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Within a broader national project aimed at the hybridization of a standard city car (the 998 cc Mitsubishi-derived gasoline engine of the Smart W451), our team tackled the problem of improving the supercharger performance and response. The originally conceived design innovation was that of eliminating the mechanical connection between the compresso...
Contexts in source publication
Context 1
... gasoline-fueled ICE, most turbocharger units today are back-to-back, radial/radial compressor/turbine assemblies ( Figure 1 Standard Turbocharger assembly): the exhaust gases from the ICE power the turbine that in turn drives the compressor. A schematic representation of the process and of the subsumed ideal and real (indicated) cycle [5] are shown in Figure 2. ...
Context 2
... radial extension of the diffuser is the same as in the original GT12 compressor; Again an extension of the domain by 1.5 diameters was introduced to smooth the downstream boundary condition ( Figure 10); ...
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... mesh sensitivity analysis was run on each configuration, the objective function being the shaft torque. Quite obviously, the results are geometry-dependent (Figure 11): the final meshes contained 1.6 × 10 6 and 1.2 × 10 6 nodes for the standard and tandem rotor, respectively. The diffuser mesh contained 1.6 × 10 5 (Garrett) and 1.2 × 10 5 (Tandem) nodes. ...
Context 4
... diffuser mesh contained 1.6 × 10 5 (Garrett) and 1.2 × 10 5 (Tandem) nodes. The final rotor meshes are shown in Figure 12. ...
Context 5
... most interesting global result is the compressor characteristic. Figure 13 shows that the Tandem A configuration displays a better efficiency than the Garrett compressor over the entire operating range (except very close to the choking line). This result was expected, as it is also well-documented in the relevant literature [17]. ...
Context 6
... result needs a more careful analysis on the basis of a detailed examination of the flowfields and will be discussed in the next section. The relative Ma plots of Figure 14 show that the Tandem A rotor has substantially lower sonic losses at the intake, while at rotor exit the Ma profiles are similar. Both plots refer to 50% span near the choking limit [7]. ...
Context 7
... the original configuration (left) incipient choking is visible in the circled regions, where the local Ma is near or even in excess of one. The presence of the inducer provides a partial cure to this situation but reduces the critical mass flowrate (see also Figure 13). This undesired result is originated by the appearance of a jet flow (highlighted in Figure 15) between the pressure side of the inducer blade and the suction side of the exducer (where Ma 0.8): this high-speed flow flattens the boundary layer on the exducer suction side (improving work transfer in that area) but also distorts the pressure field, attracting some fluid from the suction side BL and maintaining its "jet" profile up to the rotor exit, resulting in high sonic losses. ...
Context 8
... presence of the inducer provides a partial cure to this situation but reduces the critical mass flowrate (see also Figure 13). This undesired result is originated by the appearance of a jet flow (highlighted in Figure 15) between the pressure side of the inducer blade and the suction side of the exducer (where Ma 0.8): this high-speed flow flattens the boundary layer on the exducer suction side (improving work transfer in that area) but also distorts the pressure field, attracting some fluid from the suction side BL and maintaining its "jet" profile up to the rotor exit, resulting in high sonic losses. A second undesirable characteristic of the Tandem A rotor is the mismatch between the velocity at inducer exit and the tangent to the chord of the exducer leading edge: this results in an excessive incidence that-at low flowrates-promotes BL separation on the pressure side of the exducer (Figures 15 and 16). ...
Context 9
... undesired result is originated by the appearance of a jet flow (highlighted in Figure 15) between the pressure side of the inducer blade and the suction side of the exducer (where Ma 0.8): this high-speed flow flattens the boundary layer on the exducer suction side (improving work transfer in that area) but also distorts the pressure field, attracting some fluid from the suction side BL and maintaining its "jet" profile up to the rotor exit, resulting in high sonic losses. A second undesirable characteristic of the Tandem A rotor is the mismatch between the velocity at inducer exit and the tangent to the chord of the exducer leading edge: this results in an excessive incidence that-at low flowrates-promotes BL separation on the pressure side of the exducer (Figures 15 and 16). This effect is caused by the previously discussed decision of maintaining the exducer geometry of the conventional machine, to highlight the influence of the sole inducer on the flow field. ...
Context 10
... angular overlapping of the exducer was reduced to 40°, to increase the critical mass flowrate. This modified design eliminated the two defects discussed above (see Figures 17 and 18): the high-Ma regions near rotor exit are much less extended, the jet flow has disappeared and the inducer/exducer BL transition is much smoother. At this point it became clear that it would be possible to tune the two parameters that most influence the creation of a jet flow at the inducer/exducer interface, namely the axial clearance between the two (the larger this clearance, the more fluid "leaks" from the pressure to the suction side) and the "clock", i.e., the circumferential angle between the two blades, which is the main factor controlling the interblade jet flow. ...
Context 11
... this point it became clear that it would be possible to tune the two parameters that most influence the creation of a jet flow at the inducer/exducer interface, namely the axial clearance between the two (the larger this clearance, the more fluid "leaks" from the pressure to the suction side) and the "clock", i.e., the circumferential angle between the two blades, which is the main factor controlling the interblade jet flow. Both are defined in Figure 19. Therefore, after introducing the above corrections, a Design of Experiment campaign was conducted to identify the best clock/clearance combination. ...
Context 12
... B design (see Figure 13) shows a choke margin extension and outperforms the conventional impeller, while the C version (overlap increased to 50°) is slightly less efficient and just as sensitive to choking as the Garrett rotor, due to its higher Mach losses. ...
Context 13
... it is intuitively clear that the most influential performance governing feature in a tandem compressor configuration is the interaction between the inducer boundary layer and the exducer blades, and it is also clear that in general the stage efficiency increases when the inducer boundary layer falls in the pressure side of the exducer, there seems to be no general agreement on how the circumferential (clock) and axial (gap) separation between inducer outlet and exducer inlet affect performance (Figure 19). A first clue is provided by the consideration that the compression ratio increases when the boundary layer at inducer exit merges with the one at exducer inlet on the suction side: our calculations show that this enhances the airfoil performance and promotes a smoother flow throughout the exducer, as shown in Figure 20 (see Appendix A). ...
Context 14
... first clue is provided by the consideration that the compression ratio increases when the boundary layer at inducer exit merges with the one at exducer inlet on the suction side: our calculations show that this enhances the airfoil performance and promotes a smoother flow throughout the exducer, as shown in Figure 20 (see Appendix A). The clock has a remarkable influence on this effect: the 0% clock configuration reflects perfectly the previous considerations, while both the 25% and 50% clock geometris are dominated by Mach losses generated at a throat appearing between the inducer trailing edge and the exducer leading ( Figure 21). The peak Mach number increases with the decrease of the axial distance, degrading efficiency. ...
Context 15
... our analysis emerges that a 75% clock weakens the Mach over most of the domain, as it is apparent from the "cleaner" midchannel sections displayed in Figure 22. This configuration achieves the highest efficiency throughout the operating range (Figures 13 and 23) and exhibits promising performance for a full-scale application. ...
Context 16
... the choking behavior of the Tandem B geometry (Figure 27), it appears that the addition of the inducer leads to higher velocities downstream and through the exducer, shifting chocking towards lower mass flowrates. This is contrary though to consolidated experience, since in conventional centrifugal compressors the shock should appear in the fore section of the blade, near the leading edge, and this indeed is the case for the GT12 conventional impeller (Figure 14). This odd behavior is thus the consequence of poor design, which in turn means that the exducer blade channel must be redesigned. ...
Context 17
... simulations are conducted at the expected design point with pre-assigned total pressure inlet and static pressure outlet. The results are shown in Figures A1 and A2, and some of the corresponding flow fields are displayed in the main text of this paper. ...
Context 18
... gasoline-fueled ICE, most turbocharger units today are back-to-back, radial/radial compressor/turbine assemblies ( Figure 1 Standard Turbocharger assembly): the exhaust gases from the ICE power the turbine that in turn drives the compressor. A schematic representation of the process and of the subsumed ideal and real (indicated) cycle [5] are shown in Figure 2. ...
Context 19
... radial extension of the diffuser is the same as in the original GT12 compressor; Again an extension of the domain by 1.5 diameters was introduced to smooth the downstream boundary condition ( Figure 10); ...
Context 20
... mesh sensitivity analysis was run on each configuration, the objective function being the shaft torque. Quite obviously, the results are geometry-dependent (Figure 11): the final meshes contained 1.6 × 10 6 and 1.2 × 10 6 nodes for the standard and tandem rotor, respectively. The diffuser mesh contained 1.6 × 10 5 (Garrett) and 1.2 × 10 5 (Tandem) nodes. ...
Context 21
... diffuser mesh contained 1.6 × 10 5 (Garrett) and 1.2 × 10 5 (Tandem) nodes. The final rotor meshes are shown in Figure 12. ...
Context 22
... most interesting global result is the compressor characteristic. Figure 13 shows that the Tandem A configuration displays a better efficiency than the Garrett compressor over the entire operating range (except very close to the choking line). This result was expected, as it is also well-documented in the relevant literature [17]. ...
Context 23
... result needs a more careful analysis on the basis of a detailed examination of the flowfields and will be discussed in the next section. The relative Ma plots of Figure 14 show that the Tandem A rotor has substantially lower sonic losses at the intake, while at rotor exit the Ma profiles are similar. Both plots refer to 50% span near the choking limit [7]. ...
Context 24
... the original configuration (left) incipient choking is visible in the circled regions, where the local Ma is near or even in excess of one. The presence of the inducer provides a partial cure to this situation but reduces the critical mass flowrate (see also Figure 13). This undesired result is originated by the appearance of a jet flow (highlighted in Figure 15) between the pressure side of the inducer blade and the suction side of the exducer (where Ma 0.8): this high-speed flow flattens the boundary layer on the exducer suction side (improving work transfer in that area) but also distorts the pressure field, attracting some fluid from the suction side BL and maintaining its "jet" profile up to the rotor exit, resulting in high sonic losses. ...
Context 25
... presence of the inducer provides a partial cure to this situation but reduces the critical mass flowrate (see also Figure 13). This undesired result is originated by the appearance of a jet flow (highlighted in Figure 15) between the pressure side of the inducer blade and the suction side of the exducer (where Ma 0.8): this high-speed flow flattens the boundary layer on the exducer suction side (improving work transfer in that area) but also distorts the pressure field, attracting some fluid from the suction side BL and maintaining its "jet" profile up to the rotor exit, resulting in high sonic losses. A second undesirable characteristic of the Tandem A rotor is the mismatch between the velocity at inducer exit and the tangent to the chord of the exducer leading edge: this results in an excessive incidence that-at low flowrates-promotes BL separation on the pressure side of the exducer (Figures 15 and 16). ...
Context 26
... undesired result is originated by the appearance of a jet flow (highlighted in Figure 15) between the pressure side of the inducer blade and the suction side of the exducer (where Ma 0.8): this high-speed flow flattens the boundary layer on the exducer suction side (improving work transfer in that area) but also distorts the pressure field, attracting some fluid from the suction side BL and maintaining its "jet" profile up to the rotor exit, resulting in high sonic losses. A second undesirable characteristic of the Tandem A rotor is the mismatch between the velocity at inducer exit and the tangent to the chord of the exducer leading edge: this results in an excessive incidence that-at low flowrates-promotes BL separation on the pressure side of the exducer (Figures 15 and 16). This effect is caused by the previously discussed decision of maintaining the exducer geometry of the conventional machine, to highlight the influence of the sole inducer on the flow field. ...
Context 27
... angular overlapping of the exducer was reduced to 40°, to increase the critical mass flowrate. This modified design eliminated the two defects discussed above (see Figures 17 and 18): the high-Ma regions near rotor exit are much less extended, the jet flow has disappeared and the inducer/exducer BL transition is much smoother. At this point it became clear that it would be possible to tune the two parameters that most influence the creation of a jet flow at the inducer/exducer interface, namely the axial clearance between the two (the larger this clearance, the more fluid "leaks" from the pressure to the suction side) and the "clock", i.e., the circumferential angle between the two blades, which is the main factor controlling the interblade jet flow. ...
Context 28
... this point it became clear that it would be possible to tune the two parameters that most influence the creation of a jet flow at the inducer/exducer interface, namely the axial clearance between the two (the larger this clearance, the more fluid "leaks" from the pressure to the suction side) and the "clock", i.e., the circumferential angle between the two blades, which is the main factor controlling the interblade jet flow. Both are defined in Figure 19. Therefore, after introducing the above corrections, a Design of Experiment campaign was conducted to identify the best clock/clearance combination. ...
Context 29
... B design (see Figure 13) shows a choke margin extension and outperforms the conventional impeller, while the C version (overlap increased to 50°) is slightly less efficient and just as sensitive to choking as the Garrett rotor, due to its higher Mach losses. ...
Context 30
... it is intuitively clear that the most influential performance governing feature in a tandem compressor configuration is the interaction between the inducer boundary layer and the exducer blades, and it is also clear that in general the stage efficiency increases when the inducer boundary layer falls in the pressure side of the exducer, there seems to be no general agreement on how the circumferential (clock) and axial (gap) separation between inducer outlet and exducer inlet affect performance (Figure 19). A first clue is provided by the consideration that the compression ratio increases when the boundary layer at inducer exit merges with the one at exducer inlet on the suction side: our calculations show that this enhances the airfoil performance and promotes a smoother flow throughout the exducer, as shown in Figure 20 (see Appendix A). ...
Context 31
... first clue is provided by the consideration that the compression ratio increases when the boundary layer at inducer exit merges with the one at exducer inlet on the suction side: our calculations show that this enhances the airfoil performance and promotes a smoother flow throughout the exducer, as shown in Figure 20 (see Appendix A). The clock has a remarkable influence on this effect: the 0% clock configuration reflects perfectly the previous considerations, while both the 25% and 50% clock geometris are dominated by Mach losses generated at a throat appearing between the inducer trailing edge and the exducer leading ( Figure 21). The peak Mach number increases with the decrease of the axial distance, degrading efficiency. ...
Context 32
... our analysis emerges that a 75% clock weakens the Mach over most of the domain, as it is apparent from the "cleaner" midchannel sections displayed in Figure 22. This configuration achieves the highest efficiency throughout the operating range (Figures 13 and 23) and exhibits promising performance for a full-scale application. ...
Context 33
... the choking behavior of the Tandem B geometry (Figure 27), it appears that the addition of the inducer leads to higher velocities downstream and through the exducer, shifting chocking towards lower mass flowrates. This is contrary though to consolidated experience, since in conventional centrifugal compressors the shock should appear in the fore section of the blade, near the leading edge, and this indeed is the case for the GT12 conventional impeller (Figure 14). This odd behavior is thus the consequence of poor design, which in turn means that the exducer blade channel must be redesigned. ...
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Citations
... Full 3D CFD simulations were performed at three different speeds: 2000 rpm, 3500 rpm, and 5500 rpm, respectively. They noted that the final geometry had a higher pressure ratio than the original unit, an improved surge margin, and a lower sensitivity to choke [18]. Noman et al. present a comprehensive experimental and numerical study on the performance of a medium pressure ratio, shrouded, TB centrifugal compressor compared to a conventional compressor used commercially in China for turbocharging applications. ...
Centrifugal compressors are frequently used in both military and commercial areas because they can be easily manufactured and reach high-pressure compression ratios. The factor that limits the performance and operating range of compressors is flow instability. Many ideas have been put forward for performance improvement, but tandem blade radial compressors, which do not require an extra air system, have attracted the most interest. In this study, computational fluid dynamics (CFD) analyses were carried out on various parameters of the tandem blade (TB) radial compressor, and an optimization study was carried out to find the best design using a genetic algorithm on a whole operating curve. It was investigated how these parameters affected the efficiency and total pressure ratio between the determined lower and upper limits. The numerical analyses of the optimum design obtained as a result of the iterations were carried out. As a result of the iterations, three optimum designs were obtained and numerical analysis was carried out according to one of them, and then they were compared with the results in the literature. The general agreement of computational fluid dynamics and the literature data served as a validation for the computational approach. The error rates between the numerical analysis results and the experimental results in the literature were calculated for different flow rates and were found to be 1.98% as the highest and 0.35 as the lowest. The work carried out in this article will provide a valuable reference for future advanced tandem blade compressor designs.
... Another modification was to more thoroughly define the compressor map based on data found in [32] so as to improve predictions close to the surge line. ...
Hydrogen is seen as a prime choice for complete replacement of gasoline so as to achieve zero-emissions energy and mobility. Combining the use of this alternative fuel with a circular economy approach for giving new life to the existing fleet of passenger cars ensures further benefits in terms of cost competitiveness. Transforming spark ignition (SI) engines to H2 power requires relatively minor changes and limited added components. Within this framework, the conversion of a small-size passenger car to hydrogen fueling was evaluated based on 0D/1D simulation. One of the methods to improve efficiency is to apply exhaust gas recirculation (EGR), which also lowers NOx emissions. Therefore, the previous version of the quasi-dimensional model was modified to include EGR and its effects on combustion. A dedicated laminar flame speed model was implemented for the specific properties of hydrogen, and a purpose-built sub-routine was implemented to correctly model the effects of residual gas at the start of combustion. Simulations were performed in several operating points representative of urban and highway driving. One of the main conclusions was that high-pressure recirculation was severely limited by the minimum flow requirements of the compressor. Low-pressure EGR ensured wider applicability and significant improvement of efficiency, especially during partial-load operation specific to urban use. Another benefit of recirculation was that pressure rise rates were predicted to be more contained and closer to the values expected for gasoline fueling. This was possible due to the high tolerance of H2 to the presence of residual gas.
... Other OEM data were used for building equivalent turbine and compressor maps [27,28] and for validating (at least partially) model output. More to the point, the simula- Table 1 shows the main engine characteristics when fueled with gasoline. ...
... More to the point, if the model predicted the occurrence of knock, spark timing was reduced by 0.2 deg for the next cycle. Other OEM data were used for building equivalent turbine and compressor maps [27,28] and for validating (at least partially) model output. More to the point, the simulations predicted peak power with a boost pressure of 0.5 bar, which is completely in line with OEM specifications. ...
In the efforts to achieve zero-emission transportation, hydrogen offers a valid choice as a complete replacement of gasoline. Adapting spark ignition (SI) engines to this alternative fuel can be implemented with relatively minor changes and limited investment in added components. The conversion of a small-size passenger car to hydrogen fueling was evaluated initially from the perspective of achievable range and peak power. Overall, the concept was found to be feasible and comparable to the fully electric version of the vehicle. Cylinder imbalance was found to be one of the possible issues compared to gasoline operation. This study looks in more detail at cycle-to-cycle variability (CCV) and how this could influence vehicle dynamics as well as noise–harshness–vibration (NHV). CCV was simulated with a 0D/1D approach in vehicle-relevant engine speed–load conditions. A dedicated laminar flame speed sub-model was implemented so as to include fuel chemistry effects, while CCV was simulated by inducing perturbations in the initial combustion stages and fuel system characteristics as well as variation of air–fuel ratio throughout flame propagation. Significant improvement of stability was predicted with hydrogen, while cylinder imbalance was found to be one of the main sources of variability. Applying algorithms that compensate for the imbalance through individual injection valve regulation may not be enough to mitigate the identified issue, and more extensive changes of control strategies could be required. The start of injection settings may need to be adapted for each operating condition to maximize the effect of H2 combustion stabilization.
... Hybrid power trains for city cars were also developed in tight contact with turbocharger systems [3]. Furthermore, these applications were made for hybrid city cars [4]. The center development area was the turbocharger, which was tested with experimental and CFD calculation for better performances optimization [5]. ...
... In this case, the flue gas energy (area 1-4-5-6-1) is used to drive a compressor. Prolonged expansion (4)(5) is achieved in the blade network of the turbine, which drives the compressor. The air is compressed (6-1) to the pressure ps. ...
... So, the pressure and density of In this case, the flue gas energy (area 1-4-5-6-1) is used to drive a compressor. Prolonged expansion (4)(5) is achieved in the blade network of the turbine, which drives the compressor. The air is compressed to the pressure p s . ...
Research in the process of internal combustion engines shows that their efficiency can be increased through several technical and functional solutions. One of these is turbocharging. For certain engine operating modes, the available energy of the turbine can also be used to drive an electricity generator. The purpose of this paper is to highlight the possibilities and limitations of this solution. For this purpose, several investigations were carried out in the virtual environment with the AMESim program, as well as experimental research on a diesel engine for automobiles and on a stand for testing turbochargers (Turbo Test Pro produced by CIMAT). The article also includes a comparative study between the power and torque of the naturally aspirated internal combustion engine and equipped with a hybrid turbocharger. The results showed that the turbocharger has a very high operating potential and can be coupled with a generator without decreasing the efficiency of the turbocharger or the internal combustion engine. The main result was the generation of electrical power of 115 W at a turbocharger shaft speed of 140,000–160,000 rpm with an electric generator shaft speed of 14,000–16,000 rpm. There are many constructive solutions for electrical turbochargers with the generator positioned between the compressor and the turbine wheel. This paper is presenting a solution of a hybrid turbocharger with the generator positioned and coupled with the compressor wheel on the exterior side.
This paper investigates a two-stage hybrid boosting system aimed at minimizing the delay in torque delivery that commonly characterizes turbocharged engines. Turbo-lag, particularly at low loads, reduces drivability, making the vehicle less competitive in the market. However, turbocharging is currently a simple and effective way of achieving high levels of specific power and efficiency, making its application mandatory. Hybridizing the turbocharging system by integrating a conventional turbocharger with an electrically assisted compressor can offer a solution to mitigate turbo-lag. The high dynamic response of the e-compressor significantly reduces time-to-boost, thus improving the engine’s response to load changes. This work presents the hybrid configuration with reference to a specific experimental campaign conducted on the University of Genoa’s test bench for components of propulsion system. The main results are presented, focusing on the boost pressure dynamic response during transient operations, highlighting the system’s behavior in various conditions and the benefits obtained by adopting an e-compressor in terms of time-to-boost. Furthermore, the experimental tests allow for the evaluation of the e-compressor electric power consumption under different operating conditions. The experimental results are then used as a reference to build a 1D model in GT-Power, reducing costs and time related to the experimental campaign while validating the data measured on the test bench.
div class="section abstract"> Converting spark ignition (SI) engines to H<sub>2</sub> fueling is an attractive route for achieving zero carbon transportation and solving the legacy fleet problem in a future scenario in which electric powertrains will dominate. The current paper looks at a small size passenger car in terms of vehicle dynamics and electronic control unit (ECU) remapping requirements, in the hypothesis of using H<sub>2</sub> as a gasoline replacement. One major issue with the use of H<sub>2</sub> in port fuel injection (PFI) engines is that it causes reduced volumetric efficiency and thus low power. The vehicle considered for the study features turbocharging and therefore complete or partial recuperation of lost power is possible. Other specific requirements such as injection phasing were also under scrutiny, especially as PFI was hypothesized to maximize cost effectiveness. A 0D/1D model was used for simulating engine running characteristics as well as vehicle dynamics. One of the main conclusions is that at low rpm there should be only a minor influence on vehicle dynamics, while at the higher end completely comparable performance is achievable. In terms of acceleration, the small passenger car considered for the study loses around 10% performance between 0-100 km/h, but it is possible to have same dynamic response when accelerating from 70-120 km/h. After optimizing the gear shift strategy, the energy consumption between gasoline and H<sub>2</sub> version are the same, with zero tailpipe CO<sub>2</sub> emissions for the hydrogen.
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