THE ARCHIVES OF AUTOMOTIVE ENGINEERING

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1 THE ARCHIVES OF AUTOMOTIVE ENGINEERING Archiwum Motoryzacji Vol. 67, No. 1, 2015 Kwartalnik wydawany od 1996 roku Wydawnictwo Naukowe PIMOT Scientific Publishing House of PIMOT

2 Scientific Council / Rada Naukowa Marijonas Bogdevičius, Vilnius Gediminas Technical University, Lithuania; Ken`ichi Hiratsuka, Chiba Institut of Technology, Japan; Matti Juhala, Helsinki University of Technology, Finland; Gustav Kasanicky, Institute of Forensic Engineering, Slovakia; Krzysztof Maruszewski, Institute for Health and Consumer Protection of the Joint Research Centre, European Commission, Italy; Steffan Nordmark, VTI - The Swedish National Road and Transport Research Institute, Sweden; Pietro Perlo, Politecnico di Torino, Italy; Radivoje Pesič, University of Kragujevac, Serbia; Giuseppe Rovera, FIAT - Research Center, Italy; Victor Shehovtsov, Volgograd State Technical University, Russia; Ezio Spessa, Politecnico di Torino, Italy; Herman Steffan, Graz University of Technology, Austria; Annika Stensson Trigell, KTH - Royal Institute of Technology, Sweden; Andrew P. Tarko, Purdue University, School of Civil Engineering, USA EDITOR-IN-CHIEF / REDAKTOR NACZELNY Krzysztof Bajdor EDITORIAL OFFICE SECRETARY / SEKRETARZ REDAKCJI Dominika Trębacz EDITORIAL SECRETARIATE / SEKRETARIAT REDAKCJI Elżbieta Dolega-Radzikowska Beata Biernacka LANGUAGE EDITORS / REDAKTORZY JĘZYKOWI Małgorzata Ciecierska (polish language, język polski) Stephen Howard Merrett (english language, język angielski) STATISTICAL EDITOR / REDAKTOR STATYSTYCZNY Jakub Szczepaniak EDITORS THEMATIC SECTIONS / REDAKTORZY DZIAŁÓW TEMATYCZNYCH: VEHICLES / POJAZDY Dariusz Więckowski FUELS AND ENERGY / PALIWA I ENERGIA Krzysztof Biernat TRANSPORT SAFETY / BEZPIECZEŃSTWO TRANSPORTU Andrzej Żuchowski ANNOUNCEMENTS / KOMUNIKATY Editorial Office / Redakcja EDITORIAL OFFICE ADDRESS / ADRES REDAKCJI Przemysłowy Instytut Motoryzacji Wydawnictwo Naukowe PIMOT ul. Jagiellońska Warszawa tel , 92, fax: wydawnictwonaukowe@pimot.org.pl Wszystkie artykuły są recenzowane. Copyright by Scientific Publishing House PIMOT Composition and printing / Skład i druk: Mdruk Sp. z o.o., Sp.k. Ark. Wyd 9, Ark. Druk. 11 Printing completed / Druk zakończono: r. The original version: paper / Wersja pierwotna: papierowa

3 THE ISSUE OF ENERGY CO-GENERATION USING THERMOELECTRIC GENERATORS ADRIAN CHMIELEWSKI 1, KAMIL LUBIKOWSKI 2, STANISŁAW RADKOWSKI 3, MICHAŁ WIKARY 4, JĘDRZEJ MĄCZAK 5 The Warsaw University of Technology Summary The development of the renewable energy sources technologies and the energy policy emphasise the energy co-generation systems. In the automotive industry, investments are located in the development of heat pumps, Stirling engines, energy accumulators, gas turbines, piezo mats, suspensions and enfeeblements, linear motors, and other energy retrieval systems retrieving energy that is expelled in the process of the combustion of the fuel and air mixture in conventional combustion engines [1,2] and lost irretrievably. The energy co-generation systems increase efficiency in the use of the energy contained in the fuel and air mixture. Currently, there is a tendency of combination of the energy micro-cogeneration systems with other vehicle systems, e.g. motor control systems, motor power supply systems, safety systems, etc. [3-8]. One of such ways is the retrieval of heat energy thanks to thermoelectric generators (TEG) using the Seebeck effect. Keywords: co-generation of energy, thermoelectric generators, Seebeck effect, Stirling engine 1. Introduction The article presented the issue of energy co-generation from heat dissipated in the exhaust system of the combustion engine using thermoelectric generators commonly called "Peltier Modules" [9]. The publication presents the results of analyses and computer simulations of phenomena occurring in the thermoelectric Peltier modules. Then, the results of the analyses conducted in the ANSYS computer programme were compared with the results of the calculations from the adopted mathematical model and the results from the bench test. The laboratory tests were conducted in the Environmentally Integrated Mechatronic Systems Laboratory [Zintegrowane Środowiskowo Laboratorium Systemów Mechatronicznych Pojazdów i Maszyn Roboczych] at the Faculty of Automotive and Construction Machinery Engineering of the Warsaw University of Technology located in at Narbutta 84 street in Warsaw. 1 The Warsaw University of Technology, the Faculty of Automotive and Construction Machinery Engineering, the Institute of Vehicles, ul. Narbutta 84, Warsaw, Poland, a.chmielewski@mechatronika.net.pl, tel The Warsaw University of Technology, the Faculty of Automotive and Construction Machinery Engineering, the Institute of Vehicles, ul. Narbutta 84, Warsaw, Poland, k.lubikowski@mechatronika.net.pl, tel The Warsaw University of Technology, the Faculty of Automotive and Construction Machinery Engineering, the Institute of Vehicles, ul. Narbutta 84, Warsaw, Poland, ras@mechatronika.net.pl, tel The Warsaw University of Technology, the Faculty of Automotive and Construction Machinery Engineering, the Institute of Vehicles, ul. Narbutta 84, Warsaw, Poland, m.wikary@mechatronika.net.pl, tel The Warsaw University of Technology, the Faculty of Automotive and Construction Machinery Engineering, the Institute of Vehicles, ul. Narbutta 84, Warsaw, Poland, jma@mechatronika.net.pl, tel

4 4 Adrian Chmielewski, Kamil Lubikowski, Stanisław Radkowski, Michał Wikary, Jędrzej Mączak It should be mentioned that, in the laboratory, in the study of issues concerning the process of co-generation of energy, piezoelectric devices, the Stirling engine, and, recently, the thermoacoustic engine are used. The energy policy of the European Commission's goal is to reduce the EU countries' dependence on imported oil and to produce their own local energy sources, which can be biofuels [1]. In issues of renewable technologies and the energy policy, emphasis is put on the co-generation systems. In the Directive 2009/28/EC of April 2009, the requirements for the member states of the European Union on the promotion of the use of energy from renewable sources were clearly defined. Investments are located in the development of heat pumps, Stirling engines [2], energy accumulators, and gas turbines in the automotive industry, as well as energy retrieval systems retrieving energy that is expelled in the process of the combustion of the fuel and air mixture in conventional combustion engines [9]. One of such methods is the retrieval of thermal energy thanks to the thermoelectric generators (TEG) [10-12] using the Seebeck effect. Conducting scientific and research works on thermoelectric generators as energy converters, thermoelectric generators' operating parameters in a retrieval of electricity from thermal energy dissipated in a combustion engine in the exhaust system were developed. In order to model and conduct computer simulations, the finite element method (FEM) was used [13-14]. In the mathematical description of a continuous medium, an object is regarded as a model in the Euclidean space, whose points are identified with the material particles of a body. Continuity [15] is modelled mathematically, and continuity of internal discontinuities separating continuous areas appearing in the theory of functions, with an acceptable exception on a limited number is assumed. In comparison to continuous models, discrete models allow modelling of discontinuities and fragmentation of the material through an approach to the model as the assembly of a finite number of discrete objects. Currently, the discrete models can be built at different levels of observation (macro/micro/nano) from the point of view of the structure of the material. 2. Analysis of thermoelectric generator (steady-state condition) The main task of the experiment is the analysis of the commercial Peltier module using the finite element method and the comparison with the mathematical model and results of empirical and commercial parameters of the module. A typical task of thermoelectric generators (from the commercial point of view), which is visible nowadays, is generation and maintenance of the required temperature at the appropriate level (either positive or negative one) by means of the electricity supplied to the system. For the purposes of the analysis, the process was reversed providing a stream of thermal energy with the observed result of energy values collected at the terminals of the thermoelectric generator.

5 The issue of energy co-generation using thermoelectric generators 5 The model consists of 142 p- and n-type semiconductor components, which creates 71 p-n pairs. Semiconductor objects are connected together with thin copper connectors, as it was shown in Figure 1. The model does not include sockets, which means that it does not create additional connections. Ceramic tiles were not modelled. Fig. 1. Geometric model 3. Results In this part of the paper, the results of the analysis of the model discussed earlier were presented. Figure 2 shows the values of voltage of retrieved energy (and its distribution) in the last step of the analysis (for the temperature difference of 60 C). The maximum value that was recorded is V. The voltages that were obtained during the "n" steps are presented in Table 1. Table 1. Voltage values Time [s] Max. [mv] Time [s] Max. [mv] E E E

6 6 Adrian Chmielewski, Kamil Lubikowski, Stanisław Radkowski, Michał Wikary, Jędrzej Mączak Fig. 2. Voltage distribution Fig. 3. Temperature distribution. The red line shows the simulated temperature on the cold side of the TEG, while the green line shows the temperature of the heated side of the TEG

7 The issue of energy co-generation using thermoelectric generators 7 Figure 3 presents the temperature distribution in the semiconductor junctions in the modelled TEG. Table 2. Temperature values Time [s] Min [ C] Max [ C] Time [s] Minimum [ C] Maximum [ C] The computer analysis results were compared with the results of the laboratory tests. These results have already been presented at various conferences and symposia [1,5]. The figure below shows pictures of the benches, where the tests were conducted. Fig. 4. The bench tests of the TEGs: a) The bench for tests of the TEGs' properties, b) The bench for tests of the TEGs on the ECOTEC X18XE engine The laboratory tests were conducted on laboratory benches at the Faculty of Automotive and Construction Machinery Engineering (SiMR) of the WUT, in the Environmentally Integrated Mechatronic Systems Laboratory [Zintegrowane Środowiskowo Laboratorium Systemów Mechatronicznych Pojazdów i Maszyn Roboczych] in two stages. First, the TEGs' properties were researched by means of heating and cooling sides of the cell, as

8 8 Adrian Chmielewski, Kamil Lubikowski, Stanisław Radkowski, Michał Wikary, Jędrzej Mączak well as reading values describing electricity i.e. voltage, current, and electric power on the measuring apparatus. Next, measurements were conducted on the real bench, both at room temperature (conditions in the laboratory) and ambient temperature during the winter that is 12ºC. On the bench built on the ECOTEC X18XE petrol engine rebuilding its exhaust gas system. Initially, the measurements of the surface temperature of this system were conducted in order to determine a suitable place for mounting the TEGs. In the selected place, the system was separated and the double tube of rectangular cross section was incorporated in order to mount the TEGs easily using their entire surface. In addition, the system with the rectangular pipe was equipped with the running wheel of the waste gas stream. At the time of supplying energy to the TEGs, the waste gas stream was directed into this part of the pipe, on which the TEGs were mounted. At the boundary limit of the exceedance of temperatures, which could damage the semiconductor structure, waste gas stream was directed to the free tube (the bypass without TEGs). The measurements results are presented in Table 3. Table 3. Comparison of the energy retrieved in the different environmental conditions [5] At temp. of +28 [ C] At temp. of -12 [ C] 800 [rpm] 2000 [rpm] 800 [rpm] 2000 [rpm] Without the exhaust gas flow 1.4 [V] 2.5 [V] 0.9 [V] 1.44 [V] With the exhaust gas flow 1.9 [V] 3.15 [V] 1.14 [V] 2.24 [V] Ultimately, the results of the research were compared with the results of the computer simulations and model calculations. The results of the comparison are shown below, in Figure 5, and summarized in Table 4. Table 4. Comparison of the value of the voltage of electricity from the laboratory measurements (the first column), the FEM simulation (the middle column), and the mathematical calculations (the column at the right) C the cold side H the hot side ΔT the temperature difference Temp (ºC) Temp (ºC) - U voltage U voltage U voltage Voltage (V), empirically Voltage (V), FEM Voltage (V), manual calculations

9 The issue of energy co-generation using thermoelectric generators 9 Fig. 5. TEGs energy retrieval characteristics 5. Conclusions The conducted research enabled to claim that despite the low efficiency of the TEGs, they work perfectly as passive components retrieving energy irretrievably dissipated in the exhaust gas system of the combustion engine. Then, it was further found that the use of the TEGs in the exhaust system requires the preparation of the surface it must be flat (most vehicles on the roads are equipped with circular exhaust systems) and appropriately cleared of debris. Furthermore, the tests of increased number of generators were conducted. The TEGs should be mounted in packages connecting them serially and parallel. Each retrieved watt means saving and the better use of the lost energy in the form of joules discharged to the environment. In the future, the construction of the complex energy recovery bench at the SiMR faculty of the WUT is planned. The building-in of the cooler with the Peltier tiles, mounting the TEGs on the cover of the engine valves, and the building-in of the exhaust system with the hightemperature TEG cells are anticipated.

10 10 Adrian Chmielewski, Kamil Lubikowski, Stanisław Radkowski, Michał Wikary, Jędrzej Mączak References [1] Lubikowski K., Radkowski S., Szczurowski K., Wikary M.: Analysis of possibility of use Peltier module In task of energy scavenging, Key Engineering Materials, Vol. 588, 2014, pp [2] Chmielewski A., Gumiński R., Lubikowski K., Radkowski S., Szulim P.: Bench testing and simulation model of a cogeneration system with a Stirling engine, Journal of KONES Powertrain and Transport, Vol. 20, No. 3, 2013, pp [3] Wierzbicki S.: Laboratory Control and Measurement System of a Dual-Fuel Compression Ignition Combustion Engine Operating in a Cogeneration System. Solid State Phenomena Vol. 210 (2014), Priya S, Inman D. J., Energy Harvesting Technologies, Springer, ISBN [4] Wierzbicki S., Śmieja, M.: Visualization of the Parameters and Changes of Signals Controlling the Operation of Common Rail Injectors. Solid State Phenomena Vol. 210 (2014), [5] Śmieja M. & Wierzbicki S.: Influence of content of methane in biogas on emission of toxic substances in diesel engine supplied with bifuel. International Conference on Environmental Engineering (2014). [6] Śmieja M., Wierzbicki S., Mamala J.: Sterowanie dawką wtryskiwanego paliwa w układzie Common Rail z wykorzystaniem środowiska LabView. Combustion Engines 123 CD (2013). [7] Wierzbicki S., Śmieja M., Grzeszczyk R.: Zintegrowane sterowanie stanowiskiem badawczym silników o ZS w środowisku fast prototyping. Combustion Engines 123 CD (2013). [8] Śmieja M. & Wierzbicki S.: The concept of an integrated laboratory control system for a dual - fuel diesel engine. Journal of KONES Vol. 19, No. 3, pp (2012). [9] Kumar C. R., Sonthalia A., Goel R.: Experimental study on waste heat recovery from an internal combustin engine Rusing thermoelectric technology, Thermal Science, 2011, Vol. 15, No. 4, pp [10] Chmielewski A., Lubikowski K., Radkowski S., Szczurowski K..: Research and simulation work of TEG in cogeneration task of the exhaust system, Journal of KONES Powertrain and Transport, Vol. 20, No. 2, 2013, pp [11] Wojciechowski K., Merkisz J., Fuć P., Lijewski P., Schmidt M., Zybała R.: Study of recovery of waste heat from exhaust of automotive engine, 5th European Conference on Thermoelectrics, Odessa, Ukraine, September 10-12, 2007, pp [12] Antonova E.E., David C.: Finite Elements of Thermoelectric Device Analysis In ANSYS, Looman ANSYS Inc, ANSYS Release 9.0 Documentation, [13] Angrist S. W.: Direct Energy Conversion, 3 rd Edition, Allyn and Bacon, Boston, 1976, pp ] Silvester P.P., Ferrari R.L.: Finite Elements for Electrical Engineers, 3 rd Edition, University Press, Cambridge, [15] Landau L.D., Lifshitz E.M.: Electrodynamics of Continuous Madia, 2 nd Edition, Butterworth-Heinemann, Oxford, [16] Chmielewski A.: Modelowanie procesu kogeneracji energii z wykorzystaniem badań stanowiskowych na silniku Stirlinga, Praca Magisterska, Warszawa The work was conducted within the research project: N N entitled: "The co-generational increase of the energy efficiency of the multi-combustion engine using the criteria of minimizing the vibro-acoustic activity and environmental threats'' [Kogeneracyjne zwiększenie efektywności energetycznej wielopaliwowego silnika spalinowego z wykorzystaniem kryteriów minimalizacji aktywności wibroakustycznej i zagrożeń środowiskowych] The project was funded by the National Science Centre.

11 THE USE OF MICROWAVE PYROLYSIS FOR BIOMASS PROCESSING JOANNA CZARNOCKA 1 Automotive Industry Institute Summary The method of processing biomass of various kinds by microwave-assisted pyrolysis has been presented. The fast pyrolysis process, characterized by rapid heating of the feedstock in the absence of oxygen and rapid cooling of the volatile intermediate reaction products, is one of attractive liquid biofuel production methods. However, the pyrolysis still requires improvements as regards the process yield, quality of liquid biofuel products, and energy efficiency of the process as a whole. The microwave pyrolysis is a promising attempt to solve these problems thanks to the fast and efficient feedstock heating through the effect of microwave dielectric heating. Before proceeding to the main topic of this paper, the conventional pyrolysis has been characterized. At such a technology, the thermal energy necessary to heat the feedstock is transmitted from the surface into the depth, which is rather a slow process. This has been followed by a presentation of the microwave pyrolysis, where the microwave radiation causes fast and productive bulk heating of the material having been finely ground (the material should be susceptible to the action of microwaves). Moreover, a review of materials used as microwave radiation absorbers, biomass types, and methods of biomass preparation for the process, as well as qualitative and quantitative characteristics of the pyrolysis products obtained, i.e. raw bio-oil, which should be subjected to further processing, and synthesis gas ( syngas ) have been provided. Keywords: pyrolysis, microwave pyrolysis, biomass, bio-oil, syngas Introduction Pyrolysis, gasification, and direct combustion are the three major thermochemical methods of biomass processing into fuels, chemicals, and electric energy, with pyrolysis playing a predominating role among them. The pyrolysis finds application not only as a separate biofuel production process but also as an initial stage of the combustion and gasification processes. Pyrolysis is a process of thermal degradation of selected feedstock in an oxygen-free environment. In result of the pyrolysis, the feedstock is transformed into liquid, gaseous, and solid products. The pyrolysis is considered to consist of two basic stages. The first one includes the processes of feedstock degassing (carbonization) and thermal 1 Automotive Industry Institute, Department for Fuels, Biofuels & Lubricants, ul. Jagiellonska 55, Warsaw, Poland, a.czarnocka@pimot.eu, tel

12 12 Joanna Czarnocka decomposition of main feedstock components (dewatering, dehydrogenation, and decarboxylation). At the second stage, secondary reactions between solid and volatile products (e.g. polymerization or condensation) take place. The course of the pyrolysis process is determined by many factors, which include the composition and fineness of grinding of the feedstock, feedstock heating rate, and residence time (i.e. the time of the feedstock being held in the reactor). Depending on the process temperature, heating rate, and reaction time, pyrolysis can be classified into three main categories: slow, fast and flash pyrolysis. It is difficult to characterize unequivocally individual pyrolysis categories and to assign specific classification criteria to each of them. Actually, two basic parameters, i.e. temperature and time, are chiefly used for this purpose. In most cases, the pyrolysis process is run at temperatures ranging from 400 C to 1000 C and the residence time is short, from several minutes for slow pyrolysis to less than 0.5 s for flash pyrolysis. The process parameters are selected depending on the types of the feedstock to be processed and of the product to be obtained. Low process temperatures and low heating rates conduce to the generation of large quantities of solid product, the fast pyrolysis at higher temperatures gives a lot of liquid product, and the flash pyrolysis at temperatures of about 900 C is conducive to the generation of pyrolytic gases. The process efficiency is also affected by the catalysts used and the feedstock diversification often determines the specific pyrolysis method adopted. The materials used as feedstock for the pyrolysis process are chiefly process wastes generated by the food-processing industry, agriculture, and forestry. This means that wood biomass (woodchips, tree branches, bark, wood shavings, and lignified plant stalks), agricultural biomass (lucerne, miscanthus giganteus, millet, cereal straw, fruit remains, seed shells, pomace, food wastes), waterborne biomass (e.g. algae), animal biomass (e.g. poultry-processing offal), sewage sludge, and paper industry wastes may be a source of the feedstock. As mentioned previously, there are three final products of the pyrolysis process: a) Solid carbon-containing residue (carbonization product), chiefly consisting of elemental carbon, unreacted organic compounds, and solid particles. The carbonization product may be utilized as a solid fuel granulated with another biomass type, as a raw material for the production of activated carbon, as a raw material for the generation of hydrogenrich gas by gasification, or as a raw material for the production of catalysts with high specific surface area. b) Pyrolytic oil (bio-oil), which is a mixture of organic and inorganic compounds and consists of a water fraction and an oil fraction. Pyrolytic oils contain carboxylic acids, alcohols, phenols, esters, aldehydes, ketones, and heterocyclic oxygen compounds. The water contained in the bio-oil chiefly comes from moisture content of the material, but may also be a product of the dehydration reaction that takes place during the pyrolysis process; therefore, the water content may vary within a wide range depending on the feedstock material and process conditions. The water fraction may contain acetic acid and phenols.

13 The use of microwave pyrolysis for biomass processing 13 c) Pyrolytic gas, chiefly consisting of inflammable gases such as H 2, CO, CH 4, C 2 H 2, or C 2 H 4. It also contains smaller quantities of CO 2, SO 2, and NO x. The pyrolytic gas may be directly burnt, used for the fuelling of gas turbines, and used for the production of synthesis gas ( syngas ). 1. Microwave pyrolysis process The biomass pyrolysis process consists of the following stages: feedstock receiving and storage; feedstock pre-treatment (e.g. drying or grinding); pyrolysis proper in an appropriate reactor; separation of solid residue (carbonization product and ash); vapour cooling and condensation; and bio-oil collection. Before the condensation, the pyrolytic vapours may be subjected to catalytic reforming in order to obtain adequate process selectivity in respect of the product preferred. A part of the carbonization product may be recovered and returned to the microwave reactor, where it would be used as a microwave radiation absorber and it would make it possible to recuperate a part of the heat. A part of the gaseous product may be burnt to provide thermal energy for the feedstock pretreatment (e.g. drying). The process of pyrolysis with a reactor heated by microwave radiation has been schematically shown in Fig. 1. Fig. 1. Schematic diagram of the process of microwave-assisted pyrolysis of biomass

14 14 Joanna Czarnocka The basic difference between the processes of conventional pyrolysis and microwave pyrolysis lies in the feedstock heating method. At the conventional heating, thermal energy is transmitted from the surface into the depth of the feedstock by convection, radiation, and conduction. Such a process is relatively slow and requires the feedstock material to be finely ground. Instead, the microwave heating is a process of conversion of electromagnetic energy into thermal energy. The microwave energy induces molecular motion by dipole rotation and ion migration [1]. The microwave heating is a contactless and fast process, which takes place throughout the entire material volume; hence, the heat is generated throughout the entire volume of each material particle. The microwave heating is a selective process, i.e. the feedstock behaviour in a microwave field will not be identical for every feedstock material. The materials that are most susceptible to microwave radiation are dielectrics, such as e.g. water or methanol. Materials of this type are referred to as microwave radiation absorbers. The materials that have not dielectric properties will reflect or transmit microwave radiation without being heated. Therefore, the microwave pyrolysis may only be applied to the materials that fully or partly absorb microwave radiation, thanks to which the heating of such materials is possible. An important process parameter is the residence time. The fast internal heating causes fast release of moisture from the feedstock and, in consequence, a growth in the volatile substances release area during the pyrolysis process. In a microwave reactor, volatile vapours (including small dipolar molecules) loaded with solid particles (chiefly fine particles of the carbonization product) can be easily heated by microwaves to a higher temperature. Therefore, the pyrolytic vapours must be carried away from the reactor very quickly for the secondary cracking of the vapours within the reactor space to be reduced and for water vapour to be removed. The efficient microwave energy transfer to the feedstock in the bed is another important issue related to the microwave reactor. The reactor vessel, made of materials transparent to microwaves (e.g. quartz), must be carefully and appropriately cleaned, especially at continuous operation mode. The presence of solid particles in the vapours and fine carbon particles on the vessel walls will cause significant difficulties in introducing microwaves into the reaction environment or even local burns of the reaction vessel. It is also important that the feedstock mixture should be homogenous for the microwave field action in the reactor to be uniform and for the forming of ignition points ( hotspots ) to be thus avoided. The hotspots may easily cause the loss of control of local pyrolysis temperature and, thus, of the entire reaction process. When the pyrolysis reaction is completed, the solid residues, chiefly the carbonization product capable of catalysing the secondary cracking in the gaseous phase, must be efficiently separated. Even if the liquid reaction product has been cooled, the carbonization product conduces to the creation of stability problems because it speeds up the polymerization process and raises the viscosity of the liquid reaction product. For this reason, the carbonization product must be separated quickly and completely from the volatile vapours. This process may be carried out by means of solid substance separators such as those used for conventional pyrolysis. A liquid collector used at conventional pyrolysis may be used as well. The collector is necessary to condense the vapours and

15 The use of microwave pyrolysis for biomass processing 15 to collect the liquid phase. The liquid biofuel obtained from this process usually consists of two fractions, i.e. a water fraction and an insoluble oil fraction. The former one consists of water and water-soluble organic compounds, e.g. furfural, and the latter contains a mixture of the hydrocarbons that occur in oils and require further refining. Optionally, the pyrolysis process may include catalytic reforming, which is employed to improve the process selectivity in respect of the product type preferred (liquid or gas) [2]. In this case, attention should also be paid to the vapour temperature and residence time in order to reduce the secondary vapour cracking. 2. The use of microwave pyrolysis to process various biomass types The field of lignocellulosic biomass pyrolysis has already been quite well explored. It is generally known that each of the lignocellulose components decomposes with forming other substances, where cellulose and hemicellulose are volatile products and lignins make the solid residue. As mentioned at the beginning, however, other biomass types are now increasingly often used to obtain chemicals or fuel components. Growing importance has been recently attached to microalgae because of their numerous good points in comparison with lignocellulosic raw materials: they are characterized by higher process yield, they do not compete with traditional agricultural products as they can be grown on idle land or in wastewater treatment facilities, and they are extremely rich in oil, which sometimes makes more than 60 % of dry mass in some algae species [3]. Moreover, such materials are now used for this purpose as wheat, maize, and rice straw; coffee hulls; by-product of the distillation of alcohol from grain [4]; oil palm shells [5]; or sewage sludge produced at municipal sewage treatment plants Biomass from algae Research on the microwave pyrolysis process, where fresh-water algae Chlorella sp. were used as the raw material, was carried out by Du Zhenyi et al. [6]. The algae were grown on a piloting basis in special photo-reactors. Before the pyrolysis process was started, the algal paste with about 85 % water content was dried. Since the algal paste insufficiently absorbs the microwave radiation, it was mixed with the carbonization product obtained from the first experiment with the pyrolysis process. The biomass thus prepared was subjected to pyrolysis at various values of the microwave heating power, i.e. 500 W, 750 W, 1000 W, and 1250 W, which corresponded to process temperatures of 460 C, 570 C, 600 C, and 625 C, respectively. The volatile substances involved in the reaction were cooled in five condensers by means of cooling water and the non-condensing gases were accumulated in special gasbags. The pyrolysis time was 20 min.

16 16 Joanna Czarnocka Table 1. Percentage yield of individual fractions, by mass, depending on the microwave heating power Fraction Heating power [W] [% (m/m)] Oil fraction Water fraction Carbonization product Gaseous phase The percentage yield, by mass, of individual products of the pyrolysis process at various values of the heating power has been presented in Table 1. For the bio-oil fraction, the highest yield (28.5 %) was recorded for a microwave power of the order of 750 W. The highest and the lowest percentage of the gaseous phase (35 %) were obtained at a power of 1250 W and 500 W, respectively, while the latter power value simultaneously yielded the highest percentage of the carbonization product. The yield of the water fraction remained on an approximately constant level of about 21 % in the power range examined. The bio-oil was found to contain aliphatic and aromatic hydrocarbons, phenols, indoles, and other nitrogen-containing compounds, polycyclic aromatic hydrocarbons, as well as oleic acid and its derivatives. The gaseous phase consisted of hydrogen, carbon monoxide, carbon dioxide, and light hydrocarbons, i.e. methane and ethane. With growing microwave power, the percentage of carbon dioxide decreased and the hydrogen and carbon monoxide contents increased. The highest concentration of the synthesis gas, also referred to as syngas (H 2 + CO) was 49.8 %. Similar research on biomass obtained from algae Chlorella vulgaris was carried out by Hu Zhifeng et al. [7]. This research work included a number of microwave pyrolysis experiments with various substances being used as microwave absorption improvers. Apart from the carbonization product mentioned above, the researchers used activated carbon, calcium oxide CaO, and silicon carbide SiC. The catalysts were dried and ground so that the catalyst particles were identical in size to those of the algal biomass prepared for the process. The pyrolysis experiments were carried out at three values of the heating power, i.e. about 200 C, 600, and 800 C, and the process time was 1200 s. All the catalysts used caused a significant increase in the pyrolysis temperature in comparison with that recorded for the pure algae feedstock, which resulted in an increase in the yield of the gaseous phase and a drop in the bio-oil percentage. Besides, it was noticed during the experiments that the activated carbon reduced the forming of solid pyrolytic residue.

17 The use of microwave pyrolysis for biomass processing 17 Fig. 2. The course of the microwave pyrolysis process depending on the absorber used The time histories of the pyrolysis temperature show that the process may be divided into four stages. At the first stage, the process temperature grew with a relatively slow rate, the specimen was dried, and volatile components vaporized. The second stage was characterized by rapid growth in the process temperature. This is explained by the fact that the dry solid residue formed during the first stage conduced to the absorption of microwave radiation. At this stage, the bio-oil and gaseous fractions were also formed. At the third stage, a drop was observed in the process temperature because the formation of bio-oil and gas was an endoergic process. At the fourth stage, the temperature initially slightly rose and then it became stabilized, because the pyrolysis process was completed and heat was no longer taken over by the pyrolytic gases. A small amount of heat was still generated by the solid residue, which caused a slight temperature growth to a constant value resulting from the equilibrium achieved between the heat losses and the residual heat supply. The experiments carried out by D. Beneroso et al. [8] have shown that a properly run process of microwave pyrolysis of algal biomass yields much more syngas (CO + H 2 ) than the conventional pyrolysis does. At a reaction temperature of the order of 800 C, a syngas yield of 87.7% (by volume) was achieved, as against 53.5% (by volume) of syngas obtained from a conventional pyrolysis process run in identical conditions. Conversely, the amount of carbon dioxide produced at the microwave pyrolysis was far less than that observed at the conventional pyrolysis.

18 18 Joanna Czarnocka 2.2. Coffee hulls Comparative examinations of the conventional pyrolysis and microwave pyrolysis of biomass consisting of coffee bean processing wastes have been presented in a publication by A. Dominguez et al. [9]. As the biomass, granulated coffee hulls obtained from the coffee bean treatment process were used. The experiments were carried out at temperatures of 500 C, 800 C, and 1000 C. The reaction time was 25 min. at the conventional pyrolysis and 20 min. at the microwave pyrolysis. The first pyrolysis experiment was performed to obtain a carbonization product that was then used at the next experiments as a microwave radiation absorber. As it is at every pyrolysis process, three product phases, i.e. solid, liquid, and gaseous phase, were obtained. The conventional pyrolysis yielded a larger amount of the bio-oil fraction than the microwave pyrolysis did; for the gaseous phase, an opposite dependence was observed. The quantities of the solid phase were comparable for both the process types. The gaseous fractions obtained from the conventional and microwave-assisted pyrolysis processes comprised such components as hydrogen, carbon monoxide, carbon dioxide, methane, ethane, and ethene. The largest amounts of CO 2 were produced at the conventional pyrolysis; at the microwave pyrolysis, the main product was hydrogen, with carbon monoxide being ranked second. A comparison between the amounts of individual components of the gaseous phase obtained from the microwave and conventional pyrolysis processes run at temperatures of 500 C and C has been presented in Fig. 3. Fig. 3. Comparison between the volumes of gases yielded by the pyrolysis processes of both types at temperatures of 500 C and C: CP conventional pyrolysis; MP microwave pyrolysis

19 The use of microwave pyrolysis for biomass processing 19 The amounts of the hydrogen and carbon monoxide yielded by the process increased with the process temperature. This finding did not depend on the pyrolysis type. In consequence, the syngas obtained from the conventional pyrolysis and microwave pyrolysis processes, in both cases carried out at a temperature of 1000 C, made 52.9 % (v/v) and 72.8 % (v/v) of the total pyrolytic gases, respectively. On the other hand, the amounts of CH 4 and C 2 H 6 slightly decreased and the amount of C 2 H 4 insignificantly increased with the process temperature. Presumably, this was caused by dehydrogenation of ethane to ethene and liberation of molecular hydrogen, which contributed to the growth in the syngas amount. The high concentrations of CO 2 and CO in the pyrolytic gases resulted from the deoxidation process that took place due to decarbonylation and decarboxylation reactions. It is presumed that the decrease in the CO 2 amount with rising temperature of the pyrolysis process may be related to the carbon gasification reaction, which in turn led to a growth in the production of CO. The research carried out by Raveendran et al. [10] has shown that the processing of potassium-reach biomass is conducive to the carbon gasification reaction and, thus, to a growth in the quantity of the carbon monoxide produced. The calorific value of the oil and gaseous fractions obtained from microwave pyrolysis is higher than that of these substances produced during the conventional pyrolysis process; only the calorific values of the solid residues are comparable with each other. For the microwave pyrolysis process run at a temperature of 1000 C, the calorific values of the gaseous phase, solid residue, and bio-oil are about 15 MJ/kg, about 24 MJ/kg, and about 34 MJ/kg, respectively. The microwave pyrolysis process yields much more gaseous fraction than the conventional pyrolysis process does, regardless of the process temperature. The decline in the yield of the bio-oil fraction with rising process temperatures suggests that the microwave heating is conducive to the secondary cracking reaction, which leads to the obtaining of lighter products with shorter chains Wood biomass: Douglas-fir The microwave pyrolysis of lignocellulosic biomass leads, as mentioned before, to the obtaining of liquid and gaseous fractions and a carbonization product (solid residue). Depending on the pyrolysis process conditions, biomass type used, and catalyst applied, a product having different quantitative and qualitative composition of individual fractions may be obtained. Douglas-fir pellets were subjected to microwave pyrolysis at different temperatures ( C) and at different process duration time (4 12 min.), with activated carbon being added as a catalyst. The bio-oil obtained from the process contained aliphatic and aromatic hydrocarbons, phenols, furan derivatives, guaiacols, esters, and phenolic acids [11]. The maximum amount of phenolic compounds in bio-oil, of the order of 67%, was obtained when the pyrolysis process was run at a temperature of 315 C for 8 min., at an activated carbon-to-biomass ratio of 3:1. When the pyrolysis process was run without participation of activated carbon and at a process temperature of 400 C, considerable amounts of guaiacols (2 methoxyphenol and its derivatives), even of up to about 52%, were obtained. The phenols obtained may be used in the chemical industry for the synthesis

20 20 Joanna Czarnocka of phenol-formaldehyde resins and the guaiacols may find application in the pharmaceutical industry. By further processing of the bio-oil, esters may be obtained. The bio-oil upgrading process was carried out in a closed-type reactor, at a temperature of about 230 C, with powdered zinc being used as a catalyst. The reaction medium consisted of ethanol and formic acid. The formic acid-to-ethanol and catalyst-to-bio-oil ratios were 1:1 and 5:1, respectively. When the reaction was completed, the reactor was cooled to the room temperature. The ethanol was vaporized from the reaction mixture in a rotary evaporator at a temperature of 60 C. After the evaporation, the upgraded bio-oil was separated by decantation. An identification procedure indicated that the upgraded bio-oil contained about 83 % of long-chain esters of fatty acids (with more than 10 carbon atoms in a molecule). This seems to be a good method for the obtaining of a valuable fuel biocomponent in the form of esters of fatty acids from non-oily raw materials. 3. Recapitulation The examples presented to illustrate the use of microwave-assisted pyrolysis show that the pyrolysis of biomass may be an effective method for the obtaining of substrates for chemical and fuel industry applications. Regardless of the type of the biomass processed, a several common features of the pyrolysis processes may be distinguished, i.e. fast heating to high temperatures, short process time, and use of activated carbon or another substance as a microwave energy absorber. By appropriate setting of process conditions and selection of an appropriate type of the biomass to be processed, two major utility products, i.e. synthesis gas (syngas) and bio-oil, may be obtained. The raw bio-oil should be subjected to further processing, e.g. hydrogenation or esterification, and only then it may find application as a usable fuel component. The syngas obtained from the pyrolysis may be used as a substrate for chemical synthesis reactions. The microwave pyrolysis is a more productive syngas production method than the conventional pyrolysis. Thanks to the fact that microwaves can heat materials throughout the entire material volume, the course of the pyrolysis process can be modified and the composition of the process products can be controlled. References [1] RUMIAN M.; CZEPIRSKI L.: Zastosowanie promieniowania mikrofalowego w technologii adsorpcyjnej (The use of microwave radiation in adsorption technology). Przemysł Chemiczny, 84/5 (2005), pp [2] YIN C.: Microwave-assisted pyrolysis of biomass for liquid biofuels production. Bioresource Technology, 120 (2012), pp [3] GOUVEIA L.; OLIVEIRA A. C.: Microalgae as a raw material for biofuels production. J. Ind. Microbiol. Biotechnology, 36, 2009, pp [4] LEI H. et al.: Microwave pyrolysis of distillers dried grain with solubles (DDGS) for biofuel production. Bioresource Technology, 102 (2011), pp

21 The use of microwave pyrolysis for biomass processing 21 [5] SALEMA A. A.; ANI F. N.: Microwave induced pyrolysis of oil palm biomass. Bioresorce Technology, 102 (2011), pp [6] DU Z. et al.: Microwave-assisted pyrolysis of microalgae for biofuel production. Bioresource Technology, 102 (2011), pp [7] HU Z. et al.: A study on experimental characteristic of microwave-assisted pyrolysis of microalgae. Bioresource Technology, 107 (2012), pp [8] BENEROSO D.; BERMUDEZ, J. M.; ARENILLAS, A.; MENENDEZ, J. A.: Microwave pyrolysis of microalgae for high syngas production. Bioresource Technology, 144 (2013) pp [9] DOMINGUEZ A. et al.: Conventional and microwave inducted pyrolysis of coffee hulls for the production of a hydrogen rich fuel gas. J. Anal. Appl. Pyrolysis, 79 (2007), pp [10] RAVEENDRAN K.; GANESH A.; KHILAR K. C.: Influence of mineral matter on biomass pyrolysis characteristics. Fuel, 74 (1995), pp [11] BU Q. et al.: Production of phenols and biofuels by catalytic microwave pyrolysis of lignocellulosic biomass, Bioresource Technology, 108 (2012), pp

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23 CAPABILITIES AND LIMITATIONS OF TORQUE VECTORING SYSTEMS (WHICH CORRECT THE DIRECTION OF MOVEMENT BY WHEEL DRIVING FORCES) IN MOTOR VEHICLES JAN DZIDA 1 University of Bielsko-Biała Summary The presentation covers the idea and purpose of the systems that influence vehicle s drive direction by torque vectoring. Based on results of model simulations and experimental testing of existing systems, the effectiveness of such systems has been shown. The basic variants of Torque Vectoring systems, capable to fit in wheeled vehicle s single drive axle, have been presented and compared with each other. Particularly much attention has been dedicated to the description and analysis of the group of designs referred to as active differential gears, featuring an additional inner kinematic bond. A few known designs of this kind, including those available in the market, have been described in detail. A comparison between them has highlighted significant differences in their kinematic layouts and control systems. The author has also tried to define directions of further development and standardization of the active differential gears. A particular design of such differential gears applied to electric and hybrid vehicles has been discussed and an author s own concept has been presented. In the final part, an attempt has been made to answer a question how the Torque Vectoring systems affect the active safety of motor vehicles, with highlighting the necessity of taking into account the capabilities of such systems in respect of the handling and transverse dynamics of a vehicle at post-accident simulations and analyses. Keywords: power split devices, active differential gears, vehicle handling, transverse dynamics 1. Introduction The impact of power split devices in wheeled vehicles on the direction of driving and the vehicle handling has been perceived for a very long time, or rather from the very outset of motorization. At first, it was found that two wheels of one axle, rigidly connected with each other by a shaft, caused significant difficulties in the vehicle turning and an increase in the resistance to motion when a vehicle moved along a curve. It was because of the necessity 1 University of Bielsko-Biała, Faculty of Mechanical Engineering and Computer Science, Department of Combustion Engines and Vehicles, ul. Willowa 2, Bielsko-Biała, Poland, jdzida@ath.bielsko.pl, tel

24 24 Jan Dzida to eliminate this drawback that an inter-wheel differential gear was invented over 100 years ago. However, differential gears in their simplest form brought new problems, including the one considered as probably most important, that is the worsening of vehicle s driving properties. To improve the situation, different methods of restraining the operation of differential gears were introduced, from various kinds of solutions referred to as differential locks to an extremely wide range of differentials with increased inner friction. A final effect of this period of development efforts was a situation that, depending on the degree of improving the vehicle s traction, the differential gear more or less impaired the handling and turning radius of the vehicle. This may be concisely expressed in a statement that until quite recently, the more advanced construction of the vehicle s differential(s) was, the worse handling and transverse dynamics characteristics of the vehicle were. Only the present-day look at the motor vehicle and giving the prime importance to the safety requirements resulted in raising other expectations about differential gear components, including in particular power split devices. An idea emerged to drive vehicle wheels in a way influencing the direction of vehicle movement, most often referred to as torque vectoring, with building special systems for active distribution of driving forces among vehicle wheels. Now it is known that the driving system can modify the direction of vehicle movement by changing the distribution of driving forces between front and rear axle wheels (in 4WD systems), by changing the distribution of driving forces between left and right wheels, or by employing both methods at the same time. In this presentation, most attention has been dedicated to the second method, which is implemented by applying solutions referred to as active differential gears. Thanks to special design, such mechanisms make it possible to direct a higher driving force to the wheel that rotates with a higher speed and thus to assist in making a turn by the vehicle (Fig. 1). Fig. 1. Distribution of driving forces between wheels in a turning vehicle, in the case of various differential gears: a) simple (open) differential; b) limited slip differential; c) active differential gear performing the torque vectoring function This means that the Torque Vectoring systems and their active differential gears can play an almost identical role as that played by the systems known previously, in most cases referred to as ESP (which stands for electronic stability program ), where braking forces are used for this purpose. However, the basic difference and, simultaneously, the