Improved combustion stability of biogas at different CO_(2) concentrations using inhomogeneous partially premixed stratified flames

Biogas is a renewable and clean energy source that plays an important role in the current environment of lowcarbon transition.If high-content CO_(2) in biogas can be separated,transformed,and utilized,it not only realizes high-value utilization of biogas but also promotes carbon reduction in the biogas field.To improve the combustion stability of biogas,an inhomogeneous,partially premixed stratified(IPPS)combustion model was adopted in this study.The thermal flame structure and stability were investigated for a wide range of mixture inhomogeneities,turbulence levels,CO_(2) concentrations,air-to-fuel velocity ratios,and combustion energies in a concentric flow slot burner(CFSB).A fine-wire thermocouple is used to resolve the thermal flame structure.The flame size was reduced by increasing the CO_(2) concentration and the flames became lighter blue.The flame temperature also decreased with increase in CO_(2) concentration.Flame stability was reduced by increasing the CO_(2) concentration.However,at a certain level of mixture inhomogeneity,the concentration of CO_(2) in the IPPS mode did not affect the stability.Accordingly,the IPPS mode of combustion should be suitable for the combustion and stabilization of biogas.This should support the design of highly stabilized biogas turbulent flames independent of CO_(2) concentration.The data show that the lower stability conditions are partially due to the change in fuel combustion energy,which is characterized by the Wobbe index(WI).In addition,at a certain level of mixture inhomogeneity,the effect of the WI on flame stability becomes dominant.

A Direct Liquid Fuel Cell with High Power Density Using Reduced Phosphotungstic Acid as Redox Fuel

Direct liquid fuel cells(DLFCs)are proposed to address the problems of high cost and complex storage and transportation of hydrogen in traditional hydrogen-oxygen proton exchange membrane fuel cells.However,present fuels of organic small molecules used in DLFCs are restricted to problems of sluggish electrochemical kinetics and easily poisoning of precious metal catalysts.Herein,we demonstrate reduced phosphotungstic acid as a liquid fuel for DLFCs based on its advantages of high chemical and electrochemical stability,high electrochemical activity on common carbon material electrodes,and low permeability through proton exchange membranes.The application of phosphotungstic acid fuel effectively solves the problems of high cost of anode catalysts and serious fuel permeation loss in traditional DLFCs.A phosphotungstic acid fuel cell achieves a peak power density of466 mW cm^(-2)at a cell voltage of 0.42 V and good stability at current densities in the range from 20 to 200 mA cm^(-2).

Chemical looping based ammonia production--A promising pathway for production of the noncarbon fuel

Ammonia, primarily made with Haber-Bosch process developed in 1909 and winning two Nobel prizes, is a promising noncarbon fuel for preventing global warming of 1.5 °C above pre-industrial levels. However,the undesired characteristics of the process, including high carbon footprint, necessitate alternative ammonia synthesis methods, and among them is chemical looping ammonia production(CLAP) that uses nitrogen carrier materials and operates at atmospheric pressure with high product selectivity and energy efficiency. To date, neither a systematic review nor a perspective in nitrogen carriers and CLAP has been reported in the critical area. Thus, this work not only assesses the previous results of CLAP but also provides perspectives towards the future of CLAP. It classifies, characterizes, and holistically analyzes the fundamentally different CLAP pathways and discusses the ways of further improving the CLAP performance with the assistance of plasma technology and artificial intelligence(AI).

Molecular and heterogenized dinuclear Ir-Cp^* water oxidation catalysts bearing EDTA or EDTMP as bridging and anchoring ligands

The development of efficient water oxidation catalysts(WOCs)is of key importance in order to drive sustainable reductive processes aimed at producing renewable fuels.Herein,two novel dinuclear complexes,[(Cp^*Ir)2(μ-κ^3-O,N,O-H4-EDTMP)](Ir-H4-EDTMP,H4-EDTMP^4-=ethylenediamine tetra(methylene phosphonate))and[(Cp^*Ir)2(μ-κ^3-O,N,O-EDTA)](Ir-EDTA,EDTA^4-=ethylenediaminetetraacetate),were synthesized and completely characterized in solution,by multinuclear and multidimensional NMR spectroscopy,and in the solid state,by single crystal X-Ray diffraction.They were supported onto rutile TiO2 nanocrystals obtaining Ir-H4-EDTMP@TiO2 and Ir-EDTA@TiO2 hybrid materials.Both molecular complexes and hybrid materials were found to be efficient catalysts for WO driven by NaIO4,providing almost quantitative yields,and TON values only limited by the amount of NaIO4 used.As for the molecular catalysts,Ir-H4-EDTMP(TOF up to 184 min^-1)exhibited much higher activity than Ir-EDTA(TOF up to 19 min^-1),likely owing to the higher propensity of the former to generate a coordination vacancy through the dissociation of a Ir–OP bond(2.123A,significantly longer than Ir–OC,2.0913A),which is a necessary step to activate these saturated complexes.Ir-H4-EDTMP@TiO2(up to 33 min^-1)and IrEDTA@TiO2(up to 41 min^-1)hybrid materials showed similar activity that was only marginally reduced in the second and third catalytic runs carried out after having separated the supernatant,which did not show any sign of activity,instead.The observed TOF values for hybrid materials are higher than those reported for analogous systems deriving from heterogenized mononuclear complexes.This suggests that supporting dinuclear molecular precursors could be a successful strategy to obtain efficient heterogenized water oxidation catalysts.

The rheological model of biodiesels at elevated pressures and temperatures

In the present study,an approximation is used to study viscosity as a function of pressure at different temperatures.The correlation so obtained is applied to study the viscosity of biodiesels extracted from soybean,Vistive soybean,canola,used canola,coconut and rapeseed.The computed values of viscosity from the proposed model were found to be in good agreement with experimental data throughout the range of pressure and temperature studied.The maximum average absolute relative deviation(AARD%)and mean AARD%are found to be 0.52 and 0.20,respectively,over the entire range of pressure(0.1-140 MPa)and temperature(283.15-373.15 K)for all biodiesels except rapeseed biodiesel,for which the values are 1.1 and 0.62,respectively.Furthermore,this work includes the very first investigation conducted so far on the variation of the pressure-viscosity coefficient(PVC)with pressure at different temperatures for biodiesels.The variation in PVC with the temperature is more sensitive at elevated pressures as compared to atmospheric pressure whereas the variation in PVC with pressure is more sensitive at elevated temperatures as compared to room temperature.

Biomethane use for automobiles towards a CO_(2)-neutral energy system

To pursue the goal of sustainable mobility,two main paths can be considered:the electrification of vehicles and the use of biofuels,replacing fossil fuels,in internal combustion engine(ICE)vehicles.This paper proposes an analysis of different possible scenarios for automobiles towards a CO_(2)-neutral energy system,in the path of the use of biofuels and the production,distribution and use of biomethane.The study,an update of work presented previously,focuses on different scenarios that take into account numerous parameters that affect the overall efficiency of the production-and-use process.A Well-to-Wheel analysis is used to estimate the primary energy savings and reduction in greenhouse-gas emissions compared both to the use of fossil-based methane and to other fuels and automotive technologies.In particular,the study shows that the Non-Renewable Primary Energy Consumption(NRPEC)for biomethane is slightly higher(+9%)than that of biodiesel,but significantly lower than those of all the other power trains analysed:-69%compared to the battery electric vehicle(BEV)and-55%compared to bioethanol.Compared to the use of fossil natural gas,the NRPEC is reduced to just over a third(2.81).With regard to CO_(2) emissions,biomethane has the lowest values:-69%compared to BEV,-176%compared to bioethanol and-124%with respect to biodiesel.Compared to the use of fossil natural gas,the CO_(2) emissions are reduced over a third(3.55).Moreover,the paper shows that biomethane can completely cover the consumption of fossil methane for vehicles in Italy,proposing two different hypotheses:maximum production and minimum production.It is evident,therefore,that biomethane production can completely cover the consumption of fossil methane for vehicles:this means that the use of biomethane in the car can lead to a reduction in NRPEC equal to 28.9×10^(6) GJ/year and a reduction of CO_(2) emissions equal to 1.9×10^(6) t/year.