Thermal management for the reduction of emissions and fuel consumption in trucks

Thermal management for the reduction of emissions and

fuel consumption in trucks

Heat up. Cool down.

Technical Press Day 2010


Contents

3

4

10

18

Introduction

Energy effi cient commercial vehicle engine cooling systems for Euro VI

Visco® fans and water pump drives to reduce fuel consumption in commercial vehicles

Waste heat recovery: the next challenge for truck engine development

Thermal management for the reduction of emissions and fuel consumption in trucks 3

Introduction

2009 was a diffi cult year for the commercial vehicle industry. Alongside the economic cycle and the fi nancial crisis, there were also structural causes for the markets collapsing. Since the beginning of 2010 the market has been recovering. In general we expect slight increases over the next few years but with major shifts between regions. Despite these cycles, the truck market remains important to Behr and Behr is important to the truck business too. A signifi cant factor in this are the new products outlined below.

Euro VI continues to be the No. 1 driving force in the truck business. In this context thermal management is becoming increasingly important, as Euro VI cannot be implemented effectively without exhaust gas recirculation, i.e. only with SCR. In practice this means that in the future, cooling systems will have to dissipate more heat, not less. For this, larger and more effi cient radiators and more powerful fans are needed, which in turn require new drives.

Another driver for the truck business is reducing fuel consumption either because of statutory regulations in the future or economic necessity. How can we meet these challenges?

Electronically controlled Visco® fan drives now dominate the European market. The control system, which responds to demand, can be transferred to other applications such as the water pump, thus reducing parasitic power losses.

Hybrid solutions will not play the same role in the classic truck applications as they do for light vehicles. Challenges arise here from the extra costs of such a system, the specifi c operating modes of the trucks, which for example make it diffi cult to effectively recover the braking energy, and the as yet insuffi cient power and storage density of current Li-ion batteries.

So another potential solution is to use the thermal energy remaining in the exhaust gas. For example, it can be converted directly into mechanical energy by means of a Rankine process

and made available to the powertrain. Initial research by our development engineers shows that this technology has considerable potential.

As you can see, the truck business remains exciting and technologically challenging, a challenge that we are happy to embrace, for which we have the right approach and are developing the right solutions. In the following pages we will be showing you some specifi c approaches for implementing thermal management, ensuring that trucks will continue to fulfi ll emissions and fuel consumption directives in the future.

We hope you’ll fi nd the following pages to be an interesting read.

4

Energy effi cient commercial vehicle engine cooling systems for Euro VI

From 2013, commercial vehicle engines in Europe must meet the Euro VI emissions limit values. Similarly strict regulations are already in force today in Japan, while standards in the US are even stricter. Other countries will follow suit in due course. As opposed to the emissions standards Euro III to V, it is unlikely that the much lower Euro VI limit values can be achieved without in creasing fuel consumption. In order to keep this additional fuel consumption to a minimum, Behr has made the commercial vehicle engine cooling system generally more energy effi cient, through the use of new and optimised components and by im proving the interaction between these components. This optimized cooling system is also a key to the implementation of further technologies to cut emissions and fuel consumption.

Eberhard Pantow,Manager, Advanced Engineering, Systems, Modules and Fans, Trucks

An optimized cooling system is also a key to the implementation of further technologies to cut emissions and fuel consumption.

Exhaust gas recirculation will be introduced across the board The predictions that Behr made at the 2008 Press Day about forthcoming exhaust gas recirculation technologies for Euro VI have become reality: for example, the overwhelming majority of applications will feature a combination of cooled exhaust gas recirculation with selective catalytic reduction, Fig. 1. With this combination, neither of the two systems needs to be operated at the limits of what is technically feasible, where, in the majority of cases, operating and system costs may be unacceptable. In addition, irrespective of the reduction in nitrogen oxides, Behr anticipates that all systems will feature a particulate fi lter. What is important for Behr is that, following the US and Japan, exhaust gas recirculation is now becoming a more or less across the board technology in Europe as well.

Figure 1 | Possible technologies to achieve Euro VI limit values

00All systems with Diesel particulate fi lter (DPF) NOx [g/kWh]

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Euro VDPF

SCR (>85%)

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5

Even though reducing engine emissions generally leads to increased fuel consumption, it was possible, at the Euro III to V standards, to compensate for this drawback through technical advances. In the case of Euro VI, this is no longer entirely feasible, which makes the contribution of the cooling system to vehicle fuel consumption all the more im-portant. The optimization steps taken by Behr to minimize this additional fuel consumption are described below.

Two development paths for Euro VIThe engine cooling system required with the combine cooled EGR and exhaust aftertreatment essentially consists of the charge air cooler, radiator, water pump, thermostat, and fan.

In principle, there are two different approaches that can be used to meet the Euro VI standard: with the fi rst, the emphasis is on the SCR process (SCR focus), and with the second it is on the cooled EGR (EGR focus).

SCR focus: tail-pipe NOx reduction In the case of the SCR focus, Fig. 2, an SCR system that is more complex in comparison to that Euro V is primarily responsible for NOx re duction. As a result, the EGR system can be relatively simple. It needs only to reduce the formation of NOx in the cylinder by lowering the combustion temperature suffi ciently so that the SCR system does not become too complex, and to ensure that the AdBlue® consumption does not increase too much. (AdBlue® is a urea solution that is used as a NOx reductant.)

EGR focus: NOx reduction inside the engine In the case of the EGR focus, Fig. 3, the emphasis is on reducing NOx inside the engine with the help of an effi ciently cooled EGR system, high pressure fuel injection and a turbocharger with VGT (variable geometry turbine) or a two-stage of charging arrangement. Systems such as this are already being used today to meet Euro V NOx limit values, or the American US ‘07 regulations

without SCR. Specifi cally, the EGR focus means that, owing to the substantial reduction in NOx inside the engine, a comparatively simple SCR system, similar to that used for Euro V, can also be used for Euro VI. In addition, with the EGR focus, only a very small quantity of AdBlue® is required.

With a cooling system employing indirect charge air cooling, as illustrated in Fig. 3, in which the

Figure 2 | Combined system for Euro VI with SCR focus

Figure 3 | Combined system for Euro VI with SCR focus

Cool

ing

air

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ing

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ad.

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DOC

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Exhaust

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Main cooling circuit

Main cooling circuit

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CAC: Charge air coolerRad.: Radiator EGRC: EGR cooler

LT Rad.: Low temperature radiator Rad.: Radiator

DOC: Diesel oxidation catalytic converter DPF: Diesel particulate fi lter SCR: SCR catalytic converter

HT EGRC: High temperature EGR coolerLT EGRC: Low temperature EGR coolerCAC: Charge air cooler

HC: Hydrolysis catalytic converterSC: Ammonia catalytic converter

DOC: Diesel oxidation cat. converter DPF: Diesel particulate fi lterSCR: SCR catalytic converter

AdBlue® tank

AdBlue® tank

Thermal management for the reduction of emissions and fuel consumption in trucks

CAC

charge air is cooled with coolant, the fuel consumption can be reduced by upto 2 percent compared to that with direct charge air cooling, thanks to the improved system dynamics and lower pressure loss. This improvement in system dynamics is based on the smaller air volume, which allows the boost pressure to build up more quickly. In addition, the thermal buffering effect of the indirect charge air cooling limits the charge air temperatures in the event of load changes. Both factors reduce the emissions that occur in dynamic operation, permitting more fuel effi cient engine tuning. The system can also be expanded relatively easily to include low temperature EGR cooling. The increased cooling of the recirculated exhaust gas further reduces the combustion temperature and NOx formation. Here too, as Behr has shown earlier, the reduction in emissions allows more fuel effi cient tuning of the engine. This also generates fuel savings of approximately 2 percent.

Stricter requirements for the cooling system What impact will the Euro VI standard and the approaches set out above, on the cooling system have (Fig. 4)?

Greater heat quantities to be dissipated:With most applications, there is an in-crease in the quantity of heat that the cooling system has to dissipate; the new EGR coolers have to discharge up to 100kW more via the cooling system to the ambient air. The larger quanti-ties of cooling air required for this are provided by new fans, which, in turn, necessitate new fan drive systems.

Higher temperatures and pressures in the cooling system:The radiators also have to withstand greater loads: the pressures in the cooling system are increased because of more powerful coolant pumps, higher temperatures and changes in the circuit architectures.

Higher charge air temperatures and boost pressures: The use of EGR means higher boost pressures of up to 4 bar (formerly up to ~3.5 bar) and temperatures of up to 240 °C (formerly up to ~200 °C), which result in an additional pressure load on the charge air coolers.

Additional requirements from utilizing exhaust gas heat:Owing to the future utilization of exhaust gas heat, additional heat

quantities are anticipated, particularly in the intermediate engine load operating range, which is relevant to fuel consumption. In many systems, these heat quantities must be discharged at a low temperature. This makes new low temperature radiators necessary or, alternatively, the effi ciency of existing radiators must be signifi cantly increased.

Avoidance of additional fuel consumption:The increases in air and coolant quantities require more powerful fans and coolant pumps (water pumps). The additional fuel consumption that normally accompanies an increase in output is avoided by demand controlled regulation of the fan and pump drives. The new E-Visco® drives from Behr are used for this purpose (see also “Visco® Fans and Water Pump Drives to Reduce Fuel Consumption in Commercial Vehicles”).

An effi cient and high performance cooling system The above requirements can be met only by an effi cient, high per-formance cooling system featuring a range of new and improved com-ponents. In the following, we describe how the new components from Behr will meet these stricter requirements in the limited packaging space available in a truck.

EGR coolers: optimized fl ow control through simulation Virtual product development was consistently used for the new EGR coolers for Euro VI. Using fl ow simu-lations, the winglets in the cooler tubes that generate turbulence were designed in such a way that the

6

Figure 4 | The Behr product portfolio has been consistently and comprehensively developed to meet theEuro VI requirements

New Behr charge air cooler Behr airfl ow improvement New generation of Behr fans

New Behr Visco® clutches

New Behr low temperature radiator New Behr radiator

New Behr EGR cooler

Additional low temperature cooling

Increasing boost pressures and temperatures

Increasing coolant pressures and temperatures

Up to 100 kW EGR heat


exhaust gases to be recirculated can be cooled by up to 50K more (Fig. 5) within the same package size. At the same time, the fouling characteristics were improved so that EGR cooler performance remains stable at a high level with, at the same time, only a slight increase in pressure loss.

The stable output level means that the engine developers can employ a smaller safety margin to ensure compliance with the emissions limit values; this gives them greater scope to tune the engine more effi ciently, in order to optimize fuel economy. Overall, fuel savings of up to 2 percent are possible.

Optimized radiators: heat transfer, strength and weight The new Euro VI radiators, Fig. 6, re-duce the package axial depth required by up to 12mm, while maintaining the same surface area specifi c perfor-mance. Hence, the distance between the radiator and fan can be increased, allowing an improved fl ow across the radiator and, thus, a further increase in performance. Alternatively, using the existing package space, the performance can be boosted by up to 4 percent. These improvements are possible thanks to higher heat transfer on both the air side and the coolant side. The simulation methods developed by Behr were also used for this development.

The heat transfer from the cooling air fi n and the radiator tubes was optimized with the help of a three-dimensional fl ow simulation (CFD).In order to meet the stricter require-ments in terms of radiator strength, the radiator’s component structures

were also optimized. The system boundary conditions were determined for the components based on load data from actual vehicle operating conditions. Then, using the fl ow simulation (CFD), load scenarios were simulated and these, in turn, provided the basis for strength calculations using the fi nite element method (FEA). Next, manufacturing processes were developed for these new structures. This resulted not only in an improve-

ment in strength but also in a re-duction in the specifi c weight of the radiators, so that the larger radiator matrix often required for Euro VI can now be implemented without any increase in weight.

Charge air coolers: reduced package space, weight and costs For the development of the new Euro VI charge air coolers, Fig. 7, the simulation methods described above

7

Figure 5 | The new Euro VI EGR coolers from Behr save package space and fuel

Figure 6 | The new Euro VI radiators from Behr save package space,fan power and weight

6050 100

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+ FEA tube header

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Coolant pressure [bar]

Core depth [mm]

Pressure drop [%]Basis: current production clean

CFD: Computational Fluid Dynamics (numerical fl ow simulation)

CFD: Computational Fluid Dynamics (numerical fl ow simulation)FEA: Finite Element Analysis radiators (numerical strength calculation)

Optimization of the tube fl ow with the help of CFD

Current production New development

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Current production

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were again employed. The new geo-metries developed in the process, in conjunction with refi nements to the manufacturing processes, mean that the CAC weight can be reduced further. Despite the larger cooler surface areas involved and much greater load capacity and service life, it was possible to keep the weight of the charge air coolers unchanged.

8

It was also possible to improve power density, by reducing the package depth from 64 mm to 50 mm, whilst maintaining identical performance. The charge air coolers thus allow a further reduction of 14mm in the package depth of the engine cooling module and, consequently, an improved throughfl ow of air. This means that the power requirements for the fan

can be reduced, whilst maintaining the same cooling capacity. In turn, the pressure drop in the charge air is greatly reduced if there is no change in the package depth of the charge air cooler. This reduces the compressor work required from the turbocharger, which helps reduce fuel consumption.

A new generation of fans Improvements in both the air mass fl ow rates and effi ciency are features of the new generation of fans, Fig. 8, along with a reduction in the specifi c noise level. This was possible through refi nements to the fan blades and fan hub. In the same way as with the radiators, the weight of the fan was reduced by structural optimization to the point where the larger fan diameters required for Euro VI can be achieved without any weight increase. A new fan concept, featuring special integration of the fan into the engine cooling module, ensures extremely stable operation with little separation of fl ow. This has the joint effect of enhancing effi ciency and reducing the noise level. It was also possible to reduce the axial package space, which allows good airfl ow through the radiator, even in tight installations.

Optimization of cooling air fl owHolistic optimization of the cooling air fl ow is a special focus of develop-ment activities at Behr, Fig. 9. Based on the comprehensive product range and a consistent system approach to development, it has been possible to achieve a whole series of aerodynamic improvements. Such improvements allow commercial vehicle manufac-turers to use the available cooling air effi ciently, and to signifi cantly reduces the impact of engine cooling

Figure 7 | The new Euro VI charge air coolers from Behr save package space, weight and reduce pressure drop

Figure 8 | The new Euro VI fans from Behr save package space, weight and power demand

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CFD: Computational Fluid Dynamics (numerical fl ow simulation)FEA: Finite Element Analysis (numerical strength calculation)

CFD: Computational Fluid Dynamics (numerical fl ow simulation)FEA: Finite Element Analysis (numerical strength calculation)

+ FEA tube header


9

on fuel consumption. For example, these infl uences may consist of greater power requirements for the fan, or a poorer vehicle cd value because of a larger radiator.

Engine cooling is part and parcel of vehicle aerodynamicsIn order to properly understand the infl uence of engine cooling on fuel consumption, it needs to be recognised that the former has a crucial infl uence on vehicle aerodynamics. Depending on the vehicle, cooling can account for between 5 to 10 percent of the vehicle air resistance. If we consider, for example in the case of long distance haulage on a highway, that approximately 40 percent of fuel consumption is a result of air resistance, between 2 and 4 percent of this fuel consumption is caused by the engine cooling. With increasing heat loads, such as we will see in future systems aimed at reducing emissions and fuel consumption, there is the risk that the fan, which to date has played a negligible role in average fuel consumption, must be

switched on more often, thus leading to increased fuel consumption.

We can compensate for this effect almost entirely, thanks to the new engine cooling systems with opti-mized components and larger surface areas. The only negative effect from the larger radiators is slightly poorer vehicle aerodynamics. This is where aerodynamic optimization of the fl ow of cooling air comes in. By more effi cient utilization of the airstream, in conjunction with a special installa-tion of the fan, which improves the fan’s inlet and outlet fl ow and prevents recirculation, the fuel consumption arising from engine cooling can actually be reduced to below its former level. Summary The EGR and SCR technologies aimed at further reducing emissions and fuel consumption place heavy demands on the engine cooling system. This affects the system’s effi ciency and the requirements in terms of load capacity and reliability, in equal measure.

Figure 9 | Aerodynamic optimization allows improved cooling performance without impacting fuel consumption

At Behr, our development work is geared to designing new technologies and products for Euro VI vehicles. Some of the new products have already been transferred from Advanced Engineering to Series Development, to ensure that fully mature and reliable products are available by the time the Euro VI standard is introduced in 2013. These products will meet the stricter demands for engine cooling, without the increase in fuel con-sumption that might otherwise be expected, and without increasing the weight of the components.

With the new components, fuel consumption in a Euro VI vehicle will be up to 3 percent lower than a vehicle fi tted with an existing cooling system. In addition, changes to the architecture of the engine cooling system in the form of indirect charge air cooling and low tempe-rature EGR cooling will allow fuel consumption to be reduced even further.

Proportion of fuel consumption because of cooling system

Euro Vheat rejection

Enlarged cooling system and new Behr components

As above, plusaerodynamic optimization

Present cooling system

Futureheat rejection

Numerical example, typical commercial vehicle intercity trip at 25 °C

0 2 4 6

cd value Fan


10

Visco® fans and water pump drives to reduce fuel consumption in commercial vehicles

Most of the commercial vehicles in use today in Europe are fi tted with Behr Visco® fans, providing the vehicles with on-demand fuel-effi cient engine cooling. One of today’s most pressing requirements is to make fuel savings, whilst the other is to reduce emissions. In order to meet the extremely strict requirements of the Euro VI emissions standard, catalytic reduction of NOx (SCR pro-cess) needs to be supplemented with cooled exhaust gas recirculation (EGR). This increases the amount of heat to be dissipated, with the result that between 15 and 20 percent more cooling air is required. To meet this requirement, Behr has developed a new generation of electronically controlled Visco® fan drives and has optimized the fans. Series production of the new E-Visco® drives and fans is scheduled to begin in 2011/2012.

The E-Visco® principle, which pro -vides fuel savings of 1 percent when used instead of on/off drives, is now being extended to water pumps. Water pumps worldwide are almost exclusively equipped with direct, unregulated drives. With an E-Visco® drive, water circulation can be regulated as required, yielding an additional fuel saving of 1 percent. Prototypes of this type of water pump drive are now undergoing trials, and series production is also planned for 2011.

Modern fan drives need to be variable Ultimately, the heat from a commercial vehicle’s engine compartment can be transferred only to the cooling air. When the dynamic pressure re-sulting from the airstream is no longer

The Euro VI emission standard increases the amount of heat to be dissipated, with the result that between 15 and 20 percent morecooling air is required.

suffi cient to transport the air through the heat exchangers and engine compartment in order to dissipate the heat, the fans supply the additional pressure required. Since a fan drive output of up to 40 kW is needed to meet the maximum cooling air require-ment, this power needs to be supplied by the engine’s crankshaft. With such a high drive output, a drive that uses electric motors, such as in a passenger car, is insuffi cient. However, good adjustability of the speed, something that is easily achieved with electric motors, also needs to be ensured for the fan drives so that only the exact quantity of air required is conveyed. Any excessive delivery of air results in unnecessarily high fuel consumption and noise emissions.

The Visco® principle: power transmission through shear frictionThe most advanced variable fan drive for commercial vehicles is the electronically controlled Visco® drive, abbreviated to E-Visco® drive, Fig. 1. With the Visco® principle, which Behr has been using for decades, the drive energy is transferred from the crankshaft through shear friction of a specifi c fl uid on the driven side of the clutch connected to the fan.

Structure of an E-Visco® drive Fig. 2 shows a cross-section of an E-Visco® drive. The drive side (primary side), consisting of a rigidly connected fl anged shaft and a drive disk, is powered by the crankshaft or by an interstage belt drive at the primary speed. The secondary side, a housing enclosing the drive disk, is supported on the fl anged shaft by an low friction bearing. The housing and the fan attached to it rotate at the secondary

Matthias Banzhaf, Head of Fan Drives and Visco® Applications


Figure 3 | Operation of an E-Visco® drive

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speed or at the speed of the fan. The solenoid, which is also supported on the fl anged shaft by bearing, remains at rest, facilitating the electrical connection between the drive and the engine. Continuously variable speed control The speed control is shown in Fig. 3. In state ➊, the opening (port) in the annular reservoir chamber on the drive disk, which is fi lled with silicon fl uid, is kept tightly closed by a valve lever. Despite a particular drive speed, no torque is transferred to the secondary side. The clutch is disconnected or idling at a low speed solely as a result of the bearing friction.

In state ➋, with the port temporarily open, there is silicon fl uid in the working chamber, conveyed there by the centrifugal force that is present. Torque transmission takes place in the extremely narrow, profi led working chamber between the drive disk and the housing, through the shear friction of the oil. The speed difference that

always occurs between the drive disk and the housing as a result of the slip is used to generate a static pressure with the help of a pump element on the outer circumference of the drive

disk, which pumps the oil back into the reservoir chamber through a return port in the disk – against the centrifugal force. According to how much the valve lever is opened, the

Figure 1 | Commercial vehicle fan with E-Visco® drive Figure 2 | Cross section of an E-Visco® drive

Rotation with drive = primary speedFlanged shaft with drive disk

ndrive

ndrive

nfan

nfan

Rotation with fan = secondary speedHousing with fan

2,400

00 20 40 60 80 100

No rotationSolenoid

PWM [%]

n [m

in–1]

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working chamber can be fi lled to any level, providing fan speeds between idle ➊ and full engagement ➌. In ➌, the fan almost reaches the drive speed as present, apart from a small remaining slip.

The degree of opening of the valve lever is controlled by a pulsing magne-tic fi eld generated by a solenoid. The valve lever closes when the magnetic fi eld is “on,” and opens when it is “off.” The degree of opening depends

on the on-off time proportions. A continuous magnetic fi eld closes the valve lever fully, so that fl uid is drained off, and the clutch switches to idle speed. If the magnetic fi eld is constantly off, the valve lever can be opened fully, more fl uid is introduced than is drained off, and the clutch becomes fully engaged. This is also the failsafe device, ensuring that the fan is completely engaged and there is full cooling capacity even if the electricity supply to the solenoid is interrupted.

The engine control system includes a software program that requests a particular fan speed based on parameters such as coolant tempe-rature, charge air temperature, cabin air conditioning, or retarder operation. The actual fan speed is recorded by a sensor integrated into the solenoid and the result reported to the engine control system, thus closing the control loop. Thanks to the E-Visco® control, the required speed is achieved

Figure 5 | Required fan operating conditions and those possible with a fan drive

12

Figure 4 | Load spectrum for a long haul truck

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quickly and smoothly, and is then maintained at a constant level. All of these are important criteria for a precise regulation system.

What is meant by on-demand cooling?To answer this question, we fi rst need to look at the different operating modes, i.e. the load spectrum, for the engine in a long-haul truck, Fig. 4. The size of the circles in this illustration shows the frequency at which a long-haul truck is driven at a particular speed and with a particular engine load. Apart from idling speed at 600 rpm, midrange engine loads at 1,400 and 1,500 rpm predominate, a typical scenario for rolling operation on the highway at a speed of roughly 80km/h.

In each of the three diagrams in Fig. 5 (one for each fan drive mode), the fan speeds required for all opera-ting conditions have been entered. These have been derived from the characteristics map for the engine operating conditions. Taken together, these points yield the gray areas between the diagonals and x-axes in the diagrams. Each diagonal re-presents the maximum possible fan speeds, which can never exceed the drive speeds. Fan operating points are also required along these diagonals and along with the x-axes for the operating points that require only very low fan speeds. If we now compare the areas of the required fan operating points with the operating points that can be achieved by the fan drives, one thing becomes clear: an unregulated rigid fan directly connected to the speed of the engine almost invariably operates at much too high a speed.

Even with a fan equipped with • an on/off drive, there is still no optimum cooling process. Only continuously variable speed • control from an E-Visco® clutch allows each fan operating point to be properly set; this minimizes the drive output. Compared with a rigid fan, fuel • consumption is reduced by roughly 4 percent, and by approximately 1 percent compared with a fan with an on/off drive.

Needless to say, the fan’s power connection will also depend on the size and capacity of the heat ex changers (in proportion to the quantity of heat to be dissipated), and on the cooling air throttling in the engine compartment. In situations that facilitate cooling (a high installed cooling capacity and little air throttling), the cooling produced by the airstream is often

suffi cient without any assistance from the fan.

However, circumstances such as these are most likely to be found in US heavy-duty trucks, in which the typical cab-behind-engine vehicles often feature large radiators with large frontal areas. In addition, since the engine compartment in these trucks is less tightly packed than it is in European trucks, there is also less throttling of the cooling air. On/off clutches predominate in these trucks because the fans only seldom need to be powered up. Nevertheless, since the trend in vehicle and engine development in the US, too, is towards more sloping hoods, smaller radiator frontal areas, and more tightly packed engine compartments, an increasing number of US trucks are being fi tted with continuously variable E-Visco® drives. In Europe, this kind of drive has been

Figure 6 | Comparison of control using on/off fan operation and an E-Visco® drive

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Coolant temperature

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the dominant technology for almost ten years, because there was always little available space under European cabs. In other parts of the world, several other drive techniques are employed, with even rigid fans still in use. E-Visco® drives are seldom available, but with each new piece of emissions legislation and the ever increasing obligation to make fuel savings, this kind of drive will become increasingly important in the future.

Precise cooling with E-Visco® drives Fig. 6 contrasts oscillating on/off cooling with precise cooling using an E-Visco® drive. With on/off cooling, the drive remains switched off until the coolant temperature exceeds the permissible threshold. The fan must then be fully switched on, which, however, leads to “overcooling”: the fan switches off again after a short time and a phase with too little cooling follows. Despite the constant

speed, the temperatures of the media that need to be cooled (in particular the coolant and the charge air), and the loads placed on the heat exchangers and fan drive itself, are subject to extreme fl uctuations. In the case of on-demand cooling (Fig. 6 below), such fl uctuations are eliminated and the strain on the heat exchangers and belt drive is also reduced. The E-Visco® drive is also maintenance-free, whereas an on/off drive requires regular maintenance owing to the frequent switching impulses.

As a simulation calculation has shown, when used in the long distance haulage application mentioned above, the E-Visco® drive requires a much lower drive output than an on/off drive in every load situation, with the exception of the light engine load range (up to around 25 percent). It is true that the on/off drive does not need to be powered up in light-load operation. However, as soon as oscillating operation is required, a much higher mid-range drive power is needed. This results in lower fuel consumption with E-Visco®, as illustrated in Fig. 7.

E-Visco® is only slightly less effi cient with a light engine load, since, unlike the on/off drive, it always operates at a low idling speed, even when the drive is switched off. Taken together across the load spectrum for long-distance haulage, the E-Visco® drive delivers a 0.7 percent improvement in terms of fuel consumption.

The Euro VI challengeIt is very likely that the much lower Euro VI exhaust emissions limits in com parison with Euro V can be

14

Figure 7 | E-Visco® fuel consumption benefi ts compared with on/off drive in fans

Figure 8 | Development trends to achieve increased fl ow of cooling air

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Fuel savings with E-Visco® fanSimulation at 1,500 rpm engine speedin comparison with on/off drive

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Engi

ne lo

ad [

%]

Engine speed [rpm]

Fan output

Fan effi ciency

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-0.7%

Transmission

ratio

Crank

shaft

1:1

High sp

eed

• High performance fan• Preferably on crankshaft

• High effi ciency fan• Preferably above crankshaft


achieved only if SCR technology is used in combination with cooled exhaust gas recirculation (EGR). The resulting increase in the amount of heat to be dissipated requires an increase in cooling air quantities of between 15 and 20 percent. Since, as already mentioned, there is no space for larger radiators or a less restricted airfl ow, there are two ways of achieving the greater air quantity:

By increasing fan effi ciency 1. and fan speed By boosting the air output 2. (dotted line in) Fig. 8.

Method 1 largely retains the current fan dimensions in terms of axial package depth and diameter

15

Figure 9 | New E-Visco® fan drive developments

Figure 10 | Cold start improvement (CSI) Figure 11 | Improvement in slip power capability

Torq

ue [

Nm]

Spee

d [r

pm]

Spee

d [r

pm]

0ER100 ER130 ER175 NF ER ERS160 ERS250

20406080

100120140160180200220240260280300320340360380400

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ERS250

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pm]

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0 500 1,000 1,500 2,000 2,500 3,000

Operating range

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(max. 750 mm), whilst optimizing fan effi ciency by reducing the levels of fl ow friction and fl ow separation. These fans are then powered with a

larger transmission ratio than before. A transmission ratio of up to 1:1.5 may be needed to achieve the air quantities required (green area in

Fig. 8). Accordingly, the enhanced cooling performance is largely the result of the higher fan speed.

With Method 2, on the other hand, the blade depths and diameters are increased (up to 813 mm), thus boosting the air output of the new fans. These fans can deliver the required air quantity at lower trans-mission ratios, or even at a ratio of 1:1 when used on the crankshaft (yellow area in Fig. 8).

New products are being developed at Behr for both areas, Fig. 9. Drives with transmittable torques of up to 200 Nm are required for the fans with optimized effi ciency and higher

transmission ratios. In this case, the current ER-Visco® clutch series, with maximum torques of 100, 130 and 175 Nm, will be replaced by a successor generation whose upper limit will be around 200 Nm. Extremely robust drives with high torque are required for the fans with optimized air output and low transmission ratios through to use on the crankshaft. To meet these requirements, the current ERS series in the 250 Nm size will be refi ned and complemented by a new high-end product with a torque capacity of up to 350 Nm.

In addition to the increased • torque, all new developments will feature a number of functional improvements:

Higher dynamics for switching• on and off behaviour, i.e. quicker adjustment of the actual fan speed to the desired speed. Improved cold start behaviour: • owing to their internal hydraulics, E-Visco® drives have up to now tended to run for a few minutes at full power after a cold start, accompanied by a high noise level, even though there is no need for cooling and there fore no need for a high fan speed. This behaviour will no longer occur with any of the new developments, Fig.10.An extended operating range, • because the physically induced generation of heat (slip power), which occurs at high drive speeds and when the clutch is partially engaged, can be dissipated more effi ciently by enhanced integral cooling. Thanks to this high slip power capability, there are no restrictions on fan operation, at least up to the nominal speed of the engine, even if cooling air quantities are increased by between 15 and 20 percent as mentioned above, Fig.11.

The fi rst new developments for these fan drives will go into production in 2011 and 2012.

Visco® fl exibility also for water pumps? The question arises whether the benefi ts of the E-Visco® drive are applicable only to fans: why not to water pumps as well? There are many indications that the evolution of pumps will follow that of the fans

16 Technical Press Day 2010

Figure 12 | Water pump with fi xed drive compared with E-Visco® drive

Belt pulley not shown Engine speed [rpm]

Water pump capacityFull load

0900 1,100 1,300 1,500 1,700 1,900 2,100

2

3

4

5

6

7

1

Pum

p ca

paci

ty [

kW]

Conventional pump Visco® pump

with a certain time lag, i.e. from rigid to fl exible and from unregulated to on-demand. This would mean that the maximum water quantity would not need to be constantly pumped, since this is required only at full load and maximum torque, i.e. in the range around 1,500 rpm. At higher engine speeds, the output can be signifi cantly reduced, as illustrated by the red curve in Fig. 12. Of course, the output can also be reduced at partial load.

The driving power of a water pump, at up to 6 kW, is much lower than that of fans (up to 40 kW and more). However, since a major leap forward has been made here with an E-Visco® drive from a rigid drive to a continuously variable drive, the Visco® water pump also provides extremely lucrative potential fuel savings of approximately 1 percent. At the engine speeds most frequently used, around 1,500 rpm, simulation calculations based on the long-haul truck mentioned above show that, in turn, the lower the engine load, the greater the fuel savings. Taken cumulatively across the full load spectrum, the result is a fuel saving of 1.3 percent, Fig. 13, which has been confi rmed in road trials.

This new development will also go into production for the fi rst time in 2011.

SummaryE-Visco® is the leading technology • for commercial vehicle fan drives in Europe.Not many E-Visco® fans are yet • in use in the US, but they are

Figure 13 | Fuel savings with E-Visco® drive compared with rigid drive in water pumps

17

500

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Engine loadFuel savings with E-Visco®water pumpSimulation at 1,500 rpm engine speedin comparison with fi xed pump drive

75%

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Engi

ne lo

ad [

%]

Engine speed [rpm]

0.1%

0.4%

0.9%

4.0%


attracting considerable interest thanks to - benefi ts in terms of fuel consumption,- the lower demands placed on heat exchangers and the belt drive,- and on the fan drive itself.In countries such as China, India, • and Brazil, there are still only a small number of E-Visco® fans in use. These markets predominantly feature rigid fans, on/off or bi-metal Visco® drives. Here too, however, the trend shifts further towards E-Visco® each time emissions standards are tightened. Between 15 percent and 20 percent • more cooling air will be required to meet the Euro VI standard. In order to comply with the new

limit values, we will see designs with powerful fans and a low drive ratio, and high-effi ciency fans with a high drive ratio. E-Visco® drives will be either refi ned or developed from scratch for both set-ups. Common features of all developments will include improved cold start behaviour, enhanced slip power capability, and better dynamics.The E-Visco® drive for water • pumps will also be available for the fi rst time for Euro VI. For long-haul transport, in which fuel consumption is so crucial, fuel savings of around 1 percent will be possible compared with conventional pumps, thanks to the continuously variable coolant fl ow control system.

18

Waste Heat Recovery: The Next Challenge for Truck Engine Development

New legislation will drive the development of waste heat recovery systemsWhen the Euro 6 legislation comes into force in 2013 the commercial vehicle industry will have experienced over 20 years of successful emissions reduction (Fig. 1). Whilst further reductions may be theoretically possible, in practice they are unlikely, as is further emissions legislation in the USA, Europe or Japan. For these regions, driven by concerns about global warming, the need to protect limited fossil fuel resources and/or simply because of the need to reduce vehicle operating costs, the reduction of vehicle fuel con-sumption, consequently CO2 emissions, will become the focus.

It is certain that there will be legis lation to limit the CO2 output of commercial vehicles in the future. In Japan the legislation is

already defi ned and will come into force in 2015: it will mean a 12% reduction in vehicle fuel consumption relative to 2002 levels. In the USA the opinions of the legislative body, the EPA, are already well formed and legislation is likely in the timeframe 2014 to 2017, probably starting with an incentive programme. In Europe the discussions are just beginning.

This legislation will set levels for complete vehicle operational fuel consumption. Therefore, the engine, the vehicle and its operation must be improved. In Japan the legislation measures the engine fuel consumption and simulates the vehicle via a “hardware in the loop” procedure, in order to give an overall value for the vehicle fuel consumption. In the USA it is likely that targets will be set and measured separately for the engine CO2 output, which will be

There will be legislation to limit CO2 emissions in the future. It will therefore be necessary to improve the engine, the vehicle and itsoperation.

Simon Edwards,Head of Advanced Engineering, Engine Cooling, Trucks

Figure 1 | Following the reduction of pollutant emissions up to Euro VI,the main focus now is on reducing CO2 emissions

EGR

1990 1995 2000 2005 2010 2015 2020

Emis

sion

s

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sum

ptio

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?

SCR ?

LT-EGR

2-stage boosting

EGR, SCR & DPF

Euro IEuro II

Euro III

Euro VI

Euro IV

Euro V


19

in g/bhp.h (equivalent to g/kWh) over the SET (which is the European Steady State Test Cycle) or FTP test cycle, and the vehicle CO2 output during operation, which will be set in g/ton.mile. In Europe the levels and test procedures still have to be defi ned.

The relative contribution to the CO2 output of the engine, the vehicle and its operation, thus the possible improvement with each of these three measures, varies depending upon the type of commercial vehicle. For long haul trucks the split engine:vehicle:operation is approximately 40:30:30, and for utility vehicles around 50:30:20. Improved vehicle aerodynamics or operational logistics will provide some easily reached benefi ts. How-ever, even with the application of hybridization to some vehicle types, such as buses or intra-urban delivery vehicles, improvements to engine fuel effi ciency must be made.

Therefore, it is important to look again at the losses in the internal

combustion engine. The energy fl ows for a heavy duty engine running at the B50 engine operating point (this is an intermediate speed and load con dition) have been considered.

In Fig. 2 the energy fl ows for the engine are shown. 39.8% of the supplied fuel energy is converted into mechanical power. Without signifi cant static pressure assistance, the fan power requirement is 2.5 kW, which is 0.7% of the fuel energy. The complete effi ciency of the pro-cess is then 39.1%.

We see that about 30% of the fuel energy is lost to the exhaust, either directly (18.1%) or through cooling the EGR (11.5%). If it were possible to recover some of this lost energy and turn it into useful work, then there is a potentially signifi cant fuel effi ciency improvement. Since this lost energy is “heat”, the problem is a thermal management issue: here Behr has world leading technology to apply.

Figure 2 | Energy fl ows from an internal combustion engine

Figure 3 | The Rankine cycle

Fuel = 100%

39.8%

0.7%

3.4%

11.5%

11.5%

Netoutput39.1%

Max. fan power

Radiation and other losses

Heavy duty engine with EGR at the B50 engine operating point

EGR

Superheater

Expander

50100

200

300

400

Torque

Working fl uid

Pump

Exhaust gas

Evaporator

Condenser

Pre-heater

4 1’

1

1 1’ 2 3 4 5

5

3 2

Temperature [°C] Pressure [bar] Working fluid: water; heat source: EGR

Cooling

Exhaustgas

38.7%

18.1%

27.2%


The application of a Rankine Cycle system requires complete system understandingIn truck engines with EGR, the exhaust gas temperatures are up to 600°C before the turbocharger and up to 450°C thereafter. This waste heat does still contain a signifi cant potential for work, which could be realised through a secondary heat to power process, such as a Bottoming cycle. In order to choose the appropriate cycle, it is necessary to consider the boundary conditions resulting from the vehicle operation:

there is limited packaging space • and there is a limit to the allowable system weightthe cycle must be suitable for • transient operation the requirement for additional vehicle cooling must be low.

It has been found that the Rankine cycle (named after the Scottish physicist William John Macquorn Rankine), as shown in Fig. 3, is an appropriate cycle. In this closed steam power cycle, a pressurised working fl uid is heated using an

external heat source, it evaporates and is super heated before being expanded across a machine to pro-duce usable work (in this case mechanical although it could be converted to electrical energy). The Rankine cycle is already established in the power generation industry and in highly effi cient gas and steam power stations where the cycle can be repeatedly applied, it can reach an overall electrical effi ciency of up to 60%. Furthermore, some truck engine and vehicle demonstrators have been built in the past, proving the potential of the cycle for commercial vehicle application.

For a given heat source, the usable power derived from a Rankine cycle is determined primarily from the pressure ratio across the expander. This, in turn, depends directly upon the pressures losses in the system and indirectly upon the temperatures in the heat source and sink. In order to generate suffi cient power from the Rankine cycle, such that the engine fuel consumption can be reduced, large amounts of heat must be transferred. Consequently, the potential to cool the cycle within the engine cooling circuit is important. Since this cooling power requirement must compete with those for EGR and charge air cooling, effects upon the fan power requirement and, via the inlet manifold temperature, on the engine combustion are to be expected. Therefore, concepts using different heat sources and sinks have been investigated. In particular four concepts were studied, as shown in Fig. 4.

For a steam process with water as the working fl uid, a high temperature

20

Figure 4 | Four Rankine system concepts were studied

Figure 5 | BISS model for an engine with a Rankine cycle for waste heat recovery

1 42 3

Tail-pipe exhaust Heat source

Heat sink

Concept

Low temperature circuit High temperature circuit

Tail-pipe exhaust and EGR

EGR

EGR evaporator

Expansionmachine

Tail-pipe exhaust evaporator WHR valves

Inlet manifold

WHR condenser Engine cooling module including fan


heat source or sources are needed. For an EGR engine there are the following possibilities.

The full exhaust fl ow after the 1. turbocharger and aftertreatment(this is subsequently called tail-pipe exhaust).On the engine mentioned above, above 25% load, the tailpipe exhaust temperatures lie between 250 and 380°C. In order to determine the usable work, it is necessary to remember that a Rankine evaporator increases the exhaust back pressure, which can lead to a fuel consumption increase of around 1%.The re-circulated exhaust gas2. With high pressure EGR the temperatures are higher than in the tail-pipe: they lie between 350 and 600°C. Whether an advantage in the usable power can be realized from these temperature differences depends upon the maximum allowable pressure in the system. For example, with an allowable pressure up to 40 bar, the boiling temperature is 250°C. Using both heat sources it is possible to reach this temperature or even higher (super heating) over much of the engine operating map.

The pressure ratio and, therefore, the back pressure of the expansion machine is determined, via the condensation pressure, by the heat sink. There are many possible heat sinks in the vehicle. However, only those heat sources that can use the existing vehicle infrastructure should be considered, such that synergies can be realized and the Rankine cycle system costs and additional

21

complexity kept under control. In effect there are two possibilities:

Condensation in the main engine 1. cooling circuit where, condensation temperatures of around 100°C are achievable.Condensation in a low temperature 2. cooling circuit (e.g. for indirect charge air cooling). Here conden-sation temperatures of 70°C are achievable (if the condenser is installed in series after the charge air cooler).

The application of a Rankine Cycle to a long haul truck could deliver fuel savings of 5% or moreA numerical simulation was under-taken using BISS (Behr Integrated Simulation System) in order to analyse the effects of the Rankine cycle on the engine operation and on the cooling system (Fig. 5). In addition to the heat balance and mass fl ow rates in the engine circuits, the simulation represented the cooling system in detail and allowed the easy integration of the various

Rankine cycle concepts. An ambient temperature of 25°C and a driving speed of 20 km/h were assumed. The results of this analysis are shown in Fig. 6.

The objective of this analysis was not to achieve a power increase, rather a fuel consumption reduction for the powertrain. Consequently, the required engine power, at each operating point, was reduced by the power derived from the Rankine cycle. As such, less fuel could be injected but the same net power achieved. Therefore, the heat rejected by the engine, the charge air mass fl ow rates and the charge air pressures could be reduced for a given net power: each of these factors reduced the load on the engine cooling system.

Under these conditions Concept 1 shows relatively little advantage compared to the baseline. Part of the power derived from the Rankine cycle is absorbed by the increased

Figure 6 | Four Rankine system concepts were studied

1 42 3

Tail-pipe exhaust Heat source

Heat sink

Basis: Euro V EGR focus engine, with 2 g/kWh NOx engine-out emissions

@B50Fuel

consumption

- 2.2%

- 3.9%

- 4.8%

- 6.9%

Charge air temperature

Back pressureFan output

Concept 2

Concept 3

Concept 4

Concept

Low temperature circuit High temperature circuit

Tail-pipe exhaust and EGR

EGR

Concept 1


fan power requirement. In addition, the engine effi ciency reduces because of the higher inlet manifold tempera-tures and the higher exhaust back pressure. Overall, a fuel consumption improvement of just 2.2% is achieved with Concept 1, at B50.

Concept 2 is clearly an improvement. In addition to the energy recovered via the Rankine cycle there is a reduction in the fan power requirement. How-ever, the engine effi ciency is reduced because of the higher inlet manifold temperatures. Since the evaporator replaces the EGR cooler, the higher exhaust back pressures in Concept 1 are not seen and it is likely that the system costs will be lower. Overall, at the B50 operating point a fuel consumption reduction of 3.9% is predicted.

Concept 3 has a better effectiveness but the same system complexity as Concept 2. In addition to the power recovered via the Rankine cycle, the fan power requirement is reduced and there is no signifi cant effect upon the inlet manifold temperatures compared to the baseline engine. As such a possible fuel consumption reduction of 4.8% is calculated.

With Concept 4 the largest fuel consumption improvement is possible. Even when the effects of the in-creased fan power requirement and the exhaust back pressure are taken into account, an effi ciency increase of 6.9% is possible.

This is refl ected in the energy fl ow diagram shown in Fig. 7. When compared to that shown in Fig. 1 we see that the fuel energy input for constant power has reduced to 93.1%

and that the energy lost in the exhaust is reduced to only 6.2%. However, it must be remembered that this system concept is the most complex and that the load on the vehicle cooling system has increased, from 38.7% of the fuel energy input to 43.6%.

This increase in system complexity is shown in a schematic simplifi ed layout of the likely Rankine and cooling system for a Concept 4 solution in Fig. 8. What is important to note here is that such a system would require at least two new heat exchangers on the engine, the tail-pipe evaporator and the condenser, plus the replacement of the normal EGR cooler with an EGR evaporator.

New components are being developed by Behr, but the industry as a whole needs to rise up to the challenge of waste heat recoveryFor the develoment of these new components Behr has invested in new simulation and test bench methods. Functional models have been running successfully on engine

tests, delivering fi rst test results. The components are shown in Fig. 9 and are being development with an earliest possible SOP in 2015.

The EGR and tail-pipe evaporator are based upon our latest EGR cooler technology. Despite the high temperatures and pressures signifi cantly greater than in existing truck heat exchangers, these new products package into the space of today’s EGR cooler or into space available in the exhaust silencer alongside the aftertreatment.

The condenser, as shown here, uses technology similar to our stack plate oil cooler and, again, is not much bigger than a passenger car automatic transmission oil cooler.

However, despite the very promising and signifi cant developments over the last two years challenges remain, not just for the heat exchangers but for the complete Rankine system and the commercial vehicle industry as a whole. Two challenges are paramount and need to be addressed urgently:

22

Figure 7 | Energy fl ows from an engine with a Rankine system

Fuel = 93.1%

36.7%

40.1%

1.0%

3.2%

6.2%

10.6%10.6%3.4%

17.8%

Netoutput39.1%

Max. fan output

Cooling

Exhaust gas

43.6%25.8%

Radiation and other losses

Concept 4 at the B50 engine operating point

EGRWHR


To date there is no consensus as 1. to which working fl uid is best for a truck Rankine system. Fluids under investigation include water, as described here, alcohols, such as ethanol, and other organic fl uids. Each fl uid has advantages and disadvantages and the choice of working fl uid has signifi cant impact on the system layout, the vehicle cooling system and the potential risks inherent when in vehicle operation or maintenance. Currently Behr has is working on solutions for each of the fl uids under consideration, but these parallel development paths cannot be maintained through to series production. It is incumbent upon the industry as a whole and the OEMs in particular to work together to defi ne a single solution, to optimize the system, components and operation based upon this solution and to drive the often

Figure 8 | Circuits in an engine with a Rankine system

23

Figure 9 | Behr components for a Rankine system

is turbine or piston technology coupled mechanically or elec-trically to the driveline, will have a signifi cant effect on the overall system performance and its applicability to long haul truck applications. Here there are opportunities for new suppliers need to enter the market and drive the technology development.

In the end, the rising to the challenge of using exhaust heat to recover useful work will benefi t the industry, vehicle operators and society as a whole. Within just two years Behr has made great advances in under-standing the system requirements Within a further two years we expect to see such systems running in demonstrator vehicles, naturally fi tted with Behr components.

long homologation process in order to have a Rankine system ready for the fuel economy legislative timescales.The development of the other 2. Rankine system components is lagging that of the heat exchangers. In particular the expansion machine, whether it

Exhaust gas aftertreatmentCondenser

Condenser Evaporator

Evaporator

Superheater

E

E

CAC

HT

radi

ator

LT r

adia

tor

Air

Evaporator

Evaporator

Superheater

Charge air

Exhaust gas

Exhaust gas

HT circuit

HT circuit

LT circuit

WHR working fl uid

WHR working fl uid


EGR evaporator

Behr GmbH & Co. KGMauserstrasse 370469 StuttgartGermanyPhone: + 49 711 896-0Fax: + 49 711 896-4000www.behrgroup.com

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Thermal management for the reduction of emissions and fuel consumption in trucks

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