High Pressure Exhaust Gas Recirculation Research Articles

Efficiency improvement of a spark-ignition engine at full load conditions using exhaust gas recirculation and variable geometry turbocharger – Numerical study

The numerical analysis of performance of a four cylinder highly boosted spark-ignition engine at full load is described in this paper, with the research focused on introducing high pressure exhaust gas recirculation for control of engine limiting factors such as knock, turbine inlet temperature and cyclic variability. For this analysis the cycle-simulation model which includes modeling of the entire engine flow path, early flame kernel growth, mixture stratification, turbulent combustion, in-cylinder turbulence, knock and cyclic variability was applied. The cylinder sub-models such as ignition, turbulence and combustion were validated by using the experimental results of a naturally aspirated multi cylinder spark-ignition engine. The high load operation, which served as a benchmark value, was obtained by a standard procedure used in calibration of engines, i.e. operation with fuel enrichment and without exhaust gas recirculation. By introducing exhaust gas recirculation and by optimizing other engine operating parameters, the influence of exhaust gas recirculation on engine performance is obtained. The optimum operating parameters, such as spark advance, intake pressure, air to fuel ratio, were found to meet the imposed requirements in terms of fuel consumption, knock occurrence, exhaust gas temperature and variation of indicated mean effective pressure. By comparing the results of the base point with the results that used exhaust gas recirculation the improvement in fuel consumption of 8.7%, 11.2% and 1.5% at engine speeds of 2000rpm, 3500rpm and 5000rpm is obtained. Additionally, by using the presented numerical methodology the influence of the specific operating parameter on the overall behavior of the complex charging system was shown.

Enhanced combustion model with fuel-wall impingement oriented to injection pattern tuning in automotive Diesel engines

Nowadays the high competition reached by the automotive market forces original equipment manufacturers (OEMs) towards innovative solutions. Strict emission standards and fuel economy targets make the work hard to be accomplished. Therefore modern engines feature complex architecture and embed new devices for exhaust gas recirculation (EGR), turbocharging (e.g. multi-stage compressors), gas after-treatment (e.g. selective catalyst reduction (SCR)) and fuel injection (either high or low pressure). In this context the engine management system (EMS) plays a fundamental role to optimize engine operation. The paper deals with fuel spray and combustion simulation by a multi-zone phenomenological model aimed at the optimal tuning of the injection pattern. The fuel spray model simulates the injection process, the fuel-air mixture formation, the in-cylinder gas mixture evolution and accounts for the fuel-wall impingement that usually occurs in case of low-medium injection pressure or advanced injection timing. This feature is fundamental to investigate a wide range of injection pattern set-points, as those applied for advanced combustion concepts (i.e. Premixed Charge Compression Ignition (PCCI)). The impingement of the spray on cylinder walls is modeled by a zero-dimensional approach, simulating dynamics and evaporation of the fuel film with two different semi-empirical models. The numerical and experimental analyses have been performed with respect to an automotive Common-Rail Diesel engine, equipped with high pressure EGR and VGT turbocharger. The experimental measurements have been carried out at the engine test stand, investigating operating conditions with highly advanced injection timing and low rail pressure, in order to induce the fuel impingement process. Model validation against the experimental data exhibits satisfactory accuracy in predicting the impact of injection pattern control on impingement.

Three-Input-Three-Output Air Path Control System of a Heavy-Duty Diesel Engine

In this paper, the control requirement of the air path system of a Heavy Duty (HD) diesel engine which was equipped with a High Pressure (HP) Exhaust Gas Recirculation (EGR), a Variable-Geometry Turbocharger (VGT), and an Electric Turbocharge Assist (ETA) is discussed. A Three-Input-Three-Output (3130) multivariable control structure is proposed. The engine dynamic model required for controller design was obtained using system identification and the controller was tuned by solving an Hoo optimization problem. The engine experimental test results show that this 3130 closed-loop control system has excellent tracking performance, disturbance rejection performance, and gain scheduling capability. The control system has been demonstrated to work with a practical ETA device to make a substantial improvement to engine transient performance.

Switching strategy between HP (high pressure)- and LPEGR (low pressure exhaust gas recirculation) systems for reduced fuel consumption and emissions

EGR (Exhaust gas recirculation) plays a major role in current Diesel internal combustion engines as a cost-effective solution to reduce NOx emissions. EGR systems will suffer a significant evolution with the introduction of NOx after-treatment and the proliferation of more complex EGR architectures such as low pressure EGR or dual EGR. In this paper the combination of HPEGR (high pressure EGR) LPEGR (low pressure EGR) is presented as a method to minimise fuel consumption with reduced NOx emissions. Particularly, the paper proposes to switch between HPEGR and LPEGR architectures depending on the engine operating conditions in order to exploit the potential of both systems. In this sense, given a driving cycle, in the case at hand the NEDC, the proposed strategy seeks the EGR layout to use at each instant of the cycle to minimise the fuel consumption such that NOx emissions are kept below a certain limit. The experimental results obtained show that combining both EGR systems sequentially along the NEDC allows to keep NOx emission below a much lower limit with minimum fuel consumption.

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.

고압/저압 EGR 공급 비율에 따른 디젤 엔진의 연소 및 배기 특성

The effects of high pressure and low pressure exhaust gas recirculation (HP/LP EGR) portion on diesel engine combustion and emissions characteristics were investigated in a 2.2 L passenger-car diesel engine. The po3rtion of HP/LP EGR was varied from 0 to 1 while fixing the mass flow rate of fresh air. The intake manifold temperature was lowered with the increasing of the portion of LP EGR, which led to the retardation of heat release by pilot injection. The lowered intake manifold temperature also resulted in low nitrogen oxide (NOx) emissions due to decreased in-cylinder temperature and prolonged ignition delay, however, the carbon monoxide (CO) emission showed opposite trend to NOx emissions. The brake specific fuel consumption (BSFC) was decreased as the portion of LP EGR increased due to lowered exhaust manifold pressure by wider open of turbocharger vane. Consequently, the trade-off relationship between NOx and BSFC could be improved by increasing the LP EGR portion.

Experimental study on the effects of high/low pressure EGR proportion in a passenger car diesel engine

An experimental study was conducted to investigate the effects of the proportion between high pressure and low pressure exhaust gas recirculation (HP/LP EGR) on engine operation. The study focused on the characteristics of combustion, emissions, and fuel consumption in a 2.2L passenger car diesel engine. The experiments were performed under three part-load and steady-state operating conditions. The LP EGR portion was swept from 0 to 1, while the mass flow rate of fresh air and boost pressure were fixed. The results showed that the intake manifold temperature decreased gradually as the LP EGR portion increased due to its greater cooling capability by a longer supply line and an intercooler. However, the required cooling power for the intercooler increased because the LP EGR gas, which has a higher temperature than the fresh air, was induced upstream of the compressor. The lowered intake manifold temperature with the increase of the LP EGR portion led to the prolonged ignition delay of pilot injections, which resulted in a slightly higher peak heat release rate in the main combustion. A higher LP EGR portion showed a lower fuel consumption level than the HP EGR only case because the variable geometry turbocharger (VGT) nozzle opened more widely to maintain the boost pressure, which means a lower pumping loss. Nitrogen oxide (NOx) emissions were also decreased as the LP EGR portion increased due to lowered intake charge temperature. Consequently, it was possible to improve the trade-off relationship between NOx emissions and fuel consumption with the increase of the LP EGR portion under steady-state operating conditions.

Control-Oriented Gas Exchange Model for Diesel Engines Utilizing Variable Intake Valve Actuation

Modeling and control of the gas exchange process in modern diesel engines is critical for the promotion and control of advanced combustion strategies. However, most modeling efforts to date use complex stand-alone simulation packages that are not easily integrated into, or amenable for the synthesis of, engine control systems. Simpler control-oriented models have been developed; however, in many cases, they do not directly capture the complete dynamic interaction of air handling system components and flows in multicylinder diesel engines with variable geometry turbocharging (VGT), high pressure exhaust gas recirculation (EGR), and flexible intake valve actuation. Flexibility in the valvetrain directly impacts the gas exchange process not only through the effect on volumetric efficiency but also through the combustion process and resulting exhaust gas enthalpy utilized to drive the turbomachinery. This paper describes a low-order, five state model of the air handling system for a multicylinder variable geometry turbocharged diesel engine with cooled EGR and flexible intake valve actuation, validated against 286 steady state and 62 transient engine operating points. The model utilizes engine speed, engine fueling, EGR valve position, VGT nozzle position, and intake valve closing (IVC) time as inputs to the model. The model outputs include calculation of the engine flows as well as the exhaust temperature exiting the cylinders. The gas exchange model captures the dynamic effects of the not only the standard air handling actuators (EGR valve position and VGT position) but also IVC timing, exercised over their useful operating ranges. The model's capabilities are enabled through the use of analytical functions to describe the performance of the turbocharger, eliminating the need to use look-up maps; a physically based control-oriented exhaust gas enthalpy submodel and a physically based volumetric efficiency submodel.

Experimental Investigation of Transient Response and Turbocharger Coupling for High and Low Pressure EGR Systems

Experimental Investigation of Transient Response and Turbocharger Coupling for High and Low Pressure EGR Systems

Air-fraction modeling for simultaneous Diesel engine NOx and PM emissions control during active DPF regenerations

This study develops a control-oriented air-fraction model which can accurately predict the air-fraction dynamics for a Diesel engine and the coupled aftertreatment system (mainly Diesel oxidation catalyst (DOC)) during active DPF regenerations. NOx and particulate matter (PM) emissions are the two main concerns for modern Diesel engine development. Diesel particulate filters (DPFs) have become a standard device for reducing the PM emissions from Diesel engine powertrains. To maintain high filtration efficiencies and avoid high back pressures, active DPF regenerations have to be implemented periodically by significantly elevating the exhaust gas temperatures. However, during active DPF regenerations, the selective catalytic reduction (SCR) deNOx performance may be significantly decreased, while the high temperature durability and total hydrocarbon (THC) poisoning of SCRs may be potential issues. To simultaneously meet the NOx emission standard, high-pressure loop EGR needs to be applied. Since in-cylinder NOx reduction relies heavily on the in-cylinder oxygen content, an accurate air-fraction model is necessary, and the effects of recycled THC and CO emissions should be considered. The developed air-fraction model has been experimentally validated to show its capability of capturing the actual air fraction dynamics accurately. Such a model can be instrumental in simultaneous NOx and PM emission control during active DPF regenerations and in advanced combustion mode control.

Modeling and Control of Diesel Engines with a High-Pressure Exhaust Gas Recirculation System

This work presents an alternative way of exhaust gas recirculation (EGR) systems implementation in the turbocharged compression ignition engines. This sort of EGR has been studied as well as the most commonly used EGR system, where the intake and the exhaust manifolds are directly connected with a hose. However, in authors opinion the setup described in this paper has not been investigated enough, as most of the research papers concentrate on a conventional configuration modeling and control design. A problem of overcoming a positive scavenging pressure drop and delivering high amount of EGR is addressed in this article. It comes from the fact that in this kind of engines the exhaust pressure is lower than the intake, making it difficult to deliver high and stable portion of EGR over the engine operating range. A generic mean value engine model is developed in this work and an initial simple control structure is proposed.

Considerations on the low-pressure exhaust gas recirculation system control in turbocharged diesel engines

Although high-pressure exhaust gas recirculation has been commonly used in turbocharged diesel engines for controlling the NOx formation, recent advances in after-treatment and material technology ...

Control of diesel engine dual-loop EGR air-path systems by a singular perturbation method

This paper presents a singular perturbation based method for controlling the dual-loop exhaust gas recirculation (DL-EGR) air-path systems on advanced diesel engines. A DL-EGR air-path system, consisting of a high-pressure loop EGR (HPL-EGR) and a low-pressure loop EGR (LPL-EGR), has significantly different time-scales (fast and slow) due to the inherent difference in the HPL-EGR’s and LPL-EGR’s corresponding control volumes. Such a feature of the DL-EGR systems makes the cooperative control of intake manifold gas conditions challenging. By considering the DL-EGR air-path system as a singularly perturbed system, a composite control law was devised to achieve systematic control of the air-path conditions including gas pressure, temperature, and oxygen fraction in the intake manifold. The effectiveness of the control method is experimentally evaluated on a medium-duty diesel engine.

Control oriented air path model for compressed air boosted Diesel engines

In this paper an air path model of a diesel engine is presented for control system design. The model was developed for common-rail, direct injected, turbocharged and intercooled commercial vehicle diesel engines which are equipped with compressed air booster system (PBS® – Pneumatic Booster System)[12], high pressure exhaust gas recirculation loop (EGR) with EGR-cooler and exhaust brake (EB). In current and next generation emission standards and legislation introduced significant limitations for NOx and soot. It is really challenging to handle these components, especially at transient engine operations. Additionally the fuel economy and driveability requirements also have to be fulfilled. It is widely known that the nitric oxide formation can be limited with an appropriate amount of exhaust gas recirculation. It can be achieved even in transient modes with precisely controlled EGR-valve operation and with a suitable backpressure generation by the exhaust brake. The soot formation is influenced mainly by the air-fuel ratio of the mixture which can be affected by the intake manifold pressure in case of a desired engine load and EGR rate. With the compressed air booster system the intake manifold pressure can be controlled in transients arbitrarily. Therefore with a suitable air path controller the modeled engine setup is able to handle both the NOx and soot formation in transient cases. To solve the presented control problem a model based controller design is targeted. The reported model is the first step of this work.

Influence of high and low pressure EGR and VGT control on in-cylinder pressure diagrams and rate of heat release in an automotive turbocharged diesel engine

An experimental study was developed to compare high and low pressure exhaust gas recirculation systems (HP and LP EGR) fitted on an automotive turbocharged diesel engine, analysing the effects of their control on fuel consumption, pollutant emissions and combustion process. An extensive range of operating modes was considered at different engine part-load conditions, starting from the reference one without EGR, then considering the simple activation of the HP or LP EGR circuit, followed by the simultaneous application of high and low pressure recirculation and the addition of variable geometry turbine (VGT) control. The paper focused on different goals: firstly, to highlight the change of selected operating parameters (intake pressure and mass flow rate, EGR fraction) in the different configurations affecting the development of in-cylinder pressure curves, ignition delay and combustion process. Secondly, to analyse how rate of heat release is affected by the different EGR and VGT control strategies. Finally, to justify the observed trends of fuel consumption, NOx and soot emissions according to the pressure diagrams and heat release curves, as LP EGR and a different VGT position allowed reductions of 2.1, 50 and 22.8% of these parameters referring to the standard operating mode in the presented experimental point.

Autoignition of Methyl Decanoate, a Biodiesel Surrogate, under High-Pressure Exhaust Gas Recirculation Conditions

The autoignition of methyl decanoate, a standalone biodiesel surrogate or surrogate component, is studied under high-pressure exhaust gas recirculation (EGR) conditions relevant to internal combustion engines. Ignition delay times were determined in reflected-shock experiments using measured pressure and electronically excited OH chemiluminescence for stoichiometric methyl decanoate/air/EGR mixtures containing 0–60% EGR at 900–1300 K and 20 and 50 atm. Ignition delay time dependence upon pressure and EGR fraction was found to obey τ ∝ P–0.8 and τ ∝ (1 – EGR %/100)−1 for the conditions studied. Experimental results are compared to three comprehensive kinetic models for methyl decanoate oxidation from the recent literature: Herbinet et al. (Herbinet, O.; Pitz, W. J.; Westbrook, C. K.Combust. Flame 2008, 154, 507−528 and Herbinet, O.; Pitz, W. J.; Westbrook, C. K.Combust. Flame 2010, 157, 893–908), Glaude et al. (Glaude, P. A.; Herbinet, O.; Bax, S.; Biet, J.; Warth, V.; Battin-Leclerc, F.Combust. Flame 2010...

On the combination of high-pressure and low-pressure exhaust gas recirculation loops for improved fuel economy and reduced emissions in high-speed direct-injection engines

In this paper, an experimental study of the combination of low-pressure and high-pressure exhaust gas recirculation architectures has been carried out. In the first part of the paper, the effects of both high-pressure and low-pressure exhaust gas recirculation architectures on engine behaviour and performance are analysed by means of a series of steady tests. In the second part, the effects of the combination of both architectures are addressed. The results show that the low-pressure configuration improves high-pressure exhaust gas recirculation results in brake-specific fuel consumption, nitrogen oxides and exhaust gas opacity; nevertheless, hydrocarbon emissions are increased, especially during the engine warm up. In addition, the exhaust gas recirculation rate achieved with low-pressure systems is limited by the pressure difference between diesel particulate matter outlet and compressor inlet; therefore, the high-pressure system can be used to achieve the required exhaust gas recirculation levels without increasing pumping losses. In this sense, the combination of both exhaust gas recirculation layouts offers significant advantages to reduce emissions and fuel consumption to meet future emission requirements.

Experimental study on the effects of HP and LP EGR in an automotive turbocharged diesel engine

An experimental investigation was performed with a view to comparing high and low pressure exhaust gas recirculation systems (HP and LP EGR) fitted on an automotive turbocharged diesel engine, focusing on analysing their influence on fuel consumption, pollutant emissions and the combustion process. Following the development of a prototype cooled LP EGR circuit, the main engine and turbocharger parameters were measured in six part-load operating conditions related to the European driving cycles. Different operating modes were considered, from the simplest and most commonly investigated (without EGR, with HP or LP EGR) to more complex schemes, namely the simultaneous application of high and low pressure recirculation and the addition of variable nozzle turbine (VNT) control. The extensive experimental database made it possible to confirm literature concerning the comparison of recirculating systems and the potential of LP EGR on engine intake temperature and NOx reductions. New aspects were also analysed, such as the balance of the high and low pressure EGR rate in order to achieve maximum NOx reductions in simultaneous applications, the interactions between EGR circuit management and the application of VNT control in order to improve the trade-off between fuel consumption and NOx and soot emissions.

Soot particle size and pollutant emissions characterization from a LD diesel engine equipped with high pressure and low pressure EGR system and operated with conventional and PCCI combustion

The paper analyses the soot Particle Size Distribution Function (PSDF) measurements carried out at the exhaust of a modern automotive diesel engine equipped with a low-pressure Exhaust Gas Recirculation (EGR) system and operating with conventional and Premixed Charge Compression Ignition (PCCI). The results have indicated significant benefits in terms of exhaust raw particle number emission with the adoption of low-pressure EGR system and PCCI calibration and, thanks to the peculiarity of the operating mode of Low Pressure EGR (LPEGR) system, have highlighted the complex link between in-cylinder charge composition and the PSDF characteristics.

Study on the Combustion Process and Emissions of a Turbocharged Diesel Engine with EGR

A high pressure EGR system was adopted to a turbocharged inter-cooled diesel engine, to analyze its combustion and emission characteristics under the condition of different loads and constant speed. Under the same steady operating mode, with the increase of EGR rate, the temperature of compressed gas ascended, the ignition delay was shortened, the pressure and temperature of the burned gas descended, and the combustion process was prolonged. According to the experimental data, it was found that, at the same EGR rate, lower the load of engine was, lower the temperature in cylinder, and higher the increase rate of CO was. However, the increase rate of HC present a falling trend. The decrease rate of the specific emission of NOxlinearly varied with EGR rate with a slope of 1.651. The increase rate of smoke opacity behaved a second-order polynomial uprising trend, and the higher the load was, the sharpener the smoke opacity deteriorated, with the increase of EGR rate. From the point of emission view, the engine with EGR system can achieve the lesser exhaust emissions in some operations by adjusting the engine parameters.