Variable Geometry Turbocharger Research Articles

Experimental and simulation research on the lean combustion characteristics of direct-injection hydrogen engine

At a constant engine speed of 2000 r/min and 5 bar gross indicated mean effective pressure, experiments were carried out on a 1.5 L engine with a variable geometry turbocharger to examine the combustion and emission characteristics of a direct injection hydrogen engine under lean combustion conditions. Additionally, a CFD simulation model was established to investigate the formation process of the air-fuel mixture and the generation of nitrogen oxides (NOx). The findings demonstrated that the uniformity of the hydrogen-air mixture in the cylinder descended with a delay in SOI (start of injection), and that the thermal efficiency often rose initially before declining. When SOI was set at −80°CA ATDC, the engine achieved maximum indicated thermal efficiency, brake thermal efficiency, and output torque values of 40.8%, 36.22%, and 61.2 Nm, respectively. However, as the SOI was delayed, the combustion variability ascended, and when the SOI was delayed to −20°CA ATDC, there was a significant chance that abnormal phenomena like pre-ignition would occur. BTE achieves a maximum of 36.38% when λ is 2.2 and SOI is −40°CA ATDC. Under lean combustion conditions, temperature was a major factor in the generation of NOx, and homogenous combustion can substantially reduce NOx emissions. NOx emissions are always less than 100 ppm when SOI is before −80°CA ATDC.

LQTI boost pressure and EGR rate control of a diesel air charge system with eBoost assistance

Turbocharged diesel engines often suffer significant response delay due to so-called turbo-lag, especially engines with large displacement. For this reason, many technologies have been developed to reduce turbo-lag. This paper develops a coordinated control strategy for a diesel engine equipped with an eBoost (electrical compressor) system to significantly reduce turbo-lag. A multiple-input and multiple-output (MIMO) Linear Quadratic Tracking with Integral (LQTI) control strategy, along with its scheduling logic, is developed for the Ford 6.7 L 8-cylinder diesel engine equipped with a variable geometry turbocharger (VGT), exhaust gas recirculation (EGR), and added eBoost along with a bypass valve. Note that the existing production engine does not have an eBoost and bypass valve. Multiple model-based LQTI controllers were designed at different engine operational conditions based on the associated linearized models, and the control outputs are scheduled based upon the engine load condition and bypass valve position. The developed control strategy is validated in both simulation and experimental studies, and the test results show a reduction in engine response time by up to 81.36% in terms of reaching target intake manifold (boost) pressure following a load step-up, compared with the production configuration (without eBoost and bypass valve) with no significant impact on NOx emissions.

Experimental study on the transient-state performance of diesel engines at different speeds using the synergistic regulation of VGT and VVT

Heavy-duty diesel engines, the heat engines with the highest thermal efficiency, usually operate under transient conditions. Thus, it is important to study the transient performance of heavy-duty diesel engines. This paper aims to solve the problems of combustion deterioration, poor response, and emission deterioration caused by the mismatch between the air intake response and the fuel system under the strong transient condition of sudden loading of 1 s under constant speed. In this paper, an experimental study on the transient performance at different speeds under the coordinated regulation of a variable geometry turbocharger (VGT) and variable valve timing (VVT) is conducted. The study found that the transient torque response is affected by combustion in the cylinder and pump work. During the low-speed transient process, due to reduced airflow and pumping losses, the VVT is switched off while the VGT delay is increased to improve air response. Consequently, the mixture in the cylinder is fully burned, and improved transient performance is obtained. In the high-speed transient process, the engine air intake flow is improved. Through the VVT is ON at the appropriate time and the VGT hysteresis control, the pumping loss can be effectively reduced, and excellent transient performance can be achieved to ensure the fast response of the in-cylinder charge. Given sudden loading from 10% to 100% within 1 s under a high speed of 1600 r/min, the VVT switches on with a 0.15 s delay, and the VGT is controlled with a 0.4 s delay. A torque response of 0.82 s can be achieved, and the soot peak value is reduced by 66.26%, and the accumulated value of soot is reduced by 46.91%. At a low speed of 1000 r/min, given sudden loading from 10% to 100% within 1 s, the 0.6 s VGT delay can reduce the accumulated value of soot by 78.57% and 56.22% compared with delays of 0.2 and 0.4 s.

Influence of cooling loss on the energy and exergy distribution of heavy-duty diesel engines based on two-stage variable supercharging, VVT, and EGR

The application of mechanisms such as exhaust gas recirculation (EGR) coupled with variable valve timing (VVT) and a variable geometry turbocharger (VGT) can improve engine efficiency; however, the energy laws and loss distribution after EGR, VVT, and VGT changes are unclear, restricting the optimization of engine structures and corresponding strategies. Herein, a six-cylinder engine is studied, revealing that the cooling loss of the high-pressure (HP) EGR loop is an important factor affecting the engine energy distribution. The cooling loss accounts for 10.00%–20.00% of the total energy, with an average increase of 1.73%, surpassing other energy losses growth rates. The low-pressure (LP) EGR loop considerably reduces cooling losses. The cooling loss of the LP EGR loop is only 64.05% of the HP EGR loop at a 20% EGR rate. When the EGR rate is >10%, the resulting lower cooling losses effectively improve the engine efficiency and the indicated thermal efficiency (ITE) of the LP EGR loop is 0.20%–0.33% higher than that of the HP EGR loop; when the EGR rate is 21%, the ITE of the LP EGR loop reaches 49.52%. By studying the variation in exergy with operating parameters, it is found that while increasing the EGR rate from 15% to 20%, the proportion of available exergy increases by adjusting the VVT to −85° crank angle after top dead center (CA ATDC) or adjusting the VGT to 47.5% under the original operating scheme of the LP EGR loop (−146° CA ATDC; VGT = 42.5%). The available exergy increases from 71.22%–71.42% (−146° CA ATDC; VGT = 42.5%; original device) to 71.88%–71.58% (−146° CA ATDC; VGT = 47.5%) and 72.02%–72.21% (−85° CA ATDC; VGT = 42.5%). This study explores the energy distribution under different operating schemes, providing theoretical guidance for further improving the thermal efficiency of the entire device.

A matching method for Twin-VGT systems under varying expansion ratios at high altitudes

In this study, we established a matching method for a twin variable geometry turbocharging (Twin-VGT) system under varying expansion ratios at high altitudes. In addition, we developed an equivalent thermodynamic model of a two-stage variable turbine with the effective flow areas of turbines obtained under velocity constraints for altitudes ranging from 0 to 5500 m. The effects of altitudes on the matching efficacy of a two-stage compressor under different operating conditions were evaluated. Additionally, an optimal distribution of the total boost pressure was determined to minimize the output power of the two-stage compressor during non-isothermal compression at various altitudes. Furthermore, the interplay between exhaust available energy (EAE), total expansion ratio (TER), exhaust temperature, and turbine power was investigated. Lastly, the peak efficiency of the turbocharging system was evaluated by analyzing the distribution of the TER and total enthalpy drop, aimed at optimizing EAE at different altitudes.

Experimental Study on the Flow Characteristics of Two-Stage Variable Turbines in a Twin-VGT System

The twin variable geometry turbocharger (VGT) System, through efficient use of exhaust energy, maximizes internal combustion engine (ICE) power, reduces exhaust emissions and improves reliability. However, the internal flow characteristics of the twin-VGT system are greatly affected by the environment. To ensure that the two-stage adjustable supercharged internal combustion engine is efficient in all geographical environments and under all operating conditions, it is necessary to conduct in-depth research on the internal flow characteristics of high- and low-pressure turbines. In this paper, an experimental system of the flow characteristics of a double variable-geometry turbocharging (twin-VGT) system is designed and developed. A two-stage variable turbine flow characteristic test was carried out, focusing on the relationship between the initial rotational velocity of high variable-geometry turbocharging (HVGT) and blade opening in low variable-geometry turbocharging (LVGT). The effects of high- and low-pressure variable-geometry turbocharger (VGT) blade opening on available exhaust energy, expansion ratio distribution, blade velocity ratio, compressor power consumption and isentropic efficiency were studied. The results show that when the available energy of exhaust gas is constant, with the increase in HVGT turbine speed, when the LVGT blade opening decreases by 10%, the low-pressure turbine expansion ratio increases by about 0.23.

Experimental investigation of the working boundary limited by abnormal combustion and the combustion characteristics of a turbocharged direct injection hydrogen engine

In the process of hydrogen energy conversion and utilization, the direct-injection hydrogen internal combustion engine has been proven to produce zero carbon emissions with high thermal efficiency. However, the risk of abnormal combustion and high requirements of turbocharging limits the improvement of engine performance. This paper focuses on exploring the performance boundary of a 2.0 L turbocharged direct injection hydrogen engine with bench test under all working conditions. Applied variable geometry turbocharger can provide high intake pressure of 270 kPa with proper exhaust back pressure under all engine speed working conditions by changing the turbo opening angle. Delayed injection timing can enhance the performance, while improper injection timing may cause severe pre-ignition and afterburning. The burn duration ranges from 11 °CA to 29 °CA is significantly impacted by the engine speed and the excess air fuel ratio, whereas the load exerts less influence. Furthermore, the boundary of the minimum excess air fuel ratio limited by knock with different intake pressure, compression ratio and ignition timing are investigated and optimized. The minimum excess air fuel ratio limited by knock reaches 1.80 with a maximum torque of 325 Nm at the engine speed of 2500 rpm due to the limitation of the pre-ignition and super -knock. A high brake thermal efficiency of 43.02 % and a maximum power of 125 kW are achieved with the minimum excess air fuel ratio limited by knock of 2.05 and 1.4 respectively.

Effect of variable geometry turbocharger on the performance of the opposed piston engine – An experimental approach

The increasing trend of low-carbon policy obligates engine manufacturers to implement new solutions to meet demanded emission reduction. Thus, a growing interest has been in reviving the 2-stroke, opposed-piston engine concept to improve engine thermal efficiency. Although such an engine offers advantages over classic, 4-stroke engines, its application was limited only to the marine sector. Also, recent research activities were mostly limited to scavenging and combustion process simulations due to the lack of available test engines and challenging experimental setup requirements.The authors tested a prototypical 2-stroke, axially opposed-piston engine under various variable turbocharger geometry settings. The author's previous paper on experimental tests with a fixed vane turbocharger influenced the current research activities. The experimental research of a unique axial opposed-piston engine with a wobble-plate mechanism, combined with variable turbocharger geometry application, signified the novelty of such research. The engine test stand accurately measured instantaneous intake and exhaust pressure, in-cylinder pressure and temperature, brake thermal efficiency, and emission. The study demonstrated that the axial opposed-piston engine provides high efficiency of 49.2%. However, the variable turbine geometry actuation increases its efficiency to 51.2% at high load conditions, contributing to CO, HC, and soot emission reduction by 25.1%, 52.5%, and 14.7%, respectively.

Physics-informed neural networks for predicting gas flow dynamics and unknown parameters in diesel engines

This paper presents a physics-informed neural network (PINN) approach for monitoring the health of diesel engines. The aim is to evaluate the engine dynamics, identify unknown parameters in a “mean value” model, and anticipate maintenance requirements. The PINN model is applied to diesel engines with a variable-geometry turbocharger and exhaust gas recirculation, using measurement data of selected state variables. The results demonstrate the ability of the PINN model to predict simultaneously both unknown parameters and dynamics accurately with both clean and noisy data, and the importance of the self-adaptive weight in the loss function for faster convergence. The input data for these simulations are derived from actual engine running conditions, while the outputs are simulated data, making this a practical case study of PINN’s ability to predict real-world dynamical systems. The mean value model of the diesel engine incorporates empirical formulae to represent certain states, but these formulae may not be generalizable to other engines. To address this, the study considers the use of deep neural networks (DNNs) in addition to the PINN model. The DNNs are trained using laboratory test data and are used to model the engine-specific empirical formulae in the mean value model, allowing for a more flexible and adaptive representation of the engine’s states. In other words, the mean value model uses both the PINN model and the DNNs to represent the engine’s states, with the PINN providing a physics-based understanding of the engine’s overall dynamics and the DNNs offering a more engine-specific and adaptive representation of the empirical formulae. By combining these two approaches, the study aims to offer a comprehensive and versatile approach to monitoring the health and performance of diesel engines.

Study on the Effect of Exhaust Gas Recirculation Coupled Variable Geometry Turbocharger and Fuel Quantity Control on Transient Performance of Turbocharged Diesel Engine

With increasingly stringent emissions regulations, there are growing demands for the transient performance of diesel engines. This study conducted a transient bench test on a two-stage turbocharged heavy-duty diesel engine to optimize its performance during a load increase (20% to 100% in 1 s) at a constant speed (1200 RPM) transient process. The results showed that the transient control scheme using the low-pressure EGR system resulted in a 42.1% reduction in the peak value of soot emission, a 24.8% decrease in the peak value of NOx emission, a 9.14% decrease in ISFC and a 30.6% increase in maximum IMEP achieved in 1 s, compared to the steady-state optimization control scheme without EGR. Transient control scheme using the high-pressure EGR system resulted in a 24.4% reduction in the peak value of soot emission, a 31.8% reduction in the peak value of NOx emission, a 9.52% reduction in ISFC, and a 31.7% increase in maximum IMEP achieved in 1 s. The comparison of high and low-pressure EGR systems revealed that the low-pressure EGR system produced lower compromising emissions, while alterations in control parameters for the diesel engine with a high-pressure EGR system had a more significant impact on the transient process performance.

Enabling off-highway diesel engine downsizing and performance improvement using electrically assisted turbocharging

Internal combustion engine (ICE) downsizing through various turbocharging configurations is generally known by the powertrain design community as an effective means to reduce frictional losses, increase waste heat recovery, and improve fuel efficiency while increasing engine power density. However, often is the case that turbocharging strategies, including variable geometry turbochargers, and regulated two-stage turbochargers, incur the performance tradeoff between transient response and fuel economy (pumping losses) at high engine speeds. For off-highway vehicles having particularly transient and high-powered duty cycles, efforts to improve this tradeoff and increase operational flexibility have turned to evaluating various electrified air system architectures. In this study, a 4.5 L diesel-ICE configured with an electrically driven compressor (eBooster®) is placed in series with a conventional turbocharger and integrated into a 48 V mild-hybrid powertrain architecture. The objective of this powertrain configuration is to enable engine downsizing by 34%, replacing the current 6.8 L ICE platform with the hybridized 4.5 L ICE concept. The commercial 1-D simulation software GT-SUITE is used for powertrain system development and system optimization. Development and validation of the GT-SUITE model and air system controls is concurrently supported through experimental data collection. The simulation model development includes using machine learning methods for optimizing exhaust gas dilution, injection timing, and eBooster® power to improve steady-state and transient brake-specific fuel consumption while minimizing criteria pollutant emissions. It was found that total specific fluid consumption over the standardized non-road transient engine duty cycle could be reduced by 18% over the current 6.8 L engine by using an optimized eBoosted 4.5 L engine. The hybridized 4.5 L engine concept concurrently showed sufficient transient response capability and nearly an order of magnitude reduction in duty cycle total soot production.

Numerical Analysis of the Effects of Grooved Stator Vanes in a Radial Turbine Operating at High Pressure Ratios Reaching Choked Flow

The flow through the stator vanes of a variable geometry turbocharger turbine can reach supersonic conditions and generates a shock wave on the stator vanes, which has a potential impact on the flow loss as well as on unsteady aerodynamic interaction. The shock wave causes a sudden increase in pressure and can lead to boundary separation and strong excitation force, besides pressure fluctuation in the rotor blades. Thus, in this study, the flat surface of the vanes of a commercial variable geometry turbocharger turbine has been modified to analyze the effects of two grooved surfaces configuration using CFD simulations. The results reveal that the grooves change the turbine efficiency, especially at higher speed, where the increase in the efficiency is between 2% and 6% points. Additionally, the load fluctuation around the rotor leading edge can be reduced and minimize the factors that compromise the integrity of the turbine. Furthermore, the grooves reduce the supersonic pocket developed on the suction side of the vane and diminish the shock wake intensity. Evaluating the effectiveness of the available energy usage in the turbine, on the one hand, at lower speed, the fraction of energy at the inlet destinated to produce power does not change significantly with a grooved surface on the stator vanes. On the other hand, at higher speed and higher pressure ratio with 5 grooves occurs the most effective approach of the maximum energy.

Influence of the low-pressure exhaust gas recirculation injection point on engine performance

The use of low-pressure exhaust gas recirculation (EGR) has been extended in spark-ignited engines in recent years due to advantages from efficiency perspective. However, the potential condensation of the water contained in the exhaust gases and eventual compressor erosion can limit the usage of such systems during engine warm-up and/or cold ambient conditions. One possibility to avoid condensation at cold ambient is to place the EGR injection close to the compressor wheel, avoiding a complete mixture of both streams, but it alters the flow distribution upstream of the compressor, potentially affecting its performance. In order to assess the impact of this phenomenon in engine operation, a detailed experimental campaign in a state-of-the-art spark-ignition engine was performed comparing this close-coupled configuration with another one where the injection point was far upstream the compressor, ensuring a perfect mixing. A previously developed and validated one-dimensional model of the variable geometry turbocharger was used to analyze in further detail the compressor and turbine operation. The results show a general deterioration of the engine pumping mean effective pressure (up to 0.02 bar) and the specific fuel consumption (up to 4 g/kWh) when applying the close configuration, higher as the EGR rate increases, which is partially due to the change in turbine operation induced by the new compressor working point.

Experimental Case Study of Stochastic Surrogate-Assisted Engine Calibration

Reducing experimental calibration cost to achieve optimal system performance is challenging, especially for highly nonlinear engine systems. With the advancement and widespread adoption of machine learning methods for control applications, it is now possible to use an intelligent black-box model to efficiently optimize nonlinear control systems without the detailed knowledge of system dynamics. The surrogate-assisted optimization approach has been recently proven to work effectively to reduce the overall experimental budget (cost). However, its application to calibrate and optimize a practical control system experimentally is a challenge due to stochastic system and measurement noises. This article experimentally calibrates and optimizes the control parameters of a 6.7L Ford diesel engine using the stochastic surrogate-assisted optimization automatically based on a stochastic Kriging model, which is the first step toward automating the engine calibration process. Two engine control variables, namely, exhaust gas recirculation valve and variable geometry turbocharger vane positions, are calibrated to obtain a tradeoff between engine efficiency, in terms of brake-specific fuel consumption, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{NO}_{x}$</tex-math></inline-formula> emissions, utilizing both the deterministic and stochastic surrogate-assisted learning algorithms. Experimental results show a much better representation of the output response surfaces with the stochastic surrogate-assisted optimization than that from the deterministic approach. Note that the stochastic approach helps direct the search toward the global optimal region without wasting the evaluation budget in exploring the local optima, and the deterministic approach cannot effectively handle stochastic system and measurement noises, resulting in overfitting the data. Therefore, to solve a practical optimization problem with noises, stochastic surrogate-assisted optimization is recommended.

Research on exhaust energy distribution regulation for fuel economy improvement of turbocompound diesel engine

The stringent requirements for reducing CO2 emissions from internal combustion engines promote the development of waste heat recovery (WHR) technologies. Turbocompounding is a promising WHR technology offering fuel-saving potential along with low volume and weight requirements. Meanwhile, the exhaust energy distribution regulation plays a significant role in improving the engine fuel economy. In this study, the coupling influence and mechanism of the variable geometry turbocharger (VGT) turbine and power turbine (PT) regulation on the recovery power and engine performance were studied from novel perspective of exhaust energy distribution. And the cooperative control strategies of VGT rack position and PT speed under whole operating conditions were first proposed. It is concluded that the increase in the VGT rack position and the PT speed leads to a decrease in the proportion of exhaust energy distributed to the VGT turbine, which affects the intake and exhaust conditions, resulting in changes in PT power and net engine output power. In addition, as the engine speed increases under full load, the optimal VGT rack position and PT speed increase. Compared to the base engine, the equivalent brake specific fuel consumption can be reduced by 3.8% at the engine speed of 2200 r/min with the optimized control of the exhaust energy distribution for the turbocompounding. The control strategy of exhaust energy distribution is of great significance to explore the maximum potential of energy efficiency improvement of turbocompound diesel engines.

Thermodynamic analysis on coupling characteristic of Twin-VGT and fuel injection parameters at variable altitudes

ABSTRACT The decrease of inlet charge and mismatch of air and fuel are main reasons for the decrease of engine performance at variable altitudes. Understanding coupling mechanism between two-stage turbocharging and fuel injection system is key to maximize its potential for engine power recovery at variable altitudes. This paper focused on the coupling characteristic of twin variable geometry turbocharging (Twin-VGT) and fuel injection parameters on key parameters of gas path, in-cylinder combustion, and energy flow of the diesel engine at variable altitudes. Firstly, a thermodynamic cycle model of a Twin-VGT diesel engine aiming at variable altitudes was established and validated by experimental data. Furthermore, the coupling mechanism of high-pressure variable geometry turbocharging (HVGT) and low-pressure variable geometry turbocharging (LVGT) vanes on exhaust available energy (EAE), global expansion ratio (GER) and its distribution, global boost ratio (GBR) and its distribution, isentropic efficiency of the Twin-VGT, combustion process, and energy flow of the engine were studied at different altitudes. Enthalpy drop ratio is regulated by HVGT and LVGT and the isentropic efficiency of two-stage turbine reaches to maximum when openings of HVGT and LVGT at 0.35 and 0.75, respectively, at the altitude of 5500 m. Finally, this paper investigated the coupling characteristic of turbocharging and fuel injection parameters on combustion process and engine performance, which provides the theoretical basis for collaborative controlling of the Twin-VGT and fuel injection parameters at variable altitudes. Brake thermal efficiency (BTE) is affected by exhaust temperature which is mainly controlled by HVGT openings and injection advance angle (IAA) at variable altitudes, and BTE reaches to maximum when openings of HVGT at 0.4 and IAA at −5.5°CA under fixed engine load at the altitude of 5500 m.

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.

Thermodynamic cycle characteristics of twin-VGT diesel engine and its control method at variable altitudes

Matching characteristics between two-stage turbocharging and fuel injection significantly affect energy flow distribution in diesel engine thermodynamic cycles at variable altitudes. This paper investigates thermodynamic cycle characteristics of the Twin variable geometry turbocharged (VGT) diesel engine and proposes a control method to optimize the engine’s energy flow at variable altitudes. First, a thermodynamic analysis model was built to investigate the influence mechanism of key thermal parameters on in-cylinder combustion, intake, and exhaust processes at variable altitudes. Furthermore, a principle of four maximum and three minimum was proposed to achieve thermodynamic cycle efficiency for the Twin-VGT diesel engine at variable altitudes. The maximum intake density is based on the interaction of two-stage compression and cooler, which corresponds to a maximum brake thermal efficiency (BTE). The maximum intake density, coupled with fuel injection strategy, would achieve the lowest fuel consumption under a part-load condition and the largest torque corresponding to the minimum air–fuel ratio under a full-load condition. Maximum global expansion ratio (GER) and isentropic efficiency can be achieved by reasonably controlling the effective flow area of high-pressure (HP) and low- pressure (LP) VGT to fully utilize exhaust available energy at variable altitudes. The minimum power consumption for the two-stage compressor is obtained based on the distribution method of global boost pressure (GBR) to reach the targeted boost pressure. This paper provides an energy flow control method to realize an efficient thermodynamic cycle for the Twin-VGT at variable altitudes.

Study on turbocompound system for a heavy-duty diesel engine by combining matching analysis with experiments

In this work, to improve the fuel economy of long-haul commercial vehicles, the effects of turbocompound system matching on engine performance were numerically and experimentally studied. Firstly, a 1D GT-POWER simulation model of an 11 L heavy-duty diesel engine was established and verified by the experimental data. Secondly, the performances of the turbocompound engine matching with different sizes of fixed geometry turbine (FGT) and power turbines were analyzed. It was found that the exhaust energy distribution between the turbocharger turbine and power turbine had a significant impact on engine performance, and the size of the turbocharger turbine had a more noticeable impact than the power turbine. Based on the FGT turbocompound system simulation result, an appropriate variable geometry turbocharger (VGT) and three wastegate turbochargers (WGT) were selected for further simulation and experimental research. In addition, the impacts of the transmission ratio between the power turbine shaft and the engine crankshaft, and the fuel injection timing on the engine performance were experimentally studied. The engine test result showed that the fuel economy was improved by 1.6% under European Steady State (ESC) cycle while keeping the weighted NOx emission the same as the original engine. Finally, the turbocompound engine with WGT was installed on a heavy-duty long-haul commercial vehicle for road tests. The fuel economy of the vehicle was improved by 2.54% under the 80 km/h constant speed road test.

Data-driven model-based calibration for optimizing electrically boosted diesel engine performance

Engine calibration is a process of optimizing its control variables, which is a crucial step to achieve the desired performance from the engine system. However, its complexity has increased dramatically due to the constant evolution of the engine architecture with multiple control variables interacting with each other, making it difficult to calibrate its control variables with significantly increased experimental costs. System complexity also affects the physics-based modeling process as it makes the system model highly non-linear and difficult to capture system dynamics under all engine operating conditions. To overcome these challenges, the current work proposes a machine learning-based framework to reduce the required calibration effort. The work implements a stochastic surrogate assisted optimization approach on an actual engine experimental test setup, which efficiently looks for the global optimal solution based on only the input-output data set. This work performs a steady-state calibration of a turbocharged diesel engine with an additional external electric-assisted boosting system (eBoost). Three control parameters are considered for this study: Variable Geometry Turbocharger (VGT) vane position, Exhaust Gas Recirculation (EGR) valve position, and eBoost speed to identify the optimal trade-off between engine efficiency (Brake Specific Fuel Consumption) and emissions ( NO x). The addition of eBoost makes the calibration problem difficult because the two control parameters, VGT and EGR, also depend on eBoost speed. Using the proposed data-driven calibration approach, the experimental results showed enhanced engine performance in terms of efficiency and emissions using the eBoost compared with the case without eBoost. At the same time, the experimental cost was reduced significantly due to the reduced number of testing points required to achieve the optimum.