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6/4/2003 FLUENT UGM 2003

CFD ANALYSIS OF PZEV EXHAUSTCFD ANALYSIS OF PZEV EXHAUSTMANIFOLDSMANIFOLDS

Srikanth Ranganathan

CFD Section

Analytical Powertrain

Ford Motor Company

Dearborn, Michigan


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OBJECTIVEOBJECTIVE

To demonstrate a FLUENT based technique for evaluating a

PZEV exhaust manifold for PETA effectiveness

Cylinders

Exhaust

ValvesPETA Tube

PETA Air

Inlets

Substrate

PZEV Partial Zero Emissions Vehicle

PETA Ported Electric Thermactor Air


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PETA ExhaustPETA Exhaust -- IntroductionIntroduction

During the initial 20-30 seconds after engine start the air-fuel

mixture is run extra rich.

Prior to the catalyst brick, fresh air is injected from the PETA

tube directly into the exhaust gases.

The partially combusted fuel laden exhaust gas that is hot

but depleted of oxygen is spontaneously combusted again in the

manifold volume leading to increase in gas temperature.

Early elevation of substrate temperatures ensures an early

conversion of exhaust gases in the catalytic converter and thus

lowered emissions

PETA Effectiveness is measured by temperature increase of

exhaust gases from port to CAT face


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PETA Exhaust Flow RegimePETA Exhaust Flow Regime

Transient (Engine Cycle)a

Moving boundaries (Exhaust Valves)r

Compressibler

Multi-species mixing (Exhaust gases + Air)a

Combustion (Fuel + O2

Products + Heat)a


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Analysis ProcedureAnalysis Procedure

Physical Model (TGRID)Ports + Manifold + Converter + PETA

Transient Inlet

Mass Flux1-D Tool (GT-Power)

Chemistry Model (PrePDF)Species, Composition, Stoichiometry,

Streams, PDF, Heat Transfer, Rates

CFD Model (FLUENT)

Engine Cycle Simulation

(3-5 Cycles)

Convergence

No

Flow Temperature

Increase

Yes


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Model & DataModel & Data

I4 PZEV Exhaust @ 1500 Engine RPM (Time Period = 0.08s)

Non-Premixed Combustion:

1 Fuel + 1 Oxidizer Stream

4 Fuel Inlet: 923K [0.9N2 + 0.1CH4]

1 Oxidizer Inlet: 300K [0.79N2 + 0.21O2]

Flame Sheet Model (Infinite rates, Mixed-Is-Burned)

Reaction Stoichiometry: CxHy + (x+y/4)O2 xCO2 + (y/2)H2O

CH4 + 2O2 CO2 + 2H2O

Outlet: Atmospheric

Adiabatic Walls


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I4 PZEVI4 PZEV -- ResultsResults

Engine Cycle Averaged:

Exhaust Manifold Inlet Temperature = 923K

CAT Face Temperature = 1050 K

Temperature Growth = 127K


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CHCH44 on Coreon Core


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CHCH44 on C/Son C/S


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OO22 on Coreon Core


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OO22 on C/Son C/S


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Temperature on CoreTemperature on Core


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Temperature on C/STemperature on C/S


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AdvantagesAdvantages

Relatively quicker turn around time than full fledged

combustion model; Crucial as an optimization tool

PDF approach to turbulence and flow induced

mixing/combustion

Energy equation is not solved; Temperature determined

from scalar distribution

DisadvantagesDisadvantages

Reaction rates do not play a role

No intermediate species simulation

Risk of combustion/temperature over prediction


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ConclusionConclusion

Demonstrated a simple and quick FLUENT based CFD method

for evaluation of PETA effectiveness

Suitable for optimization studies of PETA/Exhaust Manifold design

A/F ratio

PETA air flow rate

Air injection location and angles

Manifold core shape

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