# Internal Combustion Engine Induction Tuning

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

Port Sizing Considerations

Swept and Displaced Volumes
Inlet Port Swept Volume/cylinder: s x Ap Vs = swept volume dB = bore diameter s = stroke 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. s

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

Port Sizing and Mach Index (Z)
For instantaneous relationships: s = length of stroke L = length of connecting rod θ = crank position Cd = flow coefficient

Port Sizing and Mach Index (Z)
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)
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.

Inlet Air Density and Performance

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

Inlet air density Inlet Pressures and Densities:
ma = 29 mw = 18 mgas = 113 Fc = chemically correct mix Fi = % vaporized (Fc)

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

Inlet air density Inlet Densities: for P in psia and T in oR

Inlet air density Example Problem:
Find the change in indicated power when changing from Gasoline to Natural Gas fuels Assume: Pi = 14.0 psia Ti = 100oF  = 1.2 => 20 % Rich h = 0.02 lbm/lbm air GASOLINE: F/A = 1.2 x 1/14.8 = lbfuel/lbair Assume fuel is 40% vaporized (Use fuel distilation curves)

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

Inlet air density NATURAL GAS:

Inlet air density NATURAL GAS: INDICATED POWER RATIO:

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

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

ACOUSTIC MODELING

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

Acoustic Modeling Closed Ended Organ Pipe:

Acoustic Modeling Closed Ended Organ Pipe:

Acoustic Modeling Helmholtz Resonator:

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

Acoustic Modeling Induction System Model

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

Acoustic Modeling For a single degree of freedom system
A1 = Average Area of Runner and Port L1 = LPort + Lrunner K1 = 77 (English) K1 = 642 (Metric) C = Speed of Sound

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

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).

Helmholtz Tuning The tuning peak will occur when the natural Helmholtz resonance of the cylinder and runner is about twice the piston frequency. Volume (V1) = Cylinder Volume Volume (V2) = Volume in the path from V1 to the Plenum Using Engelman's electrical analogy we can define the system as a system defined by capacitances and inductances.

Helmholtz Tuning 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 INDUCTANCE RATIO (a)
The CAPACITANCE RATIO (b) is defined as the ratio of the Secondary Volume to the Primary Volume. V2 = Secondary Volume = Volume of Intake Runners that are ineffective (n-1)

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

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

Helmholtz Tuning Determine the Primary Resonance:
Determine the Frequency Ratios: Determine the Tuning Peak: A1 = Average Area of Runner and Port L1 = LPort + Lrunner K1 = 77 (English) K1 = 642 (Metric) C = Speed of Sound

Helmholtz Tuning Intake Tuning Peaks become:

Helmholtz Tuning A combined equation is possible indicating it’s 2nd order

David Visard’s “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

The End Thank You!