DRAFT IMECE

Transcription

1 Proceedings of IMECE7 27 ASME International Mechanical Engineering Congress and Exposition November -6, 27, Seattle, Washington, USA DRAFT IMECE D MODEL AND EXPERIMENTAL TESTS OF PRESSURE WAVE SUPERCHARGER Luděk Pohořelský Josef Božek Research Center Czech Technical University in Prague Technicka 4,CZ-66 7 Praha 6 Phone Fax ludek.pohorelsky@fs.cvut.cz Philippe Obernesser RENAULT TCR GRA 85-, avenue du Golf Guyancourt cedex, France tel: fax: philippe.obernesser@renault.com Jiří Vávra Josef Božek Research Center Czech Technical University in Prague Technicka 4,CZ-66 7 Praha 6 Phone Fax jiri.vavra@fs.cvut.cz Vojtěch Klír Josef Božek Research Center Czech Technical University in Prague Technicka 4,CZ-66 7 Praha 6 Phone Fax vojtech.klir@fs.cvut.cz Jan Macek Josef Božek Research Center Czech Technical University in Prague Technicka 4,CZ-66 7 Praha 6 Phone Fax jan.macek@fs.cvut.cz ABSTRACT In this contribution an interesting boosting device, called pressure wave supercharger (PWS) according the wave phenomena inside it and taking advantage of speed of sound for air compression, is investigated both at diesel engine and at combustion chamber test bench using -D simulation and experimental measuring. Moreover, combustion engine supercharged by PWS has been compared using -D simulation to turbocharged one at steady state and transient operations. Pressure wave supercharger is simulated using detailed model based on the partial differential equations capturing non-linear effects of gas dynamics. The work has been performed using the commercial -D code GT-Power. Concept of modeling used enables to integrate the PWS model with all other models which are already created in the commercial codes (like more precise model of combustion, vehicle model, etc.) The PWS takes advantage of the direct pressure and enthalpy exchange between exhaust gases and fresh air in narrow channels to provide boost pressure. Due to the direct contact between exhaust gas and fresh air a mixing occurs. Nevertheless, this internal recirculation of exhaust gas can be used for lowering of NOx emissions, but in the same time it could deteriorate engine power as the result of a lack of oxygen. The internal mixing has been investigated using -D simulation and different possibilities to avoid mixing have been tested. The PWS has showed during the simulation work behavior it could fulfill demand on a modern car propulsion system. Finally PWS measurements with a combustion chamber have been undertaken and compared to the -D simulation results. Using the results of PWS measurement at the test bench and the -D simulation the usage of PWS in fuel cell applications is discussed, as well. This work is resulting from the collaboration between Josef Božek Research Center and Renault SA. Keywords: -D code simulation, pressure wave supercharger, diesel engine, test bench, flow characteristics, fuel cell INTRODUCTION Current research activities on new propulsion systems insist on the increase of their efficiency and power. On the other hand the stake consists in reducing the fuel consumption and the level of the pollutants produced by such new concepts. Lowering of emission of the green house gas CO 2 forces Copyright 27 by ASME

2 manufactures to develop more economical vehicle and therefore more efficient engines. Moreover, in case of car propulsion systems the satisfactory driveability to satisfy driver s demands during the accelerations has to be provided at the same time. An approach of utilization of downsized propulsion systems may lead successfully up to these aims. The main idea of downsizing is the reduction of the swept volume of the engine without lowering the original output power. The performance increase of the downsized engine to the same power level of the original one is achieved by boosting devices. Engine researchers and developers are nowadays wondering, which boosting devices are the most suitable and so are trying to find compromises with regards to costs, packaging, engine behavior and emission regulations. In addition to commonly utilized turbocharger mechanical superchargers as for instance Roots-type supercharger are more and more placed on the market. In comparison with these boosting devices the pressure wave supercharger (PWS) with usage of today s control possibilities represents mainly in transient and low-end torque behavior an extraordinary possibility. The PWS takes advantages of a unique principle of direct pressure energy exchange between the exhaust gas and the fresh air in a narrow channel using nearly -D unsteady flow with a distinctive contact surface between the both gases. The idea of the energy exchange between two mediums without any separation goes down to the beginning of the 2 th century. Namely in its second decade, along the longitudinal axis perforated drum, a channeled rotor, has been patented by the German engineer Burghard - [24] - a machine delivering an uninterrupted mass flow of the pressurized air. As the unsteady flow theory, a necessity for the development of a usable machine has not been developed until the 92 s and 93 s, the Burghard s invention did not succeed to an available device. In the 94 s, the Brown Boveri (BBC, today ABB) turbocharger engineer Seippel designed a pressure exchanger as an air compressor of a gas turbine used as the propulsion of an experimental locomotive - [28]. He started to call this exchanger COMPREX according to the processes in the rotor compression-expansion. In the 95 s took place first experimental attempts in using COMPREX for supercharging of truck diesel engines - [2], [26], in framework of partnership among the ETH Zürich, the I-T-E Circuit Breaker Company, the BBC and the Saurer Company. In the 97 s, first experiments of COMPREX supercharged car diesel engines followed (partnership between BBC and Mercedes-Benz) [3]. In 979 BBC developed a race version of PWS for supercharging of F engine [], which has been used only for the practice runs. In 995, the Swissauto Wenko Company, which is dealing with development of pressure wave supercharger up to now - [9], designed for the environmental organization Greenpeace a so-called SmiLE car with SI engine with displacement of 36cm 3 and PWS supercharging [2]. Moreover, in 98 s many companies tested the COMPREX - supercharged diesel engines, but only two started the serial production. The Opel Company sold in a special Opel Senator set of about 7 units with 2.3l diesel engine and pressure wave supercharging [3] whereas Mazda sold about 5 COMPREX diesel passenger cars [4]. Recently, several Universities (ETH Zürich, Indiana University Purdue University Indianapolis, Michigan State University, University of Tokyo, Warsaw University and Beijing University of Technology), companies (Swissauto Engineering S.A., Rolls Royce Alison) and governmental research centers (NASA) investigate pressure wave process intensively for various thermal applications. In [4] a comprehensive review of past and current research in developing of wave rotor technology is explained in more details and in a well arranged way. In framework of our study the PWS has been investigated and analyzed at first using -D diesel engine simulation. Then by means of experimental tests at the test bench to find out whether the pressure wave supercharging with regard to today s state of art in control, actuation, materials and technology could fulfill requirements on a modern and perspective car propulsion system and become a serious competitor to current boosting systems. -D SIMULATION OF PWS SUPERCHARGED DIESEL ENGINE For the study the Renault.5 diesel engine has been used for -D investigations to compare PWS supercharged engine to the turbocharged one. Stroke 8.5 mm Bore 76 mm Total swept volume 46 cm3 Number of cylinders 4 Compression ratio 6: Combustion system 2valves/cylinder Direct injection Table : Diesel engine parameters -D model of PWS used, whose qualitative reaction to changes in design are in good agreement with published sources [],[2] and with a simple model based on the theory of adiabatic shock waves and on the linear gas dynamics principles, has been created in commercial code GT-Power and is introduced and described in detail in [37]. Simulation of Full Load of Engine with PWS Diagrams in Figure -Figure 7 point out comparisons of PWS supercharged engines with turbocharged one. PWSs with unity length-to-diameter ratio of rotor (quadratic design) have been simulated. The PWS sucks more air into its channeled rotor than it compresses and delivers to the engine cylinder [25]. This fresh air scavenges and cools down the rotor and 2 Copyright 27 by ASME

3 flows direct to the low pressure part of exhaust manifold PWS downstream. Therefore, the diameter of fresh air pipings and diameter of exhaust pipings PWS downstream have been enlarged in comparison to turbocharged engine. (In this study the diameter of particular pipings equals to 75% of PWS rotor diameter.) Air fuel ratio for PWS supercharged engines has been kept the same as for turbocharged engine. Proper function of PWS depends on the control geometry (i.e. location of inlet and outlet orifices at the air and exhaust flanges of PWS).Two different types of control geometry have been simulated: control geometry previously optimized by method of characteristics based on the linear gas dynamics [37] and patented geometry from Swissauto Engineering S.A. [7] The PWS speed has been optimized to reach maximum engine torque at each operation point. Boost pressure behavior is presented in Figure. The smaller the PWS the higher boost pressure can be achieved. The PWS7 (i.e. with rotor diameter and rotor length of 7 mm) achieves the highest boost pressure. The usage of the control geometry from Swissauto Company at and PWS95 increased the boost pressure significantly. Boost pressure [bar] Boost pressure comparison _patented_swissauto_geometry PWS7 PWS95 Turbo PWS95_patented_Swissauto_geometry Engine speed [/min] Figure : Comparison of PWS and turbocharger boost pressure In comparison to boost pressure, the engine torque (Figure 2) of PWS supercharged engines falls down at highest engine speeds. This is caused by internal exhaust gas recirculation (Figure 3) over the channeled rotor of PWS, which deteriorates the engine torque. Due to the direct contact of exhaust gas and fresh air, the exhaust gas can be delivered direct to the engine cylinder together with the compressed air. The smaller PWS the higher internal exhaust gas recirculation. Torque [N.m] Engine torque comparison 4 _patented_swissauto_geometry 2 PWS7 PWS95 Turbo PWS95_patented_Swissauto_geometry Engine speed [/min] Figure 2: Comparison of engine torque Figure 4 presents the indicated specific fuel consumption. As the computation model of combustion for PWS supercharged engines was the same as in case of turbocharged engine (i.e. it did not take into account the increased amount of exhaust gas in the engine cylinder) the differences in indicated specific fuel consumption are given only by pumping work during the cylinder exchange. Figure 4 and Figure 5 demonstrate favorable behavior of the exhaust back pressure of the PWS supercharged engines. Up to the middle engine speed the boost pressure is distinctly higher than the back pressure. EGR [%] Exhaust gas recirculation into engine cylinder _patented_swissauto_geometry PWS7 PWS95 PWS95_patented_Swissauto_geometry Engine speed [/min] Figure 3: Exhaust gas recirculation into engine cylinder of PWS engines ISFC [g/kw/h] Idicated specific fuel consumption _patented_swissauto_geometry PWS7 PWS95 Turbo PWS95_patented_Swissauto_geometry Engine speed [/min] Figure 4: Comparison of indicated specific fuel consumption 3 Copyright 27 by ASME

4 Pressure [bar] Boost pressure and exhaust back pressure Turbo-boost pressure PWS95_patented_Swissauto_geometry-boost pressure Turbo-back pressure PWS95_patented_Swissauto_geometry-back pressure Engine speed [/min] Figure 5: Boost pressure and back pressure behavior PWS Speed Figure 6 shows the PWS speed characteristics. As the time of pressure wave propagation from exhaust to air side decreases with the reduction of the PWS size, the smallest PWS achieves the highest speeds. Diagrams on Figure 7 present dependences of the engine toque, boost pressure, indicated specific fuel consumption and the exhaust gas recirculation on the PWS speed. Each observed quantity achieves its optimum at a certain PWS speed. The increase of the PWS speed contributes to the lowering of the exhaust gas recirculation. PWS speed [/min] PWS speed optimized for maximum engine torque PWS7 PWS Engine speed [/min] Figure 6: PWS speed characteristics Engine torque [N.m] 2 5 Influence of PWS speed on engine parameters -engine torque -boost pressure PWS speed [/min] Boost pressure [bar] ISFC [g/kw/h] Influence of PWS speed on engine parameters -ISFC -EGR PWS speed [/min] Figure 7: Dependence of engine parameters on PWS speed for engine speed of 5rpm Variable Gas Pocket In order to extend the operating range of the PWS, so called pocket in the inner face of air and exhaust flanges have been patented by BBC in the 96 s. Compression pocket, expansion pocket and gas pocket (Figure 8) by pass the gas between the channels and the control orifices and thus improve EGR [%] the operation of the supercharger away from the optimum (tuned) point. Moreover, the gas pocket can be used in function of the waste-gate for control of the boost pressure. Variable Gas Pocket Exhaust inlet orifice Exhaust outlet orifice Exhaust Flange Channel Low-Pressure part Air inlet orifice Expansion Pocket Air outlet orifice High-Pressure part Compression Pocket Air Flange Figure 8: Pressure wave diagram and variable gas pocket in function of waste gate The variable gas pocket bypasses pressurized exhaust gas to the exhaust outlet via the rotor channel. The bypassed exhaust gas amplifies the expansion wave in the low-pressure part, which provides better fresh air suction into channeled rotor. The function and efficiency of the variable gas pocket have been confirmed by means of the simulation. Simulation results presented in Figure -Figure 7 show turbocharger controlled by the variable turbine geometry, whereas the boost pressure of PWS has not been controlled. Diagrams on Figure 9 show results of boost pressure control for PWS95 with the variable gas pocket at highest engine speeds (Figure 9 left). Moreover, utilization of the variable gas pocket for boost pressure control contributes to the lowering of the internal exhaust gas recirculation (Figure 9 right). Boost pressure [bar] Boost pressure control by variable gas pocket PWS95 w/o VGP control PWS with VGP Engine speed [/min] EGR [%] Influence of gas pocket control on the internal gas recirculation Engine speed [/min] PWS95 w/o VGP control PWS with VGP Figure 9: Influence of variable gas pocket control (VGP) on the boost pressure and internal exhaust gas recirculation Influence of Flow Losses Figure describes influence of flow losses on the PWS behavior. Flow losses have been increased by changing inlet (Air inlet orifice upstream -Figure 8) and outlet (Exhaust outlet orifice downstream -Figure 8) pipings diameters from 75% to 4% of PWS rotor diameter. From the -D simulation follows that to throttle the air inlet and exhaust outlet of PWS deteriorates scavenging of the PWS 4 Copyright 27 by ASME

5 rotor by increasing internal exhaust gas recirculation, and consequently lowers engine torque considerably. Internal exhasut gas recirculation during transient Engine torque comparison Torque [N.m] _pipings with diameter of 75% of PWS rotor diameter _pipings with diameter of 5% of PWS rotor diameter _pipings with diameter of 4% of PWS rotor diameter Engine speed [/min] Figure : Influence of flow losses on the PWS engine torque Transient Simulation of Engine with PWS To investigate the transient response of PWS supercharged engine the engine torque vary from the low load to full load at a constant engine speed. The load of engine was defined to be equal to the instantaneous engine torque, which prevents speed changes. Since the engine torque rises during the load step faster than the engine speed, this test of dynamic behavior corresponds to the first instant of vehicle acceleration. EGR [%] Time [sec] Figure 3: Internal exhaust gas recirculation in transient operation During the simulation of spark-ignited engine, presented in [38], more considerable deterioration of engine torque appeared than in case of.5 diesel engine. Change of PWS speed (Figure 4 right) during the transient operation was an efficient remedy to improve engine torque behavior (Figure 4 left) and to decrease the internal exhaust gas recirculation in transient operation. Boost pressure response.8.2 SI Engine torque response PWS speed control during the load step Boost pressure [bar] Turbo Time [sec] Figure : Boost pressure response for.5 diesel engine with at engine speed of 25 rpm The PWS boost pressure increases steeper than the turbocharger one (Figure ). During the load step an increased internal exhaust gas recirculation appears (Figure 3), this is the reason of the decreasing delay at the middle of the load step between the PWS supercharged and turbocharged engine (Figure 2). Engine torque [N.m] Engine torque response Turbo Time [sec] Figure 2: Torque response for.5 diesel engine with at engine speed of 25 rpm Engine torque [N.m] _constant_speed Turbo _with_speed_control Time [s] Time [s] Figure 4: Engine torque and its remedy during the load step of spark ignited.2l engine at engine speed of 2rpm from [38] EXPERIMENTAL TESTS ON PWS For the engine -D simulation, presented in this paper, a PWS model has been used, whose physical behavior was representative enough. From the -D engine simulation a favorable PWS low end torque behavior and transient response arise. Moreover, the PWS could be with advantage used for control of quantity of recycled exhaust gas to combustion engine. However, the internal exhaust gas recirculation, boost pressure and mass flow value should be checked and settled to enable the model. Therefore, to keep developing -D model of supercharging system with PWS the PWS operating points have been tested and measured at the combustion chamber test bench with open circuit (Figure 5). The specimen of tested PWS was model CX93 used by Mazda Company for supercharging of 2.l diesel engine [27]. In framework of experimental testing of PWS the mass flow range at PWS air inlet (AI), air outlet (AO) and exhaust inlet (EI), the PWS speed range and range of the PWS exhaust inlet (EI) temperature have been largely explored. 5 Copyright 27 by ASME

6 Electrical motor Mass flow control m2 ( to 2g/s) p 2 T 2 (RPMc from to 2) p m 2, C AO AI m p pressure control ( to 3b) Tatm Noise Figure 5: Scheme of the test bed p 3 T 3 EI EO Mass flow control m3 ( to 2g/s) p 4 m 3, C Backpressure floodgate p4 pressure control ( to 3 b) The PWS test bench has been created using the existing turbocharger test bench (equipped with the combustion chamber and the external source of constant boost air pressure of 35 kpa and mass flow up to approximately kg/h) and its adopting for PWS tests at Josef Božek Research Center (JBRC) - Figure 6. All temperature measurements have been carried out by electrically isolated thermocouples. The most problematic temperature measurement was the temperature T 3 at EI after the combustion chamber. Therefore, five thermocouples have been utilized to obtain the temperature distribution within the manifold. To estimate the internal exhaust gas recirculation of PWS molar fractions of CO 2 at EI and AO have been measured by means of exhaust gas analyzer. The PWS has been driven directly by electrical motor, whose speed has been controlled by frequency converter and could vary between -2 rpm. The PWS speed has been measured using optical sensor. As the PWS had to be braked in specific operation regimes, the brake resistors had to be additionally connected to the frequency converter. In framework of this project a new automated data acquisition system has been developed under the Testpoint development environment, which enabled to display all instant measured values and control panel with diagrams showing their trends (Figure 7). DAQ Control Panel with time history diagram for settling identification EI AI AO EO Gas analyzer display Figure 7: Displays of measured values and DAQ software control panel with time history diagrams. Figure 6: PWS at the combustion chamber test bed Mass flow and temperature have been enforced at the exhaust inlet (EI). EI mass flow was continuous and has been varied between -2 g/s. Air outlet (AO) and exhaust inlet (EI) mass flows have been controlled separately by means of remotely controlled slide valves enabling precise tuning of flows. Mass flow at air outlet (AO) has been controlled at the same value as that of exhaust inlet (EI). The temperature has been scanned from 8K to 5K at exhaust inlet. Measuring of EI and AO mass flows has been performed using metering orifices in pipelines. AI mass flow has been measured using intake nozzle. Performance maps of measured PWS Diagrams on Figure 8-Figure 23 show performance maps for exhaust inlet temperature of 9K. The total PWS efficiency, AO temperature, internal exhaust gas recirculation, air inlet mass flow and electrical input to PWS are depicted legible in form commonly used for turbochargers, so these maps can be with advantage used for direct comparison to turbochargers maps. From the flow characteristics diagram on Figure 8 the influence of PWS speed on boost pressure ratio is clearly visible. For PWS speed from 4 rpm to 8 rpm the highest PWS total efficiencies are achieved (Figure 9). Lowering of the PWS speed decreases the PWS efficiency and increases the boost pressure (Figure 8). From a certain mass flow, here for mass flow higher than 55kg/h, the PWS boost pressure ratio falls abruptly down. 6 Copyright 27 by ASME

7 Figure 8: PWS performance map of PWS speed for EI temperature of 9K Internal exhaust gas recirculation over the channeled rotor is presented in Figure 2. In the PWS speed range from rpm to 2rpm no recirculation appears up to the mass flow of 4kg/h. The AO temperatures traces are shown in Figure 2. Up to the PWS speed of 6 rpm the increase of PWS speed decreases the AO temperature. AO temperature starts to rise significantly bellow the PWS speed of rpm. The PWS sucks in AI much more fresh air than it delivers to the air outlet. Amount of sucked fresh air increases with the increase of the AO mass flow (Figure 22) whereas for the EI mass flows from 4 to 65 kg/h there is no considerable difference between the sucked amounts of fresh air into PWS. The diagram on Figure 23 presents power input to the electrical motor, which drives the PWS. The negative sign of the power input means that the PWS drives the el. motor. Figure 2: PWS performance map of internal exhaust gas recirculation for EI temperature of 9K Figure 2: PWS performance map of air outlet (AO) temperature for EI temperature of 9K Figure 9: PWS performance map of PWS total efficiency for EI temperature of 9K Figure 22: PWS performance map for air inlet mass flow for EI temperature of 9K 7 Copyright 27 by ASME

8 A lower EI mass flow is necessary with EI temperature increase to achieve the same EI pressure (Figure 25). The increase in EI temperature decreases the internal exhaust gas recirculation (Figure 26) and deteriorates the PWS efficiency (Figure 27)..5.4 egr [].3.2. Figure 23: PWS performance map for electrical power input/output of PWS for temperature of 9K Influence of the temperature at PWS exhaust inlet Diagrams in Figure 24-Figure 27 present influence of the EI temperature for four different levels of EI pressure p3 (.5, 2, 2.5 and 3 bar - absolute). The PWS operation points have been measured for EI temperature of 8K, 9K and 5K. The increase of the EI temperature increases the boost pressure. The highest EI temperature of 5K extended the range where the boost pressure is higher than the back pressure p3 (Figure 24). 2 Relative pressures p3=5kpa T3=8K p3=kpa T3=8K p3=5kpa T3=8K p3=2kpa T3=8K p3=5kpa T3=9K p3=kpa T3=9K p3=5kpa T3=9K p3=2kpa T3=9K p3=5kpa T3=5K p3=kpa T3=5K p3=5kpa T3=5K p3=2kpa T3=5K Figure 26: Internal exhaust gas recirculation in dependence on EI temperature etapws [] p2 [kpa] T3=8K p3=5kpa p3=5kpa T3=8K p3=kpa T3=8K p3=2kpa T3=8K p3=5kpa T3=9K p3=kpa T3=9K p3=5kpa T3=9K p3=2kpa T3=9K p3=5kpa T3=5K p3=kpa T3=5K p3=5kpa T3=5K p3=2kpa T3=5K Figure 24: Boost pressure in dependence on the EI temperature m3 [kg/h] T3=8K p3=5kpa p3=5kpa T3=8K p3=kpa T3=8K p3=2kpa T3=8K p3=5kpa T3=9K p3=kpa T3=9K p3=5kpa T3=9K p3=2kpa T3=9K p3=5kpa T3=5K p3=kpa T3=5K p3=5kpa T3=5K p3=2kpa T3=5K Figure 25: EI mass flow in dependence on the EI temperature p3=kpa T3=8K p3=kpa T3=9K p3=kpa T3=5K Figure 27: Total efficiency of PWS in dependence on EI temperature Influence of Flow Losses in Air Inlet The influence of the flow losses in AI has been investigated at EI temperature of 9K and PWS speed of 5 rpm for two orifice plates with diameters of 35 mm and 5 mm (origin AI manifold diameter of mm). The orifice with diameter 35 mm deteriorates the boost pressure significantly above the mass flow of 4 kg/h. The throttling of the AI mass flow increases the AO and EO temperatures and the internal exhaust gas recirculation. On the other hand, the reduction of the AI mass flow improves the PWS efficiency at low EI mass flow rates (Figure 29 left). All diagrams described in above paragraphs have been measured without boost pressure control using waste gate (WG). Diagrams in Figure 28 and Figure 29 show influence of waste gate control on PWS operation, as well. The waste gate trims the boost pressure and tries to keep it approx. constant (Figure 28 left). The waste gate does not influence the internal exhaust gas recirculation (Figure 29 right). 8 Copyright 27 by ASME

9 Flow losses 4 2 πc [] dia 35 mm dia 5 mm WG w / o Loss m 2red [kg/h] p [kpa] dia 35 mm dia 5 mm m 3 [kg/h] Figure 28: Influence of pressure losses (right) and waste gate on pressure ratio in dependence on reduced AO mass flow etapws [] dia 35 mm dia 5 mm WG w / o Loss m2, m3 [kg/h] egr [] m2, m3 [kg/h] dia 35 mm dia 5 mm WG w / o Loss Figure 29: Influence of pressure losses in AI manifold on PWS efficiency and internal egr Relative pressure p2 [kpa] 8 6 kg/h 3kg/h 4kg/h 5kg/h Absolute pressure p4 [kpa] Figure 3: Influence of the EO pressure on the boost pressure egr [] kg/h 3kg/h 4kg/h 5kg/h Influence of Flow Losses in Exhaust Outlet The EO pressure has been increased using throttle which has been controlled by stepper electric motor. A snail gear box has been placed between the throttle and the electrical motor to prevent throttle flapping by EO flow. PWS EO Figure 3: EO throttle controlled by stepper electrical motor with snail box Diagrams in Figure 3 and Figure 32 present the sensitivity of the PWS on the EO pressure for EI mass flows of (,3,4 and 5) kg/h and for EI temperature of 9K. The PWS speed has been kept at 5 rpm. The change in EO pressure by 2kPa deteriorates the boost pressure significantly (Figure 3). The increased EO pressure lowers the amount of sucked AI mass flow and increases the internal exhaust gas recirculation rises (Figure 32). Moreover, increased EO pressure may cause the back flow of the exhaust gas to the AI Absolute pressure p4 [kpa] Figure 32: Influence of the EO pressure on the AI mass flow Supercharging of the PWS In framework of the measurement the feasibility of the PWS for the two stage supercharging has been investigated. To enable pressure increase in AI the test bench has been equipped with inlet pipeline of pressurized air (Figure 33). External source could deliver constant boost air pressure of 35kPa and mass flow approx. of kg/h into AI. AI mass flow has been controlled using slide valve, which has been actuated by an electric stepper motor. Moreover, metering orifice has been placed into the AI pipeline. The measurement has been performed for EI mass flow of 3 kg/h and for two different PWS speeds of 5 rpm (Figure 34) and rpm (Figure 35). As in the all previous paragraphs the mass flow at air outlet (AO) has been controlled at the same value as that of exhaust inlet (EI). The EI temperature has been kept at 9K. For the fully opened EO throttle (Figure 3) the air inlet mass flow has been set to be the same as the naturally aspirated mass flow for this PWS operation point. By adjusting of the EO throttle the EO and AI pressures have been increased. 9 Copyright 27 by ASME

10 shown for EI mass flows of kg/h, 4kg/h and 5kg/h.) The -D model predicts maximal boost pressure higher than the measured one (Figure 36). The simulated difference between boost pressure and back pressure is higher and in larger PWS speed range than measured one. -D PWS model recirculates more exhaust gas than the real PWS (Figure 37 right). Boost and back pressure comparison Figure 33: Supercharging of PWS The boost pressure and EI pressure rise with the AI pressure increase both for rpm and 5rpm (Figure 34 and Figure 35 left).the boost pressure increases by the same value as that set at AI. The AI mass flow did not change with the AI pressure increase (Figure 34 and Figure 35 right). No internal exhaust gas recirculation appeared at both cases. Relative pressures [kpa] PWS Supercharging 5 rpm, m2=m3=3 kg/h, T3=9K p2_3 p3_3 p4_ Relative pressure p [kpa] m, m2, m3 [kg/h] Mass flows Relative pressure p [kpa] Figure 34: Influence of AI pressure on AO, EI and EO pressures and on AI mass flow for PWS speed of 5 rpm Relative pressures [kpa] Pipeline of pressurized air to PWS air inlet PWS Supercharging rpm, m2=m3=3 kg/h, T3=9K p2_3 p3_3 p4_ Relative pressure p [kpa] m, m2, m3 [kg/h] Mass flows Relative pressure p [kpa] Figure 35: Influence of AI pressure on AO, EI and EO pressures and on AI mass flow for PWS speed of rpm COMPARISON OF -D MODEL SIMULATION TO MEASUREMENT To compare the simulation results to measurements a -D model of the tested PWS at the test bench has been developped in GT-Power, whereas the PWS without pockets has been simulated. Analogous to experiment the mass flow at air outlet (AO in Figure 5) has been controlled at the same value as that of exhaust inlet (EI). Diagrams on Figure 36 and Figure 37 present comparison of boost pressure p2, back pressure p3, air inlet mass flow and internal exhaust gas recirculation for constant exhaust inlet mass flow of 3kg/h. (In Annex A the same comparison is m m2 m3 m m2 m p2-3kg/h-measured p3-3kg/h measured p2-3kg/h -D model without pockets p3-3kg/h -D model without pockets Absolute pressure [bar] Figure 36: Comparison of measured and computed pressures for EI mass flow of 3kg/h Mass flow [g/sec] Mass flow comparison m-3kg/h-measured m-3kg/h -D model without pockets m2-3kg/h -D model without pockets m3-3kg/h -D model without pockets EGR [] Internal exhaust gas recirculation egr-3kg/h-measured egr-3kg/h -D model without pockets Figure 37: Comparison of measured and computed AI mass flow and internal exhaust gas recirculation for EI mass flow of 3kg/h Diagrams on Figure 38 - Figure 4 compare -D simulation results for three different EI temperatures (8K, 9K and 5K) and for constant EI pressure of 2 bar Absolute. The qualitative reaction of the -D model on EI temperature change is in a good agreement with the measurement for every observed quantity. The boost pressure increases with the EI temperature. The maximal simulated boost pressure is for every temperature higher than the EI pressure (Figure 38). An increase of EI temperature increases the amount of fresh air which is sucked into the PWS (Figure 4) and decreases the internal exhaust gas recirculation (Figure 4). p2 [bar] Absolute boost pressure for absolute back pressure of p3=2bar p3=2bar T3=8K measured p3=2bar T3=9K measured p3=2bar T3=5K measured p3=2bar T3=8K -D model w/o pockets p3=2bar T3=9K -D model w/o pockets p3=2bar T3=5K -D model w/o pockets Figure 38: Comparison of measured and computed boost pressures for tree different EI temperatures and constant EI absolute pressure of 2bar Copyright 27 by ASME

11 m2 [g/s] Air outlet mass flow for absolute back pressure of p3=2bar p3=2bar T3=8K measured p3=2bar T3=9K measured p3=2bar T3=5K measured p3=2bar T3=8K D model w/o pockets p3=2bar T3=9K D model w/o pockets p3=2bar T3=5K D model w/o pockets Figure 39: Comparison of measured and computed air outlet mass flows for tree different EI temperatures and constant EI pressure of 2bar Absolute pressure [bar] Absolute pressure comparison p3-3kg/h with pockets p2-3kg/h with pockets p2-3kg/h-measured p3-3kg/h-measured p2-3kg/h without pockets p3-3kg/h without pockets Figure 42: Comparison of measured and computed pressures for EI mass flow of 3kg/h and -D PWS model with pockets m [g/s] Air inlet mass flow for absolute back pressure of p3=2bar p3=2bar T3=8K measured p3=2bar T3=9K measured p3=2bar T3=5K measured p3=2bar T3=8K D model w/o pockets p3=2bar T3=9K D model w/o pockets p3=2bar T3=5K D model w/o pocktes Figure 4: Comparison of measured and computed air inlet mass flows for tree different EI temperatures and constant EI absolute pressure of 2bar EGR [%].3.2. Internal exhaust gas recirculation for absolute back pressure of p3=2bar p3=2bar T3=8K measured p3=2bar T3=9K measured p3=2bar T3=5K measured p3=2bar T3=8K D model w/o pockets p3=2bar T3=9K D model w/o pockets p3=2bar T3=5K D model w/o pockets Figure 4: Comparison of measured and computed internal exhaust gas recirculations for tree different EI temperatures and constant EI absolute pressure of 2bar PWS model with all pockets has been simulated, as well (see diagrams on Figure 42 and Figure 43). Pockets extended the working range of the PWS model. Nevertheless, the modeled pockets increased the boost pressure in low PWS speed too much in comparison to measurement. Mass flow [g/sec] Mass flow comparison m3-3kg/h with pockets m-3kg/h with pockets m-3kg/h without pockets m2-3kg/h with pockets m-3kg/h-measured EGR [] EGR comparison egr-3kg/h with pockets egr-3kg/h without pockets egr-3kg/h-measured Figure 43: Comparison of measured and computed AI mass flow and internal exhaust gas recirculation for EI mass flow of 3kg/h and -D PWS model with pockets Presented and described comparisons in diagrams above indicate that the flow losses in the -D model of PWS rotor channel should be tuned with regard to pressure traces to come closer to the measurement. Following paragraph discusses the problematic of increased simulated exhaust gas recirculation in comparison to measurement. In the channel of the PWS rotor the fresh air and exhaust gas are in direct contact. GT-Power is based on the finite volume method. Thus, the -D model is discretized into many volumes and the solution is carried out by time integration of equations of continuity, energy and momentum. Finer discretization results in better accuracy and extends the computation time vice versa. Diagrams in Figure 44 and Figure 45 show influence of the discretization length on the simulated results. The influence has been investigated for constant mass flow of 3kg/h and EI temperature of 9K. By lowering of the dicretization length by one third of the original length (here to 5mm) the internal exhaust gas recirculation decreased by % (Figure 45) and the simulated boost pressure increased by 5%. At the same time the computation time has been.8 times longer than the original one. Copyright 27 by ASME

12 Absolute pressure [bar] Absolute pressure comparison p2-3kg/h-measured p3-3kg/h measured p2-3kg/h -D model without pockets p3-3kg/h -D model without pockets p2-3kg/h -D model without pockets with dx=5mm p3-3kg/h -D model without pockets with dx=5mm Figure 44: Influence of discretization length of PWS rotor channel on pressure traces Mass flow [g/sec] Mass flow comparison m-3kg/h-measured m-3kg/h -D model without pockets m2-3kg/h -D model without pockets m3-3kg/h -D model without pockets m-3kg/h -D model without pockets with dx=5mm EGR [] EGR comparison egr-3kg/h-measured egr-3kg/h -D model without pockets egr-3kg/h -D model without pockets with dx=5mm Figure 45: Influence of discretization length of PWS rotor channel on computed mass flow and internal exhaust gas recirculation PWS IN FUEL CELL APPLICATIONS Fuel cells are among the most promising alternative energy sources of the future with regard to clean and efficient power generation [33]. Hydrogen reacts with oxygen producing water, electric current and heat. Running of the fuel cell at higher pressure increases the power due to the polarization curve improvement [32], [35] and reduces the cell dimensions. Therefore, the fuel cells of kw or more utilize boosting device for air compression to increase oxygen partial pressure [32]. As the flow through the fuel cell can be described as the flow through a throttle the boost pressure has to be higher than the back pressure. The proton exchange membrane (PEM) fuel cell, the most preferred fuel cell type for automotive systems, must have sufficient water content in the polymer electrolyte and the humidity of the air must be carefully controlled [32]. From the combustion chamber measurement of the tested PWS model CX93 follows (Figure 24) that its boost pressure is higher than the back pressure for EI temperature higher than 9K. This makes a burner PWS upstream necessary to have enough energy for air compression. Due to the direct contact of air and vapor in the rotor channel, the PWS could be of advantage if used for air humidification realized by throttling at AI of PWS (Figure 29). Using the -D simulation the PWS93 with in [7] patented geometry, which provided significantly increased boost pressure (Figure ), has been computed at the test bench for back pressure of 2bar Absolute and EI temperatures of 5 C and 5 C. From the diagrams (Figure 46 and Figure 47) is visible that at the lower temperature of 5 C the PWS is unsuitable for full cell applications. At the temperature of 5 C the boost pressure surpass the back pressure. Another way of using PWS for this purpose would be a combination with serial connected, electric driven, compressor, which is necessary as a starter in any case. Absolute boost pressure for absolute back pressure of 2bar Absolute pressure p2 [bar] p3=2bar T3=5degC -D model without pockets p3=2bar T3=5degC -D model without pockets Figure 46: Computed boost pressure for back pressure of 2bar and two different temperatures Air outlet mass flow for absolute back pressure of 2bar AO mass flow m2 [g/sec] p3=2bar T3=5degC -D model without pockets p3=2bar T3=5degC -D model without pockets Figure 47: Computed air outlet mass flow for back pressure of 2bar and two different temperatures CONCLUSIONS In framework of the study presented in this paper the pressure wave supercharger (PWS) has been investigated using -D engine simulation and experimental measurement at the combustion chamber test bench. -D simulation of different PWS sizes contributed to understanding of PWS behavior in engine application. The PWS has higher boost pressure at low engine speeds than the turbocharger. Using the variable transmission ratio between the PWS and the engine the boost pressure can be hold on high level over the whole engine speed range. Whereas the engine speed increases the scavenging of the PWS rotor decreases. At the highest engine speeds the internal exhaust gas recirculation rises and deteriorates the engine power. The variable gas pocket improves the rotor scavenging and can be with advantage used for boost pressure control. During the transient operation the increased internal exhaust gas recirculation appeared. Change of PWS speed during the load step improved transient behavior. The PWS has been largely explored at the combustion chamber test bench and performance maps of measured PWS created. The measurement showed high sensitivity of PWS on flow losses mainly in exhaust outlet. Pressure increase in air inlet of PWS increases the boost pressure by the same pressure. 2 Copyright 27 by ASME

13 The -D model of PWS at the test bench has been created to compare simulation to experiment. The established database of measured data creates very good basis for further -D model calibration. The qualitative reaction of PWS model is in a very good agreement with the measurement. The -D model predicts higher difference between boost pressure and back pressure and in larger PWS speed range than measurements. In next steps mainly the flow losses in the model should be tuned to calibrate the model. Utilization of the PWS in the fuel cell application makes a burner PWS upstream necessary. -D model and measured database could be with advantage used for further investigations on this topic. NOMENCLATURE AI Air inlet AO Air outlet C Molar fraction of CO2 EI Exhaust inlet EO Exhaust outlet etapws Total efficiency of PWS ISFC Indicated specific fuel consumption [g/kw/h] m Mass flow in AI [kg/h] m2 Mass flow in AO [kg/h] m2red Reduced air mass flow in AO [kg/h] m3 Air mass flow in EI [kg/h] p Ambient pressure [kpa] p2 Relative boost pressure [kpa] p3 Relative EI pressure [kpa] p4 Relative EO pressure [kpa] pic Pressure ratio [] PWS Pressure wave supercharger t Ambient temperature t Inlet temperature [deg C] t2 AO temperature [deg C] t3 EI average temperature [deg C] t4 EO temperature [deg C] ACKNOWLEDGMENTS The authors would like to express their grateful thanks to Czech turbocharger maker ČZ a.s., division Turbo, namely to Mr. Stulík, Mr. Havelka, Mr. Mach and division director Mr. Pinkas for fruitful cooperation and support throughout the project. Special thank belongs to prof. Takats from JBRC for his kindly help with taking CO 2 measurement into operation. Additional thanks belong also to author s colleges from JBRC prof. Uhlíř and prof. Novák for their kind help with taking of PWS electric drive into operation.. REFERENCES [] Spring, P.: Modeling and Control of Pressure-Wave Supercharged Engine Systems. Dissertation ETH Zürich 26, No.649 [2] Weber, F., Guzzella, L.: Control Oriented Modeling of a Pressure Wave Supercharger. SAE Paper , 2, pp. 9- [3] Spring, P., Guzzella, L., Onder, C.: Optimal Control Strategy for a Pressure-Wave Supercharged SI Engine. Technical Paper, ICES23-645, Spring Technical Conference of the ASME International Combustion Engine Division, Salzburg, Austria, 23 [4] Akbari, P., Nalim R., Müller,N.: A Review of Wave Rotor Technology and its Applications. IMECE24-682, 24 ASME International Mechanical Engineering Congress, Anaheim, California USA [5] Akbari, P., Müller,N.: Wave Rotor Research Program at Michigan State University. AIAA , 4 st AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Tucson, Arizona [6] Iancu, F.: Integration of a Wave Rotor to an Ultra-Micro Gas Turbine. Dissertation Michigan State University 25, [7] Wenger, U., Martin, R., Swissauto Eng. S.A.: Gas-Dynamic Pressure Machine. International Patent No.: WO 99/93 [8] Martin, R., Wenger, U., Swissauto Eng S.A.: Gasdynamische Druckwellenmaschine. European Patent, EP A [9] Wenger, U., Martin, R., Swissauto Eng S.A.: Verfahren zur Regelung einer Verbrennungsmaschine mit einer gasdynamischen Druckwellenmaschine. European Patent, EP A [] Oguri, Y., Suzuki, T., Yoshida, M., Cho, M.: Research on Adaptation of Pressure Wave Supercharger (PWS) to Gasoline Engine. SAE Paper , 2, pp. -7 [] Jenny, E.: Berechnungen und Modellversuche über Druckwellen grosser Amplituden in Auspuff-Leitungen. Dissertation ETH Zürich, Ameba Druck Basel 949 [2] Berchtold, M.: Druckwellenaufladung für kleine Fahrzeug-Dieselmotoren. Schweizerische Bauzeitung 79, No. 46, Switzerland, 96, pp [3] Shapiro, A. H.: The Dynamics and Thermodynamics of Compressible Fluid Flow. The Ronald Press Comp., New York 953 [4] Piechna, J., Lisewski, P.: Numerical Analysis of Unsteady Two Dimensional Flow Effects in the Comprex Supercharger. The Archive of Mechanical Engineering, Vol. XLV, No. 4, 998, pp [5] Piechna, J.: Numerical Simulation of the Pressure Wave Supercharger Effect of Pockets on the Comprex Supercharger Characteristics. The Archive of Mechanical Engineering, Vol. XLV, No. 4, 998, pp [6] Selerowicz, W., Piechna, J.: Comprex Type Supercharger as a Pressure-Wave Transformer Flow Characteristics. The Archive of Mechanical Engineering, Vol. XLVI, No., 999, pp [7] Piechna, J.: Numerical Simulation of the Comprex Type of Supercharger: Comparison of Two Models of Boundary Condition. The Archive of Mechanical Engineering, Vol. XLV, No. 3, 998, pp Copyright 27 by ASME

14 [8] Zehnder, G.: Berechnung von Druckwellen in der Aufladetechnik. Brown Boveri Mitteilung, 4/5, 97 [9] Flückiger, L., Tafel, S., Spring, P.: Hochaufladung mit Druckwellenlader für Ottomotoren. MTZ 2, 26, pp [2] Guzzella, L., Martin, R.: Das SAVE-Motorkonzept. MTZ, 998, pp [2] Mayer, A., Nashar, I. El., Perewusnyk, J.: Comprex with Gas Pocket Control. Institution of Mechanical Engineers, C45/32, 99, pp [22] Kollbrunner, T. A.: Comprex Supercharging for Passenger Diesel Car Engines. SAE Paper 8884, West Coast International Meeting, Los Angeles 98 [23] Croes, N.: Die Wirkungsweise der Taschen des Druckwellenladers Comprex. Motortechnische Zeitschrift, Vol. 4, No. 2, 979, pp [24] Mayer, A.: COMPREX-Aufladung von PKW- Dieselmotoren. Beitrag für die Tagung Moderne PKW- Dieselmotoren im Haus der Technik, Essen am 7./8. März 988 [25] Schruf, G.M., Kollbrunner, T. A.: Application and Matching of the Comprex Pressure-Wave Supercharger to Automotive Diesel Engines. SAE Paper 8433, International Congress and Exposition, Detroit, 984 [26] Berchtold, M., Gull, H.P.: Road Performance of a Comprex Supercharged Diesel Truck. SAE Paper 8U, SAE National Diesel Engine Meeting, La Salle Hotel, Chicago, Illinois, 959 [27] Tatsutomi, Y., Yoshizu, K., Komagamine, M.: Der Dieselmotor mit Comprex-Aufladung für den Mazda 626. MTZ 5(99), pp [28] Jenny, E., Bulaty, T.: Die Druckwellen-Maschine Comprex als Oberstufe einer Gasturbine. Teil and 2, MTZ 34 (973) and 2, pp , [29] Endres, H.: Comprex-Aufladung schnellaufender direkteinspritzender Dieselmotoren. Dissertation RWTH Aachen, 985 [3] BBC Brown Boveri: Comprex bulletin 3. Ausgabe: Januar 978, Gedruckt in der Schweiz ( ) [3] Gygax, J., Schneider G.: Betriebserfahrungen mit dem Druckwellenlader Comprex im Opel Senator. MTZ 49,988, pp [32] Larminie, J., Dicks, A.: Fuel Cell Systems Explained. SAE International, 2nd edition (May, 23), ISBN [33] Gruden, D., Borgmann, K., Hiemesch, O.: Power Units for Transporation. The Handbook of Environmental Chemistry Vol. 3. Part T, Springer-Verlag Berlin Heidelberg 23 [34] Pischinger, S., Schönfelder, C., Bornscheuer, W., Kindel, H., Wiartalla: Integrated Air Supply and Humidification Concepts for Fuel Cell Systems. SAE , SAE 2 World Congress Detroit, Michigan March 5-8,2 [35] Wiartalla, A., Pischinger S., Bornscheuer,W., Fieweger, K., Ogrzewalla, J.: Compressor Expander Units for Fuel Cell Systems. SAE 2--38, SAE 2 World Congress Detroit, Michigan March 6-9,2 [36] Cantemir, C.-G,. Hubert, Ch., Rizzoni, G., Demetrescu, B.,: High Performance Fuel Cell Sedan. SAE 24--3, SAE 2--38, SAE 24 World Congress Detroit, Michigan March 8-,24 [37] Pohořelský, L., Macek,J., Polašek M., Vítek, O.: Simulation of a COMPREX Pressure Exchanger in a -D Code.SAE Paper 24--, SAE International Warrendale 24, 3 pp. [38] Pohořelský, L.: Simulation of a COMPREX Supercharger in Transient Operations. MECCA, September 25, Volume III., ISSN 24-82, Extended issue 3/25 Transient Processes in International Combustion Engines and Automotive Powertrains 4 Copyright 27 by ASME

15 ANNEX A COMPARISON OF -D MODEL SIMULATION TO MEASUREMENT Absolute pressure [bar] Absolute pressure comparison p2-kg/h-measured p3-kg/h-measured p2-kg/h -D model without pockets p3-kg/h -D model without pockets Figure A: -D simulation vs. measurement for constant EI mass flow of kg/h Absolute pressure [bar] Absolute pressure comparison p3-4kg/h-measured p2-4kg/h-measured p2-4kg/h -D model without pockets p3-4kg/h -D model without pockets Figure A2: -D simulation vs. measurement for constant EI mass flow of 4kg/h Mass flow [g/sec] Mass flow comparison m-kg/h-measured m-kg/h -D model without pockets m2-kg/h -D model without pockets m3-kg/h -D model without pockets Mass flow comparison m-4kg/h-measured m-4kg/h -D model without pockets m2-4kg/h -D model without pockets m3-4kg/h -D model without pockets Mass flow [g/sec] EGR comparison egr-kg/h-measured egr-4kg/h -D model without pockets EGR [] EGR comparison egr-4kg/h-measured p2-4kg/h -D model without pockets EGR [] Absolute pressure [bar] Absolute pressure comparison p2-5kg/h-measured p3-5kg/h-measured p2-5kg/h -D model without pockets p3-5kg/h -D model without pockets Mass flow comparison m-5kg/h-measured m-5kg/h -D model without pockets m2-5kg/h -D model without pockets m3-5kg/h -D model without pockets Mass flow [g/sec] EGR [] EGR comparison kg/h-measured 5kg/h -D model without pockets Figure A3: -D simulation vs. measurement for constant EI mass flow of 5kg/h 5 Copyright 27 by ASME