Exhaust Gas Recirculation System Research Articles

Analysis on the Forces of Ellipsoidal Particle in Turbulent Flow Channel

The movement and deposition of the diesel particles have important effect on the particle sampling measurement, the operation of the exhaust gas recirculation system and the trapping of the particles. The configuration of the particles decides the force imposed on the particles in a turbulent flow channel, and the force imposed on the particles has important effect on the movement and deposition of the particles in a turbulent flow channel. The kinematics and dynamics equations of the ellipsoidal particle and the force and torque models of the ellipsoidal particle in the turbulent flow field are built up, and the force and torque imposed on the particles in a turbulent flow channel are investigated by using the kinematics and dynamics equations and the force and torque models. The emphases of the analysis are the effect of the particle configuration on the force and torque imposed on the particles in a turbulent flow channel. The results show that for the particles of sub-micron and micron order, the change of the particle configuration can arouse the change of the force and torque imposed on the particles, and can have effect on the status of the Stokes drag force, Brownian force, Saffman lift force, thermophoresis force, gravitation force and buoyancy force in the process of the particle movement and deposition also. The results of this research can deepen the comprehending of the movement and deposition characteristics of the particles in the turbulent flow channel.

Nonlinear control for a diesel engine: A CLF-based approach

Abstract In this paper, we propose a control Lyapunov function based on a nonlinear controller for a turbocharged diesel engine. A model-based approach is used which predicts the experimentally observed engine performance for a biodiesel. The basic idea is to develop an inverse optimal control and to employ a Lyapunov function in order to achieve good performances. The obtained controller gain guarantees the global convergence of the system and regulates the flows for the variable geometry turbocharger as well as exhaust gas recirculation systems in order to minimize the NOx emission and the smoke of a biodiesel engine. Simulation of the control performances based on professional software and experimental results show the effectiveness of this approach.

에멀젼연료와 EGR의 동시적용 디젤엔진에 있어서 연료 분사 패턴이 연소와 배기가스에 미치는 영향

The use of emulsified fuel and EGR (Exhaust gas recirculation) system are effective methods to reduce NOx emission from diesel engines. In general, it is considered that EGR method influences diesel engine combustion in three different ways: thermal, chemical and dilution effect. Among others, the thermal effect is related to the increase of specific heat capacity due to the presence of CO 2 and H 2O in inlet air. Meanwhile, emulsified fuel method of utilizing latent heat of vaporization and miro-explosion has been recognized as an effective technique for reducing diesel engine emissions. In this paper, an author studied on combustion and emission characteristics by using emulsified fuel (EF, Light oil : 80% + Water : 20%) and EGR ( 30% EGR ratio) system. And the effect of fuel injection pattern control was investigated.

Robust Air-to-Fuel Ratio and Boost Pressure Controller Design for the EGR and VGT Systems Using Quantitative Feedback Theory

This paper describes robust multi-input, multi-output controller for the exhaust gas recirculation (EGR) and variable geometry turbocharger (VGT) systems of passenger car diesel engines. The air-to-fuel ratio of the exhaust gas and boost pressure of the intake manifold were selected as performance indicators in this paper. To enable the online calibration of the controller, proportional-integral-derivative (PID) was used as a feedback controller. Using quantitative feedback theory (QFT), two control loops for air-to-fuel ratio and boost pressure were independently designed with linearized models and parameter uncertainties. The prefilters and PID gains of two control loops were designed for satisfying required robust stability and tracking performance using the QFT design framework. Furthermore, the problems originated from the cross-coupled dynamics between the EGR and VGT systems were mitigated by a static decoupler. Using the proposed design steps, PID and decoupler gains of the representative 15 engine operating points which are mainly used in New European Driving Cycle were obtained. The proposed controller was validated through various test conditions of engine experiments. From the step responses and transient experiments, it was demonstrated that the required robustness and tracking performance were successfully achieved.

English

With the enormous energy demand and environmental concern the interest on the alternate fuels to the diesel engine has been increased. This simulated the world wide search for the renewable, less pollutant and agricultural based alternate fuel. In our country majority of the people lives in the villages and depends on the agriculture. Further, if this alternate fuel is prepared by the farmers, they become independent for their needs. Among all the crops, aloevera is best based on its properties. In the diesel engines much amount of heat is lost in exhaust. This heat can be utilized with exhaust gas recirculation system. The present experimental work is focused on the performance and emissions of the aloevera and diesel blends with EGR system. Here the EGR is maintained at constant (5%). The experiment conducted on single cylinder, four stroke, constant speed, water cooled, electric loaded, D.I Diesel Engine. The acquired data is analyzed for various blends of aloevera and diesel blends and the same is presented

Combined Effects of Late IVC and EGR on Low-load Diesel Combustion

The increasing demand for improved efficiency of diesel engines requires more advanced combustion solutions. These solutions include the use of variable valve timings in combination with more traditional methods such as EGR, turbocharging and advanced injection systems. By modifying the characteristics of the charge air, further hardware optimization becomes possible. In the current investigation, the effect of late intake valve closing (LIVC) was investigated together with the effect of (external) exhaust gas recirculation (EGR) in a single cylinder heavy duty diesel engine. Different injection timings and injection pressures were investigated. The mass flow of oxygen was kept constant in order to show how the density and temperature of the reactant mixture affect the combustion and emission characteristics. The combustion results showed that if the oxygen mass flow is kept constant, an EGR approach is more efficient than LIVC in lowering fuel consumption due to the effects of increased cylinder gas flow which improves fuel conversion efficiency. It was shown that the ignition delay for a fixed combustion phasing was independent of EGR but could be increased by LIVC. The peak pressure was more strongly affected by EGR due to the larger gas flow but this response can be reduced by means of LIVC. After compensating for combustion timing effects, the reduced peak pressure was mainly attributed to reduced effective compression ratio resulting from the LIVC. The results show how variable valve timing can be used as one important tool to obtain better combustion characteristics and thus enable more efficient powertrains.

A review of the application of variable geometry turbines to the downsized gasoline engine

Engine downsizing through turbocharging is a proven method of improving fuel economy by using a smaller engine operating at higher levels of specific engine load and higher efficiency. Turbocharging is more challenging for the gasoline engine than the diesel engine due to the higher variability in the flow rate of air and the higher exhaust gas temperature. Although the variable geometry turbine offers the potential for improving the low-end torque, lowering part-load fuel consumption and delivering a fast transient response on a downsized gasoline engine, the cost, durability and the limited allowable turbine inlet temperature on the currently available devices present challenges to widespread application. This article details the main operating principles and types of the variable geometry turbine, its potential to deliver performance improvements, implementation challenges on the gasoline engine and the measures available to alleviate those challenges. Of the available types of variable geometry turbine, the variable nozzle form has the highest efficiency over a wide flow range while the variable flow and sliding wall types have better reliability and lower cost. Using additional technologies such as the water-cooled exhaust manifold, specialist turbocharger materials, exhaust gas recirculation and novel combustion systems in combination with advanced control strategies will facilitate variable geometry turbine application and hence allow further downsizing of the gasoline engine.

A predictive model for knock onset in spark-ignition engines with cooled EGR

A predictive knock model is crucial for one dimensional (1-D) engine cycle simulation that has been proven to be a powerful tool in both optimization of the conceptual design and reduction of calibration efforts in development of spark-ignition (SI) engines. With application of advanced technologies such as exhaust gas recirculation (EGR) in modern SI engines, update of knock model is needed to give an acceptable prediction of knock onset. In this study, bench tests of a turbocharged gasoline SI engine with cooled EGR system operated under knocking conditions were conducted, the cylinder pressure traces were analyzed by the band-pass filtering technique, and the crank angle of knock onset was determined by the signal energy ratio (SER) and image processing method. A knock model considering multi-variable effects including pressure, temperature, EGR ratio and excess air ratio (λ) is formulated and calibrated with the experimental data using the multi-island genetic algorithm (GA). The calculation method of the end gas temperature, the impacts of the ratio of specific heats as well as the temperature at the intake valve closure on the end gas temperature are discussed. The performance of the new model is compared with the widely-used phenomenological knock models such as Douaud–Eyzat model and Hoepke model. While the widely-used knock models fail to give acceptable predictions when increasing EGR with fuel enrichment operations, the new model predicts the knock onset with high accuracy under the fuel enrichment conditions both with and without EGR. Performance of the newly developed model is also examined in a different engine and a higher predictive accuracy of the new model than other models is obtained.

Mixed-Potential NOx and NH3 Sensors Fabricated by Commercial Manufacturing Methods

Lean-burn operation of both diesel and gasoline direct injection engines has the potential to increase fuel economy by consuming almost all of the fuel in the presence of excess air. However, the oxygen rich exhaust prevents reduction of NO via three-way catalytic converters commonly used to reduce emissions in stoichiometric engines1. Vehicle manufactures are pursuing selective catalyst reduction (SCR) and exhaust gas recirculation (EGR) systems to meet EPA emissions regulations for lean-burn engines. SCR systems typically use a zeolite catalyst that selectively adsorbs NOx molecules and converts them to N2 and H2O with the injection of a urea water solution. In EGR, exhaust gas is mixed into the intake manifold air in order to lower the temperature of combustion, reducing NOx emissions. EGR systems have been used in gasoline engines for several decades, however the higher oxygen content of diesel exhaust requires that it be pre-cooled before mixing with the air intake. The percentage of recirculation and temperature of the exhaust gas need to be carefully controlled in order to reduce emissions without sacrificing engine efficiency and fuel economy. Exhaust gas sensors are needed to monitor emissions and control and maintain efficient operation of SCR and EGR systems. Oxygen λ-sensors are an integral part of onboard diagnostics (OBD) of today’s stoichiometric vehicle emission systems, but a suitable analog is not available for NOx and NH3 detection and discrimination in lean-burn engines.Mixed-potential sensors fabricated via well-established commercial manufacturing methods present a promising avenue to enable the widespread utilization of NOx and NH3 sensing technology. These electrochemical devices develop a non-Nernstian potential due to differences in the redox kinetics of various gas species at each electrode/ electrolyte/ gas interface. The electrode potential is not fixed by equilibrium thermodynamics as it is in the O2 λ-sensor, but rather by the rates of different electrochemical reactions occurring simultaneously at each electrode/ electrolyte interface. Therefore, device-to-device reproducibility of the triple phase interface, as well as long term morphological stability are required. The patented LANL sensor design incorporates dense electrodes and a porous electrolyte 2. The use of dense electrodes minimizes deleterious heterogeneous catalysis, and the increased morphological stability of dense electrodes yields a robust electrochemical interface, increasing lifetime durability 3. The Materials Synthesis and Integrated Devices group at LANL has worked in collaboration with Electro-Science Laboratories (ESL, King of Prussia, PA) to fabricate planar mixed-potential sensors via the readily scalable, cost-effective high temperature co-fired ceramic (HTCC) technology already employed in the manufacturing of planar O2 λ-sensors.The two sides of a planar, self-heated, tape cast sensor prototype are shown in Figure 1. A Pt-heater with independent leads is printed on the backside of the ceramic substrate. A heater is employed to operate the devices between 400-600˚C where the YSZ possesses sufficient ionic conductivity and the rates of the electrochemical reactions do not impede the response time of the device. The sensing element is printed on the opposite side of the ceramic substrate and consists of dense, screen-printed electrodes coated with a porous YSZ electrolyte layer. We have developed two distinct sensing platforms for NOx and NH3 detection. The NOx sensor consists of La1-xSrxCrO3 and Pt electrodes. Under open circuit conditions, this sensor responds to many of the constituents of concern in emissions monitoring, however, the selectivity may be tuned by operating conditions 4. By operating at a small positive current bias, this sensor becomes preferentially selective to NOx species. Selectivity towards non-methane hydrocarbons (NMHC) is improved by operation at elevated temperatures, however sensitivity is reduced. The NH3 sensor consists of Au/Pd and Pt electrodes and is minimally sensitive to NOx species with varying sensitivity to NMHCs depending on operating temperature. The voltage response of both sensor constructs to various gases is shown in Figure 2.

A study of the fouling characteristics of EGR coolers in diesel engines

Diesel emission regulations have recently become more severe. An important goal in diesel engine research is the development of methods to reduce the emissions of NOx and PM (particulate matter). Cooled EGR (exhaust gas recirculation) system has been widely used to reduce the NOx and PM emissions of light-duty diesel engines. In this study, numerical analyses, rig tests and engine tests were performed to assess how changes in internal shape characteristics can improve the heat exchange efficiencies of EGR coolers. The heat exchange efficiencies of EGR coolers have been numerically and experimentally measured during a fouling process. The results show that the second type of oval EGR cooler tested (oval #2) exhibited better heat exchange efficiency than either the first type of oval EGR cooler was tested (oval #1) or the shell and tube cooler examined. The turbulence generated in exhaust gas flows by the wavy-finned design of the oval EGR coolers facilitated PM desorption that allows these coolers to self-purify. With respect to the two similar oval EGR coolers, the cooler with fin pitch 4 mm has better efficiency than the cooler with fin pitch 6 mm due to differences in the heat transfer areas of these coolers. Both CFD analyses involving extreme conditions of engine operation and engine fouling tests involving conditions experienced during vehicular operation indicate that the two oval coolers differed by less than 4% with respect to both initial heat transfer efficiency and heat transfer efficiency after a 78-hour fouling test.

A Numerical Study on the Thermal and Strain Characteristics of EGR Cooler

The Exhaust-Gas Recirculation (EGR) is the effective method to reduce the exhausted NOx from diesel engine. The EGR system needs to be cooled to lower the combustion temperature, which results in the reduced engine power. To improve the performance of EGR Cooler, maximizing heat transfer coefficient, heat transfer area and corrosion resistant material should be considered while the thermal stress produced by the temperature difference between exhaust gas and coolant is also considered as a highly important factor from the point of safety operation. The thermo-flow characteristics inside the EGR Cooler and surface temperature have been investigated by using CFD code STAR-CCM+ 9.0. Finally, as a result of the simulation, the stress location and crack spots has been experimentally observed and compared with simulation. The focus is going to be mainly on CFD simulation and flow behavior inside the EGR which is considered important in order to improve the efficiency.

Exhaust Pressure Estimation Using a Diesel Particulate Filter Mass Flow Model in a Light-Duty Diesel Engine Operated With Dual-Loop Exhaust Gas Recirculation and Variable Geometry Turbocharger Systems

This paper presents a novel method to estimate an exhaust pressure at 357 different steady-state engine operating conditions using a diesel particulate filter (DPF) mass flow model to precisely control the air quantity for a light-duty diesel engine operated with dual-loop exhaust gas recirculation (EGR) and variable geometry turbocharger (VGT) systems. This model was implemented on a 32 bit real-time embedded system and evaluated through a processor-in-the-loop-simulation (PILS) at two transient engine operating conditions. And the proposed model was validated in a vehicle. By applying Darcy's law, the DPF mass flow model was developed and shows a root mean square error (RMSE) of 3.7 g/s in the wide range of the DPF mass flow and above 99% linear correlation with actual values. With such reasonable uncertainties of the DPF mass flow model, the exhaust pressure was estimated via the application of a nonlinear coordinate transformation to the VGT model. The DPF mass flow based exhaust pressure estimation exhibits below 6% error of the exhaust pressure under steady-state conditions. The method was also validated through the PILS and the vehicle test under transient conditions. The results show a reasonable accuracy within 10% error of the exhaust pressure.

Observer design for exhaust gas recirculation rate estimation in a variable-geometry turbocharger diesel engine using a model reference identification scheme

Exhaust gas recirculation systems are used in diesel engines to reduce nitrogen oxide emissions. Since excessive recirculation in the cylinders may lead to an increase in generation of particulate matter and to unstable combustion, the exhaust gas recirculation rate should be measured correctly and should be controlled precisely. Unfortunately, the harsh conditions of the exhaust gas recirculation path make it difficult to measure the exhaust gas recirculation mass flow rate directly by using the relevant sensors. Therefore, precise control of the exhaust gas recirculation system depends on accurate estimation of the exhaust gas recirculation rate. To estimate accurately the exhaust gas recirculation rate in a turbocharged diesel engine, we propose an observer based on a model reference identification scheme. A linear parameter-varying model of the intake manifold pressure was derived to serve as the observer’s reference model. An update rule of the observer was designed with the model reference identification scheme. The intake and exhaust temperature models were developed through an empirical approach. Convergence of the proposed observer was proven in terms of the Lyapunov stability criterion. The proposed observer was implemented on a real-time embedded system and validated successfully through experiments on the engine.

The effect of exhaust gas recirculation on the process of combustion in the self-ignition engine

The paper compares the basic parameters of the process of combustion in the Fiat MultiJet 1.3 SDE 90 KM with and without an exhaust gas recirculation system, running according to load characteristics with the following engine

Experimental study on the spiral and oval spiral EGR cooler efficiencies in a diesel engine

The cooled exhaust gas recirculation (EGR) system is one of the most effective techniques currently available for reducing nitrogen oxide emissions in diesel engine. Because the combustion characteristics in diesel engine involves high temperature and load, the amount of particulate matter (PM) emission tends to increase, thereby the PM fouling in EGR cooler degrades the heat transfer performance considerably, which in turn has a significant influence on the design of the EGR cooler. In the present study, engine dynamometer tests are performed to investigate the influences of PM fouling on the heat exchange characteristics of spiral and oval-spiral type EGR coolers equipped with a diesel engine. The evaluation test results show that the oval-spiral type EGR cooler has higher efficiency by approximate 10 % than the spiral type EGR cooler because of the increase of heat transfer area and the increased removal of PM from the deposit layer due to fluid shear force.

A physics-based time-varying transport delay oxygen concentration model for dual-loop exhaust gas recirculation (EGR) engine air-paths

Dual-loop exhaust gas recirculation (EGR) systems can provide control authorities to adjust the engine in-cylinder gas conditions. The significant transport delays in the EGR air-paths can affect the performance of some simple oxygen concentration dynamic models under transient operating conditions. In this paper, a physics-based dual-loop EGR air-path oxygen concentration model considering the time-varying transport delays is developed and a method to calculate the delay time based on the continuity of fluid velocity is presented. Simulation studies with a high-fidelity, one-dimensional, computational GT-Power engine model and experimental validations on a Diesel engine test bench show that the developed model performs well under all tested operating conditions while the comparison models cannot capture the oxygen concentration dynamics under some transient operating conditions.

Nonlinear sliding mode observer for exhaust manifold pressure estimation in a light-duty diesel engine

In this paper, a sliding mode observer is proposed to estimate exhaust pressure for a diesel engine equipped with variable geometry turbocharger (VGT) and exhaust gas recirculation (EGR) systems. Since the exhaust pressure directly affects generation of the VGT power and the EGR rate in the cylinder, the exhaust pressure information is important for precise control of the VGT and EGR systems. In order to estimate the exhaust pressure accurately, a dynamic model of intake and exhaust pressure was derived. Furthermore, the mass flow rate and temperature of the air system in the diesel engines were modeled by consideration of physical phenomena and the thermodynamic law. Based on the developed models, a nonlinear sliding mode observer was designed to estimate the exhaust pressure. Convergence of the proposed observer was verified by the Lyapunov stability criterion. The proposed observer was implemented on a real-time embedded system and validated with the engine experiments. The experimental results show that the observer estimates the exhaust pressure accurately in both steady and transient engine operating conditions. Moreover, as a case study, the estimation results of the proposed observer could be applied for detecting a fault of the EGR system. The fault of the EGR system was detected precisely using the estimation result and the limited sensor information in mass-produced engines.

Dynamometer Testing of Planar Mixed-Potential Sensors

Recently strengthened federal regulations are driving the reduction of pollutants emitted from heavy-duty diesel engines. The use of selective catalyst reduction (SCR) and exhaust gas recirculation (EGR) systems combined with regenerative particulate traps have reduced NOx and particulate matter (PM) tailpipe emissions from heavy-duty diesel vehicles by 95%.1 Despite these recent advances, there is a lack of low cost exhaust gas sensor technology to monitor tailpipe emissions and to control and maintain optimized SCR and EGR system efficiencies2. Derivatives of the hugely successful robust, zirconia-based electrochemical sensors currently used for gasoline engine control and OBD in conjunction with three-way catalytic converters, has attracted considerable interest in diesel applications. However, the implementation of the diesel analogue to OBD has proved to be more complicated.Mixed-potential sensors fabricated via well-established commercial manufacturing methods present a promising avenue to enable the widespread utilization of NOx sensing technology. The Materials Synthesis and Integrated Devices group at LANL has worked in collaboration with Electro-Science Laboratories (ESL, King of Prussia, PA) to fabricate planar mixed-potential sensors via the readily scalable, cost-effective high temperature co-fired ceramic (HTCC) technology already employed in the manufacturing of planar O2 λ-sensors.The two sides of the planar, self-heated, tape cast sensor prototype are shown in Figure 1. A Pt-heater with independent leads is printed on the backside of the ceramic substrate. The sensing component consists of dense La1-xSrxCrO3 (LSCrO)- working and Pt-counter electrodes coated with a porous YSZ electrolyte layer. The voltage response of a sensor operated at 490˚C to 100 ppm of varying analyte gases is shown in Figure 2. Operated at open circuit, this combination of electrode materials serves as a sensor for reducing gases, such as hydrocarbons and ammonia. However, the sensor can be transformed to a total NOx sensor by appropriate tuning of the current bias and operating temperature3. The performance of the planar sensors under engine-out conditions was recently evaluated at the Oak Ridge National Laboratory National Transportation Research Center. The sensor was mounted in a quartz tube with the Pt heater resistance set to correspond to an operating temperature of 490˚C. The sensor was placed in the exhaust gas downstream of an orifice regulating the flow to 1000ccm and upstream of the FTIR used to analyze the exhaust gas components. A California Instruments Flame-Ionized Detector (FID) was also used to analyze total hydrocarbon content (THC) immediately upstream of the orifice. Figure 3 shows the sensor response during varying engine operating conditions. The sensor response while operating in hydrocarbon sensing mode (0 bias) during engine start-up is shown in Figure 3a. The sensor response closely tracks the THC measured by the FID, while the THC measured via FTIR lags the response of both the FID and the sensor. Figure 3b shows the sensor response while operating in NOx sensing mode (+0.2 μA bias) while the engine was held at 1600 rpm and EGR was cycled on and off. The sensor response qualitatively tracks the NO concentration in the exhaust stream, with the sensor response becoming more negative with increasing NO, in agreement with the biased response shown in Figure 2. In this work, we will discuss the performance of the planar, mixed-potential sensors under engine-out conditions and compare the dynamometer performance with laboratory measurements.

Observations on the Measurement and Performance Impact of Catalyzed vs. Non Catalyzed EGR on a Heavily Downsized DISI Engine

Increasingly stringent regulations and rising fuel costs require that automotive manufacturers reduce their fleet CO2 emissions. Gasoline engine downsizing is one such technology at the forefront of improvements in fuel economy. As engine downsizing becomes more aggressive, normal engine operating points are moving into higher load regions, typically requiring over-fuelling to maintain exhaust gas temperatures within component protection limits and retarded ignition timings in order to mitigate knock and pre-ignition events. These two mechanisms are counterproductive, since the retarded ignition timing delays combustion, in turn raising exhaust gas temperature. A key process being used to inhibit the occurrence of these knock and pre-ignition phenomena is cooled exhaust gas recirculation (EGR). Cooled EGR lowers temperatures during the combustion process, reducing the possibility of knock, and can thus reduce or eliminate the need for over-fuelling. It has also been shown to reduce exhaust gas temperature and improve combustion efficiency through improved combustion phasing. This paper reviews data collected on ‘ULTRABOOST’, a collaborative research project which is co-funded by the Technology Strategy Board, the UK's innovation agency. The project is based on a prototype, heavily downsized 2.0L DISI engine running under controlled boost conditions, featuring low pressure or ‘long route’ EGR. This allows for the EGR feed gas to be fed from either pre- or post-catalyst sampling points. This paper will present data collected at equivalent operating conditions using both catalyzed and un-catalyzed exhaust gas to feed the EGR system. Some comparison of equivalent BMEP levels will be made but this is not the focus of the investigation. Current standards utilize a CO2 ratio for EGR measurement, but the results presented highlight inaccuracies in this measurement method when repeatable test conditions for pre- and post-catalyst EGR routes are required due to the significant changes in gas composition pre- and post-catalyst. The test engine was artificially boosted utilizing a Combustion Air Handling Unit to simulate commercially available turbo-machinery, which allowed for the catalyst effects to be assessed in isolation. Results from the engine are presented for constant intake manifold pressure and constant EGR mass flow to highlight the effects of the EGR feed gas composition on a range of engine performance metrics.

A control strategy of low-pressure loop exhaust gas recirculation and NOx storage catalyst for diesel engines

Low-pressure loop exhaust gas recirculation systems are effective means of simultaneously reducing the NOx emissions and fuel consumption of diesel engines. Further lower emission levels can be achieved by adopting a system that combines low-pressure loop exhaust gas recirculation with a NOx storage and reduction catalyst. However, this combined system has to overcome the issue of combustion fluctuations resulting from changes in the air–fuel ratio due to exhaust gas recirculation from rich operating conditions. The aim of this research was to reduce combustion fluctuations by developing low-pressure loop exhaust gas recirculation control logic. In order to control the combustion fluctuations caused by low-pressure loop exhaust gas recirculation, it is necessary to estimate the recirculation time. First, recirculation delay was investigated, and a model was developed. A good correlation was found between actual measurements and the recirculation delay estimated by this model. Next, the control logic for low-pressure loop exhaust gas recirculation was studied. The recirculation gas under rich operating conditions was detected by an air–fuel ratio sensor to examine a method of controlling the exhaust gas recirculation valve in accordance with the timing for the rich gas to reach the exhaust gas recirculation valve actually. Thus, fluctuations in torque and combustion noise were improved.