Dual-loop Exhaust Gas Recirculation Research Articles

A Modular Approach for Diesel Engine Air Path Control Based on Nonlinear MPC

This article presents a systematic approach to realize highly dynamic control strategies for the air path of diesel engines. It is based on grey-box models of individual air path components, designed to be applied in nonlinear model predictive control (NMPC). Specifically, they are suited for algorithmic differentiation and gradient-based optimization. This modular approach allows to derive models for a variety of complex air path systems and can be identified with a low amount of measurement data. An NMPC structure, which is based on these models, enables the tracking of arbitrary air path reference signals and allows the introduction of further control objectives for overactuated systems. We demonstrate our approach’s general applicability and effectiveness on two different laboratory engines using rapid control prototyping hardware. For a turbocharged light-duty diesel engine with dual-loop exhaust gas recirculation (EGR), we apply the proposed control structure to track intake manifold gas conditions while simultaneously minimizing engine pumping losses. Experimental results show an excellent tracking performance and reduced pumping losses compared to other control strategies. For a turbocharged heavy-duty engine with high-pressure EGR, we experimentally demonstrate a superior tracking performance to that obtained with a reference controller. Due to the modular and systematic approach, the algorithm design is straightforward, and the experimental calibration effort is low.

Ranking of four dual loop EGR modes

Modern Diesel engines contain sophisticated control systems to keep their environmental impact low for sustainable road transport. One of these systems is the dual loop exhaust gas recirculation, which can change combustion properties in several ways. This article presents an engine dyno measurement based on analyzing the duel loop EGR with a medium-duty Diesel engine. Intake throttles and exhaust brakes for the highest freedom in the air-fuel ratio setting support the EGR systems. The EGR modes are compared from fuel consumption, NOx emission, and exhaust gas opacity in steady and transient operations. There are expected results, for instance, in the HP EGR’s faster reaction time or the LP EGR’s boost pressure holding property. Unexpected results are also presented. Contrary to theory, LP EGR generally provides a fuel consumption advantage in many operation points due to its higher boost pressure. Typically, HP EGR can provide lower fuel consumption at higher engine power. In the emission results, LP EGR is favourable both in NOx emission and exhaust gas opacity, whereas the intake throttle-supported HP EGR usually shows the highest emission. Besides, with high EGR rates at lower engine loads, LP EGR can realize low-temperature combustion, where both emissions decrease. No difference can be detected between the LP EGR’s support valves’ results. HP EGR was faster in the transient operation, with about half the reaction time. The results can be utilized for dual-loop EGR layout and control design.

Hybrid Physics-Based Neural Network Models for Diesel Combustion Phasing Prediction

Conventional control-oriented physics-based models can be leveraged for combustion phasing control in modern diesel engines, but very accurate models often require significant computational power. On the other hand, Artificial Neural Network (ANN) models can have high predictive capabilities and lower computational costs but their heuristic nature may make them less desirable for complex and impactful parameters like combustion phasing. This paper addresses these issues by leveraging the advantages of both modeling methodologies in an integrated modeling framework which can be utilized for real-time combustion control for a modern diesel engine. The models are validated with data from a 2.0 L turbocharged diesel engine which is fitted with dual loop exhaust gas recirculation. The results of the modeling frameworks are compared and show that the proposed hybrid model framework can have a Pearson Product-Correlation Coefficient (PPMCC) of a 100% and an RMSE of 8.79 × 10-8 CAD; as compared to the physics-based model with a PPMCC of a 95% and an RMSE of 0.17 CAD.

Effect of EGR strategy on combustion and emission of DMDF engine for meeting China VI emission legislation

Study on EGR mode and demand were carried out to meet with the requirements of main emission limits of China VI on a diesel methanol dual fuel (DMDF) engine equipped with Hybrid exhaust gas recirculation (EGR) system coupled with back pressure valve (BPV). According to the World Harmonized Steady-State Cycle (WHSC) test cycle, the effects of EGR mode under high methanol energy ratio (MER) on the combustion, emissions and economy of DMDF engines were studied without the help of selected catalyst reduction (SCR). Considering the weight based on WHSC test cycle of full load was only 0.083, and EGR demand of full load was low, the optimal EGR strategy under different loads except full load was determined for DMDF engine. The results demonstrated that through the early injection strategy with high MER, particulate matter (PM) emissions were all at an extremely low level, far below the requirements by legislation limit of 0.01 g/kWh. With the increase of EGR rate, nitrogen oxides (NOx) emissions were significantly reduced under different loads, accompanying with one or more EGR modes at 25%, 50%, and 70% loads to ensure that NOx emission could meet the requirements by legislation limit of 0.4 g/kWh, while PM emissions were at a very low level at the same time. Demand for EGR rate of light loads was generally higher than that for medium loads, but under light loads, each of hybrid EGR modes could meet the demand of China VI legislation. While under medium loads, the dual loop (DL) EGR modes, i.e., both low pressure (LP) and high pressure (HP) EGR mode must be needed. In LP EGR mode combined with back pressure valve (BPV), higher EGR rate was required under the same NOx control target, owing to the higher intake air volume than those of other modes. The trade-off relationship in HP_BPV mode between NOx and PM emissions still existed, and high EGR rate often leaded to an increase in PM.

Tailored Air-Handling System Development for Gasoline Compression Ignition in a Heavy-Duty Diesel Engine

The simultaneous application of new low-NOx emissions standards and greenhouse gas (GHG) rules has placed great pressure on the commercial vehicle industry and has driven demand for innovative solutions. One potential solution, gasoline compression ignition (GCI), utilizes gasoline’s lower reactivity to promote partially premixed combustion and extract efficiency while reducing the PM-NOx trade-off curve. Gasoline’s volatility allows for the use of higher levels of exhaust gas recirculation (EGR), a key enabler of GCI combustion. In order to deliver higher levels of EGR while maintaining sufficient boost pressure, a tailored and efficient air-handling system is critical. This work presents the analysis-led development of a low-NOx GCI air-handling system including both turbocharger matching and EGR configuration for a prototype heavy-duty GCI engine based on a model year 2013 Cummins ISX diesel engine using low octane gasoline (RON80). In the analysis-driven development process, a 1D engine system-level analysis was closely coupled with closed-cycle 3D CFD GCI combustion development. Three different boost systems were investigated using a validated 1D engine model: 1) the production turbocharger; 2) an off-the-shelf single-stage waste-gate turbocharger; 3) a prototype single-stage variable geometry turbocharger. For each boost system, three EGR configurations were evaluated: 1) a high-pressure EGR route; 2) a low-pressure EGR route; 3) a dual-loop EGR route. The air-handling system performance was first investigated over five steady-state engine operating conditions extracted from the ramped modal cycle supplemental emissions test. Then, through cosimulation using a Simulink-based engine controls model, the best performing candidates under transient operation through the Heavy-Duty Federal Test Procedure certification cycle were identified. The production turbocharger, designed for 4–6 g/kWh engine-out NOx, suffered from low combined turbocharger efficiency under the low-NOx GCI thermal boundary conditions. The prototype 1-Stage variable geometry turbocharger, when used with a high-pressure EGR configuration, demonstrated higher combined efficiencies, while the waste-gate turbocharger showed the best results when used with a dual-loop EGR system. All low-pressure only EGR configurations were found to incur additional pumping penalties due to the need for a back pressure valve to drive sufficient EGR levels. In the transient test cycle analysis, the single-stage high-pressure EGR system was capable of delivering the target boost and EGR, while the off-the-shelf waste-gate turbocharger, with its higher mass inertia, showed slower turbine response and a resulting lag in boost response. Unsurprisingly, the dual-loop EGR system also suffered from delays in EGR delivery during engine acceleration. In summary, the prototype single-stage variable geometry turbocharger with a high-pressure EGR system produced the best performance over both the steady-state and transient engine cycles and was identified as the best candidate for the prototype low-NOx heavy-duty GCI engine.

Simultaneous control of NOx, soot and fuel economy of a diesel engine with dual-loop EGR and VNT using economic MPC

This paper proposes a nonlinear Economic Model Predictive Control (eMPC) strategy for the airpath management of diesel engines with dual-loop Exhaust Gas Recirculation (EGR) and Variable Nozzle Turbocharger (VNT). The controller directly controls the VNT and dual-loop EGR valves to simultaneously minimise NOx, soot and pumping loss. The novelty of this management strategy is to use a merged controller to replace a conventional combination of supervisory and tracking controllers, as well as eliminating the offline determination of the intake manifold pressure and cylinder oxygen concentration set points. The eMPC computes the set points online based on the engine operating condition, state feedback and the weightings of each economic objective, namely NOx, soot and fuel economy. The eMPC is simulated with an experimentally validated EURO 6 2L four-cylinder engine model. The performance of the eMPC is compared to a production controller over the Worldwide harmonised Light vehicles Test Cycles (WLTC). Compared to the production controller, the eMPC demonstrates NOx and soot emission reductions as well as improved torque tracking and fuel economy.

Model development and experimental validation of an exhaust brake supported dual loop exhaust gas recirculation on a medium duty Diesel engine

Due to the new European emission norms internal combustion engines have to comply stricter rules. The new norms contain new requirements that were not included in previous regulations for example the decreased temperature of the cold start or the real driving emission part. The emission cycles for passenger vehicles are completely news, the stricter emission norms for commercial vehicles will follow them within a few years. Despite the increasing spread of alternative transmission systems in road transport Diesel engines are going to be remain in commercial vehicles in the next decades due to their good torque and fuel consumption performance. The emission of Diesel engines can be kept low by several way: by the modification of combustion processes, or by exhaust gas after treatment. To comply future regulations both of them seems to be necessary. By exhaust gas recirculation systems alternative Diesel combustion processes can be realized which can provide lower nitrogen-oxide emission and in several operation points also lower fuel consumption. Exhaust gas recirculation systems also can support the thermal management of a Diesel engine. To utilize the advantages of the recirculated exhaust gases a complex system is necessary to get a freedom in control possibilities: duel loop exhaust gas recirculated systems supplemented with supporter valves on the intake or on the exhaust side. In this paper a pressure and mass flow rate based control oriented engine model will be presented which contains high and low pressure exhaust gas recirculation systems and both of them are supported by exhaust brakes. The model considers four balance volumes and it has five state variables. The model is validated by an engine dyno measurements on a medium duty Diesel engine.

Numerical investigation on a dual loop EGR optimization of a light duty diesel engine based on water condensation analysis

Exhaust gas recirculation (EGR) is widely used in most current automotive diesel engines as a simple, economical, and highly effective NOX reduction technology. The low pressure (LP) loop EGR has higher deNOX efficiency, but also has problem of water condensation, which causes wear of the turbocharger compressor wheel, and corrosion or freeze rupture of intake components. Using a one-dimensional engine simulation, we built a real-time water condensation model based on heat transfer analysis around the intercooler, and optimized the dual loop EGR control strategy to minimize water condensation while maintaining NOX reduction performance. As a result, water condensation decreased by up to 20.54% at 100 km/h constant-speed driving, depending on ambient temperature and humidity. At 23 °C temperature / 80% humidity, which is the standard condition of worldwide harmonized light-duty test procedure (WLTP), the amount of condensed water decreased by up to 33.39%, for various engine speeds and loads. During worldwide harmonized light-duty test cycle (WLTC) driving, condensed water decreased by up to 30.56%, while fuel consumption increased by maximum of 1.13%. Since the water condensation prediction model presented in this study was constructed through the general energy analysis, it could be applied to various types of engines and operating conditions.

Performance Optimization of a Diesel Engine with a Two-Stage Turbocharging System and Dual-Loop EGR Using Multi-Objective Pareto Optimization Based on Diesel Cycle Simulation

The effects of an electric supercharger (eS) and a dual-loop exhaust gas recirculation (EGR) system on a passenger car’s diesel engine’s emissions and fuel efficiency under various worldwide harmonized light-duty vehicles test procedure (WLTP) reference operation points were investigated using a one-dimensional engine cycle simulation, called GT-Power. After heavy EGR application, the in-cylinder pressure and temperature declined due to a dilution effect. As eS power and rpm increased, the brake-specific fuel consumption (BSFC) decreased because the effects of the air flow rate increased. However, it was unavoidable that nitrogen oxide (NOx) emissions also increased due to the higher in-cylinder pressure and temperature. To induce more EGR to the intake system, a dual-loop EGR system was applied with eS at different low-pressure EGR (LP-EGR) fractions (0, 0.25, 0.5, 0.75, and 1.0). Under these conditions, a design of experiment (DoE) procedure was carried out and response surface plots of the BSFC and brake-specific NOx (BSNOx) were prepared. A multi-objective Pareto optimization method was used to improve the trade-off in results between the BSFC and BSNOx. Through optimization, optimal Pareto fronts were obtained, which suggested design parameters for eS power and rpm to control the engine under various LP fraction conditions.

Numerical methodology on virtual model extension and system-level optimization of light-duty diesel vehicle with dual-loop exhaust gas recirculation

Because of the increased need for virtual analysis during the vehicle manufacturing processes, more stringent optimization methods are required for the simulation field. Owing to the use of big data from engine testing, 1D analysis can provide more powerful approaches in the conceptual design phase for car makers. In this study, system-level optimization of dual-loop EGR was performed at both the engine and vehicle level, whereas our previous research had been performed at the engine level. Depending on the virtually developed engine and vehicle models and control scheme from our previous works, improved driving capabilities could be observed under light-duty diesel vehicle systems under the world-harmonized light-vehicles test procedure (WLTP). The numerical model was extended through two steps. The first step includes model conversion from the base engine model with an HP EGR system to a virtual engine model with a dual-loop EGR system. The second step represents mode extension from the virtual engine model with a dual-loop EGR system to a vehicle model with a dual-loop EGR system. Optimizing the dominant parameters and using design of experiment (DoE)-based multi-objective Pareto optimization methods in each step, fuel economy could be improved by approximately, 1.5% and the deNOX rate was approximately 5% that of the conventional NEDC. It is implied that the dual-loop EGR system and gear strategy could improve vehicle performance under difficult driving conditions.

Intelligent transient calibration of a dual-loop EGR diesel engine using chaos-enhanced accelerated particle swarm optimization algorithm

This article proposes an intelligent transient calibration method for the air-path controller of a light-duty diesel engine. This method is developed based on the chaos-enhanced accelerated particle swarm optimization algorithm. The target is to reduce the engine’s fuel consumption during transient scenarios by optimizing the controller parameters. The advanced dual-loop exhaust gas recirculation system is first introduced. Then, it formulates the transient calibration process as a multiple-objective optimization problem with constraints. Different from steady state calibration, the proposed method designs a new cost-function to evaluate the controller’s transient performance. The intelligent transient calibration module is programmed in MATLAB code. Interface between the calibration module and a physical engine plant is established via ETAS INCA. The optimization result of the proposal method is discussed by comparing it with the result of existing calibration methods. The engine performance with the calibrated controller is evaluated based on engine tests.

Exhaust Pressure Estimation for Diesel Engines Equipped With Dual-Loop EGR and VGT

This paper describes an observer design method that estimates the exhaust manifold pressure in a diesel engine with limited sensor information. In the modern model-based control of air flows, information on the exhaust pressure is often necessary for control stability. However, it is not easy to measure the exhaust pressure with sensors due to the unfavorable environment for measurement and the high cost of sensors. Therefore, a robust observer, which is applicable to engines equipped with a dual-loop exhaust gas recirculation (EGR) system and a variable geometry turbine, is designed to estimate the exhaust pressure. The observer takes the form of a Luenberger-sliding mode observer in order to guarantee its asymptotic stability upon consideration of the model uncertainties. For research on state estimation and control of dual-loop EGR engines, information on the pressure states in the low pressure EGR loop must be provided. Hence, this paper also proposes an intuitive regression modeling method for the pressure states of the compressor inlet and turbine outlet with physical insights into the engine operation. Applying the regression models to the observer algorithm, the estimation performance of the exhaust pressure observer is verified experimentally in both steady state and transient conditions with a 6-L heavy-duty diesel engine.

Tuneable model predictive control of a turbocharged diesel engine with dual loop exhaust gas recirculation

The air path of a turbocharged diesel engine is a multi-input multi-output (MIMO) system with strong nonlinearity, coupling effect, delay and actuator constraints. This makes the design and tuning of the controller complex. In this paper, a tuneable model predictive control (TMPC) controller for a diesel engine’s air path with dual loop exhaust gas recirculation (DLEGR) is presented. The objective is to regulate the intake manifold pressure and exhaust gas recirculation (EGR) mass flow in each loop to meet the time-varying setpoints through coordinated control of the variable geometry turbocharger (VGT) and EGR valves. The TMPC controller adopts the design framework of an MPC controller. This controller is also able to provide a map-based switching scheme for the local controller and the controller’s weightings. A comparison between the TMPC controller and a conventional PID controller is conducted on a validated real-time engine model. The simulation results show that the TMPC controller achieves lower overshoot, faster response and a shorter settling time on the manipulated objects. These improvements are beneficial for obtaining lower fuel consumption. In order to test the capability of the TMPC controller, it is validated on a hardware in the loop (HIL) platform. The results show that the agreement between the simulation and the actual ECU’s response is good.

Decoupled disturbance rejection control for a turbocharged engine with a dual-loop exhaust gas recirculation system

Dual-loop exhaust gas recirculation with a variable-geometry turbocharger is an effective architecture for achieving desired intake manifold conditions, such as the temperature, the pressure and the oxygen concentration of the intake manifold, which have critical roles in advanced combustion mode control. However, the widely used control-oriented model is derived on the basis that the heat transfer between the pipes and the gas is negligible, which means that it suffers from non-trivial errors. Simulation results show that other error sources, including the volumetric efficiency and the orifice equation, are difficult to calibrate accurately and also cause significant errors in the system, particularly in transient situations. Modified active disturbance rejection control with an extended state observer is utilized to deal with the non-linear, multiple-input multiple-output system in this paper. It is demonstrated that the performance of active disturbance rejection control mainly depends on the performance of the extended state observer. In this paper, an extended state observer, which is based on the sliding-mode concept rather than the conventional linear observer, is introduced. By taking advantage of its strong robustness, the system is decoupled into three loops. For each loop, the internal errors and the external errors, including the modelling error and the coupling effects, are lumped into one term; they are then actively estimated and cancelled out by the control input in real time. The proposed method was validated using calibrated GT-Power model simulations.

Optimization of dual-loop exhaust gas recirculation splitting for a light-duty diesel engine with model-based control

The objective of this research was to develop dual-loop exhaust gas recirculation (EGR) split strategies. Model-based control was performed by coupling one-dimensional (1D) cycle simulation with control logic, and the EGR split index (ESI) was developed to investigate split effects on performance and emission. The key control logic concept was to compensate the low pressure (LP) EGR rate. Additionally, ESI, a newly developed index, is a non-dimensional factor expressing the high pressure (HP) and LP portions of the total EGR rate. Using the control model and ESI, the maximum EGR rates were determined under each operating condition, thereby maintaining lean burn combustion and minimizing NOX emission. A multi-objective Pareto method was used with the model-based control to optimize the engine operating parameters and thereby minimize NOX formation and fuel consumption. The control logic applied a step transient analysis based on the optimized parameters.

Pressure model based coordinated control of VGT and dual-loop EGR in a diesel engine air-path system

This paper describes a pressure-model-based coordinated control method of a variable geometry turbine (VGT) and dual-loop exhaust gas recirculation (EGR) in a diesel engine air-path system. Conventionally, air fraction or burnt gas fraction states are controlled for the control of dual-loop EGR systems, but fraction control is not practical since sensors for fractions are not available on production engines. In fact, there is still great controversy over how best to select control outputs for dual-loop EGR systems. In this paper, pressure and mass flow states are chosen as control outputs without fraction states considering the availability and reliability of sensors. A coordinated controller based on the simple control-oriented model is designed with practical aspects, which is applicable for simultaneous operations of high pressure (HP) EGR, low pressure (LP) EGR, and VGT. In addition, the controller adopts the method of input-output linearization using back-stepping to solve the chronic problems of conventional pressure-based controllers such as coupling effects between operations of HP EGR, and VGT. The control performance is verified by simulation based on the proven GT-POWER model of a heavy-duty 6000cc diesel engine air-path.

Decoupled, Disturbance Rejection Control for A Turbocharged Diesel Engine with Dual-loop EGR System

Dual-loop exhaust gas recirculation (EGR) with variable geometry turbocharger (VGT) provides a flexible architecture for achieving desired intake manifold conditions, including temperature, pressure and oxygen concentration, which are critical for advanced combustion mode control in modern engines. However, the highly nonlinear system dynamics and strong coupling effects between loops make the widely used, control oriented model failed to trace the system states well, especially in transient situations. This paper presents a control method for this nonlinear, multi-input multi-output (MIMO) system with the compensation for modeling error and disturbance. By taking both the advantages of the knowledge of system dynamics and the idea of disturbance rejection, the modified active disturbance rejection control (ADRC) with extended states observer (ESO) was utilized to achieve such a control objective. Here, the term "disturbance" lumps all the internal and external errors, including the modeling errors and coupling effects. By actively estimating the disturbance and compensating its effects, the intake manifold conditions can be controlled in a decoupled fashion. The proposed method was validated through high-fidelity GT-Power model simulations.

Control of a dual-loop exhaust gas recirculation system for a turbocharged Diesel engine

Dual-loop exhaust gas recirculation (EGR) with variable geometry turbocharger (VGT) is an effective technique to simultaneously control intake manifold conditions (pressure, temperature, and burned gas mass fraction) in Diesel engines. To address the control problem for this highly coupled and complicatedly dynamic multi-input multi-output (MIMO) system, this paper proposed a control method with decoupled-feedforward loop. Through investigating the dynamics of airpath loop system, a linear-quadratic regulator (LQR) with a decoupled-eedforward control strategy was utilized for the control of the intake manifold conditions. The proposed method was validated and compared with the conventional LQR method via a high-fidelity GT-Power model.

Air Fraction and EGR Proportion Control for Dual Loop EGR Diesel Engines

Este artículo describe una nueva técnica para controlar la fracción de aire fresco en el colector de admisión de motores Diesel con doble circuito de recirculación de gases de escape (RGE). Esta estrategia de control permite regular eficientemente la fracción de aire, satisfaciendo al mismo tiempo una proporción deseada entre las RGEs de alta y baja presión. Basado en un modelo físico de la dinámica de la fracción de aire a lo largo del sistema de aire del motor, un regulador lineal cuadrático a parámetros variables (LPV-LQR) es diseñado para asegurar la estabilidad de la fracción de aire y minimizar un índice de desempeño cuadrático. La controlabilidad del sistema, necesaria para garantizar la existencia del controlador LPV-LQR, se verifica mediante la definición de un subespacio convexo de parámetros utilizando un enfoque politópico. El controlador es evaluado bajo fuertes condiciones transitorias utilizando como referencia, un modelo del motor validado experimentalmente.

Numerical investigation of a dual-loop EGR split strategy using a split index and multi-objective Pareto optimization

A proposed dual-loop exhaust-gas recirculation (EGR) system that combines the features of high-pressure (HP) and low-pressure (LP) systems is considered a key technology for improving the combustion behavior of diesel engines. The fraction of HP and LP flows, known as the EGR split, for a given dual-loop EGR rate play an important role in determining the engine performance and emission characteristics. Therefore, identifying the proper EGR split is important for the engine optimization and calibration processes, which affect the EGR response and deNOX efficiencies. The objective of this research was to develop a dual-loop EGR split strategy using numerical analysis and one-dimensional (1D) cycle simulation. A control system was modeled by coupling the 1D cycle simulation and the control logic. An EGR split index was developed to investigate the HP/LP split effects on the engine performance and emissions. Using the model-based control system, a multi-objective Pareto (MOP) analysis was used to minimize the NOX formation and fuel consumption through optimized engine operating parameters. The MOP analysis was performed using a response surface model extracted from Latin hypercube sampling as a fractional factorial design of experiment. By using an LP rich dual-loop EGR, a high EGR rate was attained at low, medium, and high engine speeds, increasing the applicable load ranges compared to base conditions.