Effect Of Recirculation Research Articles

A new low NOx emission technique for NH3/H2 blends in a flameless combustor through offset injection

The application of ammonia (NH3) as a possible future fuel presents a plausible solution for green energy storage. It helps provide a carbon-neutral fuel alternative for industrial power generation and transportation. However, the combustion of NH3 presents a formidable challenge due to its low reactivity, inadequate flame stability, sluggish flame propagation, and high NOx emissions. Consequently, its integration into combustion systems necessitates substantial system and strategy modification to enable its deployment to industrial systems. The current study presents a novel fuel/air injection technique, which emphasizes the high recirculation of hot combustion products and the extended residence time of fuel/air mixtures. A comprehensive experimental and numerical investigation is conducted using a swirl air injection and offset fuel injection to achieve the flameless combustion mode for optimized NH3/H2 fuel blends. A range of mixture conditions (ϕ = 0.5–1.2) and NH3/H2 compositions (50/50–70/30) are experimentally examined. The investigations helped elucidate the effect of residence time and recirculation on NOx emissions through kinetic simulations using a reactor network model. Subsequently, 3-D numerical simulations helped identify regions of high recirculation, quantified through reactant dilution ratios and uniform temperature distribution. These aspects are determined using a new parameter, the temperature uniformity index along the axial direction of the combustor. The emissions of NOx, unburnt NH3, and unburnt H2 are quantified for different equivalence ratios and NH3 mole fractions in the fuel mixture. The investigations reveal that NOx emissions reached their minimum (450–654 ppm) and (344-211 ppm), when the burner operated at lean (ϕ = 0.5–0.8) and rich (ϕ = 1.0–1.2) conditions, respectively, for 70/30 NH3/H2 blend. The emissions of unburnt NH3 and H2 species remain minimal for lean conditions. Both lean and rich operational regimes demonstrated similar or superior emission characteristics in flameless combustion mode when compared to the conventional combustion mode.

Effects of recirculation dredging on density, strength, settling and oxygen concentration of fluid mud in the port of Emden

Abstract Purpose Recirculation dredging is a port maintenance concept developed in the Port of Emden, Germany to create a navigable fluid mud layer. This study investigates the effects of recirculation on key sediment properties, including density, yield stress, and oxygen concentration. Methods Six field monitoring surveys were carried out at two locations at different times of the year to assess changes before and after recirculation. Bathymetry, bulk density, yield stress, and oxygen concentration profiles were measured in situ. The settling properties and oxygen concentration levels on collected fluid mud samples were analyzed in the laboratory. Results The investigation reveals minimal changes in the density of recirculated fluid mud. However, the post-recirculation measurements showed a decrease in yield stress, ranging from 18 to 51% at Große Seeschleuse (GS) and 36% to 52% at Industriehafen (IH). The yield stress and density vary depending on the frequency of dredging. After structural density (1166 kg m−3 in GS and 1173 kg m−3 in IH), the yield stress of fluid mud increased exponentially. Therefore, monitoring of the yield stress is important for recirculation. A slight increase in oxygen concentration was observed post-recirculation, especially during winter. Yet, the rapid decline in oxygen levels post-mixing in the laboratory showed that sustaining long-term elevated oxygenation levels is not feasible by recirculation dredging alone. Conclusions The findings highlight the effectiveness of the recirculation on the yield stress, density, and oxygen concentration of fluid mud and illustrate the importance of considering both density and yield stress in sediment management practices. Future research should address the temporal evolution of density, yield stress, and oxygen levels following a dredging intervention and the influence of extracellular polymeric substances (EPS) and organic matter decay on sediment behavior.

Effects of recirculation and air change per hour on COVID-19 transmission in indoor settings: A CFD study with varying HVAC parameters

COVID-19 has already claimed over 7 million lives and has infected over 775 million people globally [1]. SARS-CoV-2, the virus that causes Covid-19, spreads primarily through droplets from infected people's airways, rendering Heating, Ventilation, and Air Conditioning (HVAC) systems critical in controlling infection risk levels in the indoor environment. To understand the dynamics of exhaled droplets and aerosols and the percentage of particles that are inhaled, escaped, recirculated, or trapped on different surfaces for a variety of environmental settings, we have presented our findings from the Computational Fluid Dynamics (CFD) modeling to investigate the impact of changing HVAC parameters in this paper. When combined with the spatial and temporal distribution of droplets, this method can be used to assess the potential risk and strengthen resilience. This finding demonstrates the viability and usefulness of CFD for modeling the distribution and dynamics of droplets and aerosols in confined environments. Our study demonstrates that raising the Air Change per Hour (ACH) from 2 to 8 reduces the risk of particle inhalation by nearly 70 %. Additionally, limiting the amount of air recirculation or increasing the amount of fresh air helps to reduce the number of airborne particles in an indoor space. To reduce the potential for respiratory droplet-related transmission and to provide relevant recommendations to the appropriate authority, the same computational approach could be applied to a wide range of ventilated indoor environments such as public buses, restaurants, exhibitions, and theaters.

Experimental investigation of NOx emission control using carbon nanotube additives and EGR configuration on CRDI engine fueled with ternary fuel

This study aims to investigate the impact of the combined effects of carbon nanotubes and exhaust gas recirculation (EGR) of a common rail direct injection (CRDI) engine fueled with ternary fuels. Three rates of EGR (0%, 10%, and 20%) were used at a standard injection timing of 23° before Top Dead Centre (bTDC). This study involves substituting diesel with biofuels, reducing oxides of nitrogen and soot emissions by 30–40%. The experimental investigation involves the exploration of combustion, exhaust emissions, and performance parameters for a single-cylinder CRDI engine using ternary fuels, which consist of diesel, biodiesel, and bioethanol by volume %. At full load with 20% EGR, the experimental analysis indicated a 2% decrease in BTE, a 3.33% increase in BSFC, and a 3.16% increase in BSEC across the blends in performance. In terms of combustion analysis, results show a 5.25 bar in-cylinder pressure drop, 4.14% reduction in HRR, and 12.62% drop in MGT. However, in terms of emissions, 20% EGR yielded the most favorable results, showing a 62.94% reduction in NOx emissions across all blends, albeit accompanied by a 13.89% increase in hydrocarbons (HCs) and 5% rise in carbon monoxide at full load. The 20% EGR rate effectively minimized NOx emissions while slightly impacting HC and CO emissions.

Effects of exhaust gas recirculation and ethanol-gasoline blends on combustion and emission characteristics of spark ignition engine

The combined influences of exhaust gas recirculation (EGR) and ethanol-gasoline blends on the combustion process and emissions of a single-cylinder spark ignition engine were numerically examined. Four different EGR values were employed, i.e. 0%, 2.5%, 5%, and 10%, to reveal the effect of EGR on engine performance. The engine was operated at a load of 100% and a speed of 3000 rpm. The peak values of in-cylinder pressure and temperature gradually decreased as increasing the EGR ratios. These peaks move towards the TDC as increasing the ethanol fraction in blends due to high oxygen in the mixture and burning flame speed in the cylinder. Ethanol fractions ranging from 5% to 15% can effectively improve the negative effects of EGR ratios. When increasing the ethanol fraction, the CO2 rapidly increased and concentrated around the TDC. The NOx emissions are significantly increased with increasing ethanol fraction. In the case of pure gasoline, the NOx emissions are substantially suppressed and exhibit a remarkably low value as increasing the EGR ratios. The best combination for diluting NOx emissions to a very low level is ethanol fraction ranging from E5 to E10, while the EGR rates range from 5% to 10%.

Experimental Assessment of the Flow Recirculation Effect on the Noise Measurement of a Free-Flying Multi-rotor UAS in a Closed Anechoic Chamber

AbstractThe flow recirculation effect on the noise measurement of a multi-rotor unmanned aircraft system (UAS) hovering in a closed anechoic chamber is experimentally characterized in this work. The measured acoustic spectrogram reveals that the recirculation forms around 30 s after the UAS’s take-off, manifested as prominent fluctuations in blade passage frequency and its harmonics. However, the instantaneous overall sound pressure level shows no obvious increase with the development of the recirculation. The result indicates that the recirculation effect does not significantly change the total acoustic energy but increases the uncertainties in the spectral distribution, which can be quantified by spectral entropy. The quantitative analysis of different noise components shows that the recirculation has a minimal effect on the tonal noise levels but slightly increases the broadband noise level out of the rotors’ plane. The results from parametric tests suggest that this broadband noise increment has a positive correlation with the UAS’s hover height but a negative correlation with the UAS’s gross mass. The comparison with existing studies highlights the difference in the recirculation effect on the noise of isolated rotor(s) and free-flying multi-rotor UAS in confined spaces.

Investigation of Hydrothermal Carbonization of Exhausted Chestnut from Tannin Extraction: Impact of Process Water Recirculation for Sustainable Fuel Production

This study explores the hydrothermal carbonization (HTC) process applied to the exhausted chestnut produced by the tannin extraction industry, utilizing process water recirculation to enhance the efficiency and sustainability of the conversion process. Tannin extraction from wood typically involves hot water treatment, leaving behind residual wood biomass known as exhausted wood. These by-products maintain their renewable properties because they have only been exposed to hot water under a high pressure, which is unlikely to cause major alterations in their structural components. Hydrothermal treatment was carried out at temperatures of 220 °C and 270 °C for 1 h, with process water being recirculated four times. This investigation focused on analyzing the effects of recirculation on the yield and fuel properties of hydrochar, as well as characterizing the combustion behavior of the obtained hydrochar. The results indicated that recirculation of process water led to improvements in both the mass and energy yields of hydrochar. The mass yield of the hydrochar samples increased by 5–6%, and the ERE of the hydrochar samples increased by 5–8% compared to the HTC reference sample. However, alterations in the combustion characteristics were observed, including decreases in ignition temperature and combustion reactivity. The results indicate that, with PW recirculations, the combustion index decreased by about 14% and 18% for 220 °C and 270 °C, respectively. Overall, this research demonstrates the potential of utilizing HTC on chestnut tannin residue with process water recirculation to produce stable solid fuel and provides insights into the combustion behavior of the resulting hydrochar.

The influence of injection pressure and exhaust gas recirculation on a VCR engine fueled by microalgae biodiesel

AbstractBiodiesel has been chosen as a decent alternative to diesel in the context of establishing environmentally pleasant conditions and saving petroleum‐based resources for future generations. It is well‐established that biodiesel‐powered diesel engines may achieve outcomes equivalent to those of diesel engines. The current investigation was conducted to study the effect of injection pressure (190, 210, and 230 bar) and exhaust gas recirculation (EGR) (5%, 10%, and 15%) on a single‐cylinder variable compression ratio (VCR) diesel engine running using a B20 (20% MB + 80% PD) blend of microalgae biodiesel (MABD). This experiment was conducted in two stages. During the first stage of experimentation, the efficiency and emission characteristics of a diesel engine with a B20 blend of MABD at various fuel injection pressures and fresh air were investigated. During the second phase, fresh air was mixed with 5%, 10%, and 15% exhaust gases, and the experiment was conducted. It was discovered that increasing injection pressure to 230 bar provided considerable improvements. Brake thermal efficiency increased by 2.35%, brake‐specific fuel consumption decreased by 3.57% and pollutants such as carbon monoxide (CO), hydrocarbon, and smoke were reduced by more than 50% compared to conventional diesel. These reductions were similarly significant (over 22%) as compared to the B20 blend at lower injection pressure (210 bar). However, there was a slight trade‐off: nitrogen oxide (NOx) emissions increased partially (3.14%), while exhaust gas temperature (EGT) increased by 1.72% at a higher pressure. The study then investigated the influence of EGR (5%, 10%, and 15%) at various injection pressures. The optimal value seems to be 10% EGR at 230 bar injection pressure. This combination substantially reduced NOx emissions (by over 41% compared to the normal B20 blend) and EGT (by more than 8%), while having no notable effect on other performance or emission variables. Overall, the results show that employing a B20 MABD blend with high injection pressure (230 bar) and moderate EGR (10%) improves engine performance while reducing hazardous emissions.

#3022 Rationale and design of the CORDIAL first-in-human clinical trial: a system for sorbent-assisted continuous flow peritoneal dialysis

Abstract Background and Aims Peritoneal dialysis has important disadvantages, including low plasma clearance and a limited technique survival. A new device for sorbent-assisted continuous flow peritoneal dialysis has been designed (Wearable Artificial KIDney, WEAKID) that is based on continuous recirculation (rapid cycling) of peritoneal dialysate via a single-lumen peritoneal catheter with regeneration of dialysate using sorbents. Anticipated benefits are a better plasma clearance a higher mass transfer area coefficient with continuous flow of dialysate and enhanced diffusion due to a higher time-averaged plasma-dialysate concentration gradient with sorbent-based dialysate regeneration, and a prolonged technique survival thanks to lower peritonitis risk (less (dis)connections) and a lower glucose exposure. Method This is a first-in-human, prospective, open-label, non-randomized, single-arm, multicenter study, that will be performed at the University Medical Center Utrecht (Utrecht, The Netherlands), Università degli studi di Modena e Reggio Emilia (Italy), and Instituto de Investigación Hospital Universitario La Paz, Servicio Madrileño de Salud (Spain). We aim to include 12 stable, adult PD patients. In the first week, blood, urine, and dialysate samples will be collected over three separate days to assess the efficacy of the patient's standard PD schedule. The WEAKID system will then be tested in a clinical setting on 6 days over a period of 2 weeks (three consecutive days per week). During the first week, participants will be treated with WEAKID without sorbents for 4h (first day) or 8h (second and third day). The second week, treatment will consist of WEAKID with sorbents for 4h (first day) or 8h (second and third day). This way, exposure to new components of the system is incremental and the effectiveness of continuous recirculation of dialysate and that the added effect of sorbent-based dialysate regeneration can be analyzed separately. Outcomes The primary aim of this first-in-human clinical trial is to evaluate the (short term) clinical safety and performance of WEAKID treatment in a clinical setting. The primary safety objective will be assessed by describing and examining the incidence of: Key secondary objectives include an evaluation of efficacy in terms of plasma clearance, ultrafiltration, net base release, and patient tolerance. Planning Inclusion of the first patient is expected in January 2024, the final inclusion is expected to take place in November 2024.

Effect of exhaust gas recirculation on the performance and emission characteristics of diesel engine with hydrogen fuel and nano additives

One of the most popular techniques for reducing emissions, in particular nitrogen oxide (NOX), carbon monoxide (CO), carbon dioxide (CO2), and particulate matter (PM), is exhaust gas recirculation (EGR). In an EGR system, the intake manifold is used to re-introduce some of the exhaust gases into the combustion chamber. Diesel engine performance could be enhanced by employing the right number of nano additives. Nano additions aid in increasing efficiency when using hydro fuel. The following systems are impacted by the use of EGR: brake specific fuel consumption (BSFC), diesel engine combustion characteristics, brake thermal efficiency (BTE), engine speed, CO2 and HC emissions, turbocharged diesel engine performance characteristics, fuels, temperature, and on EGR.

Picosecond laser-driven coded-source radiography with high resolution and contrast

The X-ray sources for Compton radiography of ICF experiments are generated by using intense picosecond lasers to irradiate wire targets. The wire diameter must be designed thin enough, for example ∼ 10 µm in many published works, to comply a high spatial resolution. This results in a low laser-target interception, which limits the photon yield. We investigated a technique of coded-source radiography based on laser-driven annular sources via Monte Carlo and PIC simulations. The annular X-ray source is formed by laser irradiating tube target in which the effect of electron recirculation plays an important role. We proved that this technique has an increased spatial resolution and contrast than that using the Gaussian source produced by wire targets. Therefore, the diameter of the backlighter target can be significantly increased to uplift laser-target interception without compromising on spatial resolution. This contributes towards a reconciliation between the spatial resolution and photon yield for Compton radiography. The results predict the possibility of improving source photon yield by several times in future experiments.

Natural draft direct dry cooling system performance at various application scales under windless and windy conditions

The natural draft direct dry cooling system (NDDDCS) presents a promising alternative to conventional forced draft air-cooled condensers (ACCs) and indirect natural draft dry cooling systems, overcoming their limitations by efficiently condensing process steam directly and passively. The NDDDCS achieves superior thermal efficiencies while reducing system complexities, operational costs, and auxiliary power consumption. Potential reductions in operational expenses for the system may offset initial capital investments, resulting in lower lifetime costs. While research to date has focused on large-scale NDDDCS performance under varying wind conditions, this work addresses a critical gap by investigating the system’s scalability for various applications, including a large-scale coal-fired power plant (900 MWt, 165 m total height), a medium-scale concentrated solar power plant (CSP) (100 MWt, 65 m total height), and a small-scale water desalination plant (1 MWt, 11.5 m total height) under both windless and windy conditions. To achieve this, a steady-state 3-D computational fluid dynamics (CFD) model is developed, validated and scaled, incorporating innovative features such as an atmospheric pressure gradient and the ability to capture reversed flows through the system’s heat exchangers. Additionally, the model assesses inlet air temperature data at a per-cell resolution, enabling the ability to predict non-uniform temperature distributions in the heat exchangers, including hot-spots caused by airflow recirculation. Analysis of velocity and temperature fields across all scales reveals that recirculation effects negatively impact NDDDCS performance, particularly at the middle circumferential heat exchanger sector. The hyperbolic shape of the tower shell induces internal recirculation zones and reduces the effective flow volume. Under windy conditions, performance losses of 44%, 40%, and 40% are observed at crosswind speeds of 3 m/s, 6 m/s, and 9 m/s for small, medium, and large-scale towers, respectively. Beyond these speeds, the relationship between system performance and draft driving potential becomes non-linear due to crosswind effects dominating. Furthermore, a novel effect is identified at wind speeds of 9 m/s, 15 m/s, and 18 m/s for small, medium, and large-scale systems, respectively, where an inflection point allows for system performance recovery. This study underscores the NDDDCS’s potential as a cooling solution for modern power cycles across various scales, while highlighting the implications of scaling the system for medium- and small-scale thermal applications.

Effect of exhaust gas recirculation(EGR) on combustion and emission of butanol/gasoline combined injection engine

N-butanol is a kind of biomass alcohol which can be produced by fermentation, and it is also a clean alternative fuel. The combustion and emissions characteristics of n-butanol/gasoline SI engine under different combined injection modes with the introduction of EGR was studied. N-butanol inlet injection plus gasoline in-cylinder direct injection is called N-GXDI; Gasoline inlet injection plus n-butanol in-cylinder direct injection is called G-NXDI. Through the analysis of combustion and emission performance under different EGR rates, injection modes and direct injection ratios (DIr), it is found that with the increase of DIr, cylinder temperature, pressure, and IMEP increase first and then decrease. Under the DIr = 50%, the combustion is more complete when the EGR rate is 5%. Under the same DIr, with the increase of EGR rate, CO emission decreased first and then increased, NOx emission opposite, THC emission increased. Under the same EGR rate, the total particle number of the two modes decreases first and then increases with the increase of DIr. The G-NXDI mode has advantages in combustion and primary emissions, while the N-GXDI mode has advantages in particulate emissions, suitable injection mode combined with EGR can greatly improve combustion and emission performance.

Effect of flue gas recirculation on combustion instability and emission characteristics of premixed CH4/NH3/air flame

The hydrogen carrier ammonia is considered a prominent carbon-free alternative fuel. This paper examines the impact of flue gas recirculation (FR) on combustion instability and emission behavior of premixed CH4/NH3/air swirl flame at different equivalence ratios (Φ) and ammonia mole fractions (χNH3). Experimental results show that FR is beneficial to suppressing the self-excited pulsating pressure and pulsating heat release rate of CH4/NH3/air flame, and the pulsating frequency decreases monotonically with the increase of FR. Under fuel-lean and stoichiometric conditions, FR is beneficial to suppressing NOx formation but will increase CO and NH3 emissions. Under fuel-rich conditions, FR reduces CO emissions but increases NOx emissions. The NO emissions obtained from the chemical reactor network simulation are in qualitative agreement with the experimental results. The results show that the elementary reactions related to HNO and NHi radicals play a crucial role in the influence of FR on NO formation.

Effect of syngas recirculation in the pyrolysis zone on the rice husk gasification process using the downdraft reactor

As one of the world's largest rice producers, Indonesia has an abundance of rice husk as a byproduct of rice milling. Rice husks were utilized to examine downdraft gasification with syngas recirculation system. This study attempts to produce better syngas than conventional downdraft gasifier. With an equivalency ratio of 0.20, syngas was recirculated into the reactor in the pyrolysis zone with valve openings at 25%, 50%, and 75%. This study determined the syngas recycling ratio that maximizes H2 and CO gas and decreases tar. Increasing the syngas recirculation valve (25%, 50%, and 75%) accelerates flame propagation and pyrolysis zone temperature. Syngas study showed no recirculation condition produces the maximum CO2 and CH4. Different recirculation valve openings little affect CO and CH4 gas composition. The H2 gas composition demonstrates that valve openings significantly change H2 gas generation and that the peak was at 50% syngas recirculation. Tar content decreased to 30% and 35% at 50% and 75% valve openings. Based on H2/CO comparison and tar concentration, 50% opening syngas recirculation became the optimum case.

Co-hydrothermal carbonization of styrofoam and sawdust: fuel properties evaluation and effect of water recirculation on hydrochar properties

Co-hydrothermal carbonization of styrofoam and sawdust: fuel properties evaluation and effect of water recirculation on hydrochar properties

Effects of geometry on the thermal-fluid dynamics of a transition water flow in a square heated asymmetric cavity channel

Cavity channels candidate as a promising passive cooling configuration in thermal management. The superior performance and the limited scientific investigation regarding cavity channels dictate the need for better understanding of the thermal-fluid dynamics. To the best knowledge of the authors, there are few works investigating the effect of the geometry on the thermal-fluid dynamics of cavity channels with no focus on thermal data and quantification of the recirculation effect which can depend on geometrical parameters. In this work, numerical RANS simulations were performed in ANSYS Fluent with the kT-kL-ω turbulence model for a transitional water flow in an asymmetric square cavity channel with different attachment angles in the range of 20°–90°. The optimal heat transfer performance in terms of uniform and high Nusselt numbers is provided by the configuration with an angle in the range of approximately 30°–40°. Recirculation plays an important role in enhancing heat transfer and its strength is associated with the penetration capacity in the boundary layer. Two regions of strong and weak recirculation are identified along the channel; when the recirculation is weak, other mechanisms such as the thinning of the thermal boundary layer play a more important role. By increasing the attachment angle it is shown the local thinning of the thermal boundary layer, an augmentation of the magnitude of the negative turbulent heat flux peak, and a similarity of the conductive sublayer thickness with the recirculation strength.

Multiphysics modeling and experimental validation of heat and mass transfer for the vacuum induction melting process

Vacuum induction melting is crucial in casting nickel-based superalloy components, ensuring excellent properties for aero-engine applications. Precise melting temperatures are vital for achieving optimal metallurgical quality before casting. Hence, a multiphysics numerical model is developed to simulate the induction melting process for the Inconel 718 superalloy. The proposed holistic model integrates magnetic fields, induced currents, and heat and momentum transfer phenomena in a single coupled model. A moving mesh approach reproduces the magneto-hydrodynamic behavior of the free surface, simulating the oscillations of the melt. The stabilized deformed surface profile is correlated with experimental measurements, reporting a proper correlation. Then, the flow field and recirculation effect are modeled with a Low Reynolds Number turbulence approach and coupled with the melt convective heat transfer, developing a complete magneto-thermo-hydrodynamic model. In a laboratory-scale vacuum induction melting furnace, transient melting operation variables are characterized and introduced to the numerical model to compute the temperature evolution. An accurate reproduction of the transient melt temperature variations is reported with a relative error of less than 5%. The influence of the crucible thermal insulating capacity is assessed, emissivity dependence evaluated, and melt homogenization is reported at different process stages. This comprehensive numerical and experimental approach offers valuable insights for enhancing vacuum induction melting for Ni-based superalloys.

A 35-year monitoring of an Italian landfill: Effect of recirculation of reverse osmosis concentrate on leachate characteristics

“Fossetto” landfill (Monsummano Terme - Tuscany, Italy) started operation in 1988 as a controlled landfill accepting mixed municipal solid waste collected without any attempt of recycling. Then, progressively, following the evolution of the state-of-the-art, it adopted biogas extraction and valorisation systems and mechanical-biological treatment for incoming waste (both since 2003). Finally, since 2006, in the plant is performed on-site reverse osmosis leachate treatment with the concentrated leachate being recirculated back into the landfill body. Recently a new landfill cell, separate from the others, was put in operation adding a capacity of 200,000 m3 to the already available 1,095,000 m3. This plant can provide long term leachate composition data to study the evolution and impact of changing landfill technology and waste composition on various parameters. The rise in leachate production (+84 % in 2018–2022 respect to the period before recirculation) cannot be totally attributable to recirculation but could be also linked to the increase in the amount of landfilled waste. The concentration of certain parameters (NH4+, Cl− and to a less extent of COD) increased (+60 %, +58 %, +17 % respectively in the last five years with respect to the period before recirculation); however, this increase did not influence the performance of the treatment plant. Nevertheless, the overall leachate management would benefit from an optimized reinjection system.

Effects of exhaust gas recirculation on nitrogen oxides, brake torque and efficiency in a hydrogen direct injection spark ignition engine

This study investigated the effects of exhaust gas recirculation (EGR) on emission and efficiency in a hydrogen direct injection spark ignition engine. EGR was supplied as the low-pressure (LP)-EGR system by controlling EGR valve from zero to 18.7% in terms of mass fraction. The result showed that EGR effect on nitrogen oxides (NOx) reduction became enlarged as higher engine speed due to increasing residual gas fraction. Also, under the same excessive air ratio (λ:2.2), EGR addition made NOx reduction from 89.9 to 98.7 % as varying engine speed. As NOx limit was low, the maximum brake torque was also reduced. However, by using appropriate EGR, NOx margin could be converted to increasing brake torque under the same NOx concentration level from 1.9% to 18.2% as varying engine speeds. From this result, to achieve the maximum output when reaching the turbocharger’s limit in a hydrogen engine and effectively reduce nitrogen oxide emissions, it is not only dependent on lean combustion but also effective to incorporate approximately 20% EGR into the operating strategy.