Construction of an indicator diagram of a diesel engine. Engine Indication. Secondary efficient pressure internal

Indicator engine diagram internal combustion It is built using the workflow calculation data.

When constructing on the abscissa axis, a segment AB, (Figure 8), corresponding to the working volume of the cylinder, is deposited, and the value of the piston is equal to the scale of M s. The scale M s is usually taken 1: 1, 1.5: 1 or 2: 1.

The segment of OA (mm) corresponding to the volume of the combustion chamber is determined from the equation

OA \u003d AV / (ε - 1) (2.28)

Z'Z segment for diesel engines working in a cycle with a ridiculous heat supply (Fig. 9)

z'Z \u003d OA (ρ - 1) (2.29)

Thus, according to the calculation of the parameters of the actual cycle, the diagram is delayed in the selected scale of pressures at the characteristic points: a, c, z, z, b, r.

The construction of the compression and expansion politrop can be performed by an analytical or graphic method. With an analytical method of constructing a compression and expansion politrop, a number of points are calculated for intermediate volumes located between V C. and V A. and between V z. and V B., according to the polytropic equation.

Fig. 8. Indicator chart of gasoline engine

Fig. 9. Indicator diagram diesel engine

For polytrophes of compression From!

, (2.30)

where p X. and V X. - Pressure and volume in the desired point of the compression process.

Attitude V A / V X varies within 1 ÷ ε.

Similar to the expansion politrop

(2.31)

For gasoline engines Attitude V b / v x Changes in the interval 1 ÷ ε, for diesel engines - 1 ÷ δ.

Determination of the ordinates of the calculated points of the politrop of compression and expansion is conveniently produced in tabular form.

Construction of the indicator diagrams produce connecting points but And with, z and b smooth curves, and points B and A, C and Z are straight lines.

Inlet and output processes are taken with r \u003d const and v \u003d const

To verify the correctness of the constructions of the diagram determine

r I. \u003d M p / ab

where f - chart area a.c'C "Z D B'B" a..

Calculation of indicator and effective DVS indicators

Indicator indicators

The operating cycle of the internal combustion engine is characterized by an average indicator pressure, an indicator power, an indicator efficiency and a specific indicator fuel consumption.

Theoretical average indicator pressure - This is the ratio of the theoretical settlement of gases for one cycle to the move of the piston.

For gasoline engines operating on a cycle with heat supply at V \u003d const, theoretical average indicator pressure

For a diesel engine operating on a cycle with a ridiculous heat supply under V. \u003d Const I. r \u003d const

Average indicator pressure P I valid cycle differs from a value by value proportional to the decrease in the calculated diagram due to the rounding at points C, Z, b.

Reducing the theoretical medium indicator pressure due to the deviation of the actual process on the calculated cycle is estimated by the completeness coefficient of the diagram φ and the value of the average pressure of pumping losses ΔP I..

The coefficient of completeness of the φ diagram and is accepted.

for carburetor engines ......................... .... 0.94 ÷ 0.97

for engines with electronic fuel injection ...... 0.95 ÷ 0.98

for diesel engines ........................................................ 0.92 ÷ 0.95

The average pressure of pumping losses (MPa) in the intake and release processes

Δp i \u003d p r - p a. (3.3)

For four-stroke engines without chance ΔP I. positive. In engines with reducing from the drive supercharger at P A. > p R. Value ΔP I. Negative. With gas turbine superior value p A.can be both more and less p R.. Value ΔP I. It may be both negative and positive.

When calculating losses on gas exchanges are taken into account in the work spent on mechanical losses. In this regard, it is assumed that the average indicator pressure P I differs from only the factor of the chart

p I. \u003d φ and. (3.4)

When operating at full load, the value of P I (MPa) reaches:

for four-stroke gasoline engines ........................ 0.6 ÷ 1.4

for four-stroke forced gasoline engines ... up to 1.6

for four-stroke diesel engines without boost .............................. 0.7 ÷ 1.1

for four-stroke diesel engines with a superior ....................................... .. up to 2.2

Indicator power N i - The work performed by gases inside the cylinder per unit of time.

For multi-cylinder engine, indicator power (kW) is equal to

N i \u003d p i v h in/(30τ ), (3.5)

where P i is the average indicator pressure, MPa;

V H. - working volume of one cylinder, L (DM 3);

i. - the number of cylinders;

n. - rotation frequency crankshaft engine, min -1;

τ - engine cliffness. For four-stroke engine τ \u003d 4.

Indicator power of one cylinder

N i \u003d p i v h n/(30τ ), (3.6)

Indicator Kpd. η I. characterizes the degree of use in the actual cycle of fuel heat for receipt useful work And it represents the ratio of heat equivalent to the indicator operation of the cycle, to the entire amount of heat entered into the cylinder with fuel.

For 1 kg of fuel

η i \u003d l i / n and, (3.7)

where L I. - heat equivalent to indicator work, MJ / kg;

N I. - lower heat combustion of fuel, MJ / kg.

For automotive and tractor engines working on liquid fuel

η i \u003d p · l 0 · α / (n and · ρ k · η v), (3.8)

where P I is expressed in MPa; l. 0 - in kg / kg fuel.; N I. - in MJ / kg fuel.; ρ k - in kg / m 3.

In automotive and tractor engines operating on nominal mode, the magnitude of the indicator efficiency is:

for engines with electronic fuel injection ......... 0.35 ÷ 0.45

for carburetor engines ................................. 0,30 ÷ 0.40

for diesel engines ............................................................ 0.40 ÷ 0.50

Specific indicator fuel consumption G i characterizes the efficiency of the actual cycle

g I. = 3600/ (η i n i) or g I. = 3600 ρ 0 η V / (p i · l 0 · α). (3.10)

Specific fuel consumption on nominal mode:

for engines with electronic fuel injection ... g I. \u003d 180 ÷ 230 g (kWh)

for carburetor engines ........................... g I. \u003d 210 ÷ 275 g (kWh)

for diesel engines .................................................... g I. \u003d 170 ÷ 210 g (kWh)

Effective indicators

Effective indicators are called the values \u200b\u200bcharacterizing the operation of the engine, removed from its shaft and useful. Effective indicators include: effective power, torque, mean effective pressure, specific effective flow rate, efficient efficiency.

Effective power. Useful work, obtained on the shaft of the engine per unit of time is called effective power. N E..

N E.=N I. - N. MP (3.9)

where N. MP power mechanical loss.

The effective power is given to the student in the source data for the design of the internal combustion system (see Task for the Performance Procedure).

Under mechanical loss, they understand the losses for all types of mechanical friction, the implementation of gas exchange, the drive of the auxiliary mechanisms (water, oil, fuel pump, fan, generator, etc.), ventilation losses associated with the movement of engine parts in the air-oil emulsion and air environment, and also on the drive of the compressor.

Mechanical losses are evaluated by middle pressure mechanical loss p. MP, which characterizes the specific operation of mechanical losses (per unit of working volume) when carrying out a working cycle.

With an analytical definition N E. (kW) it is calculated by the formula:

N e \u003d p e v h in/(30τ ) (3.10)

where p E.=L E / V H- secondary effective pressure (MPa), i.e., useful work obtained per cycle from a unit of work volume;

V H. - the working volume of the cylinder, l;

n. - The number of turns of the crankshaft, min -1

Effective torque M E. (N ∙ m)

M E. \u003d (3 ∙ 10 4 / π) ( N E / N) (3.11)

When calculating the OI, the average effective pressure (MPa) is determined as

p E.= P I - P MP (3.12)

Average pressure of mechanical losses P. MP (MPa) for motors of various types is determined by the software is determined by empirical formulas:

for gasoline engines with the number of cylinders up to six and the ratio S / D\u003e 1

p. MP \u003d 0.049 + 0,0152 V. P.SR;

for gasoline engines with the number of cylinders up to six and the S / D≤1 ratio

p. MP \u003d 0.034 + 0,0113 V. P.Sh.

for four-stroke diesel engines with undeveloped cameras

p. MP \u003d 0.089 + 0,0118 V. P.Sh.

In the four-stroke engine work processes occur as follows:

1. Inlet tact. When the piston moves from VTC to NMT due to the resulting discharge from the air cleaner into the cylinder cavity through the open intake valve, atmospheric air is received. Air pressure in the cylinder is 0.08 - 0.095 MPa, and the temperature of 40 - 60 C.
2. Compression tact. The piston moves from NMT to NTC; The intake and outlet valves are closed, as a result of this, the piston moving up the piston compresses the air received. To ignite fuel, it is necessary that the compressed air temperature is higher than the temperature of the fuel self-ignition. During the piston, the cylinder is injected through the nozzle diesel fuelsupplied by the fuel pump.
3. Extension tact, or work move. The fuel injected at the end of the compression cycle, mixing with heated air, flammifies, and the combustion process begins characterized by a rapid increase in temperature and pressure. At the same time, the maximum gas pressure reaches 6-9 MPa, and the temperature of 1800-2000 C. Under the action of gas pressure, the piston 2 moves from the NTT in the NMT - the working stroke occurs. NMT pressure drops to 0.3-0.5 MPa, and the temperature to 700 - 900 C.
4. Issue tact. The piston moves from NMT to VTC and through the open exhaust valve 6 spent gases are pushed out of the cylinder. Gas pressure decreases to 0.11-0.12 MPa, and the temperature is up to 500-700 C. After the end of the issue is completed, with further rotation of the crankshaft, the working cycle is repeated in the same sequence.

The indicator diagram, removed using the indicator instrument, is called an indicator diagram (Fig. 1).

Fig. one

Consider a chart:

0-1 - filling the cylinder with air (with internal mixing formation) or a working mixture (with outer mixture formation) at a pressure slightly lower than atmospheric due to the hydrodynamic resistance of the intake valves and the suction pipeline,
1-2 - compression of air or working mixture,
2-3 "-3 - a period of burning of the working mixture,
3-4 - the workforce of the piston (expansion of combustion products), mechanical work is performed,
4-5 - exhaust exhaust gases, the pressure drop to atmospheric occurs almost at a constant volume,
5-0 - the release of the cylinder from combustion products.

In real thermal motors, the heat transformation into work is associated with the flow of complex irreversible processes (there are friction, chemical reactions in the working body, the end-velocity of the piston, heat transfer, etc.) Thermodynamic analysis of such a cycle is impossible Gelman V.M., Moskvin M.V. Agricultural tractors and cars. - M.: Agropromizdat, 1987, H I and P ..

The indentation is understood to be the removal, followed by the processing of the indicator diagrams, which are the graphical dependence of the pressure developed in the working cylinder in the function of the piston of the piston S or the volume of the cylinder V s proportional to it (see Fig. 1 and 2).

Indicators "Maigak"

Charts are removed from each working cylinder using a special instrument - the Maigak piston type indicator. The presence of the diagram allows you to determine the parameters important to analyze the workflow P I, R S and R Max. Diagram in fig. 1 Typical for engines, when operating which the main task consisted in reducing the level and content in the exhaust of nitrogen oxides. For this, as previously noted, a later fuel injection is carried out and the combustion occurs with less pressure and temperatures in the combustion chamber.

Fig. 1 Indicator Engine Diagram Man-BV KL-MC

If the main goal is to increase the engine efficiency, then the combustion is organized with an earlier fuel supply and, appropriate, more pressure growth. In the presence of electronic system Fuel Management This restructuring is easily implemented.

On the fig chart. 2 Clearly visible two hump - compression and then bore. Such a character is achieved by even later fuel supply. The figures contain two types of diagrams - rolled, according to which the average indicator pressure is defined, and the deployed, allowing to visually assess the nature of the development of processes. Similar diagrams can be obtained using the Maigak piston indicator, for which it is necessary to prevent

Fig. 2 Indicator Engine Diagram Man-BV SMC

synchronize the rotation of the beam of the indicator with the movement of the piston of the indicator cylinder. Connecting the drive allows you to get a rolled diagram, the planimization of the area of \u200b\u200bwhich is determined average indicator pressurewhich is some mean conditional pressure acting on the piston and performing work perpetrators for one job equal to the operation of gases per cycle.

P i \u003d F ind.d / l M, where F ind.d - chart area proportional to the operation of gases per cycle, L. - the length of the diagram, the proportional value of the working volume of the cylinder, m. - a large-scale multiplier, depending on the rigidity of the springs of the indicator piston.

By P I. calculated indicator power cylinder N i \u003d c p i nwhere η - the number of revolutions 1 / min and FROM - constant cylinder. Effective power N e \u003d n i η fur kw η meh. -mechanical efficiency enginewhich can be found in the engine documentation.

Before proceedings, check the status of the indicator crane and drive. Possible errors in their state are illustrated in Fig. 3.

The comb (Fig. 2) is removed when manually controlled with a cord disconnected from the indicator drive. The presence of a comb look-will estimate the stability of cycles and more accurately measure R Max. If peaks are the same, this indicates stable work Fuel equipment.

It is important to note that the piston indicators have a small frequently, of their own oscillations. The latter should, at least 30 times to exceed the number of engine speeds. Otherwise, the indicator charts will be removed with distortions. Therefore, application

Fig. 3 Errors in setting the indicator drive

piston indicators are limited to 300 rpm. Indicators with a rod spring have a greater frequency of own cooles and their use is allowed in the engines with the frequency of rotation to 500-700 rpm. However, in such engines there is no indicator actuator and have to be limited to the removal of a comb or times-returned diagrams for which it is not possible to determine.

The second limitation concerns the magnitude of the maximum pressure in the cylinders. IN modern engines from high levels Forcing it reaches 15-18 MPa. As used in the "Maigak" indicator, the port-screen for diesel engines with a diameter of 9.06 mm is the maximum rigid spring limit-fishes p max \u003d 15 MPa. With such a spring, the measurement accuracy is very low, since the springs scale is 0.3 mm by 0.1 MPa.

It is also significant that the work on indistions is quite tire and laborious, and the accuracy of the results is low. Small accuracy is due to errors arising from the imperfection of an indian drive and the inaccuracy of processing indicator charts during their manual planning. For information - The inaccuracy of the indicator actuator, expressed in the displacement of the drive from its true position by 1 °, leads to an error of about 10%.

Indicator diagram

a graphic image of a gas pressure change or steam in a piston machine cylinder depending on the position of the piston. I. d. Draws out usually using the pressure indicator (see the pressure indicator). According to the abscissa axis, the volume occupied by gases in the cylinder is postponed, and according to the axis ordinate - pressure. Each point on I. d. ( fig. ) Shows the pressure in the engine cylinder at this volume, i.e. at this piston position (point r. corresponds to the beginning of the intake; point but - the beginning of compression; point from - the end of the compression; point z. - the beginning of the expansion; point b. - the end of the expansion).

I. d. Gives an idea of \u200b\u200bthe value of work produced by an internal combustion engine or pump, and about their power. The working body makes useful work only during the working stroke. Therefore, it is necessary to determine useful work from the area, limited expansion curve. zB., subtract the area, limited compression curve aC. The theoretical and valid I. d. Theoretical is built according to thermal calculation and characterizes the theoretical cycle; Valid I. d. Removed from the operating machine using the indicator and characterizes the actual cycle (see fig. ).

For the convenience of making calculations and comparison different engines The variables in the course of the pressure piston are replaced by the conditional constant pressure, in which the percentage of the piston turns out the operation equal to the operation of the gases per cycle with variable pressure. This constant pressure is called medium indicator pressure and is the operation of gases related to the working volume of the piston machine.

B. A. Kurov.

Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

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The main difference between the 2-stroke engine from a 4-stroke is the method of gas exchange - cleaning the cylinder from combustion products and charging it with fresh air or a hot mixture.

Devices for gas distribution 2-stroke engines - slots in the cylinder sleeve, overlapped by piston, and valves or spools.

Working cycle:

After combustion of fuel, the gases expansion process (work stroke) begins. The piston moves to the bottom of the dead point (NMT). At the end of the expansion process, the piston 1 opens the intake slots (windows) 3 (point B) or exhaust valve open, reporting the cylinder cavity through exhaust pipe With an atmosphere. In this case, part of the combustion products comes out of the cylinder and the pressure in it drops to the pressure of PD purge air. At point D, the piston opens the blowing windows 2, through which a mixture of fuel with air under pressure 1.23-1.42 bar is supplied to the cylinder. Further drop slows down, because The cylinder enters the air. From point d to NMT, output and purge windows are open at the same time. The period during which the purge and exhaust windows are open at the same time, called purge. During this period, the cylinder is filled with a mixture of air, and combustion products are displaced from it.

The second beat corresponds to the move of the piston from the bottom to the upper dead point. At the beginning of the progress continues the purge process. Point F - End of purge - closing inlet windows. At the point, the outlet windows are closed and the compression process begins. The pressure in the cylinder by the end of the charging is slightly higher than atmospheric. It depends on the pressure of purge air. Since the end of the purge and full overlap of the outlet design, the compression process begins. When the piston does not reach the 10-30 grade on the corner of the key of the knees. It is up to the NTC (point C /), fuel is supplied to the cylinder through the nozzle or the mixture is ignited and the cycle is ignited.

With the same sizes of the cylinder and the speed of rotation, the capacity of the 2-stroke is significantly larger, 1.5-1.7 times.

The average pressure of the theoretical DVS diagram.

The average indicator pressure of the engine.

It is such a conditional constant pressure, which, acting on the piston, makes a job equal to the internal operation of gas throughout the entire working cycle.

Graphically P i on a specific scale is equal to the height of the rectangle MM / HH /, along the area of \u200b\u200bequal area of \u200b\u200bthe chart and having the same length.

f-area indicator chart (mm 2)

l - Ind. Diagram - MH

k P - Pressure Scale (Pa / mm)

The average effective pressure of the engine.

This is a product of mechanical efficiency on average indicator pressure.

Where η fur \u003d N E / N i. Under normal operation, η fur \u003d 0.7-0.85.

Mechanical efficiency of DVS.

η fur \u003d n E / N i

The ratio of efficient power to indicator.

Under normal operation, η fur \u003d 0.7-0.85.

Indicator power engine.

Ind. The power of the engine, obtained inside the Windra, can be determined using the indicator diagram taken by a special instrument - indicator.

Ind. Power - the work performed by the working fluid in the engine cylinder in the uncle.

Ind. Power of one cylinder -

k- Main engine

V-working cylinder

n-number of work moves.

Effective internal combat power.

Useful power used, removed from the knees.

N e \u003d n i -n tr

N Tr - the amount of power loss of friction between moving parts of the engine and to actuate the auxiliary mechanisms (pumps, generator, fan, etc.)

Definition of the EF. Motor power in laboratory conditions or under bench tests are produced using specials. Mixed devices - mechanical, hydraulic or electrical.

Indicators "Maigak"

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