Internal Combustion
Engine
Induction Tuning
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ME 468 Engine Design |
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Professor Richard Hathaway |
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Department of Mechanical and
Aeronautical Engineering |
Port Sizing
Considerations
Swept and Displaced
Volumes
Port Sizing and Mach
Index (Z)
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Mach Index is the ratio of the velocity
of the gases flow area to the speed of sound |
Port Sizing and Mach
Index (Z)
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For instantaneous relationships: |
Port Sizing and Mach
Index (Z)
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Speed of Sound: |
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Temperature and F/A ratio dependant |
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At Standard Temperature and Pressure |
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Port Sizing and Mach
Index (Z)
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Modern performance engines will use
multiple inlet and exhaust valves per cylinder. |
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Many are using multiple intake runners
per cylinder to improve cylinder filling over a broader range of RPM. |
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A single runner is used at lower RPM
while a second runner will be opened at higher RPM. |
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The second and the combined each have
their own tuning peak. |
Inlet Air Density and
Performance
Inlet air density
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Law of Partial Pressures: |
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If each is considered as a perfect gas |
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Inlet air density
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Inlet Pressures and Densities: |
Inlet air density
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Inlet Pressures and Densities: |
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From Ideal Gas Law |
Inlet air density
Inlet air density
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Example Problem: |
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Find the change in indicated power when
changing from Gasoline to Natural Gas fuels |
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Assume: Pi = 14.0 psia Ti =
100oF |
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j = 1.2 => 20 % Rich |
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h = 0.02 lbm/lbm
air |
Inlet air density
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Gasoline: |
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Natural gas: |
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F/A = 1.2 x 1/17.2 = 0.0697 lbfuel/lbair |
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Fuel is a gaseous fuel and is
100% vaporized |
Inlet air density
Inlet air density
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NATURAL GAS: |
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INDICATED POWER RATIO: |
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Inlet air density
Inlet air density
ACOUSTIC MODELING
Induction System
Comparisons
Acoustic Modeling
Acoustic Modeling
Acoustic Modeling
Build Considerations
Acoustic Modeling
Multiple Stack with
pressure box
Acoustic Modeling
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For a single degree of freedom system |
Individual Throttle Body
with Plenum
Helmholtz Tuning
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Writing Clearance Volume in Terms of
Compression Ratio: |
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The Primary Volume is considered to be
the Cylinder Volume with the Piston at mid-stroke (effective volume). |
Helmholtz Tuning
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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. |
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. |
Helmholtz Tuning
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INDUCTANCE RATIO (a) |
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The CAPACITANCE RATIO (b) is defined as
the ratio of the Secondary Volume to the Primary Volume. |
Helmholtz Tuning
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Calculate the Separate Inductances: |
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Determine the Inductance Ratio (a) |
Helmholtz Tuning
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Determine the Capacitance Ratio (b) |
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Determine the Induction system
Resonances |
Helmholtz Tuning
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Determine the Primary Resonance: |
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Determine the Frequency Ratios: |
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Determine the Tuning Peak: |
Helmholtz Tuning
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Intake Tuning Peaks become: |
Helmholtz Tuning
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A combined equation is possible
indicating it’s 2nd order |
David Vizard’s “Rule of
thumb” Equations
The End