Analysis and Design of a Formula SAE Powertrain · 2019-03-08 · Using Helmholtz resonator principle, required runner lengths were calculated so that the peak volumetric efficiency

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056

Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072

© 2018, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 448

Analysis and Design of a Formula SAE Powertrain

Prasantha Laxman Pujari

1Mechanical Engineering Department, G.V. Acharya Institute of Engineering and Technology, Shelu Road, Shelu, Maharashtra – 410101, India

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Abstract - This project aims are to design and develop the powertrain system for formula SAE race car and the design that used for the car must fulfill the standard regulation that made by SAE for Formula SAE competition. Besides that, the load of the axle also been determined to get the maximum torque applied using three different approached that are engine performance, tire friction, and predicted acceleration and the cornering force acting on the race car.

Key Words: Engine Unit, Cbr250R, Intake & Exhaust, Cooling System, Fuel Pump

1. INTRODUCTION The stiffness of mounting system determines the vibration isolation ability of the transmitted path, which is the key factor that affects the vibration and noise of vehicle. In order to improve the vibration isolation ability of the powertrain mounting system, considering the powertrain of front wheel drive car as the research object, the vibration decoupling rate and its corresponding frequency of the powertrain mounting system are analyzed by rigid body dynamics and energy method

2. ENGINE UNIT

2.1 MODULE OBJECTIVES To deliver a reliable and weight optimized engine system with sufficient power and the possibility for low fuel consumption. An engine has to be selected from either Honda CBR250R or Honda CBR600RR.

2.2 ENGINE SPECIFICATIONS

Fig -1: Honda CBR600RR, Honda CBR250

Table -1: Engine Comparison

Engine Comparison

Specifications CBR 250R CBR 600RR

Bore (mm) 76 67

Compression Ratio 10.71 12.21

Cooling Liquid Liquid

Cylinders 1 4

Displacement (cc) 249.4 599

Engine Configuration Single - Cylinder

Horizontal In - Line

Engine Type 4 - stroke 4 - stroke

Fuel Injector Yes Yes

Stroke 55 42.5

Valves Per Cylinder 4 4

Peak Torque 23 Nm @7000 rpm

66 Nm @ 11250 rpm

Peak Power 20 kW @8500 rpm

88 kW @ 13500 rpm

Power / Weight 0.67 kW / kg 1.25 kW / kg

2.3 REASONS FOR CHOOSING CBR250R

[1] The CBR250R engine stays in the power band for a longer time than its 600cc counterpart over the course of a lap.

[2] The CBR250R is around 40 kg lighter than the commonly used CBR600RR. The lighter load of the engine would enable the team to use a lighter chassis, further reducing the weight.

[3] It would be easier for the driver to handle the CBR250R on track than the 600RR, leading to consistency in performance.

[4] Higher fuel efficiency can be achieved.

[5] Since Honda CBR600RR engines are not readily available in India, importing spare parts becomes a problem and leads to high costs.




2.4 SIMULATIONS TO SUPPORT THE CHOICE

Simulations have been performed for the Honda CBR250R and the Honda CBR600RR engines on different track layouts with varying weights of the car. The results indicate that at lower weights, both engines perform similarly, while at higher weights; the CBR250RR loses its advantage. However, the difference in lap-times over a simulated circuit is less than 1 second under ideal conditions. It is expected that when the driver’s accuracy and real conditions are taken into account, the performance difference would be much lesser.

Fig -1: Engine torque and power curves (black: torque,

blue: power)

Some of the results after the simulation are as follows:

Fig -2: Engine speed over the course of the lap (red: 250cc, green: 600cc)

Variation of lap-times of the car with its net weight on a

custom-made autocross track


Weight of Car Lap Time

600 cc 250 cc 600 cc 250 cc

260 210 57.81 57.8

270 220 57.8 57.81

280 230 57.8 57.84

290 240 57.8 57.87

300 250 57.79 57.91

310 260 57.79 57.95

320 270 57.79 58.01

2.5 PERFORMANCE AT DIFFERENT TRACKS


Track Layout Lap Time (sec)

250 cc (Wt:

220 kg)

600 cc

(Wt: 270

kg)

Acceleration (75m) 5.48 5.01

Skid Pad test (Circle,

r=5m) 5.75 5.75

55.47 55.41

44.11 43.93

57.81 57.80

53.05 53.05

Consider Track 3, which has a combination of high-speed straights and low-speed corners. On this track, the speed of both the engines over the course of the lap is plotted and compared. It is observed that the 250cc engine remains in the power band for a longer duration than the 600cc engine. This is possible because while the 600cc engine is predominantly in the first and second gears only, the 250cc engine makes full use of all the gears.




A smaller engine combined with its greater usage at full open throttle improves the fuel efficiency too.

2.6 RESULTS


Parameter 250 cc 600 cc

Acceleration Poor acceleration and top speed

Huge advantage. Longer the straights, better the performance.

Skid Pad event Lighter car, hence better cornering and turning

Heavier car hence may be slower during cornering

Handling Lighter car and a smaller engine makes it very easy to handle; maximum performance can be extracted

Difficult to run the engine at its optimum conditions

Fuel Efficiency Good Poor

Faster in tight and twisty circuits

Faster in high-speed circuits

Fig -3: Gear used over the course of the lap

3. INTAKE & EXHAUST

3.1OBJECTIVES

[1] To determine the appropriate length of the intake runner to achieve high volumetric at high speeds without compromising on volumetric efficiency at low speeds.

[2] To determine the advantage of a plenum and to decide on its maximum volume.

[3] To determine the gain in volumetric efficiency achieved by using the new camshafts over the OEM cams.[3]

3.2 PRINCIPLE

Concept: A wave which reflects from a closed end maintains its phase whereas a wave reflecting from an open-end changes its phase by 90 degrees. While the engine is running, the intake valve opens and closes once every two revolutions. While the valve is open, air flows through the valve from the intake manifold to the engine cylinder. As it closes (and an area of flow decreases) the velocity of air increases (through the equation of continuity). When the valve closes, the flow is stopped abruptly and a compression wave is created which travels upstream from the valve. This is called the ramming effect. [6] This compression wave reaches the open end, reflects back towards the valve as rarefaction wave subsequently reflects from the closed valve as a rarefaction wave and reflects again from the open end as a compression wave flowing downstream. By the time this compression wave occurs, we want the valve to open for the next cycle. The length of the intake runner (location of the open end) has to be accordingly tuned to ensure that the compression wave reaches the valve just as the next cycle begins. When the intake valve opens, there is low pressure downstream of the pipe and hence a rarefaction wave travels from the valve upstream the intake runner. This wave reflects from the open end as a compression wave and travels back towards the pipe. The rarefaction wave begins just as the intake valve opens and the compression wave must reach the valve just before it closes. Both these effects help in pumping as much air as possible into the cylinder when the intake valve is open and the intake system is tuned for the same. AVL Boost software has been used for intake tuning. A model of the engine was simulated in this software and focus was given only to volumetric efficiency.

3.3 RESTRICTOR DESIGN

A CD nozzle was used to house the 20 mm intake restrictor. The converging section upstream of the restrictor is angled at 140 and the diverging section downstream of the restrictor is angled at 70 to the axis.[1] Ideally, the angle should not be more than 70 to the axis because of any further increase in the angle will result in flow separation in the diverging part and also lead to vortices formation both of which are undesirable because they cause pressure loss. For the same reason, the diverging part is also longer than the converging part. The open ends have a diameter of 38 mm which corresponds to the diameter of the throttle butterfly valve.




Fig -4: Intake restrictor- CD nozzle

3.4 DETERMINATION OF INTAKE RUNNER LENGTH

The entire intake runner has been modelled into three sections, two of which are inside the engine block and the other being the fabricated section. From upstream to downstream, they are

[1] Fabricated intake section [2] Small section of 20mm length and 38mm

diameter just inside the engine block. [3] Split section which leads to two intake valves.

Fig -5: Intake restrictor- CD nozzle

Sections 2a and 3 were held constant and the length of section 1 was changed. The diameter of section 1 was kept at 38 mm. Using Helmholtz resonator principle, required runner lengths were calculated so that the peak volumetric efficiency occurs at 6000, 7000, 8000 and 9000 RPM. These lengths were tested in the software.

The software was configured to run separate cases for all speeds between 5000 RPM and 11000 RPM in intervals of 500 RPM and the variation of volumetric efficiency with speed was plotted. This process was repeated for all the runner lengths. The results are plotted below.

Fig -6: Simulation model in AVL Boost

Variation of volumetric efficiency with Intake and exhaust runner lengths

0.7

0.75

0.8

0.85

0.9

0.95

1

Vo

lum

etr

ic E

ffic

ien

cy A

mb

(-)

5000 6000 7000 8000 9000 10000 11000

speed (rpm)

in 250, ex 600 (-)

in 220, ex 600 (-)

in 220, ex 500 (-)

in 250, ex 500 (-)

Fig -7: Simulation model in AVL Boost

From the simulation it was observed that 250mm was the optimum intake runner length and 600mm was the optimum exhaust runner length that gave high volumetric efficiency at both low and high speeds.

3.5 EFFECT OF PLENUM

Constraint- Located downstream of throttle. A plenum is used by all teams using 4-cylinder engines to avoid choking at the restrictor and for the even distribution of the air in all cylinders.[2] To determine whether it would prove useful in a single cylinder engine, a plenum was simulated in the software and the volumetric efficiency curves were plotted for different plenum volumes.

3.6 SIMULATION RESULT

As plenum volume increased, volumetric efficiency increased However, the software simulated only steady-state response. Since the throttle is upstream of the plenum, larger the plenum, slower is the throttle response. Literature survey showed that the plenum volume is typically 4 times that of the engine displacement volume. Therefore a 1 litre plenum was chosen.




Fig -8: Effect of different plenum volumes based on steady

state simulation

Fig -9 Intake runner and plenum

3.7 OBSERVATION

[1] Very weak throttle response was observed when this was mounted on the car (much weaker than expected)

[2] Engine was not able to idle and died every time the throttle was released. Engine breaking seemed to be the only way to control it. We had ensure high RPM even while slowing the car down by quickly shifting to lower gears.

The idling problem could have been because: While designing the runner, volumetric efficiency curve was observed only between 5000 and 11000 RPM. It could have been possible that this curve fell sharply at lower idling RPM (~ 1500 RPM) as a result of which the volumetric efficiency could have been very low at idling RPM leading to shutting down of the engine.[6] When the engine was run at idle for quite some time, the throttle response seemed to improve. However, the idling issue could not be rectified with this intake system.

3.8 CHANGE OF INTAKE SYSTEM

The plenum was then removed from the design and a different intake system was used, where the intake runner was directly connected to the CD nozzle. This design:

[1] Gave good throttle response [2] Engine remained very stable even at idling

Therefore, the new intake system (without the plenum) was chosen.

3.9 CHANGE OF CAMSHAFTS

The OEM Honda camshafts were replaced by new Takeaway camshafts that offered longer intake and exhaust durations with the same lift. This configuration would improve volumetric efficiency at high speeds and slightly lower that at lower speeds, thereby shifting the power-speed curve to the right. As expected, idling became more difficult once these camshafts were installed. To counter this, the butterfly valve was adjusted so that the idling RPM was increased from 1500 RPM to 2000 RPM, where the engine remained more stable. In the volumetric efficiency curve, it can be observed that there are two intake peaks and one exhaust peak which occurs between the two intake peaks. The exhaust runner length in the simulation model was changed till the three peaks gave a fairly flat volumetric efficiency curve. Through iterations, a length of 600mm was chosen. The muffler used for previous car was 30 cm in length and had a diameter of 10 cm. This muffler barely managed to clear the noise test recording 109.7 dB at the required speed, which is too close for comfort. Hence, a longer muffler (40 cm) was bought having the same diameter (10cm) and packaging thickness. Since there is packaging material for a longer distance, we expected the output noise to be considerably lesser. On performing noise test, a sound level of 110 dB was recorded at 9000 RPM and 107 dB was recorded at 8500 RPM (designated RPM) with the new camshafts.

3.10 MUFFLER ROUTING


Front facing Rear facing

Advantages: Advantages:

Longer muffler length possible. Easier to clear

Exhaust gases exit at the rear.




noise test.

Low mounting of the muffler, lowers the CG of the car.

No need of firewall or casing. Well shielded from the driver.

Fewer bends in the exhaust pipe.

Disadvantages: Disadvantages:

Unconventional layout. Packaging is difficult.

Pressure at end of tailpipe is stagnant pressure, not static pressure.

Higher mounting of the muffler increases CG of the car.

Extra bodywork needed to cover the muffler, greater weight.

Extra sharper bends in the exhaust pipe, routing is difficult.

3.11 MANUFACTURING OF INTAKE SYSTEM

3.11.1 CONSTRAINT

The intake system must remain within the envelope defined by the top of the main roll hoop and the edge of rear tires. Since the wheelbase has been reduced and the tires are smaller owing to 10” rims, this envelope has become much tighter than what it was for previous car The entire intake system was manufactured out of FRP.

3.11.2 MOULD MAKING A PVC pipe of OD 38 mm was taken to form the mould. In order to bend it accordingly, it was first stuffed with special sand and blocked on both sides. This is done to ensure that the PVC does not fold while bending. After both the sides are blocked and sealed, a hot air gun is used to blow hot air onto the pipe. The air is uniformly blown across the area where the pipe would be bent. Adequate time was given in between for the heat to transfer to the sand inside the pipe too. When enough heat is provided, the PVC begins to bend. At this point, the pipe is stretched and bent to the required angle. Sharper the bend, greater the chance of folding in the pipe. After the required bend is achieved, the pipe is cooled and brought back to room temperature. The bent pipe is cut into two longitudinally equal halves which are used to lay FRP. Two halves of FRP are made which are then joined together with another layer of FRP to form a single pipe. The plenum is manufactured similarly too. Advantage: Easier to detach moulds from the FRP layer.

Disadvantage: Inner surface of the pipe is not smooth as two halves are joined together. This may impact air flow by decreasing coefficient of discharge. The throttle bodies are connected to the FRP mould using small sections of a rubber tube of ID 45mm (corresponding to OD of throttle body) and clamped. These must be fastened so that there is no air leakage from any of these joints.

3.12 MANUFACTURING OF EXHAUST SYSTEM

OEM exhaust pipes of the CBR250R are used to complete the routing of the system. Three OEM pipes were used and sections were cut such that when welded together, the required configuration was achieved. During manufacturing, the following constraints were kept in mind:

[1] The muffler must be parallel to the side impact structure so that the mount on which the exhaust rests may be as small as possible. Additionally, this would keep the muffler as close to the chassis as possible and ease driver egress.

[2] The muffler must be inclined in such a way that it remains higher than the lowermost chassis member at that point throughout the length.

The pipes were routed from behind the main roll hoop to ensure that there was sufficient distance between the exhaust runner and electricals to avoid heating.

The exhaust runner was welded to the flange of the muffler which was connected to the muffler through six Allen bolts. To avoid exhaust gas leakage, two exhaust gaskets were placed between the muffler flange and the muffler.

3.13 FINAL ROUTING OF EXHAUST MANIFOLD

Length of Exhaust pipe (In CAD) = 60.729cm Starting from the engine port, length description is given below

[1] 53.374 mm straight-line [2] 82.030 mm curve length (angle = 94-degree, bend

radius = 50 mm) [3] 353.386 mm straight-line [4] 73.792 mm curve length (angle = 84.56-degree, bend

radius = 50 mm) [5] 45.012 mm straight-line [6] Outer diameter of pipe in CAD = 45mm [7] Inner diameter in CAD = 38 mm

3.14 MUFFLER DIMENSIONS

[1] Length = 600mm [2] Outer diameter = 100 mm [3] Inner diameter = 45mm




Fig -10 CAD showing the side view of the exhaust and its connection to the engine

Fig -11 Overall view of system

4. COOLING SYSTEM

4.1 PRINCIPLE

To cool down the engine, a coolant is passed through the engine block, where it absorbs heat from the engine. The hot coolant is then fed into the inlet tank of the radiator (located on the top of the radiator), from which it is distributed across the radiator core through tubes to another tank on the opposite end of the radiator. As the coolant passes through the radiator tubes on its way to the opposite tank, it transfers much of its heat to the tubes which, in turn, transfer the heat to the fins that are lodged between each row of tubes. The fins then release the heat to the ambient air. Fins are used to greatly increase the contact surface of the tubes to the air, thus increasing the exchange efficiency. The cooled coolant is fed back to the engine, and the cycle repeats. Normally, the radiator does not reduce the temperature of the coolant back to ambient air temperature, but it is still sufficiently cooled to keep the engine from overheating.

The coolant we are using is normal tap water, because of its boiling point being close to the standard engine operating temperature - 110 C.

4.2 SET UP

Since side-pods were not present on the car, the positioning of the radiator could be done as required. Possible locations considered were

[1] Same place as PREVIOUS CAR, where side pods would have been present

[2] Mounted to the main roll hoop at the lowest position.

[3] Main roll hoop bracing

Locating it in the same place where side pods would have come has the following issues

[1] The radiator has to be angled so that it fits within the height of the side impact structure, meaning lesser cooling area

[2] Additional firewall for the driver Very low position, hence it will not be very effective for the cooling pump to circulate water

[3] We thought this was the reason why we were facing radiator issues in previous car

Locating it on the bottom most vertical structure of main roll hoop. Very low position with respect to engine.

We assumed that locating the radiator lower than the engine would mean that there is no head available at the engine inlet (cooling pump inlet). Hence, this would make water circulation difficult, leading to cooling issues. Hence, we decided to place the radiator on the roll hoop bracing higher than engine inlet.

Fig -12 Rear view of the car showing radiator, catch can and hoses

http://en.wikipedia.org/wiki/Coolant

http://en.wikipedia.org/wiki/Engine_block

http://en.wikipedia.org/wiki/Fin_(extended_surface)




4.3 PROBLEMS AND SOLUTIONS Problem 1 Bursting of radiator hoses while

running the car

Experiment 1 Hose clamps were changed

Experiment 2 Checking water circulation inside the engine

Experiment 3 Changing hose quality

Reason This experiment was carried out because the bursting occurred mostly near the end of the hoses, where it was clamped

Reason This was because the hoses were getting very hot, so suspicions about the circulation itself and not the radiator or hoses developed

Reason This was because of suspicions in the quality of hoses

Solution Instead of using the standard “Worm Drive” Clamps, a “Wire Hose Clamp” were used

Solution The hoses were removed and water was directly filled into the engine inlet

Solution The standard rubber hoses were replaced with metal braided hoses with a maximum pressure capacity of 125bar

Observations & Inference The problem still persisted. Moreover, the cracks appeared even at the middle

Observations & Inference The cold water poured inside came out as steam through the other end. The outlet water was so hot that the bottle could not be held without insulation. This means that water circulation and heat transfer from engine to water was happening properly

Observations & Inference No more bursting of hoses. The metal braided hoses are capable of sustaining the pressure and temperature of the coolant

Problem 1 eliminated.

Therefore, the radiator has been placed on the main roll hoop bracing and metal reinforced hoses have been chosen to transport coolant water between the radiator and the engine.

Problem 2 Steam released from the radiator after twenty minutes or so of running the engine

Experiment 1 Mounting the catch can at the same height of radiator overflow vent

Experiment 2 Increasing the boiling point of coolant

Experiment 3 To condense the steam coming out of catch can

Reason We learnt that radiators not only vent water to the catch cans but also suck water back from them

Reason The pressure of cap defines the boiling point of coolant. The pressure was expected to be very less that boiling starts within very short time.

Reason The steam gets condensed from the water in the catch can

Solution The catch can was mounted on the bracing at the same level of the overflow vent

Solution The radiator cap was changed from 1.1 bar cap to 1.4 bar cap of KTM Duke 390

Solution Catch can was filled with water and a vent from the cap was immersed in this water

Observations & Inference Steaming still continued. The amount of water in the catch can was 400ml and the amount of water lost by radiator was 350ml. Hence, 50ml was converted to steam. This was a huge loss, and it will critically affect the engine performance during endurance

Observations & Inference No considerable positive results, as steaming still persisted and the loss was about 50ml.We understood simulating race track conditions would not work, and hence took it to actual testing of the whole car

Observations & Inference No steam was observed during the whole endurance run

Running conditions were simulated by using a high speed fan and running the car on jacks




Fig -13 Isometric view of the radiator

Fig -14 Isometric view of the car showing the coolant hose connections to radiator and catch can

5. FUEL TANK

5.1 OBJECTIVES & CHALLENGES

The tank has to be securely attached to the vehicle all times and if made of rigid material should not be used to carry structural loads.

[1] Sloshing occurs at low volumes, which creates imbalance to the car during braking, acceleration and deceleration

[2] Sloshing also creates an interrupted supply of fuel to the pump.

[3] The tank has to be easily mounted and accessible in the car.

[4] The weight of the tank should be minimum to lower down the CG of car.

5.2 MATERIAL OF THE TANK

The material of the tank should be checked for corrosion with gasoline.

Aluminium

[1] Lesser weight to the tank [2] Easily fabricated into any desired shape [3] Good resistance for corrosion with gasoline [4] Easy availability in the market

Plastic

[1] Reduces lot of weight but punctures in contact with sharp things.

[2] Mounting of flexible material is quiet difficult. [3] HDPE (High Density Poly Ethylene) is the best

material mostly used and heat sources should be avoided in such case

Aluminium and Poly urethane were selected for manufacturing the tank

[1] Aluminium for body [2] Flexible PU hose for filler neck

5.3 MOUNTING

[1] Mounting should be below or close to the existing CG, so the CG doesn't change much as the fuel tank empties.

[2] The tank has to be away from heat sources like exhaust.

[3] To avoid change in lateral weight distribution, tank has to be mounted close to the horizontal CG.

[4] The tank is placed in an aluminum basket and for secure mounting Velcro’s were used

5.4 Sloshing

The effect of sloshing can be reduced by many ways

Foam- The tank has to be designed such that there is accessibility to stuff the foam. The fuel is added with foam particles. These foam particles create stability to the fuel and reduce the turbulence. The main disadvantage of foam is, little bits of foam gets blocked in the pump when excess of




foam is used. This results in surging of fuel tank but by careful baffling surge can be avoided.

Baffles- These baffles trap the fuel between them and result in a constant supply of fuel to the intake manifold. Baffles result in increasing weight and complexion of the tank. Welding the baffles to the tank is also difficult.

Fig -15 Baffles

Filler neck- Advantage can be taken in assigning some part of tank volume to neck. This ensures that significant amount of fuel stores in the neck when the tank is full. The issue regarding this is that the CG of the car goes a little bit up as the volume of fuel is significantly distributed from top to bottom.[7]

Low pressure lift pumps

It can be tricky to recover the fuel as it moves around in the tank, particularly at low level - imagine drinking with a straw from water bumping around on a tray compared with drinking the same water with a straw in a bottle.

The tank is therefore provided with a low pressure electrically powered ‘lift pumps’ at the corners to suck the fuel. These deliver the fuel to a small tank known as collector. This collector is provided with an external pump. This pump can constantly recover fuel to the intake manifold. The issue regarding low pressure lift pumps is it will increase in complexion and manufacturing of the tank.

5.5 Shape of fuel tank One of the simplest design is taking a cuboid fuel tank and placing internal baffles. Further we can modify the cuboid shape by making the two opposite rectangular sides into

quadrilaterals by pulling down only the top edge to reduce the effect of sloshing as shown in the below figure. Foam can also added to further minimize sloshing. This design

has geometry, baffles, foam. This design is also easy to manufacture.

Fig -15 Manufactured Fuel tank

Cylindrical tank

We can also design the tank in cylindrical shape. This reduces the effect of sloshing to a greater extent but mounting the cylindrical tank into the car is a major issue.

Conical tank

A conical tank can also be used with an internal suction pump at the bottom. Mounting of a conical tank is also an issue. But as the radius of the tank is high at the top the effect of sloshing is more at the top even when the fuel is more compared to other tanks. This is more useful when fuel is low and baffles are used.[8]

Since the 250cc has a higher fuel efficiency, the fuel tank capacity was kept at 4 liters. To reduce complexity, we split the total volume as approximately 3 liters (3.072 lit) stored in an aluminium cuboid and 1 liter (0.981 lit) in a flexible fuel resistant hose made of polyurethane. The pump occupied one fifth area of bottom part of the tank which left approximately 200 sq.cm (205.76 sq.cm), for which sloshing was very less and there wasn’t any space for baffles. Hence baffles weren’t used. The transparent filler neck eliminated the use of sight tube

5.6 Fuel Tank

The fuel tank is a trapezoidal box made from aluminium plates of thickness 2mm. The main aim of making it a trapezium and not a box is to make it have a clearance of 10mm from the flexing of seat. It was fitted with a bottom mounted pump. The volume of the tank was designed to be 3L, as the mileage of the CBR250R engine is average 10kms/l and we need to cover a distance of 22kms non stop. There was a plate beneath the tank to lock the fuel pump to the tank.




Fig -16 Seat Clearance

5.7 FUEL PUMP

Fuel must be recovered from the tank and supplied to fuel injection system at pressures of 4 to 5 bar. For the recovery of fuel from the cell there are two types of pumps

[1] External fuel pump [2] Internal fuel pump

External fuel pump

In some cases the pump is located outside the tank and these doesn’t involve submersion. These pumps are called external fuel pumps. Fuel lines are drawn from the tank and connected to these pumps. These pumps suck the fuel and supply them to the fuel injection system.

[1] External fuel pumps are noisy [2] External pump are easier to maintain and service

due to location but requires additional fittings and space, adds to weight and cost report

[3] External pumps are mounted lower than the tank cause they don't pump against gravity

5.8 INTERNAL FUEL PUMP

There are cases where pumps are inside or submerged in the tank. These work under submersion. These are called as internal fuel pumps.

[1] Internal fuel pumps are difficult to change. [2] Internal the pump, it stays cooler because the fuel

keeps it cool. [3] It also may be a safety factor in a crash because the

pump is not exposed. [4] Internal fuel pumps are harder to maintain and

service [5] An internal fuel pump does not require additional

plumbing and mounting brackets therefore it saves weight and space (depending on design)

Property External pump Internal pump Noise High Low Maintenance Easy to maintain

and service Difficult to remove, maintain and service

Weight Adds weight and cost

Less compared to external pump

Additional fittings Requires additional fittings

Doesn’t require

Space Adds space Consumes less space

Removability Easily removable Difficult to remove

Safety of pump Safety is a bit less Pump is more safer as it always stays cool because of fuel and lasts long

There are two types of internal fuel pumps

[1] Top mounted fuel pump [2] Bottom mounted fuel pump

5.9 TOP MOUNTED FUEL PUMP A hole is made on top of the tank and the pump is placed in this hole carefully because it has to be submerged always in the fuel for continuous supply to the engine. If the above requirement is absent, in case of low fuel level it sucks only air and burns itself.[9] Pump is highly accessible and can be replaced immediately with ease if there is any failure at any time independent of the fuel level. Sloshing has a slight effect on top mounted fuel pump. The pump must extend from top of the tank to bottom for constant submerge where the size of the pump increases as a result, size and weight of the tank increases compared to the bottom mounted pump in order to compensate the volume. Fuel can leak through the top-hole spilling over the driver and the engine. Firewall and other safety precautions must be designed to prevent the spill.

Fig -16 Top Mounted Fuel Pump




5.10 BOTTOM MOUNTED FUEL PUMP

[1] A hole is placed on the bottom of the fuel tank and

the pump is placed in this hole. [2] As the pump and all its fuel lines are situated below

the tank accessibility to the pump is less. [3] There is also a restriction that pump can be

removed only after all the fuel is consumed and nothing is left over in the tank.

[4] There is no immediate replacement for the pump during failure.

[5] As all the equipment is below, the tank has to be mounted at a certain height above from the lowest member of the chassis. This increases the CG of the tank and the car which is the major issue regarding the usage of this pump.

[6] The sloshing effect is minimal compared to top mounted pump.

[7] The bottom of the tank must be carefully sealed because there is a greatest possibility of leakage.

[8] A pan is generally placed below the tank to collect the leaked fuel. This can be ignored in bottom-mounted pump because all the leaked fuel will spill over the ground where there is no problem.

[9] The size of the pump is small compared to top mounted pump.

Fig -17 Bottom Mounted Fuel Pump Table Comparison of top and bottom mounted fuel pumps

Property Top mounted Bottom mounted Accessibility Easily accessible

as the pump is at the top of the tank

Accessibility is less because the pump is located below the tank

Centre of gravity No effect on CG of the car

The CG of the car decreases because of the mounting of the tank due to the pump and all fuel

lines Pump removal The pump can be

easily removed at all fuel levels

The pump can be removed only after all the fuel is consumed and removing the pump involves pain over top mounted

Sloshing effect Medium Low Leakage Fuel can leak

from top and spill over the driver and engine

Fuel leakage has no major problems except loss of fuel

Size The size of top mounted pump is high and hence size of tank increases

The pump occupies less volume

Submersion Care should be taken such that pump is always submerged

Pump is always submerged except during low fuel level and lateral forces

The CAD model of the pump is made, to help in the assembly. The pump has three nozzles at the bottom - two for filters and one connecting to the engine intake.

[1] Seventh Plate: The seventh plate is an Aluminium plate of 6mm thickness, to hold the fuel pump with the fuel tank.

A innovative locking mechanism has been created. Two slots for three of the holes are made. The pump will be inserted at an angle and rotated to ensure locking.

Fig -18 Locking mechanism of the fuel pump to the seventh plate




An extra length at the back has been provided for mounting it to the chassis. One side mounting is done to ensure no load is carried by the tank. It has the same dimension as the base of the fuel tank with M6 holes for holding it and M8 holes for holding it to the chassis member. There is step provided for 3mm and diameter of 110mm for the outer diameter of the pump.[10]

[2] Gasket: The gasket is made of Silicon. It is 2mm thick and its use is to fill the gap between the seventh plate and the tank to ensure there is no fuel leakage.

[3] Box Channel: A 1inch aluminium box channel is used at the bottom to simply support the assembly using M8 nuts and bolts.

[4] Chassis Member: This 1inch solid MS member will be the one on which the fuel system is mounted. Two mounts are welded onto it, with M6 holes that go into the seventh plate mounts.

Fig -20 The L channel on which the fuel tank is resting is in turn mounted to the chassis member.

REFERENCES

[1] Aho, Christopher, Scott Duncan, Dan Cullen, Dan Swan, Adam Panzica, and Ryan Lehrmitt. 2009 Formula SAE Racecar.Tech. 2009. Print.

[2] Milliken, William. (1995). Race car vehicle dynamics (1st ed.). Troy, MI: SAE International.

[3] Timmins, Steve. Formula SAE Powertrain Phase 4: Performance Validation and Path Forward. University of Delaware. 2010. Web.

[4] Young, D. (2011). A Brief Introduction to Fluid Mechanics (5th ed.). Hoboken, NJ: Wiley.

[5] Alspaugh, David, Aquadro, Alessandro, Barnhill, Dylan, Beasley, Nicholas, Bennett, Andrew, Francis,

John. Design and Analysis of a FSAE Racecar. Tech. 2012. Print.

[6] "Torsen 012000 print" http://www.torsen.com/files/University%20Special%20012000.pdf

[7] James, R. (2004) Design of an Aluminum Differential Housing and Driveline Components for High Performance Applications. Unpublished undergraduate thesis, Massachusetts Institute of Technology.

[8] Durand, K. (2005) Design of a Chain Driven Limited Slip Differential and Rear Driveline Package for Formula SAE Applications. Unpublished undergraduate thesis, Massachusetts Institute of Technology.

[9] "Assembly and Timing Notes" http://www.torsen.com/files/012000%20Gear%20Assembly%20&%20Timing.pdf

[10] "NTN Radial Ball Bearings" http://www.ntnamerica.com/Engineering/PDFs 1000/A 1000/A OOORadial.pdf

http://www.torsen.com/files/University%20Special%20012000.pdf

http://www.torsen.com/files/University%20Special%20012000.pdf

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