2001-01-1708

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SAE TECHNICALPAPER SERIES 2001-01-1708

Economical Engine Cooling System

N. S. Ap, A. Maire, P. Jouanny and J. C. Le PrigentValeo Engine Cooling

Reprinted From: The Proceedings of the 2001 Vehicle ThermalManagement Systems Conference

(P-363)

Vehicle Thermal Management SystemsConference & Exhibition

Nashville, TennesseeMay 14-17, 2001

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ISSN 0148-7191Copyright 2001 Society of Automotive Engineers, Inc.

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ABSTRACT

The previous study presented during the last VTMS 4showed the following results, for all engine coolingsystem and depending on the vehicles:- Cost reduction by - 10 to -15%,- Weight reduction by -15 to - 21%,- Coolant volume reduction by –25%- Fuel consumption by -3%,- Thermal comfort improvement.Despite of these good results, most of car manufacturershesitated to use this new concept due to thistechnological breakthrough of engine cooling systembecause of expensive durability studies.In this paper the electric fan has been simply suppressedand replaced by the heating blower allowing to cool theengine at idle and at low vehicle speed.By suppressing the electric cooling fan, the advantagesof this new economical engine cooling system become:- cost reduction up to – 30%,- weight reduction up to – 30%.

INTRODUCTION

The previous study presented in VTMS 4 (reference 1below) showed the following results, for all enginecooling systems and based on the vehicles:- Cost reduction by - 10 to -15%,- Weight reduction by -15 to - 21%,- Coolant volume reduction by –25%- Fuel consumption by -3%,- Thermal comfort improvement.

To obtain these results, new and specific componentshave been designed and developed. For this study, theelectric fan has been suppressed and replaced by theheating blower allowing to cool the engine at idle and atlow vehicle speed. The heating device has been speciallydesigned and equipped with the additional flap allowingto evacuate the hot air dissipated by the heater core tothe outside of vehicle. At high vehicle speed, from 90km/h to max. speed, the performance of cooling systemwithout fan and shroud is better than the system withcooling fan even if it is in “on or off” position.Two compact vehicles were tested in the climatic windtunnel according to the engine cooling specification:

- Renault « Twingo » equipped with a D7F 1.2 litergasoline engine,

- Seat « Arosa » equipped with a 1.7 liter dieselengine direct injection SDI,

The cooling performance of the new engine coolingsystem without electric cooling fan is approximately thesame as the conventional cooling system with coolingfan.

BACK GROUND

NEW ENGINE COOLING SYSTEM - The new enginecooling system called « REROM » (see reference 1) is abreakthrough in engine cooling. This study is based onthe new concept of engine cooling by using a smallelectric water pump 30 to 60 W, instead of theconventional engine driven pump of 1 to 2 kW. Thissmall electric pump provides a flow rate of approximately1 000 to 1 500 l/h. Other features of this concept are:- Low relative pressure in the coolant circuit; only 0.2

bar instead of 1 to1.5 bar,- Maximum coolant temperature of 115°C,- Conventional engine cooling for low and medium

engine load (up to 150 km/h),- Nucleate boiling engine cooling for high engine load

(max. speed and hill climbing for example).In spite of the important advantages of this new coolingsystem compared to the conventional engine coolingsystem, some more efforts have to be continued in orderto reduce cost and weight.

2001-01-1708

Economical Engine Cooling System

N. S. Ap, A. Maire, P. Jouanny and J. C. Le PrigentValeo Engine Cooling

Copyright © 2001 Society of Automotive Engineers, Inc.


Figure 1 : Cooling architecture of “REROM”

AIR COOLING SYSTEM - Engine cooling radiator heatperformance on the vehicle is very different from the heatperformance in a component wind tunnel. This is due tothe many mitigating factors: the water pump, the fanpower, and other vehicle components like the: grill, airinlet cross sectional area, bumper position, ram air,pressure coefficient at the front end and at the air outletof underhood, ...Reference 2 shows the influence ofeach parameter separately on the engine coolingperformance. Among these parameters, we interest inparticularly the influence of the fan (fan and fan off) andfan shroud on the engine cooling performance.

A new cooling radiator coefficient η = Ur / Uv called« adaptation coefficient » has been defined as the ratioof the average air velocity Ur across the radiator and thevehicle speed Uv. Figures 2 and 3 show the influence offan on and off and different shrouds on the “adaptationcoefficient” and the heat dissipation of radiator:

Full Fan Shroud (FFS),

Partial Fan shroud (PFS),

Without Fan Shroud (WFS).

Without fan and without shroud (WFWS). Thisconfiguration corresponds to the suppression of fanand shroud, that means there is no fan and no shroudin the engine cooling system.

These results correspond to:

- the 130 Watts electric fan,

- the mechanical radiator of 245x470x34 mm size, 8mm round tube and 3 passes of liquid circuit,

- coolant flow rate of 3000 liters/h.

According to these results we can see the WFWSconfiguration is:

- better than the fan off for all fan shroudconfigurations.

- The same as or better than the fan on configurationfor high vehicle speeds (150 - 160 km/h).

- smaller than the fan on configuration at low andmedium vehicle speed. The differential is moreimportant at low vehicle speed and small at mediumvehicle speed. It becomes practically null or better athigh vehicle speeds.

The fan “on” is necessary at low and medium vehiclespeeds but unnecessary at high vehicle speeds. For thiscondition the fan, even it is on, disturbs the cooling flowrate through the radiator. In fact the “fan on” works in thenegative efficiency area. It is better for the coolingradiator to suppress simply the fan and shroud but wehave to evacuate the differential heat dissipation versusradiator without fan and without shroud. This operationwill be assumed by the heater core and the blower.

ADAPTATION COEFFICIENT OF 34R8 RADIATOR FOR DIFFERENT FAN SHROUD (130 W electric fan)

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0,45

0,5

0 20 40 60 80 100 120 140 160

VEHICLE SPEED (km/h)

ET

A =

Ur/

Uv

Without fan shroud(fan on)

With full fan shroud(fan on)

With partial fan shroud(fan on)

Without fan shroud(fan off)

With full fan shroud(fann off)

With partial fan shroud(fan off)

Without fan and shroud

Figure 2 : Influence of fan and fan shroud on the airvelocity through the radiator

HEAT FLUX OF 34R8 RADIATOR FOR DIFFERENT FAN SHROUDS (130 W electric fan on and off and 3 000 L/h flow rate)

0

5

10

15

20

25

30

35

0 20 40 60 80 100 120 140 160

VEHICLE SPEED (km/h)

Qr7

5 (k

W)

Without fan shroud(fan on)

With full fan shroud(fan on)

With partial fan shroud(fan on)Without fan shroud(fan off)

With full fan shroud(fan off)

With partial fan shroud(fan off)

Without fan and shroud

Figure 3 : Influence of fan and fan shroud on the radiatorheat dissipation


EXPERIMENTAL MEASUREMENT

- The cooling electric fan has been simply suppressedand replaced by the heating blower allowing to coolthe engine at idle and at low and medium vehiclespeeds. The heating device has to be speciallydesigned and equipped with the additional flapallowing to evacuate the hot air dissipated by theheater core to the outside of vehicle

COOLING SYSTEM WITH ELECTRIC FAN – Figure 4below shows the architecture of a cooling circuitequipped with an 80 Watts cooling fan and an electricwater pump of 50 watts according to our “REROM”cooling system (see references 1 and 3).

Twingo REROM : Cooling Loop Architecture with Electric Fan

Engine

Thermostat

Electric Water Pump

Expansion Tank

Heater

Radiator

Fan

Figure 4 : Cooling system with electric fan

COOLING SYSTEM WITHOUT ELECTRIC FAN –Figure 5 below concerns the same cooling circuit except:

- the electric cooling fan has been suppressed,

- the heat dissipation of the heater core will be used tocool the engine if necessary for the normal load ofengine. It will be used for the full load and low vehiclespeed like hill climbing for example.

To avoid some steam bubble at the inlet of the electricwater pump for the hill climbing or max. speedconditions, it has been moved at the outlet of heatercore.

Twingo REROM : Cooling Loop Architecture without Electric Fan

ThermostatElectric Water Pump

Radiatorwithout Fan

Engine

Expansion Tank

Heater

Blower

Figure 5 : Cooling system without electric fan

CLIMATIC WIND TUNNEL TEST RESULTS - Twovehicles have been equipped with different sensors andtested in the climatic wind tunnel according to the enginecooling specifications:

- hill climbing condition : vehicle speed of 50 km/h,12% grade at 30 °C ambient temperature,

- max. speed of 150 km/h, flat road at 35 °C outsidetemperature.

Two compact vehicles were considered:- a Renault « Twingo » equipped with a D7F 1.2 liter

gasoline engine,- and a Seat « Arosa » equipped with a 1.7 liter diesel

engine direct injection SDI

These two vehicles were tested according to twodifferent engine cooling configurations:

- cooling radiator equipped with the fan,

- cooling radiator without fan. Also the blower will beswitched in “on” and at max. speed position.

Tables 1 and 2 show the climatic wind tunnel test resultsfor these two vehicles under the two fan configurations.The two main engine cooling physical parametersexamined were:

- the coolant temperature at the outlet of engine,

- the oil sump temperature,

for each vehicle these temperatures are practically thesame for the two configurations of fan.


Véhicule : RENAULTTwingo

with without

CoolingFan

CoolingFan

13% grade Hill Climbing ,Power : 23kw

Speed : 50 km/h , Ambient30°C

Outlet Coolant Temperature(°C)

107 103

Oil Sump Temperature (°C) 139 137

Cooling Radiator HeatRejection (kw)

20 17

Heater Core Heat Rejection(kw)

0 5

Max Speed, 155 km/h

Full Power , Ambient : 35°C


105 102



20 20

Heater Core Heat Rejection 0 0

Table 1 : Climatic wind tunnel test results comparison onRenault Twingo

Concerning the heat dissipation of cooling radiator Qrwith or without fan, we expected some problem ofthermal balance at the hill climbing conditions due to thenucleate boiling in the engine. The coolant was themixture ethylene glycol – water 50 – 50 %. The boilingtemperature at the atmospheric pressure is about 107 –108 °C.

Total heat flux = Forced convective part + nucleateboiling part

Qr = qm . Cp .( Tcint – Tcout ) + m . L

At max. speed conditions (see tables 1 and 2):

- the nucleate boiling part is equal zero due to thecoolant temperature remained below boilingtemperature,

- the “without” fan configuration is slightly better thanthe “with” fan configuration.

Véhicule : SEAT Arosa with without

CoolingFan

CoolingFan

13% grade Hill Climbing ,Power : 23kw

Speed : 50 km/h , Ambient30°C


107 108



21 15


0 5

Max Speed, 155 km/h

Full Power , Ambient : 35°C


106 104



26 27


0 0

Table 2 : Climatic wind tunnel test results comparison onSeat Arosa

HEATING DEVICE

Heating was accomplished by using:

- the heater core dissipation (blower “ on ” ) as theadditional cooling radiator dissipation

- and the heat dissipated by the cooling radiatorwithout fan

the total of both dissipations is enough to cool the engineaccording to the cooling specifications. The heatingdevice has to be specially designed and equipped withthe additional flap allowing to evacuate the hot airdissipated by the heater core to the outside of vehicle.The additional flap functionality has to ensure thefollowing conditions:

- Cab heating,

- Engine cooling, particularly at high and full load ofengine,

- Fresh air in the cab during summer.


The additional flap position could be managed by theconventional mechanical button on the dashboard. Theheater blower could be controlled by:

- the passenger for the thermal comfort,

- and by the conventional thermo-switch mounted onthe cooling radiator or by the ECU of engine.

CAB HEATING CONDITIONS – The additional flap inthe heater device has to ensure the same thermalcomfort as the conventional heater device, that meansthe thermal comfort should be the same for all seasons :fall, winter and spring.

Winter operation – At the cold start of engine and in thecold winter the flap position is as shown figure 6. By theheater blower “ on ”, the cold air goes through the heatercore and the hot air heads to the passenger cab or to thewindscreen. In this condition there is no coolant flow ratein the cooling radiator due to the main thermostat. Whenthe coolant temperature reaches the opened value ofthermostat, the heat dissipation of radiator is enough tocool the engine even at the high vehicle speed. At thehigh engine load and low vehicle speed (hill climbing forexample) the heat dissipation of heater core (if needed)adds to the heat from cooling radiator without fan (seefigure 7). The total heat is normally enough to cool theengine in this condition. The thermal comfort ofpassenger compartment could be unchanged due to thehigh coolant temperature.

Figure 6 : Heater maximum to the cab (cold winterconditions)

Fall and spring operations – For these seasons theheater device operates in the same condition as thewinter except the hot air distribution of heater core (figure7) is to the cab and to the outside of the vehicle. Thecab needs less heat flux than the cold winter allowing tomaintain the same thermal comfort level. At low andmedium vehicle speeds the heater flaps position couldbe according to figures 8 and 9.

Figure 7 : Partially air heating to the cab and to theoutside (Winter operation)

Figure 8 : Mixture hot air and cold air to the cab

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AIR INLET CAB

AIR INLET

COOLANT

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AIR INLET CAB

AIR INLET

HOT AIR OUT

COOLANT

HE

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AIR INLET CAB

AIR INLET

COOLANT


Figure 9 : Partially and mixture of hot and cold air to thecab and hot air to the outside

ENGINE COOLING CONDITIONS – The cooling radiatorwithout fan and the heater device concept have toensure the good engine cooling according to the carmanufacturing specifications : max. speed and hillclimbing. Additionally the heater device has to satisfy thefresh ambient air request, particularly during thesummer.

Summer and flat road operation – Depending on thevehicle speed, there are several possibilities :

- low vehicle speed : the heat dissipation of radiatorwithout fan is not enough to cool the engine,particularly at idle. In these conditions the enginecooling is ensured by the radiator without fan and bythe heater core (see figures 10 and 12).

- medium vehicle speed : the heat dissipation ofradiator without fan becomes interesting and couldbe enough to cool the engine. The additional engineheat dissipation is ensured by the heater core (seefigure 10). If the fresh ambient air is needed in thecab, the heater flaps are in position according tofigure 12.

- high vehicle speed : the heat dissipation of radiatorwithout fan is enough to cool the engine. Dependingon the need of fresh ambient air in the cab, there aredifferent flap positions of heater device (see figures10 to 13). Figure 11 shows the maximum freshambient air needed in the cab. Figure 13 shows theflap positions in the “no fresh air” in the capcondition.

Figure 10 : Heater air to the outside of vehicle

Figure 11 : Fresh air in the cab (summer conditions)


Figure 12 : Partially fresh air to the cab and hot air to theoutside of vehicle

Figure 13 : No air in the cab

Summer and hill climbing operation – This is the hardcondition for the engine cooling system. The heatdissipation of cooling radiator without fan and the heatercore should be enough to cool the engine. The flappositions are shown in figure 10. All air flows go throughthe heater core and the hot air passes to the outside ofvehicle.

CONCLUSION

The cooling performance of the new engine coolingsystem without electric cooling fan is approximately thesame as the conventional cooling system with coolingfan.

By suppressing the electric cooling fan on theradiator, the advantages of this new economical enginecooling system are:- cost reduction up to – 30%,- weight reduction up to – 30%. Obviously this study concerns the vehicles withoutair conditioning and particularly the small compactvehicle range when the cost reduction is an importanttarget.

ACKNOWLEDGMENTS

The authors acknowledge Valeo Engine cooling R&Dteam for their help and collaboration.

REFERENCES

1. N.S.AP - A.MAIRE - P.MENEGAZZI - P.POROT -F.SOUIDI - C.LE DEVEHAT, D.GODEAU -P.OLIVIER - J.Y.LORIN - G.VINCENS. “NewComponents Development for New Engine CoolingSystem” VTMS 4 Technical paper London 1999.

2. N.S.AP “ A Simple Engine Cooling SystemSimulation Model ” SAE technical paper n° 1999-01-0237.

3. P.POROT – N.S.AP – A.MAIRE – P.MENEGAZZI –S.HENRIO – C.LE DEVEHAT – D.GODEAU –P.OLIVIER – J.Y.LORIN – G.VINCENS “ NewComponents for an Innovative Engine CoolingSystem “ FISITA technical paper n° F98T054 Paris1998.

4. N.S.AP and N.C.GOLM , « New Concept of EngineCooling System (Newcool) », VTMS-3 paper n°971775 , 1997.

5. . P.A.POROT, P.MENEGAZZI and N.S.AP,« Understanding and Improving Evaporative EngineCooling at high load, high speed by Engine Testsand 3D Calculations », VTMS-3 paper n° 971792,1997.

6. . M.PRETSCHER and N.S.AP, « Nucleate BoilingEngine Cooling System - Vehicle Study », VTMS-1paper n° 931132, 1993.

CONTACT

Dr.-Ing. N.S.AP VALEO Engine Cooling 8 rue LouisLormand 78321 La Verriere France. Tel. (33) 1 30 13 5268 Fax . (33) 1 30 13 50 67 Email: [email protected].

HE

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AIR INLET CAB

AIR INLET

HOT AIR OUT

COOLANT

HE

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AIR INLET CAB

AIR INLET

COOLANT


DEFINITIONS, ACRONYMS, ABBREVIATIONS

- Ur: Average air velocity through the cooling radiator,

- Uv: Vehicle speed,

- η = Ur / Uv : adaptation coefficient,

- Qr : Radiator heat dissipation,

- qm : Mass flow rate of coolant through the radiator

- Cp : Specific heat of coolant,

- m : Mass flow rate by nucleate boiling,

- L : latent heat of coolant,

- Tcint : Coolant temperature at the inlet of radiator,

- Tcout : Coolant temperature at the outlet of radiator


2001-01-1708

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