Slide 1 Internal Combustion EngineInduction Tuning

ME 468 Engine Design

Professor Richard Hathaway

Department of Mechanical and Aeronautical Engineering

Slide 2 Port Sizing Considerations

Slide 3 ### Swept and Displaced Volumes

Inlet Port

s x Ap

Vs = swept volume dB = bore diameter s = stroke

s

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.

Slide 4 ### 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:

Slide 5 ### Port Sizing and Mach Index (Z)

- For instantaneous relationships:

s = length of stroke L = length of connecting rod

θ = crank position Cd = flow coefficient

Slide 6 ### 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

Slide 7 ### 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.

Slide 8 Inlet Air Density and Performance

Slide 9 ### Inlet air density

- Law of Partial Pressures:
- If each is considered as a perfect gas

Slide 10 ### Inlet air density

- Inlet Pressures and Densities:

ma = 29 mw = 18 mgas = 113

Fc = chemically correct mix

Fi = % vaporized (Fc)

Slide 11 ### Inlet air density

- Inlet Pressures and Densities:
- From Ideal Gas Law

R = 1545 ft-lb/(lbm-mole-oR)

Slide 12 ### Inlet air density

for P in psia and T in oR

Slide 13 ### Inlet air density

GASOLINE:

F/A = 1.2 x 1/14.8 = 0.081 lbfuel/lbair

Assume fuel is 40% vaporized

(Use fuel distilation curves)

Slide 14 ### 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

Slide 15 Slide 16 ### Inlet air density

- NATURAL GAS:
- INDICATED POWER RATIO:

Slide 17 ### Inlet air density

The above indicates an approximate 10% loss in power output by changing to the gaseous fuel.

Slide 18 ### Inlet air density

Note: Gasoline performance decreases more rapidly with increasing temperature.

Slide 19 Slide 20 ### Induction System Comparisons

Courtesy: Dan Butts, Derek Harris, Chris Brockman, Tiffany Dickinson

Slide 21 Slide 22 Slide 23 ### Acoustic Modeling

Helmholtz Resonator:

Slide 24 ### 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

Slide 25 ### Acoustic Modeling

Induction System Model

Slide 26 ### Multiple Stack with pressure box

Courtesy: Dan Butts, Derek Harris, Chris Brockman, Tiffany Dickinson

Slide 27 ### Acoustic Modeling

- For a single degree of freedom system

A1 = Average Area of Runner and PortL1 = LPort + Lrunner

K1 = 77 (English)K1 = 642 (Metric)

C = Speed of Sound

Slide 28 ### Individual Throttle Body with Plenum

Courtesy: Dan Butts, Derek Harris, Chris Brockman, Tiffany Dickinson

Slide 29 ### 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).

Slide 30 ### 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.

Slide 31 ### 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.

Slide 32 ### 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)

Slide 33 ### Helmholtz Tuning

- Calculate the Separate Inductances:
- Determine the Inductance Ratio (a)

Slide 34 ### Helmholtz Tuning

- Determine the Capacitance Ratio (b)
- Determine the Induction system Resonances

(IND)1 = Inductance of the primary length

(IND)1 = Iport + Irunner

Slide 35 ### Helmholtz Tuning

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

A1 = Average Area of Runner and PortL1 = LPort + Lrunner

K1 = 77 (English)K1 = 642 (Metric)

C = Speed of Sound

Slide 36 ### Helmholtz Tuning

- Intake Tuning Peaks become:

Slide 37 ### Helmholtz Tuning

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

Slide 38 ### 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

Slide 39