Wireless technology for real-time temperature monitoring of crank pin and crosshead bearings in diesel engines. ------00-----By: Dr. Ing. Steinar Fossen, Managing Director, SensIT AS, Norway. Surveys aiming to isolate the main causes of severe marine diesel engine damages clearly indicate the need for crank pin and big end bearing instrumentation to reduce the number of high cost damages on medium and high speed engines. However, both the hostile environment inside the engines and the need for a highly flexible system that can easily be installed and adjusted to different mechanical tolerances have kept existing solutions from being reliable methods of temperature monitoring on these bearings. Using wireless technology the electronics company SensIT AS in Trondheim, Norway has developed a sensor system named Sentry, that provides real-time temperature monitoring of rotating bearings in diesel engines.
1. Introduction Developments in wireless technology have created an opportunity for new sensor systems that make it easier to provide endto-end wireless telemetry solutions both in maritime and industrial applications. These solutions act as a layer of technology easing the management of a process by monitoring data and alerting to situations that can be hazardous or costly, such as operating problems of high cost machinery. This represents a situation that should be detected as early as possible.
Figure 1: The Sentry wireless sensor GBW-100
This is especially true for marine diesel engines, as a serious malfunction is likely to develop very quickly and may even threaten the general ship safety. Since serious bearing damages always cause temperature increases monitoring of bearing temperature represents a valuable indicator in a monitoring system, enabling timely action to protect vital engine parts
against expensive damages. At this time a new system named Sentry, having the needed functionality in terms of fast response and installation flexibility is in its test phase. The final developments and tests of this system are done in cooperation with Wärtsilä Technology Ltd.
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2. Engine damages Main engine damage statistics collected by Det Norske Veritas in the periode from 1990-96, show that crank pin and big end bearing damages in diesel engines are the second most important cause of damages in 4-stroke engines. In total, such damages are responsible for 14,2% and 16,9% of all reported damages on medium and high-speed 4-stroke engines, respectively.
(IACS) have also highlighted the importance o f bearing temperature monitoring by formulating a new SOLAS (Safety of life at sea) regulation, demanding “an equivalent device [to oil mist detection]” (SC133/1998). This indicates that also IACS promotes new innovations in the field of bearing monitoring.
Main eng ine damages repo rted to DNV from 1990 to 1996
Slow speed <250 RPM
10,6 10,9 10,9
Cylinder liner
13,3 12,5
Piston
Cross-head bearing & guides
15,5
7,9
0 0 6,3
Crank bearing & pin
14,2
6
Main bearing & journal
0
Medium speed 250 - 1000 RPM High speed 1000 RPM >
5
16,9 15,7
10
15
18,4 20
25
Percentage of all reported damages
Figure 2: Main engine damages reported to DNV from1990 to 1996
To date, oil mist detection has been used as a warning signal of an imminent bearing seizure. However, it can be questioned if this method has the fast response time that is needed to protect the engine against damages caused by ruined big end bearings. The International Association of Classification Societies
3. System description One major advantage of the Sentry system is the high flexibility in arranging sensor and antenna both with respect to the gap, angle and lateral position between these units. The system is in its core based on a specialised radar technology.
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This enables the possibility of using high quality wireless passive sensors with no need for external power sources. Figure 3 shows the principal design of the system.
This is a time consuming process and it has to be done in close relationship with the engine builders. One main reason for this is that the wireless temperature sensor needs to be placed in a carefully drilled hole in the connecting rod.
Figure 3: Technological principle and system functionality
As illustrated in the figure the signal processing unit generates a low energy, high frequency radar pulse, which is transmitted to the wireless sensor via the stationary antenna. When the wireless sensor passes the stationary antenna the radar pulse is transferred. The sensor will then immediately reflect a pulse signal, which is received by the signal-processing unit via the stationary antenna. The shape and characteristics of the received signal is then used to uniquely determine the temperature of the sensor. This information is then communicated to the engine control and monitoring system.
The stationary antenna is installed in such a way inside the engine that the wireless sensor passes the antenna with a maximum distance of 50 mm. This shows that the installation of the stationary antenna related to the wireless sensor is extremely flexible and non-critical. The embedded “self verify” functionality makes any other configuration superfluous. The SENTRY GBP100 Signal Processing Unit
Plug
Monitoring and Control System
Multicable Coaxial Cable Gland
The SENTRY GBS100 Stationary Antenna
4. Mechanical design and installation Diesel engines have different design and number of cylinders. Each engine type therefore needs to have specific instructions and drawings for the installation of the Sentry system.
The SENTRY GBW100 Wireless Sensor
Plug
Inside engine
INSIDE
ENGINE
Figure 4: Mechanical design and installation
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shown graphically in figure 5. The bold black curve shows the temperature in the connecting rod monitored by the Sentry wireless sensor. The hairline dotted curve is a reference temperature monitored by a thermocouple sensor that was placed 12 mm under the surface of the crank pin. The main conclusion from the seizure test is that the response time of the system is fast enough to save the crank pin from being damaged.
5. Big-end bearing seizure test The final developments of the Sentry system have been done throughout a technical cooperation between SensIT, Kongsberg Maritime Ship Systems and Wärtsilä Technology Ltd. As a part of this technical cooperation Wärtsilä has performed a series of functional tests, including a big end seizure test on a Wärtsilä W4L20 engine. Figure 5 shows the results from the seizure test.
Big-end bearing seizure test on a Wärts ilä W4L20 200,0
35
SENTRY sensor in con-rod Thermocouple ref.
180,0
30
Engine speed (/10) Lub.oil flow bearing
160,0 ) C ° (
25
140,0
20
e r u t a r e p m120,0 e T
15
100,0
10
80,0
5
60,0
0 0
30
60
90
120
150
180
210
240
270
300
330
360
] n i m / s e r t i l [ w o l f l i o . b u L
390
Time (s)
Figure 5: Test results from big-end bearing seizure test performed by Wärtsilä
The seizure test was conducted by cutting the supply of lubrication oil to one of the cylinders of the engine. This was done while the engine was running on approximately 1050 rpm. Both the engine speed and the flow of lubrication oil are
6. Market launch Currently the system is being tested on pilot installations to verify long-term stability on both 4-stroke and 2-stroke engines. The results from these tests and the timetable for the type approval by the major classification societies
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will impact on the decision to make the system available on the market. Following these plans a limited market launch is planned later this year. Kongsberg Maritime Ship Systems AS will coordinate the market introduction of the Sentry system, as they will be responsible for the sales and marketing to the international maritime markets.
For further information, please contact:
SensIT AS Phone: +47 7382 6970 Fax: + 47 7382 6951 Mail:
[email protected] www.sensit.no
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