Impact Engineering - Reciprocating Engine Analysis

Reciprocating Engine Analysis

Analysis Technique

Dynamic test data are gathered during normal operational load levels from each individual cylinder, in turn, after an initial warm-up period. Most of the vibration and ultrasound locations are on the cylinder head to evaluate the dynamic action of the intake and exhaust valves as well as the injector.

Several sets of readings are taken with different sensors from the following locations:

An indicator cock is used to connect a dynamic pressure sensor which gathers pressure data through the complete cylinder cycle;
An optical/mechanical encoder was connected via special adapters to the engine being tested, which is used to record the engine RPM and crankshaft position continuously. This instrument, after manual synchronization, provided the monitoring computer with engine speed and timing data via a strobe device;
An accelerometer is magnetically mounted at various positions on each cylinder head, engine and fuel pump to gather vibration data in relation to crank angle;
A magnetically mounted ultrasonic transducer is used to collect/translate passive ultrasound data being emitted from each cylinder head and injector/piping into waveform data.

The CARMA system saves pressure data in a pressure vs. crank angle (P/T Diagram) domain, translates this data into a pressure vs. volume curve (PV Diagram) and calculates the following performance characteristics:

indicated power [IHP or IkW]
peak pressure angle after TDC [Pmax angle in crank degrees]
pressure at 20 deg. before TDC (Pcomp) [dynamic compression indicator]
cylinder peak pressure [Pmax]
terminal pressure (P term) [5 deg. before exhaust valve/port opens]
indicated mean effective pressure [IMEP]

The CARMA system also displays the vibration and ultrasound traces as both acceleration vs. crank angle and voltage vs. crank angle domain, respectively. The pressure, vibration and ultrasound signals are displayed simultaneously on the screen as time waveform in order to determine characteristic anomalies.

The displays of ultrasound and vibration signals allow for good evaluation of the mechanical events in relation to cylinder TDC. This in turn allows accurate assessment of the condition of the mechanical components such as valves, injectors, liners and rings.

By comparing the signals (pressure, vibration and ultrasound) and performance calculations for each individual cylinder, the analyst can assess the performance characteristics of each cylinder and detect anomalies due to damaged or deteriorating components.

CARMA 8 - Sensor Setup

The following series of photos show the actual setup of the CARMA 8 system on the engine. The photo figures are described as follows:

FIGURE 1: Data Acquisition System: Computer, CARMA 8 Interface Module, and SDT	FIGURE 2: Optical Encoder Attached to Generator -End of Engine
FIGURE 3: Pressure Transducer - Attached to pressure cock on cylinder head	FIGURE 4: Vibration Accelerometer - Mounted vertically on cylinder head. Ultrasonic Transducer - Mounted on the side of the cylinder head.

System Setup / Diagram

Data Plot Orientation - Annotated Traces

Three (3) different sets of data are taken on each cylinder at different locations in order to evaluate the operating condition. Selected data is plotted from each cylinder and included with annotated comments of anomalies detected. The plots for each cylinder are identified as follows:

Upper Plot: The Vibration and Ultrasound transducers are mounted next to the Indicator Cock in the vertical orientation.

Center Plot: The Vibration and Ultrasound transducers are mounted on the opposite side of the Indicator Cock in the vertical orientation.

Lower Plot: The Vibration transducer is mounted on the side of the Head adjacent to the Fuel Pump and the Ultrasound transducer is mounted directly on the Fuel Pump. This setup is used to analyze the injection timing and pump operation.

Data Plot - Sample Trace

Analysis Terminology

The engine cylinder performance parameters are derived from the saved data including:

IHP/IkW		Indicated horsepower or kilowatts
IMEP		Indicated mean effective pressure
TDC		Top dead center
Pmax	Peak Pr.	Peak pressure
Pmax Angle	Peak Deg. ATDC	Peak pressure angle after TDC on power stroke
Pcomp	Pres. @ 20 Deg. BTDC	Compression pressure at approximately 20° before TDC power stroke
Pterm	Terminal Pressure	Pressure left in cylinder before exhaust valve opens

Engine Data

DIESEL ENGINE WARTSILA VASA 12V32D

DIESEL ENGINE WARTSILA VASA 6R22

Engine Speed	720 RPM	Engine Speed	1200 RPM
Engine Output	4440 Kw	Engine Output	990 Kw
Engine Output	6040 HP	Engine Output	1344 HP
Cylinder Bore	320 mm	Cylinder Bore	220 mm
Stroke	350 mm	Stroke	240 mm
Swept Volume	337.8 dm3	Swept Volume	54.7 dm3
Compression Ration	12:1	Compression Ration	11.8:1
Compression Pressure, Max.	100 bar	Compression Pressure, Max.	90 bar
Firing Pressure, Max.	145 bar	Firing Pressure, Max	. 140 bar
Charge Air Pressure	2.4 bar	Charge Air Pressure	2.0 bar
Mean Effective Pressure	21.9 bar	Mean Effective Pressure	18.0 bar
Mean Piston Speed	8.4 m/s	Mean Piston Speed	9.6 m/s
Idling Speed	500 rpm	Idling Speed	600 rpm

Test Results: MAIN GENERATOR - #1 (approximately 21750 hours)

Preliminary Findings

Several of the cylinders demonstrated double closures on the intake valves.

Exhaust valves have doubles on (1A and 6A).

Cylinder 4A shows a wide spaced 'chatter' pattern.

The most probable cause of this symptom is excess clearance in the valve train, see recommendations below.

Other possible causes for anomalies (in order of severity) could be:

Soft valve springs, or worn spring retainer collets and clips;
Loose fasteners or locking devices in the valve train or rocker arm support structure;
Damaged support brackets or fasteners;
Worn/damaged bushings or shafts in the rocker arms;
Worn/damaged pushrod, follower, or cam/roller's surface; or
Worn or damaged camshaft bearings.

Injectors
The injectors on Cylinders 2A, 2B, 3B, and 4B show abnormal ultrasound patterns. Fuel pump racks settings are within a close range (between 28 and 31 mm) at the tested load.

Overall Analysis
Engine runs well, with good speed stability and power output.
Power spread/balance is very good at a little greater than 13.5%.
"A" bank has the higher spread with over 34 kW between the highest and lowest cylinders.
"B" bank has an excellent spread at just over 16 kW.

Recommendations

Verify all valve clearances and examine valve train for signs of damage or wear. Adjust/renew as required using factory recommended procedures;
Look for secondary causes, where tappet settings are found to be good/normal;
Remove and test or change injectors listed above, renew as required. The use new OEM, or OEM approved rebuilt injectors is recommended;
Check security locking devices on the fuel pump, governor and rack linkages; and
After the above inspections/repairs have been completed, retest the engine at first opportunity to evaluate the results.

Main Generator - #1 -

Test Load was 2700 IkW on Main Switchboard
(Other engine operating conditions are part of the Plant's permanent log)

Cylinder	Avg/Cyl IkW	Speed RPM	IME Pbar	Avg Pmax bar	Avg Pmax deg ATDC	Pcomp bar	E.G.T. Deg. °C	E.G.T. MCR °F
1A	309.7	721.6	18.3	117.4	19.5	30.8	410	604
2A	315.5	721.7	18.6	115.1	20.2	29.8	430	726
3A	321.5	721.8	19.0	115.6	20.3	31.2	480	786
4A	313.7	721.8	18.5	114.6	20.1	30.7	465	721
5A	344.2	721.8	20.3	116.7	20.4	30.1	450	780
6A	332.4	721.8	19.6	120.9	19.5	31.4	480	822
1B	340.1	721.8	20.1	115.4	19.4	29.0	415	712
2B	341.4	721.7	20.2	120.2	20.5	28.8	475	761
3B	339.7	721.9	20.0	113.5	23.0	28.2	490	786
4B	338.4	721.7	20.0	125.2	31.5	28.0	455	736
5B	339.7	721.85	20.0	116.2	22.6	28.4	455	763
6B	354.5	721.9	20.9	120.0	20.9	29.4	480	612
Avgs	332.6	721.8	19.6	117.6	21.5	29.7	457.1	734.1

3990.8		13.5 %
Total IkW		Engine Power Spread

"A" bank avg.	322.8		"B" bank avg.	342.3
"A" bank spread	10.7%		"B" bank spread	4.7%

Main Generator - #1

Main Generator - #1 RIGHT BANK

Cyl	Exhaust	Intake	Injector	Wrist Pin	Big End Brg	Main Brg	Cyl Head	Liner	Rack"mm"	Inject Starts @	Additional Comments:
1A	D	-	-	-	-	-	-	-	28	17	Check - MCR Temp. Indicator.
2A	-	D	CHECK	-	-	-	-	-	29	16	-
3A	-	-	-	-	-	-	-	-	30	14	-
4A	-	D	-	-	-	-	-	-	30	15	-
5A	-	S	-	-	-	-	-	-	31	15	-
6A	D	D	-	-	-	-	-	-	30	12	-

LEFT BANK

Cyl	Exhaust	Intake	Injector	Wrist Pin	Big End Brg	Main Brg	Cyl Head	Liner	Rack"mm"	Inject Starts @	Additional Comments:
1B	D	D	-	-	-	-	-	-	30	12	-
2B	D	D	CHECK	-	-	-	-	-	29	12	-
3B	-	D	CHECK	-	-	-	-	-	30	13	-
4B	D	D	CHECK	-	-	-	-	-	30	10	-
5B	D	-	-	-	-	-	-	-	31	12	-
6B	HD	D	-	-	-	-	-	-	30	12	Check - MCR Temp. Indicator.

Annotation Legend

D	Double/Multi Impact	E	Excess Clearance		U/S	Ultrasound Anomaly
H	Hard Impact	L	Leakage at Hi Press		B/B	Blow-by
S	Sharp Impact	W	Weak Signal		R/L	Ring-Liner Chattering
M	Minimal Impact	T	Abnormal Timing		*	See Report Notes
XN	Cross Talk other Cyl	LC	Loose Sensor Conn	.		Other

SUMMARY:
Detailed reciprocating analysis now allows the following information to be available for Predictive Maintenance:

Mechanical
Condition
Analysis

Injector Performance
Piston Ring Blowby
Cracked Heads & Crowns
Leaking Valves
Leaking Head Gaskets
Deteriorating Piston Rings
Cylinder Lubrication
Rough Liners
Combustion
Valve Closures
Piston Slap
Piston Ring to Liner Activity
Excess Bearing Clearances
Out of Phase Knocks
Loose Counterweights
Broken Fasteners

Engine
Performance
Analysis

No Combustion
Early Combustion
Late Combustion
Detonation
Pre-Ignition

Overall
Combustion
Quality