Recirculation Strategy Research Articles

Start-up strategy of single-stage partial nitrification-anammox process for anaerobic digestion effluent

The objective of this study was to improve the nitrogen removal efficiency and reduce the start-up period of a single-stage partial nitritation-anammox (SPNA) system using iron particle-integrated anammox granules (IP-IAGs). Anammox granules were enriched in sequencing batch and expanded granular sludge bed (EGSB) reactors. The EGSB reactor produced larger and more uniform granules with higher specific anammox activity. IP-IAGs were then inoculated into a two-stage partial nitritation-anammox reactor treating anaerobic digestion (AD) effluent, followed by an internal recirculation strategy to acclimate the granules to oxygen exposure for SPNA. Finally, the SPNA process operated to treat real AD effluent under optimal conditions of 0.05 L/min aeration intensity (0.01 vvm) and 24 h of hydraulic retention time, achieving TNRE of 86.01 ± 2.64 % and nitrogen removal rate of 0.74 ± 0.04 kg-N/m3·d for 101 d.

Toward zero carbon emissions: High thermal efficiency low speed two-stroke marine engine using pure ammonia fuel

As the future development trend and the crucial link to achieving the carbon peaking and carbon neutrality goals in China, the achievement of “zero carbon” emissions in low-speed two-stroke marine engines is currently in the preliminary stages of exploration. Ammonia fuel is one of the main zero-carbon energy sources of interest for marine engines. The primary challenges associated with ammonia application include its high self-ignition temperature, low laminar flame speed, and lengthy ignition delay time. Although stable combustion can be achieved with the assistance of a small amount of highly active carbon-based fuel, carbon emissions are still inevitable. To obtain “zero carbon” emissions, the high-temperature cylinder gas recirculation strategy (HTCGR) was innovatively proposed to realize the possible application of pure ammonia. However, the heat transfer loss by using pure ammonia fuel is enhanced by 289% compared to the diesel mode. Therefore, the main objective of this article is to investigate ways to decrease heat transfer loss and further improve the thermal efficiency of the two-stroke engine from the perspective of energy distribution, and the effect of the circulating high-temperature gas, swirl ratio, and fuel distribution on heat transfer loss was systematically numerically studied in this manuscript. As a result, the heat transfer losses can be decreased up to 38.80% by lowering the CGR rate and adjusting the fuel distribution, and the ITE can be improved from 48.85% in the diesel model to 51.19% in the ammonia mode. However, to avoid incomplete combustion in the engine, a minimum CGR rate of 13.3% is basically required for the compression ignition of pure ammonia fuel.

Analysis of the influence of cathode recirculation strategy on proton exchange membrane fuel cell from internal polarization and external characteristics perspectives

Cathode recirculation provides a new solution to the accelerated degradation of proton exchange membrane fuel cells (PEMFCs) due to low humidity and high potential at low load conditions. Analyzing the internal impact mechanisms is basis for a more appropriate use of this technology. This paper presents a systematic investigation of the mechanisms by which key operating parameters of the cathode recirculation, including current density, cathode recirculation ratio, and stoichiometry of the fresh air path, affect the internal and external properties of PEMFCs. The voltage suppression effect and humidification effect under different cathode recirculation strategies are first analyzed. Then, as a novelty, the distribution of relaxation times (DRT) method is used to deconvolve electrochemical impedance spectra and qualitatively resolve the polarization impedance under different strategies. DRT is enabled to separate up to five polarization processes with different time constants and assign them to oxygen diffusion, oxygen reduction reaction and proton transport processes affected by the cathode recirculation. Finally, DRT quantified the change in ohmic impedance due to cathode recirculation and confirmed the effect of external humidity changes. This work provides a more in-depth insight into internal mechanisms of cathode recirculation in PEMFCs, and especially provides a comprehensive theoretical basis for the development of idle controllers for automotive PEMFCs in terms of improved durability.

Anaerobic Treatment of Food Waste with Biogas Recirculation under Psychrophilic Temperature

Food waste has emerged as a pressing concern, and thus advanced techniques to valorize food waste into nutrition rich materials as well as renewable energy are highly important. The exceptional biodegradability of food waste renders it a highly suitable substrate for anaerobic treatment. This leads to energy production and a reduction in the carbon footprint. Nevertheless, in frigid territories like Canada, the conventional mesophilic anaerobic digestion at 30–40 °C can require substantial amounts of energy. Consequently, this study introduces a new approach to treat food waste at psychrophilic temperatures (1–20 °C). Lower temperatures can negatively impact cellular processes during anaerobic treatment, rendering substrates less accessible to microscopic organisms. To address this challenge associated with lower temperatures, the study introduces an innovative biogas recirculation strategy. The primary objectives of this study are to assess the viability of anaerobic treatment for food waste at psychrophilic temperatures and to investigate the effectiveness of reintroduction of the produced biogas to the anaerobic system in enhancing biomethane generation and stability of the system. Batch experiments were conducted on food waste in various assessments, both with and without biogas recirculation. The outcomes revealed a methane concentration ranging from 68% to 93% when biogas recirculation was employed, whereas without this technique, methane concentration varied between 10% and 45%. Moreover, with biogas recirculation, the reduction in volatile solids reached a maximum of 92%, and there was an 82% decrease in chemical oxygen demand. In conclusion, the utilization of the recirculation of biogas at the psychrophilic temperature range enhanced biomethane production and reduction of volatile solids and chemical oxygen demand. This study underscores the potential of employing anaerobic treatment with reintroduction of produced biogas into the system in cold regions as an economically viable and sustainable choice for treating food waste with nominal energy consumption.

A system dynamic modeling to evaluate fluidized bed dryers under tempering and recirculation strategies

Grain drying control strategies aim for a rational energy use and a final product with low breakage levels. However, an experimental approach may be prohibitive due to the costs, scale, and theoretical complexity of this operation. The simulation environment is suitable to design equipment’s and plan operations strategies with low cost and high certainty. This work utilized system dynamics modelling to quantify the percentage of product breakage during drying in fluidized bed dryers under recirculation and tempering strategies. A sensitivity analysis of the model’s input parameters including different fractions of recirculation was performed, showing their effects on drying and post-drying product quality. Finally, we present optimizations from different objectives of drying operations. The recirculation strategy worked as an attenuator to the drying rates and combined with tempering strategy reached a minimum breakage level.

An adaptive cabin air recirculation strategy for an electric truck using a coupled CFD-thermoregulation approach

Cabin climatization is one of the largest auxiliary loads in an electric vehicle, and its performance significantly affects the driving range. Recirculating climatized air from the cabin has been shown to reduce energy consumption, but at the risk of fogging the windows and deteriorating the air quality. Therefore, many automobile manufacturers refrain from adopting it at low ambient temperatures. In this paper, an adaptive recirculation strategy that takes these issues into account is proposed and studied on an electric truck cabin while heating. Numerical simulations were performed using a coupled CFD-thermoregulation model, with the consideration of humidity and CO2. The JOS-3 thermoregulation model was employed for estimations of skin temperatures and evaporation of vapor from the skin, and the Berkeley comfort model was used to evaluate the comfort metrics. Ten scenarios were considered at various vehicle speeds, temperatures, and relative humidity levels while evaluating them with and without the proposed return-air strategy. The controller adapted between humidity and CO2-critical conditions during run-time. The fresh-air mass flow requirements reduced with increasing difference between the setpoint and ambient vapor mass fractions under humidity critical conditions, and plateaued at 10 g/s where CO2 was more critical. The proposed strategy provided energy savings ranging from 9% to 34% depending on the operating condition.

Numerical study on the effect of the combustion system parameters on combustion and emission characteristics for a HPDI natural gas/diesel dual fuel engine

Replacing diesel by natural gas in diesel engine is of great interest for transportation and power station industry due to larger availability and lower environmental impact of natural gas compared to diesel fuel. In addition, the high-pressure direct injection (HPDI) natural gas engine is widely recognized as a positive development prospect and an ideal alternative to conventional diesel engine. However, the trade-off relationship between indicated thermal efficiency (ITE) and NOx emissions limits the development of dual-fuel engines. In order to resolve this problem, we established a three-dimensional model combined with a multicomponent reduced chemical kinetic model and a phenomenological soot model. Using the 3D simulation model, we jointly optimized the combustion chamber (CC) structure, diesel/natural gas (NG) injection pressure (IP), and exhaust gas recirculation (EGR) strategy for HPDI NG engine in the two combustion modes. The results show that the adoption of the straight crater type (SCT) CC improves the mixture space equivalent ratio gradient distribution, slightly increases NOx emissions, rises ITE and reduces CO emissions in the two combustion modes. In NG mixture-limited combustion (NMLC) mode, increasing the diesel injection pressure (DIP) while appropriately increasing the NG injection pressure (NIP) promotes multi-point ignition and faster flame propagation and further optimizes CO emissions. In NG slightly premixed combustion (NSPC) mode, high ITE and low CO emissions can be maintained by increasing DIP while slightly increasing NIP, but the NOx increases substantially. In the moderate NOx emissions region (1.0 g/kW·h ∼ 2.0 g/kW·h), as the EGR rate increases, an overall improvement in trade-off relationships of NOx-CO, NOx-soot, and NOx-ITE in NMLC mode can be achieved. In NSPC mode, as the EGR rate increases, although CO and soot emissions can maintain lower values, it is difficult to improve the trade-off relationship of NOx-ITE.

Analysing the mechanism of food waste anaerobic digestion enhanced by iron oxide in a continuous two-stage process

The food waste (FW) digestion performance can be enhanced by introducing iron oxide (IO) into digesters. However, the role of IO in continuous two-stage digesters in enhancing the FW anaerobic digestion remains unclear. In this study, the effect of IO on the bioenergy recovery from a two-stage digestion process was investigated. The bioenergy recovery was significantly increased by up to 208.43 % with IO addition. The activities of dehydrogenase, α-amylase, and protease increase by 0.82–1.44, 7.24–14.56 and 7.97–20.45 times, respectively, as compared with that of the blank. With IO addition, the metabolic pathway in hydrolytic–acidogenic (HA) reactor shifted from lactic acid fermentation to butyric fermentation, which promoted stable methane production in methanogenic (MG) reactor. The activity of coenzyme F420 increased by 19.19–39.01 times, indicating that IO facilitated FW digestion by promoting hydrogenotrophic methanogenesis. The enhancement in the enzyme activity was attributable to the Fe2+ generated by dissimilatory iron reduction. According to the microbial analysis, IO enhanced interspecies hydrogen transfer between Methanobacterium and Syntrophomonas. Furthermore, IO improved direct interspecies electron transfer between Geobacter sulfurreducens and Methanosarcina. The effluent recirculation strategy greatly facilitated the hydrolysis and acidification of FW, which was critical for improving the two-stage process performance.

Investigation of osmosonication pretreated chili (Capsicum frutescensL.) drying in solar‐assisted fluidized bed dryer utilizing dehumidified air

AbstractThe heat and moisture sensitivity of spices and a consistent supply of electrical energy is the challenging factors in developing a relevant drying system for rural applications. A novel solar‐assisted fluidized bed dryer was developed for drying locally harvested unique spices like bird's eye chili (Capsicum frutescens L.). The chili was pretreated by the osmosonication method prior to drying to expedite the elimination of intercellular and intracellular moisture. In order to make the dryer more reliable, the recirculation strategy and dehumidified air supplied by liquid desiccant were acclimatized to constrict the heat loss through outflowing moist drying air. The experiments were conducted up to the permissible water activity (0.4–0.6) under variable drying conditions (50–70°C). By raising the ambient inlet temperature (maximum 25.9°C), the developed solar FBD was able to supply the drying air up to 50°C (in continuous mode) and a maximum of up to 65°C without aiding any heat energy sources except solar. It was found that osmosonication opened up the possibility of reducing the required drying temperature (↓10°C) and energy consumption (up to ↓31.7%). The dried red chili was fortified by pretreatment, as it could retain more capsaicin (>6%) and reddishness (>5%) compared to untreated samples. The Fourier transform infrared (FTIR) analysis showed the structural integrity of pretreated samples. The relative humidity of the drying air could be reduced by as much as 5% using the composite lithium chloride and calcium chloride (35% + 5%) desiccant dehumidifier. Dehumidification of air was found advantageous, with an inclination to shorten the drying duration (about ↓0.5 h) and energy (↓12.43%).Practical ApplicationsThere are various commercially valuable unique agro‐products that are exclusively being produced in rural areas. The inaccessibility of relevant drying technology and inconsistency of grid electricity are the main constraints in the value addition of those products. Open sun drying is most popular in rural areas; however, it is not reliable, and the product quality can't maintain. The developed solar‐assisted fluidized bed dryer utilizing dehumidifying air and integrated with osmosonication pretreatment could be a relevant technology for drying heat and moisture‐sensitive products like spices. Cost‐effective drying using locally accessible solar energy compared to open sun drying and superior dried product quality can be achieved by using the current drying system.

Investigation on suitable swirl ratio and spray angle of a large-bore marine diesel engine using genetic algorithm

The swirl flow and spray angle are crucial to the organization of the combustion process in marine engines. In this work, to explore the suitable swirl ratio and corresponding spray angle for large-bore marine diesel engines, the artificial neural network (ANN) coupled with the genetic algorithm (GA) was used. At the same time, to increase the swirl ratio without affecting the scavenging efficiency, the cylinder gas recirculation (CGR) strategy was adopted in this manuscript. Compared with the original design, results indicate that the optimal swirl ratio is about 10 for the large-bore marine diesel engine when applying the CGR strategy. Due to the improved fuel–air mixing process and combustion process, the thermal efficiency and the output power of the optimal case increased by 4.86% and 5.2%, respectively. The present results are helpful for the design and optimization of the fuel–air mixing and combustion processes for large-bore marine diesel engines.

Performance analysis and dynamic characteristics of a proton exchange membrane fuel cell with dual recirculation pumps for air-free applications

The exhaust gas recirculation strategy is usually used to ensure the stable and continuous operation of hydrogen–oxygen proton exchange membrane fuel cells (H2/O2 PEMFCs). However, few studies have focused on how the operating conditions of recirculation pumps affect the dynamic characteristics and performance of H2/O2 PEMFCs. In this study, a PEMFC system with dual anodic and cathodic gas recirculation pumps is investigated and the dynamic performance of the stack is also studied. The pump mode is proven to alleviate water flooding and enhance the stack performance effectively. When the rotating speed of recirculation pump reaches 5000 revolutions per minute, it can increase the gas flow rate inside the stack channel to 0.44 m s−1 (equivalent to a stoichiometric ratio of 2.85), which terminates the low-velocity flow inside the H2/O2 PEMFC and facilitates the removal of liquid water inside the stack. Moreover, the voltage undershoot during the current loading process is moderated by increasing the intake flow rate of the fuel gas through the pump-based recirculation subsystem, which could effectively solve the gas shortage problem of the stack. The presented findings are expected to provide more insights into the impact of the gas recirculation strategy on the performance of high-power stacks.

A semi-continuous algal-bacterial wastewater treatment process coupled with bioethanol production

Harnessing the biomass energy potential through biofuel production offers new outlets for a circular economy. In this study an integrated system which combine brewery wastewater treatment using algal-bacterial aggregates instead of activated sludge was developed. The use of algal-bacterial aggregates can eliminate the aeration requirements and significantly reduce the high biomass harvesting costs associated with algal monocultures. A sequencing batch reactor (SBR) setup operating with and without biomass recirculation was used to investigate pollutant removal rates, aggregation capacity and microbial community characteristics under a range of hydraulic retention times (HRTs) and solid retention times (SRTs). It was observed that biomass recirculation strategy significantly enhanced aggregation and pollutant removal (i.e., 78.7%, 94.2% and 75.2% for d-COD, TKN, and PO43--P, respectively). The microbial community established was highly diverse consisting of 161 Bacterial Operational Taxonomic Units (B-OTUs) and 16 unicellular Eukaryotic OTUs (E-OTUs). Escalation the optimal conditions (i.e., HRT = 4 d, SRT = 10 d) at pilot-scale resulted in nutrient starvation leading to 38–44% w/w carbohydrate accumulation. The harvested biomass was converted to bioethanol after acid hydrolysis followed by fermentation with Saccharomyces cerevisiae achieving a bioethanol production yield of 0.076 g bioethanol/g biomass. These data suggest that bioethanol production coupled with high-performance wastewater treatment using algal-bacterial aggregates is feasible, albeit less productive concerning bioethanol yields than systems exclusively designed for third and fourth-generation biofuel production.

Combined assessment of injection timing and exhaust gas recirculation strategy on the performance, emission and combustion characteristics of algae biodiesel powered diesel engine

ABSTRACT Currently, the vehicle industry is confronted with issues such as the depletion of fossil resources, an increase in crude oil costs, and stricter emission regulatory standards. In this scenario, the use of viable alternatives to diesel as a fuel is necessary. This study discusses the combined effects of injection time and exhaust gas recirculation (EGR) on neat algal biodiesel-powered diesel engines. The transesterification technique was used to extract algal oil methyl ester (AOME), and the majority of the fuel qualities of AOME were quite comparable to diesel. The practicality of neat AOME for diesel engines operating at varied injection timings such as 19º BTDC, 23º BTDC, and 27º BTDC was investigated. The results of the tests revealed that advanced injection timing has a 3.02% higher BTE than standard fuel injection timing at maximum load for the AOME. Compared to other injection timings at full load, the neat AOME at 27º BTDC has better combustion characteristics and lower exhaust emissions. At full load, however, NOx emissions were higher. NOx emission was reduced by 35.24% when AOME was burned at 27º BTDC combined with 10% exhaust gas recirculation (EGR) compared to 27º BTDC without EGR.

High Power Density Fuel Cell Systems for Portable Electric Generators

It is of utmost importance to develop light weight fuel cell stacks and find the ways to integrate these to light weight and low temperature fuel cell systems. In order to meet the future energy demands non-polluting, compact, transportation and portable applications are required. Current energy systems have lower power density (kW/kg) resulting in optimized power only at higher overall weight. Systems with higher power density demands higher initial setup costs. Low temperature PEMFC, on other hand offers various advantages but fails to provide the required output without exceeding the weight of the fuel cell stack and thereby fuel cell systems. A fuel cell system consists of a fuel cell stack, compressed gas in cylinder, pressure relief valves, regulators, water pump, sensors and cvm. A fuel cell stack is the main component consisting of one of the devices with maximum weight and cost contribution. In such case, developing a system with stack having higher power density reduces overall weight and increases power density (kW/kg). PowerUP Energy Technologies has developed light weight fuel cell stack to achieve higher power density. Experiments considering flow field designs, recirculation strategy, different anode configuration has been a subject of study. Dead-end anode, closed cathode configuration of fuel cell stack further improves fuel utilization. Recirculation line of hydrogen if further added can improve in overall fuel utilization. Counter flow arrangement for reactant distribution further removes the necessity of humidifying the gases. This result in removal of humidifiers and thereby reducing the weight of the fuel cell system in total. Portable fuel cell systems have flexibility for ease in transportation and stationery solutions. Furthermore, lighter fuel cell stacks add advantage for higher output power at lower overall weights. This stack developed is further optimized with improved flow field designs and design of manifold. These fuel cell stacks are used in PowerUP’s portable fuel cell electric generators that are more efficient and sustainable than the currently used fossil fuel based solutions.

Analysis on the potential of EGR strategy to reduce fuel consumption in hybrid powertrains based on advanced gasoline engines under simulated driving cycle conditions

The increased concern for environmental problems has boosted the electrification of passenger cars to remove air pollutant emissions from urban areas. Automotive manufacturers have predominantly opted for hybrid powertrains with advanced gasoline engines, because of the current limitations of battery electric vehicles and the higher costs of diesel aftertreatment systems. Meanwhile, the exhaust gas recirculation (EGR) strategy decreases fuel consumption and CO2 emissions in gasoline engines. The powertrain hybridization may increase the EGR benefit in fuel consumption, given that the dependence of internal combustion engine (ICE) operation on the driver’s power demand is reduced. The ICE can usually operate at medium loads, around its maximum efficiency zone, where the EGR benefit is greater than at low loads. Therefore, this research aimed to quantify the fuel saving achieved with EGR in a gasoline-electric hybrid powertrain under driving cycle conditions. To this end, vehicle 0D simulations were performed using a map-based engine fuel consumption model. Engine tests and 1D simulations were carried out to obtain ICE fuel maps with and without EGR. Besides, the transient performance of the vehicle 0D model was validated with experimental data. Both rule- and optimization-based strategies were used to manage the power split between the engine and electric motor. Modeling results revealed that EGR improves fuel economy by 4.6% in the hybrid powertrain during a WLTP class 3b driving cycle, 2% more than in the conventional one.

Numerical research of the injected exhaust gas recirculation strategy on a two-stroke low-speed marine diesel engine

To meet the stringent emissions legislation and higher fuel economy requirements of the low-speed two-stroke marine diesel engine, a new method named Injected Exhaust Gas Recirculation (IEGR) strategy was proposed in this paper. The effects of the IEGR strategy on the fuel/air mixture quality, combustion performance, and emission characteristics were numerically investigated. The simulation results show that the IEGR strategy could not only increase the in-cylinder swirl ratio but also achieve the distribution of EGR stratification. As a result, compared with the base case, both reduction of brake specific fuel consumption (BSFC) and NOx emissions could be realized by the IEGR strategy. Additionally, based on stratified EGR distribution, the NOx emissions could be further reduced by adjusting the fuel injection angle to control the main combustion area to be restricted to the high EGR rate region. Finally, on the premise of meeting the Tier III emission standards, the BSFC of the engine by using the IEGR strategy is reduced by 2.73% compared with the base case (Tier II emission standards). This study provides a new and reasonable solution for low-speed two-stroke diesel marine engines to meet the Tier III standards with better fuel economy.

Assessment of the effect of alkali chemistry on post-flame aerosol formation during oxy-combustion of biomass

The oxy-combustion of biomass enables negative CO2 emissions by combining subsequent CO2 capture technology. The potassium sulfation process significantly affects deposition and corrosion in heat transfer surfaces during biomass combustion. In the present work, a detailed aerosol dynamics model coupling with the detailed gas-reaction chemistry of K-S-Cl is proposed to investigate the effect of alkali chemistry on the evolution of post-flame aerosol during oxy-combustion of biomass. According to the modelling results, the mass-based particle size distributions are generally unimodal. Changing the environment from the air (N2 as a balance gas) to oxy (CO2 as balance gas) has a slight effect on the particle size distribution; yet, a slight left-shift particle size distribution was observed. The difference is mainly explained by the more substantial diffusion capacity of KCl(g) and K2SO4(g) in N2 than that in CO2, indicating a bit higher heterogeneous condensation of KCl(g) and K2SO4(g) in a CO2-based atmosphere. Further, the modelling results revealed that oxy-combustion significantly affects the evolution of aerosol and sulfation of KCl regardless of flue gas recirculation strategy. The wet oxy-combustion case has the largest particle size of PM1.0, that is due to the higher concentration of water and SO2, which increased KCl sulfation with value of ∼ 92%. The increased K2SO4 concentration in the flue gas causes earlier onset nucleation and prolonged the residence time for particle growth. Further ROP analysis results indicate that the reaction pathway for the sulfation of KCl via SO3 and K2SO4 condensation significantly influences the overall sulfation.

Identifying and Evaluating Recirculation Strategies for Industry in the Nordic Countries

The manufacturing industry in the Nordic countries aims to include closing product and material loops to recover values in their circular economy strategies. Recirculating strategies for products and materials are required for existing products that are part of the stock and are also anticipated to be aligned with products designed for circularity and circular business models in the future. Options to capture value of discarded products are diverse and include reuse, remanufacturing and material recycling. The Circular Economy Integration in the Nordic Industry for enhanced sustainability and competitiveness (CIRCit) project developed a framework to guide decision makers in the industry on how to identify suitable treatments and subsequent use at the end of use or end of life of a product and how to select among different options. Factors considered in the assessment include technical feasibility, necessary efforts, networks of business partners, legal implications and overall sustainability aspects. Our empirical studies show great support for decision-makers in the value recovery of different products with different complexity levels. It is also concluded that the properties of products at their end of use are the main drivers behind selecting a proper recirculation strategy. This study contributes with an empirical evaluation and a consistent terminology framework for recirculation options. The general setup is relevant for the Nordic countries.

Study on the process wastewater reuse and valorisation during hydrothermal co-carbonization of food and yard waste

The commercial success of hydrothermal carbonization (HTC) is contingent on seeking solutions for the downstream wastewater (process water) generated during the process which is still regarded largely as a nuisance. In the present study, the reusability and valorization strategy of process wastewater generated during co-HTC of organic fraction of municipal solid waste (food and yard waste) at 220 °C for 1 h was established. The process wastewater was anaerobically digested in the first part to determine its methane-generating capacity; and in the second part, it was recirculated up to five times to understand the evolution of physicochemical and fuel characteristics of hydrochar. The process water was characterized by the presence of high total organic carbon (up to 40 g/L) and chemical oxygen demand (up to 96 g/L). The decreasing trend of heavy metals with increasing recirculation suggested possible adsorption/immobilization mechanism taking place to the hydrochar surface. The process water generated from co-HTC condition has anaerobic biodegradability of 72% while experimental and theoretical methane yield observed were 224 mL/g COD and 308 mL/g COD, respectively. The presence of high organic and ionic species in recirculated process water promoted the overall carbonization process which was evident from the increased energy yield (86 to 92%), carbon content (68 to 71%) and calorific value (20 to 27 MJ/kg). The recirculation also enhanced overall combustion characteristics of hydrochar as analyzed by thermogravimetric analysis. The recirculation strategy enhanced fuel properties of hydrochar while making sure upstream and downstream water related burden is reduced (as illustrated by life cycle analysis) to create a cleaner production system for renewable solid biofuels production.

Effect of the novel continuous variable compression ratio (CVCR) configuration coupled with spark assisted induced ignition (SAII) combustion mode on the performance behavior of the spark ignition engine

The paradox of low efficiency and high fuel consumption at low-load and high efficiency and knocking combustion at high-load are pushing the engine community to optimize compression ratio (CR) in the spark ignition (SI) engine. However, it is difficult to balance the performance under a wide load range with using a fixed CR. In this paper, a novel continuous variable compression ratio (CVCR) system was proposed and successfully used in a SI engine, which could continuously change the auxiliary combustion chamber volume, thereby achieving different compression ratios from 10.0:1 to 17.8:1. The results indicated that the total mass of residual exhaust gas in the cylinder of the engine equipped with CVCR system was increased, and the residual gas fraction (RGF) in the auxiliary cylinder was increased, while the RGF in the main cylinder wasn’t changed dramatically with increasing CR. In addition, combustion rate was increased and combustion duration was decreased with increasing CR. The heat transfer rate and its percentage in the total fuel energy was decreased with the increase of the CR. The BSFC and effective thermal efficiency of the engine equipped with CVCR system could be improved by 15.85% and 15.57% by adopting CR 17.8:1 and 10% external EGR under the operating condition of 2000 r/min and BMEP 9.59 bar, respectively. However, the intensity of knocking combustion was increased with CR and limited the utilization of the high CR in the SI engine. Using external exhaust gas recirculation strategy could greatly alleviate the knocking combustion and reduced the heat transfer rate through the combustion chamber wall, which was beneficial to increase the indicated thermal efficiency and adiabatic efficiency.