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Examination of lubricant oil components affecting the formation of combustion chamber deposit in a two-stroke engine
JSAE Review 22 (2001) 281–285
Examination of lubricant oil components affecting the formation of combustion chamber deposit in a two-stroke engine Masato Fukuia, Tadafumi Satob, Naotake Fujitac, Michio Kitanoc b
a Graduate Student, Iwate University, 4-3-5, Ueda Morioka, Iwate 020-8551, Japan Iwate Industrial Technology Junior College, 10-3-1, Minamiyahaba, Yahaba, Shiwa, Iwate 028-3615, Japan c Iwate University, 4-3-5, Ueda Morioka, Iwate 020-8551, Japan
Received 6 February 2001; received in revised form 29 March 2001
Abstract In this study, influence of fuel and lubricant oil components on the combustion chamber deposit (CCD) formation was investigated using both a two-stroke engine and an autoclave. The results obtained show that the influence of lubricant oil on CCD formation was greater than that of the fuel and most CCD was formed from the detergent dispersant added to the lubricant oil. In particular the metallic detergent formed a larger amount of CCD than the ashless dispersant. The influence of deposit formation under the low-pressure condition on CCD accumulation at the engine appeared to be greater than that of deposit formation under the high-pressure condition. r 2001 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved.
1. Introduction The two-stroke engine has kept a high market share for mopeds, small utility engines and handheld equipment because of its superiority in specific power and convenience. However, it has a problem of producing a large amount of combustion chamber deposit (CCD). It is known that excessively accumulated CCD generally causes an increase in the octane requirement [1] and NOx emission in the exhaust gas [2]. It is also reported that the formation in a squish area clearance causes mechanical interference between the piston crown and the cylinder head [3]. In addition, the states of lubrication and wear will become serious if the deposit which comes off the combustion chamber wall should enter into the rubbing surface between the piston and the cylinder liner [4,5]. The CCD formation thus spoils performance, reliability and maintainability of the engine and is disadvantageous in the circumstances that the emission regulations are applied to mopeds and utility engines [6]. Accordingly, reducing the CCD formation is an important problem to be solved for making use of the characteristics of two-stroke engines. Many studies have been made concerning the cleanliness of combustion chamber in a two-stroke engine, Fujimoto et al. [7] investigated the influences of additives and base oils and proposed a prototype lubricant oil with harmonious detergency. We also
discussed the relationship between the operating conditions and the CCD formation in a two-stroke engine [8], but the conditions of CCD formation and the fuel or oil components from which deposits were derived were not quantitatively observed. However experiments on the CCD formation were conducted using the apparatus which simulated the quench area near the combustion chamber wall and the autoclave which offered the circumstances of the high temperature and pressure without combustion, and aromatic hydrocarbons and hydrocarbons with high boiling point in fuels were shown to be key components for the CCD formation [9,10]. From the results obtained using infrared absorption spectroscopy and solid state 13 C nuclear magnetic resonance spectroscopy, it was also shown that the CCD was an oxidative condensation polymer of aromatic hydrocarbons [9,11]. Most of the studies on the CCD formation factors, however, dealt with four-stroke engines, and only a few studies were made on two-stroke engines, which had a unique mechanism that fuel and lubricant oil are supplied together into the cylinder. In this study, the deposit weight on the piston crown surface was measured using a two-stroke utility engine, and the relative contribution of fuel and lubricant oil to the CCD formation was discussed. The weight of the deposits derived from fuels, lubricant oils and detergent dispersants was also measured using an autoclave with
0389-4304/01/$20.00 r 2001 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved. PII: S 0 3 8 9 - 4 3 0 4 ( 0 1 ) 0 0 1 1 5 - 1
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the above-mentioned characteristics, and the results were compared with the CCD formation data in the engine test
2. Experimental apparatus and procedure 2.1. Engine test The test engine in this experiment was an air-cooled single cylinder two-stroke SI engine whose displacement was 175 cm3, and an AC electric dynamometer was used to control engine speed and power. In order to weigh the deposit on the piston crown surface, the piston was separated into two parts, the main body and the crown, as shown in Fig. 1. Test fuels were regular gasoline available on the market and i-octane. A latter was used to examine the influence of unsaturated hydrocarbons included in gasoline. Two types of lubricant oil, available on the market for two-stroke engines (Oil A) and base oil containing no detergent dispersants (Oil B) were used. Two other lubricant oils made of the base oil were also used. One contained metallic detergent (calcium sulfonate type) of 7wt% (Oil C) and the other contained ashless dispersant (succinimide type) of 7wt% (oil D). Properties of Oil A and Oil B are shown in Table 1. A separate oiling system was adopted to supply the lubricant oil at any rate. Oil was introduced immediately before the suction port with a motor pump. The engine operating conditions were: stoichiometric ratio, engine speed of 2200 min 1, delivery ratio of 0.40
and lubricant oil supply rate of 0.95 cm3 min 1. For these conditions, the engine was operated for 2.5 h, including 15 minutes idling for the warm-up and for the cool-down, and the operation was repeated twice. After the operation, the crown part was detached from the separate piston and washed with gasoline and acetone, and then dried completely. The crown was weighed using an electronic force balance, and the CCD weight was obtained as the weight difference between before and after the operation. Elemental analysis of the CCD sample scraped from the piston crown was also made qualitatively with an electron probe X-ray microanalyzer (EPMA). 2.2. Autoclave test A schematic diagram of the experimental apparatus for autoclave test is shown in Fig. 2. Compressed-air cylinder, check valve and autoclave were connected in series by a high-pressure hose, and the autoclave was pressurized with the compressed air in the cylinder. Cartridge heaters were inserted in the autoclave to heat up the test cell and control its temperature. Inside pressure of the autoclave was indicated with a strain gauge type transducer, and inner wall temperature of the test cell was measured at its bottom using a sheathed type thermocouple to represent the temperature of the Table 1 Properties of test lubricant oils Oil A Specific gravity Kinematic viscosity (mm2/s) at 401C at 1001C Viscosity index Flash point (1C) Pour point (1C) Total base Number (mgKOH/g) Detergent dispersant (wt%)
Fig. 1. Schematic diagram of separate piston.
Oil B
0.858 41.0 7.35 153 98 30 2.4 7
Fig. 2. Schematic diagram of experimental-apparatus.
0.855 36.0 7.35 175 100 30 0 0
M. Fukui et al. / JSAE Review 22 (2001) 281–285
deposit formation field. A pen recorder was used to log the data of pressure and temperature. Reagents used in this experiment and the engine test were the same: regular gasoline, Oil A and Oil B. In addition, detergent dispersants (metallic detergent and ashless dispersant) contained in Oil A were also used. The procedure of autoclave test is as follows: set the test cell containing reagent of 100 mg in the autoclave; pressurize the inside of the autoclave at an initial condition using the compressed-air cylinder; heat up and keep the inner wall of test cell bottom at a stated temperature by cartridge heaters; keep this condition for 30 min; cool down the whole autoclave rapidly to below the temperature at which the reagent evaporates in the atmosphere; the pressure in the autoclave to atmospheric pressure. After the test, the test cell taken out of the autoclave was washed with gasoline and acetone and dried. The test cell was weighed using an electronic force balance, and the weight difference between before and after the test was calculated as the deposit weight.
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the CCD sample with the physical vapor deposition of aurum. Fig. 4 shows that the CCD weight derived from Oil C was about 80 mg, over twice as heavy as that derived from Oil A. On the other hand, the CCD derived from Oil D was about 15 mg, under half as heavy as that derived from Oil A. Consequently, the lubricant oil containing detergent of calcium sulfonate type affected the CCD formation more than that containing dispersant of succinimide type. Also both sulfur and calcium were detected in the CCD derived from Oil A, as shown in Fig. 5(a). Fig. 5(b) shows that the same elements were also detected in the CCD derived from Oil C; but not detected in that derived from Oil D, as shown in Fig. 5(c). Hence, the sulfur and the calcium included in the CCD accumulated in the operation with Oil A were found to be derived from the detergent of calcium sulfonate type. Considering these results, it can be said that most of the CCD, was formed from the detergent dispersant added to the lubricant oil, and that the
3. Experimental results and discussion 3.1. Engine test In order to investigate the influences of fuel and lubricant oil on the CCD weight, the engine was operated with gasoline and i-octane as fuel and Oil A and Oil B as lubricant oil. Results are shown in Fig. 3. In the operation with i-octane, the CCD weight was about 35 mg for Oil A but the CCD was scarcely formed for Oil B. Also in the operation with gasoline, the CCD of about 39 mg was accumulated for Oil A but the CCD weight was only about 3 mg for Oil B. Therefore, the influence of detergent dispersants in lubricant oil on the CCD accumulation was found to be larger than that of unsaturated hydrocarbons included in the fuel. For the purpose of examining the influence of detergent dispersant on the CCD formation, the engine was operated with i-octane as fuel and Oil A, Oil C and Oil D as lubricant oil. Fig. 4 shows the CCD weight accumulated. The elemental analysis of CCD derived from these lubricant oils are shown in Fig. 5. The detection of aurum element is due to the pretreatment of
Fig. 3. Influence of fuel and lubricant oil on CCD formation.
Fig. 4. Comparison of CCD formation among detergent dispersants.
Fig. 5. Elemental analysis of CCD using EPMA.
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metallic detergent exerted greater influence than the ashless dispersant.
3.2. Autoclave test The influence of test cell surface temperature on the deposit formation for gasoline and Oil A at the autoclave pressure of 1.5 MPa is shown in Fig. 6. The deposit derived from gasoline was formed within the temperature range between 1501C and 3501C, and its weight was about 5 mg in the range between 2001C and 3251C. The lower temperature limit for the deposit formation from Oil A was almost 1501C, which was the same as gasoline, and the deposit weight increased to about 10 mg with the temperature increase up to nearly 2251C. The deposit weight was between 5 to 10 mg for the temperature above 2251C, and it showed no decrease even at the temperature of 3501C, the upper limit of deposit formation for gasoline. Setting the temperature above 3501C was impossible due to the performance of heaters, and further study will be required to investigate the upper temperature limit of reagent which still formed a deposit at high temperatures above 3501C. In the engine test which examined the deposit weight on the piston crown, Oil A formed much more deposit than gasoline. However, the deposit weight difference between gasoline and Oil A in the autoclave test was not as large as that in the engine test, as shown in Fig. 6. The piston crown temperature of the test engine was estimated to be between 2001C and 3001C, since its combustion chamber wall temperature was between 2001C and 2701C, and the durability of the piston dropped off for the piston temperature over 3001C in general [12,13]. In this range of temperature in the autoclave test, there existed little distinction between tendencies of deposit formation for gasoline and Oil A. The reason why Oil A formed much more CCD than gasoline in the engine test was not, therefore, attributable to the difference between the temperature characteristics of deposit formation for both reagents. Instead, the reason seems to be related to the fact that, in the quench area, Oil A can exist in greater quantities compared with gasoline having high volatility.
Fig. 6. Influence of temperature on deposit formation for gasoline and lubricant Oil A at chamber pressure of 1.5 MPa.
Figs. 7 and 8 show the influence of test cell surface temperature on the deposit formation for Oil A and Oil B, and for metallic detergent and ashless dispersant, respectively, at the autoclave pressure of 1.5 MPa. Judging from Fig. 7, the lower temperature limits of the deposit formation for Oil A and Oil B were about 1501C whether they contained detergent dispersants or not, and the deposit weights formed from them were also nearly the same for the higher temperature. However, the lower temperature limit of the deposit formation for detergent dispersants was almost 2101C and was higher than the limits for Oil A and Oil B, as shown in Fig. 8. Furthermore, the weight of deposit from the ashless dispersant was a little larger than that from metallic detergent, although both weights increased with temperature up to 2751C and fluctuated in the range from 3001C to 3251C. The conversion ratio from the detergent dispersant to the deposit was about 30%, which implied that the deposit weight formed from detergent dispersants of 7% included in Oil A was only about 2 mg by a simple estimation. Therefore, this was the reason why Oil A and Oil B containing no detergent dispersants showed a similar tendency of deposit formation, as illustrated in Fig. 7. Incidentally, in the engine test, the influence of metallic detergent on the CCD formation was more remarkable than that of ashless dispersant. In the autoclave test , however, the ashless dispersant generally
Fig. 7. Influence of temperature on deposit formation for lubricant Oil A and Oil B at chamber pressure of 1.5 MPa.
Fig. 8. Influence of temperature on deposit formation for metallic detergent and ashless dispersant at chamber pressure of 1.5 MPa.
M. Fukui et al. / JSAE Review 22 (2001) 281–285
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(2) The metallic detergent formed deposit less than the ashless dispersant at high-pressure condition; however, this relation was reversed under low-pressure condition. (3) Deposit formation under the low-pressure condition dominated CCD formation in an engine compared with that under the high-pressure condition.
Acknowledgements Fig. 9. Influence of pressure on deposit weight produced by detergent dispersant at cell surface temperature of 2751C.
tended to form a heavier deposit than the metallic detergent under the high-pressure condition, as shown in Fig. 8. Accordingly, it seems that the temperature characteristics of deposit formation under the highpressure condition did not affect the difference of CCD weight between the two lubricant oils in the test engine. Fig. 9 shows the influence of in-autoclave pressure on the deposit weight formed from the metallic detergent and the ashless dispersant at the test cell surface temperature of 2751C. At the pressure of 1.5 MPa, the ashless dispersant formed significantly more deposit compared with the metallic detergent. At low pressure, the metallic detergent formed more deposit than the ashless dispersant, in particular, at the pressure of 0.1 MPa, almost no deposit formation from the ashless dispersant was observed. In the engine test, the maximum in-cylinder pressure of the test engine was about 1 MPa for the motoring cycle, and the higher pressure was indicated over a range of about 50 deg CA, which was only 15% of all the operating time for a cycle in the conventional operation. Consequently, the lowpressure condition dominated the CCD accumulation rather than the high-pressure condition in the engine, which made the metallic detergent more remarkable in the influence on the deposit formation than the ashless dispersant.
4. Conclusion The CCD weight and the characteristics of deposit formation from fuels, lubricant oils and detergent dispersants were investigated using a two-stroke utility engine and an autoclave apparatus. The results obtained were as follows: (1) The influence of lubricant oil on CCD formation was greater than that of fuel and most CCD was formed from the detergent dispersant added to the lubricant oil. In particular the metallic detergent formed a larger amount of CCD than the ashless dispersant.
The authors would like to thank Mr. Y. Maruka of Fuji Heavy Industries Ltd. and Mr. S. Shido of Idemitsu Kosan Co. Ltd. for their support on this study. The authors also express many thanks to Mr. T. Kuwajima of the Iwate Industrial Research Institute and his colleagues; H. Yoshida, R. Iwabuchi, O. Arakawa, S. Usui, M. Kosegawa and J. Takahashi in the Power System Engineering Laboratory of Iwate University for their assistance in experiments and analyses.
References [1] Price, R.J. et al., Prediction of combustion chamber deposit growth in SI engines, SAE Trans. , Vol. 106, No. 4, pp. 612–624 (l997). [2] Omata, T. et al., Analytical studies of combustion chamber deposit and effects of CCDs on emissions, SAE Paper, No. 971721 (1997). [3] Moore, S.M., Combustion chamber deposit interference effects in late model vehicles, SAE Trans., Vol. 103, No. 4, pp. 81–94 (1994). [4] Fujita, N. et al., Tribology for small 2 stroke cycle spark ignition engine fueled by methanol (in Japanese with English summary), JSME Trans. C, Vol. 60, No. 571, pp. 229–304 (1994). [5] Saito T, Bore polishing related to the engine oil properties F(in Japanese), JUNKATU, J JSLE, Vol. 27, No. 5, pp. 392–394 (1982). [6] Ministry of the Environment, Government of Japan, News release (in Japanese), 31 March 1997. [7] Fujimoto,Y., A study of 2-stroke engine lube problems (in Japanese with English summary), JUNKATU, J JSLE, Vol. 14, No. 4, pp. 173–179 (1969) . [8] Iwabuchi, R., et al. Effect of lubricant oil supply and excess air ration on the formation of CCD in a two-stroke cycle engine (in Japanese with English summary), Proc. JSAE, No. 70-98 pp. 17–20 (1998). [9] Uehara, T., et al., Study on combustion chamber deposit formation, SAE Trans., Vol. 106, No. 4, pp. 741–759 (1997). [10] Price, R.J., et al., A laboratory simulation and mechanism for the fuel dependence of SI combustion chamber deposit formation, SAE Trans., Vol. 104, No. 4, pp. 1364–1379 (1995). [11] Kelemen, S.R., et al., Fuel, lubricant and additive effects on combustion chamber deposits, SAE Paper, No. 982715 (1998). [12] Huruhama, S., Internal combustion engine (in Japanese), pp. 268– 270, Morikita Shuppan Co., Ltd. (1979). [13] Someya, T., et al., Lubrication of internal combustion engine (in Japanese), pp. 54–63, Saiwai Syobou Co., Ltd. (1988).
Examination of lubricant oil components affecting the formation of combustion chamber deposit in a two-stroke engine Masato Fukuia, Tadafumi Satob, Naotake Fujitac, Michio Kitanoc b
a Graduate Student, Iwate University, 4-3-5, Ueda Morioka, Iwate 020-8551, Japan Iwate Industrial Technology Junior College, 10-3-1, Minamiyahaba, Yahaba, Shiwa, Iwate 028-3615, Japan c Iwate University, 4-3-5, Ueda Morioka, Iwate 020-8551, Japan
Received 6 February 2001; received in revised form 29 March 2001
Abstract In this study, influence of fuel and lubricant oil components on the combustion chamber deposit (CCD) formation was investigated using both a two-stroke engine and an autoclave. The results obtained show that the influence of lubricant oil on CCD formation was greater than that of the fuel and most CCD was formed from the detergent dispersant added to the lubricant oil. In particular the metallic detergent formed a larger amount of CCD than the ashless dispersant. The influence of deposit formation under the low-pressure condition on CCD accumulation at the engine appeared to be greater than that of deposit formation under the high-pressure condition. r 2001 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved.
1. Introduction The two-stroke engine has kept a high market share for mopeds, small utility engines and handheld equipment because of its superiority in specific power and convenience. However, it has a problem of producing a large amount of combustion chamber deposit (CCD). It is known that excessively accumulated CCD generally causes an increase in the octane requirement [1] and NOx emission in the exhaust gas [2]. It is also reported that the formation in a squish area clearance causes mechanical interference between the piston crown and the cylinder head [3]. In addition, the states of lubrication and wear will become serious if the deposit which comes off the combustion chamber wall should enter into the rubbing surface between the piston and the cylinder liner [4,5]. The CCD formation thus spoils performance, reliability and maintainability of the engine and is disadvantageous in the circumstances that the emission regulations are applied to mopeds and utility engines [6]. Accordingly, reducing the CCD formation is an important problem to be solved for making use of the characteristics of two-stroke engines. Many studies have been made concerning the cleanliness of combustion chamber in a two-stroke engine, Fujimoto et al. [7] investigated the influences of additives and base oils and proposed a prototype lubricant oil with harmonious detergency. We also
discussed the relationship between the operating conditions and the CCD formation in a two-stroke engine [8], but the conditions of CCD formation and the fuel or oil components from which deposits were derived were not quantitatively observed. However experiments on the CCD formation were conducted using the apparatus which simulated the quench area near the combustion chamber wall and the autoclave which offered the circumstances of the high temperature and pressure without combustion, and aromatic hydrocarbons and hydrocarbons with high boiling point in fuels were shown to be key components for the CCD formation [9,10]. From the results obtained using infrared absorption spectroscopy and solid state 13 C nuclear magnetic resonance spectroscopy, it was also shown that the CCD was an oxidative condensation polymer of aromatic hydrocarbons [9,11]. Most of the studies on the CCD formation factors, however, dealt with four-stroke engines, and only a few studies were made on two-stroke engines, which had a unique mechanism that fuel and lubricant oil are supplied together into the cylinder. In this study, the deposit weight on the piston crown surface was measured using a two-stroke utility engine, and the relative contribution of fuel and lubricant oil to the CCD formation was discussed. The weight of the deposits derived from fuels, lubricant oils and detergent dispersants was also measured using an autoclave with
0389-4304/01/$20.00 r 2001 Society of Automotive Engineers of Japan, Inc. and Elsevier Science B.V. All rights reserved. PII: S 0 3 8 9 - 4 3 0 4 ( 0 1 ) 0 0 1 1 5 - 1
JSAE20014342
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M. Fukui et al. / JSAE Review 22 (2001) 281–285
the above-mentioned characteristics, and the results were compared with the CCD formation data in the engine test
2. Experimental apparatus and procedure 2.1. Engine test The test engine in this experiment was an air-cooled single cylinder two-stroke SI engine whose displacement was 175 cm3, and an AC electric dynamometer was used to control engine speed and power. In order to weigh the deposit on the piston crown surface, the piston was separated into two parts, the main body and the crown, as shown in Fig. 1. Test fuels were regular gasoline available on the market and i-octane. A latter was used to examine the influence of unsaturated hydrocarbons included in gasoline. Two types of lubricant oil, available on the market for two-stroke engines (Oil A) and base oil containing no detergent dispersants (Oil B) were used. Two other lubricant oils made of the base oil were also used. One contained metallic detergent (calcium sulfonate type) of 7wt% (Oil C) and the other contained ashless dispersant (succinimide type) of 7wt% (oil D). Properties of Oil A and Oil B are shown in Table 1. A separate oiling system was adopted to supply the lubricant oil at any rate. Oil was introduced immediately before the suction port with a motor pump. The engine operating conditions were: stoichiometric ratio, engine speed of 2200 min 1, delivery ratio of 0.40
and lubricant oil supply rate of 0.95 cm3 min 1. For these conditions, the engine was operated for 2.5 h, including 15 minutes idling for the warm-up and for the cool-down, and the operation was repeated twice. After the operation, the crown part was detached from the separate piston and washed with gasoline and acetone, and then dried completely. The crown was weighed using an electronic force balance, and the CCD weight was obtained as the weight difference between before and after the operation. Elemental analysis of the CCD sample scraped from the piston crown was also made qualitatively with an electron probe X-ray microanalyzer (EPMA). 2.2. Autoclave test A schematic diagram of the experimental apparatus for autoclave test is shown in Fig. 2. Compressed-air cylinder, check valve and autoclave were connected in series by a high-pressure hose, and the autoclave was pressurized with the compressed air in the cylinder. Cartridge heaters were inserted in the autoclave to heat up the test cell and control its temperature. Inside pressure of the autoclave was indicated with a strain gauge type transducer, and inner wall temperature of the test cell was measured at its bottom using a sheathed type thermocouple to represent the temperature of the Table 1 Properties of test lubricant oils Oil A Specific gravity Kinematic viscosity (mm2/s) at 401C at 1001C Viscosity index Flash point (1C) Pour point (1C) Total base Number (mgKOH/g) Detergent dispersant (wt%)
Fig. 1. Schematic diagram of separate piston.
Oil B
0.858 41.0 7.35 153 98 30 2.4 7
Fig. 2. Schematic diagram of experimental-apparatus.
0.855 36.0 7.35 175 100 30 0 0
M. Fukui et al. / JSAE Review 22 (2001) 281–285
deposit formation field. A pen recorder was used to log the data of pressure and temperature. Reagents used in this experiment and the engine test were the same: regular gasoline, Oil A and Oil B. In addition, detergent dispersants (metallic detergent and ashless dispersant) contained in Oil A were also used. The procedure of autoclave test is as follows: set the test cell containing reagent of 100 mg in the autoclave; pressurize the inside of the autoclave at an initial condition using the compressed-air cylinder; heat up and keep the inner wall of test cell bottom at a stated temperature by cartridge heaters; keep this condition for 30 min; cool down the whole autoclave rapidly to below the temperature at which the reagent evaporates in the atmosphere; the pressure in the autoclave to atmospheric pressure. After the test, the test cell taken out of the autoclave was washed with gasoline and acetone and dried. The test cell was weighed using an electronic force balance, and the weight difference between before and after the test was calculated as the deposit weight.
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the CCD sample with the physical vapor deposition of aurum. Fig. 4 shows that the CCD weight derived from Oil C was about 80 mg, over twice as heavy as that derived from Oil A. On the other hand, the CCD derived from Oil D was about 15 mg, under half as heavy as that derived from Oil A. Consequently, the lubricant oil containing detergent of calcium sulfonate type affected the CCD formation more than that containing dispersant of succinimide type. Also both sulfur and calcium were detected in the CCD derived from Oil A, as shown in Fig. 5(a). Fig. 5(b) shows that the same elements were also detected in the CCD derived from Oil C; but not detected in that derived from Oil D, as shown in Fig. 5(c). Hence, the sulfur and the calcium included in the CCD accumulated in the operation with Oil A were found to be derived from the detergent of calcium sulfonate type. Considering these results, it can be said that most of the CCD, was formed from the detergent dispersant added to the lubricant oil, and that the
3. Experimental results and discussion 3.1. Engine test In order to investigate the influences of fuel and lubricant oil on the CCD weight, the engine was operated with gasoline and i-octane as fuel and Oil A and Oil B as lubricant oil. Results are shown in Fig. 3. In the operation with i-octane, the CCD weight was about 35 mg for Oil A but the CCD was scarcely formed for Oil B. Also in the operation with gasoline, the CCD of about 39 mg was accumulated for Oil A but the CCD weight was only about 3 mg for Oil B. Therefore, the influence of detergent dispersants in lubricant oil on the CCD accumulation was found to be larger than that of unsaturated hydrocarbons included in the fuel. For the purpose of examining the influence of detergent dispersant on the CCD formation, the engine was operated with i-octane as fuel and Oil A, Oil C and Oil D as lubricant oil. Fig. 4 shows the CCD weight accumulated. The elemental analysis of CCD derived from these lubricant oils are shown in Fig. 5. The detection of aurum element is due to the pretreatment of
Fig. 3. Influence of fuel and lubricant oil on CCD formation.
Fig. 4. Comparison of CCD formation among detergent dispersants.
Fig. 5. Elemental analysis of CCD using EPMA.
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metallic detergent exerted greater influence than the ashless dispersant.
3.2. Autoclave test The influence of test cell surface temperature on the deposit formation for gasoline and Oil A at the autoclave pressure of 1.5 MPa is shown in Fig. 6. The deposit derived from gasoline was formed within the temperature range between 1501C and 3501C, and its weight was about 5 mg in the range between 2001C and 3251C. The lower temperature limit for the deposit formation from Oil A was almost 1501C, which was the same as gasoline, and the deposit weight increased to about 10 mg with the temperature increase up to nearly 2251C. The deposit weight was between 5 to 10 mg for the temperature above 2251C, and it showed no decrease even at the temperature of 3501C, the upper limit of deposit formation for gasoline. Setting the temperature above 3501C was impossible due to the performance of heaters, and further study will be required to investigate the upper temperature limit of reagent which still formed a deposit at high temperatures above 3501C. In the engine test which examined the deposit weight on the piston crown, Oil A formed much more deposit than gasoline. However, the deposit weight difference between gasoline and Oil A in the autoclave test was not as large as that in the engine test, as shown in Fig. 6. The piston crown temperature of the test engine was estimated to be between 2001C and 3001C, since its combustion chamber wall temperature was between 2001C and 2701C, and the durability of the piston dropped off for the piston temperature over 3001C in general [12,13]. In this range of temperature in the autoclave test, there existed little distinction between tendencies of deposit formation for gasoline and Oil A. The reason why Oil A formed much more CCD than gasoline in the engine test was not, therefore, attributable to the difference between the temperature characteristics of deposit formation for both reagents. Instead, the reason seems to be related to the fact that, in the quench area, Oil A can exist in greater quantities compared with gasoline having high volatility.
Fig. 6. Influence of temperature on deposit formation for gasoline and lubricant Oil A at chamber pressure of 1.5 MPa.
Figs. 7 and 8 show the influence of test cell surface temperature on the deposit formation for Oil A and Oil B, and for metallic detergent and ashless dispersant, respectively, at the autoclave pressure of 1.5 MPa. Judging from Fig. 7, the lower temperature limits of the deposit formation for Oil A and Oil B were about 1501C whether they contained detergent dispersants or not, and the deposit weights formed from them were also nearly the same for the higher temperature. However, the lower temperature limit of the deposit formation for detergent dispersants was almost 2101C and was higher than the limits for Oil A and Oil B, as shown in Fig. 8. Furthermore, the weight of deposit from the ashless dispersant was a little larger than that from metallic detergent, although both weights increased with temperature up to 2751C and fluctuated in the range from 3001C to 3251C. The conversion ratio from the detergent dispersant to the deposit was about 30%, which implied that the deposit weight formed from detergent dispersants of 7% included in Oil A was only about 2 mg by a simple estimation. Therefore, this was the reason why Oil A and Oil B containing no detergent dispersants showed a similar tendency of deposit formation, as illustrated in Fig. 7. Incidentally, in the engine test, the influence of metallic detergent on the CCD formation was more remarkable than that of ashless dispersant. In the autoclave test , however, the ashless dispersant generally
Fig. 7. Influence of temperature on deposit formation for lubricant Oil A and Oil B at chamber pressure of 1.5 MPa.
Fig. 8. Influence of temperature on deposit formation for metallic detergent and ashless dispersant at chamber pressure of 1.5 MPa.
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(2) The metallic detergent formed deposit less than the ashless dispersant at high-pressure condition; however, this relation was reversed under low-pressure condition. (3) Deposit formation under the low-pressure condition dominated CCD formation in an engine compared with that under the high-pressure condition.
Acknowledgements Fig. 9. Influence of pressure on deposit weight produced by detergent dispersant at cell surface temperature of 2751C.
tended to form a heavier deposit than the metallic detergent under the high-pressure condition, as shown in Fig. 8. Accordingly, it seems that the temperature characteristics of deposit formation under the highpressure condition did not affect the difference of CCD weight between the two lubricant oils in the test engine. Fig. 9 shows the influence of in-autoclave pressure on the deposit weight formed from the metallic detergent and the ashless dispersant at the test cell surface temperature of 2751C. At the pressure of 1.5 MPa, the ashless dispersant formed significantly more deposit compared with the metallic detergent. At low pressure, the metallic detergent formed more deposit than the ashless dispersant, in particular, at the pressure of 0.1 MPa, almost no deposit formation from the ashless dispersant was observed. In the engine test, the maximum in-cylinder pressure of the test engine was about 1 MPa for the motoring cycle, and the higher pressure was indicated over a range of about 50 deg CA, which was only 15% of all the operating time for a cycle in the conventional operation. Consequently, the lowpressure condition dominated the CCD accumulation rather than the high-pressure condition in the engine, which made the metallic detergent more remarkable in the influence on the deposit formation than the ashless dispersant.
4. Conclusion The CCD weight and the characteristics of deposit formation from fuels, lubricant oils and detergent dispersants were investigated using a two-stroke utility engine and an autoclave apparatus. The results obtained were as follows: (1) The influence of lubricant oil on CCD formation was greater than that of fuel and most CCD was formed from the detergent dispersant added to the lubricant oil. In particular the metallic detergent formed a larger amount of CCD than the ashless dispersant.
The authors would like to thank Mr. Y. Maruka of Fuji Heavy Industries Ltd. and Mr. S. Shido of Idemitsu Kosan Co. Ltd. for their support on this study. The authors also express many thanks to Mr. T. Kuwajima of the Iwate Industrial Research Institute and his colleagues; H. Yoshida, R. Iwabuchi, O. Arakawa, S. Usui, M. Kosegawa and J. Takahashi in the Power System Engineering Laboratory of Iwate University for their assistance in experiments and analyses.
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