Maximization of Flow through Intake & Exhaust Systems

P M V SubbaraoProfessor

Mechanical Engineering Department

Use Complex Wave Gas Dynamics for effective breathing….

Acoustic Theory of Piping

• The intake manifold to an internal combustion (IC) engine will consist of a network of interconnecting pipes.

• The lengths of these pipes, and to a certain extent their diameters, must be chosen carefully as they will determine the resonant frequencies of the manifold.

• When the engine is run at a speed where one or more of these resonances is excited, then both the volumetric efficiency and the intake noise level maybe affected.

Acoustic Modeling of Complex Piping System

Induction System Model

Build Considerations for Resonating Piping System

• 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

Experimental Methods to Understand Resonant Frequencies of Induction System

Modulation of Acoustic Waves

Pipe with Throttle

JunctionsThe most complex cause of pressure waves is when the intake valve closes.Any velocity left in the intake port column of air will make high pressure at the back of the valve. This high pressure wave travels toward the open end of the intake tract and is reflected and inverted as a low pressure wave.

Central Theorem for Acoustic Design

• The tuning peak will occur when the natural Helmholtz resonance of the cylinder and runner is about twice the piston frequency.

• The Engine can generate highest Torque at turning peak conditions.

• The aim of acoustic design is to achieve tuning peak at highest speed or highest power conditions.

• Tuned port simply means that the intake runners are tuned to have highest volumetric efficiency at specific rpm range.

Using Engelman's electrical analogy we can define the system as a system defined by capacitances and inductances.

A

L = )I( Inductance

Acoustic Characterization of Components

V= (C) eCapacitanc

)(2 222

2

txkydt

dy

dt

ydnnn

Ideal Helmholtz Resonator:

V L

A

2

c = f H

Acoustic Modeling of Runner

length effective = .3d + l = L

The theory behind what happens in the intake (and exhaust systems) is called A Helmholtz Resonator.Induction pressure waves can have an effect on how well the cylinders are filled. It can help (or hurt) power in a narrow rpm Range.

Primary Volume/Capacitance

Determination of Primary Capacitance

• Writing Clearance Volume in Terms of Compression Ratio:

V

V + V = CRCC

CCS

1) - (CRV = V

SCL

1) - (CRV +

2V = V

DDP

1) - 2(CRV 2 + 1) - (CR V = V

DDeff

1) - (CR

1) + (CR

2V = V

Deff

• The Primary Volume is considered to be the Cylinder Volume with the Piston at mid-stroke (effective volume).

V + 2

V = V CLD

P

• For a single degree of freedom system

Acoustic Modeling of Runner with Port

1 + CR

1 - CR

V L

A C K = fd1

11H

A1 = Average Area of Runner and Port

L1 = LPort + Lrunner

K1 = 642

C = Speed of Sound

Primary & Secondary Induction Systems

• The prime system responsible for flow of air is called as primary system.

• The remaining part of the system, which is not actively feed the cylinder is called as secondary system.