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

QQ

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.