Carbon nanotubes based internal combusition engine oils applied for military vehicles

MINISTRY OF EDUCATION AND TRAINING VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY  NGUYEN MANH HONG CARBON NANOTUBES BASED INTERNAL COMBUSITION ENGINE OILS APPLIED FOR MILITARY VEHICLES Major: Electronic Materials Cod: 9.44.01.23 SUMMARY OF SCIENCE MATERIALS DOCTORAL THESIS Hanoi – 2018 The thesis was completed at Key Laboratory for Electronic Materials and Devices, Institute of Materials Science, Vietnam Academy of Science and Technology. Supervisors: Prof. Dr. Phan Ngoc Minh Reviewer 1: Reviewer 2: Reviewer 3: The thesis is defended to the thesis committee for the Doctoral Degree, at Graduate University of Science and Technology – Vietnam Academy of Science and Technology, on.....Date...Month...Year 2018. Hardcopy of the thesis can be found at: - Library of Graduate University of Science and Technology - National Library of Vietnam 1 INTRODUCTION 1. Rationale for Study Vehicles such as trucks, battle tanks, amoured vehicles, ships are fundamental facilities in military. Those vehicle-engine durability, lifespan, and horsepower are important factors and enhancement of such parameters is necessary. Previous research works have been shown that the presence of carbon nanotubes (CNTs) in internal combustion engine oils (lubricating and thermal transfer oils) gives rise to the reduced engine friction and the increased heat sink. This contributes positively to engine yield performance, durability, lifespan, and fuel savings as well. The CNT-based engine oils have been manufactured in USA, EU, Japan, and Korea and used mostly in military sectors. Therefore, know-how finding and successful fabrication of the CNT-based engine oils are necessary and meaningful in many facets. Given that fact, author is focused on the field of research “Carbon nanotubes based internal combustion engine oils applied for military vehicles” for his PhD course. 2. Aims - Fabrication of the carbon nanotube based internal combustion engine oils from the Poly-alpha-olephin (PAO) oils; - Building the heat transfer model of the internal combustion engines using the CNTs-based oils, and characterization; - Applications of the CNTs-based oils in military vehicles and equipment. 3. Main points of thesis - Fabrication of the carbon nanotube based internal combustion engine oils; 2 - Measurement, characterization of CNTs-based oils regarding their structures, physical, thermal, and electrical properties; - Heat dissipation modeling and thermal-conductivity computation of the carbon nanotube based internal combustion engine oils, and comparison with the experimental results; - Field tests of the as-fabricated CNTs-based oils in some military vehicles; - Optimization of the CNTs-based oil parameters that includes processing techniques, aiming to practical applications. 4. Thesis presentation The thesis work includes 142 pages, consisting of Preface – 04 pages; Chapter 1: An overview of carbon nanotubes based fluids – 39 pages; Chapter 2: Experimental methods – 10 pages; Chapter 3: Fabrication of CNTs-based engine oils: Experimental results – 31 pages; Chapter 4: Applications of the carbon nanotube based internal combustion engine oils in military vehicles- 41 pages; Conclusion: 02 pages; Publications - 03 pages; References - 11 pages. 5. Main findings and contributions of the thesis - Know-how finding and successful fabrication of the carbon nanotube based internal combustion engine oils from the Poly-alpha- olephin (PAO) oil and well-applied for military vehicles. - Four types of the carbon nanotube based internal combustion engine oils have been manufactured and successfully tested for small ships, battle tanks, amoured vehicles, and military trucks. - The carbon nanotube based internal combustion engine oils (military vehicles) have been tested, the test results confirmed 3 engines‟ high performance in general, fuel saving of 10-15% and the oil change intervals reduced 04 (four) times, in particular. Chapter 1: Overview of carbon-nanotube-based fluids 1.1 Introduction 1.1.1. Introduction to carbon nanotubes Carbon nanotubes are nanoscale materials which have been researched with promising application potentials. They consist of two main forms: carbon nanotubes (CNTs) and carbon nanofiber (CNF). In 1991, Sumio IiJma, scientist at Japanese company – NEC, discovered tiny hollow-tubular crystals with the diameter of approximately 1.4 nm and the length of few microns to even millimeters. He soon published his discovery on Nature and the term “carbon nanotubes” was born. 1.1.2. CNT structure The nature of carbonous linkage inside CNTs matrix is explained by the orbital overlaps. It is formed completely by sp2 hybridization (comparably to graphite), which is stronger than sp3 bond in diamond. As a result, CNTs have very high strength with strong Van der Waals interaction in their rope-like network. There are two types of CNTs: single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). 1.1.3. Methods of CNTs synthesis There are plenty of ways to synthesize CNTs materials, most commonly laser ablation and chemical vapor deposition (CVD). 1.1.4. CNT properties 1.1.4.1. Mechanical properties 4 CNTs inherit high strength, high elasticity and high hardness in comparison to other materials. 1.1.4.2. Optic and Optoelectronic properties Based on the different non-monotonic structures of CNTs, especially SWCNTs, they possibly have the specific band gap. Because of these metallic and semiconductor behaviors, CNTs can be applied in optic and optoelectronic fields. 1.1.4.3. Thermal properties CNTs have very high thermal conductivity along their axis. Many works have been focus on thermal properties of carbon nanotubes in order to find application in opto-electronic devices, LED, microprocessor heat transfer 1.2. Carbon nanotube based thermal dissipation fluids 1.2.1. Introduction to heat transfer nanofluid Nanofluilds are made of nanomaterials dispersed in aqueous solution, e.g, water, ethylene glycol, oil. In other words, nanofluids are mixture of two-phase compounds, nanomaterials and solvents. 1.2.2. Fabrication methods There are two main approaches to fabricate nanofluids, the two- step process and the one-step process. 1.2.3. CNTs-based fluid 1.2.3.1. Fabrication of the CNTs-based fluid To achieve the CNTs-based fluids, the most important point is to well disperse carbon nanotubes into oil solvents. To avoid nanotube aggregation, CNTs have to be functionalized in advance. 1.2.3.2. Thermal properties of CNTs based nanofluids 5 Carbon nanotubes have excellent thermal conductivity, three orders better than those of other fluid materials. Therefore it is used in thermal management applications. 1.2.3.3. Heat transfer model of carbon nanotube based fluids To explain the heat transfer of the CNTs based fluids, many research groups have introduced theoretical models. In particular, In Hemanth‟s model, thermal conductivity of the CNTs-based fluid has been formulated as follow 1 (1 ) p m eff m m p k r k k k r           In H E Patel„s model 1 (1 ) s l eff l l s k r k k k r          However, we can see that there is inaccuracy in H E Patel‟s model, there is difference in experimental value and modeling calculation. 1.2.4. Nanofluid applications Nanofluids can be used in thermal applications. For example, heat transfer, thermal dissipation, thermal interface management in engines, electronics. 1.3. Heat dissipation lubricant oils 1.3.1. Introduction Lubricant oils include two compounds, base oil and additives. Lubricant oils can be applied in engine (tribological decrease, metal- oxidation proof, self-cleaning, heat sink). 1.3.2. Lubricant oil specifications There are two specifications of typical lubricant oils including SAE and API: 6 - SAE index: Classify the lubricant oils following temperature (American Society of Mechanical Engineers – ASME). - API index: Determine oil quality, established by American Petroleum Institute – API. 1.3.3. Additives in lubricant oils Additives in lubricant oils are organics and/or inorganic compounds that is added in the based oil in order to increase oil performance. In practice, the additives are widely used in engine oils which help increase oil viscosity, oxidation proof, detergent ability, and reduce tribological coefficient. 1.3.4. Fabrication of lubricant oil using carbon nanotubes as additives Lubricant oils have been used widely in many industries. Much research have been carried out to optimize and enhance the oil performance. However, fabrication of the engine oil in general is an uneasy process. There few tens compounds in the commercial engine oils. Ones have to find the proper mixture ratio of those compounds that require tremendous experiments and tests. 1.3.5. Heat transfer CNTs-based oils In heat dissipation lubricant oils , carbon nanotubes disperse in petroleum with a small size when exposed to a metal surface that forms a protective film for the components. As the temperature and pressure in the engine increase, the nano carbon particles form a tough protective film, which makes the lubrication even more effective, no abrasion, maximum friction reduction. Lubricants use high-pressure carbon nanotubes to seal the combustion chamber in the engine, thus minimizing the leakage of fuel and impurities generated during fuel combustion. The engine is 7 always clean, fuel-efficient and resistant to the formation of deposits at the bottom of the engine caste. 1.4. CNTs-based nanofluid research in Vietnam and Oversea 1.4.1. CNTs-based nanofluid research Oversea There are many research works regarding lubricant oils based on carbon nanotubes. Scientists over the world try to disperse carbon nanotubes into the base oil to increase thermal transfer, tribological coefficient, engine lifespan CNTs-based oils can be used in engine industry, thermal management. Some oil companies have introduced nanomaterial filled oils into the markets. 1.4.2. CNTs-based nanofluid research in Vietnam As far as the thesis author understands, there is no laboratory or oil companies in Vietnam can manage to manufacture lubricant oils for automobile engine adding carbon nanotubes. Most research is to disperse nanomaterials in base oil and measure their thermal properties. Therefore, the thesis author believes that fabrication of the CNTs- based engine oils is new in Vietnam. This research can open the way to fabricate lubricant oils and apply in military vehicles (truck, tanks,). Chapter 2: Research Methods 2.1. Practical Methods 2.1.1. Method of functionalizing CNTs By using strong oxidants, functionalized groups, mostly hydroxyl (-OH) and carbonyl (-COOH) will “attach” or bond to CNT surface. 2.1.2. Dispersion method of additives in base oil Each engine has its own requirements to function efficiently so the specification of lubricant for them is depended. 8 2.1.3. Measurement and characterization To measure and characterize the properties of CNTs and nano- lubricant oil, author and coworker have done various techniques such as Scanning Electron Microscopy, Raman Spectroscopy, Fourier Transform Infrared Spectroscopy and Zeta-sizer. 2.1.4. Measurement of nano-lubricant oil specifications To investigate the specification of nano-lubricant oil, we have used some lab-instruments, namely Kinematic Viscometer 9410p (Belgium), Total Alkalinity Meter, Tensiometer, Total Metal Analyzer, Petroleum Pour Point, Electrical conductivity meter. 2.2. Simulation modeling and theoretical calculation From the theoretical works of many research groups worldwide, a novel model will be built with less drawbacks and higher accuracy than the previous ones. 2.3. Precursor materials 2.3.1. Precursors for lubricant oil Anti-abrasion additives (triphenylphosphorothionate), anti- corrosion additives (alkylated succinic acid), less-friction functionalized additives (molybdenum disulfide), foam-control additives (Ethylene Bis-Stearamide), anti-oxidants (zinc dialkyl dithiophosphates), 2.3.2. Precursors for heat dissipation - Carbon nanotubes - Poly α-olefin oil (US) - Tween-80 surfactant (Sigma-Aldrich) - CNT functionalizing chemicals: HNO3 (Merck), H2SO4 (Merck), SOCl2 (Sigma Aldrich), H2O2 (Merck),... 9 - Other solvents: DI water, ethanol, acetone, 2.4. Research instrument 2.4.1. CNTs-lubricant-dispersing Instrument Ultrasonication Machine Microson XL2000, Ultrasonic bath Elma S40H, Stirrer, 2.4.2. Other instruments for synthesizing nano-carbon based lubricant Vacuum filtration machine, Micro Balance, Fume Hood, Vacuum Oven, Chapter 3: Fabrication of CNTs-based engine oils: Experimental results 3.1. Functionalization of carbon nanotubes Figure 3.2: FTIR spectra of carbon nanotubes before and after functionalization regarding –COOH and –OH groups. The FTIR spectra of CNTs - COOH show peaks in corresponding to carbon nanotubes functionalized by H2SO4 and và HNO3 mixture, 10 it confirmed appearance of functionalized group on the carbon nanotube walls. Figure 3.3: Raman spectroscopy of carbon nanotubes before and after functionalization regarding –COOH and –OH groups. There occur two typical D (1333,69 cm -1 ) and G 1583,10 cm - 1) bands, ID /IG intensity ratios are 0,99 and 1,87 in response to CNTs - COOH and CNTs - OH, respectively. Both ID /IG intensity ratio of the functionalized CNTs are greater than that of the pristine CNTs (0,79). It can be assumed that the CNT structure has been changed due to functionalization. 3.2. Fabrication of the heat dissipation CNTs-based engine oil 3.2.1. Carbon nanotube dispersion in base oil (PAO) 11 Figure 3.5: Dispersion process of carbon nanotubes in PAO oil 3.2.2. Optimization of carbon nanotube weight ratio in engine oil - The ultra-sonication parameters for 60 minutes - CNTs %wt: 0,12 3.2.3. Carbon nanotube dispersion Carbon nanotubes are dispersed into the base oil following processes: - Chemical functionalization - Surface surfactant addition - Experimental process: ultra-sonication 3.2.4. Optimization of the additives: weight ratio and types 3.3. Heat transfer model and thermal conductivity of the CNTs- based oils 3.3.1. Heat transfer model   1 1 3 1 eff CNT l l l CNT k k r k k r      3.3.2. Heat transfer model: analysis and comparison 12 The heat transfer model in the thesis has been compared with other research works, for example, Hwang‟s (2006), Lifei Chen‟s (2008), Gensheng Wu‟s (2009). The analysis shows that the theoretical calculation in the thesis is good agreement with previous study, in particular, CNTs dispersion in H2O, ethylene glycol, R113 fluids. Figure 3.15. Thermal conductivity of the CNTs-based engine oils with different CNTs weights: Experimental results and theoretical calculation The results show that the highest thermal conductivity is 0,292 W/mK (theory) and 0,298 W/m (experiment) in corresponding to the CNTs dispersion of 0,12% in weight. 3.4. Characterization of the CNTs-based engine oil during field tests 3.4.1. Viscosity coefficient 13 In general, the as-prepared oil‟s viscosity increases following the CNTs weight in the oils. However, with CNTs 0,03 % in volume, the viscosity at 100 o C and 40 o C tends to reduce slightly. The observed result is consistent with the previous research carried out by Ehsan-o- llah Ettefaghi. 3.4.2. Specifications of the as-fabricated CNTs-based engine oils The properties of the nano heat dissipation lubricant oils include dynamic viscosity, viscosity index, total alkalinity, ignition point, total metal content, surface tension, freezing point measured by us. The results show that the heat dissipation produced to meet the technical standards set out. Determining the specifications of the lubrication oil for each engine type shows that when adding CNTs, the lubricating oil heat dissipation reduces friction, fuel savings and increased thermal conductivity. Requires not to break the oil structure and still meet the world standards. Chapter 4 – Applications of the carbon nanotube based internal combustion engine oils in military vehicles 4.1. Field tests of the CNTs-based engine oils in small ships 4.1.1. Engine oil temperature The oil‟s saturation point is 50,6 oC (after 20 minutes in operation). The commercial engine oil, temperature of about 49,8 o C while as for the CNTs-based engine oils, temperature of about 46,1 o C. 4.1.2. Engine tribology coefficient Using the CNTs-based engine oils help reduce the engine tribology coefficient and order of 1,22 in comparison with the one of the commercial engine oil. 14 4.1.3. Fuel consumption Using the CNTs-based engine oils help save the fuel consumption of 10,88%. 4.1.4. Characterization of the CNTs-based engine oil during field tests The field test results show that the CNTs-based oil is still good in quality after 250 hours in use (constant engine running), the oil sample has been accordance with ГОСТ 12.337-84 (Russia). 4.2. Field tests of the CNTs-based engine oils in military tanks 4.2.1. Engine oil temperature The oil‟s saturation point is 54,6oC (after 20 minutes in operation). The commercial engine oil, temperature of about 53,8 o C after 20 minutes in operation while as for the CNTs-based engine oils, temperature of about 45,0 o C. 4.2.2. Engine tribology coefficient Using the CNTs-based engine oils help reduce the engine tribology coefficient and order of 1,21 in comparison with the one of the commercial engine oil. 4.2.3. Fuel consumption Using the CNTs-based engine oils help save the fuel consumption of 10,39%. 4.2.4. Characterization of the CNTs-based engine oil during field tests The field test results show that the CNTs-based oil is still good in quality after 250 hours in use (constant engine running), the oil sample has been accordance with ГОСТ 6360-83 (Russia). 4.3. Field tests of the CNTs-based engine oils in amoured vehicles 4.3.1. Engine oil temperature 15 The oil‟s saturation point is 44,6oC after 20 minutes in operation. The commercial engine oil, temperature of about 43,7 o C while as for the CNTs-based engine oils, temperature of about 40,4 o C. 4.3.2. Engine tribology coefficient Using the CNTs-based engine oils help reduce the engine tribology coefficient and order of 1,24 in comparison with the one of the commercial engine oil. 4.3.3. Fuel consumption Using the CNTs-based engine oils help save the fuel consumption of 11,21%. 4.3.4. Characterization of the CNTs-based engine oil during field tests The field test results show that the CNTs-based oil is still good in quality after 250 hours in use (constant engine running), the oil sample has been accordance with ГОСТ 6360-85 (Russia). 4.4. Field test of the CNTs-based oils in military transport vehicles 4.4.1. Engine oil temperature The oil‟s saturation point is 45,4oC. The commercial engine oil, temperature of about 44,2 o C after 20 minutes in operation while as for the CNTs-based engine oils, temperature of about 41,2 o C. 4.4.2. Engine tribology coefficient Using the CNTs-based engine oils help reduce the engine tribology coefficient and order of 1,29 in comparison with the one of the commercial engine oil. 4.4.3. Fuel consumption Using