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Internal Combustion Engine Induction Tuning

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Internal Combustion EngineInduction Tuning

ME 468 Engine Design

Professor Richard Hathaway

Department of Mechanical and Aeronautical Engineering

Port Sizing Considerations

Inlet Port

- Swept Volume/cylinder:

s x Ap

Vs = swept volumedB = bore diameters = 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.

- 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:

- For instantaneous relationships:

s = length of strokeL = length of connecting rod

θ = crank positionCd = flow coefficient

- Speed of Sound:
- Temperature and F/A ratio dependant
- At Standard Temperature and Pressure

c = 1100 ft/sec

c = 340 m/sec

- 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

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

- Inlet Pressures and Densities:

ma = 29mw = 18mgas = 113

Fc = chemically correct mix

Fi = % vaporized (Fc)

- Inlet Pressures and Densities:
- From Ideal Gas Law

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

- Inlet Densities:

for P in psia and T in oR

- Example Problem:
- Find the change in indicated power when changing from Gasoline to Natural Gas fuels
Assume:Pi = 14.0 psiaTi = 100oF

= 1.2 => 20 % Rich

h = 0.02 lbm/lbm air

- Find the change in indicated power when changing from Gasoline to Natural Gas fuels

GASOLINE:

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

Assume fuel is 40% vaporized

(Use fuel distilation curves)

Gasoline:

Natural gas:

F/A = 1.2 x 1/17.2 = 0.0697 lbfuel/lbair

Fuel is a gaseous fuel and is 100% vaporized

- NATURAL GAS:

- NATURAL GAS:
- INDICATED POWER RATIO:

- Indicated power ratio:

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

Note:Gasoline performance decreases more rapidly with increasing temperature.

ACOUSTIC MODELING

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

- Closed Ended Organ Pipe:

- Closed Ended Organ Pipe:

Helmholtz Resonator:

- 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

Induction System Model

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

- 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

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

- 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).

- 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.

- 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.

- 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)

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

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

(IND)1 = Inductance of the primary length

(IND)1 = Iport + Irunner

- 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

- Intake Tuning Peaks become:

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

- 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!