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Internal Combustion Engine Induction Tuning ME 468 Engine Design Professor Richard Hathaway Department of Mechanical and Aeronautical Engineering

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Port Sizing Considerations

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Swept and Displaced Volumes Swept Volume/cylinder: V s = swept volumed B = bore diameter s = stroke s s x A p Inlet Port Note: In valve design the Volume which flows into the cylinder must equal the volume which flows through the inlet port. The velocity past the valve must then be considerably greater than the velocity in the cylinder.

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Port Sizing and Mach Index (Z) Mach Index is the ratio of the velocity of the gases flow area to the speed of sound D b = cylinder bore dia. D p = port dia. n = number of ports For mean values:

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For instantaneous relationships: s = length of strokeL = length of connecting rod θ = crank positionC d = flow coefficient Port Sizing and Mach Index (Z)

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Speed of Sound: –Temperature and F/A ratio dependant –At Standard Temperature and Pressure c = 1100 ft/sec c = 340 m/sec Port Sizing and Mach Index (Z)

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Modern performance engines will use multiple inlet and exhaust valves per cylinder. Many are using multiple intake runners per cylinder to improve cylinder filling over a broader range of RPM. –A single runner is used at lower RPM while a second runner will be opened at higher RPM. –The second and the combined each have their own tuning peak. Port Sizing and Mach Index (Z)

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Inlet Air Density and Performance

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Inlet air density Law of Partial Pressures: If each is considered as a perfect gas

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Inlet air density Inlet Pressures and Densities: m a = 29m w = 18m gas = 113 F c = chemically correct mix F i = % vaporized (F c )

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Inlet air density Inlet Pressures and Densities: From Ideal Gas Law R = 1545 ft-lb/(lbm-mole- o R)

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Inlet air density Inlet Densities: for P in psi a and T in o R

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Inlet air density Example Problem: –Find the change in indicated power when changing from Gasoline to Natural Gas fuels Assume:P i = 14.0 psiaT i = 100oF = 1.2 => 20 % Rich h = 0.02 lb m /lb m air GASOLINE: F/A = 1.2 x 1/14.8 = 0.081 lb fuel /lb air Assume fuel is 40% vaporized (Use fuel distilation curves)

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Inlet air density Gasoline: Natural gas: F/A = 1.2 x 1/17.2 = 0.0697 lb fuel /lb air Fuel is a gaseous fuel and is 100% vaporized

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Inlet air density NATURAL GAS:

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Inlet air density NATURAL GAS: INDICATED POWER RATIO:

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Inlet air density Indicated power ratio: The above indicates an approximate 10% loss in power output by changing to the gaseous fuel.

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Note:Gasoline performance decreases more rapidly with increasing temperature. Inlet air density

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ACOUSTIC MODELING

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Induction System Comparisons Courtesy: Dan Butts, Derek Harris, Chris Brockman, Tiffany Dickinson

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Closed Ended Organ Pipe: Acoustic Modeling

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Closed Ended Organ Pipe:

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Helmholtz Resonator: Acoustic Modeling

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Build Considerations Variable Length Runners for RPM matching Materials Selection Criteria: –Weight, Fabrication, Surface Finish, Heat Isolation Intake placement –Isolate from heat sources (Engine, Exhaust, Radiator, Pavement) Fuel Injector Placement Courtesy: Dan Butts, Derek Harris, Chris Brockman, Tiffany Dickinson

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Acoustic Modeling Induction System Model

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Multiple Stack with pressure box Courtesy: Dan Butts, Derek Harris, Chris Brockman, Tiffany Dickinson

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For a single degree of freedom system Acoustic Modeling A 1 = Average Area of Runner and Port L 1 = L Port + L runner K 1 = 77 (English) K 1 = 642 (Metric) C = Speed of Sound

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Individual Throttle Body with Plenum Courtesy: Dan Butts, Derek Harris, Chris Brockman, Tiffany Dickinson

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Helmholtz Tuning Writing Clearance Volume in Terms of Compression Ratio: The Primary Volume is considered to be the Cylinder Volume with the Piston at mid-stroke (effective volume).

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The tuning peak will occur when the natural Helmholtz resonance of the cylinder and runner is about twice the piston frequency. Volume (V 1 )= Cylinder Volume Volume (V 2 )= Volume in the path from V 1 to the Plenum Using Engelman's electrical analogy we can define the system as a system defined by capacitances and inductances. Helmholtz Tuning

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The EFFECTIVE INDUCTANCE for a pipe with different cross-sections may be defined as the sum of inductances of each section. The INDUCTANCE RATIO (a) is defined as the ratio of the secondary inductance to the primary inductance. Helmholtz Tuning

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INDUCTANCE RATIO (a) The CAPACITANCE RATIO (b) is defined as the ratio of the Secondary Volume to the Primary Volume. Helmholtz Tuning V 2 = Secondary Volume = Volume of Intake Runners that are ineffective (n-1)

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Calculate the Separate Inductances: Determine the Inductance Ratio (a) Helmholtz Tuning

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Determine the Capacitance Ratio (b) Determine the Induction system Resonances Helmholtz Tuning (IND) 1 = Inductance of the primary length (IND) 1 = I port + I runner

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Determine the Primary Resonance: Determine the Frequency Ratios: Determine the Tuning Peak: Helmholtz Tuning A 1 = Average Area of Runner and Port L 1 = L Port + L runner K 1 = 77 (English) K 1 = 642 (Metric) C = Speed of Sound

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Intake Tuning Peaks become: Helmholtz Tuning

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A combined equation is possible indicating its 2 nd order Helmholtz Tuning

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David Visards Rule of thumb Equations Using Visard's Equation for Runner Length 1. Starting point of 7 inches for 10,000 RPM 2. Add length of 1.7 inches for each 1000 RPM less Using Visard's Equation for Runner Diameter

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The End Thank You!

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