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Proceedingsof the

ITRN201131stAugust 1stSeptember,University College Cork

Kennedy, Woods, Forrest: Development of an airintake and exhaust system for a race car.

DEVELOPMENT OF A NEW AIR INTAKE AND EXHAUST SYSTEM FOR ASINGLE SEAT RACE CAR

Mr. Damien Kennedy

Dublin Institute of Technology

Dr. Gerry Woods


Mr. Darragh Forrest


Abstract

This paper deals with the design, analyses and testing of a new air intake system for a singleseat race car designed and manufactured by a team of DIT students for the 2011 formulastudent competition in Silverstone. It also deals with the design, CFD analyses and noiseemission testing of a new exhaust system for the vehicle which is powered by a 600ccSuzuki GXR engine. The new air intake system was developed to satisfy the rules of theformula student competition which required a 20mm restriction to be placed on the air intakesystem. It was a requirement that all engine airflow passed through this restrictor.Implementation of the air restriction also meant that a new engine map was required foreffective operation of engine. This paper looks at a number of different alternative air intakedesigns and compares the air flow simulations using CFD analyses. The use of rapid

prototyping techniques to produce a physical model is discussed. The design andmanufacture of a new throttle body is also presented. The process for engine remapping anddyno test results are also presented. The competition also required an exhaust system withnoise emissions below 110db. This paper presents the design and analyses of alternativeexhaust paths and noise emission testing.

1. INTRODUCTION

The basic function of an air intake system is to provide the throttle bodies with air where it isthen mixed with the fuel and sent to the combustion chamber. The construction of the intakesystem has a major influence on how the engine performs at various RPMs.

With reference to Fig 1 an air intake system compiles of four main parts:

Filterwhich is normally a paper element, of conical shape that filters the air from dust anddirt particles before it reaches the engine.Filter to Plenum Runner his is the tube/pipe that takes the air from the filter to the plenum.The Plenum is the chamber or reservoir of air that supplies the engine. The Intake Runnerswhich are the tubes that feed the air from the plenum to the throttle bodies. Long runnersgive good top end speed whereas shorter runners give good low end torque.

Most performance cars will require a certain RPM range where they will want most of theirpower. This is known as the Peak Torque Location. The range of the peak torque location isdependent on what kind of tracks the car is driving on. Winding tracks with short straights willrequire an engine tuned for low end torque to power out of the corners and have a low peaktorque location. Wide and open tracks with long straights will require an engine tuned forgood top end speed and will subsequently have a higher peak torque location. The peak

torque location is depicted by three main features of the air intake system plenum volume,runner length, runner area.

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Kennedy, Woods, Forrest: Development of an airintake and exhaust system for a race car

31stAugust 1stSeptember,University College Cork

Proceedingsof the

ITRN2011

Fig 1 Intake System [5]

In the case of the formula student rules a restriction of 20mm was placed on the main intake.

The challenge therefore was to optimise the design of the intake system and remap the fuel

injection system to optimise the engine performance for the expected racing conditions.

2. DESIGN CALCULATIONS

The Formula Student Silverstone track is geared toward the low end powerful andnimble race car as can be depicted from the track description. With average speeds in theendurance race between 48 km/hr to 57 km/h and top speeds of approximately 105 km/hrthe engine spends most of its time it the lower region of its power band. As a result an RPMlevel of 5000 was chosen as the most suitable for intake tuning. The main designcalculations were in relation to plenum volume, runner length and runner diameter. Researchinto other plenums used in the Formula SAE competition showed a volume of approx. 2.5litres recommended as a good base line volume.[1,3]

Vizards rule [2] was used in the calculation of the runner length. Thisstated that

You should begin with a runner length of 17.8 cm for a 10,000 rpm peak torque location,

from the intake opening to the plenum chamber. You add 4.3 cm to the runner length forevery 1000 rpm that you want the peak torque to occur before the 10,000 rpm.

For Peak Torque Location at 5000RPM

Or 393mm

The optimum runner length for a peak torque location of approximately 5000 rpm 393mmwhich can be rounded up to 400mm for ease of manufacture. Vizard also states the idealrunner diameter can be calculated using the following formula

[(target rpm for peak torque x Displacement x VE)/ 3330 ]

VE = Volumetric Efficiency of Engine (assumed to be 90% or 0.9)

For a peak torque of 5000 rpm

5000 x 0.599 x 0.09/3330 = 0.8168

= 0.90376 in =22.96 mm

The designs outlined in this paper were all based around these calculations such that theintake would keep the optimum peak torque location of approximately 5000 rpm.

3. CONCEPT DESIGNS & FEA ANALYSES

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Four different design concepts were examined in the SolidWorks flow simulation. The

results of the CFD analyses are shown in Fig 2- Fig 5. Detailed data for each runner is also

shown in Table 1Table 4.

Air was introduced from the inlet at a speed of 22m/s. The four outlets were set to

atmospheric pressure. In the first 3 designs A-C the airflow is concentrated around the two

central runners leaving the outside cylinders running lean and the inside cylinders running

rich. There is also a substantial amount of turbulence to be seen in all three cases.

It was apparent that the base plate was causing turbulence so it was necessary to design a

profile with no flat edges. A new concept was developed as shown in Fig 5. This consisted of

a central inlet with curved plenum which transferred the air at right angles to four tapered

runners. The concept here is that the air enters the plenum and travels to the back wall

where the profile of the wall will disperse the air to all four runners. With this concept an even

distribution of air among all four runners was achieved with minimum turbulence. This design

was manufactured using Fused Deposition Modelling Rapid prototyping and later testing on

the race car.

4. TESTING & ENGINE MAPPING

The GSX-R engine comes fitted with eight sensors as standard that relay real time enginecharacteristics back to the engine management system so it can control the amount of fuelbeing injected. The sensors include Intake air pressure (IAP), Manifold Air Pressure (MAP),Atmospheric Pressure (AP) ,Intake Air Temperature (IAT) ,Engine Temperature (ET) ,CrankPosition (CKP) ,Cam Position (CMP) ,Throttle Position (TP)

The crank position sensor uses an 8 toothed wheel on the crankshaft and a magnetic sensorwhich tells the ECU the RPM of the engine. The cam position sensor uses a pin positionedat a known location on the camshaft and a Hall Effect sensor to tell the ECU when cylinder#1 is at Top Dead Centre (TDC). These two sensors work together to control the timing of

ignition and sequence of fuel injection system.

The throttle position sensor uses a rotary potentiometer to sense the driver throttle positionand controls how much fuel is injected into the engine. During mapping the throttle positionwas the primary sensor for fuel map tuning.

Engine Temperature and Intake Air Temperature were used as compensation tools whereasIntake Air Pressure, Manifold Air Pressure and Atmospheric Pressure were not used.

To tune the engine to the new air intake system the main fuel table had to be modified to suitthe restricted airflow. To achieve peak power a 14.7:1 air fuel ratio or 1.0 lambda was thetarget.

A lambda sensor was installed in the exhaust system upstream of the muffler whichmeasures the air fuel mixture.

The engine was tuned across the rev range and throttle position on a dynamometer or rollingroad.

Lambda readings in excess of 1.00 indicates a lean air fuel mixture and lambda readingslower than 1.00 indicates an air fuel mixture. [4]

Tuning required the engine to be loaded and run until the engine reached the RPM limit.

Data during the run was logged in the Motec ECU and then analysed using the data logging

software.

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ITRN2011

Fig 2 Design AFig 3 Design B

Fig 4 Design C Fig 5 (a) Design D

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Fig 5(b) Design D Plan view

Total Cylinder 1 Cylinder 2 Cylinder 3 Cylinder 4

-9.72Litres/Sec

-0.634Litres/Sec

-5.37Litres/Sec

-1.39Litres/Sec

-2.3Litres/Sec

Table 1 Design A Results


-81.63Litres/Sec

-17.35Litres/Sec

-29.9Litres/Sec

-18.19Litres/Sec

-16.36Litres/Sec

Table 2 Design B Results


-10.2Litres/Sec

3.23Litres/Sec -8.32 Litres/Sec -8.27 Litres/Sec

3.13Litres/Sec

Table 3.

Design C Results


-47.5Litres/Sec

-14.8Litres/Sec -8.8 Litres/Sec -9.1 Litres/Sec

-14.8Litres/Sec

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ITRN2011

Fig 9 Noise Testing

7. CONCLUSIONS

Results of FEA analyses showed the air-intake design in Fig 5 to be the most suitable interms of air distribution. Subsequent dyno testing with the air intake also supported theseconclusions. Physical testing however did highlight some issues with the strength and rigidityof the ABS material used in the rapid prototype. Contraction of the walls of the intake systemwere visible due to the vacuum created at high RPM. As the intake system was generatedfrom a number of assemblies sealing the unit proved difficult. It is recommended that adifferent manufacturing process be used eg carbon fibre or plastic moulding.

The exhaust system design passed all the formula student requirements and gave a readingof 78 bhp on dyno testing. However this is a highly baffled silencer in order to meet noiseemissions and is likely to have adverse effects on engine performance. It is recommended

that future vehicle designs accommodate twin exhaust approach instead of the four into oneexhaust as this would have the potential to improve engine performance.

REFERENCES

[1]Devlin, Barry,Investigation into Engine Mapping & Design and Manufacture of an IntakeSystem For a Formula Sudent Car. 2010.

[2]Vizard, David,Rule for Intake Manifold Runner Length.

[3] Claywell, Mark, Horkheimer, Donald and Stockburger, Garrett, Investigation of IntakeConcepts for a Formula SAE Four Cylinder Engine Using 1D/3D (Ricardo WAVE-VECTIS)Coupled Modelling Techniques.2006, p. 24.

[4]Hartman, Jeff, 2003. How to Tune and Modify Engine Management Systems.

[5]Delaney, Michael. Intake Manifold Tech: Runner Size Calculations. www.team-integra.net. [Online] 30 09 2002. http://www.team-integra.net/forum/blogs/michaeldelaney/130-intake-manifold-tech-runner-size-calculations.html.

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