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Heavy-Duty Diesel Engine Cooling Systems
Tom McKinleyCummins, Inc.
Objectives
Provide background information useful to tomorrow’s lab project (Evaluation of a Water Cooled Exhaust Manifold). Topics covered: Typical heavy-duty (HD) diesel engine designs Common HD automotive diesel applications Introduction to engine cooling systems
Arrangement Development Tools Design Constraints
Typical HD Diesel Engine Design
10 to 15 liters displacement Inline-six Turbocharged Air-to-Air Aftercooling 300-600 hp at 1600-2100 rpm 1250-2000 lb-ft Max Torque at
1200 rpm Dry weight 2000-2800 lb Reliability/Durability
250,000 mile/2 year base warranty
500,000 mile/5 year extended warranty
1,000,000 mile life expectation
Typical HD Diesel Engine Application
80,0000 lb GVW 100,000 to 150,000 miles per
year 6 MPG Operating range from sea
level to >8,000 ft altitude Ambient temperatures from
below zero to 115 deg F
Typical HD Diesel Engine Duty Cycle
Average load of 180-200 hp Most of fuel used at “cruise”
rpm of 1400-1700 rpm Varying load at cruise due to
operation of cruise control Varying engine speed due to
road speed changes in traffic or urban operation
HD Truck - Percent Time by Speed/Load
0
200
400
600
800
1000
1200
1400
1600
1800
2000
1000 1200 1400 1600 1800 2000 2200
Engine Speed (rpm)
Bra
ke
To
rqu
e (
lb-f
t)
Thermo-Fluid Systems on HD Diesel Engines
Cooling System Air Handling System Lube System Fuel System
Qhead+Qblock
Engine Cooling System Layout
CYLINDER LINER / HEAD LOWER WATER MANIFOLD
Water Pump
T-STAT
RA
DIA
TO
R
BY
PA
SS
HEAD UPPER WATER MANIFOLD
OIL COOLERSQoil
Qmnf
Qrad
Wpump
Functions of the Cooling System
To prevent excessively high and low engine component temperatures
To provide a heat sink for the lube system To reject engine heat to the ambient To provide a heat source for the truck cab To provide a coolant source for other OEM
equipment (e.g. torque converter coolers, fuel heaters)
The optimal cooling system meets system requirements whileminimizing life cycle cost (initial cost, warranty/reliability,operating/fuel cost). Tomorrow’s lab will give you the opportunityto evaluate designs from a life cycle cost perspective.
Design Control Responsibilities
Water Pump Oil Cooler Liners Heads Water Manifold/Water Header Thermostat Bypass
Radiator Charge Air Cooler Freon Condenser Radiator Fan Fan Drive (Drive Ratio, Fan
Clutch) Fan Shroud Air Dams Cab Heater Auxiliary Coolers
Engine Manufacturer Truck Manufacturer
Cooling System Development Techniques
Water Pump Performance Testing Engine Flow Stand Flow Bench Flow Circuit Simulation CFD Analysis FE Analysis Thermal Mapping Test Oil Cooler Performance Testing Chassis Dyno
Cooling System Constraints
Constraint WP
Tes
t
Flo
w S
tand
Cha
ssis
Dyn
o
Oil
Coo
ler
Test
Flo
w B
ench
Flo
w C
ircu
it S
iml
CF
D
FE
The
rmal
Map
Tes
t
WP Cavitation X XWP Seal Temp X XMax Oil Temp X X X X X XMax Coolant Temp XMax Component Temps X X XFilm Boiling X X X X XAluminum Erosion/Corrosion X X X X XParasitic Power X X X X X X
Water Pump Performance Test
Used to determine: Pump capacity (flow rate)
as a function of pressure rise and pump speed
Pump efficiency and parasitic power
NPSH and cavitation temperature
Water Pump Cavitation
What is It? The formation of vapor at the pump inlet due to local
pressures dropping below the saturation pressure.
When does it Occur? High coolant temperatures (high saturation pressure) High coolant flow rate (low local static pressure)
Why is it Important? Leads to a reduction of pump flow rate, therefore lower
radiator effectiveness, therefore higher coolant temps, therefore more cavitation (runaway coolant temperatures)
Leads to an increase in water pump seal temperature (fails the seal)
Theoretically can lead to erosion of the impeller but generally the failure modes listed above occur first.
Typical Water Pump Map
0
5
10
15
20
25
30
35
40
0 25 50 75 100 125 150 175 200
Flow Rate (gpm)
Sta
tic
-to
-Sta
tic
He
ad
Ris
e (
ps
i) 4000 rpm
3429 rpm
2858 rpm
2286 rpm
1714 rpm
1143 rpm
0.000.050.100.150.200.250.300.350.400.450.500.550.600.65
0 25 50 75 100 125 150 175 200
Flow Rate (gpm)
Tota
l-to
-Sta
tic
Eff
icie
nc
y
4000 rpm3429 rpm2858 rpm2286 rpm1714 rpm1143 rpm
Engine Flow Stand
Used to determine: Radiator flow rate
vs radiator restriction
Coolant pressure distribution within engine
Coolant flow rate through external components
Allows estimation of coolant flow distribution within engine using flow circuit modeling
1
2
3
45
6
78
1721
22
23
2425
Engine Restriction Curve Overlayon Pump Map
0
5
10
15
20
25
30
35
40
0 25 50 75 100 125 150 175 200
Flow Rate (gpm)
Sta
tic
-to
-Sta
tic
He
ad
Ris
e (
ps
i)
DP is proportional to the square of the flow rate (energy equation -> DP is proportional to V squared)
Pump head rise is proportional to the square of the pump speed
Flow rate is linear with engine speed
Flow Bench
Used to determine: Component coolant flow
vs pressure drop relationship (“hydraulic resistance”)
On-engine component coolant flow rates and parasitic power using flow circuit simulation or flow stand testing
Hydraulic Resistance:Analogy to Electrical Circuits
PAKKV T
T
2
2
22
1
“Geometric” Elements “Resistive” Elements
Both equations are of the form:
Note that voltage (v) is analogous to pressure drop,and current (i) is analogous to volumetric flow rate.
Hydraulic resistance is a function of the flow rate. Because ofthis non-linearity, iteration is needed to obtain hydraulic circuitsolutions.
riv
QRRP QQNN
1ˆ
Flow Circuit Simulation Based on the analogy of
hydraulic and electrical circuits
Used to determine: Cooling system parasitic
power by component and for the entire system
Coolant flow distribution within the engine
Approximate coolant velocity
Assists the design effort by allowing the design to be iterated quickly before hardware is procured.
CYLINDER LINERS / HEADS
RADIATOR
PUMP
OILCOOLER
T-STATWATER MANIFOLD
CFD Analysis
Used to determine Coolant pressure
drop for use in flow circuit modeling
Velocity distribution Coolant side
boundary conditions (temperature and heat transfer coefficient) for thermal FE analysis
Model predictions are validated by thermal mapping, flow bench testing, and flow visualization.
FE Analysis
Used to determine Component
temperatures Component stresses Fatigue life
Model calibrated to thermal mapping engine measurements
Thermal Mapping Test
Used to calibrate thermal FE models
Oil Cooler Performance Test
Used to determine: Oil cooler heat transfer
rate as a function of oil flow, coolant flow, and fluid temperatures
Oil cooler coolant and oil side restriction
On-engine oil cooler coolant flow rates and parasitic power using flow circuit simulation or on-engine testing
0
100
200
300
400
500
600
700
800
900
10 15 20 25 30
Oil Flow (GPM)
UA
(B
tu/m
in-4
0 d
eg
F IT
D)
25 GPM Coolant
20 GPM Coolant
15 GPM Coolant
Truck Cooling Package Layout
Air
Air atFan BlastTemp
CONDENSER
C
A
C
RADIATOR
Ram Air atAmbientTemp
Air
Freon fromTruck AC
System
Charge Airfrom
Turbo
Coolant fromEngine Tstat
Freon toTruck AC
System
Charge Airto
Intake Mnf
Coolant toEngine Wtr
Pump
Note: Tomorrow’s lab includes optimization of a truck cooling package
Chassis Dyno Facility
Used to determine coolant temperatures and engine heat rejection under simulated hot ambient conditions
Capable of handling the largest HD trucks and engines
5 foot by 7 foot air tunnel can provide up to 35 MPH ram air into radiator
Mixing ambient air with recirculated air allows the air temperature into the radiator to be varied to limiting ambient conditions (100-115 deg F)
Chassis Dyno Schematic
ROOF
Dyno Rollers
Diffuser exit
OUTSIDE
External VerticalLouvers
Internal HorizontalLouvers
Air Flow
Vertical Exhaust Louver
Cover Grates
Blower
GARAGE DOOR
Summary
Cooling system design requires the optimization of components and the system as whole to meet competing objectives of: Initial Cost Warranty/reliability Operating/fuel cost
Cooling system components are under the design control of both the engine and truck manufacturer. Cooperation is needed to deliver the best product to the end user.
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