Part 7 - Diesel Combustin adn SI Knock Modeling

40 Pages·2014·4.63 MB·English

Part 7: Diesel combustion and SI knock modeling
Reciprocating Internal Combustion Engines

Prof. Rolf D. Reitz
Engine Research Center
University of Wisconsin-Madison

2014 Princeton-CEFRC
Summer School on Combustion
Course Length: 15 hrs

(Mon.- Fri., June 23 – 27, 2014)
Copyright ©2014 by Rolf D. Reitz.
This material is not to be sold, reproduced or distributed without
prior written permission of the owner, Rolf D. Reitz.
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Part 7: Diesel combustion and SI knock modeling
Short course outine:

Engine fundamentals and performance metrics, computer modeling supported
by in-depth understanding of fundamental engine processes and detailed
experiments in engine design optimization.

Day 1 (Engine fundamentals)
Part 1: IC Engine Review, 0, 1 and 3-D modeling
Part 2: Turbochargers, Engine Performance Metrics
Day 2 (Combustion Modeling)
Part 3: Chemical Kinetics, HCCI & SI Combustion
Part 4: Heat transfer, NOx and Soot Emissions
Day 3 (Spray Modeling)
Part 5: Atomization, Drop Breakup/Coalescence
Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays
Day 4 (Engine Optimization)
Part 7: Diesel combustion and SI knock modeling
Part 8: Optimization and Low Temperature Combustion
Day 5 (Applications and the Future)
Part 9: Fuels, After-treatment and Controls
Part 10: Vehicle Applications, Future of IC Engines
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Part 7: Diesel combustion and SI knock modeling
Diesel engine applications
On-Highway Vehicles
Marine – Propulsion or auxiliary
Power Generation – Prime power for remote
locations, or standby power for edifices
Locomotive – Switchyard engines, passenger
engines, European light freight
Off-Highway Vehicles – Mine trucks (haulers,
loaders, etc)
Off-Highway Stationary – Petroleum industry (drill
rigs, pumps, etc.)

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Part 7: Diesel combustion and SI knock modeling
Diesel engine applications
http://maniacworld.com/Worlds-
Most-Powerful-Diesel-Engine.html
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Part 7: Diesel combustion and SI knock modeling
Diesel combustion
Air alone is drawn in and
compressed

Fuel injected into high
temperature, high
pressure air to initiate
combustion
Parameter Quiescent Medium Swirl High Swirl

Load controlled by quantity Cylinder Size Largest Medium Smallest
of fuel injected
Maximum Speed 100–1800 1800–3000 3000–5000
(rpm)
Range of Bore 900–150 mm 150–100 mm 130–80 mm
Highly heterogeneous
(mm, inches)
mixture in cylinder Compression 12–15 15–16 16–18
Ratio
- wide range of mixture
Combustion Shallow Bowl Moderate Bowl Deep Bowl
Chamber
concentration over which
Injection Pressure Highest High Moderate
combustion occurs
Number of nozzle Multiple Multiple Multiple
- wide range of operating
holes
air-fuel ratios In-Cylinder Air Quiescent Medium Swirl High Swirl
Flow
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Part 7: Diesel combustion and SI knock modeling
Diesel combustion - General Rules
Center fuel injector in bowl, and if possible, center bowl in piston
Trade off fuel injection pressure versus air motion to provide required mixing
while not over-mixing at light load
Injection timing
Injection pressure and Number, diameter, and angle of
rate shape spray holes
Reentrancy
Intake port geometry
Rim width
Air supply pressure and
temperature
Bowl depth and
geometry
Compression ratio
Exhaust Gas Recirculation
Supply sufficient air to meet peak torque smoke limits
Select injection timing and compression ratio for best fuel economy within
emission constraints

Other constraints: peak cylinder pressure, fuel injection pressure
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Part 7: Diesel combustion and SI knock modeling
Dec, 1997

Diesel combustion
(Conceptual model of Dec, 1997)
Time to mix fuel/air to “combustible” ratios
Time at given T and P to initiate combustion
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Part 7: Diesel combustion and SI knock modeling
Park, 2007
Diesel combustion regimes
Kamimoto plot
2.0

o
1.5
i
t
a
Soot
R

e
c
n1.0
e
l
a
v High Efficiency
i
u Clean Regime
0.5
q
E NOx
HCCI
CO
0.0
1400 1600 1800 2000 2200 2400
Cylinder Temperature [K] HCCI
Requires precise charge
preparation and combustion
control mechanisms (for
auto-ignition and combustion
timing)
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Part 7: Diesel combustion and SI knock modeling
Musculus 2006
Dec, 1997
Diesel combustion regimes
Conventional Diesel
LTC diesel Combustion

Dec used optical diagnostics to
Musculus developed a similar
develop a conceptual model of
conventional diesel combustion conceptual model for diesel LTC

OH exists only at periphery of the jet Low temperature reactions fill the
 thin diffusion flame surrounding a
head of the jet with intermediates
soot filled jet
(e.g., CH O)
2
OH is observed across the entire jet
cross-section
Dec’s conceptual model
LTC conceptual model
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Part 7: Diesel combustion and SI knock modeling
Diesel combustion modeling
KIVA-CHEMKIN-G code
CHEMKIN II based chemistry solver used for volumetric heat release
Each cell considered a well-stirred reactor (WSR)
Diesel fuel chemistry is modeled with ERC reduced n-heptane mechanism
Flame propagation considered through level set based model  G equation
Spray modeled with ERC spray models

injector nozzle tip firedeck
Gasjet theory used to reduce grid
size dependency of droplet drag
squish region
calculations

Collision model considers bounce,
coalescence, and fragmenting and
non-fragmenting separations
cylindrical piston bowl

KH-RT breakup model
piston bowl wall

crevice region
Tetradecane used for fuel physical
properties

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