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Dual level vehicle heat rejection system
Dual level vehicle heat rejection system C MALVICINO, F DI SCIULLO and M CUNIBERTI Centro Ricerche Fiat S.C.p.A., Italy F VESTRELLI and F BELTRAMELLI Fiat Group Automobiles, Italy
ABSTRACT In perspective of the incoming CO2 emission regulation, the on board heat management is becoming even more relevant to assure the engine performance improvement minimizing the impact on the vehicle lay out, cooling drag and cost. The paper highlights the benefit of dual level heat rejection system where, the front module constituted by heat exchangers carrying different fluids (e.g. water-glycol, air, refrigerant fluid…), is replaced by a two coolant-to-air exchangers module and where the charge air cooler and condenser are liquid cooled. This approach allows to review the engine bay design allowing a deeper integration level: the charge air cooler can be integrated in the air intake manifold while the condenser can be placed near the compressor minimising the tube lengths and refrigerant charge. In addition, the coolant thermal inertia reduces the temperature fluctuations of the engine intake air temperature. These effects compensates the introduction of an intermediate temperature level allowing to reduce the overall vehicle fuel consumption in real use and could enable the front aerodynamic improvement. The experimental results show that it is possible to reduce the fuel consumption of up to the 4% when the air conditioning is operating and to reduce the refrigerant charge of up to the 30%. In the paper is described the system concept and the experimental results related to an application on a Fiat 500 are discussed highlighting the benefits and the open issues. 1
INTRODUCTION
The European Commission is promoting the reduction of the CO2 and CO2equivalent emissions of road transports thanks to and Integrated Approach mainly based on: • a regulatory framework for reducing the CO2 emissions of the average new fleets [1] • the replacement of the air conditioning refrigerant with more environmental friendly alternatives [2]
______________________________________________ Copyright of the author(s) and/or their employer(s), 2011
Figure 1– A Fiat 500 85HP MultiAir MTA has been adopted as vehicle demonstrator for the Dual Level cooling system
473
• the technology development sustaining the research in the domain with the Green Car Initiative and other funding measures In the overall effort to achieve sustainability, advanced technological solutions have to be developed to reduce fuel consumption and carbon dioxide emissions from vehicles. In the scenario towards more efficient road transports the improvement of the on board thermal management could play a relevant role enabling a finer subsystem control, more compact engine and engine compartment packaging and the cooling drag reduction. Following the state of the art approach, each subsystem (e.g. charge air cooler, condenser, engine coolant, oil cooler, …) has its own cooling system where the fluidto-be-cooled is brought on the front of the vehicle and then back in the engine compartment. TRANSMISSION OIL
L/T Radiator
INTERCOOLER
H/T Radiator
CONDENSER
Radiator ENGINE
ENGINE
CONDENSER INTERCOOLER TRANSMISSION OIL
BATTERY
BATTERY
ELECTRONICS
ELECTRONICS
GENERATOR FUEL
GENERATOR
(a)
FUEL
(b)
Figure 2 – Standard System (a) and Two-levels heat rejection approach (b) allows to increase the modularity and standardisation simplifying the thermal module and enabling the aerodynamic improvement of the overall vehicle This approach implies that • the front end module changes according to the powertrain and to the optional equipment making more difficult to optimise the vehicle aerodynamics • all the subsystems share the same fan and it is activated on a single system need; this implies higher energy demands • the introduction of new subsystems (e.g. electronics, e-motor, batteries) will require a proper cooling system and any additional heat exchanger on the front has a negative impact on cooling drag and heat rejection • in case of small accident all the exchangers could be damaged and the fluids dispersed in the environment (refrigerant, oil, …) To overcome to these points and to enable the design review of the engine compartment and of the vehicle front it has been evaluated an approach based on a simplified version of what already presented by Valeo [3] in the recent past and where the coolant is
474
brought in the subsystems-to-be-cooled, but the engine, and then to a radiator placed in the front of the vehicle (Figure 2). This concept enables to • standardise the vehicle thermal module and optimise the front end aerodynamics; • activate the fan only on the basis of the average needs: the thermal inertia of the shared coolant allow to buffer the heat rejection need; • reduce the “fluid-to-be-cooled” amount (e.g. air conditioning refrigerant); • integrate the fluid coolers in the subsystems (e.g. charge air cooler in the air intake manifold); • share the cooling loop cost among the systems; • limit the impact on the front end architecture and size (modularity) in case of an additional (e.g. electronics, e-motor, batteries) cooler is required; • limit damage and fluid dispersion (only water-glycol) in case of small accidents; • reduce the refrigerant charge; 2
PROTOTYPE SYSTEM 50%
The adopted system scheme is shown in figure 3: the high temperature loop is almost unchanged while a low temperature loop is devoted to changer air cooler and condenser cooling. An electrical pump assures the coolant flow in the low temperature loop while, to keep the system simple, no valves have been integrated. The system has been prototyped on a Fiat 500 85 HP MultiAir (gasoline 2-cilynders turbocharged engine) with MTA and experimentally validated.
Condenser Subcooling
Charge Air Cooler
40%
High Temperature Radiator Expansion Vase
Low Temperature
50 W
Low Temperature
Subcooling
1800 l/h
Pump
10%
Figure 3 – System Scheme
Figure 4 – Two-levels cooling system prototyped on the Fiat 500 2-cilinders gasoline turbocharged engine
475
The Figure 4 shows the impact on the system lay out highlighting that the replacement of the standard charge air cooler allows to adopt a larger high temperature radiator using part of its surface to enhance the heat transfer of the low temperature loop. To evaluate the maximum integration level, the charge air cooler has been integrated in the air intake manifold and the condenser has been placed near the evaporator and compressor. The system components have been realised in cooperation with tier one suppliers (i.e Magneti Marelli and Denso Thermal Systems). Table 1 – Heat Exchangers’ dimensions
The air intake system becomes more compact and the air ducts shorter, the air conditioning loop is also more compact and the front end module is now constituted by only two heat exchangers of the same technology (air – coolant) instead of three element of different type (air-to-air, air-to-coolant and air-to-refrigerant). Finally, the higher air conditioning system compactness enabled a refrigerant charge reduction of about the 30 % (from 450 g to 300 g). The components have been then prototyped and the system has been installed on a Fiat 500 demonstrator and experimentally validated. The design phase allowed also to evaluate the Dual Loop system impact on weight that, if the system is properly designed and sized, should not be affected or only slightly increased. This is due to the compensation effect among added components (weight increase) and simplification of the systems lay out (weight reduction). 3
TESTING PROCEDURES
On the demonstrator vehicle have been evaluated fuel consumption, air conditioning cooling performances and energy demands. The New European Driving Cycle (NEDC) has been used to qualify the two level cooling system impact on the homologation CO2 emission while the procedure developed and proposed within the B-COOL EU project [3] has been adopted to assess the impact on the air conditioning energy on the vehicle fuel consumption. The procedure is based on a modified NEDC performed in a climatic chamber at 28 °C and 50% R.H. with the A/C system set point of 20 °C in fresh air mode. Then, the demonstrator vehicle has been submitted to the tests to assess the heat rejection capacity in severe thermal conditions and the overall A/C cooling performance under high thermal load. The A/C cooling performance has been evaluated in a climatic wind tunnel set as follows:
476
• • •
Ambientt: 43 °C andd 30% R.H. Irradiatioon: 900 W/ssqm Soaking: head levell air at 60 °C C
The test starts once the soaking coondition aree achieved with the air conditio oning regullated at full power in ree-circulationn mode, folllowing the steps listed in Table 2. T Table 2 – Coool Down test t sequencce
4
E EXPERIM MENTAL RESULTS R
v dem monstrator has h been characterised before the Two-Levels cooling sy ystem The vehicle integgration and then after having h integrated it on n board, thee results aree reported in i the following paragraphs. 4.1 Fuel Consumption The fuel consum mption perfo formance is reported in n the Table 3. The resuults show that the Two Levels coooling system m doesn’t afffect the veh hicle fuel ecconomy in thhe homolog gation cyclee and has a relevant and a positivve effect on n the air coonditioning energy demand reduccing it of abbout the 25% (28 °C – 50% R.H.)), it should be mentionned that eacch test pointt has been repeated r at least l three tiimes. Table 3 – Fuel Con nsumption performan nce (l/100 km) k on NED DC cycle
4.2 Engine Cooling Perfformance The comparisonn of the enggine coolingg performan nce is show wn in Figuree 5 showing g that T Levelss cooling syystem guaraantees the target t achieevement even if the ov verall the Two perfoormance is slightly s low wer than the baseline. In n addition shhould be unnderlined th hat the air teemperature at the CAC C outlet is lower l in caase of the duual loop syystem than in i the baselline.
477
90 80
DL - Po ower @ wheels [k kW] SP - Po ower @ wheels [k kW]
70
DL - Air CAC outlet
60
DL - HT T Radiator outlett - coolant [°C]
50
SP - Air CAC outlet [°C]]
DL - LT T Radiator outlet - coolant [°C] SP - Ra adiator outlet - coolant c [°C]
40 30
A/C ON
A/C C ON
A/C ON
Test pe erformed in a climatic c wind tu unnel @ 30 °C with 800 w/sqm m of solar irradiiation
20 10
IDLE
0 2 24
46
4 140 14 46 40
0
14 40
S Speed (kph h) Figgure 5 – En ngine Coolin ng Perform mance: the Dual Loop p cooling syystem allow ws to keeep the cooolant tempeerature equ ual or lowerr than the baseline b syystem and the L Tempeerature looop values gu Low uarantee lo ower enginee air inlet ttemperaturre ditioning Peerformancee 4.3 Air Cond In figgure 6 is reeported the air conditiooning coolin ng performaance of the baseline veehicle and of the dem monstrator vehicle: the performaance is equuivalent andd only the high presssure is a bit b higher in i the firstt part of th he test (300 kph) duee to the ind direct conddensation.
Figure 6a - Cool Down D test results r – Prressures
478
Figure 6b b – Cool Doown test ressults – Tem mperatures 5
N NEXT STE EPS
Three additionaal vehicle prototypess (two B segment passenger p ccar and a light comm mercial vehhicle) are under u realiisation and their full experimenttal validation is expected to be completed c b before Marcch 2011. Thesse system will w differ from f the onne here described beccause they will includ de the adopption of an Internal Heaat Exchangeer in the air conditioninng loop and will be designed and operated o wiith the HFO O-1234yf as refrigerant. 6
C CONCLUS SIONS
mental valiidation of a Two The results collected after the design,, prototype and experim Leveels cooling system s allow ws to affirm m that the ap pproach: • has no neggative effect on the hom mologation fuel econom my • allows to reduce up to the 25% % the air co onditioning fuel consum mption (28 °C – 50% R.H.) • has no neggative impaact on the airr conditioniing cooling performancce • allows to reduce the refrigerant charge of up u the 30% (dependingg on the basseline layout) Finallly, besides the above listed l quantitative featu ures, the Tw wo Levels syystem: • Enables thhe simplification and sttandardisation of the frront end module • Reduces thhe damagess and the fluuids dispersion in the environment e t in case of small accidents.
479
REF FERENCE LIST [1] [2] [3] [4]
480
REGULA ATION (EC) No 443/22009 Setting g emission performannce standard ds for new passeenger cars as part of the Comm munity’s inteegrated appproach to reeduce CO2 emisssions from light-duty vehicles v REGULA ATION (EC)) No 842/20006 On certaain fluorinaated greenhoouse gases UltimateC Cooling™ new n coolingg system co oncept usinng the samee coolant to o cool all vehiclee fluids, N.S. Ap et all., Vehicle Thermal Management M t Systems, 2003, 2 Brighton (UK), ( C5999/0101/20033 B-COOL Project - Foord Ka and Fiat Panda R-744 MA AC systems,, C. Malviciino et al., SAE paper p 2009-001-0967
ABSTRACT In perspective of the incoming CO2 emission regulation, the on board heat management is becoming even more relevant to assure the engine performance improvement minimizing the impact on the vehicle lay out, cooling drag and cost. The paper highlights the benefit of dual level heat rejection system where, the front module constituted by heat exchangers carrying different fluids (e.g. water-glycol, air, refrigerant fluid…), is replaced by a two coolant-to-air exchangers module and where the charge air cooler and condenser are liquid cooled. This approach allows to review the engine bay design allowing a deeper integration level: the charge air cooler can be integrated in the air intake manifold while the condenser can be placed near the compressor minimising the tube lengths and refrigerant charge. In addition, the coolant thermal inertia reduces the temperature fluctuations of the engine intake air temperature. These effects compensates the introduction of an intermediate temperature level allowing to reduce the overall vehicle fuel consumption in real use and could enable the front aerodynamic improvement. The experimental results show that it is possible to reduce the fuel consumption of up to the 4% when the air conditioning is operating and to reduce the refrigerant charge of up to the 30%. In the paper is described the system concept and the experimental results related to an application on a Fiat 500 are discussed highlighting the benefits and the open issues. 1
INTRODUCTION
The European Commission is promoting the reduction of the CO2 and CO2equivalent emissions of road transports thanks to and Integrated Approach mainly based on: • a regulatory framework for reducing the CO2 emissions of the average new fleets [1] • the replacement of the air conditioning refrigerant with more environmental friendly alternatives [2]
______________________________________________ Copyright of the author(s) and/or their employer(s), 2011
Figure 1– A Fiat 500 85HP MultiAir MTA has been adopted as vehicle demonstrator for the Dual Level cooling system
473
• the technology development sustaining the research in the domain with the Green Car Initiative and other funding measures In the overall effort to achieve sustainability, advanced technological solutions have to be developed to reduce fuel consumption and carbon dioxide emissions from vehicles. In the scenario towards more efficient road transports the improvement of the on board thermal management could play a relevant role enabling a finer subsystem control, more compact engine and engine compartment packaging and the cooling drag reduction. Following the state of the art approach, each subsystem (e.g. charge air cooler, condenser, engine coolant, oil cooler, …) has its own cooling system where the fluidto-be-cooled is brought on the front of the vehicle and then back in the engine compartment. TRANSMISSION OIL
L/T Radiator
INTERCOOLER
H/T Radiator
CONDENSER
Radiator ENGINE
ENGINE
CONDENSER INTERCOOLER TRANSMISSION OIL
BATTERY
BATTERY
ELECTRONICS
ELECTRONICS
GENERATOR FUEL
GENERATOR
(a)
FUEL
(b)
Figure 2 – Standard System (a) and Two-levels heat rejection approach (b) allows to increase the modularity and standardisation simplifying the thermal module and enabling the aerodynamic improvement of the overall vehicle This approach implies that • the front end module changes according to the powertrain and to the optional equipment making more difficult to optimise the vehicle aerodynamics • all the subsystems share the same fan and it is activated on a single system need; this implies higher energy demands • the introduction of new subsystems (e.g. electronics, e-motor, batteries) will require a proper cooling system and any additional heat exchanger on the front has a negative impact on cooling drag and heat rejection • in case of small accident all the exchangers could be damaged and the fluids dispersed in the environment (refrigerant, oil, …) To overcome to these points and to enable the design review of the engine compartment and of the vehicle front it has been evaluated an approach based on a simplified version of what already presented by Valeo [3] in the recent past and where the coolant is
474
brought in the subsystems-to-be-cooled, but the engine, and then to a radiator placed in the front of the vehicle (Figure 2). This concept enables to • standardise the vehicle thermal module and optimise the front end aerodynamics; • activate the fan only on the basis of the average needs: the thermal inertia of the shared coolant allow to buffer the heat rejection need; • reduce the “fluid-to-be-cooled” amount (e.g. air conditioning refrigerant); • integrate the fluid coolers in the subsystems (e.g. charge air cooler in the air intake manifold); • share the cooling loop cost among the systems; • limit the impact on the front end architecture and size (modularity) in case of an additional (e.g. electronics, e-motor, batteries) cooler is required; • limit damage and fluid dispersion (only water-glycol) in case of small accidents; • reduce the refrigerant charge; 2
PROTOTYPE SYSTEM 50%
The adopted system scheme is shown in figure 3: the high temperature loop is almost unchanged while a low temperature loop is devoted to changer air cooler and condenser cooling. An electrical pump assures the coolant flow in the low temperature loop while, to keep the system simple, no valves have been integrated. The system has been prototyped on a Fiat 500 85 HP MultiAir (gasoline 2-cilynders turbocharged engine) with MTA and experimentally validated.
Condenser Subcooling
Charge Air Cooler
40%
High Temperature Radiator Expansion Vase
Low Temperature
50 W
Low Temperature
Subcooling
1800 l/h
Pump
10%
Figure 3 – System Scheme
Figure 4 – Two-levels cooling system prototyped on the Fiat 500 2-cilinders gasoline turbocharged engine
475
The Figure 4 shows the impact on the system lay out highlighting that the replacement of the standard charge air cooler allows to adopt a larger high temperature radiator using part of its surface to enhance the heat transfer of the low temperature loop. To evaluate the maximum integration level, the charge air cooler has been integrated in the air intake manifold and the condenser has been placed near the evaporator and compressor. The system components have been realised in cooperation with tier one suppliers (i.e Magneti Marelli and Denso Thermal Systems). Table 1 – Heat Exchangers’ dimensions
The air intake system becomes more compact and the air ducts shorter, the air conditioning loop is also more compact and the front end module is now constituted by only two heat exchangers of the same technology (air – coolant) instead of three element of different type (air-to-air, air-to-coolant and air-to-refrigerant). Finally, the higher air conditioning system compactness enabled a refrigerant charge reduction of about the 30 % (from 450 g to 300 g). The components have been then prototyped and the system has been installed on a Fiat 500 demonstrator and experimentally validated. The design phase allowed also to evaluate the Dual Loop system impact on weight that, if the system is properly designed and sized, should not be affected or only slightly increased. This is due to the compensation effect among added components (weight increase) and simplification of the systems lay out (weight reduction). 3
TESTING PROCEDURES
On the demonstrator vehicle have been evaluated fuel consumption, air conditioning cooling performances and energy demands. The New European Driving Cycle (NEDC) has been used to qualify the two level cooling system impact on the homologation CO2 emission while the procedure developed and proposed within the B-COOL EU project [3] has been adopted to assess the impact on the air conditioning energy on the vehicle fuel consumption. The procedure is based on a modified NEDC performed in a climatic chamber at 28 °C and 50% R.H. with the A/C system set point of 20 °C in fresh air mode. Then, the demonstrator vehicle has been submitted to the tests to assess the heat rejection capacity in severe thermal conditions and the overall A/C cooling performance under high thermal load. The A/C cooling performance has been evaluated in a climatic wind tunnel set as follows:
476
• • •
Ambientt: 43 °C andd 30% R.H. Irradiatioon: 900 W/ssqm Soaking: head levell air at 60 °C C
The test starts once the soaking coondition aree achieved with the air conditio oning regullated at full power in ree-circulationn mode, folllowing the steps listed in Table 2. T Table 2 – Coool Down test t sequencce
4
E EXPERIM MENTAL RESULTS R
v dem monstrator has h been characterised before the Two-Levels cooling sy ystem The vehicle integgration and then after having h integrated it on n board, thee results aree reported in i the following paragraphs. 4.1 Fuel Consumption The fuel consum mption perfo formance is reported in n the Table 3. The resuults show that the Two Levels coooling system m doesn’t afffect the veh hicle fuel ecconomy in thhe homolog gation cyclee and has a relevant and a positivve effect on n the air coonditioning energy demand reduccing it of abbout the 25% (28 °C – 50% R.H.)), it should be mentionned that eacch test pointt has been repeated r at least l three tiimes. Table 3 – Fuel Con nsumption performan nce (l/100 km) k on NED DC cycle
4.2 Engine Cooling Perfformance The comparisonn of the enggine coolingg performan nce is show wn in Figuree 5 showing g that T Levelss cooling syystem guaraantees the target t achieevement even if the ov verall the Two perfoormance is slightly s low wer than the baseline. In n addition shhould be unnderlined th hat the air teemperature at the CAC C outlet is lower l in caase of the duual loop syystem than in i the baselline.
477
90 80
DL - Po ower @ wheels [k kW] SP - Po ower @ wheels [k kW]
70
DL - Air CAC outlet
60
DL - HT T Radiator outlett - coolant [°C]
50
SP - Air CAC outlet [°C]]
DL - LT T Radiator outlet - coolant [°C] SP - Ra adiator outlet - coolant c [°C]
40 30
A/C ON
A/C C ON
A/C ON
Test pe erformed in a climatic c wind tu unnel @ 30 °C with 800 w/sqm m of solar irradiiation
20 10
IDLE
0 2 24
46
4 140 14 46 40
0
14 40
S Speed (kph h) Figgure 5 – En ngine Coolin ng Perform mance: the Dual Loop p cooling syystem allow ws to keeep the cooolant tempeerature equ ual or lowerr than the baseline b syystem and the L Tempeerature looop values gu Low uarantee lo ower enginee air inlet ttemperaturre ditioning Peerformancee 4.3 Air Cond In figgure 6 is reeported the air conditiooning coolin ng performaance of the baseline veehicle and of the dem monstrator vehicle: the performaance is equuivalent andd only the high presssure is a bit b higher in i the firstt part of th he test (300 kph) duee to the ind direct conddensation.
Figure 6a - Cool Down D test results r – Prressures
478
Figure 6b b – Cool Doown test ressults – Tem mperatures 5
N NEXT STE EPS
Three additionaal vehicle prototypess (two B segment passenger p ccar and a light comm mercial vehhicle) are under u realiisation and their full experimenttal validation is expected to be completed c b before Marcch 2011. Thesse system will w differ from f the onne here described beccause they will includ de the adopption of an Internal Heaat Exchangeer in the air conditioninng loop and will be designed and operated o wiith the HFO O-1234yf as refrigerant. 6
C CONCLUS SIONS
mental valiidation of a Two The results collected after the design,, prototype and experim Leveels cooling system s allow ws to affirm m that the ap pproach: • has no neggative effect on the hom mologation fuel econom my • allows to reduce up to the 25% % the air co onditioning fuel consum mption (28 °C – 50% R.H.) • has no neggative impaact on the airr conditioniing cooling performancce • allows to reduce the refrigerant charge of up u the 30% (dependingg on the basseline layout) Finallly, besides the above listed l quantitative featu ures, the Tw wo Levels syystem: • Enables thhe simplification and sttandardisation of the frront end module • Reduces thhe damagess and the fluuids dispersion in the environment e t in case of small accidents.
479
REF FERENCE LIST [1] [2] [3] [4]
480
REGULA ATION (EC) No 443/22009 Setting g emission performannce standard ds for new passeenger cars as part of the Comm munity’s inteegrated appproach to reeduce CO2 emisssions from light-duty vehicles v REGULA ATION (EC)) No 842/20006 On certaain fluorinaated greenhoouse gases UltimateC Cooling™ new n coolingg system co oncept usinng the samee coolant to o cool all vehiclee fluids, N.S. Ap et all., Vehicle Thermal Management M t Systems, 2003, 2 Brighton (UK), ( C5999/0101/20033 B-COOL Project - Foord Ka and Fiat Panda R-744 MA AC systems,, C. Malviciino et al., SAE paper p 2009-001-0967