SAE TECHNICAL PAPER SERIES
2002-01-0457
Formula SAE Dual Plenum Induction System Design Badih A. Jawad, Jeffrey P. Hoste and Brian E. Johnson Lawrence Technological Univ.
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2002-01-0457
Formula SAE Dual Plenum Induction System Design Badih A. Jawad, Jeffrey P. Hoste and Brian E. Johnson Lawrence Technological University Copyright © 2002 Society of Automotive Engineers, Inc.
ABSTRACT DUAL PLENUM INTAKE MANIFOLD DESIGN A new induction system has been developed, created, and tested for use in the 2001 Formula SAE competition. A 600 Honda CBR F4 four-stroke engine intake is designed using dual plenums, which prevents charging losses due to overlapping intake events at low engine speeds. Dual butterfly valves actuated at high engine speeds enable plenum volume combination for improved high-end performance. The intake restrictor venturi design has also been improved.
INTRODUCTION The Formula SAE competition is a nationwide event in which teams of engineers representing competing universities design, build, and race miniature Formula One cars. Vehicles must undergo significant redesign annually. Competition rules dictate specific guidelines governing power train design and engine performance. Engine displacement may not exceed 610 cubic centimeters in a four-stroke design. The intake system must include a 20-millimeter restrictor downstream of a single throttle body controlling airflow. The 2001 Lawrence Technological University Formula Team selected a Honda CBR 600 F4 four-stroke motorcycle engine. The F4 engine was chosen primarily due to its weight and power advantages over similar class engines. The stock carbureted engine was modified to a fuel-injected configuration, which required the inclusion of cam position sensing for accurate injection and spark timing. Electronic engine control is accomplished through the use of a Motec M48 ECU. The restrictor creates the primary limitation on airflow in the intake system, as it is the region of smallest diameter. Maximum flow required at peak engine speed was determined and used as a flow target for intake component testing. The restrictor was designed to incorporate a short entrance nozzle as well as a long diffuser to minimize the impact of flow separation prior to plenum entry. This nozzle and diffuser section is referred to as the venturi [Figure 2].
The distinguishing aspect of the intake manifold design is the use of dual plenums to eliminate the effects of overlapping intake events. During normal engine operation, a cylinder intake valve (V1) opens slightly before the piston reaches top dead center to enable airfuel mixture to be drawn into the cylinder as the piston descends. This occurs prior to the completion of a similar event in a nearly charged second cylinder, just before it’s intake valve (V2) closes. When a single induction manifold joins the two cylinders, the filling event of the second cylinder overlaps with that of the first, causing interference and uneven filling between cylinders. Flow to the initial cylinder is created by reduced pressure caused by outgoing exhausts gases [1,2]. The net effect is a reduction in potential cylinder charge and decreased engine power output. In an effort to significantly reduce this effect, a dual plenum manifold design was implemented. Cylinder pairs with potentially overlapping events in a Honda CBR600 F4 engine are corresponding cylinders beginning and ending their induction strokes. This occurs in the firing order sequence 1-2-4-3. For this reason, C1+C4 are fed by one manifold, and C2+C3 are fed by a second [Figure 1].
Figure 1. Dual Plenum Intake Manifold Design
Initial runner lengths were designed to take advantage of inertial wave charge primary volume reflections [3,4]. Variable intake pipe length designs allowing maximum volumetric efficiency over the range of operating speeds were discarded due to complexity and cost. Typical operating speeds of past designs were evaluated [5,6], and peak efficiency was determined to be most beneficial between 8000 and 9000 rpm. Primary runner lengths were adjusted to correspond with Helmholtz resonance tuning peaks predicted by the electrical circuit resonance analogy developed by W. Englemann [7] and demonstrated in prior designs [8,9]. Sample calculations are presented in the appendix. At higher engine speeds, it was later determined that small plenum volumes may contribute to flow limitations as well as to destructive pressure wave interference. In an attempt to eliminate these effects, the dual plenums were joined at both ends, and a butterfly valve was incorporated at each joint to allow for the separation and combination of airflow with valve actuation. VENTURI DESIGN Flow calculations involving engine displacement and fluid properties indicated the dominance of turbulence within the range of feasible intake dimensions. The initial diffuser cone length was then maximized to reduce airflow separation flow losses, while maintaining ability to be packaged. Based on historical data and reference [5,6,8], a 14 degree included nozzle angle design was used. Three prototype venturi designs incorporating 5, 6, and 7 degree included diffuser angles were created using a stereo lithographic (SLA) method [Figure 2]. Although this process enables the rapid generation of prototypes for flow comparison, the internal surface roughness of the parts causes a much higher frictional drag on airflow than that of the final carbon fiber design. Final validation is therefore expected to yield significantly higher flows than the results shown in Table 1.
Nozzle
Diffuser
FLOW BENCH VENTURI DESIGN VALIDATION Initial flow evaluation was conducted using a SuperFlow SF-600 flow bench. The bench is limited to a maximum internal pressure of 12.453 kPa. The three prototyped venturi designs were tested. Pressure was increased in 1.245 kPa steps. Pressures near the bench limit were avoided in the interest of accuracy. Flow was allowed to stabilize prior to recording. Prototype designs were tested concurrently to minimize errors due to temperature and humidity variations. As is evident in Table 1, the 6-degree diffuser demonstrated clear flow advantages at every pressure tested [Table 1].
Pressure (kPa) 0.000 1.245 2.491 3.736 4.981 6.227 7.472 8.717 9.963 11.208
5 Degree (m3 /min) 0.000 1.586 2.209 2.665 2.990 3.242 3.438 3.576 3.670 3.721
6 Degree (m3 /min) 0.000 1.603 2.257 2.730 3.061 3.307 3.514 3.650 3.726 3.760
7 Degree (m3 /min) 0.000 1.623 2.246 2.684 3.016 3.276 3.472 3.616 3.707 3.735
Table 1. Diffuser Angle Prototype Flow Results
Prototype Flow Bench Test Results 4.0 3.5 3.0
) ) n i m2.5 / 3 ^ m2.0 ( w o l 1.5 f r i A
5 Degree 6 Degree
1.0 7 Degree 0.5 0.0
20mm Restrictor
Figure 2. Venturi Restrictor Design
0
2
4
6
8
10
12
Pressure (kPa)
Figure 3. Diffuser Angle Prototype Flow Comparison
INTAKE MANIFOLD DESIGN VALIDATION A dual plenum intake was created using straight and mandrel bent aluminum tube. A comparison of maximum flow at constant pressure of 6.23 kPa was conducted using the SuperFlow SF-600 flow bench. Maximum flow through a single cylinder was measured using an adapted engine head. The initial dual plenum intake design produced less airflow than existing designs over a range of intake valve lift. Known peak performing manifolds from previous LTU Formula SAE teams were also tested. Results are shown in Table 2. [Table 2].
Flow Rate (m 3 /min) at 6.23 kPa
Intake Valve Lift
1995
1999
2000
2001
(cm)
Intake
Intake
Intake
Initial
0.254
1.415
1.426
1.446
1.412
0.381
1.927
1.927
1.958
1.873
0.508
2.326
2.275
2.363
2.199
0.635
2.530
2.451
2.550
2.326
0.762
2.598
2.533
2.612
2.391
Table 2. Flow Comparison of Intake Systems
ENGINE DYNOMOMETER SYSTEM VALIDATION A Land and Sea Dynomite water-brake engine dynomometer was used to determine engine torque and horsepower production over a range of engine speeds [Figure 4].
System performance showed low-end improvement compared to the 2000-team design. At higher engine speeds, however, design targets were not achieved [Figure 5]. DYNOmite Test by Lawrence Tech University 100
2001 Initial Intake Design vs. 2000 Intake Design
2001
Corrected Smoothed
2000
90
M P R , r e w o p e s r o H , e u q r o T
hp
80 70 60 50 TORQUE 40 30 20 10 0 2000
4000
6000
8000
10000
12000
14000
RPM
Figure 5. Dynomometer Performance Evaluation The initial design was evaluated and strategies to increase flow were considered. A new intake was constructed incorporating decreased bend angles and internal bellmouths at the primary runner and plenum transition. In order to improve flow and eliminate high-speed pressure wave interference, a joined plenum was created using butterfly valves and a pneumatic mechanism to combine plenum volumes at high engine speeds. This improved design was re-evaluated on the SuperFlow SF-600 flow bench [Table 3]. The improved system demonstrates a clear advantage over all previous designs in its ability to flow more air in the combined plenum configuration under nearly all lift conditions. As expected, flow is somewhat lower in the separated plenum configuration. As previously explained, this sacrifice is made to separate overlapping intake events, resulting in improved overall engine performance and increased power.
Flow Rate (m3/min) at 6.23 kPa
Intake Valve Lift
1995
1999
2000
2001
2001
(cm)
Intake
Intake
Intake
Sep.
Comb.
0.254
1.415
1.426
1.446
1.421
1.440
0.381
1.927
1.927
1.958
1.944
1.978
0.508
2.326
2.275
2.363
2.372
2.411
0.635
2.530
2.451
2.550
2.570
2.604
0.762
2.598
2.533
2.612
2.655
2.683
Table 3. Flow Comparison of the Improved Intake Design Figure 4. Dynomometer Testing
The new design was then tested on the engine dynomometer in separated and combined plenum configurations. An overlap performance point was found at approximately 8500 rpm. This value was programmed into the Motec M48 engine control unit for valve actuation. Dynomometer results are shown in Figure 6, which displays the valves closed state represented by the thin line, and the valves open state represented by the thicker line. 13:1 2001/B Valves Open vs. 13:1 2001/B valves closed Corrected Smoothed HP
90
Overlap Area
80
M P R , r e w o p e s r o H , e u q r o T
hp
70 60 50 torque TORQUE 40 30 20 10 0 0
2000
4000
6000
8000
10000
Future tuning of this new engine and intake system will include further improvements to the fuel mapping to gain peak performance in both the separated and combined modes of operation. The torque and horsepower curves will then again be overlaid to reveal the most beneficial engine speed at which the plenum volumes should be combined. CONCLUSION
DYNOmiteTest by Lawrence Tech University 100
high end of the range, indicating the dominance of the higher speed Helmholtz tuning peak.
12000
14000
RPM
Figure 6. Plenum Crossover Point Determination Engine performance was then compared with that of previous designs [Figure 7]. The current design was found to create at significantly more peak horsepower than the 2000 design, which was the next best performer in flow testing. The torque curve produced is flatter, and extends over a larger range of engine speeds, providing improved distribution of power.
The 2001 intake design combines proven designs, theoretical calculation, and prototype evaluation using current industry tools to enable another successful evolution of the Lawrence Technological University Formula SAE intake. Extended torque is created in the desired range by minimizing flow separation in the venturi, employing manifold system tuning techniques, and incorporating dual plenums to separate overlapping intake events. Further performance enhancement is available through the identification of proper peak volume combination speeds. The overall effect is to maximize the increased horsepower offered by the Honda CBR 600 F4 engine. ACKNOWLEDGEMENTS The authors would like to acknowledge Yazaki North America and Ford Motor Company for their continued generous support of the Lawrence Technological University Formula SAE Team. We would also like to thank Ryan Wahl for his invaluable assistance, as well as all previous LTU FSAE teams for their foundational knowledge, designs, and assistance. CONTACTS Any questions concerning this paper may be directed to Dr. Badih Jawad at
[email protected], or Jeff Hoste at
[email protected]. Dr. Jawad is the LTU FSAE faculty advisor and a professor of mechanical engineering at Lawrence Technological University. Jeffrey Hoste and Brian Johnson are both mechanical engineering students at Lawrence Technological University as well as members of the 2001 Lawrence Technological University Formula SAE team.
Figure 7. 2001 Intake vs. 2000 Intake Design Further evaluation of the newly designed intake and fuel-injected F4 engine reveals the desired performance has been achieved. The observed torque peak corresponds to the predicted 8000 to 9000 rpm target range, more closely centered in the
REFERENCES 1.
2.
3.
4.
5.
6.
APPENDIX
Winterbone, D. and Pearson, R. ‘Design Techniques for Engine Manifolds: Wave Action Methods for IC Engines,’ Ch. 4, Professional Engineering Publishing Limited, UK 1999. SAE Order No. R-274. Blair, Gordon P., ‘Design and Simulation of Fourst Stroke Engines,’ Ch. 1, 1 Edition, Society of Automotive Engineers, 1999. SAE Order No. R-186. Stone, Richard, ‘Introduction to Internal nd th Combustion Engines,’ 2 Edition, Ch. 6, 5 Edition, Society of Automotive Engineers, 1997. nd
Heisler, Heinz, ‘Advanced Engine Technology,’ 2 Edition, Society of Automotive Engineers, 1999.
2000 LTU FSAE Team, ‘2000 Formula SAE Final Report,’ Lawrence Technological University, Southfield, Michigan. 1999 LTU FSAE Team, ‘1999 Formula SAE Final Report,’ Lawrence Technological University, Southfield, Michigan.
Calculations Helmholtz Resonance Peak Determination System Characteristics
Limr
22.098
cm
Ai mr
9.581
cm
Restrictor Outlet Diameter
Dro
4.7625
cm
Intake Port Length
Lip
8.9662
cm
Aip
7.3355
cm
Intake Manifold Runner Length Intake Manifold Runner Area
Intake Port Average Area
2
2
Engine Compression Ratio
ECR
13
Displacement per Cylinder
DPC
149.75
Plenum Length
Lplen
27.000
cm
Aple n
32.774
cm
Plenum Average Area
3
cm
2
Throttle Body Inductance
Ithr
0.94488
cm
Venturi Inductance
Ivent
7.654
cm
Secondary Runner Inductance
Isr
0.4874
cm
Speed of Sound in Air @ 42oF
Cs
335.28
m
1 1 1
s Calculations
Intake Port Inductance
7.
8.
Englemann, H.W., ‘Design of a Tuned Intake Manifold,’ ASME Paper 73-WA/DGP-2, 1973. Jawad, Badih A., DeGain, Michael D., and Young, Anthony P. Jr., ‘Design of a Four Cylinder, High Speed FSAE Restricted Induction System,’ SAE
Iip
Lip Aip
Iip = 1.2223
cm
I imr = 2.3064
cm
Iplen = 0. 8238
cm
C1
=
87.3542
cm
fp
=
0.0091
1
Primary Runner Inductance
Iimr
2000-01-3090.
Limr Ai mr
1
Plenum Inductance
9.
Jameson, Renee T., and Hodgins, Patrick A., ‘Improvement of the Torque Characteristics of a Small, High-Speed Engine Through the Design of Helmholtz-Tuned Manifolding,’ SAE 900680.
Lplen
Iplen
Aplen
1
Cylinder Effective Volume
C1
DPC. ( ECR 2
( ECR
1) 1)
3
Frequency Factor
fp
1 2
1
.
.π
Iimr) . C1
( Iip
Primary Inductance
Iprim
Iip
Iimr
Iprim = 3.5287
cm
1
Secondary Inductance
Isec
Isr Ithr
Ivent
Iplen Isec = 9.9101
cm
1
Inertial Wave Charging
Inductance Ratio
Isec
a
a
Iprim
2.8084
=
Capacitance Ratio
3 . ( Limr. Aimr Lip. Aip)
b
b
C1
Engine Speed at Peak Efficiency
N
8000
rpm
Optimal Crankshaft Displacement (Target determined experimentally)
θt
85
degrees
Speed of Sound in Air
Cs = 335.28
9.5299
=
m s
Calculation Constants
a. b
A
a
1
A
θt . Cs. ( 100) .
30.5722
=
Primary Port and Runner Length 2
B
( 4 . a. b)
A
B
Lp 12. N.
28.7681
=
2. π 360
1 60
Resonant Frequencies
1
f1
( A
.
B)
f1
2 . a . b . Iprim. C1
2. π
=
Lp = 31.0874
0.0095 Primary Runner Length
1
f2
2
( A
. .
.
B)
f2
2 a b Iprim. C1
.π
.
=
fp f2 fp
X1
=
1.0529
X2
=
0.1836
.
( ECR
1)
( ECR
1)
Primary Inductance Area
( Aimr. Limr )
Aprim
Aprim
( Aip. Lip )
Limr =
Lip 2
8.9329
cm
Helmholtz Model Tuning Peak
642 . Cs.
Np
Np
=
Aprim .
( Limr
8732.7558
Lip
Limr = 22.1212 cm
f1
X2
Lp
0.0017
Frequency Ratios
X1
Limr
cm
Lip ) DPC
rpm
Helmholtz Tuning Peaks
N1
X1 . Np
N1
=
9194.6952
rpm
N2
X2 . Np
N2
=
1603.2149
rpm
