ALTERNATIVE METHODS OF TURBOCHARGER EFFICIENCY IMPROVEMENT

Transcription

1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 12, December 2017, pp , Article ID: IJMET_08_12_105 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed ALTERNATIVE METHODS OF TURBOCHARGER EFFICIENCY IMPROVEMENT Alexey Pavlovich Tatarnikov, Lev Yurievich Lezhnev, Dmitry Anatolyevich Petrichenko, Viktor Sergeevich Korotkov, Roman Viktorovich Stukolkin Moscow Polytechnic University, ul. Bolshaya Semenovskaya 38, Moscow, Russia ABSTRACT This article discusses negative environmental impacts occurring due to development in the field of internal combustion engines (ICE). Researches aimed at efficiency improvement of both vehicle energy assemblies and small-scale facilities are highlighted, negative factors and their influence on dynamic properties of ICE arising with the use of turbocharging are considered. Technical solutions are briefly analyzed with regard to modern turbocharging systems installed on commercial energy assemblies in order to improve dynamic properties of the engines. Alternative systems of efficiency improvement of turbocharging systems are described based on the use of accumulators of compressed air or waste gases as recuperative modules for subsequent supply of accumulated operating fluid into exhaust system, thus improving dynamic properties of turbocompressor. The use of electric drive or generator in turbocharging systems is considered, potentials of further development and use of such systems are discussed, and final conclusions are presented. Key words: Internal Combustion Engine, Efficiency, Turbocharging, Turbo Lag, Air Accumulator, Electric Turbocharging. Cite this Article: Alexey Pavlovich Tatarnikov, Lev Yurievich Lezhnev, Dmitry Anatolyevich Petrichenko, Viktor Sergeevich Korotkov, Roman Viktorovich Stukolkin, Alternative Methods of Turbocharger Efficiency Improvement, International Journal of Mechanical Engineering and Technology 8(12), 2017, pp INTRODUCTION In recent decades the intensive growth of technologies covered nearly all fields of human activities, also influencing global demography, the Earth population is expected to be increased by five times in comparison with the year of 2015 [1]. This resulted in significantly increased demand for energy which, on the one hand, increases its costs and, on the other hand, leads to intensification of researches in the field of improvement of energy efficiency and saving [1]

2 Andrey Mikhailovich Saykin, Sergey Evgenievich Buznikov, Denis Vladimirovich Endachev, Kirill Evgenievich Karpukhin, Alexey Stanislavovich Terenchenko Development of energy assemblies on the basis of thermal engines is widely applied both for vehicles and for small-scale facilities due to wide usage of hydrocarbon fuels, reliability and long operation lifetime as well as established production technology. In addition to improvement of efficiency of energy assemblies applied in car industry and small-scale power generation, the key development factor is improvement of their environmental properties. The issues of negative environmental impacts and approaches to their decrease gained attention only after depreciation of living standards and environment. Every year the oil production level and its consumption increase together with increase in amount of vehicles. Continuous enforcement of legislations for harmful pollution with waste gases of vehicle engines as well as limitation of industrial emissions lead to necessity to search for new technological approaches to creation of promising safe and efficient thermal engines. It should be mentioned that in two recent decades the requirements to harmful emissions of waste gases of vehicles became more stringent, further reinforcement with regard to harmful emissions by 50% is expected in future 15 years, thus promoting development of challenging technologies in the field of engine engineering. Current investigations in the field of ICE used as vehicle energy assemblies are aimed at increase in power-to-volume ratio and engine downsizing, increased torque in wide range of operational modes, especially at decreased rpm and decrease in harmful environmental emissions [2]. Downsizing as a trend of ICE development implies significant increase in power parameters, mostly by the use of turbocharging which influences positively on energy and cost efficiency of vehicle. Hence, current trend in development of engines is closely related with ICE turbocharging. If recently the turbocharger was installed mostly on diesel engines, then now more and more petrol ICE are equipped with turbochargers. ICE turbocharging is known for a long time, however, from its inception it was characterized by turbo lag, stipulated by inertia of rotor of turbocompressor upon sharp forcing of accelerator pedal. In other words, turbocompressor cannot immediately change for the required mode stipulated by preset consumption of charged air causing engine power fault. 2. METHODS Manufacturers of turbochargers both for petrol and diesel engines always attempted to solve the problem of turbo lag in order to improve dynamic characteristics. These attempts to overcome this issue include weight reduction of compressor rotor and decreasing its inertia, multiple charging systems are used on the basis of at least two turbocompressors, Twin-scroll turbines [3], as well as combined charging systems which allow to increase input pressure by means of driving units of the compressor itself (turbocompound) and displacement blowers. Since it is difficult to manufacture and to maintain a turbocompressor or a displacement blower involving high additional expenses, requirements to lubricants and maintenance increase, and the latest trends in the field of charging are aimed at cost reduction of turbocharging system, increase in efficiency of both compressor and turbine, development of combined charging systems (with electric or pneumatic driving units). Pneumatic system of compressor rotor boosting during transfer from idle to operation mode is used in Power Pulse system (Volvo) [4, 5]. This system is comprised of air compressor with electric drive, air accumulator and valve system which provides supply of compressed air to air accumulator and to the area of outlet collector. Upon start of vehicle motion compressed air under high pressure is charged into outlet collector where it is expanded, thus increasing pressure before compressor turbine wheel, significantly increasing gas pressure and flow rate via turbine wheel peculiar for this operation mode, increasing its editor@iaeme.com

3 Development of Russian Driverless Electric Vehicle rpm and power transferred to compressor wheel and increasing charging pressure. Comparison of power gain rate of reference ICE and ICE with Power pulse system is illustrated in Fig. 1. Figure 1 Power Pulse layout [6] An alternative method of improvement of dynamic characteristics of turbocharged ICE is proposed in Russian patent No. RU [7], which describes the system comprised of receiver installed in outlet collector between ICE and turbocompressor. The receiver is equipped with a set of valves which provide either free flow of waste gases to turbocompressor, or feeding waste gases to the receiver in order to accumulate them, or feeding accumulated gases from the receiver together with waste gases to turbocompressor. The proposed system is intended mainly for heavy trucks equipped with diesel engine with turbocharger. The system operates as follows: while the vehicle moves at constant speed, the ICE waste gases are fed directly to turbocompressor and actuate it; when the vehicle speed decreases, or before complete stop by motor braking, or during forced idle mode, the waste gases under pressure are fed directly to receiver for accumulation, herewith, direct flow of the waste gases to turbocompressor is prevented by closed valve. During start or during subsequent acceleration after forced braking and rpm drop the valve opens, which connects the receiver with turbocompressor, and the waste gases under pressure are fed to the compressor turbine wheel, thus increasing its rpm, increasing power on compressor shaft and charging pressure. A peculiar feature of the described system is that the receiver can be filled both by ICE waste gases and compressed air, when ICE operates in compressor mode without fuel supply. Schematic view of this system is illustrated in Fig editor@iaeme.com

4 Andrey Mikhailovich Saykin, Sergey Evgenievich Buznikov, Denis Vladimirovich Endachev, Kirill Evgenievich Karpukhin, Alexey Stanislavovich Terenchenko Figure 2 Flowchart of turbocharging system with receiver [7]: 1 - ICE cylinder, 2 - turbine wheel, 3 - compressor wheel, 4 - air filter, 5- muffler, 6 - shutdown valve, 7 - receiver inlet conduit, 8- receiver, 9 - receiver valve, 10 - reverse valve, 11 - receiver feeding circuit, 12 - control unit of valves In addition to pneumatic systems which briefly increase power on compressor shaft until the ICE waste gases are sufficient for required charging pressure, there exist systems with various designs of electric drives. This researching trend became important in recent fifteen years [8]. It became possible due to development in the field of electronic power units and electric assemblies with magnets on the basis of rare earth metals. The use of electric motors or generators in turbocharging systems either directly inside shell or as stand-alone unit (electric compressor, turbo electric generator) is more and more popular in vehicle industry and in power engineering. If some years ago only Formula 1 teams and R&D laboratories could afford such technologies, then at present this approach is considered by global car and turbocharging manufacturers, such as Volkswagen, Mitsubishi Heavy Industries, Borg Wagner Inc., Bowman Power group, Aeristech, Mahle etc. Application of electric motors together with impeller machines is possible in various modifications: electric compressor (c), turbogenerator is installed sequentially to turbocompressor (a), turbogenerator is installed parallel to turbocompressor (b), electric compressor is installed sequentially to turbocompressor (d), electric turbocompressor (e), and tandem of turbogenerator and electric compressor (f), Fig. 3 [9] editor@iaeme.com

5 Development of Russian Driverless Electric Vehicle Figure 3 Possible variants of combined electric turbocharging The advantage of electric motors in turbocharger is significant in comparison with conventional turbocompressor. The turbocompressors increase engine efficiency only in the modes which can operate only with waste gases generated by ICE. At present Volkswagen installs EPC (Electric Powered Compressor) on diesel engines equipped with two turbocompressors for its Audi SQ7 model, schematic view of this system and electric compressor is illustrated in Figs. 4 and 5. Figure 4 General view of turbocharging system of Audi SQ 7 engine with EPC [10] editor@iaeme.com

6 Andrey Mikhailovich Saykin, Sergey Evgenievich Buznikov, Denis Vladimirovich Endachev, Kirill Evgenievich Karpukhin, Alexey Stanislavovich Terenchenko Figure 5 General view of EPC [10] In the modes of constant low loads only one turbocompressor operates from one outlet valve per cylinder, herewith, when sharp boosting is required, the ECP is activated and increases charging pressure until turbocompressor reaches the required power, then the electric compressor is deactivated. The electric compressor (Valeo) rated for 48 V makes it possible to raise charging pressure to the required level nearly immediately and to provide the required engine power. Operation voltage of the electric compressor is selected purposefully, since at present there is the trend to increase nominal voltage of in-vehicle network due to increasing number of electric devices and vehicle hybridization. Thus, Valeo company uses the voltage of 48 V for its coolant electric pumps, oil pumps, electric fans for engines and cooling systems of energy accumulators, electric generators with starting function, electric drive of vehicle rare axle, according to expert forecasts most of these systems will be used in commercial vehicle models to the year of 2020 [11]. Most turbocompressors are equipped with wastegate valve, which provides bypassing of a portion of waste gases by the turbine wheel in order to maintain preset power on compressor shaft and, hence, to maintain preset charging pressure at preset air flow rate. Thus, the waste gases bypassing the turbine do not execute useful work while possessing such possibility. Similarly, the turbocompressor should provide higher charging pressure while starting. If the power, lost on turbine wheel due to bypassing of waste gases, could be transformed into electricity and stored in accumulator, then, while vehicle starts, this energy would provide the required pressure immediately due to boosting of compressor rotor by electric motor, the high rate of achievement of engine power and more efficient use of the obtained energy only when it is necessary. An electric turbogenerator is the assembly comprised of turbine part of turbine generator connected by shaft with electric generator. When waste gases are supplied, the shaft starts its rotation, and the electric generator produces energy. The difficulty of the turbogenerator development is that the turbine wheel has small sizes for small engines, hence, in order to editor@iaeme.com

7 Development of Russian Driverless Electric Vehicle obtain required power the shaft should be boosted to rpm, which is very high value for electric machines and bear units. One more variant is installation of reducer in order to decrease rpm on the shaft of electric generator, though development of such reducer is very difficult due to high rpm of input shaft. However, with increase in engine volume the flow rate of waste gases increases, thus leading to increase in size and weight of turbine wheel and, hence, decrease in rpm. In addition to turbine rpm, the cost of axial turbines upon installation is not extremely high in comparison with total cost of energy assembly, therefore, they are installed more frequently on centrifugal turbines on large assemblies with the power of more than kw. As another alternative let us consider turbogenerators. The turbogenerator by Bowman Power group was developed for installation on diesel engines with turbocharging in engine generator assembly with the power of 300 kw and higher. Figure 6 illustrates the ETC 1000 turbogenerator with the power of 110 kw at rpm. Figure 6 Bowman Power ETC turbogenerator 1000 With comparatively moderate dimensions and weight, this turbogenerator provides significant gain in electrical power. According to the data by manufacturers, the turbogenerator generates additional 10% of overall electric power of the assembly, thus reducing fuel consumption to 7%, and in small-scale power generation this is very significant result. Turbogenerator electric power as a function of diesel generator power is illustrated in Fig editor@iaeme.com

8 Andrey Mikhailovich Saykin, Sergey Evgenievich Buznikov, Denis Vladimirovich Endachev, Kirill Evgenievich Karpukhin, Alexey Stanislavovich Terenchenko Figure 7 Turbogenerator electric power as a function of diesel generator power During the operation time of Bowman Power turbogenerators, they generated more than 518 GWh of energy, which otherwise was dissipated with waste gasses [12]. 3. RESULTS This overview of alternative systems of efficiency improvement of turbocharging and energy assemblies in general demonstrated that both small-scale R&D centers and large car holdings are involved in the investigations, very soon the considered systems will be used in commercial production models. The performed analysis revealed the trend of global manufacturers of electronic components to more intensive electrification of ICE units and mechanisms, such as oil pump, cooling fluid pump and so on, as well as the trend to increase vehicle network voltage up to 48 V. This increase would promote integration of electric components and drives, thus allowing to simplify installation of electric accumulators and small-scale electric drives on vehicle non-driving axle. 4. CONCLUSION Technological development in the field of electronics, electric engines, power accumulators based on rare earth metals influenced possible applications of electric components in the systems of gasdynamic charging both for vehicle energy assemblies and for small-scale power facilities. In the nearest future alternative systems of turbocharging efficiency improvement of ICE will be used on production models with increasing frequency. 5. ACKNOWLEDGMENTS This work was financially supported by The Ministry of Education and Science of the Russian Federation within subsidiary grant agreement no (September 29, 2016; unique identifier of applied research (project) RFMEFI57716X0213) editor@iaeme.com

9 Development of Russian Driverless Electric Vehicle REFERENCES [1] Khripach, N.A., Lezhnev, L.Yu., Papkin, B.A., Shustrov, F.A., Tatarnikov, A.P. and Tingaev, N.V. Analysis of constructions providing the maximum thermodynamic effectiveness of reciprocating engines. Izvestiya MGTU MAMI. Scientific journal, 2(14), 2012, pp [2] Tatarnikov, A.P., Shustrov, F.A., Lezhnev, L.Yu., Petrichenko, D.A. and Papkin, I.A. Combined supercharging systems and down-sizing as the modern trends in the development of vehicle engines. International Journal of Applied Engineering Research, 11(22), 2016, pp [3] Walkingshaw, J., Iosifidis, G., Scheuermann, T., Filsinger, D. and Ikeya, N. A Comparison of a Mono-, Twin-, and Double-Scroll Turbine for Automotive Applications. Journal of engineering for gas turbines and power-transactions of the asme, 13(5), 2016, pp. 8. [4] PowerPulse animation. Volvo Car Group. Dec 02, [5] Volvo Cars announces range of updates for model year Volvo Car Group, Feb 25, [6] New Volvo XC60 unveiled at Geneva [7] Patent RU Control system of transport diesel turbocompressor with receiver; IPC F02B 37/04, F02B 37/14; published [8] Khripach, N., Papkin, B., Korotkov, V., Ivanov, D. and Nekrasov, A. Trends in the Development of Combined Supercharging Systems for the Internal Combustion Engine. International Journal of Applied Engineering Research, 1(22), 2016, pp [9] Arshad-Ali, S. K. Suitability of Hybrid Electric Powertrains with Electric Turbochargers (Master s Thesis). McMaster University, Hamilton, Ontario, [10] Audi SQ7 TDI - Animation EPC and 48 volt electrical subsystem. Audi MediaCenter, [11] Valeo Investor Meeting, September [12] Get more power with improved fuel efficiency. Benefits. More power. [13] G. Chiatti, O. Chiavola, E. Conti and E. Recco, Automotive turbocharger speed estimation via vibration analysis for combustion optimization, International Journal of Mechanical Engineering and Technology 8(10), 2017, pp [14] K. M. Ravichandra, D. Manikanta, M. Kotresh, CFD Simulation of an IC Engine by Producer Gas. International Journal of Civil Engineering and Technology, 8(10), 2017, pp editor@iaeme.com