Indicator diagram of a four-stroke diesel engine. Shunting locomotives Working with a detailed indicator diagram of a marine diesel engine

SCHEME OF 4-STROKE DIESEL OPERATION.

ICE MARKING.

Domestic diesel engines are labeled in accordance with GOST 4393-74. Each type of engine has a conventional letter and number designation:

H - four-stroke

D - two-stroke

DD - two-stroke double action

P - reversible

C - with a reversible clutch

P - with a reduction gear

K - crosshead

H - supercharged

G - for operation on gas fuel

GZh - for operation on gas-liquid fuel

The numbers in front of the letters indicate the number of cylinders; numbers after letters - bore / stroke in centimeters. For example: 8DKRN 74/160, 6ChSP 18/22, 6Ch 12/14

Marking of foreign diesel companies:

Engines of the SKL plant in Germany (former GDR)

Four-stroke internal combustion engines are called engines in which one working stroke (cycle) is carried out in four piston strokes, or two revolutions crankshaft... The strokes are: inlet (filling), compression, working stroke (expansion), outlet (exhaust).

I cycle - FILLING... The piston moves from TDC to BDC, as a result of which a vacuum is created in the overpiston cavity of the cylinder, and through the open inlet (suction) valve, air from the atmosphere enters the cylinder. The volume in the cylinder is increasing all the time. The valve closes behind BDC. At the end of the filling process, the air in the cylinder has the following parameters: pressure Pa = 0.85-0.95 kg / cm 2, (86-96 kPa); temperature Ta = 37-57 ° C (310-330 K).

II cycle - COMPRESSION... The piston moves in the opposite direction and compresses the fresh air charge. The volume in the cylinder decreases. Pressure and temperature rise to values: Pc = 30-45kg / cm 2, (3-4 MPa); Tc = 600-700 ° C (800-900 K). These parameters must be such that self-ignition of the fuel occurs.

At the end of the compression process, finely atomized fuel is injected into the engine cylinder from a nozzle at a high pressure of 20-150 MPa (200-1200 kg / cm 2), which spontaneously ignites under the influence of high temperature and quickly burns out. Thus, during the second stroke, the air is compressed, the fuel is prepared for combustion, the working mixture is formed and the combustion begins. As a result of the combustion process, the gas parameters increase to the following values: Pz = 55-80kg / cm 2, (6-8.1 MPa); Tz = 1500-2000 ° C (1700-2200 K).

III cycle - EXPANSION... Under the action of the forces arising from the pressure of the fuel combustion products, the piston moves to the BDC. Thermal energy of gases is converted into mechanical work movement of the piston. At the end of the expansion stroke, the gas parameters decrease to the following values: Pb = 3.0-5.0 kg / cm 2, (0.35-0.5 MPa); Tb = 750-900 ° C (850-1100 K).

IV cycle - ISSUE... At the end of the expansion stroke (up to BDC), the exhaust valve opens and gases that have energy and pressure higher than atmospheric pressure rush into the exhaust manifold, moreover, when the piston moves to TDC, forced removal occurs exhaust gases piston. At the end of the exhaust stroke, the parameters in the cylinder will be as follows: pressure P 1 = 1.1-1.2 kg / cm 2, (110-120 kPa); temperature T 1 = 700-800 ° C (800-1000 K). At TDC, the outlet valve closes. The work cycle is over.

Depending on the position of the piston, the change in pressure in the cylinder of the engine can be plotted in the PV (pressure - volume) axes of a closed curve, which is called an indicator diagram. In the diagram, each line corresponds to a certain process (clock):

1-a - filling process;

a-c - compression process;

c-z "- combustion process at constant volume (V = const);

z "-z - combustion process at constant pressure (P = const);

z-b - expansion process (working stroke);

b-1 - release process;

Po - line of atmospheric pressure.

Note: if the diagram is located above the Po line, then the engine is equipped with a supercharging system and has more power.

The extreme positions of the piston (TDC and BDC) are shown in dotted lines.

The volumes occupied by the working fluid in any position of the piston and enclosed between its bottom and the cylinder cover are plotted on the abscissa axis of the diagram, which have the following designations:

Vc is the volume of the compression chamber; Vs is the working volume of the cylinder;

Va. - full volume of the cylinder; Vx is the volume above the piston at any moment of its movement. Knowing the position of the piston, you can always determine the volume of the cylinder above it.

On the ordinate axis (on a selected scale) the pressures in the cylinder are plotted.

The indicator diagram under consideration shows the theoretical (settlement) cycle, where the assumptions are made, i.e. strokes start and end at dead center, the piston is at TDC, the combustion chamber is filled with the remains of exhaust gases.

In real engines, the moments of valve opening and closing begin and end not at the dead points of the piston position, but with a certain displacement, which can be clearly seen on the circular timing diagram. The moments of opening and closing of valves, expressed in degrees of crankshaft rotation (r.p.), are called valve timing. The optimal angles of opening and closing the valves, as well as the beginning of the fuel supply, are determined experimentally when testing a prototype at the manufacturer's stand. All angles (phases) are indicated in the engine logbook.

When the air charge enters the engine cylinder, the suction valve opens. Point 1 corresponds to the position of the crank when the valve opens. For better filling of the cylinder with air, the suction valve opens before TDC and closes after the piston BDC moves to an angle equal to 20-40 ° c.c., which is designated as the lead and lag angle of the intake valve. Usually the angle of the f.c.v. corresponds to an intake process equal to 220-240 °. When the valve closes, the filling of the cylinder ends and the crank takes the position corresponding to point (2).

After the compression process for the fuel to self-ignite, it takes time for it to heat up and evaporate. This period of time is called the autoignition lag period. Therefore, fuel injection is performed with some advance until the piston arrives at TDC at an angle of 10-35 ° sc.c.

FUEL ADVANCE ANGLE

The angle between the direction of the crank and the cylinder axis at the time of the start of fuel injection is called the fuel advance angle. UOPT is counted from the start of supply to TDC and depends on the supply system, fuel grade and engine speed. DPF for diesel engines ranges from 15 to 32 ° and is of great importance for ICE operation... It is very important to determine the optimal feed advance angle, which must correspond to the manufacturer's value specified in the engine passport.

Optimal SPS is essential for proper engine operation and economy. With proper regulation, fuel combustion should begin before the piston arrives at TDC by 3-6 ° sc.c. Highest pressure Pz, equal to the calculated one, is reached when the piston moves to TDC at an angle of 2-3 ° sc.c.v. (see "Combustion phases").

With an increase in the SOPT, the autoignition delay period ( 1st phase) increases and the bulk of the fuel burns out at the moment the piston moves to TDC. This leads to hard operation of the diesel engine, as well as to increased wear of the parts of the CPG and KShM.

A decrease in the FPS leads to the fact that the main part of the fuel enters the cylinder when the piston moves to TDC and burns in a larger volume of the combustion chamber. This reduces the cylinder power of the engine.

After the expansion process, in order to reduce the cost of pushing out the exhaust gases by the piston, the exhaust valve is opened with an advance before the piston arrives at BDC by an angle equal to 18-45 ° c.c., which is called the exhaust valve opening advance angle. Point (). For better cleaning of the cylinders from combustion products, the exhaust valve closes after the piston TDC moves to a retard angle equal to 12-20 ° sc.c., corresponding to the point () on the circular diagram.

However, it can be seen from the diagram that the suction and discharge valves are simultaneously open for some time. This opening of the valves is called the valve phase overlap angle, which adds up to 25-55 ° c.c.

Engine Indicator Chart internal combustion is built using workflow calculation data.

When plotting on the abscissa axis, the segment AB is plotted (Fig. 8) corresponding to the working volume of the cylinder, and equal in magnitude to the stroke of the piston on a scale of M s. The M s scale is usually taken as 1: 1, 1.5: 1, or 2: 1.

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

ОА = AB / (ε - 1) (2.28)

Section z′z for diesel engines operating on a cycle with a mixed heat supply (Fig. 9)

z′z = ОА (ρ - 1) (2.29)

Then, according to the calculation of the parameters of the actual cycle, the pressure values are plotted on the diagram on the selected scale at the characteristic points: a, c, z, z, b, r.

Compression and expansion polytropes can be constructed using analytical or graphical methods. The analytical method for constructing the compression and expansion polytropes calculates a number of points for intermediate volumes located between V c and V a and between V z and V b, according to the polytropic equation.

Rice. 8. Indicator diagram of a gasoline engine

Rice. 9. Indicator diagram diesel engine

For a polytropic compression , where

, (2.30)

where p x and V x- pressure and volume at the desired point of the compression process.

Attitude V a / V x varies within 1 ÷ ε.

Similarly for the extension polytropic

(2.31)

For gasoline engines attitude V b / V x varies in the range 1 ÷ ε, for diesel engines - 1 ÷ δ.

It is convenient to determine the ordinates of the calculated points of the compression and expansion polytropes in tabular form.

The construction of the indicator diagram is made by connecting the dots a and c, z and b are smooth curves, and points b and a, c and z are straight lines.

The inlet and outlet processes are assumed to take place at p = const and V = const

To check the correctness of the construction of the diagram, determine

p i= M p / AB

where F is the area of the diagram a c′c ″ z d b′b ″ a.

Calculation of indicator and effective indicators of internal combustion engines

Indicator indicators

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

Theoretical average indicator pressure Is the ratio of the theoretical settlement work gases per cycle per piston stroke.

For gasoline engines operating in a cycle with a heat supply at V = const, the theoretical average indicator pressure

For a diesel engine operating on a cycle with a mixed heat supply at V= const and R= const

Average Indicator Pressure p i of the actual cycle differs from the value by an amount proportional to the decrease in the design diagram due to rounding at points c, z, b.

The decrease in the theoretical average indicator pressure due to the deviation of the actual process from the design cycle is estimated by the completeness factor of the diagram φ and and by the value of the average pressure of pumping losses Δp i.

The completeness factor of the diagram φ and is taken equal to:

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

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

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

Average pressure of pumping losses (MPa) during inlet and outlet processes

Δp i = p r - p a. (3.3)

For naturally aspirated four-stroke engines, the value Δp i positive. In engines with supercharging from a drive supercharger at p a > p r magnitude Δp i negative. With gas turbine charging, the value p a can be more or less p r, i.e. magnitude Δp i can be either negative or positive.

When carrying out calculations, losses for gas exchange 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 by the completeness factor of the diagram

p i= 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 naturally aspirated diesel engines ………………………. 0.7 ÷ 1.1

for four-stroke diesel engines with supercharging ……………………… .. up to 2.2

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

For a multi-cylinder engine, the indicated power (kW) is

N i = 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- number of cylinders;

n- engine crankshaft rotation frequency, min -1;

τ - engine stroke. For four-stroke engine τ = 4.

Indicator capacity of one cylinder

N i = p i V h n/(30τ ), (3.6)

Indicator Efficiency η i characterizes the degree of use in the actual cycle of the heat of the fuel to obtain useful work and is the ratio of the heat equivalent to the indicator work of the cycle to the total amount of heat introduced into the cylinder with fuel.

For 1 kg of fuel

η i = L i / H and, (3.7)

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

H and Is the lowest heat of combustion of fuel, MJ / kg.

For automotive and tractor engines fueled by liquid fuels

η i = p i l 0 α / (Н and ρ k η V), (3.8)

where p i is expressed in MPa; l 0 - in kg / kg fuel; H and- in MJ / kg fuel; ρ k - in kg / m 3.

In automobile and tractor engines operating at the nominal mode, the value 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 Н and) or g i = 3600 ρ 0 η V / (p i l 0 α). (3.10)

Specific fuel consumption at nominal mode:

for engines with electronic fuel injection ... g i= 180 ÷ 230 g (kWh)

for carburetor engines ……………………… g i= 210 ÷ 275 g (kWh)

for diesel engines ………………………………………. …… g i= 170 ÷ 210 g (kWh)

Effective indicators

Effective indicators are called values that characterize the operation of the engine, taken from its shaft and useful. Effective indicators include: effective power, torque, average effective pressure, specific effective flow rate, effective efficiency.

Effective power... The useful work received on the motor shaft per unit of time is called the effective power N e.

N e=N i - N mp (3.9)

where N mp power mechanical losses.

The effective power is given to the student in the initial data for the design of an internal combustion engine (see the assignment for the course project).

Mechanical losses are understood as losses for all types of mechanical friction, gas exchange, drive of auxiliary mechanisms (water, oil, fuel pumps, fan, generator, etc.), ventilation losses associated with the movement of engine parts in an air-oil emulsion and air, as well as the compressor drive.

Mechanical losses are estimated by the average pressure of mechanical losses p mp, which characterizes the specific work of mechanical losses (per unit of working volume) during the implementation of the working cycle.

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

N e = p e V h in/(30τ ) (3.10)

where p e=L e / V h- the average effective pressure (MPa), i.e. the useful work obtained per cycle from a unit of working volume;

V h- the working volume of the cylinder, l;

n- the number of revolutions of the crankshaft, min -1

Effective torque M e(N ∙ m)

M e= (3 ∙ 10 4 / π) ( N e / n) (3.11)

When calculating the internal combustion engine, 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 engines different types determined by is determined by empirical formulas:

for gasoline engines with up to six cylinders and an S / D ratio> 1

p mp = 0.049 + 0.0152 V p.w .;

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

p mp = 0.034 + 0.0113 V p.w.

for four-stroke diesel engines with unseparated chambers

p mp = 0.089 + 0.0118 V p.w.

Indicator diagram

a graphic representation of the change in the pressure of gas or steam in the cylinder of a piston machine, depending on the position of the piston. The I.D. is usually plotted with a pressure indicator (See Pressure Indicator). The abscissa shows the volume occupied by gases in the cylinder, and the ordinate shows the pressure. Each point on the I. d. ( rice. ) shows the pressure in the engine cylinder at a given volume, i.e. at a given position of the piston (point r corresponds to the beginning of the intake; point a- the beginning of compression; point with- the end of compression; point z - the beginning of the expansion; point b- the end of the extension).

I. d. Gives an idea of the value of the work produced by an internal combustion engine or pump, and about their power. The working body does useful work only during the working stroke. Therefore, to determine the useful work, it is necessary from the area limited by the expansion curve zb, subtract the area bounded by the compression curve ac. Distinguish between theoretical and real I. The theoretical is constructed according to the data of thermal calculation and characterizes the theoretical cycle; the real I. d. is removed from the running machine with the help of an indicator and characterizes the actual cycle (see. rice. ).

For the convenience of calculating and comparing with each other different engines pressure variables along the piston stroke are replaced by conditional constant pressure, at which work is obtained in one piston stroke, equal to work gases per cycle with variable pressure. This constant pressure is called the average indicator pressure and represents the work of gases in relation to the working volume of the piston engine.

B. A. Kurov.

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

See what "Indicator Chart" is in other dictionaries:

Indicator diagram for various piston mechanisms is a graphical dependence of the pressure in the cylinder on the piston stroke (or depending on the volume occupied by the gas or liquid in the cylinder). Indicator charts are built when researching ... Wikipedia

indicator diagram- Diagram of the dependence of the pressure in the cylinder of a piston machine on its variable volume. [GOST 28567 90] Topics compressor EN pressure volume diagram DE Indikatordiagramm ... Technical translator's guide

Graphical representation of the dependence of the pressure of the working fluid (steam, gas) in the cylinder of a piston machine (engine, pump) on the movement of the piston. It is a closed curve, the area inside which is proportional to the work done by the worker ... Big Encyclopedic Dictionary

Graphic. image of the change in the pressure of steam or gas in the cylinder of a piston machine depending on the movement of the piston or the angle of rotation of the crankshaft (see Fig.). The area of I. d. Is proportional to the work done. working fluid inside the cylinder for ... ... Big Encyclopedic Polytechnic Dictionary

Graphic. image of the dependence of the pressure of the working fluid (steam, gas) in the cylinder of a piston machine (engine, pump) on the movement of the piston. It is a closed curve, the area inside the swarm is proportional to the work done by the working fluid ... Natural science. encyclopedic Dictionary

Indicator diagram- 97. Indicator diagram D. Indikalorcliagramm E. Pressure volume diagram Diagram of the dependence of the pressure in the cylinder of a piston machine on its variable volume

In a four-stroke engine, the work processes are as follows:

1. Intake stroke. When the piston moves from TDC to BDC due to the resulting vacuum from the air cleaner, atmospheric air enters the cylinder cavity through the open intake valve. The air pressure in the cylinder is 0.08 - 0.095 MPa, and the temperature is 40 - 60 C.
2. Compression cycle. The piston moves from BDC to TDC; the inlet and outlet valves are closed, as a result of which the upwardly moving piston compresses the incoming air. To ignite the fuel, the temperature of the compressed air must be higher than the autoignition temperature of the fuel. During the piston stroke to TDC, the cylinder is injected through the nozzle diesel fuel supplied by the fuel pump.
3. Expansion stroke, or working stroke. The fuel injected at the end of the compression stroke, mixing with the heated air, ignites, and the combustion process begins, characterized by a rapid increase in temperature and pressure. In this case, the maximum gas pressure reaches 6-9 MPa, and the temperature is 1800-2000 C. Under the action of the gas pressure, piston 2 moves from TDC to BDC - a working stroke occurs. Around BDC, the pressure drops to 0.3-0.5 MPa, and the temperature drops to 700-900 C.
4. Cycle of release. The piston moves from BDC to TDC and through the open exhaust valve 6, the exhaust gases are pushed out of the cylinder. The gas pressure drops to 0.11-0.12 MPa, and the temperature drops to 500-700 C. After the end of the exhaust stroke, with further rotation of the crankshaft, the operating cycle is repeated in the same sequence.

An indicator diagram taken with an indicator device is called an indicator diagram (Fig. 1).

Rice. 1

Consider the diagram:

0-1 - filling the cylinder with air (at internal mixture formation) or a working mixture (with external mixture formation) at a pressure slightly below atmospheric due to the hydrodynamic resistance of the intake valves and the suction pipe,
1-2 - compression of air or working mixture,
2-3 "-3" - the period of combustion of the working mixture,
3-4 - the working stroke of the piston (expansion of combustion products), mechanical work is performed,
4-5 - exhaust gas exhaust, pressure drop to atmospheric occurs at almost constant volume,
5-0 - freeing the cylinder from combustion products.

In real heat engines, the conversion of heat into work is associated with complex irreversible processes (there are friction, chemical reactions in the working fluid, final piston speeds, heat exchange, etc.) Thermodynamic analysis of such a cycle is impossible VM Gelman, MV Moskvin. Agricultural tractors and cars. - M .: Agropromizdat, 1987, part I and P ..

Engine indication. Determination of power

Indicator charts, taken with the necessary conditions, allow you to determine indicator power and its distribution over the engine cylinders, investigate the gas distribution, the operation of injectors, fuel pumps, and also determine the maximum cycle pressure p z , compression pressure p with, etc.

Removal of indicator diagrams is carried out after warming up the engine with a steady thermal regime. After removing each diagram, the indicator should be disconnected from the cylinder by a 3-way indicator valve and an indicator valve on the engine. The indicator drums are stopped by disconnecting the cord from the drive. The indicator piston and its rod should be lightly lubricated from time to time after taking a few diagrams. Do not indicate the engine when the sea state exceeds 5 points. When removing indicator diagrams, the indicator drive must be in good working order, indicator cocks are fully open. It is recommended to take the diagrams simultaneously from all cylinders; if the latter is not possible, then their sequential removal must be carried out as soon as possible at a constant engine speed.

Before displaying, it is necessary to check the serviceability of the indicator and its drive. The piston and indicator bushing must be completely seated; When the spring is removed from the upper position, the lubricated piston must descend in the cylinder slowly and evenly under its own weight. The piston and indicator sleeve are lubricated only by the cylinder or engine oil, but not instrumental, which is included in the indicator kit and is designed to lubricate the joints of the writing mechanism and the upper part of the piston rod. The spring and the nut (cap) holding the spring must be screwed in completely. The lifting height of the indicator writing pin must be proportional to the gas pressure in the indicated cylinder, and the drum rotation angle must be proportional to the piston stroke. The clearances in the pivot joints of the transmission mechanism should be small, which is checked by slight swinging of the lever with the piston stationary, and there should also be no backlash. When the indicator communicates with the working cavity of the cylinder with a stationary drum, the writing pin of the indicator should draw a vertical straight line.

The indicator is connected to the drive either with a special indicator cord or with a special steel tape measuring 8 x 0.05 mm. Drive cord - linen, braided; before installation, a new cord is pulled out during the day, suspending a weight of 2 - 3 kg to it. If the condition of the cord is unsatisfactory, significant distortions of the indicator diagram are obtained. A steel tape is used for engines with a speed of 500 rpm and above, as well as if the speed is less than 500 rpm, but the connection between the indicator and the drive looks like a broken line 2 - 3 m long. compression diagrams with fuel off. If the compression line matches the expansion line, then the cord is serviceable. The length of the indicator cord must be adjusted so that in the extreme positions the drum does not reach the stop. With a short cord, it breaks, with a long one - the diagram has a shortened form ("cut off"), since at the end of the piston stroke the drum will be stationary. During the indication, the cord must be constantly taut.

When drawing the atmospheric line, make sure that it is located at a distance of 12 mm from the bottom edge of the paper for indicators of model 50 and 9 mm - model 30. In this case, the writing mechanism will operate in the most optimal measuring range and maintain a correct record of the suction line under line of atmospheric pressure. The length of the diagram should be no more than 90% of the maximum drum stroke.

The indicator cord must lie in the swinging plane of the indicator drive arm. In the middle position of the lever, the cord should be perpendicular to its axis. The indicator should be installed so that the cord does not touch pipelines, machine grids and other parts. If it touches, and this is not eliminated by changing the position of the indicator, then a transition roller is installed. In this case, it is necessary to maintain the perpendicularity of the cord from the roller to the axis of the lever of the drive indicator at the middle position of the latter. The pressure of the pencil (writing pin) should be adjusted so that it does not tear the paper, but leaves a thin, clearly visible mark. The copper pin must always be well sharpened. Strong pencil pressure will increase the area of the diagrams. The paper should fit snugly against the indicator drum.

Before installing the indicator, thoroughly purge the indicator valve of the engine to avoid clogging of the channels and piston. Before removing the diagram, repeat the purge through the 3-way indicator valve. Before indicating the engine, the indicator should be well warmed up. Failure to comply with this requirement leads to distortion of indicator diagrams. When installing and removing the indicator, do not use an impact tool when tightening and kickbacking the union nut. This is done using a special key included in the indicator kit.

Indicators and indicator springs must be checked by supervisory authorities at least once every two years and have a certificate of validity. The state of the indicator drive is checked with the engine running by taking compression diagrams with the fuel supply turned off. With a properly adjusted indicator drive, the compression and expansion lines should match. If defects are detected in the gas distribution mechanism during the analysis of the indicator diagrams, it is necessary to take measures to eliminate them. After correcting the defects, re-index and process (analyze) the indicator diagrams.

Conventional indicator charts for analyzing the change in work flow of motors operating with variable load. They are filmed in series on a continuous tape, followed one after the other at a set interval.

The taken indicator diagrams are analyzed before processing, since due to insufficient motor regulation or due to a malfunction of the indicator, its drive or violation of the indication rules, the indicator diagrams may have various distortions.

Planimetry.

Indicator diagrams are processed in the following sequence: adjust the planimeter and planimetry all diagrams; determine their areas; measure the lengths of all diagrams and the values of the ordinates p c and p z, count p i , for each cylinder. The planimeter is adjusted according to the area of the circle outlined by the bar attached to the planimeter. In the absence of a special bar, the planimeter readings are checked squarely on graph paper. Planimetry is performed on a smooth board covered with a sheet of paper. When installing the planimeter, its levers in relation to the diagram are positioned at an angle of 90 °. When tracing the diagram, the angle between the planimeter levers should be 60 - 120 °.

The length of the indicator diagram is measured along the atmospheric line. The actuator travel should be selected so that the length of the diagram is 70 and 90 - 120 mm for indicators of models 30 and 50, respectively.

In the absence of a planimeter, the average indicated pressure p i is found with sufficient accuracy by the trapezoid method. To do this, the diagram is split vertical lines into 10 equal parts.Average indicatorpressure is determined by the formula

pi = Σ h/ (10m),

where Σ h- sum of heights h1, h2 h10,

mm; T - scale of indicator spring, mm / MPa. Method of measuring ordinatesh, p z and R with shown in Fig. 4.6. When taking indicator diagrams in each individual case, for a comparative assessment of the distribution of the load on the cylinders, it is necessary to take into account the temperature of the exhaust gases.

Each site is divided in half and its height is measured in the middle. When registering the results of the indication on the form of the taken diesel diagram, it is necessary to indicate the name of the vessel, the date of the indication, the brand of the diesel engine, the cylinder number, the scale of the spring, the length and area of the diagram, the obtained parameters p z, p s, p, -, N e, n... The processed indicator diagrams of each engine are pasted into the "Indexing log" with a corresponding analysis of the indexing results. The explanatory text should indicate the identified deficiencies in engine adjustment and the measures taken to eliminate them. At the end of the voyage, the "indexing log" and the set of processed diagrams must be submitted to the MSS of the fleet together with the voyage machine report. When processing diagrams taken from high-speed diesel engines, it is necessary to make a correction for the error of the indicator writing mechanism, which in some cases can reach 0.02-0.04 MPa (added to the main value).

Analysis of the combustion process using diagrams and oscillograms

An indicator diagram is a graphical representation of the relationship between cylinder pressure and piston stroke.

Methods for obtaining (removing) indicator diagrams

To obtain indicator charts, mechanical indicators are used either electronic systems measuring the pressure of gases in the cylinder and fuel during the injection process (MIPCalculator, pressureanalyzer) (NK-5 Autronica and CyldetABB). To obtain complete indicator diagrams using a mechanical indicator, the engine should be used. equipped with an indicator drive.

Types of indicator charts

With the help of mechanical indicators, the following types of indicator diagrams can be obtained: normal, displaced, comb diagrams, compression, gas exchange and expanded.

Normal indicator charts serve to determine the average indicator pressure and general analysis of the nature of the indicator process.

Rice. 1 Types of indicator diagrams

Displaced diagrams are used to analyze the combustion process, identify shortcomings in the operation of the fuel equipment, assess the correctness of setting the fuel feed advance angle, and also to determine the maximum combustion pressurep z and the pressure of the beginning of visible combustionR" with which is usually equated to the compression pressure pwith... The offset diagram is removed by attaching an indicator cord to the adjacent cylinder, if its crank is jammed at 90 or 120 °, or by using a rotary head drive, or by quickly turning the indicator drum by the cord by hand.

Comb charts serve to determine the pressure at the end of compressionR with and maximum combustion pressureR G on engines without indicatordrives.In this case, the indicator drum is turned by hand using a cord. To determine pwiththe diagram is taken with the fuel supply to the cylinder turned off.

Compression diagrams as indicated, are used to test the indicator drive. They can also determine the pressure pwithand evaluate the tightness piston rings by the size of the area between the compression line 1 and extension line2.

Gas exchange diagrams are filmingin the usual way, but weak springs with a scale of 1 kgf / cm are used2 = 5 mm (or more) and normal ("steam") piston. These diagrams are used to analyze the processes of discharge, purging and filling of the cylinder. The upper part of the diagram is limited by a horizontal line, since the indicator piston, under the influence of a weak spring, reaches the uppermost position and remains in it until the pressure in the cylinder drops to 5 kgf / cm2 .

Expanded charts serve to analyze the combustion process in the TDC area, as well as to determine p, in engines that do not have an indicator drive. Expanded diagrams are taken with an electric or mechanical indicator with a drive independent of the motor shaft (for example, from a clockwork).

To remove all of the above diagrams, with the exception of the comb, an indicator drive is required

Distortions of indicator charts occur most often when the indicator piston gets stuck (fig. 2,a), installation of a weak (Fig. 2, b) or stiff spring (Fig. 2,v), loosening the nut fastening the indicator spring, drawing out the indicator cord (Fig. 2,G) or its great length (Fig.2, e).

Rice.2. Distortionindicatorcharts

Processing indicator charts is carried out in order to determine the values of the average indicator pressure on themR i , maximum combustion pressurep z and pressure at the end of compressionR with ... The parameters are determined most simplyp z and pwithby comb charts and offset charts. To do this, use a scale bar to remove ordinates from the atmospheric line to the corresponding points (see Fig. 1,b, c) or, if not available, a simple ruler. In the latter case, the valuesR z and pwithwill be equal:

whereT is the scale of the spring.

The maximum combustion pressure can also be determined from the normal indicator diagram, and the pressure at the end of compression can be determined from the compression diagram.

The average indicator pressure is determined from normal or expanded indicator charts. By expanded diagramsp i are found in a graphic-analytical way, by rebuilding an expanded diagram into a normal one or using a special nomogram.

According to a normal indicator chart, the valueR i determined by the formula

(130)

whereF i - area of the indicator diagram, mm2 ;

T - scale of the indicator spring, mm / (kgf / cm2 );

l - length of the diagram, mm.

The length of each indicator diagram is measured between the tangents to the extreme points of the diagram contour, which are drawn perpendicular to the atmospheric line. The area of the diagram is measured with a planimeter.

It should be noted that when determining the average indicator pressureR i according to the indicator diagram, the measurement error can reach 10-15% and more. At the same time, in marine low-speed diesel engines at normal technical condition fuel supply and boost systems pressure ratioR i R τ , p z , fuel pump index and cyclic fuel deliveryg c usually remain fairly stable for a long time. Therefore, any of the above parameters can be selected to estimate the cylinder load.

In this regard, some diesel plants consider the installation of indicator drives to be impractical., and the diagnostic system developed for these engines uses the valueR z .

Therefore, the most common types of indicator charts taken by a mechanical indicator are combs and unfolded "by hand".

The comb diagram allows you to determine the pressure at the end of compression (R with ) and maximum cycle pressure (p z ), and to removeR with it is necessary to turn off the fuel supply to this cylinder. Disabling the cylinder will lead to a decrease in the power and speed of the engine, the gas turbine and the boost pressure, which in turn will affect the magnitude of the compression pressure. For measuring compression pressure, a freehand swept chart is preferred. This diagram, with a certain skill, resembles a detailed diagram taken using an indicator drive, but there is no connection between pressure and piston stroke.

The resulting valuesp with andp z needs to be analyzed. To obtain more accurate conclusions, simultaneously with taking the diagram, it is necessary to record the following data: gas temperatures behind the cylinders, before and after the turbine, charge air pressure and temperature, engine and turbine speed, engine load indicator. It is advisable to know the fuel consumption at the time of taking the diagram.

The best way analysis of the engine condition is to compare the measured values with the values obtained during the factory or running tests of the engine at the same load.

In the absence of test data, it is necessary to compare the obtained values with the average.

For exampleTable 1

date

Dv-l

GNT

Additional values

Time

Turnovers

R n

Steam / No.c

Wed zn.

p z bar

165

156

167

156

175

164

163,8

Δp z

0,71%

-4,78%

1,93%

-4,78%

6,82%

0,10%

3,5%*

p c bar

124

120

125

128

127

122

124,3

Δp c

0,27%

3,49%

0,54%

2,95%

2,14%

1,88%

2,5%*

T G ° C

370

390

380

390

372

350

375,3

ΔT G

-1,42%

3,91%

1,24%

3,91%

0,89%

-6,75%

5,0%*

Fuel pump index

Action

Rings,
valve

TP ↓

ϕ↓

* RD 31.21.30-97 Rules technical operation STS and K p. 99

p z bar

T G ° C

Action

ϕ↓

TR ↓

Rice. 3. Diagnostic complex of Autronica» NK-5

Complex NK-5 by Autronica ... With the help of the complex (Fig. 3), it is possible to obtain the most complete information about the course of the working process in all cylinders of the engine and to recognize the disturbances arising in it, including in the operation of the fuel injection equipment. For this purpose, a sensor is provided6 high pressure installed on the high-pressure fuel line at the injector, as well as sensors:4 - boost pressure; 5 - TDC and shaft rotation angle; 7 - gas pressure(3 - intermediate amplifiers of sensor signals). Measurement results in the form of pressure curves and digital values of the measured parameters are displayed on a color display 1 and a printing device2 . The microprocessor built into the system allows the measurement data to be stored in the memory and later to compare the new data with

old or reference.

As an example, the curves of gas pressures in the cylinder and in the fuel line at the injector (Fig. 4) illustrate typical disturbances in the course of processes. Reference curve 1 reflects the nature of the pressure change at the considered operating mode of the engine in a technically sound condition, curve2 characterizes the actual process with various distortions caused by malfunctions.

Leakage of the nozzle needle (fig. 4,a) due to the deterioration of fuel atomization leads to a slight increase in the angleφ z , decrease in pressureR z and significant afterburning of fuel on the expansion line. The expansion curve is flatter and higher than the reference. Exhaust gas temperature risest G and pressureR exp on the extension line at 36 ° after TDC.

With a delay in fuel injection (Fig. 4, b), the beginning of visible combustion and the entire process of fuel combustion are shifted to the right. Pressure decreases at the same timeR z temperature is risingt G and pressureR exp . A similar picture is observed with the wear of the plunger pair of the fuel pump and the loss of the density of its suction valve. In the latter case, the cyclic fuel supply decreases and, accordingly, the pressure decreases slightly.p i

Due to the early fuel supply (Fig. 4,v) the entire combustion process shifts to the left in the direction of advance, the angle φ decreases Gand the pressure is growingR z . As the process becomes more economical, thep i . Early feeding is also confirmed by the fuel pressure curve at the injector (Fig. 4, d).

Changes in the fuel pressure curve due to increased cycle flow (fig. 4,e) accompanied by an increase in the valuesR f T a NS and the duration of the supply φ f.

The drop in the rate of rise of fuel pressure Δр f/ Δφ in the section from the beginning of its rise to the moment of opening the needle, as well as the total injection pressure drop (Fig. 4,e) causes a decrease in the feed advance angle φ npand maximum pressureR f max . The reason lies in an increase in fuel leakage through the plunger pair, the needle-guide pair of the injectors due to their wear or in the loss of tightness of the pump valves, fuel pipe fittings. Coking nozzle holes or excessive increase in fuel viscosity (fig. 4,g) leads to an increase in injection pressure due to an increase in the resistance of fuel outflow from the holes.