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Regulated multi-stage turbocharging is a key technology to achieve energy conservation and CO 2 emission reduction in internal combustion engine with carbon-free fuel. The understanding of performance of the turbocharging system at the engine conditions is essential for the optimization of engine performance. This paper studies unsteady aerodynamic interaction in regulated two-stage turbocharger turbines at pulsating conditions produced by a heavy-duty diesel engine. Results show that the performance of high-pressure turbine (HPT) is highly sensitive to the unsteady stage-interaction, which is profoundly different from that of the low-pressure turbine (LPT). Specifically, when the bypass valve is opened, the cycle-average efficiency of the HPT declines significantly up to 10.8 % compared with that of closed valve. On the other hand, LPT is slightly influenced by the valve state, and the cycle-average efficiency drops by about 0.2 % when the valve is open. The entropy generation method is used to analyze the unsteady loss in HPT and LPT to unveil the mechanism of the unsteady interaction. Detailed flow analysis shows that the swirling flow result in the evident increase of entropy generation in the HPT and LPT volute. Meanwhile, tip leakage loss and incidence loss of HPT is enhanced by unsteady stage interaction. • Influence of unsteady stage interaction on loss generation in two-stage radial turbines at pulsation is firstly studied. • Influence of pulsating condition and status of bypass valve on performance of HPT and LPT are profoundly different. • Unsteady performance of HPT deteriorates dramatically compared to steady state when valve opens. • Significant loss in HPT with open-valve is resulted from both inlet swirl of volute and stronger tip leakage flow in rotor. [ABSTRACT FROM AUTHOR]

This research aims to propose a method to achieve the maximum altitude adaptability of turbocharged diesel engines with the optimum fuel consumption. Firstly, engine performance at different altitudes is studied by experimental method. It is found that the engine power recovery is restricted by three constraints, which are cylinder pressure, exhaust temperature and boosting pressure ratio. Following that, the influence of turbocharging system and fuel injection on the three constraints is studied via experimentally validated numerical model. A power-recovery-zone bounded by the three constraints is proposed, inside which engine power can be fully recovered. The altitude adaptability of the engine is discussed in details via this zone. Further analysis finds that the boosting pressure and the maximum pressure ratio are the key factors to the constraints. A new methodology which can achieve the maximum altitude with the optimum fuel consumption is proposed based the concept of the zone. Finally, the methodology is applied in the engine with three types of turbocharging systems to quantitatively compare their altitude adaptability. Results prove that the altitude adaptability of the engine is notably improved by adapting the proposed method, especially for the two stage turbocharging system. [ABSTRACT FROM AUTHOR]

Penetrating exhaust manifold systems are commonly used in low-speed two-stroke marine diesel engines owing to their potential for energy conservation. However, few studies in the literature have reported on this type of manifold system, and there are few guidelines for optimizing the configuration or predicting the performance via a mean-line model. This study investigates the loss characteristics and flow mechanism of the penetrating exhaust manifold of a low-speed two-stroke marine diesel engine using experimental and numerical methods. The loss is characterized by the entropy production, which indicates a decrease in the energy grade. The results show that the minimum loss can be achieved when the penetration depth and diffusion angle of the manifold are approximately 0.5 and 6°, respectively. Moreover, the loss coefficient is maximally reduced by 14.0 % with penetrating exhaust manifold. The flow field analysis shows that the trend of the flow loss is 'decrease-increase' owing to the interaction among three factors: the mixing loss due to the shearing of the injection flow with the main flow, the momentum loss due to the impingement on the bottom of the main pipe, and the separation loss in the branch pipe owing to the flow divergence. This investigation can provide guidance for the configuration optimization and loss modeling of the exhaust manifold for low-speed two-stroke marine engines. • Loss characteristics of penetrating exhaust manifold in low-speed engine is studied. • Loss performance of PEM shows 'decrease-increase' trend with change of key geometry. • 'V-shape' trend is due to trade-off among losses of mixing, impinging and separation. [ABSTRACT FROM AUTHOR]

Marine diesel engines can be exposed to high backpressure conditions, because various aftertreatment systems and waste heat recovery devices have been applied to reduce emissions and some exhaust outlets are below sea level. The engine performance deteriorates sharply under high backpressure. This paper aims to study power recovery method under high backpressure based on thermodynamic analysis. Firstly, thermodynamic model is established and validated by experimental data. Next, effects of turbocharger efficiency and turbine area on power recovery are studied. The results show that feasible turbine performance are limitations for power recovery. If energy of compressor can be increased without changing turbine area, limitations can be overcome. Thirdly, additional electrically driven compressor as a solution is proposed to recover engine power. A comparative study of different electrically driven compressor schemes is carried out. The most suitable scheme is the series scheme at low-pressure stage because operating points for original compressor and electrically driven compressor are within a reasonable range. Finally, research on power recovery is carried out on optimal electric compressor scheme. The results show that when backpressure is 0.65 bar, engine net power can be increased by 49.4% and exhaust temperature drops by about 77 K, which largely reduces turbine thermal load. • The feasible turbine performance are limitations for power recovery. • Limitations can be overcome by adding compressor energy while keeping turbine area. • Best scheme of AEDC to recover power is the series scheme at low-pressure stage. • When backpressure is 0.65 bar, engine net power can be increased by 49.4%. [ABSTRACT FROM AUTHOR]

Marine diesel engines can be exposed to high backpressure conditions, because various aftertreatment systems and waste heat recovery devices have been widely applied to reduce the emission level, and the outlet of its exhaust manifold is normally below sea level. This article aims to understand the influence of exhaust backpressure on turbocharged engine performance. Diesel engine tests under high backpressure was conducted and it has been found that engine output power drops sharply. To explore the reasons and further study the recovery method, analysis of energy and exergy was carried out. With the increase of backpressure, turbo expansion ratio reduces sharply. But the energy upstream turbine doesn't decrease necessary due to the increase of exhaust temperature. Simultaneously, the exhaust exergy gradually increases by 10.3% when the backpressure increases from 0 bar to 0.55 bar at 75% load, leading to improved energy grade. The turbine output power reduces 56.7% because of the combination results of reduced expansion ratio and increased exhaust energy grade. The method of power recovery should balance these two factors. The study can enlighten the method of power recovery of diesel engine confronted by high backpressure conditions. • Influence of exhaust backpressure on diesel engines were studied comprehensively. • Variation of exhaust energy and exergy under high exhaust backpressure was studied. • Expansion ratio and exhaust energy grade resulted in reduction of turbine power. • A new method for diesel engine power recovery under high backpressure was proposed. [ABSTRACT FROM AUTHOR]

Radial turbine with twin-entry scroll becomes prevailing recently due to its potential for energy recovery of internal combustion engine, especially at low speed condition. However, few quantitative comparisons of the impacts between this configuration and the conventional single-entry turbine have been performed on engine performance. This paper investigates unsteady influence of twin-entry and single-entry scroll on turbocharged engine performance via an in-house developed code ' SPEED-Engine ' coupled with the geometry-based model of twin-entry turbine. Firstly, one-dimensional performance model of turbocharged diesel engine is established. Next, engine performance with two kinds of turbines is compared via the turbo-engine coupled model and confirms the 2.3% improvement of output power for the case with twin-entry. Further discussions manifest that swallowing capacity of twin-entry turbine varies with engine operational conditions, which has a similar function as a variable geometry turbine. The location of hysteresis loop is confirmed to be the reason for this phenomenon. Furthermore, a nominated throat area of twin-entry scroll is developed to compare the influence of twin-entry scroll on engine performance. Specifically, the nominated throat area is decreased by 28% at low engine speed. This investigation develops a convenient method to directly compare the effect of scroll configuration on engine performance. • 1-D turbine model with twin-entry scroll coupled with engine model is established. • Engine power is improved at low speed due to pulse enhancement by twin-entry turbine. • Engine power is improved at high speed due to pulse separation by twin-entry turbine. • Twin-entry turbine works in similar behavior as variable geometry turbine does. • A nominated A/R is proposed to measure averaged twin-entry turbine performance. [ABSTRACT FROM AUTHOR]