Indicator Diagram is the most important parameter to understand the performance of the Engine. Starting from power calculation to engine maintenance, everything can be found in the Indicator Diagram. So, as a marine engineer, you must know how to read, understand, and analyze the indicator diagram.

There are mainly four types of Indicator Diagrams.

1. Power Card
2. Draw Card
3. Compression Card
4. Light Spring Diagram.

In this article, I’ll explain everything you need to know about the Indicator diagram. Such as the difference between each type, the purpose of each type, fault finding, indication, remedial action, and many more.

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Let’s get started.

Comparison of the Indicator Cards

Type	Method	Value	Limitations
Draw Card	90 degrees out of Phase Fuel on Condition Normal Spring	Shows pressure variations during the combustion process. Can measure Pcom. and Pmax.	Difficult to analyze Scavenging and exhaust process.
Power Card	In phase Fuel on condition Normal Spring	The area under the curve shows work done during the cycle. Can calculate MIP and IHP. Can Measure Pmax.	Difficult to analyze the pressure variations clearly.
Compression Card	In Phase Fuel Off Condition Normal Spring	Can measure Pcom. Shows Pressure variation during the compression stroke.	Only the compression process can be analyzed.
Light Spring	In Phase Fuel on condition Using Light Spring	Shows pressure variation during the scavenging and exhaust stroke more clearly	Cannot analyze the pressure variation during the combustion process.

 

The Frequency / Interval of taking Indicator Diagrams

Type	Interval
Draw Card	Every voyage or within 3 months interval for routine maintenance and engine performance. Before and After completion of the Unit Overhaul. Every completion of maintenance to fuel injectors, fuel pumps, timing check, and correction. Any suspect to abnormal running condition, such as, exhaust temp variation, TC efficiency fall, and using bad quality fuel.
Power Card	Every voyage or within 3 months interval for routine maintenance and engine performance. Before and After completion of the Unit Overhaul.
Light Spring Diagram	Before and After every change of the exhaust valve. After every Turbocharger Overhaul and Air cooler cleaning. Any suspect to abnormal running. Such as exhaust temperature variation.

 

Indicator Diagram analysis – Defects and Rectification.

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Early Injection / Early Ignition:

Indication	Exhaust temperature than normal Engine running with knocking sound and vibration
Detection	It can be detected by taking  Power card and Draw card. Power card shows peak pressure is higher than normal The draw card shows the start of injection and ignition before TDC more clearly.
Causes	Incorrect fuel pump timing or wrong VIT setting. Incorrect fuel valve setting or spring has broken. Poor fuel condition( High Cetane Number). Incorrect fuel temperature and viscosity control.
Affect to	Overheating of Engine parts within the cylinder. Scavenge fire. Running gears and bearing may damage due to shock load transmission and vibration.
Remedy	Correct fuel pump timing. Inspect fuel valve and pressure test. Correct fuel temperature and viscosity control. Correct cooling temperature of working parts.

 

Late Injection / Late Ignition:

Indication	High exhaust temperature with black smoke emission Pulsation in exhaust manifold due to high exhaust pressure.
Detection	It can be detected by taking  Power card and Draw card. Power card shows a decrease in pea pressure The drawcard shows the decrease in peak pressure more clearly. A slight dip in the compression line before fuel injection begins and ignition starts well after TDC
Causes	Incorrect fuel pump timing, worn, or defective fuel pump Faulty fuel valve(High setting pressure) Incorrect fuel viscosity and temperature control(Too low) Bad fuel condition(Low cetane number) Lack of scavenging air Excess chain slackness Under cooling of the engine parts
Affect to	Reduces engine power output Reduces turbocharger efficiency and causes surging. Fouling of the exhaust gases may lead to uptake fire. After burning effect may lead to exhaust valve burning. High temperature in cylinder liner may lead to defective cylinder liner lubrication. Engine power decreases due to a decrease in thermal efficiency.
Remedy	Correct fuel pump timing and overhaul fuel pump. Inspect fuel valve and pressure test. Correct fuel temperature and viscosity control. Maintain correct cooling temperature. Inspect chain slackness and readjust as necessary. Properly clean and maintain the charge air cooler, scavenge space, and exhaust system

 

Chocked Exhaust Ports(Late ignition):

Indication	High exhaust temperature and heavy smoke emission with soot coming out. Reduction in turbocharger rpm and surging. Increase in temperature of the internal parts.
Detection	It can be detected by Light spring diagram. It shows the exhaust pressure does not fall rapidly as normal because it prevents the blowdown of the exhaust gases.
Causes	Incorrect Tappet Clearance. Faulty fuel injection system. Lack of scavenging air. Excess cylinder lubrication Exhaust system fouling Cam clearance is too much for uniflow-type engines.
Affect to	Engine blow pass which may lead to scavenge-fire Decrease in Engine output
Remedy	Correction of Tappet clearance Correct fuel timing and good fuel injection Correct cylinder lubrication Cleaning of scavenging space, turbocharger, and exhaust grid Soot blowing of exhaust gas boiler and uptake.

 

Chocked Inlet Port(Loss of Scavenge Air):

Indication	High exhaust temperature with black smoke emission Knocking sound may occur Engine speed can not increase to the normal level
Detection	It can be detected by taking Light spring Digram It shows insufficient pressure of scavenging air
Causes	Scavenge ports / Inlet ports fouling with incomplete combustion products There might be an obstruction in the air manifold Improper cleaning of the scavenge spaces Air cooler fouling Turbocharger fouling at the blower side
Affect to	Decrease engine power output The engine might run in an Unbalanced condition Due to incomplete combustion internal corrosion of engine parts, Piston ring sticking, contamination may occur.
Remedy	Proper cleaning and maintenance of the turbocharger including water wash Regular cleaning of Air cooler, Scavenge space, and Inlet ports

 

Leaky Piston Ring / Exhaust Valve:

Indication	High exhaust temperature with smoke All unit exhaust temperature not steady
Detection	By taking the Compression Card, Power Card, and Draw card without fuel supply Measure compression pressure with other units
Causes	Excess liner wear Excess wear of piston rings and ring grooves Piston ring jamming or sticking due to the carbon deposit
Affect to	Engine Blow pass. Scavenge fire High rate of cylinder wear being insufficient lubrication due to blow pass Piston and liner overheat and may cause a seizure
Remedy	Unit overhaul Liner calibration Clean and measure piston rings and piston groove Renew the necessary parts Measure cylinder lubrication rate and correct as necessary Avoid overloading the engine

 

After Burning:

Indication	Exhaust temperature higher than normal Emission of smoky exhaust Turbocharger surging
Detection	By taking the Power card and Draw card A rise in expansion line indicate after burning condition during the expansion stoke
Causes	Incorrect fuel pump timing Leaky exhaust valve
Affect to	Exhaust valve burning Fouling the exhaust gas system and lead to uptake fire Burning of the piston crown Corrosion of Liner and piston rings die to burn away of lubrication oil film being in overheating
Remedy	Change fuel valve Correct fuel pump timing Maintain correct cooling

 

Leaky Fuel Valve:

 

Indication	High exhaust temperature with black smoke emission Knock of the pressure wave in the fuel injection system
Detection	By taking power card and drawcard It shows the fluctuation of pressure during the expansion process due to after burning of a leaky valve
Causes	Incorrect opening pressure setting of the valve( too low or spring broken) Partial opening of the fuel valve due to small debris at needle valve. Or due to carbon deposits
Affect to	After burning Incomplete combustion products Fouling at Inlet and exhaust ports Turbocharger efficiency drops
Remedy	Inspect fuel valve, overhaul, and pressure test Change fuel valve if necessary Maintain proper fuel temperature Proper fuel valve cooling temperature Proper fuel purification and separation

 

Choke Fuel valve:

Indication	Lower Exhaust temperature than normal Hammering of high-pressure pipe between the fuel pump and injector Engine speed not steady
Detection	By taking power card and draw card It shows irregularities at the peak of the diagrams
Causes	Small debris choke at fuel atomizer holes or high-pressure filter Leaky fuel valve Sticking of fuel valve due to overheating
Affect to	Engine running in an unbalanced condition Reduced engine output power
Remedy	Inspect fuel valve, overhaul, and pressure test Change fuel valve if necessary Clean all filters and strainers in F.O system Maintain efficient fuel separation Maintain good fuel valve cooling

 

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So, this was all about the basic introduction to the Indicator Diagrams. And how to analyze and find defects from the Indicator diagrams. Also, different methods to rectify the defects. Read more about the Indicator diagrams from here.

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