Low Pressure Loop EGR Research Articles

Impact of butanol isomers and EGR on the combustion characteristics and emissions of a SIDI engine at various injection timings

The impact of butanol on a SIDI engine operating with low pressure loop EGR was investigated in this study, with each of the four butanol isomers blended with gasoline by a volume fraction of 30%. Three injection timings during the intake stroke were selected, covering the representative scenarios of severe fuel impingement, adequate fuel-air mixing without obvious fuel impingement, and insufficient fuel-air mixing time prior to combustion. The results show that n-butanol, sec-butanol, and iso-butanol are capable of accelerating flame propagation and hence shorten the combustion duration, while tert-butanol would unfavorably extend the combustion duration. The addition of all the butanol isomers lead to reduced fuel consumption and reduced CO, unburnt HC and particulate number (PN) emissions, with n-butanol and sec-butanol showing more potential in high efficiency and low emission combustion at low load. EGR yields distinct influences on the PN emission at different injection timings: when injection starts at middle or late intake process, PN concentration decreases with EGR rate, which is consistent with previous studies; when injection starts early in the intake stoke, however, PN concentration would otherwise increase with the EGR rate independent of the fuel type, which could be possibly owing to the shift of the locally rich mixture in the Φ-T diagram towards the highly sooty peninsula with the cooling effect of EGR.

Improvement of BSFC and effective NOx and PM reduction by high EGR rates in heavy duty diesel engine

The test engine was a turbocharged 10.5L engine with an intercooler. A performance target was set at a rated power of 300 kW (BMEP = 1.7 MPa) and peak torque of 1842 Nm (BMEP = 2.2 MPa). Emission targets were set at a level of near future and stringent regulation standards in Japan. The engine was equipped with new technologies such as a high pressure common rail system, FCD piston, a high pressure ratio VGT and an aftertreatment system. The high and low pressure loop EGR system was installed and this system with a VGT had a high performance and could increase an EGR rate in order to reduce BSNOx while maintaining the satisfied BSFC and PM performance simultaneously not only in the steady state condition but also in the transient condition.

Emission reduction through internal and low-pressure loop exhaust gas recirculation configuration with negative valve overlap and late intake valve closing strategy in a compression ignition engine

An investigation was carried out to examine the feasibility of replacing the conventional high-pressure loop/low-pressure loop exhaust gas recirculation with a combination of internal and low-pressure loop exhaust gas recirculation. The main objective of this alternative exhaust gas recirculation path configuration is to extend the limits of the late intake valve closing strategy, without the concern of backpressure caused by the high-pressure loop exhaust gas recirculation. The late intake valve closing strategy improved the conventional trade-off relation between nitrogen oxides and smoke emissions. The gross indicated mean effective pressure was maintained at a similar level, as long as the intake boosting pressure kept changing with respect to the intake valve closing timing. Applying the high-pressure loop exhaust gas recirculation in the boosted conditions yielded concern of the exhaust backpressure increase. The presence of high-pressure loop exhaust gas recirculation limited further intake valve closing retardation when the negative effect of increased pumping work cancelled out the positive effect of improving the emissions’ trade-off. Replacing high-pressure loop exhaust gas recirculation with internal exhaust gas recirculation reduced the burden of such exhaust backpressure and the pumping loss. However, a simple feasibility analysis indicated that a high-efficiency turbocharger was required to make the pumping work close to zero. The internal exhaust gas recirculation strategy was able to control the nitrogen oxides emissions at a low level with much lower O2 concentration, even though the initial in-cylinder temperature was high due to hot residual gas. Retardation of intake valve closing timing and intake boosting contributed to increasing the charge density; therefore, the smoke emission reduced due to the higher air–fuel ratio value exceeding 25. The combination of internal and low pressure loop loop exhaust gas recirculation with late intake valve closing strategy exhibited an improvement on the trade-off relation between nitrogen oxides and smoke emissions, while maintaining the gross indicated mean effective pressure at a comparable level with that of the high-pressure loop exhaust gas recirculation configuration.

대형디젤엔진의 저온연소 시스템 최적화에 관한 연구

Abstract : According to the regulation on the environment and fuel efficiency is becoming strict, many experiments are conducted to improve efficiency and emission in internal combustion engines. LTC (Low temperature combustion) technology is a promised solution for low emissions but there are a few barriers for the commercial engine. This paper includes optimization that applies LTC method to heavy duty diesel engine. Adequate LTC was applied to low and middle load as adaptability in heavy duty diesel engine, and optimization focused on reduction of fuel consumption was proceeded at high load. Through this research, strategy for practical use of LTC was selected, and fuel consumption has improved on the condition that satisfies the emission regulation at systematic viewpoint. Key words : Heavy duty diesel engine( 대형디젤엔진), HP-EGR(High Pressure loop EGR, 고압 배기재순환), LP-EGR (Low Pressure loop EGR, 저압 배기재순환), VGT Turbocharger (Variable Geometry Turbine Turbocharger, 가변 터빈 터보차져), LTC(Low Temperature Combustion, 저온연소)

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.

Effects of H2 on the number concentration of particulate matter in diesel engines using a low-pressure loop exhaust-gas recirculation system

We investigated the effects of H2 on the number concentration of particulate matter (PM) emissions from a diesel engine fitted with a low-pressure loop exhaust gas recirculation system. We used a 2.2-L four-cylinder direct-injection diesel engine satisfying EURO V regulations, and converted this engine to include an H2 feed. The air/fuel (A/F) ratio was varied in the range of 21.9–45.5 and the brake mean effective pressure was varied in the range of 2–6 bars to control the O2 concentration and in-cylinder temperature, both of which are significant for PM emissions. The number concentration of the emitted PM was measured using a scanning mobility particle sizer. We found that the emitted PM decreased by the addition of H2 which caused the unburned gas temperature increased. Furthermore, the degree of reduction was larger as the A/F ratio, load, and H2 energy fraction increased. However, with A/F ratios of less than 21.9, the addition of H2 increased the number concentration of emitted PM which was attributed to the small O2 concentration at these A/F ratios.

Effects of tumble combined with EGR (exhaust gas recirculation) on the combustion and emissions in a spark ignition engine at part loads

The effects of tumble combined with EGR (exhaust gas recirculation) on the combustion and emissions were experimentally investigated in a spark ignition engine in this study. A low pressure loop EGR system and a variable tumble valve in intake ports were employed, by which wide range of EGR ratio and tumble ratio could be achieved. All the tests were performed at part loads, and the equivalence ratio was kept constant at 1.0. The results show that the combination of EGR and enhanced tumble motion produces a significant improvement in fuel economy (13.1–19.5%) and a reduction in the coefficient of variations of indicated mean effective pressure (CoVIMEP) due to the significantly shortened combustion duration. By optimizing the combustion process with EGR and enhanced tumble, NOx (nitrogen oxides) emissions drastically decrease, while HC (hydrocarbons) emissions slightly rise. For CO (carbon monoxide) emissions, the enhanced tumble takes a positive effect.

Observer-Based Estimation of Air-Fractions for a Diesel Engine Coupled With Aftertreatment Systems

This paper presents a control-oriented air-fraction dynamic model for a complete diesel engine and aftertreatment system, as well as an observer to estimate the air-fractions in the integrated diesel engine and aftertreatment system. To reduce engine-out emissions and further improve engine efficiency, advanced combustion modes including low temperature combustion, premixed charge compression ignition, and homogenous charge compression ignition, are under intensive investigations. With the popular configuration of dual-loop exhaust gas recirculation (EGR) systems including a high-pressure loop exhaust gas recirculation and a low-pressure loop EGR (LP-EGR), alternative combustion modes can be potentially accomplished. In addition, aftertreatment systems including diesel oxidation catalysts (DOCs), diesel particulate filters (DPFs), and selective catalytic reduction (SCR) systems, are becoming necessary to satisfy stringent emission standards. With the increasing complexity of modern diesel engines and aftertreatment systems, air-path loop control for the diesel engine systems becomes further challenging partially because LP-EGR couples the aftertreatment systems with the diesel engine air-path system. Most of the current air-fraction dynamic models and observers only consider the air-fractions through the diesel engines and air-fraction dynamics through aftertreatment systems are ignored, which, however, will introduce significant modeling errors in the situations when active DPF regenerations and post-fuel injections are implemented. The purpose of this paper is to develop a control-oriented air-fraction dynamic model for a complete diesel engine and aftertreatment system. Based on the developed model, a Luenberger-like observer is proposed and analyzed using a Lyapunov method as well as the physical meaning of system parameters. Experimental results show that the developed air-fraction model is highly accurate and the designed observer is able to make the estimated air fractions converge to the corresponding true values quickly in both steady-state and transient operations.

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.

Oxygen Concentration Dynamic Model and Observer-Based Estimation Through a Diesel Engine Aftertreatment System

Due to the chemical reactions occurring inside the diesel oxidation catalysts (DOCs) and diesel particulate filters (DPFs) that are commonly equipped on diesel engines, the exhaust gas oxygen concentrations considerably vary through the aftertreatment systems. Oxygen concentration in exhaust gas is important for the performance of catalysts such as the NOx conversion efficiencies of the selective catalytic reduction systems and lean NOx traps. Moreover, in the presence of a low-pressure loop exhaust gas recirculation, the exhaust gas oxygen concentration after DPF also influences the in-cylinder combustion. From system control, estimation, and analysis viewpoints, it is thus imperative to have a control-oriented model to describe the oxygen concentration dynamics across the DOC and DPF. In this paper, a physics-based, lumped-parameter, control-oriented DOC–DPF oxygen concentration dynamic model was developed with a multi-objective optimization method and validated with the experimental data obtained on a medium-duty diesel engine equipped with a full suite of aftertreatment systems. Experimental results show that the model can well capture the oxygen dynamics across the diesel engine aftertreatment systems. As an application of the experimentally validated model, an observer was designed to estimate the DOC-out and DPF-out oxygen concentrations in real time. Experimental results show that the estimated states from the proposed observer can converge to the measured signals fastly and accurately.

OS1-6 High Thermal Efficiency and Low Exhaust Emissions by Injection Nozzle Selection under High & Low Pressure Loop EGR(OS1: Ultimate thermal efficiency,Organized Session Papers)

OS1-6 High Thermal Efficiency and Low Exhaust Emissions by Injection Nozzle Selection under High & Low Pressure Loop EGR(OS1: Ultimate thermal efficiency,Organized Session Papers)

저압 EGR을 적용한 디젤엔진의 희석비에 따른 연소 특성 비교

Exhaust gas recirculation (EGR) is more effective than selective catalytic reduction (SCR) or lean NOx trap (LNT) for the reduction of NOx emissions in diesel engines. A large amount of EGR gas is necessary to satisfy the stringent regulations on NOx emissions. Low pressure loop (LPL) EGR is almost independent of the variable geometry turbocharger (VGT) at a specific boost pressure, so LPL EGR is better than conventional high pressure loop (HPL) EGR in terms of EGR supply. We compare the influence of HPL EGR and LPL EGR on the combustion characteristics at a constant boost pressure in a diesel engine. The dilution ratio was employed as an independent parameter to analyze the effect of the dilution of the intake charge for each EGR loop. At the same level of NOx emissions, the fuel consumption and smoke opacity were slightly lower for LPL EGR than for HPL EGR.

Development of Low Pressure Loop EGR System for Diesel Engines

Development of Low Pressure Loop EGR System for Diesel Engines

2단 터보과급기 장착 승용디젤엔진에서 EGR 배열 방식이 EGR율에 미치는 영향에 대한 시뮬레이션

본 논문에서는 승용디젤엔진에서 유해배출물을 저감시키는 동시에 고연비를 달성하기 위하여 2단 터보과급기와 EGR 장치를 장착한 디젤엔진에 대하여 EGR 배열 방식이 EGR율에 미치는 영향을 분석하기 위하여 시뮬레이션을 수행하였다. 이를 위하여 AMESim을 사용하였고 엔진 부품을 위하여 IFP Engine Library를 사용하였다. 고압, 저압, 반저압의 3가지 배열 방식이 고려되었다. 일반적으로 많이 사용되는 고압 방식과 저압 방식의 EGR 배열이 공연비 21에서 각각 6.4%, 10.0%의 EGR율을 보인 반면, 두 방식의 혼합형인 반저압 EGR 배열 방식의 EGR율은 18.0%의 값을 보였다. 따라서 2단 터보과급기와 EGR 장치를 장착한 엔진 설계시 엔진 성능과 유해배출물 발생량의 관점에서 반저압 방식 EGR 시스템이 적절함을 보였다. In this study, the simulations were carried out to show the effect of the EGR configuration in a passenger diesel engine with 2-stage turbocharger on the EGR rate. The AMESim and IFP Engine Library were used to make the program for the simulation. Three EGR configurations, HPL(high pressure loop), LPL(low pressure loop), and SLPL(semi low pressure loop), were considered. The EGR rate in the HPL and LPL EGR routes were 6.4% and 10.0% respectively but the rate in SLPL route was 18.0% and their air/fuel ratio for all three cases was 21. Therefore the SLPL EGR configuration may be positively considered in the design of the passenger diesel engine with 2-stage turbocharger.

Numerical study of a light-duty diesel engine with a dual-loop EGR system under frequent engine operating conditions using the doe method

Exhaust gas recirculation (EGR) is an emission control technology that allows for a significant reduction in NOx emissions from light- and heavy-duty diesel engines. The primary effects of EGR are a lower flame temperature and a lower oxygen concentration of the working fluid in the combustion chamber. A high pressure loop (HPL) EGR is characterized by a fast response, especially at lower speeds, but is only applicable if the turbine upstream pressure is sufficiently higher than the boost pressure. On the contrary, for the low pressure loop (LPL) EGR, a positive differential pressure between the turbine outlet and the compressor inlet is generally available. However, a LPL EGR is characterized by a slow response, especially at low and moderate speeds. In this study, of the future types of EGR systems, the dual-loop EGR system (which has the combined features of the high-pressure loop EGR and the low-pressure loop EGR) was developed and was optimized under five selected operating conditions using a commercial engine simulation program (GT-POWER) and the DOE method. Finally, significant improvements in the engine exhaust emissions and performance were obtained by controlling several major variables.

低圧Loop EGRを搭載した大型多気筒ディーゼルエンジンにおける高過給,広域多量ＥＧＲの効果

低圧Loop EGRを搭載した大型多気筒ディーゼルエンジンにおける高過給,広域多量ＥＧＲの効果

Generating efficiency and NO x emissions of a gas engine generator fueled with a biogas–hydrogen blend and using an exhaust gas recirculation system

This paper investigates the generating efficiency and NO x emissions of a gas engine generator with a low-pressure loop exhaust gas recirculation system, fueled by a model biogas. Experiments for improving the generating efficiency and reducing NO x emissions were conducted, utilizing optimum spark timings based on the maximum generating efficiencies with varying exhaust gas recirculation (EGR) rates. The test results show that both the NO x emissions and the generating efficiency generally decrease when the EGR rate is increased. Also, by utilizing optimum spark timings with varying EGR rates, the addition of hydrogen to the biogas increases the generating efficiency of the engine. In particular, the generating efficiency of the biogas–hydrogen test increased by about 1.5% in comparison with the model biogas test for the optimum spark timing at 15% EGR. Accordingly, comprehensive techniques, such as the use of a biogas–hydrogen fuel mixture and optimum spark timings with respect to EGR rates, should be employed to efficiently generate electricity with a biogas engine.

Mixed-Source EGR for Enabling High Efficiency Clean Combustion Modes in a Light-Duty Diesel Engine

The source of exhaust gas recirculation (EGR), and consequently composition and temperature, has a significant effect on advanced combustion modes including stability, efficiency, and emissions. The effects of high-pressure loop EGR (HPL EGR) and low-pressure loop EGR (LPL EGR) on achieving high efficiency clean combustion (HECC) modes in a light-duty diesel engine were characterized in this study. High dilution operation is complicated in real-world situations due to inadequate control of mixture temperature and the slow response of LPL EGR systems. Mixed-source EGR (combination of HPL EGR and LPL EGR) was investigated as a reasonable approach for controlling mixture temperature. The potential of mixed-source EGR has been explored using LPL EGR as a 'base' for dilution rather than as a sole source. HPL EGR provides the 'trim' for controlling mixture temperature and has the potential for enabling precise control of dilution targets. This approach also has a benefit where LPL EGR does not provide sufficient dilution for achieving conditions appropriate for HECC operation. The balance of the required dilution could be achieved with HPL EGR mitigating the need for throttling or a LPL EGR pump. The results of this investigation revealed significant differences in engine-out emissions and performance for various EGRmore » sources.« less