Bulletin of the Trnsilvni University of Brşov Vol. 8 (57) No. 1-2015 Series I: Engineering Sciences RESEARCHES ON THE INFLUENCE OF PRESSURE WAVE COMPRESSOR ON THE INTAKE AIR TEMPERATURE AT THE SUPERCHARGED ENGINES C.I. LEAHU 1 D.M. DOGARIU 1 A. CHIRU 1 Abstrct: In this pper, the wy how the working principle of pressure wve compressor influences the temperture field of intke ir is presented. The reserch on superchrged Diesel engine with successive configurtions, one with turbochrger nd nother with pressure wve compressor, showed tht there re different temperture fields of the intke ir t the exit of the two superchrging compressors. The pper lso presents the cuses for this increse in temperture for ech of the two compressors, these cuses being very different from one compressor to other. Key words: intke ir, temperture, pressure wve compressor, engine. 1. Introduction The intke ir temperture t the internl combustion engines hs gret influence on the necessry ir quntity for combustion. High tempertures of the intke ir reduces the ir mss trpped inside the cylinder, thus the mss of fuel involved in combustion must be reduced. Significnt rise of intke ir temperture tkes plce especilly in the cse of superchrged internl combustion engines. However, by superchrging or turbochrging the intke ir pressure is rised. In this wy, by incresing the ir consumption, the contributing mss of fuel cn be incresed too, s in the principle of downsizing. This leds to fvorble sitution for improving the energetic nd ecologicl performnces of engines. The intke ir cn be compressed with superchrging compressors like: compressors of turbochrgers or the pressure wve compressors. In both cses, the side effect of the pressure rise of the intke ir is ctully the temperture rise, which reduces the ction of the superchrging. Both superchrging compressors use the energy of the exhust gses for compressing the intke ir. However, there is significnt difference between these two, which consists in the wy the energy from the exhust gses to the intke ir is trnsmitted. In the cse of the turbochrger, the energy of the exhust gses is trnsmitted to the intke ir through two rotors mounted on common shft, while the flow pths of the two gses re well bounded [2]. 1 Dept. of Automotive nd Trnsport Engineering, Trnsilvni University of Brşov.
8 Bulletin of the Trnsilvni University of Brşov Series I Vol. 8 (57) No. 1-2015 In the cse of the pressure wve compressor, the exhust gs energy is trnsmitted directly to the intke ir since the two gses re in contct to ech other. Another difference is tht the ir nd exhust gses re trvelling successively through the chnnels [5]. Due to these functionl chrcteristics, in pressure wve compressors there is supplementry heting source of the intke ir, compring to turbochrges, nd tht is the direct contct of the ir both with the exhust gses nd with the chnnel wlls of the rotor, which took prt of the het from the exhust gses. Under these ssumptions, this pper emphses the rte of temperture rise of the intke ir due to the supplementry het sources present in the pressure wve compressors. 2. Aspects on the Influence of the Intke Air Temperture on Engine Performnces Nowdys, the fuel injection systems re working t high efficiency being ble to ssure the entire necessry fuel quntity for the burning process in optimum conditions. In order to burn lrger mount of injected fuel there is necessry to bring the corresponding mount of ir into the cylinders. So, the ir mss trpped inside the cylinders t the end of the intke stroke is n importnt prmeter, of which the qulity of the burning process nd thus, the power nd fuel consumption of internl combustion engines depend [5], [6]. The mss of ir trpped inside volume depends on the ir density, ccording to Eqution (1): m, (1) V s where: m - the mss of ir used in one cycle; - intke ir density; V s - cylinder volume. The intke ir density depends on its pressure nd temperture: P, (2) R T where: P - intke ir pressure; T - intke ir temperture; R - idel gs constnt. So, Eqution (1) cn be written s: m P Vs. (3) R T Since the rtio V s /R is constnt, Eqution (3) cn be written s: m P T const. (4) Eqution (4) emphses the influence tht the intke ir temperture hs on the mount of ir trpped inside the cylinders. The power produced by four stroke internl combustion engine, described by Eqution (5), is proportionl to the men effective pressure (p me ) nd to the engine speed (n): P const p n. (5) e me The men effective pressure cn be estimted by Eqution: 1 p me const v e, (6) where: v - volumetric efficiency; e - effective efficiency; - excess ir fctor. By replcing Eqution (2) nd (6) into Eqution (5), we obtin [1]: P 1 Pe const v e n. (7) T According to [3], it is estimted tht ech increse in T by 10 o C, P e is reduced by
Lehu, C.I., et l.: Reserches on the Influence of Pressure Wve Compressor 9 3%. Also, ccording to [7], [8], by cooling the intke ir t superchrged engine, the fuel consumption cn be reduced by lmost 6%, followed by n increse in P e by 15%. In this wy, by reducing the spired ir temperture by 25 o C, one obtined smller fuel consumption by 20 g/kwh nd higher P e with 4 kw. 3. Air Compression inside Superchrging Compressors The link between pressure nd temperture mkes the cooling of the intke ir necessry especilly when the ir is compressed in compressor. The increse in intke ir density ( ) t superchrged engine cn be estimted by Eqution [3]: p R T 1, (8) p 1 1 p 1 T 2 R T 1 p T where: with 1 - ir prmeters before entering into compressor, with 2 - compressed ir prmeters. So, the rise of temperture T hs negtive influence on the superchrging compressor. Considering n dibtic compression of the intke ir, then the temperture T my be found s follows: T k1 p k T1 p 1, (9) where: k - dibtic exponent. In relity, the rise of T is higher due to the turbulent flow of ir in compressor nd the het exchnge between intke ir nd compressor s component wlls. For this reson, the increse in T depends on the construction of ech superchrging compressor. 4. Functionl Prticulrities of Compressors Tht Use the Energy of the Exhust Gses 4.1. Turbochrger One of the most used compressors for superchrging internl combustion engines is the turbochrger (Figure 1). Here, the compressor is connected to the driving turbine through common shft. Fig. 1. The working principle of the turbochrger The turbine turns when the hot burned gses re entering into it rdilly nd re exhusted xilly. A prt of the kinetic energy of the exhust gses re trnsformed into mechnicl energy by driving the rotor of the turbine. For this reson P g4 < P g3 nd T g4 < T g3. The compressor spire the ir which enters xilly nd is exhusted rdilly. The compression inside the rotor chnges the ir prmeters, such tht: P > P 1 nd T > T 1. For the construction of this type of superchrger, the flowing pths for the exhust gses nd fresh ir chrge re entirely different nd seprte. Tht is the reson why the temperture rise of the fresh chrge is minly due to the compression process. Between compressor nd turbine there re therml insultions instlled, which decreses the conduction het trnsfer from turbine to compressor. For this type of superchrging, P nd T depends on the speed of the
10 Bulletin of the Trnsilvni University of Brşov Series I Vol. 8 (57) No. 1-2015 turbochrger rotor. This speed depends directly on the exhust gs flow (Qg). 4.2. Pressure Wve Compressor The pressure wve compressor is mde out of rotor, which is bounded t the ends by two sttors. Through one sttor exhust gses flow nd through the other one, the intke ir flows. Longitudinl chnnels on two rows re pssing through the rotor (Figure 2). Fig. 2. The chnnels of the rotor contined in pressure wve compressor In the cse of the pressure wve compressor, the intke ir is compressed by the exhust gses too. However, P nd T depend directly on P g3 nd T g3 nd not on Qg, s for the turbochrger. To relize the ir compression process, the rotor of the compressor must be turned. The pressure wve compressor cn be driven by the crnk shft or by n electric motor with vrible speed. A functionl cycle of the compressor (Figure 3) begins by introducing the exhust gses inside one chnnel of the rotor, in which fresh ir exists. The high pressure of the exhust gses is compressing the existing ir inside the chnnel. The compressed fresh ir is exhusted towrds the cylinders of the engine, while the rotor turns. Fig. 3. The compression of intke ir inside chnnel of the compressor So, it cn be observed tht during the rottion of the rotor of the pressure wve compressor, the volume of chnnel is occupied lterntively by the exhust gses nd the intke ir. Thus, het is trnsferred from one fluid to other both through convection nd conduction. 5. Experiments nd Discussions One wy to highlight the influence on intke ir temperture using pressure wve compressor compring to turbochrger is to superchrge n internl combustion engine both with turbochrger nd with pressure wve compressor. Such experimentl reserches hve been relized on four-cylinder compression ignition engine. The originl version of the engine is using turbochrging. The modified version of the engine is equipped with pressure wve compressor. This compressor ws driven by n electric motor with vrible speed. By vrying the speed of the electric motor, the efficiency of the compressor could be modified. For ech speed of the compressor, the pressure nd temperture of the intke ir ws different. At certin working regimes of the internl combustion engine, the sme vlues for intke ir pressures s in the cse for turbochrging were obtined by modifying the efficiency of the compressor. On the other hnd, the temperture of the intke ir differed. This difference in temperture my due to the het trnsfer (from the pressure wve compressor) from the exhust gses to the intke ir. This het trnsfer re: direct trnsfer exhust gses - intke ir nd indirect trnsfer exhust gses - wlls of the chnnels inside the rotor - intke ir. In Figure 4 there re presented the vlues for T of the intke ir, which is compressed t the sme pressure both in turbochrger nd in pressure wve compressor.
Lehu, C.I., et l.: Reserches on the Influence of Pressure Wve Compressor 11 Fig. 4. The temperture of the compressed intke ir in turbochrger nd pressure wve compressor In Figure 5 there is presented the influence tht the working principle of the pressure wve compressor hs on the intke ir temperture. The difference between the tempertures of the intke ir exiting the two compressors lies within the intervl 10-29 o C, on condition the sme degree of compression. It cn be observed tht the temperture of the compressed ir in the turbochrger rises with the rise of P. In the cse of the pressure wve compressor, the evolution of T is not s scending s in the cse of the turbochrger. This cn be explined by the fct tht T is significntly influenced by the time spent by the intke ir in contct with the exhust gses nd the wlls of the chnnels (exposure to het trnsfer), but lso is influenced by the exhust gses temperture. If the exposure depends minly on the rottionl speed of the compressor, the exhust gs prmeters depends minly on the speed nd lod internl combustion engine [4], [9]. However, ccording to [4] nd the Tble 1, the dependency between the speed of the pressure wve compressor nd intke ir pressure is nonliner. Tble 1 The compressor speeds to which were obtined the intke ir pressure Intke ir pressure [br] Speed pressure wve compressor [rpm] 1.05 7000 1.11 8500 1.17 11.000 1.19 10.000 1.21 12.500 1.26 8500 Fig. 5. The temperture rise of the intke ir t pressure wve compressor compring to turbochrger 6. Conclusions At pressure wve compressors, there is certin het trnsfer from the exhust gses to intke ir. The mount of het trnsferred cn be estimted through the perspective of temperture rise of the intke ir t pressure wve compressors, compring to turbochrger. For the choice of the driving speeds of the pressure wve compressor must be tken into considertion both the pressure nd temperture of the intke ir. Acknowledgements 1. This pper is supported by the Sectorl Opertionl Progrmme Humn Resources Development (SOP HRD), finnced from the Europen Socil Fund nd by the Romnin Government under the project number POSDRU/159/1.5/S/134378.
12 Bulletin of the Trnsilvni University of Brşov Series I Vol. 8 (57) No. 1-2015 2. We hereby knowledge the structurl founds project PRO-DD (POS-CCE, O.2.2.1., ID 123, SMIS 2637, ctr. No 11/2009) for providing the infrstructure used in this work. References 1. vn Bsshuysen, R., Schfer, F.: Internl Combustion Engine. Bsics, Components, Systems nd Perspectives. Wrrendle. SAE Interntionl, 2004. 2. Boricen, C., Rdu, Gh.Al.: Diesel Engine Turbochrgers: Anlysis nd Testing. In: Bulletin of the Trnsilvni University of Brşov (2012) Vol. 5 (54), Series I, p. 1-6. 3. Heisler, H.: Advnced Engine Technology. Wrrendle. SAE Interntionl, 1995. 4. Lehu, C.I., Chiru, A., Trulescu, S.: A Modlity to Optimize Common Functioning of Pressure Wve Superchrger with n Internl Combustion Engine. In: Applied Mechnics nd Mterils Journl 772 (2015), p. 350-354. 5. Rdu, Gh.Al., Lehu, C.I.: Alterntive Solutions for Superchrging with Aggregtes of Turbochrger Type. In: Bulletin of the Trnsilvni University of Brşov (2011) Vol. 4 (53), Series I, p. 13-18. 6. Sndu, G., Cofru, C., Săcărenu, S., et l.: Reserch of the Engine s Speed Influence on the Intke Process of Nturlly Aspirted Engine. In: Bulletin of the Trnsilvni University of Brşov (2011) Vol. 4 (53), Series I, p. 19-24. 7. Sndu, V., Gheorghe, V.: Adpting Vehicle Diesel Engine to Power Genertion - Conversion Aspects. In: Bulletin of the Trnsilvni University of Brsov (2014) Vol. 7 (56) No. 1, Series I, p. 13-18. 8. Sndu, V.: Improving Diesel Engine Performnce by Air-To-Air Intercooling. In: Bulletin of the Trnsilvni University of Brsov (2014) Vol. 7 (56) No. 2, Series I, p. 19-24. 9. Trulescu, S., Soic, A.: Emissions Level Approximtion t Cold Strt for Sprk Ignition Engine Vehicles. In: Applied Mechnics nd Mterils Journl 555 (2014), p. 375-384.