Volumetric Efficiency of Engine

P M V SubbaraoProfessor

Mechanical Engineering Department

Quantification of Filling & Emptying Effectiveness….

Computation of Intake Process : SI Engine

A I R

FUEL

SI Engine

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Instantaneous Heat Transfer During Intake Process

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Total Mass of mixture inhaled during Intake Process

A I R

FUEL

ivc

ivo

t

t CylIVCcyl dt

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Instantaneous mass flow Rate and Cumulate Mass

Computation of Exhaust Process : SI Engine

n

jj

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CombustionProducts

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Computation of Intake Process : CI Engine

A I R

CI Engine

Volumetric Efficiency : A Global Measure of Breathing Effectiveness

• Volumetric efficiency a measure of overall effectiveness of engine and its intake and exhaust system as a natural breathing system.

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Volumetric efficiency is defined as:

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• If the air density ra,0 is evaluated at inlet manifold conditions, the volumetric efficiency is a measure of breathing performance of the cylinder, inlet port and valve.

• If the air density ra,0 is evaluated at ambient conditions, the volumetric efficiency is a measure of overall intake and exhaust system and other engine features.

• The full load value of volumetric efficiency is a design feature of entire engine system.

Valve Lift in General (Design) Practice : Intake Valve

• The maximum valve lift is normally about 12% of the cylinder bore.

• Inlet valve opening typically occurs at 10 to 250 BTC.

• IVO should occur sufficiently before TC which leads to early fall in cylinder pressure during the intake stroke.

• IVC usually falls in the range 40 to 600 after BC.

• IVC should occur sufficiently after BC, to provide more time for cylinder filing under conditions where cylinder pressure is below the intake manifold pressure at BC.

• IVC one of the principal factors that determines the amount of air taken in high-speed engines.

tptp

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Valve Lift in General (Design) Practice : Exhaust Valve

• EVO strongly effects the engine thermal efficiency, as it affects the effective expansion ratio.

• The goal of EVO is to reduce cylinder pressure to close to manifold pressure as soon as possible.

• EVC typically falls in the range 8 to 200 after TC.

• EVC regulates the quantity of exhaust gases that flow back into the combustion chamber in SI engines.

• It also regulates the amount of cylinder burned gases exhausted.

• EVC timing should occur sufficiently far after TC so that the cylinder pressure does not rise near the end of the exhaust stroke.

• Late EVC favors high power at the expense of low-speed torque and idle combustion quality.