Pressure Exhaust Gas Recirculation Research Articles

Physically-based control-oriented modeling for turbocharged stoichiometric spark-ignited engine with cooled EGR and flexible VVT systems

Accurate estimation and prediction of engine gas exchange system and in-cylinder conditions are critical for spark-ignited engine control and diagnostic algorithm development. In this paper, a physically-based, control-oriented model for a 2.8 l turbocharged, variable valve timing (VVT) and low pressure (LP) exhaust gas recirculation (EGR)-utilizing SI engine was developed. The model includes the impact of modulation to any combination of 10 actuators, including the throttle valve, compressor bypass valve, fueling rate, waste-gate, LP EGR valve, number of deactivated cylinders, intake valve open (IVO) timing, intake valve close (IVC) timing, exhaust valve open (EVO) timing and exhaust valve close (EVC) timing. The accuracy of the model in capturing engine dynamics was demonstrated by validating it against high-fidelity engine GT-Power simulation results for various drive cycles, particularly emphasizing elevated loads. In comparison to the open literature, novel contributions of the effort described in this paper includes in-cylinder gas composition modeling and turbine-out pressure estimation.

A CFD Modelling Approach for the Operation Analysis of an Exhaust Backpressure Valve Used in a Euro 6 Diesel Engine

Harvesting residual thermal energy from exhaust gases with thermoelectric generators is one of the paths that are currently being explored to achieve more sustainable and environmentally friendly means of transport. In some cases, thermoelectric generators are installed in a by-pass configuration to regulate the mass flow entering the thermoelectric generator. Some manufacturers are using throttle valves with electromechanical actuators and electronic control in the exhaust pipe to improve techniques for active control of pollutant emissions in reciprocating internal combustion engines, such as the exhaust gas recirculation. The above-mentioned circumstances have motivated the approach of this work: computational fluid dynamics (CFD) modelling of the operation of a throttle valve used for establishing adequate exhaust backpressure conditions to achieve the low pressure exhaust gas recirculation in Euro 6 engines. The aim of this model is to understand the flow control process with these types of valves in order to incorporate them in an exhaust system that will include two thermoelectric generators used to convert residual thermal energy into electrical energy. This work presents a computational model of the flow through the throttle valve under different temperatures and mass flow rates of the exhaust gas with different closing positions. For all cases, the values of the pressure drop were obtained. In all cases studied, the level of agreement between the modelled and experimental results exceeds 90%. The developed model has helped to propose a correlation to estimate the mass flow rate of exhaust gas from easily measurable quantities.

Nonlinear model predictive control of a DISI turbocharged engine with virtual engine co-simulation and real-time experimental validation

An increasing number of control actuators are being added to internal combustion engines to reduce fuel consumption and meet with emission standards. This research utilizes Nonlinear Model Predictive Control (NMPC) to manage a spark ignition engine equipped with a turbocharger, low pressure Exhaust Gas Recirculation (EGR), and Variable Valve Timing (VVT). This paper focuses on discussing the experimental setup and validation of the proposed NMPC strategy, while an overview of the control-oriented engine model and NMPC formulation is provided. The proposed NMPC-based engine control was implemented into a rapid prototype control system and successfully deployed during dynamometer tests. With a minimum amount of calibration effort, the NMPC exhibits sophisticated transient actuator control, which would otherwise require many calibration maps to achieve. A detailed discussion of these transient maneuvers is provided and reveals that these control actions indeed optimize the control objective function without violation of combustion and hardware capacity constraints.

Experimental energy and exergy analysis of turbocharged marine low-speed engine with high pressure exhaust gas recirculation

Exhaust gas recirculation (EGR) has been widely applied on marine low-speed engine for the Tier III standard. However, few studies focus on energy and exergy analysis to improve the deterioration of fuel economy caused by EGR. This study fills in this gap based on the related experiment. Results show that about 35% EGR rate could achieve the Tier III standard, while cylinder bypass (CB) may raise NOx due to the coupling of CB and exhaust receiver. Subsequent energy analysis shows that improving fuel consumption should start with reducing the energy of heat transfer and exhaust gas. But, the exergy analysis indicates that reducing the irreversibility will be more efficient. The irreversibility mainly comes from in-cylinder, turbocharger and intercoolers. According to the instantaneous in-cylinder exergy analysis, the corresponding irreversibility is due to charge mixing and combustion. Reducing temperature gradient and proportion of premixed combustion are effective methods to inhibit it. EGR has opposite impacts on in-cylinder irreversibility caused by combustion: it enhances this irreversibility by rising maximum temperature and prolonging combustion duration (25% load); but it also raises the proportion of premixed combustion, which will inhibit this irreversibility (100% and 75% load). As for the irreversibility from turbocharger, it is negatively correlated with EGR rate, because of CB reducing exhaust temperature. Whereas, due to the existence of EGR intercooler, the irreversibility caused by intercoolers are positively related with EGR rate.

Design and thermodynamics analysis of marine dual fuel low speed engine with methane reforming integrated high pressure exhaust gas recirculation system

The carbon–neutral target leads to the development of low-carbon\\zero-carbon marine fuels. Natural gas is currently one of the most competitive low-carbon fuels, however, the low compression ratio used to control knock combustion limits the improvement of thermal efficiency of natural gas engines. Meanwhile, low-pressure injection natural gas engines also suffer from methane slip. In this paper, a system including a fuel reformer and a natural gas engine with a high-pressure EGR of 20% was proposed. EGR could reduce NOx emission and control methane slip but it will decrease the thermal efficiency. Fuel reforming could improve engine thermal efficiency and increase flame propagation speed but it will increase NOx emission. Moreover, EGR could also provide higher temperature energy for fuel reforming. Therefore, the proposed system was designed to achieve the complementary advantages between EGR and fuel reforming. The results showed that the thermal efficiency of the proposed system was 49.3% at the reforming ratio of 5%, which is 2% higher than the original engine and 4.7% higher than the EGR engine. In addition, the methane slip was reduced by 20% and the NOx emission was 2.93 g/kWh, which can meet the IMO Tier III. Finally, the thermo-economic analysis of the system and the EEDI calculation were carried out. The results showed that the annual fuel cost saved by installing the system on the ship was approximately US $151,726 and the EEDI was reduced by 3.75%

Numerical assessment of mixing of humid air streams in three-way junctions and impact on volume condensation

Flow mixing at three-way junctions is widely studied due to its usage in countless applications. Particularly, in air conditioning and internal combustion engines, the mixing of humid air streams can lead to volume condensation, provided that any local temperature achieves dew conditions. This work investigates and quantifies the correlation between mixing intensity and generated condensation. A method to define mixing indexes is developed, comparing its performance against literature references that employ temperature or passive scalar to evaluate mixing. A numerical campaign of 128 Reynolds-Averaged Navier Stokes three-dimensional (3D) simulations is designed to explore different junction operating conditions. A validated condensation submodel embedded in the 3D model enables the quantification of condensation at the junction outlet, which also can be estimated by means of a 0D model that provides the psychrometric state of a homogeneous mixture between the inlet streams. A strong linear correlation is found between condensation and the product of mixing indexes and 0D condensation mass flow rate, since the latter carries the psychrometric information of the working point. This connection allows to find junction design guidelines to reduce mixing and therefore condensation. Additional simulations confirm that removing junction valves, reducing mixing length, increasing the branch duct diameter and aligning the branch leg with the outlet duct significantly decrease condensation. In the framework of low pressure exhaust gas recirculation (EGR), this condensation damages the compressor wheel. If junctions are designed as suggested, the current constraints over EGR rates to limit condensation can be removed, which will result in internal combustion engines with lower emissions and better fuel consumption. • A new definition of mixing index is developed by calculating the unmixed area. • Flow mixing and condensation at T-junctions is assessed using 0D and 3D models. • Condensation is strongly correlated with psychometric conditions and mixing. • Mixing is reduced by decreasing length and momentum ratio and relocating valves. • Guidelines to design junctions with reduced volume condensation are provided.

Design and Thermodynamics Analysis of Marine Dual Fuel Low Speed Engine with Methane Reforming Integrated High Pressure Exhaust Gas Recirculation System

Design and Thermodynamics Analysis of Marine Dual Fuel Low Speed Engine with Methane Reforming Integrated High Pressure Exhaust Gas Recirculation System

Stage 3a environmental compliance of the 6-cylinder tractor engine

The development strategy of the Minsk Motor Plant, implemented within the framework of plant and state scientific and technical programs, is aimed at producing competitive products that meet modern technical requirements of international standards and quality. The mandatory requirement for the successful promotion of diesel engines on the off-road vehicle market is to ensure the required environmental performance, with low fuel consumption and low engine cost. The well-known technical solutions aimed to achieve environmental indicators of the Stage 3A level significantly increase the cost of diesel engines, therefore, the achievement of the required environmental standards without a significant increase in the cost of engines can be considered an urgent task. Purpose. Stage3A Environmental Compliance for 6 Cylinder Tractor Diesel. Methodology. Experimental studies were carried out for diesel engines equipped with: a Common Rail BOSCH accumulator fuel supply system with an injection pressure of 140 MPa, injectors with 7 nozzle holes; a direct-action fuel supply system with a MOTORPAL fuel pump providing a maximum injection pressure of 100 MPa, MOTORPAL injectors and AZPI with five nozzle holes; combustion chambers of two types with bowl diameters of 55 and 67.5 mm; cylinder heads providing swirl ratios 3–4 and 3.5–4.5; high pressure exhaust gas recirculation system. The tests were carried out at characteristic points of the NRSC cycle at three crankshaft speeds: minimum idle speed 800 min-1, maximum torque 1600 min-1, and maximum power 2100 min-1. Results. It turned out that it is possible to achieve Stage3A emissions standards on 116 kW diesel engines using direct fuel equipment and a semi-open combustion chamber, on 156 kW diesel engines using a Low Cost Common Rail fuel supply system and an open combustion chamber. Originality. The results of the combustion chamber shape choice, the parameters of the fuel-injection equipment, the swirl ratio of the inlet channels, valve timings and parameters of the exhaust gas recirculation system made it possible to organize diesel engine workflow of the Stage 3A ecological level. Practical significance. Construction elements of the six-cylinder diesel engines have been developed and introduced at the Minsk Motor Plant.

Development and validation of nonlinear dynamic engine airpath models for real-time advanced control application

This paper proposes model reduction techniques for reducing engine airpath models in real-time (RT), for a control oriented application in an engine equipped with high pressure exhaust gas recirculation (EGR-HP) and single stage turbocharger. There are two major challenges addressed by authors: First, reducing the order without compromising the performance in terms of accuracy by decoupling the nonlinear coupled differential equations of airpath system in-order to use them in real-time processor-in-loop control application. A model reduction technique based on different dynamic characteristics between thermodynamic states followed by semi-implicit Euler (SIE) numerical method to solve coupled dynamic multi-input multi-output (MIMO) differential equation models is demonstrated. Second, the authors have proposed a novel method to calculate gas mass flow via compressor, coupled with engine airpath model in real-time. The proposed models of airpath system coupled with turbocharger models for a diesel engine is validated with experimental data to evaluate performance of pressures, temperatures, mass flows at relevant components. The developed airpath model is used for calculating thermodynamic properties in real-time for state of art engine control unit (ECU) in production engine and become basis for feedforward as well as closed loop control of airpath variables for real-time system. Authors further propose to use this modeling approach for calculating airpath system variables for exhaust aftertreatment system, injection system, and for virtualization of sensor values in airpath systems.

Analysis of condensation and secondary flows at three-way junctions using optical visualization techniques and computational fluid dynamics

Three-way junctions are employed in almost all piping systems, whenever two streams need to be merged into one duct. In some applications, the mixing between streams plays an important role for determining the performance of downstream elements. The situation is particularly interesting for low pressure Exhaust Gas Recirculation (EGR) junctions featured in piston engines, where warm humid exhaust gases meet cold fresh air, since the mixing of both streams can produce water condensation. This condensation deteriorates the integrity and performance of the adjacent compressor wheel. This work explores the aforementioned flow configuration in a three-way junction by means of a novel gas test bench that allows the characterization of the transversal section at the junction outlet, and 3D Computer Fluid Dynamics (CFD) simulations embedded with a previously-developed condensation model. Two optical techniques are employed: laser particle image velocimetry, which is used to characterize the cross-section secondary flows, and planar laser-induced visualization, which is employed for the first time to obtain the condensation pattern. The experimental measurements are conducted at two different working points and for two different three-way junction designs, being in agreement with 3D CFD simulations. Particularly, the overall luminosity captured in the experiments presents the same trends than the numerical condensed mass fraction. This innovative validation proves that a CFD model employing a psychrometric-based condensation submodel can be used as a tool to quantify the condensation produced in a three-way junction. The proposed tools are shown to be helpful for the development of advanced LP-EGR systems to reduce NOX,CO2 and particulate matter emissions during engine warm-ups.

Feedback Error Learning Control Using OS-ELM for SI Engine Airpath Systems

Abstract Currently, due to the stricter emission legislation, spark-ignition (SI) engine with low pressure exhaust gas recirculation (LP-EGR) has become a research hotspot. However, with the increasing complexity of engine, it is difficult to obtain sufficient control performance by conventional MAP control or PID control. This paper focuses on the airpath system of a SI engine with low pressure EGR, proposes a new model-based control method for the model of the airpath system based on the Feedback Error Learning control using online sequential-extreme learning machine (OS-ELM) as controller algorithm. In this paper, the airpath model has been built and effectiveness of the proposed control method has been confirmed on the model.

Modelling and Output Predictive Control of Engine Air Path Systems for Intake Fresh-air and Exhaust Gas Recirculation

This paper deals with the control problem of an engine air path system with low pressure exhaust gas recirculation (EGR). The considered air path system with low EGR can be modelled as a system with time-delays due to the transport delay of gas flow from EGR. It results in over intake fresh air, and thus it causes torque overshoot. An output predictive control system is designed for a time delay air path system in order to obtain the desired fresh air mass flow. In the considered system, the intake fresh air mass flow and the EGR rate are taken as the outputs, and the throttle valve and the EGR valve are considered as inputs of the system in this paper. A detailed air path system model with time-delay will also be derived for confirming the effectiveness of the proposed method through numerical simulations.

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.

Down-speeding diesel engines with two-stage turbochargers: Analysis and control considerations

Diesel engines continue to be used in truck applications, so reducing fuel use and hence CO2emissions, is a priority. Single-stage turbocharged diesel engines are known to be fuel efficient under steady load at low speeds. However, the engine’s ability to track load transients becomes limited by emission constraints due to the rate of production values for smoke and the resulting higher nitrogen oxides (NOx). Modern air-path solutions including a variable geometry turbine (VGT) and high pressure exhaust gas recirculation (EGR) can be used to improve dynamic response without increasing NOxemissions, but lead to complex interactions that can be difficult to control. This paper develops a two-stage, in-series, air-path configuration, which improves the typical part-load performance at low engine-speeds through adjustments to the turbine expansion ratios. Better EGR rates (for NOxreduction) at low engine speeds can be achieved whilst the engine transient response is maintained. The air-path system is simulated using Ricardo Wave software and analysed for steady-state and transient behaviour in order to identify the relationships, constraints and performance measures for different operating regions that specify the controller requirements.

Model predictive air path control for a two-stage turbocharged spark-ignition engine with low pressure exhaust gas recirculation

Innovative air path concepts for turbocharged spark-ignition engines with exhaust gas recirculation impose high demands on the control due to nonlinearities and cross-couplings. This contribution investigates the control of the air and exhaust gas recirculation paths of a two-stage turbocharged spark-ignition engine with low pressure exhaust gas recirculation. Using exhaust gas recirculation at high loads, the in-cylinder temperature can be lowered, reducing the knock tendency, while at the same time preventing the need for the enrichment of the air/fuel ratio. Air and exhaust gas recirculation paths are cross-coupled and show different delay times. To tackle these challenges, a data-based two-stage model predictive controller is proposed: The target selector accounts for the overactuated system structure, while the dynamic controller adjusts the charging pressure and exhaust gas recirculation rate. The prediction model setup is based on a small amount of dyno-run measurement data. To ensure real-time capability, the model is kept as simple as possible. This allows for fast turnaround times of the algorithm, while maintaining the necessary accuracy in steady-state and transient operation. This study focuses on a two-stage control concept based on a target selector for optimal stationary control inputs and the dynamic controller considering the dynamic behavior of the air and exhaust gas recirculation paths. Subsequently, the control concept for the two-stage turbocharged spark-ignition engine with low pressure exhaust gas recirculation is validated via experimental tests under real-driving conditions on an automotive test track, using a prototype test vehicle. Results show that boost pressure as well as exhaust gas recirculation rate setpoints are met without overshoot and control deviation with settling times being close to the boundaries set by the hardware.

Experimental investigation on the characteristics and performance of homogeneous charge induced ignition(HCII) on a multi-cylinder heavy-duty engine

This paper is focused on the characteristics and performance of HCII in conditions close to practical engine operating. For this purpose, extensive experiments have been conducted on a modified six-cylinder heavy-duty diesel engine, with six-cylinder HCII, high pressure exhaust gas recirculation(EGR) loop and appropriate pressure rise rate. The experiments mainly include two aspects. Firstly, gasoline ratio(GR), EGR ratio and start of injection(SOI), are studied to summarize the combustion and emission characteristics of HCII. Secondly, European steady state cycle(ESC) test is conducted to evaluate HCII performance over the whole engine map.Results suggest that large GR is beneficial to effective thermal efficiency(ETE) or/and nitrogen oxide(NOx) and smoke emissions, however, it is limited by maximum pressure rise rate at low load and uncontrollable ignition time at high load. Similarly, the application of EGR can improve gasoline combustion and decrease NOx emission, while it cannot be too much because of decreased ETE at low load and uncontrollable ignition time at high load. Meanwhile, SOI can be advanced to 40 crank angle degree(CAD) before top dead center(BTDC) to achieve extremely low NOx and smoke emissions and relatively high ETE. However, this strategy can only be applied to B25 and C25 points. Finally, great success is achieved by HCII in ESC test. Just with diesel oxidation catalyst(DOC), the weighted specific emissions of NOx, particulate matter(PM), hydrocarbon(HC) and carbon monoxide(CO) can be 1.841 g/(kW·h), 0.024 g/(kW·h), 0.115 g/(kW·h) and 0.896 g/(kW·h) respectively.

Control of hybrid boosting in highly diluted internal combustion engines

A novel hybrid system enabling both flexible supercharging and limited torque assist is studied to mitigate transient response challenges of a turbocharged spark ignition engine equipped with low pressure exhaust gas recirculation. The hybrid system, called a power split supercharger (SC), is configured with a planetary gear set that splits the supercharging power between a small low-voltage electric motor and the engine crankshaft. The air path controller relies on the coordination of four actuators on the engine side and three low-level actuators on the hybrid boosting device. A decentralized control scheme is used in this work, in which the master–slave structure of the boost pressure controller decreases the turbo-lag associated with exhaust gas recirculation, while minimizing the SC operation for fuel economy. A vector reference governor is used to prevent compressor surge during engine tip-outs. In addition, the desired intake manifold pressure is modified to provide time for evacuating the exhaust gas recirculation and avoiding misfires when transitioning to low load, while the hybrid capability of the power split SC is used to recuperate the unwanted generated power. All controllers are validated on both a mean value engine model and a high-fidelity engine model. Practical challenges of implementing the vector reference governor to the highly nonlinear engine air path with pressure pulsations originating from the engine reciprocation are discussed and some solutions are proposed.

Teaching Nonlinear Model Predictive Control with MATLAB/Simulink and an Internal Combustion Engine Test Bench

Model Predictive Control (MPC) is used for more and more applications in an industrial context. The applications are characterized by increasing complexity while the available computation time is getting smaller and smaller. MPC is the most important advanced control technique with even increasing importance. Hence, this topic should be covered in control lectures during the academic studies in order to prepare students for their future work. For the successful implementation of MPC algorithms, knowledge from multiple disciplines is crucial and needs to be taught. Besides teaching knowledge in classical control theory, especially fundamentals in the fields of modeling, simulation and numerical optimization are required for understanding MPC. Programming skills are inevitable to apply the concept in real-world applications.This paper presents a concept for teaching MPC from the theory to the application to real-world systems. Details about the lectures covering the relevant topics are given. In the hands-on exercises, students implement their own linear as well as nonlinear MPC in MATLAB/Simulink. As example application in the exercises, the air path of a turbocharged diesel engine with high pressure exhaust gas recirculation is investigated. At the end of the semester, students can test their developed controllers on a real diesel engine test bench and compete against each other for the best control performance.

Numerical and thermodynamic study on effects of high and low pressure exhaust gas recirculation on turbocharged marine low-speed engine

Marine low-speed engines are one of the most favorable power devices for oceangoing vessels. However, their energy consumption reduction is currently limited because of applying the exhaust gas recirculation (EGR) to reduce the NOx emission. Consequently, high pressure (HP) and low pressure (LP) EGR are studied in this study to explore the interactive relationship among the EGR, the turbocharger and the engine. The HP EGR reduces the turbine power, causing the deterioration of scavenge air pressure and compressor surge margin. As a solution, the cylinder bypass rate should be kept approximately equivalent to the EGR rate. Moreover, to avoid unfavorable impacts on the NOx emission, it should be decoupled with the exhaust gas receiver. While, the LP EGR has opposite effects on the turbocharger: the turbine power is raised and compressor operating points move to the opposite direction. It could be preliminarily attributed to the better utilization of the increased exhaust gas temperature. From a thermodynamic analysis, the fundamental reason is the difference of compressor inlet composition. Demands of them for the compressor are concluded subsequently: the HP EGR requires a wide high efficiency area at a constant pressure ratio, while the LP EGR needs the high efficiency area as long as possible in its demand direction. Finally, detailed comparisons between them are conducted based on the re-matched turbochargers and optimized engine parameters: the control and the structure of LP EGR are simpler and more effective, but its cost and compactness are inferior to the HP EGR.

Combined Low and High Pressure Exhaust Gas Recirculation for Commercial Vehicle Diesel Engines

Combined Low and High Pressure Exhaust Gas Recirculation for Commercial Vehicle Diesel Engines