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# Fault Tree Analysis of Overheating in Marine Diesel Engines

Document Type:Dissertation

Subject Area:Engineering

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The failure rate of the FTA is found by applying the FTA numbers and its operators. The FTA probability gives the FTA results which are able to compensate when there is the vague or uncertain probability of engineering errors and basic events. The FTA method analyzes many things which may not include only the reduction of overheating through the jacket water but also to measure the importance of basic events that help reduce overheating. Calculation of the system’s FTA importance has two methods that are proposed to be used namely the GMIR which stands for Graded Mean Integration Representation and the FTA probability ranking method. In this paper, it was found that the cooling of the engine through the jacket water has proved very reliable when marine design engine is overheating. It is also concluded that the basic events of the system that increase overheating is the failure of supply air and is treated the most critical parameter. ACKNOWLEDGEMENT I would like to direct my heartfelt and deepest gratitude to my supervisor, Prof. Dr. Mr/ Mrs……………………………at the University of …………, for his/her immense knowledge, excellent guidance, caring, patience and providing me with an outstanding atmosphere for studying and doing research. I attribute the level of my……………. Degree to his/her encouragement and effort and without him/her this project report, would not have been completed or written. One purely could not wish for a better or friendlier supervisor. I am also grateful to the staff of the University of ……………, my colleagues and friends, and one and all, who indirectly or directly, have supported and encouraged me.

TABLE OF CONTENTS ABSTRACT 2 ACKNOWLEDGEMENT 3 TABLE OF CONTENTS 4 LIST OF TABLES 6 LIST OF FIGURES 7 ABBREVIATIONS 8 CHAPTER 2 13 2. RESEARCH STUDIES 13 2. Background 13 CHAPTER 3 16 3. METHODOLOGY 16 3. Introduction 16 3. Theory of the Fault Tree Analysis 16 3. Events and Gates 17 3. FTA Importance Measure 28 3. Specific Events for FTA for marine diesel engine 29 3. Overheating of Marine Design engine using FTA Analyzer software 30 4. RESULTS 32 4. FTA failure probability of the top event: 32 4. A Gantt chart is the most appropriate tool to be used in this report as it gives the layout for accomplishing the given task. This paper will be used to come up with a final paper by providing the objectives, aims and the methodology needed to meet the set objectives as well as the references of the resources used in this report that pertains the failures caused by overheating of marine engines.

The ships at sea use the marine design engines and must be supervised by skilled mechanical engineers who have specialized in the marine field (Wang, Ruxton, and Labrie, 1995). These engines run for long periods of time and due to that, the engines experience many faults. Despite the faults, the engines are still needed to work continuously considering the fact that the main engine is just one necessary for propulsion. It was developed in 1962 and used by Bell Telephone laboratories as minuteman systems for the US Airforce which was later fully used by the Boeing Company. The FTA technique has many symbols and stages representing events and causes that most frequently affect the systems that are to be analyzed (Cicek, Turan, Topcu, and Searslan, 2010). This technique will be used in this report to analyze the varied causes of overheating of marine design engines and how these causes relate to each other.

Aims and Objectives • To study all the possible causes of overheating of marine design engines and their related systems. • To analyze the probability of occurrence of these causes and the rates at which they occur. There has been previous failures that resulted in engine piston seizure, engine room fires, etc. caused by a failure in the cooling system. This problem requires reliable techniques that will give information that is used to create the machines maintenance procedures and precautions which will aid in minimizing the probability of occurrences and the rate of occurrences of overheating in the marine design engines. CHAPTER 2 2. RESEARCH STUDIES 2. A highly reliable cooling system will be obtained by combining various techniques of carrying out the failure analysis from the design to operation stage. This analysis poses a great challenge to engineers of knowing the exact value of failure probability of each component or event.

The factors that affect the failure probability of basic components and the reliability of the cooling system included weather condition, the loading state of the ship and the ships’ mobility. This research uses the Fault Tree Analysis to qualitatively analyze the cooling system, and an FTA system is also used to assign the probability of failure to all the system components in order to rule out under-estimation and overestimation and also to use qualitative analysis to get more reliable results. The FTA probability uses the existing statistical data, judgments from the experts and the influencing factors to define the likelihood of failure of the basic components of the system. Part 4 gives the results; two different methods are used to obtain the FTA failure probability of the jacket water cooling system of the marine design engine and the important measures of the FTA for all the components of the system in determination of overheating.

This report finally gives the discussion of the results obtained in the previous section. The discussion shows the order of criticality of the components of the jacket water cooling system and how their FTA failure probability and reliability is calculated using the two different methods. CHAPTER 3 3. METHODOLOGY 3. The overheating of marine design engines is the fault and the subject matter of this report. A typical FTA diagram is shown in Figure 1. The figure shows all the components included in a Fault Tree Analysis (FTA). Two major components form an FTA diagram; the events and the gates. The events are the common faults that happen within the system while the gates give the order of occurrence of the stated events and their cause of failure. Undeveloped event: an event which has scope for further development but not done usually because of insufficient data.

The following procedure will give rise to a Fault Tree Diagram, and it involves researching, calculating and finally drawing the tree; 1. The system being investigated is recognized and defined. The system boundaries and its failures are clearly specified in order to build on all the necessary information and come up with a focal point that the system will be addressed from for example shutdown, safety issues, overheating, etc. The tree loop structure is constructed to enable the drawing of the basic events causing and leading to the treetop focal point event. Through the data that will be provided, some precaution measures can also be stated to help minimize the probability of occurrence of the events and components in this system. Causes of Overheating in Marine Design Engines The marine diesel engines convey only about a third of its heat to mechanical energy for propulsion.

The amount of heat generated for an unused purse is quite high and is needed to be removed from the engine through the cooling system. This excess heat is mainly attributed to several factors in the cooling system of an engine such as; Scale formation in the cooling system: the water that is used in the cooling system of the marine diesel engine is usually salt water. The amount of ppt in the water is over 100ppm hence considered as hard water. Advantages Fault Tree Analysis (FTA) uses information obtained from reliable sources and the analyses done by different methods on various modes of system failure and events causing them, to provide a basis for system redesign and change in the systems maintenance procedures. The major aim is to reduce the possibility of occurrences of the risks and hence more reliability of the systems.

In addition, it is an easy to read diagram that gives possible problems likely to be encountered in a system and all the variations that may arrive at the failure. It is also useful in calculating estimates of the probabilities of events occurring and how frequent the events are likely to occur. It also shows the order in which the sequences occurred in the past that leads to the failure of the previous systems. fault accidents of the whole marine design engine system due to overheating. This shows that the reliability of the main engine system is very critical as compared to the whole marine engine plant. Thus this report considered studying the marine engine design system instead of the whole marine design engine. The method of evaluation the Fault Tree failure probabilities:  The machines produced by industries are not dependent on the type of product or the type of application.

They do not have a difference in the working environments, the condition of the processes or how they are inspected and maintained. These companies give the failure rates based on very similar conditions of the engines likely to be encountered at sea. It also outsources data from other non-electrical parts reliability data. These data combined with the high-end sober judgment of the design engineers come up with the FTA numbers of the basic events happening in the system. These judgments are made by all the engineers onboard the vessel; the chief engineer, the second engineer, the third engineer and the electrical engineer. Data is also obtained from the maintenance records of the systems onboard ship (PMS, preventive maintenance system) and the expert engineers onboard analyze these results in order to come up with an FTA number (Mao, Tu, and Du, 2010).

to 0. Nature at which cooling systems fail makes it suitable for triangular FTA number to be used in this study for detailed computations. The calculation of the triangular FTA number is discussed in the following sections. Calculation of the triangular FTA number For a given FTA number say Ã, it becomes a triangular FTA number only when its membership function is completely defined by the equation below provided. For a triplet (a, m, b) or Ã = (m-a, m, b-m) is a good example of a triangular FTA number representation (Mao, Tu and Du, 2010). These are Birnbaum importance measure, Criticality importance measure and Fussell-Vesely importance measure, which are done to obtain the structural importance, criticality importance (the importance of reliability to the basic components and events of the system) and integrated structural and also show the important contribution of the basic events to the various cut sets.

The calculation of an FTA importance measure of a basic event or basic component in an FTA is done by using the different measure of two FTA probabilities for a top event in the fault tree (Papadopoulos, Walker, Parker, Rüde, Hamann, Uhlig, Grätz and Lien, 2011). This is done whether or not the basic event exists. This report will use two methods to calculate the FTA importance measure and then the results obtained from the two methods are analyzed and compared. The probability of the absolute event is represented by as shown in equation 12 below. Overheating of Marine Design engine using FTA Analyzer software The failure of the marine design engine was tested by FTA software where the parameters such as cooling system; secondary cooling system and primary cooling system.

Figure 4: FTA Analyzer diagram The OR gate was used to synchronize between the secondary and primary cooling system. The primary cooling system used AND gate as connections to its filters. On the secondary cooling system, the actuators were connected to it through AND gate. OR gate means output event occurs if any of the input events occurs. FTA failure probability of the top event: The FTA gate equations and the FTA probability is used to calculate the FTA probability of all transfer gates for the top undesired event obtained using the results of the transfer gates. The top event ( which is having the temperature other than the setpoint ) is calculated using the Equation 2, and the results can be represented as a triangular FTA number, for example, {0. the failure probability each operating hour is obtained using the FTA probability of the top event using the equation as follows; 4.

Finding the FTA importance measure of basic events By using the occurrence probability of the main event when the basic event is absent in order to be able to calculate the FTA importance measure of a basic event xi, i = (1, 2, 3,. and its calculation is shown in the table shown below. The control air supply then becomes the most important event that needs to be carefully observed during maintenance processes of the engine. The components that have the lowest FTA importance measure are the high-temperature freshwater systems and the low-temperature fresh water cooling system pumps for the reason that they are redundant. These pumps have one running and the other one in standby mode. The pumps still have low FTA importance measure even if the failure rates for pumps are high. The FTA importance measures for other events which are connected through the OR gates form the top to bottom are found, each with their failure rates.

X5 0. X19 0. X2 0. X18 0. X10 0. The component of the system is more important if the distance of the component is larger. It can also be observed from the results that both the proposed methods have the same rank of FTA importance measures for all the basic events and these values can be verified for the two proposed methods. A typical fault tree for marine design engine system is the one that gives the reliability of the engine system through calculation of the probability failure occurrence rate (Jang, Yang, Song, Yeun and Do, 2002). An integrated analysis shows that the engine systems will fail in case of overheating one bottom event happens among all the other events {x2}, {x6}, {x7}, {x8}, {x9}, {x10}, {x11}, {x12}. This shows that the minimal cuts sets required for the engine fault tree are the cut sets {x2}, {x6}, {x7}, {x8}, {x9}, {x10}, {x11}, {x12}.

All the components included in this analysis. A failure in the engines cooling system is deemed to be caused by a failure in HTFW or LTFW cooling systems that leads to overheating. In the primary cooling system, the filters series 1, 2 and 3 started to have a complication. Filter 1 was blocked by debris after a period of 5 hours of the working Marine Design engine. The sequence of failure of the filters through blockage by debris. Therefore, overheating of the engine rate was 50% implying the failure rate of actuators was equal to the success of the actuator. The cooling water from both the primary and secondary cooling systems probability of failure was a half the total probability. The overheating of the engine was because the combustion in the cylinder produced a high amount of heat.

Amount of water circulating under the pistons, cylinders heads and another heated part of the engine was not cooled enough when the probability of the failure rate of both primary and secondary cooling system failed. In the transitional time from primary cooling system to the secondary cooling system also led to the overheating of the Marine design engine. The FTA Analyzer showed that the functionality of both the primary and secondary cooling system probability is 50%. The possibility of failure is high when the debris clogs the filters hence blocking it. The failure of the actuator because of malfunction also may lead to the incident of overheating of the marine design engine. The reduction of the overheating of the engine is possible by increasing the rate of cooling of water jacket that cools the engine.

It is believed that the knowledge gained in this study will provide the theoretical reference for the comprehensive reliability of marine design engine system and guide for developing the comprehensive technology of combining life prediction, fault early warning, and maintenance remission with reliability design for protecting the ships completing their missions reliably and safely. In Engineering Systems Management and Its Applications (ICESMA), 2010 Second International Conference on (pp. IEEE. Huang, D. T. Chen and M. S. Yeun, Y. S. and Do, S. H. Z. J. W. Tu and H. B. and Lien, R. Engineering failure analysis and design optimization with HiP- HOPS.  Engineering Failure Analysis, 18(2), pp. Tao, J. S. E. F. F. Goldberg, N. H. and Labrie, C. R. Design for the safety of engineering systems with multiple failure state variables.  Reliability Engineering & System Safety, 50(3), pp.