Lubricator for Gas Generators - Research Paper Example

? Proposal to Research and Develop Lubricator for Gas Generators Faisal Abdullah Indiana I would like to thank Professor Name ] for providing unwavering support and cooperation during various stages of this project. Furthermore, I would like to thank [ Course Professor Name ] for providing me a framework to accomplish this research using a structured approach. Lastly, I would like to thank the machinists and fabricators who helped me create working prototypes of the gas engine lubricator for putting their long hours and cumulative wisdom into my work. Abstract Natural gas is composed in large part of methane and finds pervasive use as a fuel globally. Internal combustion engines have also been designed to operate on natural gas since it is cheaper than crude oil derivatives. Although natural gas engines provide for cheaper operating costs, there is a constant need for maintenance on the valve assemblies. The relatively earlier failure of valves, especially exhaust valves, leads to increased maintenance costs as well as lowered machine reliability and availability. This is truer still for smaller gas engines that are employed in domestic backup power applications. This research employs a lubricator in order to improve the lubricity of natural gas so as to improve valve life and hence engine availability and reliability. Keywords: natural gas engine, lubricity, valve failure, exhaust valve, head assembly Table of Contents Statement of the Problem 11 Rationale 11 Assumptions 12 Limitations 12 Nomenclature 13 Terms. 13 Abbreviations. 13 Intellectual Property Issues 14 Patent. 14 Copyright. 14 Fair use. 14 Budget Overview 14 Analysis 16 Problem Analysis 16 Existing scenario. 16 Ideal scenario. 16 Gap analysis. 16 Performance Criteria 16 Focusing of the Task Objective 17 Limitations and delimitations of the project. 17 Governing propositions. 17 Assumptions. 17 Statement of the R&D objective. 18 Hypothesis 19 Solution Proposal Method 19 Mechanisms of the Task 19 RCA. 19 Observations and expert opinions. 19 Development Procedures 19 Computer aided engineering (CAE) techniques. 20 Machining. 20 Fabrication. 20 Fitting. 21 Governing Propositions 21 Performance Measures 21 Synthesis 21 Implementation 21 Testing 22 Equipment. 22 Methods. 23 Measurement. 24 Instrumentation. 24 Experimental Results and Data Analysis 25 Validation 26 Status of Task Objective 26 Sustainability 26 Transferability 26 Implications 27 Recommendations 27 References 28 Appendix A – Lubricator Design 29 3D CAD Models 29 Appendix B – Proposed Air Plenum 32 3D CAD Models 32 Index 34 List of Figures Figure 1 - Exhaust valve burn with the burned area visible on the right side. Continued operation of this valve could have led to catastrophic failure of the engine. 10 Figure 2 - Arrangement of inlet valve and exhaust valve in a single cylinder engine configuration 22 Figure 3 - The gas genset used for the current research sourced from (Green Power, 2013) 23 Figure 4 - MTBF against lubrication feed rate 25 Figure 5 - Lubricator body with bracket welded on 29 Figure 6 - Lubricator graduation cylinder 30 Figure 7 - Lubricator end tail for insertion into air plenum 30 Figure 8 - Complete lubricator assembly including lubrication adjustment screw (shown on the left bottom corner) 31 Figure 9 - Proposed air plenum base 32 Figure 10 - Proposed air plenum top cover 33 List of Tables Table 1 - Budget for the current research. 14 Table 2 - Lubrication feed rate used for experimentation 23 Table 3 - Lubrication feed rates and the corresponding MTBF 25 Proposal to Research and Develop Lubricator for Gas Generators Natural gas serves as a cheap fuel alternative to the more expensive diesel, gasoline, kerosene, light fuel oil (LFO) and heavy fuel oil (HFO). There has been a growing trend to utilise natural gas in power generation applications in the form of both turbines and internal combustion engines. The lubrication process in a turbine relies on an externally supplied lubricating agent only. However, internal combustion engines need to rely on both an external lubricating agent as well as the lubricity of the fuel being used (Duan, Li, & Zhang, 2012). In essence an internal combustion engine requires lubrication for its cylinder as well as the valve assemblies. The lubrication serves two distinct purposes: (1) to reduce friction between moving parts and hence increase the operating life of the engine; (2) to remove heat from static parts of the engine so that thermal fatigue and failure of engine components can be decreased. The use of liquid fuels such as those mentioned above allow for inherent lubrication to occur. The hot portions of an internal combustion engine i.e. the cylinder, piston, connecting rod and crankshaft are all lubricated by force feed using oil spraying mechanisms. In larger commercial engines, such lubrication measures are extended to the valve assemblies too. However, when it comes to smaller domestic engines, no such lubrication mechanisms are installed since the inherent cost of such mechanisms would make such small engines too expensive (Munro, 2103). The use of liquid fuels is expected to provide for lubrication demands in the valves that are installed on the top of the internal combustion engine. Internal combustion engines utilising liquid fuels tend to exhibit greater valve life than gas engines since there is a significant difference in lubricity between both kinds of fuels (Hu, 1944). The lower inherent lubricity of natural gas, compared to liquid fuels, tends to punish the valves more than anything else in an internal combustion engine. The engine components that are in constant contact with engine oil are cooled down by the flow of the oil. However, the smaller gas engines do not have direct contact between valves and engine oil so their cooling is compromised. The problem is more apparent at the exhaust valves that are burned up by the high exhaust temperatures of the combusted air and fuel mixture. The high temperatures experienced by the exhaust valve cannot be removed satisfactorily which in turn causes the valve surface to be damaged since a high thermal gradient is set up. Figure 1 - Exhaust valve burn with the burned area visible on the right side. Continued operation of this valve could have led to catastrophic failure of the engine. The exhaust valve shown above reflects a burn up situation where the valve has suffered damaged to its entire surface, especially to the right side as indicated by the black region. The high temperatures damage the surface coating and surface treatment of exhaust valves which in turn leads to their rapid surface deterioration. If a burnt up valve is kept in service, there are chances that chunks of metal might break off the valve and destroy the piston and the cylinder lining (Tai, 2006). This would lead to major damage to the internal combustion engine rendering it unusable unless significant maintenance is performed. Statement of the Problem Gas fed internal combustion engines tend to experience early failure of exhaust valves when compared to exhaust valves on internal combustion engines being run on gasoline, diesel, fuel oils, kerosene and similar liquid fuels. The typical time to failure of exhaust valves running on natural gas varies between 800 running hours and 1,000 running hours. In comparison, internal combustion engines running on gasoline experience exhaust valve failure between 2,000 running hours and 2,500 running hours. The early replacement of exhaust valves on gas run internal combustion engines reduces the reliability and the availability of the machine since maintenance is increased. Rationale Natural gas tends to have lower lubricity than fuels in the liquid phase. Since natural gas has a lower lubricity, it causes greater wear and tear of the components that it comes into contact with. Internal combustion engines rely on the lubricity of the fuel in order to remove heat and reduce working friction from certain areas of the engine such as the inlet valve and exhaust valve assemblies. The use of natural gas reduces the removal of heat and friction from the inlet valve and exhaust valve assemblies. The inlet valve experiences lower temperatures but the exhaust valve realises higher temperatures and requires greater cooling to prevent a burnt up valve. Improvements in the cooling of the exhaust valve through lubrication methods would significantly increase the useful life of the exhaust valves. Consequently, this would lead to lowered maintenance costs and greater reliability and availability of the machine. Assumptions It is assumed that the internal combustion engines being researched for improvements are: run entirely on natural gas and that no liquid fuels are used in these engines at all; being run on natural gas available for domestic use and that fuels such as liquefied petroleum gas (LPG), propane or other allied fuels are not being used; not being run continuously but are only being used for back power such that the duty cycle consists of one operating hour and one resting hour. Limitations The current research is limited purely to natural gas operated engines being utilised for power generation in back up power systems. Moreover, the current research is limited to gas gensets that are sized between 1 kW and 6.5 kW only. This research does not apply to larger gas gensets that have independent cooling systems for their head assemblies. In contrast, this research applies to smaller gas gensets that rely on air cooling alone for their head assemblies. In addition, this research will not explore methods to cool engine oil such as through the use of oil intercoolers or otherwise. Nomenclature Terms. Lubrication: The use of substances, in any phase, in order to reduce friction between moving parts. Lubrication is also intended to remove heat from parts though lubrication may not always serve this purpose. Lubricity: The ability of a lubricating agent to reduce friction between moving parts. Mean time between failure: The average time required for components in mechanical systems to fail. This quantity is usually measured in running hours. Abbreviations. CAD computer aided drawing CAE computer aided engineering CNC computer numerical control HFO heavy fuel oil kVA kilo volt amperes kW kilo watts LFO light fuel oil LPG liquefied petroleum gas MTBF mean time between failure OHV over head valves RCA root cause analysis rpm revolutions per minute Intellectual Property Issues Patent. The current research does not infringe on any existing or previous patents registered by any individual or corporation. Copyright. The current research does not utilise any copyrighted materials; whether print, electronic or otherwise without compliance to fair usage, as listed below. Fair use. This research thoroughly cites and references any materials used in order to comply with fair usage and to avert any chances of plagiarism. Budget Overview The budget utilised for the current research is provided in the table below. The listed expenses and their costs are as per the actual amounts spent for the current research. Table 1 - Budget for the current research. Activity / Item Cost (USD) Stock billet for fabrication (mild steel) 250 Machining operations (as per drawing) 342 Plenum modification 50 Welding operations 100 Engine oil 30 Tools 45 Gas costs for running 225 Total Costs 1,042 Analysis Problem Analysis Existing scenario. The mean time between failure (MTBF) of exhaust valves on natural gas gensets ranges between 800 running hours and 1,000 running hours. Low exhaust valve life results in machine downtime and increased maintenance costs. Ideal scenario. The MTBF of exhaust valves on natural gas gensets should range between 1,500 running hours and 2,000 running hours. Increased exhaust valve life would result in greater machine uptime and decreased maintenance costs. Gap analysis. Exhaust valve life needs to be improved from the existing scenario to the ideal scenario, keeping costs as low as possible for the required modifications. In addition, the modifications should be as maintenance friendly as possible. Performance Criteria Exhaust valve life performance would be gauged using the MTBF before and after the implementation of the proposed solution. The MTBF criterion is a common measure used in the maintenance domain to evaluate component performance. Focusing of the Task Objective Limitations and delimitations of the project. The current project is limited to gas engine gensets that range in size between 1 kW and 6.5 kW. In addition, the current project would be limited to gensets that are run only on natural gas. Also, the methods employed in this project would be limited to gas gensets that do not have any other cooling mechanisms other than air cooling through fins. This project cannot be applied to any gas gensets that employ jacket cooling or other allied methods. Governing propositions. The existing exhaust valve life of gas gensets is considerably lower than the life of exhaust valves of gensets running on other fuels. Significant improvements in exhaust valve life are required to make gas gensets just as reliable and available as gensets running on other fuels. Assumptions. The current project is based on the assumptions that: the gas genset runs only on natural gas that is utilised in domestic settings for heating, cooking and other purposes; no other cooling mechanisms are being used to treat the engine oil or other parts of the gas genset other than air cooling; the gas genset is not continuously operated but instead runs in a cyclic fashion with a one hour running period and a one hour resting period. Statement of the R&D objective. The current research is aimed at increasing the lubrication available to the inlet and exhaust valves in order to remove friction and heat available at the valves. The reduction in friction and heat in the inlet valve and exhaust valve assemblies would significantly improve engine life by preventing exhaust valve burn up. Hypothesis Solution Proposal Method The early failure of exhaust valves on gas gensets was treated using a root cause analysis (RCA) followed by brainstorming and expert analysis. The RCA approach identifies the exact cause of the problem based on previous findings as well as pertinent investigation techniques (Okes, 2009). Mechanisms of the Task RCA. The RCA of the failure revealed a clear link to valve burn up (please see Figure 1) due to the formation of rather high temperatures at the exhaust valve assembly. Once the root cause was identified, the next step was developing a mechanism that would be simple yet sturdy enough to remove the excess heat at the exhaust valve. Observations and expert opinions. Using a combination of observing existing machine solutions and some expert opinions, it was decided to develop a lubrication system for the air plenum to reduce the exhaust valve temperatures. Development Procedures The solution was developed using a combination of computer aided techniques and machining through lathe and milling machines. In addition, the solution required the use of fitting and fabrication facilities. Computer aided engineering (CAE) techniques. Initial concepts and instructions for machining were developed using a 3D computer aided drawing (CAD) software package. This allowed a realisation of the actual solution without initiating manufacturing. Moreover, this provided a chance to remove deficiencies such as conflicting dimensions, fitting problems, physical interference between parts etc. In addition, details such as the right size of nuts and bolts to use, the placement of welded features etc. was also configured using the methods mentioned above. Once the final design was achieved using the 3D CAD package, drawings for machining were generated in 2D. These drawings were supplied to a machine shop to provide machining instructions including dimensions as well as tolerances and fitting allowances. Machining. The major machining effort was achieved using a lathe machine while some areas were machined using a milling machine. In simpler terms, any features that required circular machining were achieved using a lathe machine while milling was employed to provide straight cuts and slotting. Moreover, a radial drill was employed to create bolt holes followed by the use of threading dies to create threads for fasteners. Fabrication. The product was held in place using a welded bracket that was fabricated from sheet metal. The machine shop was able to provide the fabrication services required for solution development. Fitting. Once machined and fabricated, the various components were fitted together to observe if there were any defects. Some machining tolerance issues and fitting issues were observed which were then subsequently removed through machining and fabrication. Governing Propositions It was kept in mind that the limited budget of the project forbade any expensive machining techniques such as computer numerical control (CNC). The part’s composition was kept as simple as possible so that conventional lathe and milling machining would work. Performance Measures The quality of the final components was checked using measuring instruments such as vernier callipers and micrometers. This provided the difference between the desired part dimensions and the achieved part dimensions. Synthesis Implementation The solution was developed as a lubricator attached to the air inlet assembly that allowed a precise control of the lubrication rate being provided along with the air fuel mixture. The lubricator was machined out of mild steel billets and was provided graduations on one end to monitor the amount of lubricating oil available in the device. The lubricator was itself installed onto a welded bracket that attached to the air inlet assembly. This bracket served as the structural member that ensured that the lubricator was in place, when faced with the vibrating load from the engine. The contention behind the lubricator was to provide a measured quantity of lubricating oil to the cylinder for combustion. The provision of lubricating oil with the air fuel mixture would help to reduce the exhaust gas temperature and to reduce wear and burn up of the exhaust valve. The figure below depicts a damaged exhaust valve (on the left) although there is no burn up damage present (please compare to Figure 1 for the colour of the valve’s surface). Figure 2 - Arrangement of inlet valve and exhaust valve in a single cylinder engine configuration Testing Equipment. The lubricator was tested on a gas genset manufactured by Green Power. The model CC55000-NG was utilised for this project. The gas genset is rated at 5 kVA (alternatively 4.2 kW) of power at an operational speed of 3,000 revolutions per minute (rpm) producing a peak current of 19.1 amperes at 220 volts (Green Power, 2013). The particular gas genset used for this project can be used with other fuels such as gasoline and LPG but this project has used natural gas as the only fuel. The engine used with this gas genset is a single cylinder, over head valves (OHV) configuration that utilises air cooling. The engine’s total displacement is 389 cc and supports an electric starter as well as a recoil starter. As such, the engine requires 0.9 litres of oil for lubricating the moving parts, other than the head assembly (Green Power, 2013). Figure 3 - The gas genset used for the current research sourced from (Green Power, 2013) Methods. The lubricator was provided with an adjustment to vary the lubrication rate (measured in drops per minute). The contention was to vary the lubrication rate and to observe its effects on the wear rate and MTBF of exhaust valves. The gas genset was run first without any form of lubrication at all and the MTBF was noted. This was then compared to various lubrication rates and their effect on the MTBF. The lubrication rates were varied as per the table shown below. Table 2 - Lubrication feed rate used for experimentation No. Lubrication feed rate (drops per minute) 1 0 2 5 3 10 4 15 5 20 6 25 The gas engine was not operated continuously since it would not represent the actual pattern of use and since it would greatly accelerate the wear rate and would hence reduce MTBF considerably. Instead, the gas genset was run in a cyclic fashion such that the gas genset was operated for an hour at a load of 2.5 kW and was then shut down for another hour. Measurement. The MTBF was measured by accumulating the total hours that the gas genset ran without experiencing failure. The failure of the gas genset was defined as the inability of the engine to start up without modifying the existing air inlet arrangements. It must be taken to note that a burnt up valve can be used by reducing the amount of air entering the engine. However, for the purposes of this project, the air inlet arrangements were not modified at all whether through the carburettor choke or otherwise. Instrumentation. No elaborate instrumentation was required for testing the MTBF except for a simple clock. It must be taken to note that the MTBF count is accurate since running engine valves do not tend to fail since they have expanded during operation on account of the elevated temperatures. Only when the engine is shut down for some time and then restarted, there is the possibility of exhaust valve failure since the valve’s size has reduced leading to significant leakage from the valve. Experimental Results and Data Analysis The MTBF were recorded from a total of three different runs using a specific lubrication feed rate as expressed in the table provided below. The MTBF were averaged for the specific lubrication feed rate and are presented in the graph shown below. Table 3 - Lubrication feed rates and the corresponding MTBF Lubrication feed rate (drops per minute) Average MTBF (running hours) MTBF (running hours) Run One Run Two Run Three 0 974 983 977 962 5 1174.333 1137 1202 1184 10 1273 1278 1249 1292 15 1560.333 1534 1569 1578 20 1792.333 1789 1792 1796 25 - - - - Figure 4 - MTBF against lubrication feed rate It must be taken to note in the graph above that the MTBF for a lubrication feed rate of 25 drops per minute is expressed as zero. This specific lubrication feed rate tends to disturb the air fuel mixture such that the engine cannot start. The high amount of lubricating oil at this lubrication feed rate upsets the basic stoichometric balance so that combustion is no longer possible. Based on the failure criterion above, any condition that results in the engine not starting without any changes to the air inlet setting is classified as a failure and so the MTBF has been reported as zero. Validation Status of Task Objective The graph above makes it abundantly clear that the use of lubrication to support the exhaust valves tends to increase the MTBF significantly. The average MTBF at a feed rate of zero drops per minute and at 20 drops per minute shows an increase of 84% over the original life of the exhaust valve. Sustainability Viable maintenance is the only real guarantee for sustainable use of machines and associated equipment. The practice of using machines for a few years and discarding them has a large environmental footprint. The current research and its results successfully demonstrate that the same gas genset can experience improved life with the proper modification. Transferability The current solution can be implemented on any gas genset operating purely on natural gas and sized between 1 kW and 6.5 kW since the operational mechanisms are similar. It must be taken to note that the lubrication feed rates for these solutions would be different and would need investigation since the air fuel mixture flow rates are different. Implications Increased exhaust valve life would lead to lower maintenance needs and reduction in maintenance costs. Moreover, this would grant the gas gensets greater reliability and availability during operation. Recommendations The current results indicate that there is a threshold between lubrication feed rates of 20 drops per minute and 25 drops per minute. An investigation of lubrication feed rates with smaller differentials such as 20, 21, 22, 23, 24 and 25 drops per minute would provide the most optimal results. It must be noticed from Figure 4 that improvements are significant as the lubrication feed rate is increased. This implies that further research into lubrication feed rates between 20 drops per minute and 25 drops per minute would lead to further improvements In addition, further research should be conducted into air plenum assemblies on gas gensets to provide for a precise control of air entry especially when exhaust valves are near the end of their useful lives. It is proposed that further research may be carried out based on designs shown in Appendix ‘B’. References Duan, C. F., Li, W., & Zhang, J. L. (2012). Simulation Study on Heat Transfer Performance of Engine Exhaust Valve. Advanced Materials Research 591-593 , 639-643. Green Power. (2013). CC5000 Series. Retrieved November 8, 2013, from Green Power: http://www.greenpower.cn/en/P-generator-06.htm Hu, S.-C. (1944). Study of Exhaust-Valve Design from Gas Flow Standpoint. Journal of the Aeronautical Sciences 11(1) , 13-24. Munro, C. D. (2103). Analysis of a failed Detroit Diesel series 149 generator. Engineering Failure Analysis . Okes, D. (2009). Root Cause Analysis: The Core of Problem Solving and Corrective Action. ASQ Publishing. Tai, C. (2006). US10 Capable Prototype Volvo MG11 Natural Gas Engine Development: Final Report: December 16, 2003-July 31, 2006. Diane Publishing Co. Appendix A – Lubricator Design 3D CAD Models Figure 5 - Lubricator body with bracket welded on Figure 6 - Lubricator graduation cylinder Figure 7 - Lubricator end tail for insertion into air plenum Figure 8 - Complete lubricator assembly including lubrication adjustment screw (shown on the left bottom corner) Appendix B – Proposed Air Plenum 3D CAD Models Figure 9 - Proposed air plenum base Figure 10 - Proposed air plenum top cover Index air fuel mixture 20 downtime 15 exhaust valves 3 fasteners 19 gensets 11 internal combustion engine 8 lubricator 2, 3 lubricity 3, 8, 9 mean time between failure 12, 15 MTBF See mean time between failure natural gas 3 uptime 15 valve life 3, 8 Read More