Performance and Emission Characteristics of Tylosema Esculentum Biodiesel in a Diesel Engine： An Experimental Investigation

Biodiesel derived from indigenous feed stocks such as Tylosema esculentum kernel oil is deemed a feasible alternative to petroleum diesel for the diesel engine. This paper presents results of investigation of performance and emissions characteristics of diesel engine using Tylosema biodiesel. In this investigation, Tylosema biodiesel was prepared, analyzed and compared with the performance of petroleum diesel fuel using a single cylinder compression ignition diesel engine. The specific fuel consumption, engine torque, engine brake power, hydrocarbons, carbon monoxide and carbon dioxide were analyzed. The tests showed a decrease in engine brake power and torque with increase in engine load, while specific fuel consumption showed an increasing trend with maximum variation of 33% between the two fuels at engine load of 90%. Emission levels of hydrocarbons, carbon monoxide and carbon dioxide showed an increasing trend with increase in load for both fuels. Tylosema biodiesel produced significantly lower concentrations of hydrocarbons than petroleum diesel, while levels of carbon dioxide and carbon monoxide were largely comparable to those of petroleum diesel. Soot production from combustion ofTylosema biodiesel was found to be approximately 98% lower than that from combustion of petroleum biodiesel, demonstrating insignificant contribution to environmental pollution.     

Characteristics of Oxyfuel and Air–Fuel Combustion in an Industrial Water Tube Boiler

The characteristics of oxyfuel combustion and air–fuel combustion in the furnace of a typical industrial water tube boiler using methane as the operating fuel are investigated. Two oxyfuel cases are considered. The analysis is conducted for two oxyfuel cases that correspond to 21% O₂ and 29% O₂ in the oxidizer mixture (O₂ + CO₂). A renormalized group (RNG) turbulence model and the eddy dissipation model are utilized in the present work to provide the turbulence characteristics and the production rate of species. The solution of the radiative transfer equation was obtained using the discrete ordinates radiation model. The set of governing equations and the boundary conditions are solved numerically using Fluent computational fluid dynamics code considering a single-step reaction kinetics model for methane–oxyfuel combustion. Comparison of both oxyfuel combustion and air–fuel combustion indicates that the temperature levels are reduced in oxyfuel combustion. The results show that the temperature levels are greatly reduced as the percentage of recirculated CO₂ is increased. It is concluded that the flame propagation speed in the CO₂ environment is lower than that in N₂. It is found that the natural gas and oxygen consumption rates are slower in oxyfuel combustion relative to air–fuel combustion. Heat transfer from the burnt gases to the water jacket along the different surfaces of the furnace is calculated. It is shown that the energy absorbed is much lower in the case of oxyfuel combustion along all surfaces except for the end part of the furnace close to the furnace rear wall. However, the same performance of the methane-oxy-flames is expected by increasing the oxygen concentration slightly above 29%.     

Combustion characteristics of methanol–air and methanol–air–diluent premixed mixtures at elevated temperatures and pressures

Combustion characteristics of the methanol–air premixed mixtures were studied in a constant volume bomb at different equivalence ratios, initial pressures and temperatures, and dilution ratios. The results show that the combustion pressure, the mass burning rate and the burned gas temperature get the maximum value at the equivalence ratio of 1.1 while the flame development duration and the combustion duration get the minimum value at the equivalence ratio of 1.1. The flame development duration, the combustion duration and the peak combustion pressure decrease with the increase of the initial temperature, while the maximum burned gas temperature increases with the increase of the initial temperature. The peak combustion pressure and temperature increase with the increase of the initial pressure. The flame development duration and combustion duration increase with the increase of the dilution ratio, while the peak combustion pressure and temperature decrease with the increase of the dilution ratio.     

Combustion and emissions performance of a hybrid hydrogen–gasoline engine at idle and lean conditions

Due to the narrow flammability of gasoline, pure gasoline-fueled spark-ignited (SI) engines always encounter partial burning or even misfire at lean conditions. Gasoline engines tend to suffer poor combustion and expel large emissions at idle conditions because of the high variation in the intake charge and low combustion temperature. Comparatively, hybrid hydrogen engines (HHE) fueled with the mixtures of hydrocarbon fuels and hydrogen seem to achieve lower emissions and gain higher thermal efficiencies than the original hydrocarbon-fueled engines due to the wide flammability and high flame speed of hydrogen. Since a HHE only requires a small amount of hydrogen, it also removes concerns about the high production and storage costs of hydrogen. This paper introduced an experiment conducted on a four-cylinder SI gasoline engine equipped with a hydrogen port-injection system to explore the performance of a hybrid hydrogen–gasoline engine (HHGE) at idle and lean conditions. The injection timings and durations of hydrogen and gasoline were governed by a hybrid electronic control unit (HECU) developed by the authors, which can be adjusted freely according to the commands from a calibration computer. During the test, hydrogen flow rate was varied to ensure that hydrogen volume fraction in the intake was constantly kept at 3%. For the specified hydrogen addition level, gasoline flow rate was reduced to make the engine operate at idle and lean conditions with various excess air ratios. The test results demonstrated that cyclic variations in engine idle speed and indicated mean effective pressure were eased with hydrogen enrichment. The indicated thermal efficiency was obviously higher for the HHGE than that for the original gasoline engine at idle and lean conditions. The indicated thermal efficiency at an excess air ratio of 1.37 was increased from 13.81% for the original gasoline engine to 20.20% for the HHGE with a 3% hydrogen blending level. Flame development and propagation periods were also evidently shortened after hydrogen blending. Moreover, HC, CO and NOx emissions were all improved after hydrogen enrichment at idle and lean conditions. Therefore, the HHE methodology is an effective and promising way for improving engine idle performance at lean conditions.     

Characteristics of electrochemical hydrogen storage using Ti–Fe based alloys prepared by ball milling

In this paper, the TiFe-based master alloy Ti_1.04Fe_0.7Ni_0.1Zr_0.1Mn_0.1Pr_0.06 was fabricated by conventional induction melting with high purity helium as the protective gas. After that, the as-cast specimens were mechanically milled with nickel powders to synthesize the as-milled Ti_1.04Fe_0.7Ni_0.1Zr_0.1Mn_0.1Pr_0.06 + 10 wt.% Ni composites with excellent electrochemical characteristics. The master alloy is composed of TiFe, Ti₂Fe and Pr phases, which has a typical crystal structure. Mechanically milling the master alloy with nickel powder leads to the reductions of the grain size and particle size, even forming amorphous structure. The experimental results showed that the specimens after ball-milling treatment can be used to hydriding and dehydriding by electrochemistry, getting the maximal discharge capacity in the first cycle, and no activation was required. The discharge capacity of the as-milled composites declined from 264.2 to 133.6 mAh/g with the milling duration extending from 5 to 30 h. The electrochemical kinetics markedly declined with prolonging milling duration. However, the electrochemical cycling stability of the specimens reduced firstly and then increased with the prolongation of grinding duration.     

Flow and Heat Transfer Characteristics of Liquid–Solid Circulating Fluidized Beds

A series of experiments was conducted to investigate the flow and heat transfer characteristics of liquid–solid circulating fluidized beds. The experimental apparatus consisted of a single riser and a downcomer. Water at ambient conditions was used as the fluidizing fluid. Six kinds of particles were tested. First, particle holdup was measured, and a set of systematic data was acquired. By analyzing the experimental data, a simple predicting correlation was derived for the particle holdup. Next, pressure drop measurement was performed, and a predicting correlation was derived. Then heat transfer coefficient was measured, where two regions were identified, i.e., the “heat transfer enhanced region” and the “liquid single-phase heat transfer region.” On the basis of the experimental data, a predicting correlation was derived for each region, and a correlation was proposed for the entire region. Lastly, making use of the already-derived correlations, an analogy was investigated between the frictional pressure drop and the heat transfer coefficient.     

Effect of Two-Level Over-Fire Air on the Combustion and NOx Emission Characteristics in a 600 MW Wall-Fired Boiler

This paper accomplishes a numerical investigation on the effect of two-level over-fire air (OFA) on the combustion and NO_x emission in a supercritical 600 MW wall-fired boiler. Different arrangements of two-level OFA nozzles and different airflow ratios between the two layers are set to examine NO_x emission and the carbon content in fly ash. According to the simulation results, the two-level OFA case releases the NO_x between the single upper layer and the single lower layer of the two-level OFA nozzles in operation. Moreover, the two-level OFA arrangement gives a lower carbon content in fly ash than the single-level OFA cases. In addition, both low NO_x emissions and low carbon content in fly ash can be obtained simultaneously when the two levels of OFAs are injected from Layers 1 and 4 with r_lower at 0.5.     

Combustion and emissions characteristics of a hybrid hydrogen–gasoline engine under various loads and lean conditions

The addition of hydrogen is an effective way for improving the gasoline engine performance at lean conditions. In this paper, an experiment aiming at studying the effect of hydrogen addition on combustion and emissions characteristics of a spark-ignited (SI) gasoline engine under various loads and lean conditions was carried out. An electronically controlled hydrogen port-injection system was added to the original engine while keeping the gasoline injection system unchanged. A hybrid electronic control unit was developed and applied to govern the spark timings, injection timings and durations of hydrogen and gasoline. The test was performed at a constant engine speed of 1400 rpm, which could represent the engine speed in the typical city-driving conditions with a heavy traffic. Two hydrogen volume fractions in the total intake of 0% and 3% were achieved through adjusting the hydrogen injection duration according to the air flow rate. At a specified hydrogen addition level, gasoline flow rate was decreased to ensure that the excess air ratios were kept at 1.2 and 1.4, respectively. For a given hydrogen blending fraction and excess air ratio, the engine load, which was represented by the intake manifolds absolute pressure (MAP), was increased by increasing the opening of the throttle valve. The spark timing for maximum brake torque (MBT) was adopted for all tests. The experimental results demonstrated that the engine brake mean effective pressure (Bmep) was increased after hydrogen addition only at low load conditions. However, at high engine loads, the hybrid hydrogen–gasoline engine (HHGE) produced smaller Bmep than the original engine. The engine brake thermal efficiency was distinctly raised with the increase of MAP for both the original engine and the HHGE. The coefficient of variation in indicated mean effective pressure (COVimep) for the HHGE was reduced with the increase of engine load. The addition of hydrogen was effective on improving gasoline engine operating instability at low load and lean conditions. HC and CO emissions were decreased and NOx emissions were increased with the increase of engine load. The influence of engine load on CO₂ emission was insignificant. All in all, the effect of hydrogen addition on improving engine combustion and emissions performance was more pronounced at low loads than at high loads.     

Combustion and emission characteristics of an off-road diesel engine fuelled with biodiesel–diesel blends

In this work, the combustion and emission characteristics were studied in a 186FA diesel engine fuelled with biodiesel–diesel to examine the effect of the percentage of biodiesel in the blends, and the experimental investigation was conducted with various blending ratios of biodiesel under different operating conditions. In addition, the combustion noise of the diesel engine fuelled with biodiesel–diesel was analysed, and then the emission characteristics of NO_x and soot were studied through simulation analysis where the formation rate and distribution of NO_x and soot for pure diesel and B20 fuel were described. Based on the simulation data of the original diesel engine fuelled with B20 fuel, the swirl ratio and fuel injection timing were optimised and the technical measures were suggested to reduce the two different emissions simultaneously. The simulation results showed the emission characteristics were optimal when the swirl ratio was 2.7 and fuel injection timing was 7.5° degree of crank angle before top dead centre respectively.     

Combustion chemistry and flame structure of furan group biofuels using molecular-beam mass spectrometry and gas chromatography – Part I: Furan

Fuels of the furan family, i.e. furan itself, 2-methylfuran (MF), and 2,5-dimethylfuran (DMF) are being proposed as alternatives to hydrocarbon fuels and are potentially accessible from cellulosic biomass. While some experiments and modeling results are becoming available for each of these fuels, a comprehensive experimental and modeling analysis of the three fuels under the same conditions, simulated using the same chemical reaction model, has – to the best of our knowledge – not been attempted before. The present series of three papers, detailing the results obtained in flat flames for each of the three fuels separately, reports experimental data and explores their combustion chemistry using kinetic modeling. The first part of this series focuses on the chemistry of low-pressure furan flames. Two laminar premixed low-pressure (20 and 40 mbar) flat argon-diluted (50%) flames of furan were studied at two equivalence ratios (? = 1.0 and 1.7) using an analytical combination of high-resolution electron–ionization molecular-beam mass spectrometry (EI-MBMS) in Bielefeld and gas chromatography (GC) in Nancy. The time-of-flight MBMS with its high mass resolution enables the detection of both stable and reactive species, while the gas chromatograph permits the separation of isomers. Mole fractions of reactants, products, and stable and radical intermediates were measured as a function of the distance to the burner. A single kinetic model was used to predict the flame structure of the three fuels: furan (in this paper), 2-methylfuran (in Part II), and 2,5-dimethylfuran (in Part III). A refined sub-mechanism for furan combustion, based on the work of Tian et al. [Combust. Flame 158 (2011) 756–773] was developed which was then compared to the present experimental results. Overall, the agreement is encouraging. The main reaction pathways involved in furan combustion were delineated computing the rates of formation and consumption of all species. It is seen that the predominant furan consumption pathway is initiated by H-addition on the carbon atom neighboring the O-atom with acetylene as one of the dominant products.     

Characteristics of Darcy–Forchheimer drag coefficients and velocity slip on the flow of micropolar nanofluid

The flow of magneto-micropolar nanofluid, that is, the composition of TiO₂ nanoparticles in an organic solvent, kerosene, and the normal water past a stretchable surface has been considered. With effectiveness idea on the application in several areas, the Darcy–Forchheimer inertial drag and the second-order velocity slip approach are vital for the current investigation. The influence of viscous, Joule and Darcy dissipations on the energy transfer cannot be neglected due to the interaction of the body forces characterized by magnetic and porosity of the medium. The dissipative heat energy with the heat generation/absorption is useful for the enhancement in the fluid temperature. Due to the complexity of the problem, a numerical solution is implemented using the in-built code bvp5c with the help of MATLAB software. The physical properties abide by the characterizing parameters that appeared in the flow profiles are presented via graphs and the computed results for the rate coefficients are also displayed through table both for water- and kerosene-based nanofluids. Finally, the main findings of the results are: the growth in the shear rate coefficient is marked due to the inclusion of second-order slip, and an attenuation in the fluid velocity is rendered with an increase in the volume fraction whereas impact is reversed in the case of nanofluid temperature.     

Combustion chemistry and flame structure of furan group biofuels using molecular-beam mass spectrometry and gas chromatography – Part III: 2,5-Dimethylfuran

This work is the third part of a study focusing on the combustion chemistry and flame structure of furan and selected alkylated derivatives, i.e. furan in Part I, 2-methylfuran (MF) in Part II, and 2,5-dimethylfuran (DMF) in the present work. Two premixed low-pressure (20 and 40 mbar) flat argon-diluted (50%) flames of DMF were studied with electron–ionization molecular-beam mass spectrometry (EI-MBMS) and gas chromatography (GC) under two equivalence ratios (? = 1.0 and 1.7). Mole fractions of reactants, products, and stable and radical intermediates were measured as a function of the distance to the burner. Kinetic modeling was performed using a reaction mechanism that was further developed in the present series, including Part I and Part II. A reasonable agreement between the present experimental results and the simulation is observed. The main reaction pathways of DMF consumption were derived from a reaction flow analysis. Also, a comparison of the key features for the three flames is presented, as well as a comparison between these flames of furanic compounds and those of other fuels. An a priori surprising ability of DMF to form soot precursors (e.g. 1,3-cyclopentadiene or benzene) compared to less substituted furans and to other fuels has been experimentally observed and is well explained in the model.     

Combustion chemistry and flame structure of furan group biofuels using molecular-beam mass spectrometry and gas chromatography – Part II: 2-Methylfuran

This is Part II of a series of three papers which jointly address the combustion chemistry of furan and its alkylated derivatives 2-methylfuran (MF) and 2,5-dimethylfuran (DMF) under premixed low-pressure flame conditions. Some of them are considered to be promising biofuels. With furan as a common basis studied in Part I of this series, the present paper addresses two laminar premixed low-pressure (20 and 40 mbar) flat argon-diluted (50%) flames of MF which were studied with electron–ionization molecular-beam mass spectrometry (EI-MBMS) and gas chromatography (GC) for equivalence ratios ? = 1.0 and 1.7, identical conditions to those for the previously reported furan flames. Mole fractions of reactants, products as well as stable and reactive intermediates were measured as a function of the distance above the burner. Kinetic modeling was performed using a comprehensive reaction mechanism for all three fuels given in Part I and described in the three parts of this series. A comparison of the experimental results and the simulation shows reasonable agreement, as also seen for the furan flames in Part I before. This set of experiments is thus considered to be a valuable additional basis for the validation of the model. The main reaction pathways of MF consumption have been derived from reaction flow analyses, and differences to furan combustion chemistry under the same conditions are discussed.     

Combustion stability limits and NOx emissions of nonpremixed ammonia-substituted hydrogen–air flames

The combustion stability (extinction) limits and nitrogen oxide (NO_x) emissions of nonpremixed ammonia (NH₃)–hydrogen (H₂)–air flames at normal temperature and pressure are studied to evaluate the potential of partial NH₃ substitution for improving the safety of H₂ use and to provide a database for the nonpremixed NH₃-substituted H₂–air flames. Considering coflow nonpremixed NH₃–H₂–air flames for a wide range of fuel and coflow air injection velocities (V_fuel and V_coflow) and the extent of NH₃ substitution, the effects of NH₃ substitution on the stability limits and NO_x emissions of the NH₃–H₂–air flames are experimentally determined, while the nonpremixed NH₃–H₂–air flame structure is computationally predicted using a detailed reaction mechanism. Results show significant reduction in the stability limits and unremarkable increase in the NO_x emission index for enhanced NH₃ substitution, supporting the potential of NH₃ as an effective, carbon-free additive in nonpremixed H₂–air flames. With increasing V_coflow the NO_x emission index decreases, while with increasing V_fuel it decreases and then increases due to the recirculation of burned gas and the reduced radiant heat losses, respectively. Given V_coflow/V_fuel the flame length increases with enhanced NH₃ substitution since more air is needed for reaction stoichiometry. The predicted flame structure shows that NH₃ is consumed more upstream than H₂ due to the difference between their diffusivities in air.     

Characteristics of Flow Boiling Heat Transfer and Pressure Drop of MWCNT–R123 Nanorefrigerant: Experimental Investigations and Correlations

In the present work, the flow boiling heat transfer characteristics and pressure drop are experimentally investigated using multiwalled carbon nanotube (MWCNT)–R123-based nanofluids flowing inside a horizontal circular tube. The effects of particle concentration, mass flux, and vapor quality on the heat transfer coefficient (HTC) and pressure drop of MWCNT–R123-based nanofluid are analyzed. Results show that flow boiling HTC and frictional pressure drop increased with nanoparticle concentration, mass flux, and vapor quality as expected. The effects of nanoparticles on the flow boiling HTC and pressure drop are quantitatively analyzed by introducing a nanoparticle impact factor. A modified correlation for predicting the flow boiling HTC of nanorefrigerants is proposed, and the proposed correlation predicts 95% of the points with a deviation of ±20%. In addition, frictional pressure drop can be predicted using the Müller-Steinhagen and Heck correlation with a mean absolute error of 13.07% if the thermophysical properties of nanofluids are substituted.     

Investigations of the radiative properties of Al–NiP foams using tomographic images and stereoscopic micrographs

Metallic open cell foams are increasingly used in various applications where their thermal properties are of interest. Most of these applications concern relatively high temperatures and thus, radiation propagation is an important mode of heat transfer. Therefore, many studies have already been interested in the prediction of their radiative behaviour. Most of these works used analytical approaches which simplify considerably the porous architecture, notably by neglecting the pore size distribution. Recently, the progress in 3D imaging such as X-ray μ-tomography or Nuclear Magnetic Resonance has led to the development of numerical models which take into account much more realistic representations of the porous structure. However, in these models, strong assumptions are still used to treat the reflection at the solid surface. Moreover, experimental validations are lacking and the authors have never evaluated and highlighted the improvements brought by the use of tomography in comparison with previous analytical models. In the present study, we propose a rather comprehensive modelling of the radiative properties of Al–NiP foam samples using both X-ray tomographies to depict the porous architecture and stereoscopic images based on Scanning Electron Microscopy to deal with the reflection at the solid–fluid interface. The optical properties have been retrieved from literature data. The numerical results are compared with the radiative properties predicted by prior analytical models. Finally, the model is validated by comparison between measured and predicted hemispherical transmittances and reflectances. The agreement is quite satisfactory and demonstrates the superiority of the numerical modelling.     

High glass forming ability correlated with microstructure and hydrogen storage properties of a Mg–Cu–Ag–Y glass

Thermal characterization of an as-cast Mg₅₄Cu₂₈Ag₇Y₁₁ bulk metallic glass revealed that this alloy exhibits excellent glass forming ability. High-resolution X-ray diffraction study and transmission electron microscopy show that heating and isothermal annealing treatment results in the nucleation of nanocrystals of several phases. The average size of these nanocrystals (∼15–20 nm) only slightly varies with prolonged annealing, only their volume fraction increases. High-pressure calorimetry experiments indicate that the as-cast fully amorphous alloy exhibits the largest enthalpy of hydrogen desorption, compared to partially and fully crystallized states. Since the fully crystallized alloy does not desorb hydrogen, it is assumed that hydrogen storage capacity correlates only with the crystalline volume fraction of the partially crystallized Mg₅₄Cu₂₈Ag₇Y₁₁ BMG and additional parameters (crystalline phase selection, crystallite size, average matrix concentration) do not play a significant role.     

Optimal design and operation of a photovoltaic–electrolyser system using particle swarm optimisation

In this study, hydrogen generation is maximised by optimising the size and the operating conditions of an electrolyser (EL) directly connected to a photovoltaic (PV) module at different irradiance. Due to the variations of maximum power points of the PV module during a year and the complexity of the system, a nonlinear approach is considered. A mathematical model has been developed to determine the performance of the PV/EL system. The optimisation methodology presented here is based on the particle swarm optimisation algorithm. By this method, for the given number of PV modules, the optimal sizeand operating condition of a PV/EL system areachieved. The approach can be applied for different sizes of PV systems, various ambient temperatures and different locations with various climaticconditions. The results show that for the given location and the PV system, the energy transfer efficiency of PV/EL system can reach up to 97.83%.     

Fabrication and testing of a H2–O2 fuel cell using MoxRuySez

We report the results obtained in the preparation and characterization of Mo_xRu_ySe_z electrocatalysts for oxygen reduction reaction and the design, construction and characterization of a H₂–O₂ fuel cell using Mo_xRu_ySe_z. The catalysts were characterized with respect to their electrocatalytic properties. The fuel cell was designed and built with Mo_xRu_ySe_z supported on carbon as cathode, Pt supported on carbon as anode, and H₂SO₄ as the electrolyte. The fuel cell was tested at room temperature and atmospheric pressure. The H₂–O₂ cell showed an efficiency in the order of 30%.