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Development of engine oil using palm oil as a base stock for four-stroke engines
Energy 35 (2010) 2552e2556
Contents lists available at ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
Development of engine oil using palm oil as a base stock for four-stroke engines Kraipat Cheenkachorn a, b, *, Bundit Fungtammasan c, d a
Department of Chemical Engineering, King Mongkut’s University of Technology North Bangkok, 1518 Piboolsongkram Rd., Bangsue, Bangkok 10800, Thailand CHE Center for Energy Technology and Environment, King Mongkut’s University of Technology North Bangkok, 1518 Piboolsongkram Rd., Bangsue, Bangkok 10800, Thailand c The Joint Graduate School of Energy and Environment, King Mongkut’s University of Technology Thonburi, 126 Prachautit Rd. Bangmod, Tungkru, Bangkok 10140, Thailand d CHE Center for Energy Technology and Environment, King Mongkut’s University of Technology Thonburi, 126 Prachautit Rd. Bangmod, Tungkru, Bangkok 10140, Thailand b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 October 2009 Received in revised form 19 February 2010 Accepted 2 March 2010 Available online 1 April 2010
The use of palm oil as a base stock for an environmentally friendly lubricant for small four-stroke motorcycle engines is investigated. Palm oil was blended with mineral oil at different compositions to the viscosity requirement of commercial lubricant. A liquid additive package was added to improve the viscosity of the lubricant. A blend that meets the viscosity requirement was then chosen for physical and chemical property characterization and subjected to an engine test. The blend consists of 50.6% (wt.) palm oil, 41.6% mineral oil, and 7.8% additive package. The properties evaluated include viscosity, viscosity index, flash point, foaming characteristics, and wear scar. The engine performance and emission tests were carried out with a 125-cc motorcycle on a chassis dynamometer using a Bangkok Driving Cycle. Compared to a mineral-based commercial oil, the palm oil-based lubricant exhibits superior tribological properties, but offers no clear advantage on engine and emission performance. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Biodegradable lubricant Four-stroke engine Palm oil
1. Introduction The use of vegetable oils and animal fats as lubricants dates back to 1650 B.C. [1]. The discovery of petroleum oil in the late 1800s, however, resulted in replacement of vegetable oils and animal fats and, eventually, mineral oils became the primary base stock for lubricants due to their lower price and superior overall performance [2]. However, the use of vegetable oils and animal fats as lubricants continues, but mostly in specialty applications. Early this century, environmental concerns have stimulated increased interest in biodegradable lubricants. Since vegetable oils and most esters are more biodegradable than mineral oils, worldwide attention on the biodegradability of lubricants has prompted many lubricant manufacturers to reconsider vegetable oils as base stocks. Many studies have explored the possibility of replacing mineral oils with vegetable oils [3e5]. When vegetable oils are used as base stocks for lubricants, they exhibit good lubricity and high viscosity index. However, their oxidative stability and low temperature properties are inferior to those of petroleum-based lubricants. Vegetable oil-based lubricants are currently used in many countries. For example, soybean oil and corn oil are used as
* Corresponding author. Department of Chemical Engineering, King Mongkut’s University of Technology North Bangkok, 1518 Piboolsongkram Rd., Bangsue, Bangkok 10800, Thailand. Tel.: þ66 2 913 2500; fax: þ66 2 587 0024. E-mail address: [email protected] (K. Cheenkachorn). 0360-5442/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2010.03.002
base stocks for lubricants in the United States while rapeseed oils are frequently used in North America and Europe [6,7]. However, a study on vegetable oil-based lubricant for motorcycles has yet been reported. Motorcycles are widely used in many Asian countries including Thailand, China, Taiwan, and Vietnam. In Thailand, with the total number of registered motorcycles being more than 16 million in 2007 [8], these vehicles contribute a significant portion of air pollution due to their large population and high emission levels. Since emission standards across the world are becoming more stringent, the motorcycle original equipment manufacturers (OEM) are shifting from two-stroke to four-stroke engine technology, hence increasing the number of four-stroke motorcycles in the market. Therefore, it is worthwhile formulating a biodegradable lubricant for four-stroke motorcycle engines. The objective of this study was to investigate the viability of palm oil as a base stock in the formulation of an environmentally friendly lubricant for four-stroke motorcycles. Specifically, physical and chemical properties of selected blends were obtained to determine whether they meet the requirements of an SAE 40 grade lubricant. A candidate blend was then selected for emission tests using a four-stroke motorcycle running on a chassis dynamometer. The analyzed emissions were total hydrocarbon (THC), nitrogen oxides (NOx), carbon monoxide (CO), and carbon dioxide (CO2). The engine performance was then evaluated on the basis of maximum power output and fuel consumption. The results were compared with those of a mineral-based oil.
K. Cheenkachorn, B. Fungtammasan / Energy 35 (2010) 2552e2556
2. Experimental
2553
Table 2 The detailed specifications of the tested vehicle.
The primary purpose of this experimental study was to determine an appropriate composition of a palm oilemineral oil mixture that may be used as a biodegradable lubricant for four-stroke motorcycle engines. The base stocks used were palm olein oil (Krabi Oil Palm Farmers Co-Op., Krabi, Thailand) and mineral oil (PTT Public Co. Ltd., Ayuthaya, Thailand), with palm oil fraction ranging from 40 to 65%. A proprietary additive package, which is a liquid mixture of high-molecular weight multifunctional components, was used to improve the quality of lubricant. Its proportion ranged from 0 to 9.09%. The lubricating properties of base oils and the selected blend are presented in Table 1. To prepare the candidate lubricant, various blends of palm oil and mineral oil were initially tested until one that meets viscosity standard was found. The lubricating properties were then determined using standard methods published by the American Society for Testing Materials (ASTM), as shown in Table 1. All measurements were repeated at least three times and the presented results were the average of the triplicate tests. The vehicle used in this study was Honda Dream 125. The detailed specifications of this vehicle are shown in Table 2. Engine performance and emission tests of the selected blend were performed at the Automotive Emission Laboratory, Pollution Control Department, Pathumthani, Thailand. A chassis dynamometer (Schenck Komeg Model 1060/GS60, Schenck Komeg GmbH, Germany) was used to simulate the average driving pattern in Bangkok Metropolis. In this study, the Bangkok Driving Cycle for motorcycle, shown in Fig. 1 and Table 3, was used as a representative of driving conditions in Bangkok, details of which can be found elsewhere [9]. To investigate the emissions, exhaust gas was collected to a dilution tunnel. The diluted exhaust was analyzed using non-dispersive infrared technique (Pierburg PIA-2000, Peirburg Instruments, Germany) for CO and CO2, flame ionization detector (Pierburg PM-2000) for total hydrocarbon (THC), and chemiluminescence detector (Pierburg CLD PM-2000) for NOx. Fuel consumption characteristics were determined using a carbon balance method from the exhaust emission data. All experiments in the engine test were conducted by a single driver. 3. Results and discussion 3.1. Physical property tests The primary effort of this research is to formulate a biodegradable lubricant, SAE 40 grade, for a four-stroke motorcycle engine. Based on an SAE specification, the viscosity of the formulated oil must be initially achieved. The corresponding viscosity range at
Engine Displacement Bore and stoke Compression ratio Transmission Weight Fuel capacity
Four stroke e overhead cam shaft air e cooled 97 cc 50.0 49.5 mm. 9.0:1 Rotary 4 gear 92 kg 4.0 L, unleaded benzene octane >91
100 C for SAE 40 lubricant is 12.5e16.3 cSt. [10]. For this experiment, the desired viscosity was set at 15 cSt. All blends of palm oil, mineral oil, and the additive showed homogenous phase, that is no phase separation and sedimentation, after a three-month storage at room temperature. Fig. 2 shows the results of viscosity of the blends, the compositions of which are shown in Table 4. Blend No. 1 (45% palm oil and 55% mineral oil with no additive) was randomly mixed to predict the viscosity of the mixture. The result shows that the desired viscosity was not reached. Therefore, Blends No. 2 and 3 were performed by addition of the additive package. The viscosity of both blends was satisfactory. However, the portion of palm oil is still less than 50%. Blends No. 4e6 were made by adjusting the compositions of vegetable oil and mineral oil while the additive dosage was kept at 7.24 %wt. The results show that an increase in palm oil fraction tended to reduce the viscosity of the blends. The same trend was observed for Blends No. 7e10, with an additive dosage of 7.80 %wt. This is due to the fact that the viscosity of vegetable oil is considerably lower than that of mineral oil, being typically 8.65 cSt and 32.51 cSt at 100 C, respectively. The viscosity indices of palm oil and mineral oil were 187.00 and 96.15, respectively. Higher viscosity index of palm oil results in higher viscosity index of the blend. This is attributed to the fact that palm oil, which contains triglycerides, has a narrow molecular weight distribution. On the contrary, mineral oil contains a mixture of various molecular weight hydrocarbons. The molecular interaction of vegetable oil also results in higher viscosity index [3]. Oils with high viscosity index can resist excessive thickening when the engine is cold. This leads to better engine starting, promoting prompt lubrication circulation [11]. It also prevents excessive thinning when the engine is hot and thus provides full lubrication to protect the rubbing surfaces. Therefore, vegetable oil can provide this advantage when used as a base stock for lubricants. After the blends of palm oil and mineral oil were made and the desired viscosity was reached, additional property tests of the selected blend, Blend No. 9, were conducted for its flash point, volatility loss, sulfate ash, foaming, and wear scar. The results are shown in Table 1. Although palm oil and mineral oil show nearly the
Table 1 Physical properties of base stocks, commercial oil, and Blend No. 9. Properties
Palm oil
Mineral oil
Commercial oil
Blend No. 9
Method
Viscosity, cSt At 40 C At 100 C
42.66 0.05 8.65 0.02
503.40 0.05 32.51 0.02
151.60 0.06 15.00 0.02
111.60 0.07 15.04 0.01
ASTM D445
Viscosity index Flash point, C Volatility loss, wt.% Sulfate ash, wt.%
187.00 304.3 1.3 0.09 0.01 0.007 0.01
96.15 302.0 1.0 12.98 0.05 1.52 0.02
99.00 256.0 2.0 3.07 0.03 0.99 0.03
140.00 278.0 0.3 2.64 0.03 1.10 0.02
ASTM ASTM ASTM ASTM
Foaming, ml/ml Sequence I Sequence II Sequence III
210/0 /0 60/0
200/0 30/0 270/0
20/2 240/0 10/0
490/310 300/50 190/10
ASTM D892
Wear scar, mm
0.58 0.01
0.95 0.01
0.60 0.01
0.34 0.02
ASTM D4172
D2270 D92 D5800B D874
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K. Cheenkachorn, B. Fungtammasan / Energy 35 (2010) 2552e2556 20.0
100
7.24 % additve
Blend No.2
90
7.80 % additve
Blend No.3
18.0
60 50 40 30
Blend No.9
14.0
9.09 % additve
Blend No.4
Blend No.10
16.0
70
Viscosity (cSt)
Velocity (km hr-1)
80
No additive
Blend No.5
Blend No.8 Blend No.6
Blend No.7
12.0 10.0
20
Blend No.1
8.0
10 0
6.0 0
200
400
600
800
1000
1200
1400
1600
1800
30
40
50
Time (s)
60
70
80
% Palm oil
Fig. 1. The Bangkok driving cycle for motorcycles.
Fig. 2. Viscosity of various blends at 100 C (ASTM D445).
same flash point temperature, blending the two oils (Blend No. 9) results in unexpectedly lower flash point than the two oils. This is possibly due to the presence of the additive package. Nevertheless, the flash point of the blend is still higher than that of the commercial oil, which is desirable. Since the lubricant is exposed to severe conditions, it may result in “volatility loss”, that is, loss of some light-weight hydrocarbon fractions while leaving behind the heavy-weight molecules. This leads to an increase in lubricant viscosity, which contributes to poor circulation, increased oil consumption, wear and emissions [12]. The volatility loss data obtained by the NOACK test indicates that Blend No. 9 has a lower loss than commercial oil. This could be due to the fact that the molecular weight distribution of Blend No. 9 has a narrower range than commercial oil. Sulfate ash is a product of the combustion of sulfur present in fuels and lubricants. Pure palm oil shows extremely low sulfate ash. However, Blend No. 9 shows higher sulfate ash than commercial oil. This is because of the presence of additive package which contains sulfur. The result agrees with the previous study by Colclough [13], which demonstrated that the main additives used in automotive lubricants, i.e., zinc dithiophosphates (ZDDP), can lead to catalytic converter poisoning. Higher sulfate ash oil contributes to an increase in particulate matter in the exhaust gas emission. A previous study demonstrated that sulfate may originate from both fuel and oil [14]. In general, the contents of sulfur in fuel and oil are 500 and 5000 ppm, respectively. The consumption ratio of fuel to oil is 1000:1. When a sulfur balance is applied to the engine fuel and oil, it was found that 99% of sulfate ash originated from the fuel and only 1% originated from the oil [15]. Foaming characteristics of selected blends were also shown in Table 1. Foaming in the lubricant is caused by the presence of water in the base oil or some chemicals such as air, grease, solid contaminants, etc. The results show that Blend No. 9 shows relatively higher foaming characteristics than commercial oil for all sequences. This may be resulted from the incompatibility between the antifoam agent in the additive package and vegetable oil. A new additive package should, therefore, be investigated. The use of this formulated blend in applications that incur foaming such as gear oil
and compressor oil should be avoided since foaming increases oxidation and reduces oil flow to the bearing [11]. The results from wear scar diameter, Table 1, show that palm oil and the commercial oil are not significantly different. Compared to the commercial oil, an addition of additive package in Blend No. 9 significantly improves wear scar. Vegetable oils are by their chemical nature long chain fatty acid triester of glycerol. The polar ester structure in vegetable oil is able to interact with the metal surfaces, leading to better wear property. The antiwear additive also forms a protective layer on the metal parts. Therefore, a good lubricity and wear property is obtained.
Table 3 The Bangkok driving cycle for motorcycles. Details
Phase I
Phase II
Phase III
Total
Distance (km) Time (s) Average velocity (km/h)
3.260 520 23.4
3.298 368 33.2
6.594 568 42.9
12.852 1456 33.5
3.2. Emission tests The results of emission measurements from the test vehicle based on the Bangkok Driving Cycle for motorcycle are summarized in Table 5. The data shows that, for all phases, the biodegradable lubricant (Blend No. 9) showed no significant difference in all emissions compared to those of commercial oil. For the biodegradable lubricant, the THC emission levels appear in the ascending order as follows: Phase III, Phase I, and Phase II. In Phases II and III, the biodegradable lubricant show slightly less THC emission than commercial oil. This is possibly due to the less volatility loss of palm oil-based lubricant during hot warming periods. One of the main sources of nitrogen oxide (NOx) emissions from the combustion engine is the oxidation of atmospheric nitrogen within the cylinder, which is directly proportional to the flame temperature. As shown in Table 5, for biodegradable lubricant, the NOx emission levels for the driving pattern are in the descending order as follows: Phase I, Phase III, and Phase II. The thickness of lubricant film in a combustion chamber varies from one phase to Table 4 Composition of various blends. Blends No.
1 2 3 4 5 6 7 8 9 10
Compositions (wt.%) Percent palm oil
Percent mineral oil
Percent additive
45.00 41.74 40.91 55.66 60.30 64.94 57.90 52.90 50.60 41.20
55.00 51.02 50.00 37.11 32.47 27.40 34.30 39.30 41.60 51.00
0 7.24 9.09 7.24 7.24 7.24 7.80 7.80 7.80 7.80
K. Cheenkachorn, B. Fungtammasan / Energy 35 (2010) 2552e2556 Table 5 The exhaust emissions from the tested vehicle on a chassis dynamometer. Fuel
Phase I (g/km)
Phase II (g/km)
Phase III (g/km)
Average (g/km)
THC
Blend No. 9 Commercial lubricant
0.277 0.270
0.261 0.283
0.288 0.291
0.279 0.284
NOx
Blend No. 9 Commercial lubricant
0.202 0.189
0.179 0.180
0.198 0.195
0.194 0.190
CO
Blend No. 9 Commercial lubricant
7.006 7.081
6.793 6.975
7.773 7.769
7.336 7.398
CO2
Blend No. 9 Commercial lubricant
34.332 33.983
29.061 28.958
30.054 29.790
30.874 30.630
7 6 5
Power output (kW)
Emission
2555
4 3 2
Blend No.9 Commercial lubricant
1 0 0
another depending on the engine temperature. The fact that Phase I shows highest NOx emission may result from the presence of thin film of lubricant in the cylinder during a warm-up period. The oxygen in lubricant may shift air/fuel ratio in favor of more NOx emission [16]. In Phases II and III, where engine temperature is higher compared to that of Phase I, a thinner film of lubricant is formed at the cylinder wall. Therefore, the effect of the oxygen presence in the lubricant is less pronounced. Compared to Phase II, NOx emission in Phase III is higher. This is because, in Phase III, the engine is operating at higher shift and vehicle speed leading to more throttle-valve opening. This results in intense combustion and hence higher combustion temperature, which lead to higher NOx emission [17]. Compared to biodegradable oil, commercial oil shows slightly lower NOx emission in Phase I which may be explained by the same reason. However, such difference was not observed in Phases II and III. The amount of CO emissions for both lubricants decreases in the descending order as follows: Phase III, Phase I, and Phase II. The biodegradable lubricant shows slightly lower CO emissions in Phases I and II than commercial oil. The oxygen in vegetable oil may lead to more complete combustion, and hence lower CO emissions. The results agree with a previous study [18] that lower aromatic content in both fuel and oil results in lower CO and THC. This beneficial effect of biodegradable lubricant agrees with the study of Weller et al. [16]. Carbon dioxide (CO2) emissions from both lubricants show a decreasing tendency from Phases I, II, to III. The higher speed drive leads to higher combustion efficiency resulting in higher CO2 emission. However, no substantial difference in CO2 emission was observed between the two lubricants.
10
20
30
40
50
60
Vechicle speed (km hr-1) Fig. 3. The power output at different speed.
groups on metal surfaces. However, the results on the fuel consumption in this study show no significant difference between biodegradable and commercial lubricants. One plausible explanation for this result could be the fact that the percentage of vegetable oil present in this biodegradable lubricant was limited to 50.60%. Hence, the improved lubricity that would have led to less fuel consumption was not clearly observed.
3.4. Engine performance Fig. 3 shows the power output at different engine speeds, which were converted from the vehicle speed. For chassis dynamometer, the maximum power is referred to as the maximum rotational power that the chassis dynamometer can be subjected to and still operate within specifications. To obtain the maximum power output from the engine of the tested vehicle at each speed, the chassis dynamometer is used to maintain a specified vehicle speed while the maximum load is performed and measured. This power output is different from an engine dynamometer since it includes frictional and mechanical losses in a driveetrain system. No significant difference was observed from the use of different lubricants. The results agree with those from the fuel consumption results. Since the amount of vegetable oil in the blend is 50.60%, the beneficial effect of vegetable oil was not obviously seen.
4. Conclusion 3.3. Fuel consumption The effect of lubricants on fuel consumption of the four-stroke motorcycle from the Bangkok driving cycle is shown in Table 6. The fuel consumption increases with the vehicle speed due to an increase in the frictional loss. The experimental results on friction and wear tests in the previous study [19] showed that the use of vegetable oil as a base stock for biodegradable lubricant results in lower friction and wear scar diameter due to the affinity of polar
Table 6 The fuel consumption in each phase. Phase
Phase I Phase II Phase III Average
Fuel consumption (km/L) Blend No. 9
Commercial lubricant
50.48 57.51 54.03 53.90
50.75 57.16 54.36 54.09
The blends of palm oil, mineral oil, and an additive package were conducted to formulate biodegradable lubricant for four-stroke motorcycle engines. The selected blend consists of 50.6%(wt.) palm oil, 41.6% mineral oil, and 7.8% additive package. The formulated blend shows better properties than commercial oil in terms of viscosity index, flash point, evaporative loss, and wear scar. However, foaming characteristics and sulfate ash are poorer because of the presence of improper additive. From the emission and engine performance tests using the Bangkok driving cycle for a motorcycle, it was found that there is no significant difference in the emissions, including THC, NOx, CO, and CO2, between the biodegradable and commercial lubricants. The engine performance and fuel consumption for both lubricants showed no significant difference either. However, the fact that palm oil-based lubricant is derived from a renewable, lower carbon source and that it offers superior tribological properties (wear scar, viscosity index, etc.), this new formulation could potentially be considered an attractive alternative to mineral oil-based lubricants.
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Acknowledgement The authors gratefully acknowledge the contribution of the Department of Chemical Engineering, King Mongkut’s University of Technology North Bangkok. The contributions of palm oil from Krabi Oil Palm Farmers Co-Op. Ltd., mineral-based oil and the additive package from PTT Public Co. Ltd., and the provision of engine test facilities from the Pollution Control Department are greatly appreciated. References [1] Dowson D. History of tribology. London, UK: Professional Engineering Publishing; 1998. [2] Dorinson A, Ludema KC. Mechanics and chemistry in lubrication tribology series 9. Amsterdam, the Netherlands: Elsevier; 1985. [3] Masjuki HH, Maleque MA, Kubo A, Nonaka T. Palm oil and mineral oil based lubricantsdtheir tribological and emission performance. Tribology International 1999;32:305e14. [4] Wan Nik WB, Ani FN, Masjuki HH, Eng Giap SG. Rheology of bio-edible oils according to several rheological models and its potential as hydraulic fluid. Industrial Crops and Products 2005;22:249e55. [5] Kodali DR. High performance ester lubricants from natural oils. Industrial Lubrication and Tribology 2004;54(4):165e70. [6] Goyan RL, Melley RE, Wissner PA, Ong WC. Biodegradable lubricants. Lubrication Engineering 1998;54(7):10e7. [7] Fuks IG, Yu A, Evdokimov AA, Luksa A. Vegetable oils and animal fats as raw materials for manufacture of commercial. Chemistry and Technology of Fuels and Oils 1992;4:203e7.
[8] Motorcycle market in Thailand. Available at: [accessed October 2008]. [9] Leong ST, Muttamar S, Laortanakul P. Influence of benzene emission from motorcycles on Bangkok air quality. Atmospheric Environment 2002;36: 651e61. [10] Society of Automotive Engineers. SAE fuel and lubricants standards. Warrendale, Pennsylvania: Society of Automotive Engineers, Inc. 1995. [11] Stambaugh RL. Viscosity index improvers and thickeners. In: Mortier RM, Orszulik ST, editors. Chemistry and technology of lubricants. Suffolk, Great Britain: Chapman & Hall; 1997. p. 144e176. [12] Rudnick LR. Synthetics, mineral oils, and bio-based lubricants. Boca Roton: CRC/Taylor&Francis; 2005. [13] Colclough T. Role of additives and transition metals in lubricating oil oxidation. Industrial and Engineering Chemistry Research 1987;26:1888e95. [14] Plumley M. Lubricant formulation and consumption effects on diesel exhaust ash emissions: measurements and sample analyses from a HD diesel engine. Available at: ; 2005. Chicago, IL[accessed May 2009]. [15] Froelund K, Yilmaz E. Impact of engine oil consumption on particulate emissions. Available at: [accessed May 2006]. [16] Weller DE, Swain WH, Hess H, Boehman AL, Perez JM. Change in particulate composition and morphology when using of vegetable oil lubricant in a low heat rejection engine. SAE 1999-01-0975; 1999. [17] Stone R. Introduction to internal combustion engines. Warrendale, Pennsylvania: Society of Automotive Engineers; 1992. [18] Yao YC, Tsai JH, Chang AL, Jeng FT. Effects of sulfur and aromatic contents in gasoline on motorcycle emissions. Atmospheric Environment 2008;42: 6560e4. [19] Cheenkachorn K, Udornthep I. A development of four-stroke engine oil using palm oil as a base stock. In: Kirtikara K, editor. The 2nd Joint International Conference on Sustainable Energy and Environment (SEE 2006), vol. 1. Bangkok, Thailand: Tanaphat Printing; 2006. p. 435e8.
Contents lists available at ScienceDirect
Energy journal homepage: www.elsevier.com/locate/energy
Development of engine oil using palm oil as a base stock for four-stroke engines Kraipat Cheenkachorn a, b, *, Bundit Fungtammasan c, d a
Department of Chemical Engineering, King Mongkut’s University of Technology North Bangkok, 1518 Piboolsongkram Rd., Bangsue, Bangkok 10800, Thailand CHE Center for Energy Technology and Environment, King Mongkut’s University of Technology North Bangkok, 1518 Piboolsongkram Rd., Bangsue, Bangkok 10800, Thailand c The Joint Graduate School of Energy and Environment, King Mongkut’s University of Technology Thonburi, 126 Prachautit Rd. Bangmod, Tungkru, Bangkok 10140, Thailand d CHE Center for Energy Technology and Environment, King Mongkut’s University of Technology Thonburi, 126 Prachautit Rd. Bangmod, Tungkru, Bangkok 10140, Thailand b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 October 2009 Received in revised form 19 February 2010 Accepted 2 March 2010 Available online 1 April 2010
The use of palm oil as a base stock for an environmentally friendly lubricant for small four-stroke motorcycle engines is investigated. Palm oil was blended with mineral oil at different compositions to the viscosity requirement of commercial lubricant. A liquid additive package was added to improve the viscosity of the lubricant. A blend that meets the viscosity requirement was then chosen for physical and chemical property characterization and subjected to an engine test. The blend consists of 50.6% (wt.) palm oil, 41.6% mineral oil, and 7.8% additive package. The properties evaluated include viscosity, viscosity index, flash point, foaming characteristics, and wear scar. The engine performance and emission tests were carried out with a 125-cc motorcycle on a chassis dynamometer using a Bangkok Driving Cycle. Compared to a mineral-based commercial oil, the palm oil-based lubricant exhibits superior tribological properties, but offers no clear advantage on engine and emission performance. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Biodegradable lubricant Four-stroke engine Palm oil
1. Introduction The use of vegetable oils and animal fats as lubricants dates back to 1650 B.C. [1]. The discovery of petroleum oil in the late 1800s, however, resulted in replacement of vegetable oils and animal fats and, eventually, mineral oils became the primary base stock for lubricants due to their lower price and superior overall performance [2]. However, the use of vegetable oils and animal fats as lubricants continues, but mostly in specialty applications. Early this century, environmental concerns have stimulated increased interest in biodegradable lubricants. Since vegetable oils and most esters are more biodegradable than mineral oils, worldwide attention on the biodegradability of lubricants has prompted many lubricant manufacturers to reconsider vegetable oils as base stocks. Many studies have explored the possibility of replacing mineral oils with vegetable oils [3e5]. When vegetable oils are used as base stocks for lubricants, they exhibit good lubricity and high viscosity index. However, their oxidative stability and low temperature properties are inferior to those of petroleum-based lubricants. Vegetable oil-based lubricants are currently used in many countries. For example, soybean oil and corn oil are used as
* Corresponding author. Department of Chemical Engineering, King Mongkut’s University of Technology North Bangkok, 1518 Piboolsongkram Rd., Bangsue, Bangkok 10800, Thailand. Tel.: þ66 2 913 2500; fax: þ66 2 587 0024. E-mail address: [email protected] (K. Cheenkachorn). 0360-5442/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2010.03.002
base stocks for lubricants in the United States while rapeseed oils are frequently used in North America and Europe [6,7]. However, a study on vegetable oil-based lubricant for motorcycles has yet been reported. Motorcycles are widely used in many Asian countries including Thailand, China, Taiwan, and Vietnam. In Thailand, with the total number of registered motorcycles being more than 16 million in 2007 [8], these vehicles contribute a significant portion of air pollution due to their large population and high emission levels. Since emission standards across the world are becoming more stringent, the motorcycle original equipment manufacturers (OEM) are shifting from two-stroke to four-stroke engine technology, hence increasing the number of four-stroke motorcycles in the market. Therefore, it is worthwhile formulating a biodegradable lubricant for four-stroke motorcycle engines. The objective of this study was to investigate the viability of palm oil as a base stock in the formulation of an environmentally friendly lubricant for four-stroke motorcycles. Specifically, physical and chemical properties of selected blends were obtained to determine whether they meet the requirements of an SAE 40 grade lubricant. A candidate blend was then selected for emission tests using a four-stroke motorcycle running on a chassis dynamometer. The analyzed emissions were total hydrocarbon (THC), nitrogen oxides (NOx), carbon monoxide (CO), and carbon dioxide (CO2). The engine performance was then evaluated on the basis of maximum power output and fuel consumption. The results were compared with those of a mineral-based oil.
K. Cheenkachorn, B. Fungtammasan / Energy 35 (2010) 2552e2556
2. Experimental
2553
Table 2 The detailed specifications of the tested vehicle.
The primary purpose of this experimental study was to determine an appropriate composition of a palm oilemineral oil mixture that may be used as a biodegradable lubricant for four-stroke motorcycle engines. The base stocks used were palm olein oil (Krabi Oil Palm Farmers Co-Op., Krabi, Thailand) and mineral oil (PTT Public Co. Ltd., Ayuthaya, Thailand), with palm oil fraction ranging from 40 to 65%. A proprietary additive package, which is a liquid mixture of high-molecular weight multifunctional components, was used to improve the quality of lubricant. Its proportion ranged from 0 to 9.09%. The lubricating properties of base oils and the selected blend are presented in Table 1. To prepare the candidate lubricant, various blends of palm oil and mineral oil were initially tested until one that meets viscosity standard was found. The lubricating properties were then determined using standard methods published by the American Society for Testing Materials (ASTM), as shown in Table 1. All measurements were repeated at least three times and the presented results were the average of the triplicate tests. The vehicle used in this study was Honda Dream 125. The detailed specifications of this vehicle are shown in Table 2. Engine performance and emission tests of the selected blend were performed at the Automotive Emission Laboratory, Pollution Control Department, Pathumthani, Thailand. A chassis dynamometer (Schenck Komeg Model 1060/GS60, Schenck Komeg GmbH, Germany) was used to simulate the average driving pattern in Bangkok Metropolis. In this study, the Bangkok Driving Cycle for motorcycle, shown in Fig. 1 and Table 3, was used as a representative of driving conditions in Bangkok, details of which can be found elsewhere [9]. To investigate the emissions, exhaust gas was collected to a dilution tunnel. The diluted exhaust was analyzed using non-dispersive infrared technique (Pierburg PIA-2000, Peirburg Instruments, Germany) for CO and CO2, flame ionization detector (Pierburg PM-2000) for total hydrocarbon (THC), and chemiluminescence detector (Pierburg CLD PM-2000) for NOx. Fuel consumption characteristics were determined using a carbon balance method from the exhaust emission data. All experiments in the engine test were conducted by a single driver. 3. Results and discussion 3.1. Physical property tests The primary effort of this research is to formulate a biodegradable lubricant, SAE 40 grade, for a four-stroke motorcycle engine. Based on an SAE specification, the viscosity of the formulated oil must be initially achieved. The corresponding viscosity range at
Engine Displacement Bore and stoke Compression ratio Transmission Weight Fuel capacity
Four stroke e overhead cam shaft air e cooled 97 cc 50.0 49.5 mm. 9.0:1 Rotary 4 gear 92 kg 4.0 L, unleaded benzene octane >91
100 C for SAE 40 lubricant is 12.5e16.3 cSt. [10]. For this experiment, the desired viscosity was set at 15 cSt. All blends of palm oil, mineral oil, and the additive showed homogenous phase, that is no phase separation and sedimentation, after a three-month storage at room temperature. Fig. 2 shows the results of viscosity of the blends, the compositions of which are shown in Table 4. Blend No. 1 (45% palm oil and 55% mineral oil with no additive) was randomly mixed to predict the viscosity of the mixture. The result shows that the desired viscosity was not reached. Therefore, Blends No. 2 and 3 were performed by addition of the additive package. The viscosity of both blends was satisfactory. However, the portion of palm oil is still less than 50%. Blends No. 4e6 were made by adjusting the compositions of vegetable oil and mineral oil while the additive dosage was kept at 7.24 %wt. The results show that an increase in palm oil fraction tended to reduce the viscosity of the blends. The same trend was observed for Blends No. 7e10, with an additive dosage of 7.80 %wt. This is due to the fact that the viscosity of vegetable oil is considerably lower than that of mineral oil, being typically 8.65 cSt and 32.51 cSt at 100 C, respectively. The viscosity indices of palm oil and mineral oil were 187.00 and 96.15, respectively. Higher viscosity index of palm oil results in higher viscosity index of the blend. This is attributed to the fact that palm oil, which contains triglycerides, has a narrow molecular weight distribution. On the contrary, mineral oil contains a mixture of various molecular weight hydrocarbons. The molecular interaction of vegetable oil also results in higher viscosity index [3]. Oils with high viscosity index can resist excessive thickening when the engine is cold. This leads to better engine starting, promoting prompt lubrication circulation [11]. It also prevents excessive thinning when the engine is hot and thus provides full lubrication to protect the rubbing surfaces. Therefore, vegetable oil can provide this advantage when used as a base stock for lubricants. After the blends of palm oil and mineral oil were made and the desired viscosity was reached, additional property tests of the selected blend, Blend No. 9, were conducted for its flash point, volatility loss, sulfate ash, foaming, and wear scar. The results are shown in Table 1. Although palm oil and mineral oil show nearly the
Table 1 Physical properties of base stocks, commercial oil, and Blend No. 9. Properties
Palm oil
Mineral oil
Commercial oil
Blend No. 9
Method
Viscosity, cSt At 40 C At 100 C
42.66 0.05 8.65 0.02
503.40 0.05 32.51 0.02
151.60 0.06 15.00 0.02
111.60 0.07 15.04 0.01
ASTM D445
Viscosity index Flash point, C Volatility loss, wt.% Sulfate ash, wt.%
187.00 304.3 1.3 0.09 0.01 0.007 0.01
96.15 302.0 1.0 12.98 0.05 1.52 0.02
99.00 256.0 2.0 3.07 0.03 0.99 0.03
140.00 278.0 0.3 2.64 0.03 1.10 0.02
ASTM ASTM ASTM ASTM
Foaming, ml/ml Sequence I Sequence II Sequence III
210/0 /0 60/0
200/0 30/0 270/0
20/2 240/0 10/0
490/310 300/50 190/10
ASTM D892
Wear scar, mm
0.58 0.01
0.95 0.01
0.60 0.01
0.34 0.02
ASTM D4172
D2270 D92 D5800B D874
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K. Cheenkachorn, B. Fungtammasan / Energy 35 (2010) 2552e2556 20.0
100
7.24 % additve
Blend No.2
90
7.80 % additve
Blend No.3
18.0
60 50 40 30
Blend No.9
14.0
9.09 % additve
Blend No.4
Blend No.10
16.0
70
Viscosity (cSt)
Velocity (km hr-1)
80
No additive
Blend No.5
Blend No.8 Blend No.6
Blend No.7
12.0 10.0
20
Blend No.1
8.0
10 0
6.0 0
200
400
600
800
1000
1200
1400
1600
1800
30
40
50
Time (s)
60
70
80
% Palm oil
Fig. 1. The Bangkok driving cycle for motorcycles.
Fig. 2. Viscosity of various blends at 100 C (ASTM D445).
same flash point temperature, blending the two oils (Blend No. 9) results in unexpectedly lower flash point than the two oils. This is possibly due to the presence of the additive package. Nevertheless, the flash point of the blend is still higher than that of the commercial oil, which is desirable. Since the lubricant is exposed to severe conditions, it may result in “volatility loss”, that is, loss of some light-weight hydrocarbon fractions while leaving behind the heavy-weight molecules. This leads to an increase in lubricant viscosity, which contributes to poor circulation, increased oil consumption, wear and emissions [12]. The volatility loss data obtained by the NOACK test indicates that Blend No. 9 has a lower loss than commercial oil. This could be due to the fact that the molecular weight distribution of Blend No. 9 has a narrower range than commercial oil. Sulfate ash is a product of the combustion of sulfur present in fuels and lubricants. Pure palm oil shows extremely low sulfate ash. However, Blend No. 9 shows higher sulfate ash than commercial oil. This is because of the presence of additive package which contains sulfur. The result agrees with the previous study by Colclough [13], which demonstrated that the main additives used in automotive lubricants, i.e., zinc dithiophosphates (ZDDP), can lead to catalytic converter poisoning. Higher sulfate ash oil contributes to an increase in particulate matter in the exhaust gas emission. A previous study demonstrated that sulfate may originate from both fuel and oil [14]. In general, the contents of sulfur in fuel and oil are 500 and 5000 ppm, respectively. The consumption ratio of fuel to oil is 1000:1. When a sulfur balance is applied to the engine fuel and oil, it was found that 99% of sulfate ash originated from the fuel and only 1% originated from the oil [15]. Foaming characteristics of selected blends were also shown in Table 1. Foaming in the lubricant is caused by the presence of water in the base oil or some chemicals such as air, grease, solid contaminants, etc. The results show that Blend No. 9 shows relatively higher foaming characteristics than commercial oil for all sequences. This may be resulted from the incompatibility between the antifoam agent in the additive package and vegetable oil. A new additive package should, therefore, be investigated. The use of this formulated blend in applications that incur foaming such as gear oil
and compressor oil should be avoided since foaming increases oxidation and reduces oil flow to the bearing [11]. The results from wear scar diameter, Table 1, show that palm oil and the commercial oil are not significantly different. Compared to the commercial oil, an addition of additive package in Blend No. 9 significantly improves wear scar. Vegetable oils are by their chemical nature long chain fatty acid triester of glycerol. The polar ester structure in vegetable oil is able to interact with the metal surfaces, leading to better wear property. The antiwear additive also forms a protective layer on the metal parts. Therefore, a good lubricity and wear property is obtained.
Table 3 The Bangkok driving cycle for motorcycles. Details
Phase I
Phase II
Phase III
Total
Distance (km) Time (s) Average velocity (km/h)
3.260 520 23.4
3.298 368 33.2
6.594 568 42.9
12.852 1456 33.5
3.2. Emission tests The results of emission measurements from the test vehicle based on the Bangkok Driving Cycle for motorcycle are summarized in Table 5. The data shows that, for all phases, the biodegradable lubricant (Blend No. 9) showed no significant difference in all emissions compared to those of commercial oil. For the biodegradable lubricant, the THC emission levels appear in the ascending order as follows: Phase III, Phase I, and Phase II. In Phases II and III, the biodegradable lubricant show slightly less THC emission than commercial oil. This is possibly due to the less volatility loss of palm oil-based lubricant during hot warming periods. One of the main sources of nitrogen oxide (NOx) emissions from the combustion engine is the oxidation of atmospheric nitrogen within the cylinder, which is directly proportional to the flame temperature. As shown in Table 5, for biodegradable lubricant, the NOx emission levels for the driving pattern are in the descending order as follows: Phase I, Phase III, and Phase II. The thickness of lubricant film in a combustion chamber varies from one phase to Table 4 Composition of various blends. Blends No.
1 2 3 4 5 6 7 8 9 10
Compositions (wt.%) Percent palm oil
Percent mineral oil
Percent additive
45.00 41.74 40.91 55.66 60.30 64.94 57.90 52.90 50.60 41.20
55.00 51.02 50.00 37.11 32.47 27.40 34.30 39.30 41.60 51.00
0 7.24 9.09 7.24 7.24 7.24 7.80 7.80 7.80 7.80
K. Cheenkachorn, B. Fungtammasan / Energy 35 (2010) 2552e2556 Table 5 The exhaust emissions from the tested vehicle on a chassis dynamometer. Fuel
Phase I (g/km)
Phase II (g/km)
Phase III (g/km)
Average (g/km)
THC
Blend No. 9 Commercial lubricant
0.277 0.270
0.261 0.283
0.288 0.291
0.279 0.284
NOx
Blend No. 9 Commercial lubricant
0.202 0.189
0.179 0.180
0.198 0.195
0.194 0.190
CO
Blend No. 9 Commercial lubricant
7.006 7.081
6.793 6.975
7.773 7.769
7.336 7.398
CO2
Blend No. 9 Commercial lubricant
34.332 33.983
29.061 28.958
30.054 29.790
30.874 30.630
7 6 5
Power output (kW)
Emission
2555
4 3 2
Blend No.9 Commercial lubricant
1 0 0
another depending on the engine temperature. The fact that Phase I shows highest NOx emission may result from the presence of thin film of lubricant in the cylinder during a warm-up period. The oxygen in lubricant may shift air/fuel ratio in favor of more NOx emission [16]. In Phases II and III, where engine temperature is higher compared to that of Phase I, a thinner film of lubricant is formed at the cylinder wall. Therefore, the effect of the oxygen presence in the lubricant is less pronounced. Compared to Phase II, NOx emission in Phase III is higher. This is because, in Phase III, the engine is operating at higher shift and vehicle speed leading to more throttle-valve opening. This results in intense combustion and hence higher combustion temperature, which lead to higher NOx emission [17]. Compared to biodegradable oil, commercial oil shows slightly lower NOx emission in Phase I which may be explained by the same reason. However, such difference was not observed in Phases II and III. The amount of CO emissions for both lubricants decreases in the descending order as follows: Phase III, Phase I, and Phase II. The biodegradable lubricant shows slightly lower CO emissions in Phases I and II than commercial oil. The oxygen in vegetable oil may lead to more complete combustion, and hence lower CO emissions. The results agree with a previous study [18] that lower aromatic content in both fuel and oil results in lower CO and THC. This beneficial effect of biodegradable lubricant agrees with the study of Weller et al. [16]. Carbon dioxide (CO2) emissions from both lubricants show a decreasing tendency from Phases I, II, to III. The higher speed drive leads to higher combustion efficiency resulting in higher CO2 emission. However, no substantial difference in CO2 emission was observed between the two lubricants.
10
20
30
40
50
60
Vechicle speed (km hr-1) Fig. 3. The power output at different speed.
groups on metal surfaces. However, the results on the fuel consumption in this study show no significant difference between biodegradable and commercial lubricants. One plausible explanation for this result could be the fact that the percentage of vegetable oil present in this biodegradable lubricant was limited to 50.60%. Hence, the improved lubricity that would have led to less fuel consumption was not clearly observed.
3.4. Engine performance Fig. 3 shows the power output at different engine speeds, which were converted from the vehicle speed. For chassis dynamometer, the maximum power is referred to as the maximum rotational power that the chassis dynamometer can be subjected to and still operate within specifications. To obtain the maximum power output from the engine of the tested vehicle at each speed, the chassis dynamometer is used to maintain a specified vehicle speed while the maximum load is performed and measured. This power output is different from an engine dynamometer since it includes frictional and mechanical losses in a driveetrain system. No significant difference was observed from the use of different lubricants. The results agree with those from the fuel consumption results. Since the amount of vegetable oil in the blend is 50.60%, the beneficial effect of vegetable oil was not obviously seen.
4. Conclusion 3.3. Fuel consumption The effect of lubricants on fuel consumption of the four-stroke motorcycle from the Bangkok driving cycle is shown in Table 6. The fuel consumption increases with the vehicle speed due to an increase in the frictional loss. The experimental results on friction and wear tests in the previous study [19] showed that the use of vegetable oil as a base stock for biodegradable lubricant results in lower friction and wear scar diameter due to the affinity of polar
Table 6 The fuel consumption in each phase. Phase
Phase I Phase II Phase III Average
Fuel consumption (km/L) Blend No. 9
Commercial lubricant
50.48 57.51 54.03 53.90
50.75 57.16 54.36 54.09
The blends of palm oil, mineral oil, and an additive package were conducted to formulate biodegradable lubricant for four-stroke motorcycle engines. The selected blend consists of 50.6%(wt.) palm oil, 41.6% mineral oil, and 7.8% additive package. The formulated blend shows better properties than commercial oil in terms of viscosity index, flash point, evaporative loss, and wear scar. However, foaming characteristics and sulfate ash are poorer because of the presence of improper additive. From the emission and engine performance tests using the Bangkok driving cycle for a motorcycle, it was found that there is no significant difference in the emissions, including THC, NOx, CO, and CO2, between the biodegradable and commercial lubricants. The engine performance and fuel consumption for both lubricants showed no significant difference either. However, the fact that palm oil-based lubricant is derived from a renewable, lower carbon source and that it offers superior tribological properties (wear scar, viscosity index, etc.), this new formulation could potentially be considered an attractive alternative to mineral oil-based lubricants.
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Acknowledgement The authors gratefully acknowledge the contribution of the Department of Chemical Engineering, King Mongkut’s University of Technology North Bangkok. The contributions of palm oil from Krabi Oil Palm Farmers Co-Op. Ltd., mineral-based oil and the additive package from PTT Public Co. Ltd., and the provision of engine test facilities from the Pollution Control Department are greatly appreciated. References [1] Dowson D. History of tribology. London, UK: Professional Engineering Publishing; 1998. [2] Dorinson A, Ludema KC. Mechanics and chemistry in lubrication tribology series 9. Amsterdam, the Netherlands: Elsevier; 1985. [3] Masjuki HH, Maleque MA, Kubo A, Nonaka T. Palm oil and mineral oil based lubricantsdtheir tribological and emission performance. Tribology International 1999;32:305e14. [4] Wan Nik WB, Ani FN, Masjuki HH, Eng Giap SG. Rheology of bio-edible oils according to several rheological models and its potential as hydraulic fluid. Industrial Crops and Products 2005;22:249e55. [5] Kodali DR. High performance ester lubricants from natural oils. Industrial Lubrication and Tribology 2004;54(4):165e70. [6] Goyan RL, Melley RE, Wissner PA, Ong WC. Biodegradable lubricants. Lubrication Engineering 1998;54(7):10e7. [7] Fuks IG, Yu A, Evdokimov AA, Luksa A. Vegetable oils and animal fats as raw materials for manufacture of commercial. Chemistry and Technology of Fuels and Oils 1992;4:203e7.
[8] Motorcycle market in Thailand. Available at: