What is the indicator diagram?
The diagrams indicating, simultaneously, the pressures and the relative position of the piston in the engine cylinder are known as indicator diagrams.
PURPOSE (WHY) OF TAKING INDICATOR
DIAGRAMS
a) Determining the indicated engine
output
b) Determining combustion (Pmax) and compression pressures (Pcomp)
c) Evaluation of the combustion process and its peculiarities
d) Evaluation of the exhausting and scavenging conditions
HOW TO TAKE INDICATOR DIAGRAM?
(SQUENCE)
a)
Check whether the spring fitted on the indicator
instrument will meet the peak pressure to be
expected (max. pressure
of Engine).
b)
Stretch diagram paper firmly over the drum.
c)
Before taking diagram, open indicator cock, two or
three firing strokes, to blow out soot and combustion residues in the cock.
d)
After drawing atmospheric pressure line, hook the cord
to indicator drive, open indicator cock, and
take power diagram
and shut the cock.
e)
Remove hook, turn the drum by hand to a place clear
from the power diagram, took compression pressure line with fuel cut-off.
f)
Having taken indicator diagrams from all cylinders,
open the indicator instrument and clean all parts
especially the piston, thoroughly. After cleaning, apply high temperature
grease into the surface of all parts.
Note: Do not allow the indicator instrument to become overheated by too many firing strokes, as it will affect the instrument accuracy.
Types of
Indicator diagram?
🢣 Power card
🢣 Draw card
🢣 Compression card
🢣 Light spring card
What is indicated power? How to calculate power?
🢣 It is the power developed in the cylinder.
🢣 Firstly, take the power diagram for each cylinder
🢣 The area of the diagram can be measured by means of a planimeter.
🢣 Measures the length of diagram; check spring scale.
🢣 Calculate the mean effective pressure
Diagram area
M.E.P
= ---------------------------- x Spring scale
Mean Length of diagram
🢣 Record the engine revolution(RPM)
🢣 Calculate the power for each unit
I.P = MEP x Length of stroke x cylinder bore area x rps (Watts)
IP = P L A N x No. of Cyls
(KW)
P = MEP (KN/m2) = (Area of diagram / Length of diagram ) x Spring scale L = Stroke Length ( m )
A = Cylinder bore area ( m2 )
N = N for 2/S single acting (rps)
= N/2 for 4/S single acting
= 2N for 2/S double acting
Purpose of Each indicator diagram
Power diagram
-
To calculate indicate
power. It also shows peak pressure.
In phase with piston movement, with fuel on.
Out-of-phase
diagram
- An out-of–phase diagram (draw card) is required
to be taken if the compression pressure
is to be accurately determined.
It shows Pmax (more accurately), P compression and ignition delay period
(Nature of expansion curve). It also shows combustion process (early or late combustion)
To evaluate injection, ignition delay, fuel quality, combustion, loss of compression, expansion process, fuel pup timing, and after-burning.
90° out of phase with piston movement, with fuel on, to determine Pmax
Compression diagram
- To know compression pressure
of the cylinder and cylinder tightness.
In phase and fuel cut-off.
The diagram shows-
à Choke exhaust ports or valves
à Loss of scavenge air
In phase, using light spring, with fuel on, to determine
When
taken?
Taken at every month and after every major O/H on the way. By according to the engine condition.
PRECAUTION NECESSARY TO AVOID INDICATOR
MALFUNCTION
F To reduce the effect of friction the indicator piston is removed,
the piston and the cylinder
cleaned and lubricated with a few drop of cylinder oil
F The tightness of the indicator
piston in the cylinder should
be checked. This can be done by dismantling the piston and allowing it to
drop slowly through the cylinder
by its own weight.
F The drum should not hit the stop at end positions. Play in the pencil mechanism
will distort the diagram
F The cock should be free from accumulation of soot and oil
F The stylus
should be adjusted
to a light writing pressure
F Before taking indicator diagrams,
open indicator cock two or three firing stroke to blow out soots and carbon
residues in the cock.
F
Check whether the spring fitted
on the indicator instrument will meet peak Pr: to be expected.
F Stretch diagram paper firmly over the drum
F After drawing
atmospheric line, hook the cock to the indicator drive, open indicator
cock and take power diagram,
shut the cock
F Remove hook, turn the drum by hand to a place
clear from power diagram, took compression pressure line with fuel cut-off
F Do not allow the indicator instrument to become overheated by too many firing strokes,
as it will affect the instrument accuracy
F Having taken indicator diagrams,
from all cylinders, open indicator instrument and clear all parts, especially the piston thoroughly.
F After cleaning, apply high temperature grease into surfaces of all parts
How to maintain good Performance
01)
Maintain good power
output per cylinder
02)
Take power Card, to check power output/cylinder
03)
Take Compression Card,
to check for cylinder tightness
04)
Check ratio of Absolute compression pressure to absolute
scavenging pressure.
05)
If the ratio is same as that during sea trial, piston rings and exhaust valves are sufficiently tight. (With B&W
engine, this ratio is about
30)
06)
If absolute pressure
ratio is less,
check for cylinder
tightness, charge air cooler, scavenge
air ports, scavenge
valves, piston rings,
exhaust valves, TC, etc.
07) Light spring diagram is taken if necessary
08) Check exhausts temperatures, exhaust
smoke, load indicator
and engine running
parameters.
09) Check fuel, CLO & LO consumption
10) Regular maintenance works and repairs.
Absolute Pressure = Gauge Pressure (of Manometer) + Atmosphere Pressure (15 psi or 30 Mercuy)
In
compression pressure is low:
a Carry out unit O/H and renew liner, piston and rings.
a TC checked, clean and overhauled, to have efficient operation
a Check Scavenge air line, charge air cooler, for insufficient scavenge air condition
a Check Inlet and Exhaust valves may be leaking.
a Clean Scavenge Ports, Scavenge Valves, if 2/S engine.
Early Combustion Effects:
1)
Very high peak pressure Pmax at about TDC
2)
Lower Exhaust temperature
3)
Increase Power
4)
Increase Thermal efficiency
5)
Heavy shock load to bearings
6)
Engine knocking
7)
Lower expansion line
8)
Ignition occurs before
TDC
9) Less S.F.O.C
Causes
1)
Overheated piston
2)
cetane number of fuel than normal
1)
Fuel injection pump plunger has been set too high (Incorrect fuel pump timing or wrong V.I.T setting)
2)
Incorrect adjustment of the fuel cam on the camshaft
3)
Incorrect adjustment of fuel valve spring pressure
(low)
LATE IGNITION
Effects:
1)
Lower peak pressure
2)
Higher Exhaust temperature with black smoke
3)
Loss of power
4)
Reduced Thermal efficiency
5)
Reduced Scavenge efficiency
6)
Higher Exhaust gas pressure at blow down period and increasing pulsation
in the exhaust manifold
7)
Higher expansion line
8)
Ignition occurs after TDC
9) Increase S.F.O.C
Causes
1)
Incorrect fuel pump timing and wrong V.I.T setting
2)
Faulty fuel valve
(Excessive injector spring
setting)
3)
Injection viscosity too low
4)
Lack of scavenge
air or cold air
5)
Bad atomization
6)
Slack chain drive
7)
Lower cetane number
of fuel
8)
Worn out fuel pump, cam and roller
9)
Low compression
10)
Under cooling of parts within
the cylider
11)
Leaky fuel pump delivery valve or spill valve It may cause:
a)
Exhaust valve burning
b)
Turbocharger surging
c)
Fouling of exhaust
system
d)
Uptake fires
e) High cylinder temperature resulting in liner lubrication difficult.
After Burning
Symptoms & Effects
1)
Rise in expansion line during latter
part of the load
2)
Exhaust temperature and Exhaust pressure
will be high, with burning fuel and carbon passing to exhaust.
3)
This may burn exhaust valves and foul the exhaust system, with risk of T/C surging or uptake
fires.
4)
High temperatures within the cylinder
cause deterioration in lubrication and possible damage to liner
surface & piston
rings. This may be the cause of piston crown burning.
5) Smoky exhaust
Causes
1)
Incorrect fuel pump timing (Slow or late combustion of fuel)
2)
Faulty fuel injector
(leaky fuel valve)
3)
Heavy fuel oil temperature too low and high viscosity
4)
Lack of scavenge
air
5)
Poor compression
6) Poor quality fuel
EXHAUST VALVE OPENING
Exhaust valve opening in a slow speed engine can be checked by means of light spring indicator diagram.
Early opening
1)
Indicates high exhaust
temperature with the risk of overheating and contamination
2) Causes a loss of power since pressure is released too soon.
Late opening
1)
Reduces the scavenge
efficiency by reducing
blow down
2)
Affects the supply
of energy to the turbocharger.
CHOKE EXHAUST PORTS OR VALVES
Symptoms
1)
Higher exhaust pressure
with sooty smoke
2)
Higher mean temperature of working parts
3)
Higher Exhaust temperature with heavy smoke
4)
Lower Pmax , Lower Pcomp
5)
Loss in power
6) Surging of Turbocharger
Causes
1)
Faulty fuel injection system
2)
Lack of scavenge
air
3)
Excessive cylinder lubrication
4)
Fouling of exhaust
system
Remedies
@ Correct fuel timing and fuel injection system
@ Maintain scavenging system in good order
@ Correct cylinder lubrication feed
@ Clean exhaust grid and Turbocharger
CHOKED FUEL VALVE
Symptoms
1)
Loss in engine
power
2) Hammering in the fuel pipes between fuel pump and injector
(This may lead to rupture
of fuel pipe)
3)
Reduce exhaust temperature
a.
It can be confirmed by indicator diagram
power and draw cards.
The diagrams show
b.
irregularities at the peak of the diagram.
Causes
1)
The contamination in the fuel in which debris may choke the small atomizer
holes in the injector
2)
A leaky injector allowing hot gas to blow back into
the injector causing carbon to form and choke
the injector.
3) Overheating of injector nozzle may also cause build-up of carbon.
Remedies
@ Change the fuel valve
@ Clean the whole fuel system
@ Ensure correct centrifuging and filtering of fuel
@ Maintain correct cooling temperature of fuel valve
LEAKY FUEL INJECTORS
Symptoms
01. Loss in power
02. High Exhaust temperature with smoke
03. Knock or pressure wave in fuel injection system
It can be detected by taking both Power card and Draw card, which shows fluctuation of pressure during the expansion process due to secondary burning of fuel leaking from the valve.
It may cause:
a. Afterburning
b. Hot gas from combustion chamber blow past into the injector and forming carbon
trumpets choking the injector
c. Fouling and loss efficiency of turbocharger due to afterburning
d. Coking of exhaust ports and grids.
Diagram showing leaking injector
Remedies
@ The fuel valve should be renewed and tested for faults and rectified.
@ Fuel purification and separation system should be kept in good order
@ Fuel system temperature and Nozzle cooling temperature must be maintained in correct levels.
LEAKY PISTON RINGS OR WORN LINER
Symptoms
1)
Loss in engine
power
2)
Lower compression (Pcom)
and combustion (Pmax)
3)
High exhaust temperature with smoke
Causes
1)
Excessive cylinder liner wear
1)
Lack of cylinder
lubrication
2)
Worn, broken, stuck
or poorly maintained piston rings
3)
Worn piston ring groove landings
allowing rings to cant and jam
4)
Carbon jamming rings in grooves
5)
Turbocharger failure due to fouling
6)
Blockages in the exhaust gas system.
It can be detected by taking Draw card which shows higher dip in compression line. It may
cause:
(1)
Blow past of combustion gas
(2)
High rate of cylinder liner
wear due to poor cylinder
lubrication
(3)
Scavenge fire
(4)
Piston seizure due to local
overheating
Remedies
@ Renew cylinder liner if necessary
@ Overhaul piston
@ Clean ring grooves and gauge
@ Machine or fit new groove inserts as necessary
@ Renew piston rings with correct clearances
@ Maintain cylinder lubrication and avoid overload
Leaking piston
rings
Cetane Number
🢣 A measure of ignition quality of fuel
🢣 The higher the Cetane Number the shorter the time between fuel injection and rapid combustion
🢣 The higher the Cetane No. the better the ignition quality
🢣 Considered as poor fuel, if C< 37 Usual range is 30-4
High Cetane Number Effects
1.
Shorter delay period
2.
Early combustion
3.
Increased power
4.
Knocking
Low Cetane Number
Effects
1.
Longer delay period
2.
Late combustion
3.
Decreased power
4.
After burning
5. High exhaust temperature and smoke
Diesel Knock
Violent knocks produced by high rate of pressure rise, RPR, during combustion, as delay period is longer then normal.
Causes
1.
Too low working
temperature
2.
Cold start
3. Too early fuel injection
Calculate the indicted power diagram by Mid ordinate Method
Calculate mean height of diagram =
Sum of mid ordinates Number of parts in diagram
Calculate MEP = Mean height of diagram x Spring scale
