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

Acoustic Modeling

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

David Vizard’s “Rule of thumb” Equations

The End
Thank You!