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water emulsion on heat flow and thermal loading in a precombustion chamber diesel engine
Applied Thermal Engineering 21 (2001) 1565±1582
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Eects of diesel/water emulsion on heat ¯ow and thermal loading in a precombustion chamber diesel engine M.Y.E. Selim a,*, S.M.S. Elfeky b a b
Department of Mechanical Engineering, Faculty of Engineering, United Arab Emirates University, P.O. Box 17555, Al-Ain, United Arab Emirates Department of Mechanical Power Engineering, Faculty of Engineering at Mattaria, Helwan University, Cairo 11718, Egypt Received 6 September 2000; accepted 28 January 2001
Abstract An experimental investigation has been carried out to study the eects of using water/diesel emulsion fuel in an indirect injection diesel engine on the heat ¯ux crossing liner and cylinder head, thermal loading and metal temperature distribution. A single cylinder precombustion chamber diesel engine has been used in the present work. The engine was instrumented for performance, metal temperature and heat ¯ux measurements. The pure gas oil fuel and dierent ratios of water/diesel emulsion were used and their eects on the heat ¯ux level and the injector tip temperature are studied. Two correlation were found for the heat ¯ux crossing the liner and the cylinder head at various water/diesel emulsion ratios, fuelling rate and thermocouple probe locations. It was found that the addition of water to diesel fuel, to control the nitrogen oxides emissions, has great in¯uence on reducing the heat ¯ux, the metal temperatures and thermal loading of combustion chamber components. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Diesel engine; Nitrogen oxides; Water emulsion; Heat ¯ux; Thermal loading
1. Introduction The use of water into diesel engines has a number of possible bene®ts. It has been found by many previous works that it has in¯uence on reducing the peak ¯ame temperature and hence reducing the nitrogen oxides, NOx emissions [1±7]. It has also been shown [8] that adding water may help to improve atomization and mixing, which is attributed to droplet microexplosions [9]. *
Corresponding author. Tel.: +971-3-7051-566; fax: +971-3-7623-158. E-mail address: [email protected] (M.Y.E. Selim).
1359-4311/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 9 - 4 3 1 1 ( 0 1 ) 0 0 0 1 9 - 9
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Nomenclature Ap HFF mf m00f NOx q00 r R r=R S Vp w
piston area (m2 ) heat ¯ux factor (kW=m2 )/[(kg=h m2 ) (m2 =s2 )] ¯ow rate of fuel (kg=h) ¯ow rate of fuel per piston area (mf =Ap ), (kg=h m2 ) nitrogen oxides heat ¯ux (kW=m2 ) radial distance (m) cylinder radius (m) bore ratio percentage of stroke mean piston speed (m=s) water/diesel emulsion ratio, by volume
The improved mixing is due to the increased vaporized fuel jet momentum, giving greater air entertainment into the fuel jet [8]. The improved mixing also assists in the reduction in the NOx emissions from the diusive burning portion of the combustion event as well as reducing the carbon formation. This eect, together with the chemical eect of the water results in an increased ignition delay [8,10]. This promotes an increase in the premixed portion of the combustion process, which decreases the diusive burning and hence also contributes to the reduction in the NOx emissions and carbon formation [7]. There is also considerable evidence that adding water to diesel fuel can reduce the particulate matter PM or smoke emissions [7]. There are three primary methods of introducing water into the diesel engines; water injection into the cylinder using a separate injector, spraying water into the inlet air, and water/diesel emulsions. Although all these methods produced a reduction in NOx but it has been concluded in a review in Ref. [11] that the use of water/diesel emulsion was the most eective technique for the reduction of diesel particulates or smoke, for four stroke DI engines. Mello and Mellor [1] have compared two methods of water admission namely strati®ed diesel± water±diesel injection inside the cylinder and intake manifold fumigation (injecting water into intake manifold). They have compared the experimental NOx results of Kohketsu et al. [5] with their modeling using a two-zone characteristic time model which is based on the dominant physical and chemical subprocesses occurring in the cylinder. They have used a fuel injection pump and water injection pump with a hybrid injection nozzle to inject the water pulse between two fuel pulses. For the intake manifold fumigation, it is claimed that it resulted in a presumably uniform distribution of water vapor in the cylinder at the time of combustion. The vaporization of water occurs as the water and air are heated through the compression stroke. However, diesel/ water emulsion reduced NOx slightly more than fumigation method. Christensen and Johansson [2] also used the intake manifold fumigation by using a common low pressure fuel injector, however, they have found that both carbon monoxide and hydrocarbons increased with water injection. Andrews et al. [7] used an emulsifying agent, Arlacel C, to create the diesel/water emulsion and suggested that ordinary liquid soap may be used.
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There is growing interest in diesel fuel industry to produce and utilize the diesel/water emulsion as ordinary fuel for diesel engines. Fuel additive manufacturers are trying to make diesel oil and water to mix, or at least they can be neighborly enough to form a pollution-cutting diesel fuel. There have been trials to produce a very stable emulsion that stays in suspension over a long period of time. If the fuel remains still for many days, larger droplets of the chemically coated water may settle to the bottom of a tank. The fuel, however, will mix again if agitated slightly, and refueling the tank agitates the fuel enough to mix it again. The in¯uence of water on the performance parameters, exhaust emissions of diesel engines has been studied by many works [8,11±14]. However, the eects of adding water to diesel engines on the heat ¯ux crossing the combustion chamber components, e.g. cylinder head and cylinder liner, chamber metal temperatures and thermal loading of such engines are still lacking. Therefore, the main objective of the present work is to experimentally investigate the eects of using dierent water/diesel ratios on the heat ¯ux crossing the cylinder liner, cylinder head and metal temperature of the injector tip. A precombustion chamber, single cylinder diesel engine was used throughout the present work. Four traversing thermocouple probes were installed along the cylinder liner, four traversing thermocouple probes are installed in the critical areas of cylinder head and one ®xed thermocouple is ®tted in the injector tip to measure its temperature. The variables studied included the location along the liner and in cylinder head, the engine load (or fuelling rate) and the ratio of water to diesel. The heat ¯ux crossing both cylinder liner and cylinder head was correlated to the above mentioned variables.
2. Experimental engine test rig A precombustion chamber diesel engine, Helwan 111, single cylinder has been used in the present work with the speci®cations shown in Table 1. The engine is coupled to a 50 Hz, threephase a.c. generator. The engine is fully equipped for measurements of brake power, crankshaft Table 1 Diesel engine speci®cations Item
Description
Model Combustion chamber type Number of cylinders Bore stroke (mm) Cycle Compression ratio Rated speed (rpm) Rated power (kW) Maximum speed (rpm) Maximum power (kW) Injection pressure (bar) Injection timing (° BTDC) Cylinder head/liner material Coolant bulk temperature (°C)
Helwan 1 1 1 IDI with prechamber 1 1 1 1 115 Four-stroke 22.4 1500 8.1 1800 9.6 145 14.5o Cast iron 70
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rotational speed, air ¯ow rate, fuel ¯ow rate, exhaust gas temperatures, coolant ¯ow rate and temperature, and heat ¯ux in cylinder head and liner. Fig. 1 illustrates the general layout for heat ¯ux and temperature measurements in liner and cylinder head. The engine has a peper-pot type precombustion chamber with two exit holes and the precombustion chamber was located at the outer periphery of bore. Figs. 2 and 3 show the locations of the heat ¯ux measurement holes along the cylinder liner and across the cylinder head. The cylinder liner is equipped with four traversing thermocouple probes to measure heat ¯ux at dierent locations. For the cylinder head, four traversing thermocouple probes are located at the critical positions (higher heat ¯ux and metal temperature). It should be noted that, the liner uppermost thermocouple, no.1, lies at the centerline of the top of the piston ring when the piston is at the top dead center. This location was deliberately chosen since this position is the most critical part in the cylinder liner where the liner scung almost always start. The thermocouple number 2 lies at the centerline of the third piston ring when the piston is at top dead center. For the cylinder head, thermocouple numbers 5 and 6 were located as close as possible to the high speed gas jets emerging from the twin exit holes of the precombustion chamber. This being so since it was expected that at these locations the thermal load would be considerable. Thermocouple number 7 was ®tted in the valve bridge since investigations on this
Fig. 1. General layout of the engine and thermocouple locations.
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Fig. 2. Thermocouple locations in cylinder liner.
Fig. 3. Locations of traversing thermocouples in cylinder head.
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type of combustion chamber have shown that this part is quite critical. Cracking and subsequent failure of the cylinder head can take place there due to high heat ¯ux and gas face metal temperature. In order to achieve full coverage of cylinder head, thermocouple number 8 was ®tted. The temperature of the injector tip was measured by ®xed thermocouple. Slot was machined in the injector as shown in Fig. 4 and the thermocouple was embedded in such hole. Heat ¯ux was measured using special thermocouple probes with traversing mechanisms as shown in Fig. 5. A hole was drilled in the component (cylinder head or liner) which stops one hole diameter short of gas face to avoid disturbing the heat ¯ow pattern [15]. A brass button was made which is in close sliding ®t in the hole. The hot junction of each type-K thermocouple wires was silver-soldered in a small hole in the button. The wires inserted in a stainless steel sheath and the output terminal of all thermocouples are connected to a digital thermometer via a selecting switch to indicate the temperature. The thermocouple probe was traversed through the hole by the traversing head shown in Fig. 5 which could aect traverses down to 0.75 mm. The thermocouple junction, is then, in contact with the brass button, which is, in turn, in contact with the metal of the component (liner or cylinder head), so the measured temperature represents the metal temperature at that location. Successive traverses give the temperature gradient, which enables the heat ¯ux to be calculated from FourierÕs equation of heat transfer by conduction.
Fig. 4. Thermocouple location in injector tip.
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Fig. 5. Traversing thermocouple probe.
3. Experimental procedure The experimental work presented in this study is carried out on a diesel engine at constant engine speed of 1300 rpm, constant coolant bulk temperature of 70°C. Variation of engine load enabled heat ¯ux to be changed. Heat ¯ux crossing the cylinder liner and cylinder head have been measured using the above mentioned thermocouple probes at dierent engine loads. At each reading, the temperatures for the eight traversing thermocouples were recorded, T1 , then all probes were traversed 0.75 mm, then the temperature readings, T2 , were recorded after steady state is reached. Engine load is then increased, and mass of diesel fuel is also increased to keep constant speed, and as the engine reaches the steady state conditions, all probes are traversed and metal temperatures are recorded again and so on. Thermocouple probes were traversed across the metal at many successive locations and heat ¯ux was computed using FourierÕs equation of conduction, Eq. (1): q00 k T1
T2 =DX
1
where q00 is the heat ¯ux in kW/m2 , DX , the traverse distance between two successive points and equal to 0.75 mm in both liner or cylinder head, k, the thermal conductivity for cast iron cylinder liner and cylinder head, kW/m °C, T1 , the metal temperature at point 1, T2 , the metal temperature at point 2. The thermal conductivity of similar metal specimen is measured at dierent temperatures and its values are taken at the metal average temperature T1 T2 =2. It may be emphasized here that the metal temperatures and heat ¯ux measured are not instantaneous values, but rather average values and all experiments have been carried out at constant coolant bulk temperature of 70°C. Engine load was varied from 700 to 7400 W, and this varied the heat ¯ux accordingly from approximately 160 to 510 kW/m2 in the cylinder liner and from 470 to 790 kW/m2 in the cylinder head.
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3.1. Diesel/water emulsion The experiments have been carried out at dierent water/diesel emulsion ratio and compared to the pure diesel case. The water/diesel emulsions were prepared in a separate tank which was well stirred. An emulsifying agent, liquid soap, was found to be an eective emulsifying agent. No separation of fuel and water was observed during the test, using visual observation of the glass tank. The emulsifying agent had no in¯uence on its own when added to the fuel. Hence, any eect of the emulsion had to be due to the water [7]. The used engine would not operate with greater emulsion ratios than 10% water in the fuel, so the present work was carried out at 2%, 4%, 6% and 8% of water by volume. This range of water in fuel ratio was found elsewhere to be eective in in¯uencing the NOx emission. An experimental error analysis has been conducted and resulted in maximum percentage error in heat ¯ux of about 5%, and error of 2% in wall temperatures [7]. 4. Results and discussion 4.1. Cylinder liner The variation of the heat ¯ux against the fuel ¯ow rate along the cylinder liner is illustrated in Figs. 6±9. The fuel ¯ow rate is divided by the piston area (Ap ) and multiplied by piston speed squared, Vp2 , since this has been shown [16] to produce the best correlation factor for the cylinder liner. The other advantage of this would be to make the results applicable to dierent sized engines with dierent piston areas, average piston speed and fuel consumption. The location of thermocouple number 1, 19% of stroke, Fig. 2, is the most important in the liner since it is adjacent to the top piston ring when the piston is at top dead center. At this location liner scung
Fig. 6. Local heat ¯ux in liner against fuel ¯ow for thermocouple number 1, at dierent diesel±water emulsion ratio.
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Fig. 7. Local heat ¯ux in liner against fuel ¯ow for thermocouple number 2, at dierent diesel±water emulsion ratio.
Fig. 8. Local heat ¯ux in liner against fuel ¯ow for thermocouple number 3, at dierent diesel±water emulsion ratio.
can take place if the metal temperature exceeds 180°C. It may be seen from Fig. 6 that generally the increase in fuel ¯ow rate increases the heat ¯ux for any emulsion ratio as well as for gas oil. This is due to the increased amount of heat released by combustion which increases the heat ¯ux
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Fig. 9. Local heat ¯ux in liner against fuel ¯ow for thermocouple number 4, at dierent diesel±water emulsion ratio.
across the liner. However, when the water is introduced to diesel fuel the heat ¯ux has dropped as the emulsion ratio increases with almost the same heat ¯ux rate. This seems to be due to the reduced gas temperatures when the water is added. As the objective of adding water to the diesel is to reduce the maximum temperature of combustion and hence reduces the amount of nitrogen oxides produced in the exhaust gases, it seems to be advantageous from the heat ¯ux point of view. Adding more water to the diesel, emulsion ratios from 2% to 8%, causes the heat ¯ux to reduce more and the heat ¯ux is always minimum for 8% water in diesel. Thermocouples 2 which is at 35% of the stroke from the top dead center exhibits similar trends for the eect of diesel emulsion ratios, as seen in Fig. 7. However, for all emulsion ratios as well as for gas oil, the values of the heat ¯ux are lower than those for thermocouple number 1. This is due to the reduced gas temperature facing the liner at this location as the piston expansion stroke proceeds and gas temperature continue to reduce. As the percentage of stroke increases more the gas temperature keeps dropping and the heat ¯ux reduces as shown in the heat ¯ux results in Figs. 8 and 9 for thermocouple numbers 3 and 4. Thermocouple numbers 3 and 4 are at 50% and 75% stroke from top dead center respectively. For the same amount of fuel or emulsion ratio, thermocouple location number 4 exhibits the lowest heat ¯ux and hence the lowest gas temperature. The drop in heat ¯ux as well as the gas side metal temperature would reduce the thermal stresses applied to the liner and reduces the possibility of liner scung and metal fatigue as well as making the engine more reliable in service. The engine uprating would then be more possible without increasing thermal stresses. The results of heat ¯ux (q00 ) against mass ¯ow rate of fuel per piston area (m00f mf =piston area), diesel/water emulsion ratio (w) and the fraction of piston stroke for each thermocouple probe (S) are fed to the Data ®t software to produce similar correlation to the one produced by [16] for the cylinder liner. They produced a correlation for the gas oil fuel for the liner of the same engine type. The correlation reads:
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q00 HFF m00f Vp2 n
1575
2
In the present study the percentage of stroke (S) and the percentage of water in diesel (w) are added to the data to produce their eect on the heat ¯ux, Eq. (3), which reads: q00 6:141 S
0:317
1
w2:87 m00f Vp2 0:451
3
where (S) is in the range of 0.19±0.75 of piston stroke, (w) is in the range 0.02 to 0.08 by volume, and (m00f Vp2 ) is in the range of 1700±7000 (kg/h m2 ) (m2 /s2 ). Fig. 10 shows the actual versus the correlated values of heat ¯ux and it may be seen that the correlation predicts the data well. At each examined liner location, and at each water emulsion ratio the heat ¯ux factor (HFF), may be then calculated by substituting the value of water ratio, w, and the fraction of stroke, S, in the correlation viz.: HFF 6:141 S
0:317
1
w2:87
q00 HFF m00f Vp2 0:451
4 5
the value of HFF at various locations of the liner and at each water/diesel ratio is illustrated in Fig. 11. As has been shown above, for gas oil or any emulsion ratio the HFF generally decreases along the cylinder liner and it also decreases when the water amount increased. The value of exponent ``n'' remains constant which re¯ects that the rate of increase of heat ¯ux is almost the same for dierent water emulsion ratios and for the dierent liner locations. The above correlation gives the heat ¯ux crossing the cylinder liner at any level of the stroke and at any fuel ¯ow rate and water emulsion ratio. It would help to determine the required liner thickness, coolant conditions and temperature distribution as well as to de®ne the possible increase in engine rating the liner can sustain when water is used to control the nitrogen oxides in
Fig. 10. Correlated versus measured heat ¯ux for cylinder liner.
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Fig. 11. HFF for cylinder liner at dierent diesel±water emulsion.
diesel engines. It may be interesting to highlight the drop in the heat ¯ux or heat losses from the cylinder liner as the water/diesel emulsion is used, as this would make the cooling system requirements less complex. It was also found [6] from engine heat balance that the cooling losses drops as the water/diesel emulsion is introduced to the diesel engine. 4.2. Cylinder head The heat ¯ux in the cylinder head at the thermocouple probes location are illustrated in Figs. 12±15. For the cylinder head the heat ¯ux variation with the fuel ¯ow rate exhibits similar trend to that of the liner. Figs. 12 and 13 show the heat ¯ux crossing the cylinder head at location of thermocouple numbers 5 and 6 while Figs. 14 and 15 show the heat ¯ux results for thermocouples 7 and 8 respectively. It may be seen that the heat ¯ux is highest for thermocouple number 5 followed by thermocouple number 6 while thermocouple numbers 7 and 8 produce less and almost similar heat ¯uxes. In all locations of the cylinder head the rate of increase of heat ¯ux is almost the same. It may be noticed that the heat ¯ux crossing the cylinder head in any location is always higher than that for the cylinder liner since it is always facing the highest combustion gas temperatures. Probe location number 5 exhibits the highest heat ¯ux since it is located close to the high speed gas jets emerging from the twin exit holes of the precombustion chamber and also is adjacent to the hot exhaust valve. Thermocouple number 6 also produces high heat ¯uxes but slightly lower than those for thermocouple number 5 since it is in the intake valve side. Thermocouple numbers 7 and 8 exhibit less heat ¯uxes since they are far from the exit of the precombustion chamber [16,17]. Similar to the liner results, when the water is added to the diesel fuel, the heat ¯ux always drops for all thermocouple locations. It may be also noticed by comparing the cylinder head results to
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Fig. 12. Local heat ¯ux in cylinder head against fuel ¯ow for thermocouple number 5, at dierent diesel±water emulsion ratio.
Fig. 13. Local heat ¯ux in cylinder head against fuel ¯ow for thermocouple number 6, at dierent diesel±water emulsion ratio.
those of the cylinder liner that the introduction of water/diesel emulsion has greater in¯uence on the heat ¯ux crossing the cylinder head than that crossing the liner. This seems to be due to the resulted drop in the combustion gases temperature during the early combustion stages which are
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Fig. 14. Local heat ¯ux in cylinder head against fuel ¯ow for thermocouple number 7, at dierent diesel±water emulsion ratio.
Fig. 15. Local heat ¯ux in cylinder head against fuel ¯ow for thermocouple number 8, at dierent diesel±water emulsion ratio.
facing the precombustion chamber and cylinder head. The eect is less noticeable during the later stages of combustion gases facing the cylinder liner. This again seems advantageous for the cylinder head thermal stresses, since it would suer less thermal fatigue when the water/diesel emulsion is used.
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The results of heat ¯ux against mass ¯ow rate of fuel, percentage water/diesel emulsion ratio (w) and the bore ratio (r=R) for each thermocouple probe are used to produce similar correlation to the one produced for the cylinder liner which reads: 0:0395
q00 99:51 r=R
1
w
1:792
0:242
m00f Vp2
6
where (r=R) is in the range of 0.08±0.68 of cylinder radius, (w) is in the range 0.02±0.08 by volume, and m00f Vp2 is in the range of 1700±7000 (kg/h m2 ) (m2 /s2 ). Fig. 16 shows the actual versus the correlated values of heat ¯ux and it may be seen that the correlation predicts the data well. At each examined cylinder head location, and at each water emulsion ratio the HFF may be then calculated by substituting the value of water ratio, w, and the bore ratio, r=R, in the correlation viz.: 0:0395
HFF 99:51 r=R q00 HFF m00f Vp2
1
w
1:792
0:242
7 8
the value of HFF at various locations of the cylinder head and at each water/diesel ratio is illustrated in Fig. 17. As has been shown above, for gas oil or any emulsion ratio the HFF generally increases with the increase in radial distance (r=R) and it also decreases when the water amount increased. The value of exponent ``n'' remains constant which re¯ects that the rate of increase of heat ¯ux is almost the same for dierent water emulsion ratios and for the dierent cylinder head locations. The valve bridge area, with lower radius, is left with lower heat ¯ux relative to the outer areas, greater radii. This may be due to the lower level of gas swirl observed in the central area of the cylinder [16].
Fig. 16. Correlated versus measured heat ¯ux for cylinder head.
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Fig. 17. HFF for cylinder head at dierent diesel±water emulsion.
The above correlation again would help to determine the required cylinder head thickness, coolant conditions and temperature distribution as well as to de®ne the possible increase in engine rating the cylinder head can sustain when water is used to control the nitrogen oxides in diesel engines. 4.3. Injector tip The injector tip temperature is measured by a ®xed thermocouple and the measured temperatures are shown in Fig. 18 for dierent fuel ¯ow rates and water/diesel emulsion ratios. The injector metal temperature generally increases with the fuelling rate. It may be also noticed from such ®gure that adding the water to the diesel fuel has great eect on reducing the metal temperature of the injector tip. The injector exhibits the highest temperature for the gas oil and the lowest temperatures when the 8% emulsion ratio is used. This is an advantage for the injector tip to run cooler when the water is introduced in such engines as it would be more reliable in service. 5. Conclusions From the experimental investigation carried out in this work on the eect of water/diesel emulsion on the heat ¯ux, combustion chamber metal temperatures, and thermal loading of diesel engines running on the emulsi®ed fuel, the following conclusions may be drawn: 1. For the gas oil fuel, heat ¯ux and hence metal temperatures drop down the cylinder liner and drop at a given location with the drop in load at a ®xed speed. 2. Adding the water to diesel fuel has reduced the metal temperatures and all heat ¯uxes crossing the liner and cylinder head at all locations examined. The heat ¯ux is always maximum for pure gas oil and minimum at the highest ratio of water in diesel used, 8%.
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Fig. 18. Eect of diesel±water emulsion ratio on injector tip temperature.
3. A correlation has been developed for the heat ¯ux crossing the cylinder liner as a function to the fuel ¯ow rate per piston area, water in diesel ratio, and thermocouple location as percentage of stroke. Another correlation has been developed for the heat ¯ux crossing the cylinder head as related to the fuelling rate per piston area, water in diesel ratio, and thermocouple location as percentage of bore. 4. The heat ¯ux crossing the cylinder head at locations near to the exit twin holes of the precombustion chamber is found to be higher than that at the central region of the cylinder head. The location near to the exit twin holes of the precombustion chamber and near to the exhaust valve exhibits the highest heat ¯ux. 5. Heat ¯ux crossing the cylinder head is higher than that crossing the cylinder liner for gas oil as well as for all water/diesel emulsion ratios. 6. Adding the water has greater in¯uence on reducing the heat ¯ux crossing the cylinder head as compared to that crossing the cylinder liner. 7. The produced correlation can be used to determine the required liner and cylinder head thickness, coolant conditions and temperature distribution as well as to de®ne the possible increase in engine rating the liner and cylinder head can sustain when water is used to control the nitrogen oxides in diesel engines. 8. Adding the water to the diesel fuel has great eect on reducing the metal temperature of the injector tip. The injector exhibits the highest temperature for the gas oil and the lowest temperatures when the 8% emulsion ratio is used. 9. Diesel engines running on water/diesel emulsion should be more reliable in service than those running on pure gas oil due to the drop in heat ¯ux as well as the gas side metal temperature which will reduce the thermal stresses applied to the liner. This reduces the possibility of liner scung and metal fatigue as well as making the engine uprating more possible without increasing thermal stresses. The cooling system requirement should also be less complex when water/diesel emulsion is used.
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Appendix A. Date ®t software Correlations produced in this work have been estimated by Date Fit Software. In this software, all experimental data are fed as heat ¯ux varied with mass ¯ow rate of fuel per piston area, m00f , at dierent values of all other parameters. Correlatoin exponential form is introduced and the program used all data to produce the correlation constants. This is repeated for cylinder liner and cylinder head.
References [1] J.P. Mello, A.M. Mellor, NOx emissions from direct injection diesel engines with water/steam dilution, SAE paper 1999-01-0836, 1999. [2] M. Christensen, B. Johansson, Homogeneous charge compression ignition with water injection, SAE paper 199901-0182, 1999. [3] K.P. Duy, A.M. Mellor, Further developments on a characteristic time model for NOx emissions from diesel engines, SAE paper 982460, 1998. [4] M.A. Psota, W.L. Easley, T.H. Fort, A.M. Mellor, Water injection eects on NOx emissions for engines utilizing diusion ¯ame combustion, SAE Trans. J. Engines 106 (1997) 1835±1843 (SAE 971657, Section 3). [5] S. Kohketsu, K. Mori, K. Sakai, Reduction of exhaust emission with new water injection system in a diesel engine, SAE 960033, 1996. [6] Y. Yoshimoto, M. Tsukahara, T. Kuramoto, Improvements of BSFC by reducing diesel engine cooling losses with emulsi®ed fuel, SAE 962022, 1996. [7] G.E. Andrews, K.D. Bartle, S.W. Pang, A.M. Nurein, Diesel/water emulsions: in¯uence on ignition delay and emissions, Proceedings of the International Center for Heat and Mass Transfer, Hemisphere Publication Corp., New York, September 1987, pp. 613±625. [8] G. Greeves, I.M. Khan G. Onion, Eects of water introduction on diesel engine combustion and emissions, 16th Symposium International on Combustion, The Combustion Institute, 1976, pp. 321±336. [9] F.L. Dryer, Water addition to practical combustion systems concepts and applications, 16th Symposium International on Combustion, The Combustion Institute, 1976, pp. 321±336. [10] M.S. Radwan, H. Salem, A study of some combustion characteristics of gas oil/water emulsions in a swirl chamber diesel engine, SAE 892056, 1989. [11] T.W. Ryan, J.O. Storment, B.R. Wright, R. Waytulonis, The eects of fuel properties and composition on diesel engine exhaust emissions ± a review, SAE 810953, 1981. [12] T. Murayama, Y. Morishima, M. Tsukahara, N. Miyamoto, Experimental reduction of NOx , smoke and BSFC in a diesel engine using uniquely produced water (0±80%) to fuel emulsion, SAE 780224, 1978. [13] C.W. Coon, Multicylinder diesel engine tests with unstabilized water in fuel emulsions, SAE 810250, 1981. [14] H.M. A®fy, N.S. Korah, D.W. Dicky, The eect of air charge temperature on performance, ignition delay and exhaust emissions of diesel engines using W/O emulsions as fuel, SAE 870555, 1987. [15] J.F. Alcock, Thermal loading of diesel engines, Trans. 1 Mar. E. 77 (1) (1965). [16] N.M. Raafat, A.S.A. Fahmy, M.S. Radwan, A.M. Shames, Measurements and prediction of the heat ¯ow and temperature level in a precombustion chamber diesel, SAE 841133, 1984. [17] M.S. Radwan, The in¯uence of some synfuels on the performance and thermal loading of a precombustion chamber diesel engine, SAE 850051, 1985.
www.elsevier.com/locate/apthermeng
Eects of diesel/water emulsion on heat ¯ow and thermal loading in a precombustion chamber diesel engine M.Y.E. Selim a,*, S.M.S. Elfeky b a b
Department of Mechanical Engineering, Faculty of Engineering, United Arab Emirates University, P.O. Box 17555, Al-Ain, United Arab Emirates Department of Mechanical Power Engineering, Faculty of Engineering at Mattaria, Helwan University, Cairo 11718, Egypt Received 6 September 2000; accepted 28 January 2001
Abstract An experimental investigation has been carried out to study the eects of using water/diesel emulsion fuel in an indirect injection diesel engine on the heat ¯ux crossing liner and cylinder head, thermal loading and metal temperature distribution. A single cylinder precombustion chamber diesel engine has been used in the present work. The engine was instrumented for performance, metal temperature and heat ¯ux measurements. The pure gas oil fuel and dierent ratios of water/diesel emulsion were used and their eects on the heat ¯ux level and the injector tip temperature are studied. Two correlation were found for the heat ¯ux crossing the liner and the cylinder head at various water/diesel emulsion ratios, fuelling rate and thermocouple probe locations. It was found that the addition of water to diesel fuel, to control the nitrogen oxides emissions, has great in¯uence on reducing the heat ¯ux, the metal temperatures and thermal loading of combustion chamber components. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Diesel engine; Nitrogen oxides; Water emulsion; Heat ¯ux; Thermal loading
1. Introduction The use of water into diesel engines has a number of possible bene®ts. It has been found by many previous works that it has in¯uence on reducing the peak ¯ame temperature and hence reducing the nitrogen oxides, NOx emissions [1±7]. It has also been shown [8] that adding water may help to improve atomization and mixing, which is attributed to droplet microexplosions [9]. *
Corresponding author. Tel.: +971-3-7051-566; fax: +971-3-7623-158. E-mail address: [email protected] (M.Y.E. Selim).
1359-4311/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 9 - 4 3 1 1 ( 0 1 ) 0 0 0 1 9 - 9
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Nomenclature Ap HFF mf m00f NOx q00 r R r=R S Vp w
piston area (m2 ) heat ¯ux factor (kW=m2 )/[(kg=h m2 ) (m2 =s2 )] ¯ow rate of fuel (kg=h) ¯ow rate of fuel per piston area (mf =Ap ), (kg=h m2 ) nitrogen oxides heat ¯ux (kW=m2 ) radial distance (m) cylinder radius (m) bore ratio percentage of stroke mean piston speed (m=s) water/diesel emulsion ratio, by volume
The improved mixing is due to the increased vaporized fuel jet momentum, giving greater air entertainment into the fuel jet [8]. The improved mixing also assists in the reduction in the NOx emissions from the diusive burning portion of the combustion event as well as reducing the carbon formation. This eect, together with the chemical eect of the water results in an increased ignition delay [8,10]. This promotes an increase in the premixed portion of the combustion process, which decreases the diusive burning and hence also contributes to the reduction in the NOx emissions and carbon formation [7]. There is also considerable evidence that adding water to diesel fuel can reduce the particulate matter PM or smoke emissions [7]. There are three primary methods of introducing water into the diesel engines; water injection into the cylinder using a separate injector, spraying water into the inlet air, and water/diesel emulsions. Although all these methods produced a reduction in NOx but it has been concluded in a review in Ref. [11] that the use of water/diesel emulsion was the most eective technique for the reduction of diesel particulates or smoke, for four stroke DI engines. Mello and Mellor [1] have compared two methods of water admission namely strati®ed diesel± water±diesel injection inside the cylinder and intake manifold fumigation (injecting water into intake manifold). They have compared the experimental NOx results of Kohketsu et al. [5] with their modeling using a two-zone characteristic time model which is based on the dominant physical and chemical subprocesses occurring in the cylinder. They have used a fuel injection pump and water injection pump with a hybrid injection nozzle to inject the water pulse between two fuel pulses. For the intake manifold fumigation, it is claimed that it resulted in a presumably uniform distribution of water vapor in the cylinder at the time of combustion. The vaporization of water occurs as the water and air are heated through the compression stroke. However, diesel/ water emulsion reduced NOx slightly more than fumigation method. Christensen and Johansson [2] also used the intake manifold fumigation by using a common low pressure fuel injector, however, they have found that both carbon monoxide and hydrocarbons increased with water injection. Andrews et al. [7] used an emulsifying agent, Arlacel C, to create the diesel/water emulsion and suggested that ordinary liquid soap may be used.
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There is growing interest in diesel fuel industry to produce and utilize the diesel/water emulsion as ordinary fuel for diesel engines. Fuel additive manufacturers are trying to make diesel oil and water to mix, or at least they can be neighborly enough to form a pollution-cutting diesel fuel. There have been trials to produce a very stable emulsion that stays in suspension over a long period of time. If the fuel remains still for many days, larger droplets of the chemically coated water may settle to the bottom of a tank. The fuel, however, will mix again if agitated slightly, and refueling the tank agitates the fuel enough to mix it again. The in¯uence of water on the performance parameters, exhaust emissions of diesel engines has been studied by many works [8,11±14]. However, the eects of adding water to diesel engines on the heat ¯ux crossing the combustion chamber components, e.g. cylinder head and cylinder liner, chamber metal temperatures and thermal loading of such engines are still lacking. Therefore, the main objective of the present work is to experimentally investigate the eects of using dierent water/diesel ratios on the heat ¯ux crossing the cylinder liner, cylinder head and metal temperature of the injector tip. A precombustion chamber, single cylinder diesel engine was used throughout the present work. Four traversing thermocouple probes were installed along the cylinder liner, four traversing thermocouple probes are installed in the critical areas of cylinder head and one ®xed thermocouple is ®tted in the injector tip to measure its temperature. The variables studied included the location along the liner and in cylinder head, the engine load (or fuelling rate) and the ratio of water to diesel. The heat ¯ux crossing both cylinder liner and cylinder head was correlated to the above mentioned variables.
2. Experimental engine test rig A precombustion chamber diesel engine, Helwan 111, single cylinder has been used in the present work with the speci®cations shown in Table 1. The engine is coupled to a 50 Hz, threephase a.c. generator. The engine is fully equipped for measurements of brake power, crankshaft Table 1 Diesel engine speci®cations Item
Description
Model Combustion chamber type Number of cylinders Bore stroke (mm) Cycle Compression ratio Rated speed (rpm) Rated power (kW) Maximum speed (rpm) Maximum power (kW) Injection pressure (bar) Injection timing (° BTDC) Cylinder head/liner material Coolant bulk temperature (°C)
Helwan 1 1 1 IDI with prechamber 1 1 1 1 115 Four-stroke 22.4 1500 8.1 1800 9.6 145 14.5o Cast iron 70
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rotational speed, air ¯ow rate, fuel ¯ow rate, exhaust gas temperatures, coolant ¯ow rate and temperature, and heat ¯ux in cylinder head and liner. Fig. 1 illustrates the general layout for heat ¯ux and temperature measurements in liner and cylinder head. The engine has a peper-pot type precombustion chamber with two exit holes and the precombustion chamber was located at the outer periphery of bore. Figs. 2 and 3 show the locations of the heat ¯ux measurement holes along the cylinder liner and across the cylinder head. The cylinder liner is equipped with four traversing thermocouple probes to measure heat ¯ux at dierent locations. For the cylinder head, four traversing thermocouple probes are located at the critical positions (higher heat ¯ux and metal temperature). It should be noted that, the liner uppermost thermocouple, no.1, lies at the centerline of the top of the piston ring when the piston is at the top dead center. This location was deliberately chosen since this position is the most critical part in the cylinder liner where the liner scung almost always start. The thermocouple number 2 lies at the centerline of the third piston ring when the piston is at top dead center. For the cylinder head, thermocouple numbers 5 and 6 were located as close as possible to the high speed gas jets emerging from the twin exit holes of the precombustion chamber. This being so since it was expected that at these locations the thermal load would be considerable. Thermocouple number 7 was ®tted in the valve bridge since investigations on this
Fig. 1. General layout of the engine and thermocouple locations.
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Fig. 2. Thermocouple locations in cylinder liner.
Fig. 3. Locations of traversing thermocouples in cylinder head.
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type of combustion chamber have shown that this part is quite critical. Cracking and subsequent failure of the cylinder head can take place there due to high heat ¯ux and gas face metal temperature. In order to achieve full coverage of cylinder head, thermocouple number 8 was ®tted. The temperature of the injector tip was measured by ®xed thermocouple. Slot was machined in the injector as shown in Fig. 4 and the thermocouple was embedded in such hole. Heat ¯ux was measured using special thermocouple probes with traversing mechanisms as shown in Fig. 5. A hole was drilled in the component (cylinder head or liner) which stops one hole diameter short of gas face to avoid disturbing the heat ¯ow pattern [15]. A brass button was made which is in close sliding ®t in the hole. The hot junction of each type-K thermocouple wires was silver-soldered in a small hole in the button. The wires inserted in a stainless steel sheath and the output terminal of all thermocouples are connected to a digital thermometer via a selecting switch to indicate the temperature. The thermocouple probe was traversed through the hole by the traversing head shown in Fig. 5 which could aect traverses down to 0.75 mm. The thermocouple junction, is then, in contact with the brass button, which is, in turn, in contact with the metal of the component (liner or cylinder head), so the measured temperature represents the metal temperature at that location. Successive traverses give the temperature gradient, which enables the heat ¯ux to be calculated from FourierÕs equation of heat transfer by conduction.
Fig. 4. Thermocouple location in injector tip.
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Fig. 5. Traversing thermocouple probe.
3. Experimental procedure The experimental work presented in this study is carried out on a diesel engine at constant engine speed of 1300 rpm, constant coolant bulk temperature of 70°C. Variation of engine load enabled heat ¯ux to be changed. Heat ¯ux crossing the cylinder liner and cylinder head have been measured using the above mentioned thermocouple probes at dierent engine loads. At each reading, the temperatures for the eight traversing thermocouples were recorded, T1 , then all probes were traversed 0.75 mm, then the temperature readings, T2 , were recorded after steady state is reached. Engine load is then increased, and mass of diesel fuel is also increased to keep constant speed, and as the engine reaches the steady state conditions, all probes are traversed and metal temperatures are recorded again and so on. Thermocouple probes were traversed across the metal at many successive locations and heat ¯ux was computed using FourierÕs equation of conduction, Eq. (1): q00 k T1
T2 =DX
1
where q00 is the heat ¯ux in kW/m2 , DX , the traverse distance between two successive points and equal to 0.75 mm in both liner or cylinder head, k, the thermal conductivity for cast iron cylinder liner and cylinder head, kW/m °C, T1 , the metal temperature at point 1, T2 , the metal temperature at point 2. The thermal conductivity of similar metal specimen is measured at dierent temperatures and its values are taken at the metal average temperature T1 T2 =2. It may be emphasized here that the metal temperatures and heat ¯ux measured are not instantaneous values, but rather average values and all experiments have been carried out at constant coolant bulk temperature of 70°C. Engine load was varied from 700 to 7400 W, and this varied the heat ¯ux accordingly from approximately 160 to 510 kW/m2 in the cylinder liner and from 470 to 790 kW/m2 in the cylinder head.
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3.1. Diesel/water emulsion The experiments have been carried out at dierent water/diesel emulsion ratio and compared to the pure diesel case. The water/diesel emulsions were prepared in a separate tank which was well stirred. An emulsifying agent, liquid soap, was found to be an eective emulsifying agent. No separation of fuel and water was observed during the test, using visual observation of the glass tank. The emulsifying agent had no in¯uence on its own when added to the fuel. Hence, any eect of the emulsion had to be due to the water [7]. The used engine would not operate with greater emulsion ratios than 10% water in the fuel, so the present work was carried out at 2%, 4%, 6% and 8% of water by volume. This range of water in fuel ratio was found elsewhere to be eective in in¯uencing the NOx emission. An experimental error analysis has been conducted and resulted in maximum percentage error in heat ¯ux of about 5%, and error of 2% in wall temperatures [7]. 4. Results and discussion 4.1. Cylinder liner The variation of the heat ¯ux against the fuel ¯ow rate along the cylinder liner is illustrated in Figs. 6±9. The fuel ¯ow rate is divided by the piston area (Ap ) and multiplied by piston speed squared, Vp2 , since this has been shown [16] to produce the best correlation factor for the cylinder liner. The other advantage of this would be to make the results applicable to dierent sized engines with dierent piston areas, average piston speed and fuel consumption. The location of thermocouple number 1, 19% of stroke, Fig. 2, is the most important in the liner since it is adjacent to the top piston ring when the piston is at top dead center. At this location liner scung
Fig. 6. Local heat ¯ux in liner against fuel ¯ow for thermocouple number 1, at dierent diesel±water emulsion ratio.
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Fig. 7. Local heat ¯ux in liner against fuel ¯ow for thermocouple number 2, at dierent diesel±water emulsion ratio.
Fig. 8. Local heat ¯ux in liner against fuel ¯ow for thermocouple number 3, at dierent diesel±water emulsion ratio.
can take place if the metal temperature exceeds 180°C. It may be seen from Fig. 6 that generally the increase in fuel ¯ow rate increases the heat ¯ux for any emulsion ratio as well as for gas oil. This is due to the increased amount of heat released by combustion which increases the heat ¯ux
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Fig. 9. Local heat ¯ux in liner against fuel ¯ow for thermocouple number 4, at dierent diesel±water emulsion ratio.
across the liner. However, when the water is introduced to diesel fuel the heat ¯ux has dropped as the emulsion ratio increases with almost the same heat ¯ux rate. This seems to be due to the reduced gas temperatures when the water is added. As the objective of adding water to the diesel is to reduce the maximum temperature of combustion and hence reduces the amount of nitrogen oxides produced in the exhaust gases, it seems to be advantageous from the heat ¯ux point of view. Adding more water to the diesel, emulsion ratios from 2% to 8%, causes the heat ¯ux to reduce more and the heat ¯ux is always minimum for 8% water in diesel. Thermocouples 2 which is at 35% of the stroke from the top dead center exhibits similar trends for the eect of diesel emulsion ratios, as seen in Fig. 7. However, for all emulsion ratios as well as for gas oil, the values of the heat ¯ux are lower than those for thermocouple number 1. This is due to the reduced gas temperature facing the liner at this location as the piston expansion stroke proceeds and gas temperature continue to reduce. As the percentage of stroke increases more the gas temperature keeps dropping and the heat ¯ux reduces as shown in the heat ¯ux results in Figs. 8 and 9 for thermocouple numbers 3 and 4. Thermocouple numbers 3 and 4 are at 50% and 75% stroke from top dead center respectively. For the same amount of fuel or emulsion ratio, thermocouple location number 4 exhibits the lowest heat ¯ux and hence the lowest gas temperature. The drop in heat ¯ux as well as the gas side metal temperature would reduce the thermal stresses applied to the liner and reduces the possibility of liner scung and metal fatigue as well as making the engine more reliable in service. The engine uprating would then be more possible without increasing thermal stresses. The results of heat ¯ux (q00 ) against mass ¯ow rate of fuel per piston area (m00f mf =piston area), diesel/water emulsion ratio (w) and the fraction of piston stroke for each thermocouple probe (S) are fed to the Data ®t software to produce similar correlation to the one produced by [16] for the cylinder liner. They produced a correlation for the gas oil fuel for the liner of the same engine type. The correlation reads:
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q00 HFF m00f Vp2 n
1575
2
In the present study the percentage of stroke (S) and the percentage of water in diesel (w) are added to the data to produce their eect on the heat ¯ux, Eq. (3), which reads: q00 6:141 S
0:317
1
w2:87 m00f Vp2 0:451
3
where (S) is in the range of 0.19±0.75 of piston stroke, (w) is in the range 0.02 to 0.08 by volume, and (m00f Vp2 ) is in the range of 1700±7000 (kg/h m2 ) (m2 /s2 ). Fig. 10 shows the actual versus the correlated values of heat ¯ux and it may be seen that the correlation predicts the data well. At each examined liner location, and at each water emulsion ratio the heat ¯ux factor (HFF), may be then calculated by substituting the value of water ratio, w, and the fraction of stroke, S, in the correlation viz.: HFF 6:141 S
0:317
1
w2:87
q00 HFF m00f Vp2 0:451
4 5
the value of HFF at various locations of the liner and at each water/diesel ratio is illustrated in Fig. 11. As has been shown above, for gas oil or any emulsion ratio the HFF generally decreases along the cylinder liner and it also decreases when the water amount increased. The value of exponent ``n'' remains constant which re¯ects that the rate of increase of heat ¯ux is almost the same for dierent water emulsion ratios and for the dierent liner locations. The above correlation gives the heat ¯ux crossing the cylinder liner at any level of the stroke and at any fuel ¯ow rate and water emulsion ratio. It would help to determine the required liner thickness, coolant conditions and temperature distribution as well as to de®ne the possible increase in engine rating the liner can sustain when water is used to control the nitrogen oxides in
Fig. 10. Correlated versus measured heat ¯ux for cylinder liner.
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Fig. 11. HFF for cylinder liner at dierent diesel±water emulsion.
diesel engines. It may be interesting to highlight the drop in the heat ¯ux or heat losses from the cylinder liner as the water/diesel emulsion is used, as this would make the cooling system requirements less complex. It was also found [6] from engine heat balance that the cooling losses drops as the water/diesel emulsion is introduced to the diesel engine. 4.2. Cylinder head The heat ¯ux in the cylinder head at the thermocouple probes location are illustrated in Figs. 12±15. For the cylinder head the heat ¯ux variation with the fuel ¯ow rate exhibits similar trend to that of the liner. Figs. 12 and 13 show the heat ¯ux crossing the cylinder head at location of thermocouple numbers 5 and 6 while Figs. 14 and 15 show the heat ¯ux results for thermocouples 7 and 8 respectively. It may be seen that the heat ¯ux is highest for thermocouple number 5 followed by thermocouple number 6 while thermocouple numbers 7 and 8 produce less and almost similar heat ¯uxes. In all locations of the cylinder head the rate of increase of heat ¯ux is almost the same. It may be noticed that the heat ¯ux crossing the cylinder head in any location is always higher than that for the cylinder liner since it is always facing the highest combustion gas temperatures. Probe location number 5 exhibits the highest heat ¯ux since it is located close to the high speed gas jets emerging from the twin exit holes of the precombustion chamber and also is adjacent to the hot exhaust valve. Thermocouple number 6 also produces high heat ¯uxes but slightly lower than those for thermocouple number 5 since it is in the intake valve side. Thermocouple numbers 7 and 8 exhibit less heat ¯uxes since they are far from the exit of the precombustion chamber [16,17]. Similar to the liner results, when the water is added to the diesel fuel, the heat ¯ux always drops for all thermocouple locations. It may be also noticed by comparing the cylinder head results to
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Fig. 12. Local heat ¯ux in cylinder head against fuel ¯ow for thermocouple number 5, at dierent diesel±water emulsion ratio.
Fig. 13. Local heat ¯ux in cylinder head against fuel ¯ow for thermocouple number 6, at dierent diesel±water emulsion ratio.
those of the cylinder liner that the introduction of water/diesel emulsion has greater in¯uence on the heat ¯ux crossing the cylinder head than that crossing the liner. This seems to be due to the resulted drop in the combustion gases temperature during the early combustion stages which are
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Fig. 14. Local heat ¯ux in cylinder head against fuel ¯ow for thermocouple number 7, at dierent diesel±water emulsion ratio.
Fig. 15. Local heat ¯ux in cylinder head against fuel ¯ow for thermocouple number 8, at dierent diesel±water emulsion ratio.
facing the precombustion chamber and cylinder head. The eect is less noticeable during the later stages of combustion gases facing the cylinder liner. This again seems advantageous for the cylinder head thermal stresses, since it would suer less thermal fatigue when the water/diesel emulsion is used.
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The results of heat ¯ux against mass ¯ow rate of fuel, percentage water/diesel emulsion ratio (w) and the bore ratio (r=R) for each thermocouple probe are used to produce similar correlation to the one produced for the cylinder liner which reads: 0:0395
q00 99:51 r=R
1
w
1:792
0:242
m00f Vp2
6
where (r=R) is in the range of 0.08±0.68 of cylinder radius, (w) is in the range 0.02±0.08 by volume, and m00f Vp2 is in the range of 1700±7000 (kg/h m2 ) (m2 /s2 ). Fig. 16 shows the actual versus the correlated values of heat ¯ux and it may be seen that the correlation predicts the data well. At each examined cylinder head location, and at each water emulsion ratio the HFF may be then calculated by substituting the value of water ratio, w, and the bore ratio, r=R, in the correlation viz.: 0:0395
HFF 99:51 r=R q00 HFF m00f Vp2
1
w
1:792
0:242
7 8
the value of HFF at various locations of the cylinder head and at each water/diesel ratio is illustrated in Fig. 17. As has been shown above, for gas oil or any emulsion ratio the HFF generally increases with the increase in radial distance (r=R) and it also decreases when the water amount increased. The value of exponent ``n'' remains constant which re¯ects that the rate of increase of heat ¯ux is almost the same for dierent water emulsion ratios and for the dierent cylinder head locations. The valve bridge area, with lower radius, is left with lower heat ¯ux relative to the outer areas, greater radii. This may be due to the lower level of gas swirl observed in the central area of the cylinder [16].
Fig. 16. Correlated versus measured heat ¯ux for cylinder head.
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Fig. 17. HFF for cylinder head at dierent diesel±water emulsion.
The above correlation again would help to determine the required cylinder head thickness, coolant conditions and temperature distribution as well as to de®ne the possible increase in engine rating the cylinder head can sustain when water is used to control the nitrogen oxides in diesel engines. 4.3. Injector tip The injector tip temperature is measured by a ®xed thermocouple and the measured temperatures are shown in Fig. 18 for dierent fuel ¯ow rates and water/diesel emulsion ratios. The injector metal temperature generally increases with the fuelling rate. It may be also noticed from such ®gure that adding the water to the diesel fuel has great eect on reducing the metal temperature of the injector tip. The injector exhibits the highest temperature for the gas oil and the lowest temperatures when the 8% emulsion ratio is used. This is an advantage for the injector tip to run cooler when the water is introduced in such engines as it would be more reliable in service. 5. Conclusions From the experimental investigation carried out in this work on the eect of water/diesel emulsion on the heat ¯ux, combustion chamber metal temperatures, and thermal loading of diesel engines running on the emulsi®ed fuel, the following conclusions may be drawn: 1. For the gas oil fuel, heat ¯ux and hence metal temperatures drop down the cylinder liner and drop at a given location with the drop in load at a ®xed speed. 2. Adding the water to diesel fuel has reduced the metal temperatures and all heat ¯uxes crossing the liner and cylinder head at all locations examined. The heat ¯ux is always maximum for pure gas oil and minimum at the highest ratio of water in diesel used, 8%.
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Fig. 18. Eect of diesel±water emulsion ratio on injector tip temperature.
3. A correlation has been developed for the heat ¯ux crossing the cylinder liner as a function to the fuel ¯ow rate per piston area, water in diesel ratio, and thermocouple location as percentage of stroke. Another correlation has been developed for the heat ¯ux crossing the cylinder head as related to the fuelling rate per piston area, water in diesel ratio, and thermocouple location as percentage of bore. 4. The heat ¯ux crossing the cylinder head at locations near to the exit twin holes of the precombustion chamber is found to be higher than that at the central region of the cylinder head. The location near to the exit twin holes of the precombustion chamber and near to the exhaust valve exhibits the highest heat ¯ux. 5. Heat ¯ux crossing the cylinder head is higher than that crossing the cylinder liner for gas oil as well as for all water/diesel emulsion ratios. 6. Adding the water has greater in¯uence on reducing the heat ¯ux crossing the cylinder head as compared to that crossing the cylinder liner. 7. The produced correlation can be used to determine the required liner and cylinder head thickness, coolant conditions and temperature distribution as well as to de®ne the possible increase in engine rating the liner and cylinder head can sustain when water is used to control the nitrogen oxides in diesel engines. 8. Adding the water to the diesel fuel has great eect on reducing the metal temperature of the injector tip. The injector exhibits the highest temperature for the gas oil and the lowest temperatures when the 8% emulsion ratio is used. 9. Diesel engines running on water/diesel emulsion should be more reliable in service than those running on pure gas oil due to the drop in heat ¯ux as well as the gas side metal temperature which will reduce the thermal stresses applied to the liner. This reduces the possibility of liner scung and metal fatigue as well as making the engine uprating more possible without increasing thermal stresses. The cooling system requirement should also be less complex when water/diesel emulsion is used.
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Appendix A. Date ®t software Correlations produced in this work have been estimated by Date Fit Software. In this software, all experimental data are fed as heat ¯ux varied with mass ¯ow rate of fuel per piston area, m00f , at dierent values of all other parameters. Correlatoin exponential form is introduced and the program used all data to produce the correlation constants. This is repeated for cylinder liner and cylinder head.
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