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Synthesis of new aluminum nano hybrid composite liner for energy saving in diesel engines
Energy Conversion and Management 98 (2015) 440–448
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Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
Synthesis of new aluminum nano hybrid composite liner for energy saving in diesel engines N. Tiruvenkadam a,⇑, P.R. Thyla b, M. Senthilkumar c, M. Bharathiraja a, A. Murugesan a a
Department of Mechatronics Engineering, K.S. Rangasamy College of Technology, Tiruchengode 637 215, Tamil Nadu, India Department of Mechanical Engineering, P.S.G. College of Technology, Coimbatore 641 004, Tamil Nadu, India c Department of Production Engineering, P.S.G. College of Technology, Coimbatore 641 004, Tamil Nadu, India b
a r t i c l e
i n f o
Article history: Received 29 December 2014 Accepted 7 April 2015
Keywords: Nano hybrid composite Cylinder liner Diesel engine Performance Emission Teardown
a b s t r a c t This work aims to replace the conventional cast iron cylinder liner (CL) in diesel engine by introducing lightweight aluminum (Al) 6061 nano hybrid composite cylinder liner (NL) by analyzing the performance, combustion, and emission characteristics of an engine. NL was fabricated by bottom pouring stir casting technique with nano- and micro-reinforcement materials. Experimental results proved that the use of NL increased brake thermal efficiency, in-cylinder pressure, heat release rate, and reduced carbon monoxide, hydrocarbon, and smoke emission in comparison with CL. However, oxides of nitrogen slightly increased with the use of the new liner. No differences in wear or other issues were noted during the engine teardown after 1 year of operation and 2000 h of running. Thus, NL has been recommended to replace the CL to save the energy and to reap environmental benefits. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Automotive manufacturers are increasingly interested in producing lightweight vehicles with environmental advantages in terms of fuel consumption and emission reductions [1,2]. Replacement of cast iron with Al in the production of the cylinder block is the contemporary method of reducing the engine weight. Failures of internal combustion (IC) engines through cylinder liner and/or piston anomalies are very destructive and affect the engine. If a failure occurs, usually, liner, piston, connecting rod and, at times, engine head are seriously damaged [3]. Excellent thermal conductivity and lower density make Al–Si alloys [4] as a suitable alternative to cast iron in the fabrication of engine components. Aluminum can be regarded as a prospective energy carrier and has a good potential for large-scale integration in global energy storage [5]. A metal matrix composite (MMC) is made up of at least two distinct phases, properly distributed to realize unique combinations of properties that are not attainable by the individual components. It is composed of a matrix and reinforcements (e.g., fibers or particulate phase), in which the reinforcements are surrounded by the matrix [6]. Al-based composites are being increasingly used in automotive, aerospace, marine, and mineral-processing industries owing to their improved specific strength, good wear resistance, higher thermal ⇑ Corresponding author. Tel.: +91 9944672671. E-mail address: [email protected] (N. Tiruvenkadam). http://dx.doi.org/10.1016/j.enconman.2015.04.017 0196-8904/Ó 2015 Elsevier Ltd. All rights reserved.
conductivity, and lower coefficient of thermal expansion, particularly for lightweight cylinder liners [7]. The piston and cylinder is a very important part in an IC engine to convert the heat energy into mechanical one. The advantages derived from MMC liners in comparison with those from cast iron liners are less weight [8], reduced fuel consumption, lower wear rate, longer component life, and lower lubricant consumption. New materials, coatings, and high-tech machining processes that were previously considered to be too expensive and therefore only used in complex applications are now becoming more affordable. Presently, owing to the advancements in processing of materials, development of new materials to suit different applications has become possible. Production of new materials for diesel engine application with extremely high thermal resistance is important so that heat losses are reduced and recovered to be partially transformed into useful work. These engines are commonly known as low heat rejection (LHR) engines and are used to store thermal energy [9–11]. Ceramic whiskers or particulates are commonly used as reinforcement in Al-based alloys because of their high modulus, high hardness, low cost, easy availability, and limited reactivity with Al. The hybrid composites containing graphite (Gr) show superior wear-resistance properties than mono reinforcement [12–14]. Multiple reinforcements (hybrid MMCs) were adopted as they impart improved mechanical, thermal and tribological properties, and they are better substitutes for composites with single reinforcement.
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Nomenclature Al BTE BP CL CO Cu Cr CNC deg. Fe Gr HC HSU IC
aluminum brake thermal efficiency brake power conventional cast iron cylinder liner carbon monoxide copper chromium computer numerical control degree ferrous graphite hydrocarbon Hartridge smoke unit internal combustion
LHR MMC Mn NL NOx ppm RoHM SiC Si SEM Ti Zn ZrO2
low heat rejection metal matrix composite manganese nano hybrid composite cylinder liner oxides of nitrogen parts per million rule of hybrid mixtures silicon carbide silicon scanning electron microscope titanium zinc zirconium dioxide
Increase in friction is detrimental to engine fuel consumption, with piston–liner friction typically accounting for 30% of the total engine friction. Therefore, the addition of lightweight Al matrix material, lower friction solid lubricant, and high-strength ceramic particles has to be considered for hybrid composite cylinder liner-manufacturing application. The combined weight savings alone could result in significant fuel savings over the life of the vehicle [15,16]. From a design viewpoint, one might expect that increase in material hardness should improve the wear resistance of ceramic particle-reinforced Al alloys and hence it will be suitable for cylinder liner application [17–19]. Nanoscale hybrid or composite materials in the form of powders, spheres, fibers, tubes, and coatings have attracted a great deal of interest in diverse fields because of their unique properties that cannot be attained in micro-scale materials [20–22]. The review of literature indicates that use of new developing materials such as MMCs, hybrid MMCs, nano hybrid MMCs, nanoand micro hybrid MMCs for engine cylinder liner application has attracted a considerable research interest in ensuring cleaner environment. However, significant research efforts have been made to study the behavior of nano hybrid composite cylinder liner (NL)-operated IC engine. In view of the earlier mentioned facts, it is felt that there is a need to study the performance, combustion, and emission characteristics of diesel engine when operated with newly developed lightweight NL in comparison with conventional cast iron cylinder liner (CL). The novelty of the present work pertains to the development of a new NL with both nano- and micro-sized ceramic reinforcements along with micro Gr inclusion to act as solid lubricant with Al matrix material. In addition to the synthesis of NL, an appropriate application of single-cylinder diesel engine has been identified and experimental investigations have been carried out to prove the suitability of the developed NL for selected application with improved performance and environmental benefits. The major advantage of the developed lightweight liner is that it can be adopted in an existing engine cylinder without any modification in the engine structure.
and the possibility of modifying the strength of the composite [23]. Al 6061 was selected as the matrix material for this study based on a multicriteria decision-making tool (the analytical hierarchy process) by comparing six alternative materials, viz., Al 6262, Al 7075, Al 6060, Al 6082, Al 6005, and Al 6061. Various criteria were considered for these materials, some of the most important being Brinell hardness number, yield strength, percentage of elongation, fatigue strength, coefficient of thermal expansion, and cost. The melting point of Al 6061 was 650 °C and its chemical composition is shown in Table 1.
2. Materials and methods
2.2. Synthesis of NL
2.1. Materials
2.2.1. Prediction of mechanical and thermal properties through rule of hybrid mixtures The physical and mechanical properties of the developed hybrid composite were evaluated through rule of hybrid mixtures (RoHM) approach [32,33]. The standard property values of matrix and
2.1.1. Matrix materials Among Al alloys, Al 6061 is quite a popular choice as matrix material for MMCs because of its better formability characteristics
2.1.2. Reinforcement materials Zirconia or zirconium dioxide (ZrO2) is also one of the most important ceramic materials because of its excellent mechanical, thermal properties, and melting point of 2200 °C that are similar to metals, which makes it suitable for its use in ceramic engines. At the same time, because of higher doping percentages (more than 2.5%), agglomeration of ZrO2 is more common problem in the Al matrix production [24,25]. Application of Gr as one of the reinforcing components permits creating a film separating the wearing couple without any additional lubricant [26–29]. Melting point of the Gr was 3500 °C, also it is used to make components such as engine bearing, piston, piston rings and cylinder liners. It has good tensile, wear resistance, and thermal conductivity properties [30,31]. The commonly used ceramic reinforcement of silicon carbide (SiC) also has fine mechanical strength, melting point of 1650 °C, and thermal properties with lower density than ZrO2. To minimize cost and time to prepare nano-scale ZrO2 particles, equal quantity of micro-SiC was selected to make hybrid NL. In this study, the developed hybrid ceramic reinforcements of nano-ZrO2, micro-SiC, and solid lubricant particles of micro-Gr were combined to make NL. ZrO2 particles were prepared by using a high-energy ball-mill with a frequent cooling time of every 2 min to avoid the formation of agglomeration. The average particle size was determined to be 98.29 nm using Particle Size Analyzer (NANOPHOX (0143 P) Sympatec GmbH, Clausthal-Zellerfeld, in Germany operated with the Windox 5 software package. The composition of NL is summarized in Table 2.
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Table 1 Chemical composition of Al 6061. Elements
Si
Fe
Cu
Mn
Mg
Cr
Zn
Ti
Others
Al
Composition percentage
0.4–0.8
0.7 Max
0.15–0.40 Max
0.15 Max
0.8–1.2
0.04–0.35
0.25 Max
0.15 Max
0.05–0.15
Balance
Table 2 Details of NL matrix and reinforcement materials. Name of the reinforcements
Size
ZrO2 SiC Gr
Less than 100 nm 220 lm Fine grade, 100 lm
Combined reinforcement weight%
Al 6061 matrix weight%
Each 2.25
93.25
reinforcement materials obtained from the metal databooks [34,35] are summarized in Table 3 along with those of cast iron and developed NL material. 2.2.2. Fabrication processes Particulate-reinforced Al composites could be processed more easily by liquid state processes. Controlled bottom pouring stir cast arrangement helps to regulate the molten metal flow to the NL molten box [36,13]. The arrangements were made as shown in Fig. 1. The mold was allowed to cool in atmospheric air for approximately 8 h. The dimensions of the NL were made to be the same as those of the CL (Fig. 2). It was machined using computer numerical control (CNC) procedure and finished through honing operation, and the new NLs were obtained, as shown in Fig. 3. To minimize the fabrication uncertainties, four liners (NL1, NL2, NL3, and NL4) were fabricated using the same procedure, and their dimensions were measured. The variations in NL weights were found to be negligible, with a maximum of 0.25%. Fig. 1. Stir casting setup.
2.2.3. Experimental engine test rig The performance, combustion, and emission characteristics of the engine were tested using the present CL and the newly fabricated NL. A four-stroke, direct-injection, water-cooled Kirloskar AV1 (3.75 kW power) engine was used as a test engine for this study. It had a cylinder bore of 80 mm and stroke length of 110 mm, and a constant speed of 1500 rpm. The schematic diagram of the test engine setup used for this study is shown in Fig. 4. Eddy current dynamometer was used to vary load on the engine. The time taken to consume 50 cc of fuel was noted using burette setup. AVL-444 DI gas analyzer was used to measure the NOx, CO, and hydrocarbon (HC) contents present in the exhaust gas of the test engine. An AVL-437 smoke meter was used to detect the amount of smoke emitted by the test engine. A pressure transducer (AVL/GM12D air cooler), a combustion analyzer (AVL 619 Indimeter) and Ind Win software, version 2.2, were used to measure combustion parameters. Iron and iron-constantan thermocouples were used to measure the exhaust gas temperature. The
engine was started with pure diesel and warmed up for 20 min. After the warm-up period, the engine was run until steady state was reached, at each load. The fuel consumption, exhaust gas temperature, engine cooling water temperature, and emission values were recorded for different loads. The readings were noted continuously for 5 min to minimize the experimental uncertainties. Each test was performed three times and the average values were noted. A similar procedure was repeated for both CL and NL with diesel fuel whose properties are listed in Table 4. 3. Results and discussion 3.1. Selection of synthesis in NLs Among the four fabricated NLs, NL2 was selected because its weight was approximately 0.25% higher than others. This shows that a complete bonding of reinforcements with Al 6061 matrix
Table 3 Properties of matrix, reinforcements, and NL material. Properties
Density Tensile strength Elastic modulus Thermal conductivity Coefficient of thermal expansion
Unit
(g/cm3) (MPa) (GPa) (W/m K) (lm/m K)
Conventional gray cast iron
Matrix material Al 6061
7.2 260 110 46 12.5
2.7 160 69 165 23.4
Reinforcement materials ZrO2
SiC
Gr
5.78 466 200 2 10.6
3.1 299 410 83.6 4.3
1.750 18 21 6 4.9
Developed NL material through RoHM 2.7548 166.565 78.1866 156.2596 20.46
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and composite liners. The BTE indicates the ability of combustion system to accept the experimental liner and provides a comparable means of assessing how efficiently heat energy was converted into mechanical output by using new the NL. At the maximum load, BTE of the engine with NL was 5.74% higher than that of the engine with CL. This increase in efficiency could be attributed to the LHR by the hybrid liner and also due to reduction in in-cylinder heat transfer and lower heat flux. This enables better combustion inside the combustion chamber, resulting in increased efficiency [40]. The earlier results show that the nano- and micro-reinforcements play a major role because of their exceptionally high surface-to-volume ratio of the reinforcing phase with Al 6061 matrix material. High temperature is maintained inside the combustion area so that the possibility of complete fuel burning is high. Thus, the suitability of the new liner for operating at different BPs has been established, with reduced fuel consumption. Fig. 7 also shows that at up to 80% of the full load, BTE increased and beyond that load decreased in both CL and NL. This could be due to increase in the fuel conversion up to 80% of full load; beyond that air/fuel ratio is reduced as oxygen has been completely used up [40,41]. It was clearly proved that the economic load of the engine was 80%.
3.4. Engine combustion analysis Fig. 2. Specifications of NL.
material was achieved during the fabrication. To validate the RoHM properties, the density of the developed NLs was experimentally verified through Archimedes’ principle [36]. A three-digit accuracy scale was used to measure the weight of the liners. The mean difference between theoretical and experimental density values of all four fabricated NL liners was 1.7%. NL2 experimental density was close to the theoretical density, as shown in Fig. 5, which proved complete bonding and good wettability (reinforcements are completely mixed with matrix during stirring process) of the reinforcement materials with Al 6061 matrix material during the fabrication process. Density of composites has a stronger impact on thermal conductivity [37] and other properties. Hence, other property values listed in Table 3 by RoHM could be an acceptable level. Also, all the properties of nano hybrid composite were greater than those of matrix material, again proving the reinforcement content contributes to increase in the properties of hybrid composite [36]. Weight is an important parameter for vehicles [38]. The selected NL weight of 1.800 kg was 43.75% lighter than present CL weight of 3.200 kg. 3.2. Photomicrographs examination A scanning electron microscope (SEM, model JSM-6360; JEOL) was used to analyze the fully fabricated and selected NL before CNC machining [39]. The bonding of nano hybrid composite reinforcements with the matrix for the entire new liner material produced through bottom pouring stir casting method could be clearly seen in Fig. 6(a) and (b). The reinforcements of nano-ZrO2, micro-SiC, and micro-Gr particles were found to be homogeneously embedded in the grains of liner Al 6061matrix material. 3.3. Engine performance analysis 3.3.1. Brake thermal efficiency vs. brake power The variation in brake thermal efficiency (BTE) and brake power (BP) for different loads are shown in Fig. 7 for both conventional
The in-cylinder thermodynamic processes include compression or expansion process of the piston, transfer of heat from the incylinder gas to the wall, leakage of gas through the piston rings, and release of heat from the combustion process [42]. The following section gives information about the combustion process of engine using CL and NL.
3.4.1. Cylinder pressure and crank angle Fig. 8 shows the variations in cylinder pressure with crank angle for CL and NL at a maximum load of 3.75 kW. The highest peak pressure of 72.151 bar for NL and 70.613 bar for CL could be seen. The reasons for slightly increased higher peak cylinder pressure are better burning of diesel inside the combustion chamber and reduction of heat lost using NL. This is also due to higher temperature of the engine cycle maintained by nano- and micro-reinforcement particles present in the NL and because Al 6061 matrix material of has a low thermal coefficient of expansion, which also aids in achieving high temperature. Solid lubricant graphite micro particles present in the NL make the operation of the engine cycle smooth. Although tensile strength and elastic modulus of the NL have been comparatively lower than those of CL, it can easily withstand the in-cylinder pressure generated during the engine cycle. This may be due to ZrO2 and SiC ceramic particles have high tensile strength and elastic modulus than CL.
3.4.2. Heat release analysis Fig. 9 shows variations in the rate of heat release with crank angle for CL and NL at a maximum load of 3.75 kW. The highest heat release rate of 76.770 kJ/m3 deg for CL and 80.537 kJ/m3 deg for NL could be observed from the plot. The slightly increased heat release is due to increased burning rate during the burning phase of diesel engine cycle, which is maintained by matrix and nanoand micro-reinforcement particles present in the NL. Generally, highest peak pressure is observed for LHR diesel operation due to the higher and early heat release [10]. This could be achieved because the thermal conductivity property of NL was higher than that of CL material.
444
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Fig. 3. Production process of NL.
Fig. 4. Test engine setup.
445
Table 4 Diesel fuel properties as per ASTM D-93 standard. Kinematic viscosity at 40 °C (cS)
Density at 40 °C (kg/m3)
Flash point (°C)
Calorific value (MJ/kg)
3.20
838
55
42.8
Theoretical density
2.80
2.75
3
Density (g/cm )
Experimental density
Brake thermal efficiency (%)
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30
25
20
Conventional cast iron cylinder liner (CL) Nano hybrid composite cylinder liner (NL)
15
10 2.70
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Brake power (kW) Fig. 7. BTE vs. BP for CL and NL.
2.65
80
2.60 NL2
NL3
NL4
Fabricated nano - hybrid composite liner Fig. 5. Comparison of theoretical and experimental density values of fabricated NLs.
3.4.3. Exhaust gas temperature Fig.10 shows that the exhaust gas temperature of an engine operated with NL and CL. One could observe from the plot that the NL has higher temperature than CL at all loads. The higher in-cylinder temperature also leads to an increase in the exhaust gas temperature [43]. The amount of the energy released while combustion affect the combustion temperature, which can be determined by exhaust gas temperature [44]. The exhaust gas temperature indicates the in-cylinder temperature, which shows the NL-operated engine has better combustion than CL-operated engine. Higher combustion gas temperature could destroy the lubricating film between piston body and liner, increasing locally metal temperature [45]. However, the developed NL was not found to be affected by the in-cylinder temperature due to its competitively high thermal conductivity and high thermal expansion than CL, as shown in Table 2. 3.5. Engine emission analysis 3.5.1. CO vs. BP Fig. 11 shows the variations of CO emission levels against BP for CL and NL. At maximum load, the CO emission levels were found to be reduced by 12.5% with the use of NL compared to CL.
(a) Magnification 500×
Brake power
70
Cylinder pressure (bar)
NL1
= 3.75 kW o
Injection timing = 23 BTDC Max pressure for CL = 70.613 bar Max pressure for NL = 72.151 bar
60 50 40
Conventional cast iron cylinder liner (CL)
30
Nano hybrid composite cylinder liner (NL)
20 10 0 -180 -150 -120 -90 -60 -30
0
30
60
90
120 150 180
Crank angle (deg.) Fig. 8. Cylinder pressure vs. crank angle for CL and NL.
CO is the product of incomplete combustion due to insufficient oxygen to convert all the carbon atoms to carbon dioxide. It is mainly dependent on the air/fuel ratio relative to the chemically correct proportion and increases when the air/fuel ratio becomes greater than stoichiometric air and fuel requirements. It is also clear from the plots that in the NL-operated engine CO emission is lower than the CL-operated engine at all loads. This is mainly due to the higher temperature of the engine cycle maintained by nano- and micro-reinforcement particles present in the NL, which
(b) Magnification 1000×
Fig. 6. (a) Magnification 500. (b) Magnification 1000.
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Heat release rate (kJ/m3 deg.)
446
Fig. 12. HC vs. BP for CL and NL. Fig. 9. Heat release rate vs. crank angle for CL and NL.
Oxides of nitride (NO x )
200 180
Conventional cast iron cylinder liner (CL)
160
Nano hybrid composite cylinder liner (NL)
140 120 100 80
0
1
2
3
Brake power (kW) Fig. 10. Exhaust gas temperature with BP for CL and NL.
Fig. 13. NOx vs. BP for CL and NL.
45
Smoke (HSU)
40 35
Conventional cast iron cylinder liner (CL) Nano hybrid composite cylinder liner (NL)
30 25 20 15 0.00
0.75
1.50
2.25
3.00
3.75
Brake power (kW) Fig. 11. CO vs. BP for CL and NL. Fig. 14. Smoke vs. BP for CL and NL.
were used to help in complete burning of oxygen content inside the combustion chamber. 3.5.2. HC vs. BP HC is an intermediate product of incomplete combustion. The variation in HC emission with BP for CL and NL is shown in Fig. 12. The plots shows a reduction in the values of HC in the engine with NL for all BPs. The percentage reduction obtained with NL at maximum load was 10.95%. The heat loss due to the coolant
use reduced (when the engine was operated with NL), leading to good flammability of fuel inside the combustion chamber, which imply reduction of HC at all loads. 3.5.3. NOx vs. BP Fig. 13 shows the variation in NOx for engines operated with CL and NL. As per the combustion theory, the formation of NOx is merely a function of in-cylinder combustion temperature [46,47]
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Fig. 15. (a) Dismantling position of NL from engine, (b) top portion of NL in engine and (c) completely dismantled NL, piston, piston pin, and piston rings.
and the amount of oxygen. A comparison of the NOx emission values showed that there was a marginal increase in NOx emission with the use of NL than with the use of CL. The increase in the levels was found to be 2.7% at maximum load. Several factors such as fuel properties, engine type, and engineoperating condition affect the engine NOx emissions. Although the higher overall cylinder temperature is an indicator of higher NOx, the temperature distribution in the cylinder is more important than other causes. Combustions that takes place over a short period of time allows less cooling time by heat transfer and dilution, which results in higher NOx formation [48–52]. Because the nano-ZrO2, micro-SiC, and micro-Gr reinforcements can withstand high temperature and Al 6061 matrix material have lower thermal expansion coefficient, the temperature inside the combustion chamber temperature is high. In-cylinder NOx reduction technique like exhaust gas recirculation is an effective way to reduce NOx emission from diesel engines [43]. It can be attached to reduce NOx when the engine is operating with NL. 3.5.4. Smoke vs. BP Fig. 14 shows the variation of smoke emission in Hartridge smoke unit (HSU) for the CL and NL. Smoke value has a reducing trend of 4.76% when operated with NL. This was due to better vaporization and quick combustion of fuel supplied inside the combustion chamber (NL cylinder wall), which were maintained by the inherent properties of reinforcements and matrix material. Lower level of unburned HC in the engine exhaust could have occurred due to the complete combustion with the help fuel-burn oxygen. This can be the reason for reduction in the smoke emission. Higher combustion temperature and intense turbulence created by reverse squish lead to reduction in smoke emission [25]. There is always a tradeoff between NOx and smoke emission in a diesel engine fuelled by any kind of fuel [53]. 3.6. Teardown analysis After running for 2000 h at frequent intervals for a period of 1 year, at various load conditions, the new NL was dismantled from the engine and it is shown in Fig. 15(a) –(c). The internal parts were inspected and evaluated to investigate wear characteristics, breakage, and other damage as well as the accumulation of dirt, sludge, and carbon. 3.6.1. Visual examination of developed NL No cracks were found both inside and outside of the NL. This again shows that developed NL has an acceptable level to perform the engine operation. During the visual inspection, very small quantities of carbon deposition were found at the top of the piston
compared to the engine with CL, which showed that more complete combustion has taken place in the engine fitted with NL. During the testing period, outside wall of the NL was continually placed in cooling water. After dismantling the NL, no corrosion effect was found outside the surface of the NL on visual inspection. This may be due to good corrosive resistance property of the hybrid composites. 3.6.2. Monitoring engine oil condition At the time of NL assembly, the oil in the sump was completely cleaned and filled with new Castrol Agri MP Plus 20W-40 engine oil. After 2000 h of running under various load conditions at frequent intervals, the engine oil was completely removed from the oil sump and was kept undisturbed for 20 h and filtered with less than 100 nm muslin cloth. No foreign particles or Al matrix debris or reinforcement debris were observed in the oil. At the same time, the bottom portion of the engine oil sump was also cleaned with neat cloth and fine brushes, which also showed absence of foreign particles. This inspection proved that there was no material loss in the developed nano hybrid composite liner under different load operating condition during the period of study. Since the friction coefficient of Al MMC was 25% more than the cast iron while sliding under identical conditions [53], so the developed NL was found to be suitable for engine’s smooth operation when compared to CL. 4. Conclusion In this synthesis and experimental work, the effect of a newly developed NL on diesel engine performance, combustion, emission characteristics, and suitability to replace the CL in the engine cylinder was studied. The results achieved in this study are summarized as follows: The selected matrix and reinforcement material was suitable to make NL based on the density, mechanical, thermal properties predicted by RoHM, and homogeneous mixture through SEM examination. The NL enhanced BTE, in-cylinder pressure, heat release, and exhaust temperature. The NL reduced CO, HC, and smoke emissions, but increased NOx emission. The teardown analysis revealed no detrimental effects with NL. Thus, this investigation has shown that the newly developed NL has good potential to replace the presently used conventional CL for achieving greater fuel economy and green environment. The fact that it can be used without any modification of the engine structure with weight saving of 43.75% is an added advantage.
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Contents lists available at ScienceDirect
Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
Synthesis of new aluminum nano hybrid composite liner for energy saving in diesel engines N. Tiruvenkadam a,⇑, P.R. Thyla b, M. Senthilkumar c, M. Bharathiraja a, A. Murugesan a a
Department of Mechatronics Engineering, K.S. Rangasamy College of Technology, Tiruchengode 637 215, Tamil Nadu, India Department of Mechanical Engineering, P.S.G. College of Technology, Coimbatore 641 004, Tamil Nadu, India c Department of Production Engineering, P.S.G. College of Technology, Coimbatore 641 004, Tamil Nadu, India b
a r t i c l e
i n f o
Article history: Received 29 December 2014 Accepted 7 April 2015
Keywords: Nano hybrid composite Cylinder liner Diesel engine Performance Emission Teardown
a b s t r a c t This work aims to replace the conventional cast iron cylinder liner (CL) in diesel engine by introducing lightweight aluminum (Al) 6061 nano hybrid composite cylinder liner (NL) by analyzing the performance, combustion, and emission characteristics of an engine. NL was fabricated by bottom pouring stir casting technique with nano- and micro-reinforcement materials. Experimental results proved that the use of NL increased brake thermal efficiency, in-cylinder pressure, heat release rate, and reduced carbon monoxide, hydrocarbon, and smoke emission in comparison with CL. However, oxides of nitrogen slightly increased with the use of the new liner. No differences in wear or other issues were noted during the engine teardown after 1 year of operation and 2000 h of running. Thus, NL has been recommended to replace the CL to save the energy and to reap environmental benefits. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Automotive manufacturers are increasingly interested in producing lightweight vehicles with environmental advantages in terms of fuel consumption and emission reductions [1,2]. Replacement of cast iron with Al in the production of the cylinder block is the contemporary method of reducing the engine weight. Failures of internal combustion (IC) engines through cylinder liner and/or piston anomalies are very destructive and affect the engine. If a failure occurs, usually, liner, piston, connecting rod and, at times, engine head are seriously damaged [3]. Excellent thermal conductivity and lower density make Al–Si alloys [4] as a suitable alternative to cast iron in the fabrication of engine components. Aluminum can be regarded as a prospective energy carrier and has a good potential for large-scale integration in global energy storage [5]. A metal matrix composite (MMC) is made up of at least two distinct phases, properly distributed to realize unique combinations of properties that are not attainable by the individual components. It is composed of a matrix and reinforcements (e.g., fibers or particulate phase), in which the reinforcements are surrounded by the matrix [6]. Al-based composites are being increasingly used in automotive, aerospace, marine, and mineral-processing industries owing to their improved specific strength, good wear resistance, higher thermal ⇑ Corresponding author. Tel.: +91 9944672671. E-mail address: [email protected] (N. Tiruvenkadam). http://dx.doi.org/10.1016/j.enconman.2015.04.017 0196-8904/Ó 2015 Elsevier Ltd. All rights reserved.
conductivity, and lower coefficient of thermal expansion, particularly for lightweight cylinder liners [7]. The piston and cylinder is a very important part in an IC engine to convert the heat energy into mechanical one. The advantages derived from MMC liners in comparison with those from cast iron liners are less weight [8], reduced fuel consumption, lower wear rate, longer component life, and lower lubricant consumption. New materials, coatings, and high-tech machining processes that were previously considered to be too expensive and therefore only used in complex applications are now becoming more affordable. Presently, owing to the advancements in processing of materials, development of new materials to suit different applications has become possible. Production of new materials for diesel engine application with extremely high thermal resistance is important so that heat losses are reduced and recovered to be partially transformed into useful work. These engines are commonly known as low heat rejection (LHR) engines and are used to store thermal energy [9–11]. Ceramic whiskers or particulates are commonly used as reinforcement in Al-based alloys because of their high modulus, high hardness, low cost, easy availability, and limited reactivity with Al. The hybrid composites containing graphite (Gr) show superior wear-resistance properties than mono reinforcement [12–14]. Multiple reinforcements (hybrid MMCs) were adopted as they impart improved mechanical, thermal and tribological properties, and they are better substitutes for composites with single reinforcement.
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Nomenclature Al BTE BP CL CO Cu Cr CNC deg. Fe Gr HC HSU IC
aluminum brake thermal efficiency brake power conventional cast iron cylinder liner carbon monoxide copper chromium computer numerical control degree ferrous graphite hydrocarbon Hartridge smoke unit internal combustion
LHR MMC Mn NL NOx ppm RoHM SiC Si SEM Ti Zn ZrO2
low heat rejection metal matrix composite manganese nano hybrid composite cylinder liner oxides of nitrogen parts per million rule of hybrid mixtures silicon carbide silicon scanning electron microscope titanium zinc zirconium dioxide
Increase in friction is detrimental to engine fuel consumption, with piston–liner friction typically accounting for 30% of the total engine friction. Therefore, the addition of lightweight Al matrix material, lower friction solid lubricant, and high-strength ceramic particles has to be considered for hybrid composite cylinder liner-manufacturing application. The combined weight savings alone could result in significant fuel savings over the life of the vehicle [15,16]. From a design viewpoint, one might expect that increase in material hardness should improve the wear resistance of ceramic particle-reinforced Al alloys and hence it will be suitable for cylinder liner application [17–19]. Nanoscale hybrid or composite materials in the form of powders, spheres, fibers, tubes, and coatings have attracted a great deal of interest in diverse fields because of their unique properties that cannot be attained in micro-scale materials [20–22]. The review of literature indicates that use of new developing materials such as MMCs, hybrid MMCs, nano hybrid MMCs, nanoand micro hybrid MMCs for engine cylinder liner application has attracted a considerable research interest in ensuring cleaner environment. However, significant research efforts have been made to study the behavior of nano hybrid composite cylinder liner (NL)-operated IC engine. In view of the earlier mentioned facts, it is felt that there is a need to study the performance, combustion, and emission characteristics of diesel engine when operated with newly developed lightweight NL in comparison with conventional cast iron cylinder liner (CL). The novelty of the present work pertains to the development of a new NL with both nano- and micro-sized ceramic reinforcements along with micro Gr inclusion to act as solid lubricant with Al matrix material. In addition to the synthesis of NL, an appropriate application of single-cylinder diesel engine has been identified and experimental investigations have been carried out to prove the suitability of the developed NL for selected application with improved performance and environmental benefits. The major advantage of the developed lightweight liner is that it can be adopted in an existing engine cylinder without any modification in the engine structure.
and the possibility of modifying the strength of the composite [23]. Al 6061 was selected as the matrix material for this study based on a multicriteria decision-making tool (the analytical hierarchy process) by comparing six alternative materials, viz., Al 6262, Al 7075, Al 6060, Al 6082, Al 6005, and Al 6061. Various criteria were considered for these materials, some of the most important being Brinell hardness number, yield strength, percentage of elongation, fatigue strength, coefficient of thermal expansion, and cost. The melting point of Al 6061 was 650 °C and its chemical composition is shown in Table 1.
2. Materials and methods
2.2. Synthesis of NL
2.1. Materials
2.2.1. Prediction of mechanical and thermal properties through rule of hybrid mixtures The physical and mechanical properties of the developed hybrid composite were evaluated through rule of hybrid mixtures (RoHM) approach [32,33]. The standard property values of matrix and
2.1.1. Matrix materials Among Al alloys, Al 6061 is quite a popular choice as matrix material for MMCs because of its better formability characteristics
2.1.2. Reinforcement materials Zirconia or zirconium dioxide (ZrO2) is also one of the most important ceramic materials because of its excellent mechanical, thermal properties, and melting point of 2200 °C that are similar to metals, which makes it suitable for its use in ceramic engines. At the same time, because of higher doping percentages (more than 2.5%), agglomeration of ZrO2 is more common problem in the Al matrix production [24,25]. Application of Gr as one of the reinforcing components permits creating a film separating the wearing couple without any additional lubricant [26–29]. Melting point of the Gr was 3500 °C, also it is used to make components such as engine bearing, piston, piston rings and cylinder liners. It has good tensile, wear resistance, and thermal conductivity properties [30,31]. The commonly used ceramic reinforcement of silicon carbide (SiC) also has fine mechanical strength, melting point of 1650 °C, and thermal properties with lower density than ZrO2. To minimize cost and time to prepare nano-scale ZrO2 particles, equal quantity of micro-SiC was selected to make hybrid NL. In this study, the developed hybrid ceramic reinforcements of nano-ZrO2, micro-SiC, and solid lubricant particles of micro-Gr were combined to make NL. ZrO2 particles were prepared by using a high-energy ball-mill with a frequent cooling time of every 2 min to avoid the formation of agglomeration. The average particle size was determined to be 98.29 nm using Particle Size Analyzer (NANOPHOX (0143 P) Sympatec GmbH, Clausthal-Zellerfeld, in Germany operated with the Windox 5 software package. The composition of NL is summarized in Table 2.
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Table 1 Chemical composition of Al 6061. Elements
Si
Fe
Cu
Mn
Mg
Cr
Zn
Ti
Others
Al
Composition percentage
0.4–0.8
0.7 Max
0.15–0.40 Max
0.15 Max
0.8–1.2
0.04–0.35
0.25 Max
0.15 Max
0.05–0.15
Balance
Table 2 Details of NL matrix and reinforcement materials. Name of the reinforcements
Size
ZrO2 SiC Gr
Less than 100 nm 220 lm Fine grade, 100 lm
Combined reinforcement weight%
Al 6061 matrix weight%
Each 2.25
93.25
reinforcement materials obtained from the metal databooks [34,35] are summarized in Table 3 along with those of cast iron and developed NL material. 2.2.2. Fabrication processes Particulate-reinforced Al composites could be processed more easily by liquid state processes. Controlled bottom pouring stir cast arrangement helps to regulate the molten metal flow to the NL molten box [36,13]. The arrangements were made as shown in Fig. 1. The mold was allowed to cool in atmospheric air for approximately 8 h. The dimensions of the NL were made to be the same as those of the CL (Fig. 2). It was machined using computer numerical control (CNC) procedure and finished through honing operation, and the new NLs were obtained, as shown in Fig. 3. To minimize the fabrication uncertainties, four liners (NL1, NL2, NL3, and NL4) were fabricated using the same procedure, and their dimensions were measured. The variations in NL weights were found to be negligible, with a maximum of 0.25%. Fig. 1. Stir casting setup.
2.2.3. Experimental engine test rig The performance, combustion, and emission characteristics of the engine were tested using the present CL and the newly fabricated NL. A four-stroke, direct-injection, water-cooled Kirloskar AV1 (3.75 kW power) engine was used as a test engine for this study. It had a cylinder bore of 80 mm and stroke length of 110 mm, and a constant speed of 1500 rpm. The schematic diagram of the test engine setup used for this study is shown in Fig. 4. Eddy current dynamometer was used to vary load on the engine. The time taken to consume 50 cc of fuel was noted using burette setup. AVL-444 DI gas analyzer was used to measure the NOx, CO, and hydrocarbon (HC) contents present in the exhaust gas of the test engine. An AVL-437 smoke meter was used to detect the amount of smoke emitted by the test engine. A pressure transducer (AVL/GM12D air cooler), a combustion analyzer (AVL 619 Indimeter) and Ind Win software, version 2.2, were used to measure combustion parameters. Iron and iron-constantan thermocouples were used to measure the exhaust gas temperature. The
engine was started with pure diesel and warmed up for 20 min. After the warm-up period, the engine was run until steady state was reached, at each load. The fuel consumption, exhaust gas temperature, engine cooling water temperature, and emission values were recorded for different loads. The readings were noted continuously for 5 min to minimize the experimental uncertainties. Each test was performed three times and the average values were noted. A similar procedure was repeated for both CL and NL with diesel fuel whose properties are listed in Table 4. 3. Results and discussion 3.1. Selection of synthesis in NLs Among the four fabricated NLs, NL2 was selected because its weight was approximately 0.25% higher than others. This shows that a complete bonding of reinforcements with Al 6061 matrix
Table 3 Properties of matrix, reinforcements, and NL material. Properties
Density Tensile strength Elastic modulus Thermal conductivity Coefficient of thermal expansion
Unit
(g/cm3) (MPa) (GPa) (W/m K) (lm/m K)
Conventional gray cast iron
Matrix material Al 6061
7.2 260 110 46 12.5
2.7 160 69 165 23.4
Reinforcement materials ZrO2
SiC
Gr
5.78 466 200 2 10.6
3.1 299 410 83.6 4.3
1.750 18 21 6 4.9
Developed NL material through RoHM 2.7548 166.565 78.1866 156.2596 20.46
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and composite liners. The BTE indicates the ability of combustion system to accept the experimental liner and provides a comparable means of assessing how efficiently heat energy was converted into mechanical output by using new the NL. At the maximum load, BTE of the engine with NL was 5.74% higher than that of the engine with CL. This increase in efficiency could be attributed to the LHR by the hybrid liner and also due to reduction in in-cylinder heat transfer and lower heat flux. This enables better combustion inside the combustion chamber, resulting in increased efficiency [40]. The earlier results show that the nano- and micro-reinforcements play a major role because of their exceptionally high surface-to-volume ratio of the reinforcing phase with Al 6061 matrix material. High temperature is maintained inside the combustion area so that the possibility of complete fuel burning is high. Thus, the suitability of the new liner for operating at different BPs has been established, with reduced fuel consumption. Fig. 7 also shows that at up to 80% of the full load, BTE increased and beyond that load decreased in both CL and NL. This could be due to increase in the fuel conversion up to 80% of full load; beyond that air/fuel ratio is reduced as oxygen has been completely used up [40,41]. It was clearly proved that the economic load of the engine was 80%.
3.4. Engine combustion analysis Fig. 2. Specifications of NL.
material was achieved during the fabrication. To validate the RoHM properties, the density of the developed NLs was experimentally verified through Archimedes’ principle [36]. A three-digit accuracy scale was used to measure the weight of the liners. The mean difference between theoretical and experimental density values of all four fabricated NL liners was 1.7%. NL2 experimental density was close to the theoretical density, as shown in Fig. 5, which proved complete bonding and good wettability (reinforcements are completely mixed with matrix during stirring process) of the reinforcement materials with Al 6061 matrix material during the fabrication process. Density of composites has a stronger impact on thermal conductivity [37] and other properties. Hence, other property values listed in Table 3 by RoHM could be an acceptable level. Also, all the properties of nano hybrid composite were greater than those of matrix material, again proving the reinforcement content contributes to increase in the properties of hybrid composite [36]. Weight is an important parameter for vehicles [38]. The selected NL weight of 1.800 kg was 43.75% lighter than present CL weight of 3.200 kg. 3.2. Photomicrographs examination A scanning electron microscope (SEM, model JSM-6360; JEOL) was used to analyze the fully fabricated and selected NL before CNC machining [39]. The bonding of nano hybrid composite reinforcements with the matrix for the entire new liner material produced through bottom pouring stir casting method could be clearly seen in Fig. 6(a) and (b). The reinforcements of nano-ZrO2, micro-SiC, and micro-Gr particles were found to be homogeneously embedded in the grains of liner Al 6061matrix material. 3.3. Engine performance analysis 3.3.1. Brake thermal efficiency vs. brake power The variation in brake thermal efficiency (BTE) and brake power (BP) for different loads are shown in Fig. 7 for both conventional
The in-cylinder thermodynamic processes include compression or expansion process of the piston, transfer of heat from the incylinder gas to the wall, leakage of gas through the piston rings, and release of heat from the combustion process [42]. The following section gives information about the combustion process of engine using CL and NL.
3.4.1. Cylinder pressure and crank angle Fig. 8 shows the variations in cylinder pressure with crank angle for CL and NL at a maximum load of 3.75 kW. The highest peak pressure of 72.151 bar for NL and 70.613 bar for CL could be seen. The reasons for slightly increased higher peak cylinder pressure are better burning of diesel inside the combustion chamber and reduction of heat lost using NL. This is also due to higher temperature of the engine cycle maintained by nano- and micro-reinforcement particles present in the NL and because Al 6061 matrix material of has a low thermal coefficient of expansion, which also aids in achieving high temperature. Solid lubricant graphite micro particles present in the NL make the operation of the engine cycle smooth. Although tensile strength and elastic modulus of the NL have been comparatively lower than those of CL, it can easily withstand the in-cylinder pressure generated during the engine cycle. This may be due to ZrO2 and SiC ceramic particles have high tensile strength and elastic modulus than CL.
3.4.2. Heat release analysis Fig. 9 shows variations in the rate of heat release with crank angle for CL and NL at a maximum load of 3.75 kW. The highest heat release rate of 76.770 kJ/m3 deg for CL and 80.537 kJ/m3 deg for NL could be observed from the plot. The slightly increased heat release is due to increased burning rate during the burning phase of diesel engine cycle, which is maintained by matrix and nanoand micro-reinforcement particles present in the NL. Generally, highest peak pressure is observed for LHR diesel operation due to the higher and early heat release [10]. This could be achieved because the thermal conductivity property of NL was higher than that of CL material.
444
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Fig. 3. Production process of NL.
Fig. 4. Test engine setup.
445
Table 4 Diesel fuel properties as per ASTM D-93 standard. Kinematic viscosity at 40 °C (cS)
Density at 40 °C (kg/m3)
Flash point (°C)
Calorific value (MJ/kg)
3.20
838
55
42.8
Theoretical density
2.80
2.75
3
Density (g/cm )
Experimental density
Brake thermal efficiency (%)
N. Tiruvenkadam et al. / Energy Conversion and Management 98 (2015) 440–448
30
25
20
Conventional cast iron cylinder liner (CL) Nano hybrid composite cylinder liner (NL)
15
10 2.70
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Brake power (kW) Fig. 7. BTE vs. BP for CL and NL.
2.65
80
2.60 NL2
NL3
NL4
Fabricated nano - hybrid composite liner Fig. 5. Comparison of theoretical and experimental density values of fabricated NLs.
3.4.3. Exhaust gas temperature Fig.10 shows that the exhaust gas temperature of an engine operated with NL and CL. One could observe from the plot that the NL has higher temperature than CL at all loads. The higher in-cylinder temperature also leads to an increase in the exhaust gas temperature [43]. The amount of the energy released while combustion affect the combustion temperature, which can be determined by exhaust gas temperature [44]. The exhaust gas temperature indicates the in-cylinder temperature, which shows the NL-operated engine has better combustion than CL-operated engine. Higher combustion gas temperature could destroy the lubricating film between piston body and liner, increasing locally metal temperature [45]. However, the developed NL was not found to be affected by the in-cylinder temperature due to its competitively high thermal conductivity and high thermal expansion than CL, as shown in Table 2. 3.5. Engine emission analysis 3.5.1. CO vs. BP Fig. 11 shows the variations of CO emission levels against BP for CL and NL. At maximum load, the CO emission levels were found to be reduced by 12.5% with the use of NL compared to CL.
(a) Magnification 500×
Brake power
70
Cylinder pressure (bar)
NL1
= 3.75 kW o
Injection timing = 23 BTDC Max pressure for CL = 70.613 bar Max pressure for NL = 72.151 bar
60 50 40
Conventional cast iron cylinder liner (CL)
30
Nano hybrid composite cylinder liner (NL)
20 10 0 -180 -150 -120 -90 -60 -30
0
30
60
90
120 150 180
Crank angle (deg.) Fig. 8. Cylinder pressure vs. crank angle for CL and NL.
CO is the product of incomplete combustion due to insufficient oxygen to convert all the carbon atoms to carbon dioxide. It is mainly dependent on the air/fuel ratio relative to the chemically correct proportion and increases when the air/fuel ratio becomes greater than stoichiometric air and fuel requirements. It is also clear from the plots that in the NL-operated engine CO emission is lower than the CL-operated engine at all loads. This is mainly due to the higher temperature of the engine cycle maintained by nano- and micro-reinforcement particles present in the NL, which
(b) Magnification 1000×
Fig. 6. (a) Magnification 500. (b) Magnification 1000.
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Heat release rate (kJ/m3 deg.)
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Fig. 12. HC vs. BP for CL and NL. Fig. 9. Heat release rate vs. crank angle for CL and NL.
Oxides of nitride (NO x )
200 180
Conventional cast iron cylinder liner (CL)
160
Nano hybrid composite cylinder liner (NL)
140 120 100 80
0
1
2
3
Brake power (kW) Fig. 10. Exhaust gas temperature with BP for CL and NL.
Fig. 13. NOx vs. BP for CL and NL.
45
Smoke (HSU)
40 35
Conventional cast iron cylinder liner (CL) Nano hybrid composite cylinder liner (NL)
30 25 20 15 0.00
0.75
1.50
2.25
3.00
3.75
Brake power (kW) Fig. 11. CO vs. BP for CL and NL. Fig. 14. Smoke vs. BP for CL and NL.
were used to help in complete burning of oxygen content inside the combustion chamber. 3.5.2. HC vs. BP HC is an intermediate product of incomplete combustion. The variation in HC emission with BP for CL and NL is shown in Fig. 12. The plots shows a reduction in the values of HC in the engine with NL for all BPs. The percentage reduction obtained with NL at maximum load was 10.95%. The heat loss due to the coolant
use reduced (when the engine was operated with NL), leading to good flammability of fuel inside the combustion chamber, which imply reduction of HC at all loads. 3.5.3. NOx vs. BP Fig. 13 shows the variation in NOx for engines operated with CL and NL. As per the combustion theory, the formation of NOx is merely a function of in-cylinder combustion temperature [46,47]
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Fig. 15. (a) Dismantling position of NL from engine, (b) top portion of NL in engine and (c) completely dismantled NL, piston, piston pin, and piston rings.
and the amount of oxygen. A comparison of the NOx emission values showed that there was a marginal increase in NOx emission with the use of NL than with the use of CL. The increase in the levels was found to be 2.7% at maximum load. Several factors such as fuel properties, engine type, and engineoperating condition affect the engine NOx emissions. Although the higher overall cylinder temperature is an indicator of higher NOx, the temperature distribution in the cylinder is more important than other causes. Combustions that takes place over a short period of time allows less cooling time by heat transfer and dilution, which results in higher NOx formation [48–52]. Because the nano-ZrO2, micro-SiC, and micro-Gr reinforcements can withstand high temperature and Al 6061 matrix material have lower thermal expansion coefficient, the temperature inside the combustion chamber temperature is high. In-cylinder NOx reduction technique like exhaust gas recirculation is an effective way to reduce NOx emission from diesel engines [43]. It can be attached to reduce NOx when the engine is operating with NL. 3.5.4. Smoke vs. BP Fig. 14 shows the variation of smoke emission in Hartridge smoke unit (HSU) for the CL and NL. Smoke value has a reducing trend of 4.76% when operated with NL. This was due to better vaporization and quick combustion of fuel supplied inside the combustion chamber (NL cylinder wall), which were maintained by the inherent properties of reinforcements and matrix material. Lower level of unburned HC in the engine exhaust could have occurred due to the complete combustion with the help fuel-burn oxygen. This can be the reason for reduction in the smoke emission. Higher combustion temperature and intense turbulence created by reverse squish lead to reduction in smoke emission [25]. There is always a tradeoff between NOx and smoke emission in a diesel engine fuelled by any kind of fuel [53]. 3.6. Teardown analysis After running for 2000 h at frequent intervals for a period of 1 year, at various load conditions, the new NL was dismantled from the engine and it is shown in Fig. 15(a) –(c). The internal parts were inspected and evaluated to investigate wear characteristics, breakage, and other damage as well as the accumulation of dirt, sludge, and carbon. 3.6.1. Visual examination of developed NL No cracks were found both inside and outside of the NL. This again shows that developed NL has an acceptable level to perform the engine operation. During the visual inspection, very small quantities of carbon deposition were found at the top of the piston
compared to the engine with CL, which showed that more complete combustion has taken place in the engine fitted with NL. During the testing period, outside wall of the NL was continually placed in cooling water. After dismantling the NL, no corrosion effect was found outside the surface of the NL on visual inspection. This may be due to good corrosive resistance property of the hybrid composites. 3.6.2. Monitoring engine oil condition At the time of NL assembly, the oil in the sump was completely cleaned and filled with new Castrol Agri MP Plus 20W-40 engine oil. After 2000 h of running under various load conditions at frequent intervals, the engine oil was completely removed from the oil sump and was kept undisturbed for 20 h and filtered with less than 100 nm muslin cloth. No foreign particles or Al matrix debris or reinforcement debris were observed in the oil. At the same time, the bottom portion of the engine oil sump was also cleaned with neat cloth and fine brushes, which also showed absence of foreign particles. This inspection proved that there was no material loss in the developed nano hybrid composite liner under different load operating condition during the period of study. Since the friction coefficient of Al MMC was 25% more than the cast iron while sliding under identical conditions [53], so the developed NL was found to be suitable for engine’s smooth operation when compared to CL. 4. Conclusion In this synthesis and experimental work, the effect of a newly developed NL on diesel engine performance, combustion, emission characteristics, and suitability to replace the CL in the engine cylinder was studied. The results achieved in this study are summarized as follows: The selected matrix and reinforcement material was suitable to make NL based on the density, mechanical, thermal properties predicted by RoHM, and homogeneous mixture through SEM examination. The NL enhanced BTE, in-cylinder pressure, heat release, and exhaust temperature. The NL reduced CO, HC, and smoke emissions, but increased NOx emission. The teardown analysis revealed no detrimental effects with NL. Thus, this investigation has shown that the newly developed NL has good potential to replace the presently used conventional CL for achieving greater fuel economy and green environment. The fact that it can be used without any modification of the engine structure with weight saving of 43.75% is an added advantage.
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