20076618(JSAE) 2007-32-0118(SAE)
The Package of the Turbocharged Engine for the FSAE Vehicle with the Custom Lubricant System (1) (1) (1) (1) (2) Hiroshi Enomoto, Hiroyuki Motoi, Kyohei Takahashi, Koichiro Saito and Masahiko Yashiro (1) (2) Kanazawa University and Honeywell Copyright © 2007 Society of Automotive Engineers of Japan, Inc. and Copyright © 2007 SAE International The turbocharged 4-stroke internal combustion engine was developed for FSAE, the annual collegiate racing competition. The dry sump lubricant system with the custom scavenge pump, KF-SC07, was designed. The crank axle height was 192mm, 76.5% of KF2004. Custom cam-shafts were designed making the torque fluctuation decreased less than 50% of KF2005. The compression ratio was changed. And the maximum boost pressure and the maximum torque gain were 25kPa (0.25 kgf/cm2) and 11%, respectively. Keywords: Human Engineering, Vehicle Dynamics, Maneuverability / Ignition Delay, Mixture Formation
1.
INTRODUCTION
Kanazawa University Formula R&D takes part in the annual student competition, FSAE Japan (organized by Society of Automotive Engineers of Japan) since 2003. FSAE Japan, held the first one in 2003, is based on the FSAE international, which was held in USA since 1981 organized by Society of Automotive Engineers. Our Kanazawa formula racing team has given the model code as KFxxxx to the successively developed racing vehicles. The four digit number xxxx signifies the year in which the team joined the race with those vehicles. For example, for the first participated year of 2003, the racing car is named as KF2003 and in the successive years the cars are named in the same manner. In this paper, the first turbocharged KF series, KF2007 for the 5th FSAE Japan in 2007, was described.
The development of the intake/exhaust system and the lubricant system were important. While the FSAE rules were changed every year, the parts of the power train were not changed significantly. Table1 shows some of major rules in the 2007 FSAE rules [1]. Surface envelope
Side view Figure 1
Front view
Definition of the surface envelope.
Table 1 FSAE major rules. Parts Engine Lubricant Cooling system Fuel system Intake system Turbocharger
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Contents The engine(s) used to power the car must be four-stroke piston engine(s) with a displacement not exceeding 610 cc per cycle. Hybrid powertrains utilizing on-board energy storage are not allowed. The engine and transmission (lubricant) must be sealed to prevent leakage. Water-cooled engines must only use plain water, or water with cooling system rust and corrosion inhibitor at no more than 0.015 liter per liter of plain water. All parts of the fuel storage and supply system, and all parts of the engine air and fuel control systems must lie within the surface defined by the top of the roll bar and the outside edge of the four tires (see figure 1). In order to limit the power capability from the engine, a single circular restrictor must be placed in the intake system between the throttle and the engine and all engine airflow must pass through the restrictor. The maximum restrictor diameters are 20mm for the gasoline-fueled cars. Turbochargers or superchargers are allowed if the competition team designs the application. The restrictor must be placed upstream of the compressor but after the carburetor or throttle valve. Thus, the only sequence allowed is throttle, restrictor, compressor, engine. Only ambient air may be used to cool an intercooler.
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Chapter 3.5.1.1 3.5.1.4 3.5.1.6 3.5.3.9 3.5.4.3
3.5.4.4
20076618(JSAE) 2007-32-0118(SAE) Crank axle line
Crank axle height 50.8mm (2inches)
Reference plane
(a) KF2004
(b) KF2005
(c) KF2006
NA, Wet sump
NA, Wet sump
NA, Wet sump
Commercial 251mm 240kg
Welding 226mm Michinao Hiramatsu 225kg
Welding 212mm Yusuke Shimada 215kg
Oil-pan Crank axle height Designed by Vehicle weight
Figure 2 2.
Crank axle height.
METHOD
2. 1 History 2. 1. 1 Intake/Exhaust manifold，Camshaft In FSAE rules shown in Table1, as a single circular restrictor must be placed, it is difficult to design the high speed/high power engine. On the other hand, the circuit for the FSAE endurance event has short straights and tight corners and the acceleration performance at the corner exit is very important. As the driver should be chosen from the student, it is difficult to perform as professional drivers, who use the higher engine speed to get the higher power. Therefore, the engine was designed to increase the torque at low/middle engine speed and to reduce the torque fluctuation on the engine speed. Not only for amateur drivers, the stress in driving will be reduced with such engine performance. The intake/exhaust system and the cooling system were mainly designed in KF2004 and KF2005. However, the inner parts of the engine were not changed and the variations of the performance were small. The large fluctuation at 6000rpm Table 2 Specifications of the custom cam-profiles. Normal Custom 1 Custom 2
Action angle Medium Narrow Wide
Lift height High Medium Low
Table 3 Try-sets of the custom-cam. Try 1 Try 2 Try 3 Try 4 Try 5
SETC 2007
In Normal Normal Custom 1 Custom 2 Custom 2
Ex Custom 1 Custom 2 Normal Normal Custom 1
(d) KF2007 Turbocharged, Dry sump Machined 192mm Tatsuya Sugiura 220kg
could not be canceled and it was hard to drive. The cam profile was designed to solve the fluctuation in KF2006. The main variables of the cam profile are the action angle, the valve lift height and the open/close timing. The action angle and the valve lift height were changed in KF2006. The two cam profiles in table 2, the custom 1 and 2, were designed with the simple hand-simulations. These camshafts were combined with the normal one as shown in table 3. While the torque fluctuation was reduced, the torque was small and not competitive. 2. 1. 2
Height of the crank axle Figure 2 shows the height of the crank axle in the KF series. The wet sump system was used. As KF2004 used the commercial oil pan, the bottom of the engine was the drain bolt. The drain bolt was removed to reduce the crank axle height in KF2005 and the oil pan was manufactured by welding. In KF2006, the oil flow was calculated carefully and the height was reduced more. In KF2007, the height was 192mm, 76.5% of KF2004. 2. 2
KF2007 engine package Figure 3 shows the schematics of the engine package
of KF2007. 2. 2. 1 Turbocharger The main purposes to use the turbocharger are increasing the torque at low/middle engine speed and decreasing the torque fluctuation. The endurance event, which is distributed the largest point, has the circuit of 1km length with many tight corners. In the event, as the averaged vehicle speed is 50-60km/h and the maximum speed was about 110km/h, the
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20076618(JSAE) 2007-32-0118(SAE) engine should have large torque at low/middle engine speed to accelerate at the corner exit. The drivers are amateur students and the torque fluctuation makes difficult them to perform well. Base engine has four cylinders and has lower torque compared with single/two cylinders engines. However, the four cylinder engine has small exhaust flow fluctuation and suits to be turbocharged. Table 4 shows the weight and power of the 2006 FSAE top teams. As the restrictor makes it difficult to perform high power at high engine speed, the large power means the large torque and the weight/power ratio (W/P) is used as the indicator. Table 4 Weight/Power of the top teams in 2006 FSAE international.
NA – 600cc Turbo – 600cc NA – 450cc KF2005 (NA – 600cc)
Weight [kg] 170 213 150
Power [PS (kW)] 75 (55.1) 100 (73.5) 60 (44.1)
225
71 (52.2)
Weight/Power 2.3 (3.1) 2.1 (2.9) 2.5 (3.4) 3.2 (4.3) Throttle body Restrictor
Fuel tank Fuel pump
Turbocharger
Oil tank
Oil cooler
The turbo-600cc team had the best W/P, 2.1kg/PS (2.9kg/kW). The NA-600cc team used titanium for the frame or the upright and the lightest among the teams that used 600cc four cylinder. KF2005 had about 1kg/PS (1.4kg/kW) behind the NA-600cc team. The weight reduction and the power increasing should be done. In our team, it was difficult to make the car under 200kg because we could not get the materials easily and the manufacturing technique or machine were not enough. On the other hand, the power could be increased with a turbocharger, a cam design or an ignition timing control. In FSAE, the 5kg weight reduction is the 2PS (1.5kW) power increasing calculated from table 4. We should aim 210kg of weight, 90PS (66.2kW) of power, 6.5kgf･m (63.7N･m) of torque, 2.3kg/PS (3.1kg/kW) of W/P. As the internal combustion engine makes the power with combustion of the mixture, the larger mixture flow rate will makes the larger power. The turbocharger makes the compressed air and increases the mass flow. The mechanisms of the turbocharger have three methods, 1) turbocharger driven by the exhaust with turbine, 2) turbocharger driven by the mechanical power (supercharger), 3) turbocharger driven by the electrical power (e-turbo). The turbocharger driven by the exhaust was used for KF2007 shown in Fig. 4 because it has 1) small size and light weight, 2) alternative layout, 3) no mechanical loss of the engine output, 4) high efficiency. Honeywell GT-12, the compressor A/R 0.33, 41mm in wheel diameter, the turbine A/R 0.43, 35.5mm in the wheel diameter, was used [2].
Oil filter Muffler
Fuel delivery line
Surge tank
Radiator Water pump Scavenge pump
(a) bottom view
Surge tank
Filler neck
Exhaust manifold
Turbocharger Muffler Oil cooler Oil filter
Muffler
Turbocharger Restrictor
Restrictor Throttle body
Throttle body Figure 4 Turbocharger layout.
(b) side view Figure 3 Schematic of KF2007 engine package.
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20076618(JSAE) 2007-32-0118(SAE) 2. 2. 2
Lubricant system --- Dry-sump/Cooling system The lubricant system was changed to introduce the turbocharger. Before KF2006, the normal wet sump system was used with developed oil pan to reduce the center of weight height. However, as such wet sump systems could not realize the significant reduction of the center of the weight height, the dry sump system, which did not need the oil buffer at the bottom of the engine, was used for KF2007. The dry sump system will aspirate the oil for the turbocharger and the turbocharger was mounted at lower position. Figure 5 shows the schematic of the oil line for KF2007. The lubricant chart before KF2006, the wet sump system, was shown in Fig. 6(a). The following developments should be challenged for the dry sump system. Oil pan Scavenge pump Remove the water pump Remove the relief valve Oil tank The thickness of the oil pan was the same of the diameter of the oil line. The scavenge pump was driven with the drive shaft for the normal water pump. The water pump was removed and driven by the crank shaft with a reduction gear. Although the relief valve was set in the crank case, a new outer relief valve was designed and set at the bottom of the engine to reduce the center of weight height. The lubricant chart of KF2007 was shown in Fig. 6(b). Scavenge pump --- KF-SP07 The scavenge pump was used to move the lubricated oil to the outer oil tank. As the inadequate capacity of the scavenge pump will cause the oil shortage of the outer oil tank, the capacity of the scavenge pump should be larger than that of the feed pump, which feeds the oil from the outer oil tank to the engine. If the feed pump breathes gas, the film of oil will be broken and the engine will be damaged.
In the races, as large horizontal/backward/forward acceleration will occur, the lubricated oil will be biased and it is difficult to prevent gas breathing of the scavenge pump. While the maximum acceleration at turn is about 1.0G with general commercial cars, it was 2.2G with KF2006 (1.0G = 9.8m/s2). At the such condition, the oil intake will be exposed to gas and the scavenge pump will breathe gas. The KF-SP07 was designed under such conditions and the capacity was much larger than the sum of the blow-by gas rate and the capacity of the feed pump. This large capacity will reduce the inner pressure of the crankcase and the pumping loss. In general, the capacity of the
Camshaft
Piston cooler
Main gallery Oil cooler
2. 2. 3
Main axle
Feed pump
Oil filter
Relief valve
Strainer
Drive axle
(a) Normal chart.
Camshaft Piston cooler Oil tank
Turbocharger Main gallery Oil tank
Oil cooler
Feed pump Scavenge pump Relief valve Oil pan
(b) KF2007 chart.
Figure 5 Oil line of KF2007.
SETC 2007
Drive axle
Strainer
Scavenge pump
Figure 6
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Main axle
Oil filter
Lubricant chart.
Relief valve
20076618(JSAE) 2007-32-0118(SAE) scavenge pump is two or three times of that of the feed pump. The blow-by gas rate was measured with the water displacement method at the maximum engine speed. KF-SP07 had two oil intakes as shown on Fig. 7 to prevent the gas breathing at turn. The oil pan had two oil ports at the left/right end. 2. 2. 5
Accommodation KF2007 does not use the intercooler for the intake air after the compressor to reduce the car weight and the intake air resistance. As the mixture temperature at the cylinder entrance is higher than these in NA case, the knocks in the combustion chambers could be occurred easily. The compression ratio was changed to prevent the knocks and the ignition/fuel injection timing should be controlled properly. Before KF2006, the normal engine control unit (ECU) with the sub-controller could not control these parameters and full-computer was used instead of the normal ECU. At a certain intake air rate and an air/fuel ratio, the combustion pressure could be increased as the ignition angle was advanced and the maximum pressure in the combustion chambers could be occurred near at the top dead center (TDC). In the theoretical Otto’s cycle, the best thermal efficiency could be realized with the maximum combustion pressure at the TDC. However, the real engine combustion, which needs 40 – 60 deg. in crank angle to finish, will increase the compression load and decrease the output power if the ignition timing was advanced too much. Moreover, too much advanced ignition timing will make the knock. On the other hand, as the retarded ignition timing will suppress the maximum pressure/temperature, the engine could be protected in exchange for the decreasing output power. As the ignition timing will mainly control the output torque, the exhaust gas compositions, we should determine the ignition timing perfectly. In this paper, the base data was made at the warming-up, a steady driving condition, and the ignition timing was advanced carefully. The throttle aperture was 2%, the engine speed was 1300rpm and the ignition timing was 10 deg. before TDC (10 deg.-BTDC). The air/fuel ratio, A/F, was controlled with the fuel flow rate. The A/F was measured at the turbine exit (A/F-boost meter, UEGO sensor, 10 –30 A/F in range, 0.1 A/F in resolution) and the fuel flow rate was measured at the fuel tank exit (the maximum allowable pressure 500kPa, 0.008L/min (1.3cc/sec) in resolution). The fuel return from the injectors was set at the downstream of the measuring point. The theoretical A/F, about 14.5, will occur the knock significantly. At large A/F, the fuel-lean combustion will occur. The fuel-lean combustion has lower combustion speed and need longer combustion duration. This longer duration will cause the knock. At small A/F, the fuel-rich combustion will occur. The fuel-rich combustion has large fuel latent heat and the engine will be cooled and protected. As the A/F was 12.6 at NA, 11.5 was used in these experiments.
SETC 2007
Drive shaft
Oil line
Figure 7 Schematic of the KF-SP07.
2. 2. 6 Torque measurement The engine power/torque was measured with the two hydraulic dynamometers (the maximum measurable power 45kW at 6000rpm, the maximum measurable torque 105.3Nm at 4000rpm) and the load cells (DC12V driven, the rated capacity 500N, 0.128N in resolution). The main axle of the engine and the dynamometers’ main shafts were linked with a chain for the easy maintenance. The net fuel consumption rate was calculated from the fuel flow measured at a steady engine speed and at a steady load. The sheathed K-type thermocouples were used to measure the temperatures, the inner air temperature of the surge tank (1.0mm in sheath diameter, 0.01K in resolution), the intake air temperature before the compressor (1.6mm in sheath diameter, 0.005K in resolution), the exhaust gas temperature before the turbine (3.2mm in sheath diameter, 0.18K in resolution) and the exhaust gas temperature after the turbine (3.2mm in sheath diameter, 0.18K in resolution). The static pressures at the temperature measurement points were measured with the pressure transducers (the rated capacity 500kPa-abs, 0.26kPa in resolution), the strain amplifiers (1 channel, AC100V driven) and the data-logger (16 channels, 400MHz in the sampling rate).
3.
RESULTS AND DISCUSSION
3. 1 Cam shaft profile As the results of the try 1 – 4, the larger lift height and the narrower action angle of the exhaust valve increased the torque at the ordinary engine speed, 7000 – 10000rpm. The smaller lift height of the intake valve decreased the torque fluctuation at the low engine speed. In this paper, we aimed the
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20076618(JSAE) 2007-32-0118(SAE) 70
Torque Normal Custom (Try 5)
60
70
120
60
60
Toruqe [Nm]
30
70 60 50
40
40 30
30
20
Normal Custom (Try 5) 2
4
6
8
10
12
20
0
0 14
70
1.8 1.6
40 1.4 30 1.2 Boost pressure 1.0
0
4
5 6 7 Engine speed [1000rpm]
8
0.8
Figure 10 Torque curves and Boost curves.
500
BSFC [g/kWh]
400
70 60 50
300
40 200
30
0
20
Power NA Turbo
100
(2)
80
BSFC NA Turbo
4
5 6 7 Engine speed [1000rpm]
10 8
0
Figure 11 BSFC curves and Power curves. (Comparison between NA and Turbo.)
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Power [kW]
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P
NA Turbo
10
3. 2 Turbocharger Figure 9 shows the torque and power curve. While the torque was 111% of NA at 8000rpm, it was 101% of NA at 7000rpm. The result at 7000rpm should be caused by that the engine was unstable and the A/F and the ignition timing could not be adjusted. Figure 10 shows the boost pressure curve. The boost pressure was set as 130kPa(0.3 kgf/cm2-gauge) and the torque was increased when the boost pressure reached the set value. Figure 11 show the Brake Specific Fuel Consumption (BSFC) and BSFC is defined as follows.
0
2.0
20
In the ordinary engine speed, 5000 – 10000rpm, the torque fluctuation with try 1 and that with try 5 was 0.40 and 0.19, respectively. While the torque fluctuation decreased about 50%, the torque at 7000rpm was unstable and not accurate. The effects of the exhaust inertia will cause the inaccuracy.
BSFC =
8
50
fT : Torque fluctuation [-] Tmax : The max. torque [Nm] Tmin : The min. torque [Nm]
m f ⋅ ρ f ⋅ 10 3
7
Toruqe
60
Toruqe [Nm]
(1)
6
Boost pressure [102kPa]
Tmax − Tmin Tmax
5
Figure 9 Torque curves and power curves. (Comparison between NA and Turbo.)
Figure 8 Torque curves and power curves. (Comparison between the normal-cam and the custom-cam.) higher torque with smaller fluctuation at the ordinary engine speed and the torque fluctuation at the high engine speed was ignored. The results of try 5 with KF2006 were shown in Fig. 8. The torque fluctuation was defined as follows.
4
10
Engine speed [1000rpm]
Engine speed [1000rpm]
fT =
Power NA Turbo
10
Power
10 0
20
40
20
Power [kW]
80
Power [kW]
40
80
Torque NA Turbo
50
100
50 Torque [Nm]
140
20076618(JSAE) 2007-32-0118(SAE) BSFC : Brake specific fuel consumption P : power [kW] mf : fuel flow rate [little/h] ρf : density = 0.76g/cm3 at 15 C-deg
[g/kWh]
The lower BSFC means the higher efficiency. While the BSFC of NA were almost 300g/kWh, that of Turbo were not constant and represented an increase of 34% in comparison with NA at 8000rpm. However, the BSFC of Turbo at 6000rpm was almost same of NA and this system worked efficiently. The exhaust pressure (the pressure before the turbine) increase should cause the worth BSFC at 8000rpm as
1.5
Before the compressor After the compressor Before the turbine After the turbine
Pressure [10kPa-gauge]
1.4 1.3
5.
1.2 1.1 1.0 0.9
4
5 6 7 Engine speed [1000rpm]
8
Figure 12 The static pressures at the temperature measurement points
60
1.3 30 Boost pressure
1.2
20 1.1
10
4
5 6 7 Engine speed [1000rpm]
8
Boost pressure [10kPa-gauge]
1.4
40
0
The turbocharger and the custom camshaft were installed in the motorcycle natural aspirated gasoline engine, to improve the power output and the fuel consumption. The custom camshaft and the turbocharger realized the flat and high torque in low/middle engine speed. However, the averaged torque and the fuel economy were not enough because the compression ratio, the ignition timing and the fuel injection timing/flow were not be adjusted. As the major troubles in turbocharged engines with the atmosphere temperature change or with the altitude change will cause the engine knock, feed-back control systems should be developed. The dry sump lubricant system with KF-SC07 realized the low crank axle height. However, the system was heavy and large. The detailed CAD study for the oil line should be made.
ACKNOLEDGEMENTS The authors gratefully acknowledge many of our colleagues who hove contributed to this work especially Mr. Noboru Hieda, research assistant of Kanazawa University Mechanical Systems Engineering, and the Kanazawa University Formula R&D team and Kanazawa University Administration. We wish to thank YAMAHA MOTOR to have sustained the presented work both through many parts and technical suggestions.
1
REFERENCES [1]
Figure 13 Temperature curves and Boost curve.
SETC 2007
CONCLUSION
1.5
Before compressor After compressor
50 Temperature [C-deg]
shown in Fig. 12. It was understood that the gain of power output to the fuel consumption was small in about 8000rpm. Though the averaged BSFC of NA was better than that of Turbo, the A/F of NA and that of Turbo were 12.6 and 11.5, respectively. The adjusted exhaust/intake manifold will improve the unsteadiness and set the A/F suit for the better BSFC. Figure 13 shows the intake temperature curves and the boost pressure curve. The temperature after the compressor was increased as the boost pressure increase and was 52 C-deg at 8000rpm. The temperature before the compressor was almost same. The volume of the surge tank should suit the characteristics of the turbocharger because the surging in the tank would make a back current to the intake of the compressor. The back current will cause an unstable action. As the temperature before the compressor was almost constant, the capacities of the compressor and the surge tank were correct in this experiment.
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Society of Automotive Engineers, 2007 Formula SAE Rules, 2006
20076618(JSAE) 2007-32-0118(SAE) [2]
William Attard and Harry C. Watson, Development of a 430cc Constant Power Engine for FSAE Competition. SAE Technical Papers, 2006-01-0745, 2006
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