Conventional Combustion Research Articles

A conceptual framework for waste heat recovery from compression ignition engines: Technologies, working fluids & heat exchangers

• The current article reviews the potentials of waste heat recovery systems in diesel engines. • The study highlights the importance of working fluids and their performance in waste heat recovery systems. • This research work reviews the importance of heat exchanger design and the choice of waste heat recovery systems. In recent years, the awareness about sustainable energy production using renewable energy sources has increased drastically due to the depletion of fossil fuels and the implementation of environmental protection measures. The effective energy conversion rate of conventional combustion engines stands at 35% whereas the rest of the energy gets dissipated as waste heat to cool the engine. Several Waste Heat Recovery (WHR) methods have been developed so far such as the Organic Rankine Cycle (ORC), thermoelectric generator (TEG), Stirling engine (SE) and the Electric turbo-compounding (ETC). Various research works have been conducted so far to enhance the efficiency of combustion engines through innovative heat recovery systems and by reducing the energy losses, especially in automotive applications. The novelty of the current review article lies in analyzing different aspects of the WHR technologies in terms of increasing the fuel economy and environmental compliance in diesel engines from the perspectives of technology and application feasibility. Further, the current study is also an initiative to present a comprehensive review of different criteria regarding working fluid selection, heat exchanger parameters and their optimization. The results of this article infer that waste heat can be used in an attractive way to produce additional power efficiently, which in turn can result in maximum overall efficiency and optimal usage of the waste energy through the implementation of an exhaust heat recovery system. The current study also recommends that the fuel economy of compression ignition engines can be significantly improved by paying special attention to innovative heat exchanger designs, different parameters of the heat exchangers and working fluid selection.

Experimental optimization of homogeneous charge compression ignition through fuel modifications and a relative comparison with reactivity controlled compression ignition

Reactivity controlled compression ignition (RCCI) and homogeneous charge compression ignition (HCCI) are suitable alternatives to improve the performance and emission metrics of conventional diesel combustion. Previous studies have shown that the gasoline/diesel RCCI outperforms diesel HCCI as it has a wider load range, higher brake thermal efficiency, and lower smoke and oxides of nitrogen emissions. The present work addressed the shortcomings of diesel HCCI by replacing diesel with low reactivity, high volatile methanol–gasoline blends. 2-ethylhexyl nitrate, an ignition quality improver, was added in small amounts (6 vol.%) to the blends to avoid misfiring, particularly at lower loads. There were two approaches to improve engine performance metrics of methanol–gasoline HCCI: exhaust gas recirculation and fuel composition variation. The best approach was chosen, and HCCI performed using the selected approach was compared with baseline RCCI. The methanol-gasoline HCCI was compared to baseline-optimized gasoline/diesel RCCI to demonstrate that the challenges associated with diesel HCCI can be overcome through fuel modifications. It was revealed that the strategy of varying methanol concentration in fuel blends was more effective than the strategy of varying EGR rate in terms of efficiency improvement and reduction of soot, carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions. The parametric investigation showed that HCCI outperformed RCCI at mid to higher loads. For instance: at 60% load (3.19 BMEP), indicated thermal efficiency decreased by 7%, specific CO, UHC, nitrogen oxides, and smoke emissions elevated by 1.3, 1.2, 2.5, and 20.5 times for baseline-optimized RCCI than 40% methanol/54% gasoline/6% 2-EHN HCCI. Also, increased methanol in fuel during HCCI improved indicated thermal efficiency at a particular load. For instance, at 60% load, the indicated thermal efficiency improved by 30% during HCCI of fuel containing 40% methanol than 20% methanol. Overall, the present work discusses a practical method to efficiently use renewable methanol fuel in HCCI engines.

Hydrogen Internal Combustion Engine Vehicles: A Review

Motor vehicles are the backbone of global transport. In recent years, due to the rising costs of fossil fuels and increasing concerns about their negative impact on the natural environment, the development of low-emission power supply systems for vehicles has been observed. In order to create a stable and safe global transport system, an important issue seems to be the diversification of propulsion systems for vehicles, which can be achieved through the simultaneous development of conventional internal combustion vehicles, electric vehicles (both battery and fuel cell powered) as well as combustion hydrogen-powered vehicles. This publication presents an overview of commercial vehicles (available on the market) powered by internal combustion hydrogen engines. The work focuses on presenting the development of technology from the point of view of introducing ready-made hydrogen-powered vehicles to the market or technical solutions enabling the use of hydrogen mixtures in internal combustion engines. The study covers the history of the technology, dedicated hydrogen and bi-fuel vehicles, and vehicles with an engine powered by a mixture of conventional fuels and hydrogen. It presents basic technology parameters and solutions introduced by leading vehicle manufacturers in the vehicle market.

Evaluation of the sample size requirements of machine learning models used in engine design and research

Machine Learning (ML) techniques have been effectively used to learn the intricate relationships between variables that play a significant role in the field of engine design. However, there are two challenges to this approach – (1) Identifying ML regression models that could capture the trends of a response variable, given a non-parametric training set of relatively small size, with an acceptable accuracy and response time, and (2) identifying the size of the dataset, with respect to the input parameters, to be used for training and validation of the ML models. There is not enough information in the literature to reach a consensus on the sampling size to be used for an engine design problem that would yield an acceptable measure of goodness-of-fit. This is evident from the varied size of the training/validation data size used within the engine research community, as will be elaborated on in the following sections. The objective of this paper is to provide an insight into the sampling size required by the different ML models to achieve an acceptable fit between the model and the data, to be used in three types of engine design/optimization problems – (1) conventional diesel combustion (CDC) engine performance over a wide range of speed and load, (2) cold-start operation of a direct-injected spark-ignition (DISI) engine, and (3) high-load performance of a dual-fuel reactivity-controlled compression ignition (RCCI) engine.

Mechanical properties evaluation and microstructural analysis study of ceramic-coated IC engine cylinder liner

In the automotive industry, the primary objectives are to bring down the fuel consumption and boost power. The diesel engine has the best performance of any conventional internal combustion engine because of its extraordinarily high compression ratio. Gasoline engines consume more fuel per unit of power than diesel ones, whilst the two have the same performance. Only 40% of the power generated by an engine is utilized for productive purposes on average. Thirty percent of the remaining heat is lost through the exhaust, and another thirty percent is dissipated as heat losses by the cooling system. Ceramic and YSZ Coatings are applied to the cylinder liners and the piston head to transform the heat generated by the combustion process into meaningful mechanical work. As a result, the engine's heat transmission will be reduced, increasing efficiency. The higher gas temperature is expected to minimize the concentration of incomplete combustion products at the expense of an increase in nitrogen oxides (NOx). Scanning Electron Microscopy (SEM) and optical microscopy studied an engine cylinder liner's top-ring reversal point surface texture. Experiments were done on a single spark ignition engine during the break-in stage and the texture of the cylinder liner is studied.

Experimental study of homogeneous charge compression ignition combustion in a light-duty diesel engine fueled with isopropanol–gasoline blends

Homogeneous charge compression ignition (HCCI) is a high-efficiency, ultra-low emission generating combustion technique that can potentially phase out conventional diesel combustion (CDC). Due to wide misfire and knocking limits, a limited load range impedes its commercial success. The present work addresses HCCI limitations using isopropanol–gasoline blends in a port fuel injected light-duty diesel engine. A cetane booster additive, 2-ethylhexyl nitrate (2-EHN), at 5vol.% was mixed with the test fuels to broaden the HCCI lower load limits. The tested fuels include biofuel isopropanol that replaced non-renewable gasoline in 20% increments to achieve higher loads during HCCI. The results show a substantial increment in HCCI operating load range (24%–86%) with test fuels over diesel HCCI (20%–38%). The characteristics of HCCI combustion in the modified test engine were benchmarked with CDC in the unmodified production engine. The significant benefits of HCCI over CDC were the concomitant reduction of indicated specific energy consumption (ISEC), oxides of nitrogen (NOx), and soot emissions, especially at higher loads. For instance, at 80% load, the ISEC, soot, and NOx were decreased by 5%, 99%, and 77%, respectively, for 60% isopropanol/35% gasoline/5% 2-EHN fueled HCCI than CDC. The exergy analysis was conducted to gain insight into irreversibility sources in thermodynamic processes during HCCI and CDC. The second law efficiency of HCCI improved with increased isopropanol content in the test fuels at a specific load. Overall, the present work shows that isopropanol–gasoline blends are viable alternatives to diesel to operate the HCCI engine that meets the desired emission and performance targets.

Comparative Study on Combustion and Flame Characteristics of Laminar Methane/Air and N-Butane/Air Flames in a Micro-Slot Burner

Combustion and flame characteristics of laminar methane/air and n-butane/air flames in a 3D-printed micro-slot burner is compared and reported in this study. The stability limit, flame appearance, and emission performance are investigated experimentally. In addition, past research on conventional burners is compared with the results of this study throughout the paper. The construction of this micro-slot burner was met by selective laser melting (SLM) process. Flame characteristics such as lift-off height, length, visible area, maximum width, and neck width are obtained using an image processing algorithm and are examined at different fuel and airflow rates. The results show that the blow-out limits of methane/air and n-butane/air flames are almost the same when compared at the same volume flow rates, although the methane/air flames are more stable than n-butane/air flames at the same thermal input powers. A region of interesting rope-like oscillatory flames (that has never been seen before in conventional burners) is observed in a small portion of a stable region for n-butane with a period ranging from 75.0 to 210.0 m s . It is also observed that the fuel type and fuel and airflow rates affect the flame shape and appearance and the flames formed by heavier fuel (n-butane) have longer length, lift-off height, maximum width, and visible area and lower neck width. Furthermore, methane/air flames exhibit lower values of C O and higher values of N O x in the flue gas when compared to n-butane/air flames.

Synthesis and characterization of MgO nanostructures: A comparative study on the effect of preparation route

In this study, MgO nanostructures were synthesized by five facile and diverse chemical synthesis routes, viz. precipitation (PT), sonication-precipitation (SPT), microwave combustion (MWC), conventional combustion (CC), and solvothermal (ST) processes. The influence of aforementioned synthesis routes on crystallinity, crystallite size, morphology, optical, and surface traits of MgO nanostructures was evaluated by XRD, BET, FESEM, FETEM, optical absorption, steady-state and time-resolved photoluminescence analyses. Furthermore, antioxidant and antibacterial properties of MgO nanostructures were examined. XRD analysis revealed that crystallite size and relative crystallinity (%) of MgO varied from 9 to 42 nm and 90.70–99.06%, respectively, depending on the synthesis route followed. The application of microwave irradiation (MWC) and sonication (ST) reduced particle size and increased specific surface area of MgO nanostructures compared to nanostructures obtained via CC and PT methods. This could be due to faster reaction kinetics in MWC and small-scale turbulence generated during sonication that restricts growth and agglomeration of nuclei during nanostructure synthesis. FESEM analysis revealed flake, sphere, natural rose, and marigold flower-like morphologies of MgO due to different methods followed, that can be attributed to the differences in nanostructure formation mechanism involved. The highest photoluminescence intensity observed with MgO synthesized via MWC is likely to produce a maximum number of reactive oxygen species. Consequently, MgO synthesized through MWC process showed highest bactericidal and antioxidant activities compared to MgO synthesized via other routes. Thus, present study demonstrated that properties of nanostructures required for a particular application could be customized by proper choice of the synthesis route.

Hydrogen Fuel-cell Technology in Electric Vehicles: Current Usage, Materials and Future Applications

A conventional combustion engine results in high greenhouse gas emissions, so the world is transforming to clean energy and electric vehicles. Developments and applications of hydrogen fuel cells in electric vehicles (EVs) lead the world toward a sustainable future. Hydrogen fuel applies to fuel cells and generates electricity through electrochemical reactions. It is exceptionally clean because the by-products are water and heat, so there has no visual pollution from vehicles. HFC technology is not commonly used for now but will take place in many EVs. Some countries planned to apply it to electric power systems, railways and spacecraft fields. Currently, HFC uses platinum as the main catalyst material because of its stability, high efficiency, and good performance that boosts the hydrogen and oxygen reactions. It is the most reliable source and a perfect catalyst that is widely applied. Other catalysts such as carbon-coated nickel, nitrogen-carbon mixtures (MNCs) and transition metal nitrides (TMNs) all show good performance and have similar efficiency with Pt. These materials could replace platinum in the future because Pt has limited sources and higher costs. Also, the study has found that scientists use ruthenium graphene as a catalyst in hydrogen fuel cells. However, its effectiveness needs long-term monitoring. Although HFC is a clean technology, it has disadvantages, for example, hard for hydrogen extraction and storage, lacking refueling systems etc. Current technology limits development, and barriers exist, such as overwhelming H2 storage and delivery and some safety issues. Even so, hydrogen energy and HFC application are the future for EVs and others.

The nature of sawtooth wave and its distinction from continuous rotating detonation wave

To pinpoint the nature of the sawtooth wave, extensive experiments of methane-air continuous rotating detonation (CRD) are conducted in a hollow chamber around the boundary of the operating range. The time occupancy ratio and the increasing ratio of pressure rise (Δti/ΔTi and ΔPi/Δti) derived from high-frequency pressure data, and the integral of chemiluminescence intensity (ICI) based on self-luminescence images are proposed as quantitative parameters to distinguish the detonation wave and the sawtooth wave. The results show that the sawtooth wave is a critical unstable mode between conventional isobaric combustion and CRD, propagating with high Δti/ΔTi and low ΔPi/Δti. Meanwhile, the reaction zone of sawtooth wave is verified to be stabilized in the center of combustor through the self-luminescence observation. Especially, the multiple transition processes from the sawtooth wave to the CRD wave are accurately captured, and simultaneously represented as the change from single-peak waveform to double-peak waveform on ICI, the rise of ΔPi/Δti, and the reduction of Δti/ΔTi. The significant distinction of the sawtooth wave and the CRD wave in the coupling characteristics is confirmed through Short-Time Fourier Transform processes on ICI and high-frequency pressure. For the CRD wave, the propagation frequency of the reaction zone matches that of the pressure wave, whereas not for the sawtooth wave. It is ascertained that the reaction zone is decoupled with the pressure wave for the sawtooth wave, and the nature of the sawtooth wave is deflagration combined with a weak pressure wave.

Recent advances in low-gradient combustion modelling of hydrogen fuel blends

Low-gradient combustion (LGC) proved to be an effective alternative technology to reduce pollutant emissions and carbon footprint, specifically when combined with hydrogen as a fuel or blend component. This novel technology offers several advantages over conventional combustion regimes, including a more effective control of emissions and providing greater flexibility in fuel application. The impact of hydrogen on this regime is still not well-known, especially when it comes to the combustion of pure hydrogen and fuels with a high hydrogen content. In the last two decades, numerical simulations have become a powerful tool that facilitates the research and design of LGC, particularly in terms of stability of the process and the emission of pollutants. This article provides an up-to-date review of recent trends and theoretical knowledge in low-gradient combustion. This includes the guidelines and recommendations applied to LGC modelling. Comparisons have been made between the recently published modelling approaches presented by the authors, including a detailed assessment of the discrepancies in the temperature predictions. The challenges and limitations associated with the LGC combustion modelling of conventional fuels (i.e., natural gas, methane, syngas) blended with hydrogen are also discussed. The review demonstrated that the Eddy Dissipation Concept (EDC) is the most common turbulent-chemical interaction model employed in LGC combustion simulations. The performance of the EDC can be significantly improved by variable constants Cγ and Cτ based on local turbulent Reynolds and Damköhler numbers. However, the most recent publications indicate that the flamelet-based approach can be considered as a promising (and more cost-effective) alternative to the EDC. Furthermore, the chemical kinetic studies considered in this review confirm that there is no detailed reaction mechanism capable of accurately predicting the temperature profile along with the emissions of the main species of interest, i.e., NOx, CO, CO2, and OH. Although GRI-Mech 2.11 is the most widely used mechanism in LGC simulations, providing satisfactory overall accuracy.

Experimental investigations on biodiesel-water emulsion as a potential fuel for early and late injection based premixed lean combustion

Low temperature combustion strategies are a suitable alternative to conventional diesel combustion to simultaneously reduce oxides of nitrogen and smoke emissions while maintaining engine performance. However, limited load range and increased unburned hydrocarbon and carbon monoxide emissions are challenges posed by these strategies. The present investigation aims to address these limitations using biodiesel-water emulsion as a potential fuel for low temperature combustion in a light-duty diesel engine. Biodiesel derived from non-edible Karanja oil and its emulsion containing 18% water was used. The surfactant employed to stabilize the biodiesel-water emulsion was the raw Karanja oil itself. Two different fuel injection strategies were explored to achieve lean premixed combustion: early/advanced injection and late injection just after the top dead centre. To implement these strategies, the mechanical fuel injection system in the production engine was replaced with an electronic injection system having complete flexibility over the injection schedule. The results are compared with conventional diesel combustion under production settings. For the early injection strategy, up to 40% load, the brake specific fuel consumption and brake thermal efficiency were on par with conventional diesel combustion for biodiesel and the emulsion. However, there was a decline in the performance for both fuels at 60% load, which was the maximum achievable load with an early injection strategy. With the late injection, the engine could be operated across its entire load range with similar reductions in oxides of nitrogen and smoke emissions. While the brake thermal efficiency and brake specific fuel consumption for biodiesel were on par with conventional diesel combustion, there was an improvement of 8 and 6%, respectively, with biodiesel-water emulsion. The emission results showed that with either injection strategies, with biodiesel and its emulsion, 85 and 80% reduction in oxides of nitrogen and smoke emissions, respectively, could be achieved compared to conventional diesel combustion. However, both strategies significantly increased hydrocarbon and carbon monoxide emissions compared to conventional diesel combustion.

Numerical Modeling of Fixed-Bed Cocombustion Processes through the Multiple Thermally Thick Particle Model

Fixed-bed cocombustion provides opportunities for utilizing various low-quality solid residues, but there still remain obstacles for quantitative numerical modeling. The difficulties originate from the particles in the thermally thick regime and the diverse properties of different fuels. This work presents the multiple thermally thick particle (MTTP) model that considers detailed transport processes and chemical reactions in subparticle and interparticle scales, and different fuels can be assigned with distinctive physical and chemical properties. The model was validated by cocombustion experiments using wood and potato as representatives of low- and high-moisture fuels. The predicted results showed satisfactory agreement with measured values, and the characteristics of asynchronous conversion were clearly revealed. For thermally thick fuels with high moisture content, the drying process extends almost across the whole conversion zone and is highly overlapped with devolatilization process. Consequently, the structure of the in-bed conversion zone is beyond the expectation of conventional fixed-bed combustion theory.

Hydrogen or hydrogen-derived methanol for dual-fuel compression-ignition combustion: An engine perspective

Synthetic fuels or e-fuels, produced from captured CO2 and renewable hydrogen, are envisaged as a feasible path towards a climate-neutral transportation in medium/heavy-duty and maritime sectors. EU is presently debating energy targets by 2030 for these fuels. As their production involves chemical processing of hydrogen, it must be evaluated if the extra cost is worthy, at least in applications where hydrogen use is possible. This manuscript focuses on the performance and environmental impact when hydrogen and methanol are fed to a heavy-duty compression-ignition engine working under dual-fuel combustion. The trade-off thermal efficiency-NOx emissions is primary considered in the assessment by combining both variables in an own defined function. During the work, engine operating settings were adjusted to exploit the potential of methanol and hydrogen. Compared to conventional combustion, methanol required centering the combustion towards TDC and doubling the EGR rate, resulting in a low temperature, highly premixed combustion, almost soot-free and with extremely low NOx emissions. The best settings for hydrogen were in the middle of those for methanol and conventional combustion. Results showed great dependance with the engine load, but methanol proved superior to hydrogen for all conditions. At high load, 20–60 % methanol even improved the efficiency and reduced the NOx emissions obtained by conventional combustion. However, at low load hydrogen could substitute 90 % of the diesel fuel, while methanol failed at substitutions higher than 55 %.

Cool flame wave propagation in high-pressure spray flames

Cool flame has an important impact on the performance and emission of advanced low-temperature combustion (LTC) internal combustion engines (ICEs) in which the liquid fuel is injected earlier at a lower ambient temperature (Tam) than that in the conventional diesel combustion engines. However, the cool flame characteristics of spray combustion under ICEs conditions are not fully understood, e.g., the effect of cool flame on the spray ignition and flame stabilization is not well studied. In this paper, the so-called cool flame wave propagation (CFWP) in the Engine Combustion Networks Spray A flames at three ambient temperatures Tam (800 K, 900 K and 1000 K) is analyzed using the data from large eddy simulation with an improved Eulerian based transported probability density function sub-grid combustion model. A good agreement between the LES results and experimental data is obtained for the spray liquid penetration length, vapor fuel penetration length, mean pressure rise profile, and flame liftoff length. It is shown that CFWP in the spray ignition process promotes the ignition of the fuel-rich and cold reactant mixture, leading to the most reactive mixture shifting toward fuel-richer locations due to the spatial stratification of temperature and concentration, and turbulent mixing. As a result, the high temperature ignition (HTI) can be shortened compared to the ignition in the homogeneous mixture. At Tam = 800 K, the HTI kernels are consistently formed following the CFWP propagating toward the spray head region. However, as Tam increases, the spatial correlation between HTI kernels and CFWP fronts is weakened. On the other hand, the turbulent mixing (quantified using local scalar dissipation rate) contributes more to the formation of HTI kernels at higher Tam. The present results indicate that CFWP is more profound at lower Tam in the spray ignition process. Finally, it is found that cool flame propagates mainly into pre-reacted fuel-rich mixture in an ignition wave propagation mode from the spray upstream region toward downstream region, whereas the ignition assisted flame mode is found in the spray upstream region where the combustion heat release is negligible.

Analysis of the effects of lubricating oil viscosity and engine speed on piston-cylinder liner frictions in a single cylinder HCCI engine by GT-SUITE program

Engines with homogenous charge compression ignition (HCCI) are the low-temperature combustion models in which automatic oxidation reactions occur with the effect of in-cylinder pressure and heat at the end of preparation of homogenous air-fuel mixture and compression stroke within the cylinder by means of port injection or early direct injection. In-cylinder gas temperatures of such engines during the cycle are lower than conventional internal combustion engines. Therefore, they cause zero NOx and soot emissions. Moreover, the occurrence of combustion in very small crankshaft angles results in a decrease in heat losses observed in cylinder walls and an increase in thermal efficiency. Reducing mechanical friction is highly significant for increasing the effective productivity of HCCI engines. In internal combustion engines, 10% of total energy obtained from the fuel is spent on the heat emerging due to mechanical frictions. 20% of mechanical friction results from the friction occurring between piston ring and liners. In this article, frictional characteristics of compression ring (TOP) and piston skirt area have been examined for two different engine speeds and lubricants, by using technical properties of single-cylinder HCCI engine and in-cylinder pressure and temperature data obtained under full load by means of GT-SUITE software. As the increase in pressure, occurring inside the cylinder at the end of the exhaust stroke and at the beginning of intake stroke, increases ring pressure load in HCCI engines, higher level of piston ring frictions has been observed when compared to internal combustion engines with the same technical properties. Piston ring contact pressure force is a more effective parameter in terms of piston frictions, when compared to hydrodynamic pressure force. The use of lubricants with higher viscosity (SAE 10W-40) has enabled the piston to move more laterally. According to the analysis results, a maximum piston speed of 3.92 m/s for 800 rpm engine speed and 7.85 m/s for 1600 rpm engine speed has been obtained. Maximum friction power losses have been found as 63.84 W at 800 rpm engine speed and 85.91 W at 1600 rpm engine speed. Oil film thickness has obtained in the middle of the piston stroke in the intake, compression, power and exhaust strokes, respectively, 1.809, 1.674, 1.547 and 1.792 µm at 800 rpm engine speed and 1.101, 1.018, 0.932 and 1.119 µm at 1600 rpm engine speed.

Effects of injection parameters on CRDI-equipped stationary diesel engine fuelled with neat biodiesel mix derived from waste feedstocks

This present work deals with the effects of injection parameters such as pilot-main injection mass ratio and dwell time on combustion, performance, and emission characteristics of a diesel engine. A single cylinder diesel engine is used in this research work with the flexibilities to modify different variables via open electronic control unit. Biodiesel mix (BDM) used in the present work is derived from waste feedstocks of used cooking oil and chicken fat. Throughout the experiment, engine load and speed were maintained constantly at 4.51 brake mean effective pressure and 1500 rpm, respectively. Different pilot mass ratios (10%, 20%, and 30%) and dwell times (20° crank angle (CA), 30° CA, and 40° CA) were tested and results were compared with conventional mode combustion. The results indicated that the pilot injections helped to reduce the ignition lag period and also shortened the combustion duration. The highest brake thermal efficiency of 34.78% was identified with the lowest pilot mass of 10%. According to the results, increased dwell time decreased the oxides of nitrogen emissions but increased the hydrocarbon emissions. The experiment revealed that BDM made of waste feedstocks could be an effective alternative for engine applications with optimized engine operating conditions.

Research on combustion and emission characteristics of circulating fluidized bed during load changes

The conventional design of circulating fluidized bed (CFB) focuses more on high combustion efficiency and low pollutant emission. However, as the proportion of new energy generation in China continues to increase, the power grid is placing higher demands on the operational flexibility of thermal power units. The CFB has the advantage of a wide range of load regulations, and it is an inevitable choice to participate in the deep and flexible peak regulation of the power grid. In order to conduct research on the features of CFB during load changes, this work used 0.1 MWth CFB as the research object and examined its combustion and emission characteristics at different loads, as well as the change in temperature and pollutant emissions during load changes. The results showed that the temperature distribution along the height direction of the furnace was not uniform at lower load, while the inhomogeneity of the temperature distribution decreased, and both the temperature and pressure of the furnace increased as the load increased. Moreover, NOx emission and combustion efficiency both rose with the load. When the load increased from 30% to 100%, the NOx emission increased from 228 mg/m3 to 324 mg/m3, the CO emission decreased from 1422 mg/m3 to 104 mg/m3, and the carbon content of the fly ash decreased from 39.2% to 27.6%. If the temperature stability was used as the reference standard for load stability, the load-change rates on the combustion side of the experiment platform from 50% load to 75% load and from 75% load to 100% load under conventional combustion were 0.69%/min and 0.81%/min, respectively. In general, the load variation range of the CFB was wide, but the load-change rate on the combustion side and the combustion efficiency at low loads need to be further improved.

Energy efficiency study of household natural gas burner using pot-bottom shield and modified pot arrangement

The study aims to design and evaluate practically applicable pot-bottom shield and finned-pot in different pot-shield arrangements for better thermal and emission performances of a conventional household radial flow NG burner to lessen the household cooking energy consumption. Eleven sets of perforated hollow cylindrical pot-bottom shields having different heights were fabricated from thin metal sheet with a provision of secondary combustion air. One of the two identical flat bottom pots was converted to spot welded finned pot. The thermal and emission performances of the NG burner were then evaluated following the standard water boiling test (WBT) protocol with four different pot arrangements, namely ordinary flat bottom pot without shield and with shield and spot welded finned pot without shield and with shield at eleven different loading heights (from 2.5 cm to 7.5 cm) and six different NG supply pressures (0.4, 0.6, 1.0, 1.4, 1.8 and 2.0 kPa) keeping the burner primary air opening fixed at 50%. The corresponding NG flow rates at SATP were 4.23, 4.30, 4.70, 4.84, 4.94, 5.15 L/min for 0.4, 0.6, 1.0, 1.4, 1.8, and 2.0 kPa, respectively. It was found that a simple inclusion of a pot-bottom shield can dramatically improve the thermal efficiency of a natural gas cooking system for the both type of pots. A 20% improved thermal efficiency was evaluated for the NG burner with ordinary pot and pot-bottom shield arrangement at 0.6 kPa pressure and 3 cm loading height corresponded to the highest efficiency of the burner at base setting (burner with ordinary pot at 0.6 kPa NG pressure and 4 cm loading height). It was also found that the operation of the burner at its highest thermal efficiency was still within the safe operation limit in terms of CO emission in comparison to international standards.

Comparative life cycle assessment of conventional combustion engine vehicle, battery electric vehicle and fuel cell electric vehicle in Nepal

Battery electric vehicles (BEV) and Fuel cell electric vehicles (FCEV) are taking momentum as an alternative to conventional internal combustion engine vehicles (ICEV). Prospects of clean transportation and congruence with zero tailpipe emission are principal reasons for the adornment of these alternate technologies. This study aims to examine the collateral environmental impacts (GHG-100) that come alongside the production, use phase and end-life of ICEV, BEV and FCEV in the present context of Nepal. The current study uses a Cradle to Grave approach to compare the life cycle assessments (LCA) of Hyundai Tucson (2021), Hyundai Kona Electric 2021, and Hyundai Nexo Blue 2021 manufactured in South Korea (SK). Similarly, the LCA is performed under future scenarios of surplus electricity in Nepal and advancements in technologies. The results show that with the current import of 32% electricity from India, BEV and FCEV have 187- and 922-g total carbon dioxide equivalent (gCO2-eq) greenhouse gas (GHG) emission per kilometer respectively, which is 507 gCO2-eq/km for ICEV under the 200,000 km lifetime assumption of vehicles. The upstream emission for both the BEV and FCEV is poised to decrease by 88% with the surplus electricity scenario in Nepal, reducing 82% of the total emission of FCEV and 50% of BEV contributing to a cleaner local and global environment. Electricity sources significantly affect GHG emissions in both the production and use phases. Use of renewable electricity sources, and improvement in battery and fuel cell technologies reducing vehicle production supply chain impact with sharpened guidelines and policies regarding e-mobility, BEV and FCEV present themselves as promising alternative transportation technologies.