Gas-dynamic processes in the exhaust system. Exhaust systems of internal combustion engines. Gas dynamics and consumables process of the output of the piston internal combustion engine with a superposition

the main / Driving

In parallel, the development of the devastating exhaust systems, the systems developed, conventionally referred to as "silencers", but designed not so much to reduce the noise level of the operating engine, how much to change its power characteristics (engine power, or its torque). At the same time, the task of stitching noise went to the second plan, such devices are not reduced, and cannot significantly reduce the exhaust noise of the engine, and often enhance it.

The work of such devices is based on resonant processes within the "silencers" themselves, possessing, like any hollow body with the properties of the gameholts resonator. At the expense of internal resonances exhaust system Two parallel tasks are solved at once: the cleaning of the cylinder is improved from the residues of the combustible mixture burned in the previous tact, and the filling of the cylinder with a fresh portion of the combustible mixture is increased for the next compression tact.
The improvement in the cleaning of the cylinder is due to the fact that the gas pillar in the graduate manifold, who scored some speed during the output of gases in the previous tact, due to inertia, like a piston in the pump, continues to suck out the remains of the gases from the cylinder even after the cylinder pressure comes With pressure in the graduate manifold. At the same time, another, indirect effect occurs: due to this additional minor pumping, the pressure in the cylinder decreases, which favorably affects the next purge tact - in the cylinder it falls somewhat more than a freshly combustible mixture than could get if the cylinder pressure was equal to atmospheric .

In addition, the reverse wave of exhaust pressure, reflected from the confusion (rear cone of the exhaust system) or blend (gas-dynamic diaphragm) installed in the cavity of the silencer, returning back to the exhaust window of the cylinder at the time of its closure, additionally "rambling" fresh fuel mixture in the cylinder , even more increasing its filling.

Here you need to clearly understand that it is not about the reciprocal movement of gases in the exhaust system, but about the wave oscillatory process within the gas itself. Gas moves only in one direction - from the exhaust window of the cylinder in the direction of the outlet at the outlet of the exhaust system, first with sharp jesters, the frequency of which is equal to the vehicle turnover, then gradually the amplitude of these jolts is reduced, in the limit turning into a uniform laminar movement. And "There and here" the pressure waves are walking, the nature of which is very similar to acoustic waves in the air. And the speed of these vibrations of pressure is close to the speed of sound in the gas, taking into account its properties - primarily density and temperature. Of course, this speed is somewhat different from the known value of the speed of sound in the air, under normal conditions equal to about 330 m / s.

Strictly speaking, the processes flowing in the exhaust systems of DSV is not quite correctly called pure acoustic. Rather, they obey the laws used to describe the shock waves, albeit weak. And this is no longer standard gas and thermodynamics, which is clearly stacked in the framework of isothermal and adiabatic processes described by laws and the equations of Boylya, Mariotta, Klapaireron, and others like them.
I came across this idea a few cases, the witness of which I myself was. The essence of them is as follows: Resonance Dudges of high-speed and racing motors (Avia, Court, and Auto), working on the proceedable modes, in which the engines are sometimes unchecked up to 40,000-45.000 rpm, and even higher, they start "sailing" - they are literally In the eyes change the shape, "pinpoint", as if not made of aluminum, but from plasticine, and even tritely roast! And it happens on the resonant peak of the "twin". But it is known that the temperature of the exhaust gases at the exit of the exhaust window does not exceed 600-650 ° C, while the melting point of pure aluminum is slightly higher - about 660 ° C, and its alloys and more. At the same time (the main thing!), It is more often melted and a non-exhaust tube megaphone is deformed, adjacent directly to the exhaust window, where it would seem the most heat, and the worst temperature conditions, and the inverse cone-confusion region, to which the exhaust gas is already reducing with a much smaller temperature, which decreases due to its expansion inside the exhaust system (remember the basic laws of gas dynamics), and besides, this part of the muffler is usually blown by the incident air flow, i.e. Additionally cooled.

For a long time I could not understand and explain this phenomenon. Everything fell into place after I accidentally hit the book in which the processes of shock waves were described. There is such a special section of gas dynamics, the course of which is read only on special taps of some universities that are preparing explosive technicians. Something similar happens (and studied) in aviation, where half a century ago, at the dawn of supersonic flights, they also encountered some inexplicable facts of destruction of the aircraft glider's design at the time of the supersonic transition.

Page: (1) 2 3 4 ... 6 "I already wrote about resonant silencers -" Dudges "and" Muffers / Mufters "(models are used by several terms, derived from English" Muffler "- silencer, Surdinka, etc.). You can read about this in my article "And instead of a heart - a fibrous engine."

Probably, it is worth talking more about the exhaust systems of DVS in general to learn how to divide "flies from the kitlet" in this not easy to understand the area. Not easy from the point of view of physical processes occurring in the muffler after the engine has already completed another worker, and, it would seem, did his job.
Then it will be about model two-stroke enginesBut all reasoning is true for four-strokes, and for the engines "non-model" cubatures.

Let me remind you that far from every exhaust dVS tractEven built according to the resonant scheme, can give an increase in power or engine torque, as well as reduce its noise level. By and large, these are two mutually exclusive requirements, and the task of the exhaust system designer is usually reduced to the search for a compromise between the noise of DVS, and its power in one or another operation mode.
This is due to several factors. Consider the "ideal" engine, in which the internal loss of energy for friction of sliding nodes is zero. We will also not take into account the losses in rolling bearings and loss, inevitable when internal gas-dynamic processes (suction and purge). As a result, all the energy released during combustion fuel mixeswill be spent on:
1) the useful work of the model drivers (propeller, wheel, etc. It is not possible to consider the efficiency of these nodes, it is a separate topic).
2) losses arising from another cyclical phase of the process the work of the DVS - Exhaust.

It is the loss of exhaust worth considering in more detail. I emphasize that it is not about the work stroke tact (we agreed that the engine "inside itself is ideal), but about the" ejecting "losses of the combustion of the fuel mixture from the engine into the atmosphere. They are determined mainly, the dynamic resistance of the exhaust path itself is the whole thing that joins the motor of the motor. From the entrance to the outlet holes of the "silencer". I hope you do not need to convince anyone that the smaller the resistance of the channels, according to which the gases from the engine are "departed", the less you will have to spend the efforts on it, and the faster the process of "gas separation" will pass.
Obviously, it is the phase of the exhaust of the internal combustion system that is the main in the process of noise formation (forget about the noise arising during suction and the burning of fuel in the cylinder, as well as about mechanical noise from the operation of the mechanism - the perfect MEX mechanical noise can simply be). It is logical to assume that in this approximation, the total efficiency of DVS will be determined by the ratio between useful work, and loss of exhaust. Accordingly, the reduction in the exhaust loss will increase the efficiency of the engine.

Where is the energy lost when the exhaust is spent? Naturally, it is converted into acoustic fluctuations in the environment (atmosphere), i.e. In noise (of course, there is also a heating of the surrounding space, but we still default about it). The place of occurrence of this noise is a cut of an exhaust window of the engine, where there is a jump-like expansion of exhaust gases, which initiates acoustic waves. The physics of this process is very simple: at the time of opening the exhaust window in a small volume of the cylinder there is a large portion of compressed gaseous residues of fuel combustion products, which when entering the surrounding space is quickly and sharply expanded, and a gas-dynamic blow occurs, provoking subsequent floating acoustic oscillations in the air (Remember the cotton arising from the scolding of a bottle of champagne). To reduce this cotton, it is enough to increase the expiration time of compressed gases from the cylinder (bottle), limiting the cross section of the exhaust window (smoothly opening the plug). But such a way to reduce noise is not acceptable for real Enginewhich, as we know, power directly depends on the revolutions, therefore, from the speed of all flowing processes.
You can reduce the noise of the exhaust in another way: do not limit the cross-sectional area of \u200b\u200bthe exhaust window and the expiration time of exhaust gases, but limit the speed of their expansion in the atmosphere. And this method was found.

Back in the 30s of the last century, sports motorcycles and cars began to equip peculiar conical exhaust pipes With a small opening corner. These silencers were called "MegaFones". They slightly reduced the level of exhaust noise of the engine, and in some cases, it was also reduced, to increase the power of the engine due to improving the cleaning of the cylinder from the remnants of the spent gases due to the inertia of the gas pillage moving inside the conical exhaust pipe.

Calculations and practical experiments have shown that the optimal angle of the megaphone is close to 12-15 degrees. In principle, if you make a megaphone with such an angle of revealed very long, it will effectively extinguish the engine noise, almost without reducing its capacity, but in practice such structures are not implemented due to obvious design deficiencies and restrictions.

Another way to reduce the noise of DVS is to minimize pulsations of exhaust gases at the output of the exhaust system. For this, the exhaust is made not directly into the atmosphere, and in an intermediate receiver of sufficient volume (ideally, at least 20 times higher than the working volume of the cylinder), with subsequent release of gases through a relatively small hole, the area of \u200b\u200bwhich can be several times less than the exhaust area window. Such systems smooth the pulsating nature of the movement of the gas mixture at the outlet of the engine, turning it into close to the uniform-progressive at the outlet of the muffler.

Let me remind you that the speech at the moment goes to the devastating systems that do not increase gas-dynamic resistance exhaust gases. Therefore, I will not concern all sorts of tricks of the type of metal grids inside the devastating chamber, perforated partitions and pipes, which, of course, allow you to reduce the noise of the engine, but to the detriment of its power.

The next step in the development of silencers was systems consisting of various combinations of the methods described above. I will say right away, for the most part they are far from ideal, because In one degree or another, the gas-dynamic resistance of the exhaust path increases, which uniquely leads to a decrease in the power of the engine transmitted to the propulsion.

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This article discusses the assessment of the effect of the resonator on the filling of the engine. In the example of the example, a resonator was proposed - by volume equal to the engine cylinder. The geometry of the intake tract together with the resonator was imported into the FlowVision program. Mathematical modification was carried out taking into account all the properties of the moving gas. To estimate the flow rate through the inlet system, estimates of the flow rate in the system and the relative air pressure in the valve slit, computer simulation was carried out, which showed the effectiveness of the use of additional capacity. An assessment of the flow rate through the valve gap, the speed of flow, flow, pressure and flow density for the standard, upgraded and intake system with the Rexiver was evaluated. At the same time, the mass of the incoming air increases, the flow rate of the flow is reduced and the density of air entering the cylinder increases, which is favorably reflected on the output TV-televons.

inlet tract

resonator

filling a cylinder

math modeling

upgraded canal.

1. Jolobov L. A., Dydykin A. M. Math modeling DVS gas exchange processes: monograph. N.N.: NGSHA, 2007.

2. Dydyskin A. M., Zholobov L. A. Gasodynamic studies of the DVS methods of numerical modeling // Tractors and agricultural machines. 2008. № 4. P. 29-31.

3. Pritr D. M., Turkish V. A. Aeromechanics. M.: Oborongiz, 1960.

4. Heilov M. A. Calculated pressure fluctuation equation in the absorbing pipe engine internal combustion // Tr. Cyam. 1984. No. 152. P.64.

5. Sonkin V. I. Study of air flow through the valve gap // Tr. US. 1974. Issue 149. P.21-38.

6. Samsky A. A., Popov Yu. P. Difference methods for solving the problems of gas dynamics. M.: Science, 1980. P.352.

7. Rudoy B. P. Applied nonstationary gas dynamics: Tutorial. Ufa: Ufa Aviation Institute, 1988. P.184.

8. Malivanov M. V., Khmelev R. N. To the issue of the development of mathematical and software Calculation of gas-dynamic processes in DVS: materials of the IX International Scientific and Practical Conference. Vladimir, 2003. P. 213-216.

The magnitude of the torque of the engine is proportional to the mass of air, attributed to the frequency of rotation. Increasing the filling of the cylinder of gasoline engine, by upgrading the intake path, will lead to an increase in the pressure of the end of the intake, improved mixing formation, an increase in the technical and economic indicators of the engine operation and a decrease in the toxicity of exhaust gases.

The basic requirements for the inlet path are to ensure minimal resistance to the inlet and the uniform distribution of the combustible mixture through the engine cylinders.

Ensuring the minimum resistance to the inlet can be achieved by eliminating the roughness of the inner walls of pipelines, as well as sharp changes in the flow direction and eliminate sudden narrowings and extensions of the tract.

Significant effect on the cylinder filling provide different kinds supervision. The simplest type of superior is to use the dynamics of the incoming air. A large volume of the receiver partially creates resonant effects in a specific rotational speed range, which lead to improved filling. However, they have, as a result, dynamic disadvantages, for example, deviations in the composition of the mixture with a rapid change in the load. Almost the ideal torque flow ensures that the inlet tube is switching, in which, for example, depending on the engine load, the rotational speed and position of the throttle are possible variations:

The length of the pulsation pipe;

Switch between pulsation pipes of different lengths or diameter;
- selective shutdown of a separate pipe of one cylinder in the presence of a large amount of them;
- Switching the volume of the receiver.

With the resonant superior group of cylinders with the same flash intervals attach short tubes to resonant receiver, which through resonant pipes It is connected to the atmosphere or with a prefab receiver acting as a gölmgolts resonator. It is a spherical vessel with an open neck. The air in the neck is the oscillating mass, and the volume of air in the vessel plays the role of an elastic element. Of course, such separation is true only approximately, since some of the air in the cavity has inertial resistance. However, with a sufficiently large value of the area of \u200b\u200bthe opening to the area of \u200b\u200bthe cross section of the cavity, the accuracy of such an approximation is quite satisfactory. The main part of the kinetic oscillation energy is concentrated in the neck of the resonator, where the oscillatory velocity of air particles has the greatest value.

The intake resonator is established between the throttle and cylinder. It begins to act when the throttle is covered enough so that its hydraulic resistance becomes comparable to the resistance of the resonator channel. When the piston moves down, the combustible mixture enters the engine cylinder not only from under the throttle, but also from the tank. With a decrease in the vacuum, the resonator begins to suck the combustible mixture. This will follow the same part, and quite large, reverse ejection.
The article analyzes the flow movement in the intake channel of 4-stroke gasoline engine at the rated crankshaft rotation frequency on the example of the VAZ-2108 engine at the rotational speed of the crankshaft N \u003d 5600min-1.

This research task was solved by the mathematical way using the software package for modeling gas-hydraulic processes. Simulation was carried out using the FlowVision software package. For this purpose, geometry was obtained and imported (under geometry means internal engine volumes - intake and exhaust pipelines, an atrigible volume of the cylinder) using various standard formats files. This allows SAPR SOLIDWORKS to create a settlement area.

Under the calculation area means the volume in which the equations are defined mathematical model, and the border of the volume on which the boundary conditions are defined, then maintain the resulting geometry in the format supported by the FlowVision and use it when creating a new calculated option.

This task used ASCII, Binary format, in the STL extension, type stereolithographyFormat with an angular tolerance of 4.0 degrees and a deviation of 0.025 meters to improve the accuracy of the resulting modeling results.

After receiving the three-dimensional model of the settlement area, a mathematical model is set (a set of laws of changes in the physical parameters of gas for this problem).

In this case, a substantially subsonic flow of gas is taken at small Reynolds numbers, which is described by the model of the turbulent flow of fully compressible gas using standard K-E Turbulence models. This mathematical model is described by a system consisting of seven equations: two Navier - Stokes equations, the equations of continuity, energy, the state of the ideal gas, mass transfer and the equation for the kinetic energy of turbulent ripples.

(2)

Energy equation (complete enthalpy)

The equation of the state of the ideal gas:

Turbulent components are associated with the remaining variables through the turbulent viscosity value, which is calculated in accordance with the standard K-ε model of turbulence.

Equations for k and ε

turbulent viscosity:

constants, parameters and sources:

(9)

(10)

σk \u003d 1; σε \u003d 1.3; Cμ \u003d 0.09; Cε1 \u003d 1.44; Cε2 \u003d 1.92

The working substance in the inlet process is air, in this case, considered as the perfect gas. The initial values \u200b\u200bof the parameters are set for the entire settlement area: temperature, concentration, pressure and speed. For pressure and temperature, the initial parameters are equal to reference. The speed inside the calculated region in directions x, y, z is zero. Variable temperature and pressure in FlowVision are represented by relative values, the absolute values \u200b\u200bof which are calculated by the formula:

fa \u003d F + Fref, (11)

where Fa is the absolute value of the variable, F is the calculated relative value of the variable, Fref - the reference value.

Boundary conditions are specified for each of the calculated surfaces. Under the boundary conditions it is necessary to understand the combination of equations and laws characteristic of the surfaces of the calculated geometry. Boundary conditions are necessary to determine the interaction of the settlement area and the mathematical model. On the page for each surface indicates a specific type of boundary condition. The type of the boundary condition is installed on the input channel input windows - free entry. The remaining elements - the wall-bound, which does not let and not transmitting the calculated parameters of the current area. In addition to all of the above boundary conditions, it is necessary to take into account the boundary conditions on the moving elements included in the selected mathematical model.

Movable parts include inlet and exhaust valve, piston. At the boundaries of movable elements, we determine the type of boundary condition of the wall.

For each of the movable bodies, the law of movement is set. Changing the piston rate is determined by the formula. To determine the laws of the valve motion, the valve lift curves were removed in 0.50 with an accuracy of 0.001 mm. Then the speed and acceleration of the valve movement were calculated. The data obtained are converted to dynamic libraries (time - speed).

The next stage in the simulation process is the generation of the computational grid. FlowVision uses a locally adaptive computational net. Initially, an initial computational grid is created, and then the criteria for grinding grid are specified, according to which FlowVision breaks the cells of the initial grid to the desired degree. Adaptation is made in both the volume of the channels of the channels and the cylinder walls. In places with a possible maximum speed, adaptation with additional grinding of the computational grid are created. By volume, the grinding was carried out up to 2 levels in the combustion chamber and up to 5 levels in valve slots, along the walls of the cylinder, adaptation was made up to 1 level. This is necessary to increase the time integration step with an implicit method of calculation. This is due to the fact that the time step is defined as the ratio of the cell size to the maximum speed in it.

Before starting to calculate the created option, you must specify the parameters of numerical modeling. At the same time, the time to continue the calculation is equal to one full cycle of operation of the engine, 7200 PK., The number of iterations and the frequency of saving these calculation options. For subsequent processing, certain stages of calculation are preserved. Set the time and options for the calculation process. This task requires a time step setting - a method of choice: an implicit scheme with a maximum step 5E-004C, explicit number of CFL - 1. This means that the time step determines the program itself, depending on the convergence of the pressure equations itself.

The postprocessor is configured and the parameters of the visualization of the results are interested in. Simulation allows you to obtain the required layers of visualization after the completion of the main calculation, based on the calculation stages remained with a certain frequency. In addition, the postprocessor allows you to transmit the resulting numeric values \u200b\u200bof the parameters of the process under study in the form of an information file into external electronic table editors and to obtain the time dependence of such parameters as speed, consumption, pressure, etc.

Figure 1 shows the installation of the receiver on the inlet channel of the DVS. The volume of the receiver is equal to the volume of one engine cylinder. The receiver is set as close as possible to the inlet channel.

Fig. 1. Upgraded with the receiver Settlement area in CadsolidWorks

The own frequency of the Helmholtz resonator is:

(12)

where F is the frequency, Hz; C0 - sound speed in the air (340 m / s); S - hole cross section, m2; L is the length of the pipe, m; V is the volume of the resonator, M3.

For our example, we have the following values:

d \u003d 0.032 m, s \u003d 0.00080384 m2, v \u003d 0.000422267 m3, l \u003d 0.04 m.

After calculating F \u003d 374 Hz, which corresponds to the rotational speed of the crankshaft N \u003d 5600min-1.

After setting the calculated option and, after setting the parameters of numerical simulation, the following data were obtained: flow rate, speed, density, pressure, gas flow temperature in the inlet channel of the intensity of the Crankshaft rotation.

From the graph presented (Fig. 2), in terms of flow flow in the valve slit, it is clear that the upgraded channel with the receiver has the maximum consumables. Consumption value is higher than 200 g / s. The increase is observed for 60 G.P.K.V.

Since the opening of the inlet valve (348 G.K.V.) The flow rate (Fig. 3) begins to grow from 0 to 170m / s (at the modernized intake channel 210 m / s, with the -190m / s receivers) in the interval Up to 440-450 G.K.V. In the channel with the receiver, the speed value is higher than in a standard approximately 20 m / s starting from 430-440. P.K.V. The numeric value of the channel in the channel with the receiver is significantly more even than the upgraded inlet channel, during the opening of the inlet valve. Next, there is a significant reduction in the flow rate, up to the closure of the inlet valve.

Fig. 2. Consumption of the gas flow in the valve slot for the channels of standard, upgraded and with the receiver at n \u003d 5600 min-1: 1 - standard, 2 - upgraded, 3 - upgraded with the receiver

Fig. 3. The flow rate of the flow in the valve slot for the channels of standard, upgraded and with the receiver at n \u003d 5600 min-1: 1 - standard, 2 - upgraded, 3 - upgraded with the receiver

Of the relative pressure graphs (Fig. 4) (atmospheric pressure, P \u003d 101000 PA is received for zero), it follows that the pressure value in the upgraded channel is higher than in the standard, by 20 kPa at 460-480 GP.K.V. (associated with a large flow rate value). Starting from 520 G.K.V. The pressure value is aligned, which cannot be said about the channel with the receiver. The pressure value is higher than in the standard one, by 25 kPa, starting from 420-440 GP.K.V. Up to the closure of the inlet valve.

Fig. 4. Flow pressure in standard, upgraded and channel with a receiver at n \u003d 5600 min-1 (1 - standard channel, 2 - upgraded channel, 3 - upgraded channel with receiver)

Fig. 5. Flow density in standard, upgraded and channel with a receiver at n \u003d 5600 min-1 (1 - standard channel, 2 - upgraded channel, 3 - upgraded channel with receiver)

The flow density in the area of \u200b\u200bthe valve gap is shown in Fig. five.

In the upgraded channel with the receiver, the density value is below 0.2 kg / m3 starting from 440 G.K.V. Compared with a standard channel. This is associated with high pressure and gas flow rates.

From the analysis of graphs, you can draw the following conclusion: the channel of the improved form provides better filling of the cylinder with a fresh charge due to a decrease in the hydraulic resistance of the inlet channel. With the increase in the piston velocity at the time of opening the inlet valve, the channel form does not significantly affect the speed, density and pressure inside the intake channel, it is explained by the fact that during this period the inlet process indicators are mainly dependent on the speed of the piston and the valve slot area ( Only the shape of the intake channel changed in this calculation), but everything changes dramatically at the time of slowing down the movement of the piston. The charge in the standard channel is less inert and more stronger "stretch" along the length of the channel, which in the aggregate gives less filling of the cylinder at the time of reducing the speed of the piston movement. Up to the closure of the valve, the process flows under the denominator of the flow rate already obtained (the piston gives the initial flow rate of the cached volume, with a decrease in the velocity of the piston, the inertia component of the gas flow has a significant role on the filling. This is confirmed by higher speed indicators, pressure.

In the inlet canal with the receiver, due to additional charge and resonant phenomena, in the Cylinder of DVS there is a significantly large mass of the gas mixture, which provides higher technical indicators of the DVS operation. The growth increase in the end of the inlet will have a significant impact on the increase in the technical and economic and environmental performance of the DVS work.

Reviewers:

Gots Alexander Nikolaevich, Doctor of Technical University, Professor of the Department of Heat Engines and Energy Installations of the Vladimir State University of the Ministry of Education and Science, Vladimir.

Kulchitsky Aleksey Ramovich, D.N., Professor, Deputy Chief Designer LLC VMTZ, Vladimir.

Bibliographic reference

Jolobov L. A., Suvorov E. A., Vasilyev I. S. Effect of additional capacity in the inlet system for Filling internal combustion // Modern problems science and education. - 2013. - № 1;
URL: http://science-education.ru/ru/Article/View?id\u003d8270 (date of handling: 25.11.2019). We bring to your attention the magazines publishing in the publishing house "Academy of Natural Science"

The gas-dynamic supervision includes methods for increasing the charge density at the inlet by use:

· The kinetic energy of air moving on the receiving device in which it is converted to the potential pressure of pressure when braking the stream - high-speed supervision;

· Wave processes in intake pipelines -.

In the thermodynamic cycle of the engine without boosting the beginning of the compression process occurs at pressure p. 0, (equal atmospheric). In the thermodynamic cycle of the piston engine with a gas-dynamic supervision, the beginning of the compression process occurs at pressure p K. , due to the increase in the pressure of the working fluid outside the cylinder from p. 0 BE p K.. This is due to the transformation of the kinetic energy and the energy of the wave processes outside the cylinder into the potential energy of pressure.

One of the energy sources to increase the pressure at the beginning of the compression may be the energy of the incident air flow, which takes place when the aircraft, car, etc. means. Accordingly, adding in these cases is called high-speed.

High-speed supervision Based on aerodynamic patterns of transformation of high-speed air flow in static pressure. Structurally, it is realized as a diffuser air intake nozzle, aimed at towing air flow when driving vehicle. Theoretically increase the pressure Δ p K.=p K. - p. 0 Depends on speed c. H and density ρ 0 incident (moving) air flow

High-speed supervision finds use mainly on aircraft with piston engines and sports carswhere speed speeds are more than 200 km / h (56 m / s).

The following varieties of gas-dynamic supervision of engines are based on the use of inertial and wave processes in the engine inlet system.

Inertial or dynamic reducing takes place at relatively high speed of moving fresh charge in the pipeline c. Tr. In this case, equation (2.1) takes

where ξ t is a coefficient that takes into account the resistance to the movement of gas in length and local.

Real speed c. The gas flow of gas in intake pipelines, in order to avoid elevated aerodynamic losses and deterioration in the filling of cylinders with fresh charge, should not exceed 30 ... 50 m / s.

The frequency of processes in the cylinders piston engines It is the cause of oscillatory dynamic phenomena in gas-air paths. These phenomena can be used to substantially improve the main indicators of engines (liter power and economy.

Inertial processes are always accompanied by wave processes (fluctuations in pressure) arising from the periodic opening and closing of the inlet valves of the gas exchange system, as well as the return-transit movement of the pistons.



At the initial stage of inlet in the inlet nozzle before the valve, a vacuum is created, and the corresponding wave of pouring, reaching the opposite end of the individual inlet pipeline, reflects the compression wave. By selecting the length and passage section of the individual pipeline, you can get the arrival of this wave to the cylinder at the most favorable moment before closing the valve, which will significantly increase the filling factor, and therefore torque M E. Engine.

In fig. 2.1. A diagram of a tuned intake system is shown. Through the inlet pipe, bypassing throttle valveThe air enters the receiving receiver, and the input pipelines of the configured length to each of the four cylinders from it.

In practice, this phenomenon is used in foreign engines (Fig. 2.2), as well as domestic engines for passenger cars with customized individual inlet pipelines (for example, zMZ engines), as well as on a 2h8.5 / 11 diesel engine, a stationary electric generator having one tuned pipeline into two cylinders.

The greatest efficiency of gas-dynamic supervision takes place with long individual pipelines. Advance pressure depends on the coordination of the engine rotation frequency n., pipeline lengths L. Tr and corners

bending the closure of the intake valve (organ) φ A.. These parameters are related addiction

where is the local sound speed; k. \u003d 1.4 - the adiabatic index; R. \u003d 0.287 kJ / (kg ∙ hail.); T. - average gas temperature for the pressure period.

Wave and inertial processes can provide a noticeable increase in charge in a cylinder at large valve discoveries or in the form of increasing recharge in compression tact. The implementation of effective gas-dynamic supervision is possible only for a narrow range of engine rotation frequency. The combination of the phases of the gas distribution and the length of the intake pipeline must provide the greatest filling coefficient. Such selection of parameters are called setting the inlet system.It allows you to increase the engine power by 25 ... 30%. To preserve the effectiveness of gas-dynamic supervision in a wider range of rotational frequency of the crankshaft can be used various methods, in particular:

· Applying a pipeline with a variable length l. Tr (for example, telescopic);

· Switching from a short pipeline for long;

· Automatic regulation of gas distribution phases, etc.

However, the use of gas-dynamic supervision for engine boost is associated with certain problems. First, it is not always possible to rationally comply with sufficiently extended intake pipelines. It is especially difficult to do for low-speed engines, because with a decrease in the speed of rotation, the length of the adjusted pipelines increases. Secondly, fixed pipeline geometry gives dynamic setting only in some, quite defined range speed \u200b\u200bregime Work.

To ensure the effect in a wide range, a smooth or step adjustment of the length of the configured path is used when moving from one speed mode to another. Step control using special valves or turning dampers is considered more reliable and successfully applied in automotive engines Many foreign firms. Most often use control with switching into two customized pipeline lengths (Fig. 2.3).

In the position of the closed flap, the corresponding mode up to 4000 min -1, air supply from the intake receivers of the system is carried out along a long path (see Fig. 2.3). As a result (compared to the base version of the engine without gas-dynamic supervision), the flow of torque curve is improved on an external speed characteristic (at some frequencies from 2500 to 3500 min -1, the torque increases on average by 10 ... 12%). With increasing rotation speed N\u003e 4000 min -1 Feed switches to a short path and this allows you to increase the power N E. on nominal mode by 10%.

There are also more complex all-life systems. For example, designs with pipelines covering a cylindrical receiver with a rotary drum having windows for messages with pipelines (Fig. 2.4). When the cylindrical receiver is rotated, the length of the pipeline is increased and vice versa, when turning clockwise, it decreases. However, the implementation of these methods significantly complicates the engine design and reduces its reliability.

In multi-cylinder engines with conventional pipelines, the efficiency of gas-dynamic supervision is reduced, which is due to the mutual influence of intake processes in various cylinders. In the car engines, intake systems "set up" usually on the maximum torque mode to increase its stock.

The effect of gas-dynamic superior can also be obtained by the corresponding "setting" of the exhaust system. This method finds use on two-stroke engines.

To determine the length L. Tr and inner diameter d. (or passage section) of the adjustable pipeline it is necessary to carry out calculations using numerical methods of gas dynamics describing the non-stationary flow, together with the calculation of the workflow in the cylinder. The criterion is the increase in power,

torque or reducing the specific fuel consumption. These calculations are very complex. More simple methods Definitions L. three d. Based on the results of experimental studies.

As a result of the processing of a large number of experimental data to select internal diameter d. The adjustable pipeline is proposed as follows:

where (μ. F. Y) MAX is the most effective area of \u200b\u200bthe inlet valve slot. Length L. The trifle pipeline can be determined by the formula:

Note that the use of branched tuned systems such as a common pipe - receiver - individual pipes turned out to be very effective in combination with turbocharging.

UDC 621.436

Effect of aerodynamic resistance of intake and exhaust systems of automotive engines on gas exchange processes

L.V. Carpenters, bp Zhilkin, Yu.M. Brodov, N.I. Grigoriev

The paper presents the results of an experimental study of the influence of the aerodynamic resistance of intake and exhaust systems of piston engines to gas exchange processes. The experiments were carried out on the on-line models of single-cylinder engine. Installations and methods for conducting experiments are described. The dependences of the change in the instantaneous speed and pressure of the flow in the gas-air paths of the engine from the corner of the crankshaft rotation are presented. The data was obtained at different intake resistance coefficients and graduation systems and different rotation frequencies of the crankshaft. Based on the data obtained, conclusions were made of the dynamic features of gas exchange processes in the engine at different conditions. It is shown that the use of the noise muffler smoothes the flow ripple and changes the flow characteristics.

Keywords: piston engine, gas exchange processes, process dynamics, speed pulsation and flow pressure, noise muffler.

Introduction

A number of requirements are made to intake and outcomes of piston engines of internal combustion, among which the main decrease in aerodynamic noise and minimal aerodynamic resistance are the main. Both of these indicators are determined in the interconnection of the design of the filter element, inlet silencers and the release, catalytic neutralizers, the presence of a superior (compressor and / or turbocharger), as well as the configuration of intake and exhaust pipelines and the nature of the flow in them. At the same time, there are practically no data on the influence of additional elements of intake and exhaust systems (filters, silencers, turbocharger) on gas dynamics in them.

This article presents the results of a study of the effect of the aerodynamic resistance of intake and exhaust systems on gas exchange processes in relation to the piston engine of dimension 8.2 / 7.1.

Experimental plants

and data collection system

Studies of the effect of aerodynamic resistance of gas-air systems on gas exchange processes in piston engineers were carried out on the simulation model of the dimension 4.2 / 7.1, driven by rotation asynchronous engineThe frequency of rotation of the crankshaft of which was adjusted in the range n \u003d 600-3000 min1 with an accuracy of ± 0.1%. An experimental installation is described in more detail.

In fig. 1 and 2 show the configurations and geometric sizes of the intake and exhaust path of the experimental installation, as well as the installation location for the measurement of instantaneous

the values \u200b\u200bof the average speed and pressure of the flow of air.

For measurements of instant pressure values \u200b\u200bin the stream (static) in the PC channel, the pressure sensor £ -10 was used by Wika, the speed of which is less than 1 ms. The maximum relative average mean-square pressure measurement error was ± 0.25%.

To determine the instantaneous medium in the section of the air flow channel, the thermoenemometers of the constant temperature of the original design, the sensitive element of which was the nichrome thread with a diameter of 5 μm and a length of 5 mm. The maximum relative average mean-of-mean error of measuring the speed WX was ± 2.9%.

The measurement of the rotational frequency of the crankshaft was carried out using a tachometric meter consisting of a toothed disk fixed on crankshaft Vale, and inductive sensor. The sensor formed a voltage pulse at a frequency proportional to the rotation speed of the shaft. According to these pulses, the frequency of rotation was recorded, the position of the crankshaft (angle f) was determined and the moment of passing the piston of VMT and NMT.

Signals from all sensors entered an analog-to-digital converter and transmitted to a personal computer for further processing.

Before carrying out experiments, a static and dynamic targeting of the measuring system was carried out in general, which showed the speed necessary to study the dynamics of gas-dynamic processes in the inlet and exhaust systems of piston engines. The total average mean-of-mean error of experiments on the effect of the aerodynamic resistance of gas-air systems of DVS Gas exchange processes were ± 3.4%.

Fig. 1. Configuration and geometric sizes of the intake path of the experimental installation: 1 - cylinder head; 2-bubbling pipe; 3 - measuring tube; 4 - thermoanemometer sensors for measuring air flow rate; 5 - Pressure Sensors

Fig. 2. Configuration and geometric dimensions of the exhaust path of the experimental installation: 1 - cylinder head; 2 - working plot - graduation pipe; 3 - pressure sensors; 4 - thermoemometer sensors

The effect of additional elements on the gas dynamics of intake and release processes was studied with different system resistance coefficients. Resistance was created using various intake filters and release. So, as one of them, a standard air automobile filter was used with a resistance coefficient of 7.5. A tissue filter with a resistance coefficient 32 was chosen as another filter element. The resistance coefficient was determined experimentally through static purge in laboratory conditions. Studies were also conducted without filters.

Effect of aerodynamic resistance on the inlet process

In fig. 3 and 4 show the dependences of the air flow rate and PC pressure in the inlet can

le from the angle of rotation of the crankshaft f at different of its rotation frequencies and when using various intake filters.

It has been established that in both cases (with a silencer and without) pulsation of pressure and air flow rates are most expressed at high speed of rotation of the crankshaft. At the same time, in the inlet channel with a silencer of noise, the values \u200b\u200bof the maximum air flow rate, as expected, less than in the channel without it. Most

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Fig. 3. The dependence of the air velocity WX in the intake channel from the angle of rotation of the crankshaft shaft at different frequencies of the rotation of the crankshaft and different filtering elements: a - n \u003d 1500 min-1; B - 3000 min-1. 1 - without a filter; 2 - standard air filter; 3 - fabric filter

Fig. 4. The dependence of the PC pressure in the inlet channel from the angle of rotation of the crankshaft f at different frequencies of rotation of the crankshaft and different filtering elements: a - n \u003d 1500 min-1; B - 3000 min-1. 1 - without a filter; 2 - standard air filter; 3 - fabric filter

it was brightly manifested with high frequencies of rotation of the crankshaft.

After closing the intake valve, the pressure and speed of the air flow in the channel under all conditions do not become equal to zero, and some of their fluctuations are observed (see Fig. 3 and 4), which is also characteristic of the release process (see below). At the same time, the installation of the inlet noise muffler leads to a decrease in pressure pulsations and air flow rates under all conditions both during the intake process and after the intake valve is closed.

Effect of aerodynamic

resistance to the release process

In fig. 5 and 6 shows the dependences of the air flow rate of the WX and the pressure PC in the outlet from the angle of rotation of the crankshaft form at different rotational frequencies and when using various release filters.

The studies were carried out for various frequencies of rotation of the crankshaft (from 600 to 3000 min1) at different overpressure on the release of PI (from 0.5 to 2.0 bar) without a silent noise and if it is presented.

It has been established that in both cases (with the silencer and without) pulsation of the air flow rate, the most brightly manifested at low frequencies of the crankshaft rotation. In this case, the values \u200b\u200bof the maximum air flow rate remain in the exhaust channel with the noise silencer

merilly the same as without it. After closing the exhaust valve, the air flow rate in the channel under all conditions does not become zero, and some speed fluctuations are observed (see Fig. 5), which is characteristic of the inlet process (see above). At the same time, the installation of the noise muffler on the release leads to a significant increase in the pulsations of the air flow rate under all conditions (especially at ry \u003d 2.0 bar) both during the release process and after the exhaust valve is closed.

It should be noted the opposite effect of aerodynamic resistance on the characteristics of the inlet process in the engine, where air filter Pulsation effects in the intake process and after closing the inlet valve were present, but they were clearly faster than without it. In this case, the presence of a filter in the inlet system led to a decrease in the maximum air flow rate and weakening the dynamics of the process, which is consistent well with previously obtained results in the work.

An increase in the aerodynamic resistance of the exhaust system leads to a certain increase in the maximum pressures in the process of release, as well as the displacement of peaks for NMT. In this case, it can be noted that the installation of the silencer of the noise of the output leads to a decrease in the pulsations of the pressure of the air flow under all conditions both during the production process and after the exhaust valve is closed.

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Fig. 6. The dependence of the pressure PC in the outlet from the angle of rotation of the crankshaft f at different frequencies of rotation of the crankshaft and different filtering elements: a - n \u003d 1500 min-1; B - 3000 min-1. 1 - without a filter; 2 - standard air filter; 3 - fabric filter

Based on the processing of dependency changes in the flow rate for separate tact, a relative change in the volume flow of air q was calculated through the exhaust channel when the muffler is placed. It has been established that with low overpressure on the release (0.1 MPa), the consumption q in the exhaust system with a silencer is less than in the system without it. At the same time, if at the frequency of rotation of the crankshaft 600 min-1, this difference was approximately 1.5% (which lies within the error), then with n \u003d 3000 min4 this difference reached 23%. It is shown that for high overpressure of 0.2 MPa, the opposite tendency was observed. The volume flow of air through the exhaust channel with the silencer was greater than in the system without it. At the same time, at low frequencies of rotation of the crankshaft, this exceeded was 20%, and with n \u003d 3000 min1 - 5%. According to the authors, such an effect can be explained by some smoothing of the pulsations of the air flow rate in the exhaust system in the presence of a silent noise.

Conclusion

The conducted study showed that the inlet engine of internal combustion is significantly influenced by the aerodynamic resistance of the intake path:

The increase in the resistance of the filter element smoothes the dynamics of the filling process, but at the same time reduces air flow rate, which corresponds to the filling coefficient;

The effect of the filter is enhanced with the increasing rotation frequency of the crankshaft;

The threshold value of the filter resistance coefficient (approximately 50-55), after which its value does not affect the flow rate.

It has been shown that the aerodynamic resistance of the exhaust system also significantly affects the gas-dynamic and consumables of the release process:

Increasing the hydraulic resistance of the exhaust system in the piston DVS leads to an increase in the pulsations of the air flow rate in the exhaust channel;

With low overpressure on the release in the system with a silent noise, there is a decrease in volumetric flow through the exhaust channel, while at high ry - on the contrary, it increases compared to the exhaust system without a silencer.

Thus, the results obtained can be used in engineering practice in order to optimally choose the characteristics of the inlet and outbuilding silencers, which can provide

the influence on the filling of the cylinder of the fresh charge (filling coefficient) and the quality of the cleaning of the engine cylinder from the exhaust gases (the residual gas coefficient) on certain high-speed modes of the work of the piston engine.

Literature

1. Draganov, B.H. Construction of intake and exhaust channels of internal combustion engines / B.Kh. Draganov, MG Kruglov, V. S. Obukhov. - Kiev: Visit School. Head ed, 1987. -175 p.

2. Internal combustion engines. In 3 kN. Kn. 1: Theory of workflows: studies. / V.N. Lou-Kanin, K.A. Morozov, A.S. Khachyan et al.; Ed. V.N. Lukanina. - M.: Higher. Shk., 1995. - 368 p.

3. Champraozs, B.A. Internal combustion engines: theory, modeling and calculation of processes: studies. In the course "Theory of workflows and modeling of processes in internal combustion engines" / B.A. Chamolaoz, M.F. Faraplatov, V.V. Clementev; Ed. Castle Deat. Science of the Russian Federation B.A. Champrazov. - Chelyabinsk: SUURSU, 2010. -382 p.

4. Modern approaches to the creation of diesel engines for passenger cars and small-calm

zovikov /a. Blinov, P.A. Golubev, Yu.E. Dragan et al.; Ed. V. S. Peponova and A. M. Mineyev. - M.: NIC "Engineer", 2000. - 332 p.

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6. On the change in gas dynamics of the process of release in piston engine in the installation of the muffler / L.V. Carpenters, bp Zhokkin, A.V. Cross, D.L. Padalak // Bulletin of the Academy of Military Sciences. -2011. - № 2. - P. 267-270.

7. Pat. 81338 RU, MPK G01 P5 / 12. Thermal mechanical temperature of constant temperature / S.N. Pochov, L.V. Carpenters, bp Vilkin. - No. 2008135775/22; Stage. 09/03/2008; publ. 03/10/2009, Bul. № 7.

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