layer interaction at various engine operating conditions. A computational study has been carried out in this regard using the commercially available software Ansys Fluent. The k–ω turbulence model has been selected for the present investigation. All the simulations have been carried out at a design Mach number of 2.2. The Independent effect of the air‐jet vortex generator (AJVG), tapered micro ramp vortex generator (MRVG), and the combined effect of AJVG with MRVG on the shock wave boundary layer interaction have been investigated. Detailed comparative studies of all controlled cases with uncontrolled cases show significant improvement in the flow field inside the air intake and improved performance. The shock train is also captured for all the cases along with shock wave boundary layer interaction at various operating conditions. The movement of the normal shocks is seen as the backpressure increases. All the essential performance parameters related to air intake have been examined in detail. The hybrid type of control showed better performance.

Shock dynamics and expansion characteristics of an aerospike nozzle and its interaction with the rotating detonation combustor

The flow of products through the aft-end of a detonation combustor is intrinsically unsteady, ultimately resulting in periodic and nonuniform flow parameters at the exit plane of a rotating detonation combustor. Therefore, the integrated design of the nozzle and combustion chamber is an important challenge in rotating detonation engines (RDEs). This paper describes a thorough three-dimensional numerical simulation of a hydrogen–air rotating detonation combustor with/without an aerospike nozzle and investigates the nozzle flow without a combustor. The simulation results allow us to analyze the coupling characteristics of the rotating detonation combustor and the aerospike nozzle. The new features of the shock wave dynamics and expansion characteristics in the nozzle with/without an integrated RDE combustor are compared. For the same rotating detonation combustor exit, the propagation mode of the detonation wave and backpressure in the RDE combustor exit are affected by the aerospike nozzle. The intensity of the shock wave and the angle with respect to the direction of the air flow are lower with the aerospike nozzle than in the nozzleless model, which is consistent with the effect of backpressure increase on the shock dynamics. Regardless of whether the nozzle is connected to the combustor, the nozzle affects the dynamic alternation of the design point state to over-expansion and under-expansion along the circumferential direction. The shock wave intensity and total pressure recovery inside the nozzle with the combustor are slightly stronger than those in the nozzle without the combustor. Consequently, the thrust and total pressure recovery of the nozzle integrated with the RDE combustor are enhanced by 7% and 5.6%, respectively. Thus, decoupling the nozzle from the rotating detonation combustor is feasible for testing the design performance of the unsteady nozzle.

Throttling process of a supersonic cascade studied by high-frequency response pressure and high-speed schlieren

In this study, a single-channel supersonic cascade model is investigated experimentally at a freestream Mach number of 2.4 to obtain a better understanding of the flow field evolution during the throttling process. A flap is placed at the channel exit to choke the flow linearly. Measurements include 1-kHz schlieren imaging and 10-kHz simultaneous fast-response wall pressure. Three stages, namely attached flow, separated flow, and oscillatory flow, are identified in the throttling process. The joint time–frequency analysis and wall pressure spectrum contour exhibit the time evolution and spatial distribution of the pressure fluctuation. With the increase in backpressure, the pressure fluctuation in the low-frequency shock oscillation range of 40–400 Hz on the suction surface located in the separated flow gradually enhances. The power spectral, coherence, and phase analyses of the schlieren images describe the dominant oscillation structure and its relationship with other regions. During the separated flow, the pressure change in the subsonic separated region first lead to a change in the state of the separated shear layer, after which the shock waves in the shock train, move. The oscillatory flow is a process wherein the upstream shock wave oscillates, causing the entire downstream channel to fluctuate.

Numerical Study of Effects of Backpressure on Self-Pulsation of a Liquid-Centred Swirl Coaxial Injector

This study investigated the effects of backpressure and operating conditions on the self-pulsation characteristics of a liquid-centred swirl coaxial (LCSC) injector. To this end, a three-dimensional numerical simulation via octree adaptive mesh refinement as well as coupled level-set and volume of fluid method were employed. Self-pulsation is suppressed by backpressure for a constant gas–liquid momentum flux ratio (MFR). When backpressure is constant, the strength of self-pulsation varies with the mass flow rate of the gas (m˙g), which is constant with experimental data due to the variation in the flow patterns in the recess chambers. The self-pulsation frequency increases with backpressure and m˙g. The trends of the spray angle and intensity of self-pulsation are consistent. As backpressure increases, the radial distribution of the mass flow rate of the liquid changes from a double- to single-peak. The central mass flow rate increases with backpressure and m˙g, which also affect the pressure oscillations inside and outside the liquid film in the injector. We proposed a self-pulsation mechanism, in which self-pulsation is closely related to the dominant surface wave and Kelvin–Helmholtz (K–H) instability. Self-pulsation under the critical mixing flow pattern is stronger than that under inner or outer mixing flow patterns. Under the critical mixing flow pattern, the K–H vortex is relatively strong, and the spray oscillation is not restricted by the wall of the recess chamber.

Effects of gasoline and ethanol on inner flows and swallowtail-like spray behaviors of elliptical GDI injector

Alternative fuels have significant effects on the nozzle inner flow and spray behaviors. The present research works focus on the gasoline and ethanol impact the inner flow and spray behaviors with elliptical GDI injector. The inner flow patterns were performed with numerical modeling method, while the spray characteristics were measured by high-speed shadowgraph technique. Results indicated that the cavitation intensity of ethanol is smaller than that of gasoline, while the mass flow rate of ethanol is higher than gasoline. Also, the gasoline is giving more turbulence vortex structures in the minor axis direction of elliptical GDI injector and higher vorticity magnitude at nozzle exit compared to ethanol. The nozzle exit velocity for gasoline is consistent higher than ethanol. Additionally, the unique swallowtail-like spray structure discharging from elliptical GDI injector for gasoline only appeared in the major view plane. However, this unique spray structure did not appear in the spray tip with ethanol. Finally, gasoline spray tip penetration and spray cone angle are larger than that of ethanol spray, and the spray tip branching angle increased with the increase of back pressure for gasoline spray.

Experimental and numerical investigation of a supersonic inlet with double S-bend diffuser

Design of a supersonic inlet with double S-bend diffuser was developed. Numerical simulation and wind tunnel experiment were carried out to investigate the aerodynamic performance and variable geometric rules of the inlet. The result indicates that the variable geometry scheme adopted solves the contradiction between starting performance at low Mach number and aerodynamic performance at high Mach number. The inlet works normally and stably over a wide speed range. At design point, the total pressure recovery coefficient reaches 0.47. In addition, two different kinds of inlets with double S-bend diffuser and single S-bend diffuser were studied. Compared with the double S-bend diffuser, the total pressure recovery coefficient of the single S-bend diffuser is higher at low Mach number (Ma0 < 3) and lower at high Mach number (Ma0 > 3). With the increase of backpressure, shock train mainly moves upstream along the low-energy flow region in the diffuser. For the double S-bend diffuser, shock train will first move along the lower corner and then along the upper corner. For the single S-bend diffuser, it will only move along the upper corner. The strong secondary flow of the double S-bend is the main reason for the above phenomenon.

Experimental and numerical investigation on inner flow and spray characteristics of elliptical GDI injectors with large aspect ratio

The application of non-circular elliptical orifice is recognized to increase the fuel spray and mixing quality, which has potential ability for modern gasoline direct injection (GDI) engines. In this research work, a single-hole elliptical GDI injector with aspect ratio of 4 was adopted. Numerical simulation and experimental spray test are both introduced to study the inner flow patterns and spray characteristics. The results indicated that the cavitation is mainly distributed on the minor axial plane of the elliptical GDI injector, and the cavitation domain decreases gradually with the increase of back pressure. Additionally, the unique swallowtail-like spray structure discharging from the elliptical GDI injector with aspect ratio of 4 was captured for the first time, and the swallowtail-like spray structure only appeared on the major view plane of the elliptic spray. Moreover, the GDI elliptical spray tip branching length reduced with the increase of the back pressure, and the high back pressure can inhibit the formation of swallowtail-like spray structure. Finally, the branching angle at the spray tip increased with the increase of back pressure, because high back pressure will enhance the effect of high aerodynamic force.

Улучшение акустических характеристик пневмомеханизмов машин контактной сварки

Welding production forms the basis of assembly production in many branches of industry. Welding equipment is the most numerous in the environment of assembly of transport engineering units. This equipment is used both at the initial stage of assembly operations and at the final stage. The most common machines are single-point and multi-point welding with pneumatic drive. Traditional disadvantage of welding machines using pneumatic drives is the presence of intense acoustic flows at the outlet of the energy carrier, the operating sound level of which significantly exceeds the established sanitary norms and worsens personnel working conditions. Among the sources of aerodynamic flows in contact welding machines, the most relevant noise is during technological release of energy from the pneumatic mechanisms of the welding machines control systems, including the existing fleet of contact welding machines. Standard noise mufflers in the contact welding machines, the acoustic elements of which are made in the form of porous metal bushings or pots, are working efficiently for a short period of time up to 200 hours, both domestic and foreign companies Festo, Camozzi, Pneumax. The reason is that when pulsed, technological release of compressed air containing oil particles, in the presence of external dust sources, the channels of porous sound-absorbing elements are clogged with a suspension of oil with the above specified particles and condensate. This leads to an increase in the hydraulic resistance of the muffler path, an increase in the back pressure in the silencing chamber, and, as a result, to the destruction of the acoustic element, which requires frequent replacement of the muffler. The results are presented concerning the development of new chamber mufflers for contact welding machines, which efficiently reduce noise, operate without maintenance for more than fifteen years without requiring replacement. They are recommended for various branches of industries operating pneumatic systems for various purposes.