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
 Swept Volume/cylinder:

Port Sizing and Mach Index (Z)
 Mach Index is the ratio of the velocity of the gases flow area to the speed of sound

Port Sizing and Mach Index (Z)
 For instantaneous relationships:

Port Sizing and Mach Index (Z)
 Speed of Sound: Temperature and F/A ratio dependant At Standard Temperature and Pressure

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:

Inlet air density
 Inlet Pressures and Densities: From Ideal Gas Law

Inlet air density
 Inlet Densities:

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 j = 1.2 => 20 % Rich h = 0.02 lbm/lbm air

Inlet air density
 Gasoline: Natural gas: F/A = 1.2 x 1/17.2 = 0.0697 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:

Inlet air density

ACOUSTIC MODELING

Induction System Comparisons

Acoustic Modeling

Acoustic Modeling
 Closed Ended Organ Pipe:

Acoustic Modeling

Build Considerations

Multiple Stack with pressure box

Acoustic Modeling
 For a single degree of freedom system

Individual Throttle Body with Plenum

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.

Helmholtz Tuning
 The EFFECTIVE INDUCTANCE for a pipe with different cross-sections may be defined as the sum of inductances of each section.

Helmholtz Tuning
 INDUCTANCE RATIO (a) The CAPACITANCE RATIO (b) is defined as the ratio of the Secondary Volume to the Primary Volume.

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

Helmholtz Tuning
 Determine the Capacitance Ratio (b) Determine the Induction system Resonances

Helmholtz Tuning
 Determine the Primary Resonance: Determine the Frequency Ratios: Determine the Tuning Peak:

Helmholtz Tuning
 Intake Tuning Peaks become:

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

The End
 Thank You!