Two-stage Turbocharging System Research Articles

Research and Application of Diesel Engine Turbocharging Technology in Plateau Environment

This article summarizes the changes and correction methods of turbocharger compressor characteristics in plateau environments, providing a basis for the plateau matching of diesel engines and turbochargers. Analyze the current research status of plateau matching between fixed cross-section turbochargers, variable cross-section turbochargers, and two-stage turbocharging systems and diesel engines, and explore the potential of variable cross-section turbocharging (VGT), ordinary two-stage turbocharging (TST), and adjustable two-stage turbocharging (RTST) for diesel engine plateau power improvement. Through comparative analysis, the two-stage adjustable turbocharging system based on VGT combines the advantages of two-stage turbocharging and VGT technology, and has the characteristics of high pressure ratio and wide flow rate, which can significantly improve the comprehensive performance of diesel engines on high altitudes.

Matching and optimization to minimize fuel consumption and NOx emission for a marine diesel engine with turbo-assisted exhaust gas recirculation

Exhaust gas recirculation (EGR) and two-stage turbocharging technology are widely used in marine diesel engines due to their advantages of reducing nitrogen oxides (NOx) emission and improving fuel economy respectively. The matching of EGR, two-stage turbocharging and diesel engine is significant to realize both advantages simultaneously. Turbo-assisted EGR (TA EGR) can achieve high EGR rate and lower fuel consumption due to a turbocharger driving EGR. In this study, a 1D model of the diesel engine with TA EGR coupling two-stage turbocharging system was established by GT-Power. A theoretical matching method was proposed based on the requirements of excess air coefficient and EGR rate. The matching laws of the coupling system were studied, and the preliminary matching results achieved good effects. A fully connected neural network was used as the optimization agent model of the 1D model, and the NSGA II algorithm was used to carry out the multi-parameter and multi-objective optimizing matching. Considering constrained and unconstrained conditions, independent optimizing matching was carried out under each single load, and the weighted brake specific fuel consumption (BSFC) and weighted NOx under all loads were taken as the target to carry out comprehensive optimizing matching. The results showed that the optimization performance is worse under constrained conditions, while TA EGR coupling adjustable two-stage turbocharging system can achieve comprehensive optimal BSFC and NOx, with weighted BSFC decreasing by 3.57% and weighted NOx decreasing by 75.28% compared with experimental results of the original engine.

Summary of Turbocharging as a Waste Heat Recovery System for a Variable Altitude Internal Combustion Engine.

The increase in altitude causes the decrease in internal combustion engine power and the increase in pollutant emission. Converting waste heat into more useful forms of energy through the recovery of waste heat from internal combustion engines is the most promising mechanism for improving both of these goals. This paper comprehensively reviews the development and research of waste heat recovery technology of an internal combustion engine in a variable altitude environment. It is found that exhaust gas turbocharging is the most promising waste heat recovery technology to restore high-altitude internal combustion engine power. Turbochargers are affected by low temperature and low pressure at high altitudes, resulting in poor environmental adaptability, inadequate supercharging ratios, and decreased supercharging efficiency. Therefore, it is very important to select the high pressurization system facing the plateau area and its reasonable matching characteristics. The quality of exhaust energy determines how much waste heat a turbine can recover, and only the exergy part of exhaust energy can realize heat/work conversion. The main disadvantage of turbocharging technology applied in the plateau area is that the speed ratio deviates from the design value, leading to the increase of flow loss inside the supercharger. Therefore, optimizing the internal flow field of a high-altitude supercharger is a key problem to improve the efficiency of energy recovery. The conclusion drawn from this Review is that a two-stage turbocharging system will be a key technology to improve the thermal efficiency and reduce the fuel consumption of high-altitude internal combustion engines in the coming decades. In addition, the efficient utilization of the exhaust energy of the two-stage turbine and the influence of the variable compression process of the two-stage compressor on the working medium in the cylinder will be the focus of future research.

Study on gasdynamic interaction in a regulated two-stage turbocharging turbines at pulsating conditions

Understanding the response of performance of two-stage turbine to pulsating flow in exhaust manifold system is essential for performance improvement of engine. This paper studies unsteady interaction of two turbines in a two-stage turbocharging system via experimental method and a reduced order model. Firstly, experimental results of the unsteady pressure ratio of two turbines are discussed in cases with different engine speeds, engine loads, and bypass valve openings. Results show that the pressure ratio distribution between two turbines is profoundly influenced by the engine condition. The pressure ratio of low-pressure turbine (LPT) increases consistently with the engine speed and load, while it increases slightly or even remains unchanged for high-pressure turbine (HPT). HPT is de-loaded when the bypass valve is open, and there are large numbers of fluctuations with high frequencies in the trace of pressure ratio when the bypass valve is open. Next, a reduced order model of the two-stage turbine is established for turbine responses at pulsating conditions, and model validations of performance and unsteady pressure in two-stage turbine all show high precision. Finally, the model is applied for performance analysis of two-stage turbine system under pulsating conditions. The results show that with the increase in engine speed, load or bypass valve opening, the hysteresis loops of both turbines are expanded around the steady performance curve. However, the deviation of cycle-average performance from steady case for two turbines is notably different. LPT shows a stronger throttling effect at pulsating inflows. Moreover, compared with steady performance for whole two-stage turbine, cycle-average performance is reduced for all pulsating cases, especially for cases of open valve. The differences in turbine performance of two-stage turbine system caused by gasdynamic coupling effect of two turbines are suggested to be considered in the turbo-engine matching.

Theoretical and experimental study on performance improvement of diesel engines at different altitudes by adaptive regulation method of the two-stage turbocharging system

The regulation of the two-stage turbocharging system according to the operation of the diesel engine is key to maximizing its potential for power recovery of an engine at high altitudes. This paper targets air intake recovery of diesel engines at different altitudes, the effects of diesel engine operating conditions, in-cylinder combustion, mechanical efficiency, exhaust temperature, turbocharging system operating parameters, and altitudes on the demand characteristics of the equivalent turbine area (ETA) were analyzed by a thermodynamic model, and a multifactor coupled prediction model for the ETA was established, which can predict the regulation of the ETA at different altitudes and operation conditions based on plain and a small amount of plateau data. To improve the accuracy of the model, the error source of the model was analyzed, and the neural network was adapted to predict major errors. Results indicate that the prediction model had high accuracy and the maximum predicted error of ETA is less than 3%. The control strategy obtained by prediction model can improve air supply and efficiency of turbocharging system, the power and economy of the diesel engine also improved at different altitudes.

Study on the altitude adaptability of single-stage and two-stage turbocharging systems for a heavy-duty diesel engine

It is important to understand the altitude adaptability of the turbocharging system for maximizing its potential in the power recovery of the diesel engine at high altitudes. This study investigated the influence of altitudes ranging from 0 to 4500 m on the performance of the single-stage and two-stage turbocharging systems in a heavy-duty diesel engine. The research was conducted using a six-cylinder, four-stroke, turbocharged, direct-injection diesel engine. An altitude simulation test bench was used to simulate altitudes of 0 to 4500 m by adjusting the temperature and pressure. According to the test results, the altitude adaptability of different turbocharging systems was analyzed based on turbine work and turbocharger efficiency. It was concluded that the high-pressure stage regulation in the two-stage turbocharging system (HRT) strengthens the regulation ability in turbine work, effectively regulating the boost pressure and maintaining high turbocharger efficiency at different altitudes. The HRT can satisfy the regulation ability for altitudes ranging from 0 to 4500 m. The low-pressure stage regulation in the two-stage turbocharging system (LRT) weakens the regulation ability in turbine work and relies on reduction of the turbocharger efficiency to regulate the boost pressure. The LRT ineffectively regulates the boost pressure at low altitudes, with altitude adaptability from 1500 to 4500 m. Due to the exhaust temperature limitation, the waste-gate in the single-stage turbocharging system (WG) is not suitable for large-span regulation to satisfy the performance of the diesel engine at altitudes above 3,000 m compared with the HRT and LRT.

Equivalent model-based optimal matching for two-stage turbocharging systems with bypass valves

A bypass valve can effectively distribute the energy of a two-stage boosting system and adapt to the demand for air intake regulation in multiple combustion modes. Gradually, it has become the direction of evolution of boosting technology. However, the existing two-stage turbocharging system matching methods do not consider the selection of bypass valves simultaneously. This study proposes an optimal matching method (H-TCB) for the critical parameters of a two-stage turbocharging system with a bypass valve based on the equivalent model of a two-stage turbocharging system. Taking the lowest comprehensive energy consumption as the constraint boundary, the theoretical constraint equations for the optimal distribution principle of the pressure and expansion ratios of the two-stage turbocharger with a bypass valve were obtained. The cooperative optimal relationship between the bypass coefficient and flow area of the high-pressure stage turbine and the similar flow of the high-pressure stage compressor were analyzed. The research results show that, as the bypass coefficient increases, the optimized matching high-pressure stage turbocharger efficiency increases gradually, the effective flow area of the high-pressure stage turbine reduces, and the flow of the high-pressure stage compressor increases.

Research on nonlinear model predictive control of regulated two-stage turbocharging system of diesel engine at high altitudes

ABSTRACT Increasingly complex air path concepts are investigated to achieve improving the power while reducing fuel consumption of diesel engines at high altitudes. One promising technology is the Twin-VGT (variable geometry turbocharger) for diesel engines. A control concept has to be developed to exploit boost potential by coordinated management of the two turbocharger stages at different altitudes. In this paper, a nonlinear model prediction control (NMPC) algorithm based on back propagation neural network (BPNN) was proposed to purpose multi-parameter control of turbocharging system at high altitudes. Optimal control sequences of NMPC were solved by improved particle swarm optimization (PSO), and boost pressure and intake flow achieved good dynamic tracking performance by collaborative control high-pressure VGT (HVGT) and low-pressure VGT (LVGT) under whole operative conditions at high altitudes. NMPC achieved better step response performance compared with PID controller at different altitudes. NMPC control error of intake flow and boost pressure are within 0.26% under steady and transient conditions, exhibiting higher control accuracy and responsiveness even under transient operating conditions at high altitudes.

Experimental investigation on the performance of the prototype of aircraft Opposed-Piston engine with various values of intake pressure

Over the last few decades, we have observed significant changes in the automotive and aviation sector regarding emission reduction and performance improvement. It is said that electrification is the main direction for the automotive industry, especially for short distances; thus, car manufacturers provide their vehicles with fully electric or hybrid engines. However, such an objective is difficult for the aviation industry, where flight endurance plays a key role, especially for small aircraft. For this reason, turbocharged internal combustion and small turbine engines are still widely used in such aircraft.This paper presents the experimental investigation of the intake pressure influence on the axial-opposed piston engine's performance, which might be used for aviation purposes. The experimental results were conducted on a prototype, axial opposed-piston engine PAMAR 4 equipped with the two-stage turbocharging system. Thanks to its variable systems, such an engine provided a wide range of intake pressure values. The tests were performed for intake pressure values up to 453 kPa. The experimental tests proved that the engine efficiency increased with the intake pressure. However, the engine's durability and reliability might be significantly affected due to the high in-cylinder pressure and temperature.

Performance Optimization of the High-Pressure Compressor in Series Two-Stage Turbocharging System Based on Low-Speed Performance Requirements of Diesel Engine

Abstract The performance of the high-pressure (HP) compressor is very important for the two-stage turbocharging system. However, the performance of HP compressor on the engine most of the time is poor at low speed and low mass flow conditions. These will lead to poor engine performance at low engine speed. The purpose of this paper is to improve the performance of the HP compressor at low speed and low mass flow conditions. The Latin hypercube design of the experiment method is used to establish the Kriging model and global optimization by multi-objective genetic algorithm NSGA-II to optimal HP compressor. The simulation results indicated that the flow field within the compressor was improved and the high entropy generation area was reduced. The new design delayed the mixing between the tip clearance leakage vortex flow and main flow. The low-speed performance of the HP compressor was improved. The turbocharger gas stand tests and engine bench tests were carried out. The results showed that the efficiency and pressure ratio of the optimized design is increased by 2.1% and 3%, respectively. The engine achieved better performance in low-speed conditions. The pumping means effective pressure (PMEP) and intake airflow increased by 7% and 4.98%, respectively, while brake specific fuel consumption (BSFC) and soot emissions decreased by 0.56% and 32.8%, respectively.

Investigation of inter-stage passive flow control for turbine performance improvement on regulated two-stage turbocharger

Abstract The flow field coupling effect between the HPT (high pressure turbine) and LPT (low pressure turbine) introduces a particular flow structure to the two-stage turbocharging system. Compared to the isolated turbines, the performance of these two connected turbines will inevitably be affected by each other. However, in the open state of the bypass valve, the influence of the bypass flow on this flow field coupling effect is still unknown. In this study, the inter-stage performance interaction of regulated two-stage turbocharger was investigated through the three-dimensional numerical method. With the bypass valve open, the influence of different positions of the bypass branch on the inter-stage coupling effects is investigated. The results manifest that the different positions of the bypass branch significantly change the performance of low pressure turbine and the flow interactions within the inter-stage. When the bypass branch is on the right, the LPT efficiency improves by approximately 2.2%. The detailed flow field analysis of the inter-stage pipe, volute and rotor is conducted to reveal the flow mechanism behind the inter-stage interactions. Based on this investigation, a new passive flow control scheme is proposed to ameliorate the swirling flow at the LPT inlet and improve the performance of LPT.

An Experimental and Computational Investigation of Tailor-Developed Combustion and Air-Handling System Concepts in a Heavy-Duty Gasoline Compression Ignition Engine

This study investigates using tailor-developed combustion and air-handling system concepts to achieve high-efficiency, clean gasoline compression ignition (GCI) combustion, aimed at addressing a future heavy-duty ultralow NOx standard of 0.027 g/kWh at the vehicle tailpipe and the tightening CO2 limits around the world by combining GCI with a cost-effective engine aftertreatment system. The development activities were conducted based on a 15 L heavy-duty diesel engine. By taking an analysis-led design approach, a first-generation (Gen1) GCI engine concept was developed and tested, encompassing tailor-designed piston bowl geometry, fuel spray pattern, and swirl motion paired with a customized, fixed-geometry, two-stage turbocharging system and a high-pressure EGR loop with two-stage cooling. Across four key steady-state operating points, the Gen1 GCI concept demonstrated 85–95% lower smoke and 2–3% better diesel-equivalent gross indicated fuel consumption compared to the diesel baseline at 1 g/kWh engine-out NOx. By upgrading to a Gen2 air-handling concept that was composed of a prototype, single-stage, variable-geometry turbocharger and a less restrictive EGR loop, 1D system-level analysis predicted that the pumping mean effective pressure was reduced by 43–54% and the diesel-equivalent brake-specific fuel consumption was improved by 2–4%, thereby demonstrating the performance enhancement potential of refining the air-handling system.

Experimental investigation on combustion and particulate emissions of the high compressed natural gas reactivity controlled compression ignition over wide ranges of intake conditions in a multi-cylinder engine using a two-stage intake boost system

Compressed natural gas (CNG)/diesel reactivity-controlled compression ignition was investigated to understand the combustion and emission characteristics over wide ranges of intake pressure and exhaust gas recirculation (EGR) rate at high load condition. Reactivity-controlled compression ignition is a dual fuel engine combustion strategy that employs in-cylinder fuel blending with two different reactivity fuels, and multiple injections for the in-cylinder fuel reactivity control to optimize the combustion phasing, duration, and magnitude as well as NOx and soot reduction. High CNG substitution was of interest since it could lead to greater CO2 and particulate matter reductions. The present 80% CNG substitution required substantial intake boosting due to the charge air displaced by CNG. The experimental engine is commissioned for the reactivity-controlled compression ignition regime using natural gas and diesel fuel with a two-stage turbocharging system. The intake boosting system achieved the intake pressure and EGR rate of 210 kPa and 25%, respectively, when the EGR valve was fully open. The intake pressure and EGR levels varied in the ranges of 150 to 210 kPa and 0 to 25%, respectively. The corresponding equivalence ratio ranged from 0.85 to 0.5. The intake system achieved the highest turbocharger efficiency of 56% at the maximum boosting operation. The highest CO2 reduction was 23.4% at the maximum boosting condition. The improvements under the enhanced intake condition were significant from the standpoints of both efficiency and emissions, including in terms of the particle concentrations.

Optimization Matching Method of Two-Stage Turbocharging System Under Variable Expansion Ratio at High Altitudes

Optimization Matching Method of Two-Stage Turbocharging System Under Variable Expansion Ratio at High Altitudes

Experimental Investigations on Control Strategy of Regulated Two-Stage Turbocharging System for Diesel Engine Under Transient Process

Experimental Investigations on Control Strategy of Regulated Two-Stage Turbocharging System for Diesel Engine Under Transient Process

Aerodynamic interaction of turbines in a regulated two-stage turbocharging system

Two-stage turbocharging becomes prevailing in internal combustion engines due to its advantage of flexibility of boosting for the variation of operational conditions. Two turbochargers are closely coupled by engine manifolds in the system especially under the requirement of compactness. This paper studies the influence of the interaction of two turbines in a two-stage turbocharging system on the performance. Results show that the performance of low-pressure turbine is highly sensitive to the stage interaction. Specifically, compared with the cases without interaction, the efficiency of low-pressure turbine increases maximumly by 2.8% when the bypass valve is closed, but reduces drastically by 7.5% when the valve is open. Detailed flow analysis shows that the combined results of swirling flow from the high-pressure turbine and the Dean vortex caused by the manifold elbow result in the alleviation of entropy generation in the turbine rotor. However, when the bypass valve is open, interaction of the swirling flow with the injected bypass flow results in strong secondary flow in the volute and distorted inlet flow condition for the rotor, leading to the enhancement of entropy generation in low-pressure turbine. The study provides valuable insights into turbine performance in a two-stage turbocharging system, which can be used for the modeling and optimization of multi-stage turbocharging systems.

Experimental study on the approach for improved brake thermal efficiency on a two-stage turbocharged heavy-duty diesel engine

The approach to achieving improved brake thermal efficiency (BTE) for a heavy-duty diesel engine was studied by experiment analysis. The engine was designed on the basis of a two-stage turbocharger system (high-pressure (HP) turbine with variable geometry turbine) and a variable effective compression ratio through retarded intake valve closing timing. The cooperative control of minimum charge density, compressor efficiency, and compressor pressure ratio distribution was proposed to optimize the BTE. The interactive principle was then clarified. Results showed that the gross indicated thermal efficiency (ITEg) increased rapidly with charge density because of the promotion of the mixing rate. However, the increased charge density had a threshold, beyond which the pumping loss (PL) increased rapidly and thus impeded the ITEg growth rate. Therefore, a minimum charge density should correspond to mixing rate requirements. Moreover, the PL decreased with the decrease of the turbocharger driving power when the charge density was kept constant. Therefore, in the case of minimum charge density satisfying the mixing rate, the minimum turbocharger driving power should be limited to minimize PL by improving the compressor efficiency and optimizing the compressor pressure ratio distribution. At the core of the cooperative control of minimum charge density, compressor efficiency, and compressor pressure ratio distribution was thus identified as the simultaneous optimization of the mixing process and the gas exchange process. Such optimization contributed to the maximization of the BTE.

Transient Simulation of the Six-Inlet, Two-Stage Radial Turbine under Pulse-Flow Conditions

In recent years, the automotive sector has been focused on emission reductions using hybrid and electric vehicles. This was mainly caused by political trends promoting “green energy”. However, that does not mean that internal combustion engines (ICEs) should be forgotten. The ICE has still the potential of recovering energy from exhaust gases. One of the promising ways to recover energy is turbocharging. Over the years engine manufacturers have designed very efficient turbocharger systems which have greatly increased the overall engine efficiency. This led to pollutant emission reductions. This paper presents the results of the three-dimensional (3-D) numerical simulations of the two-stage, six-inlet turbocharging system under the influence of unsteady, pulsed-flow conditions. The calculations were carried out for three turbine speeds. The most interesting results of this study were the separation of exhaust gases coming from the six-exhaust pipes and the performance of both stages under pulse-flow conditions. The two-stage turbocharging system was compared against the single-stage turbocharging system and the results showed that the newly designed two-stage turbine system properly separated the exhaust gases of the adjacent exhaust pipes.

Theoretical and experimental investigation of the pressure ratio distribution and the regulation strategy of a two-stage turbocharging system for various altitudes operation

Fixed two-stage turbocharging system matched at high altitude leads to engine performance deterioration at low altitudes due to unreasonable pressure ratio distribution between two stages. In this paper, a thermodynamic model of regulated two-stage turbocharging system is established. Theoretical analysis shows the pressure ratio distribution should lean towards a turbocharger with greater efficiency, and the high-altitude operation intensifies the role of HP stage. Experiments are conducted on an environment simulation test bench. Then, the optimal pressure ratio distribution and ETAR at various altitudes are proposed. Experiment results demonstrate that the turbocharging system boosts sufficient intake air with the optimal ETAR. Compared to that with the fixed turbocharging system, the maximum increment of the overall efficiency is 9.3 % at 0 m and attains 1.5 % at 3000 m. Consequently, the output torque is 100 % recovered below 3000 m, and it exceeds 91 % at 4500 m. Moreover, the optimal ETAR reduces the BSFC under low altitude conditions.

Experimental investigation of the effects of Miller timing on performance, energy and exergy characteristics of two-stage turbocharged marine diesel engine

In order to analyze and improve the thermodynamic process of marine diesel engines and improve energy efficiency, the experimental study of the influence of Miller timing on the performance, energy and exergy of marine diesel engines was realized by redesigning the camshaft and adjusting the two-stage turbocharging system. The research results shown that with the increase of Miller timing, the average pumping loss decreased, the peak HRR and the maximum combustion temperature decreased, and the crank angle corresponding to the peak HRR was delayed backward, resulting in a backward delay of the 50% point, the 10–90% combustion duration was extended, and the EER, EEE and BTE first increased and then decreased. Secondly, the Miller cycle combined with two-stage turbocharging could make marine diesel engines reduced NOx emissions by more than 25% with a small effect on the BSFC. In addition, as the Miller timing increased, the proportion of exhaust energy, heat transfer energy to coolant, mechanical loss, and combustion loss all decreased, while the proportion of brake output work first increased and then decreased. The change trends of exergy terms with load and Miller timing were similar to their corresponding energy. It was worth noting that the exhaust exergy accounted for about 40% of the exhaust energy, while the heat transfer exergy to coolant accounted for only 13% of the heat transfer energy to coolant, indicating that the exhaust energy quality was higher, the utilization potential was greater, and the efficient utilization interval was concentrated in the high load area.