Energy and Thermal Management, Air-Conditioning, and Waste Heat Utilization

Increasing the efficiency of electric vehicles is a development focus in the automotive industry in order to reach the range targets set by customer requirements. Thermal management can have a positive effect on the system efficiency of electric vehicles. In this contribution, a simulation model of the drivetrain and cooling system of an electric vehicle has been build up. The aim is to investigate the influence of the cooling system control and resulting component temperatures on the drivetrain efficiency. Thus, energetically optimal target temperatures for inverter and motor can be identified and implemented in the cooling system control.

This approach goes beyond the state of the art control strategy of keeping the temperatures under the component protection threshold. Related research suggests that the component efficiency of inverter and motor can be increased by reducing their operation temperature. The simulation results in this article show that choosing target temperatures for inverter and motor below the components’ safety limit can have a small, positive impact on the system efficiency of the electric vehicle.

As the model is yet to be validated, these results implicate that the optimal component target temperatures for inverter and motor regarding system efficiency are below the protective limit. As a next step, the model will be validated with comprehensive component and vehicle measurement data in order to give a quantitative statement on the possible benefits of optimized thermal management control.

Reducing the power demand and thus increasing the cruising range of electric vehicles is a significant challenge currently faced in the automotive industry. It is well-known that a part by no means insignificant of the energy available is used for air conditioning in vehicle interiors and batteries as well as for ensuring temperature control for the other electrical components. For this reason, electric vehicle development today is focusing very much on developing efficient and innovative thermal management systems.

Regenerative cycles, the most well-known of which is the Stirling cycle, may be used for prime movers as well as for heat pump or refrigeration applications. Furthermore, it was demonstrated experimentally in a recent research project that it is possible to devise a machine that may be toggled between different cycles and operating modes in a demand-dependent way, and to achieve a satisfactory performance in any of these. The experimental machine realized within this project may be operated as a Stirling engine, as a thermally actuated Vuilleumier cycle heat pump or in a so-called hybrid mode featuring both a mechanical power production and a heat pump effect. The original objective was to develop a convertible domestic energy supply system that may be adjusted to varying heat and power demands, but particularly the hybrid cycle also appears to be well-suited for auxiliary heating cooling and power generation in vehicular applications, possibly even without the option of switching to different modes. The thermodynamic operating principle of this cycle, potential design options as well as performance predictions are presented and discussed.

The limited nature and precariousness of non-renewable energy source supply has prompted an expanding and continuing examination request of option and regenerative fills and furthermore Increased interest for very eco-friendly impetus frameworks drives the engine improvement network to create trend setting innovations permitting enhancing the general warm effectiveness while keeping up low discharge levels. Notwithstanding enhancing the warm efficiencies of the inner ignition engine itself the advancements of fills that permit enhanced burning and in addition bring down the discharges impression has increased as of late.

This examination goes for the impacts of various fuel composes with altogether contrasting fuel properties on a cutting edge light-obligation HSDI diesel engine. The fuel selection also contains one pure biodiesel (CSOME – Cotton seed oil Methyl Ester). This study will be conducted in full load operating points at different speeds using a state of the art HSDI diesel engine and the performance and emission characteristics of the engine was analysed using different blends and by adding 1% of DTBP and the analysis shows better results with the blends.

For the recovery of unused process heat of various origins, the use of Rankine-Cycles represents an effective and well-proven strategy. As most commercially available systems are designed for comparably high power, or, if scaled down, are suffering from low efficiency or high costs, the present research project aims at designing a novel steam expansion engine for medium power (for waste heat power around 300 kW).

The so-called rotational wing-piston expander uses two pivoting shafts, each holding two wing-like pistons, within one housing, that are performing a cyclic movement relative to one another. This way, four working chambers with varying volumes are resulting, each experiencing repetitive compression and expansion. The conversion of the cyclic changing angular velocity to a constant rotation at the output shaft is done via a non-circular gear. This solution offers the possibility of sealing the lubricated gearbox against the steam-flooded section containing the working chambers via rotational seals, which is much easier than the sealing within a conventional reciprocating piston engine. The sealing of the working chambers themselves, however, poses a challenging task. Therefore, various sealing solutions have been developed and, via basic principle tests, investigated. The most promising solutions have been chosen for the use in a scaled test version of the expander, for the investigation at the steam test bench at IVT at TU Graz.

The paper shows the development and the operating principle of the expander, as well as the main challenges, focusing specifically on the sealing; additionally, first test results are presented.

To overcome the restrictions on electric vehicles ranges on winter term conditions, due to the heating demand of the interior, the use of a Thermal High Performance Storage with metallic Phase Change Materials is one possible solution. A new storage concept, using a so called Heat Transport System, enabling the heat transfer from the storage to a vehicles cooling fluid by evaporation and condensation of a working fluid within a closed circle, is introduced in this study. The influence of the storage on an electric vehicles range is exemplary shown for DLR’s Urban Modular Vehicle Concept for a motorway cycle by theoretical investigations. An increase of range by 36,3 km resp. 18,4% for an ambient temperature of –10 °C and 46 km resp. 26,7% for an ambient temperature of –20 °C could be reached. The energy densities of the designed storages reach values of more than 220 Wh/kg resp. more than 310 Wh/l. The cost estimations for those storage systems are approx. 445 € resp. 660 €. A comparison between the thermal energy storage and a conventional heating system consisting out of a PTC-Heater and a battery show, that the conventional heating system has a mass which is about two thirds higher, a volume which is more than one third higher and a quadrupled price compared to the thermal energy storage.

In recent years, strict exhaust emission legislation alongside the demand for high efficiency and low fuel consumption have caused an enormous effort in research and development in the automotive industry. As far as thermal management is concerned, a growing number of on-demand temperature control strategies is recognized. While direct heat exchanging devices offer limited possibilities for such approaches, indirect cooling systems facilitate their implementation to a large extent. This allows to adjust the temperature of the various components at or close to the vehicle’s engine, independent of the current driving situation. The aforementioned temperature control strategies usually rely on the knowledge of the state variables. The latter are expressed by means of data supplied by the vehicle’s ECU and the fluid properties. In particular, the cooling medium’s composition has a major impact on the performance of the overall cooling system. This is due to the strong dependence of the viscosity and the heat capacity on the concentration c of ethylene glycol in the coolant mixture. On the other hand, the composition of the cooling mixture may be influenced by the vehicle’s owner by adding water or glycol to the cooling circuit. This may destabilize the temperature control which, in the worst case, may cause damage to the vehicle components. Assuming a binary mixture of water and ethylene glycol we suggest an approach which allows to determine c by means of quantities which are supplied by the vehicle’s ECU. To this end, the dimensionless temperature change of the respective heat exchanger is expressed by means of the heat capacity flow of the cooling medium. This expression can be solved for the concentration either by means of characteristic maps or analytically. Exemplifying both these approaches on the basis of vehicle measurements, we discuss possible applications such as on-board diagnosis and adaptive control.

In the thermal system of a vehicle cabin, the heat transfer modes of convection, conduction and radiation all have a large impact on the thermal behavior. When trying to develop a model with reduced complexity compared to 3D CFD, it becomes essential to represent not only the physics of the solid parts (conduction), but also heat sources on surfaces (radiation) and effects resulting from the fluid flow inside the cabin (convection). The latter are summed up in the presented approach in the parameters ‘Heat Transfer Coefficients’ (HTC) on the inside surfaces, ‘weighting factors’ for the energy distribution into zones which allow a zonal resolution of air temperatures and the ‘average cabin air temperature’. With a load case specific transient modeling of these parameters a fast calculating cabin model is provided, which considers all the temperature relevant flow phenomena without resolving the fluid dynamics explicitly. From the results of transient thermal 3D CFD simulations of the load case ‘Cooldown’ a model for the respective parameters is derived by means of a Linear Time-Invariant System (LTI) approach. These parameters then serve as transient boundary conditions in an independently running, predictive thermal cabin model. The quality of the presented model is evaluated by comparison of the predicted temperatures of the model (i.e. surface and air temperatures) with the corresponding values from a transient 3D CFD test case.

This paper proposes a system for personalized air conditioning in electric vehicles based on the real-time evaluation of individual thermal comfort and model-predictive control. The goal is to continuously adjust decentralized air conditioning actuators in such a way that an optimal level of thermal comfort is maintained for the occupant while minimizing the overall energy consumption of the entire system. The latter employs contact-less skin temperature measurements using thermal imaging in combination with face and body recognition [2], seat mounted temperature and humidity sensors as well as additional ambient air velocity, operative temperature, humidity and pressure sensors in order to establish sufficient sensor data coverage. The numerical human model MORPHEUS [1] is applied to predict the thermal state of body regions, which are hidden from the thermal camera [3]. In order to assess the individual’s state of thermal comfort, the simulated and measured data is combined and evaluated using a thermal comfort model that is applicable under inhomogeneous climatic conditions [4]. This information is subsequently used to derive control strategies for local air conditioning of the occupants. Local infrared heating panels are used to heat specific zones of the human body under cold conditions. Seat ventilation as well as fans mounted close to the body are used to cool specific zones under warm conditions. In addition, individual occupant feedback acquired through an electronic feedback system is used to further fine-tune the system with respect to the occupant’s needs. The transient nature of the system at hand allows an early identification of individual-specific thermal comfort trends, which enables a much more efficient way of energy balancing.

In the last conference proceedings of ETA conference [1, 2], a new approach of an HMI concept allowing the user to enunciate his or her current thermal comfort has been presented. The goal figured is to decrease actuate complexity and reduce the quantity of user interactions to an absolute minimum. To achieve this goal, one needs to know the users preferences under every condition, which can be perfectly recorded with direct feedback of the thermal comfort.

Adaptive algorithms should be able to “learn” from user interactions and lead to the aimed degree of individualization. Therefore, in a first step, regression of specific characteristic curves in an automatic climate controller is used, combined with the above mentioned HMI concept. In contrast to other approaches, the regression of characteristic curves allows to adapt the complete climate control to the needs of a user for the full range of a selected configuration space, ensuring continuous functions and direct variation of the application instead of choosing discrete and predefined settings. In addition, these adjustments are stored in an individual user profile that can be transferred to arbitrary vehicles – equipped with this system – to provide the user with his individual application independently of his own vehicle.

Increasing fuel prizes and future legislations on CO2 emissions for European [1] and US road transport [2] lead truck manufacturers to invest in the development of fuel efficiency increasing technologies. The organic Rankine cycle (ORC) describes a promising technology for long haul heavy duty trucks.

Rankine cycle waste heat recovery for automotive applications has been studied for many years with focus on fluid selection [3], control development [4], component development [5], modeling as well as testing [6] of defined architectures in the test lab and on vehicles.

The objective of this study has been to compare different Organic Rankine Cycle architectures for different engines on a European long haul application via transient vehicle simulations tacking into account the cooling package, the exhaust after treatment system as well as the energy management of the Rankine cycle (electrical vs mechanical coupling).

Results are showing that Cyclopentane shows the best overall net fuel economy performance using indirect condensation via a low temperature loop whereas Ethanol offers the best potential using direct condensation using forced air flow.

Waste heat recovery (WHR) systems enable the heat losses of an engine to be captured and converted to power, thereby increasing engine efficiency. This paper aims to identify the combination of working fluid and thermodynamic cycle that yields the best WHR performance for the most important engine operating points of a heavy duty Diesel engine. WHR cycles were simulated using two distinct configurations of the heat sources available in a typical heavy duty Diesel engine: Conf-1: CAC-Coolant-Exhaust-EGRC and Conf-2: CAC-Exhaust-EGRC. Simulations were performed for fifty working fluids and four thermodynamic cycles, with and without a recuperator: the organic Rankine cycle (ORC), the transcritical Rankine cycle (TRC), the trilateral flash cycle (TFC), and the organic flash cycle (OFC). An analysis of a 100kW operating point revealed important performance differences between the two heat exchanger configurations, with maximum net power outputs of 5–7 kW for the ORC and TRC, 3–5 kW for the TFC, and 0.5–4 kW for the OFC. The use of a recuperator increased the net power output by 15 to 25% for Conf-1 and helped reduce the condenser load for Conf-2. For the dominant engine operating points of long haul cycle, the best performance was achieved for Conf-2. With this configuration, the ORC and TRC showed maximum power outputs with acetone, methanol, cyclopentane, ethanol or isohexane as the optimum working fluid.

As a promising solution to improve fuel efficiency of a long-haul heavy duty truck with diesel engine, Organic Rankine Cycle (ORC) based waste heat recovery system (WHR) by utilizing the exhaust gas from internal combustion engine has continuously drawn attention from industry in recent years. In this paper, a simulation study has been conducted to investigate the interaction between the internal combustion engine and an ORC based WHR-system with a parallel layout. The exhaust gas recirculation (EGR) energy and the exhaust gas Tailpipe (EGT) energy from the internal combustion engine will be used to vaporize the working fluid of the ORC-WHR system and converted to mechanical energy by employing a turbine-expander which is coupled to engine crankshaft. The truck cooling system will be used to dissipate the rest heat from the condenser of WHR-System to the ambient. The shift of the engine operating point to a lower engine torque level and the changed engine operating conditions by applying the WHR system have a strong influence on the benefit of the fuel efficiency and on the engine emission as well.

This paper aims to evaluate the impacts of the varied engine applications considering the effects of the WHR system on the global efficiency and engine emissions. A complex 0D/1D-simulation model for a turbocharged production 6-cylinder EURO-VI heavy duty engine with low-/high-temperature cooling circuit and a WHR system with ethanol as working fluid have been established in a conventional 1D-simulation software.

The publisher retracted this chapter, because as it was included due to an unfortunate administrative error. The editors and the publisher apologize for any inconvenience caused. The authors have agreed to this retraction.

Fuel consumption and the CO₂ emissions of heavy-duty vehicles are responsible for a great share of the road transport sector and substantial improvements are unlikely without further innovations. One part of this problem is that approximately of the fuel’s chemical energy is lost in waste heat through the engine’s coolant and exhaust system. Heavy-duty vehicles are expected to continue using internal combustion engines; a waste heat recovery system provides a future potential to reduce the fuel consumption and the emissions. Thermoelectric generators offer a low complexity solution. Based on the Seebeck effect, they convert thermal energy directly into electricity. Installed in the exhaust system of a vehicle, the system can supply the vehicles electrical system or charging the battery. Their benefits are low maintenance costs, relatively low system weight, small installation volume, and a competitive cost-benefit ratio. Recent research has focused on passenger cars but the potential for heavy-duty vehicles is high as well. Therefore, in this paper, the system development from potential analysis over design to experimental results, is presented for modern Euro VI heavy-duty vehicles with diesel and natural gas engines. The system integration is considered by analyzing installation positions in the exhaust aftertreatment system and its boundary conditions, such as available installation space and exhaust enthalpies for the most suitable positions. For this purpose, real road driving experimental data from long-haulage road circuit Stuttgart-Hamburg-Stuttgart and the representative World Harmonized Vehicle Cycle are presented as reference. Based on this data an approach for developing a thermoelectric generator system is investigated. The experimentally determined results of a hardware test and a simulation-based potential analysis are given for the vehicle interactions, the expected net electrical output power, and the reduced fuel consumption.