Energy recovery from hydrogen combustion at elevated pressures

Hydrogen is assumed as one of the most environmentally benign fuels. By the combustion of hydrogen enormous amount of H₂O; and therefore, latent heat is produced. Because, there is not so much need to heat at low temperatures, methods are needed to recover latent heat at higher temperatures. One of the methods to upgrade the latent heat at higher temperatures is the method of combustion at elevated pressures. Increasing the pressure of the exhaust gas makes it possible to recover latent heat and higher extra exergy output from the system. In this work, both latent and sensible heat recoveries at elevated pressures are investigated using environmentally friendly fuel hydrogen. It is shown that coefficient of performance (COP) and exergy efficiency (${\eta }_{ex}$) is very satisfactory even at high pressures.     

The influence of the addition of sodium on the transformation of alkali and alkaline-earth metals during oxy-fuel combustion

Alkali and alkaline-earth metals (AAEM) of coal directly affect the coal combustion properties and ash formation during coal oxy-fuel combustion. To further understand the influence of adding sodium on the transformation of AAEM, sodium chloride (NaCl) and sodium acetate (NaAc) were added to Shenmu coal in this study. A drop-tube reactor and ion chromatography were adopted in this study and a serial dissolution method was used to clarify the occurrence modes of the AAEM. The results showed that all types of AAEM can release and the release rates were increased with an increase in temperature during oxy-fuel combustion. Water-soluble (W-type) alkali metals react with SiO₂ and Al₂O₃ in coal and are converted into acid-soluble (H-type) silicate or acid-insoluble (I-type) aluminosilicate under certain experimental conditions. The addition of sodium can promote the release of AAEM via promoting coal combustion; the promotion effect was significant at 600 °C, and the effect of NaCl was more noticeable than that of NaAc. Furthermore, the promoting effect on alkali metals was more noticeable than that on alkali-earth metals. The added sodium can also react with SiO₂ and Al₂O₃ to form H-type sodium silicate or I-type sodium aluminosilicate.     

Thermodynamic development and design of a concentrating solar thermochemical water-splitting process for co-production of hydrogen and electricity

A concentrating solar plant is proposed for a thermochemical water-splitting process with excess heat used for electricity generation in an organic Rankine cycle. The quasi-steady state thermodynamic model consisting of 23 components and 45 states uses adjustable design parameters to optimize hydrogen production and system efficiency. The plant design and associated thermodynamic model demonstrate that cerium oxide is suitable for thermochemical water-splitting cycles involving the co-production of hydrogen and electricity. Design point analyses at 900 W/m² DNI indicate that a single tower with solar radiation input of 27.74 MW and an aperture area of 9.424 m² yields 10.96 MW total output comprised of 5.55 MW hydrogen (Gibbs free energy) and 5.41 MW net electricity after subtracting off 22.0% of total power generation for auxiliary loads. Pure hydrogen output amounts to 522 tonne/year at 20.73 GWh/year (HHV) or 17.20 GWh/year (Gibbs free energy) with net electricity generation at 14.52 GWh/year using TMY3 data from Daggett, California, USA. Annual average system efficiency is 38.2% with the constituent hydrogen fraction and electrical fraction being 54.2% and 45.8%, respectively. Sensitivity analyses illustrate that increases in particle loop recuperator effectiveness create an increase in hydrogen production and a decrease in electricity generation. Further, recuperator effectiveness has a measurable effect on hydrogen production, but has limited impact on total system efficiency given that 81.1% of excess heat is recuperated within the system for electricity generation.     

Performance and combustion characteristics of biodiesel–diesel–methanol blend fuelled engine

An experimental investigation was conducted to evaluate the effects of using methanol as additive to biodiesel–diesel blends on the engine performance, emissions and combustion characteristics of a direct injection diesel engine under variable operating conditions. BD50 (50% biodiesel and 50% diesel in vol.) was prepared as the baseline fuel. Methanol was added to BD50 as an additive by volume percent of 5% and 10% (denoted as BDM5 and BDM10). The results indicate that the combustion starts later for BDM5 and BDM10 than for BD50 at low engine load, but is almost identical at high engine load. At low engine load of 1500 r/min, BDM5 and BDM10 show the similar peak cylinder pressure and peak of pressure rise rate to BD50, and higher peak of heat release rate than that of BD50. At low engine load of 1800 r/min, the peak cylinder pressure and the peak of pressure rise rate of BDM5 and BDM10 are lower than those of BD50, and the peak of heat release rate is similar to that of BD50. The crank angles at which the peak values occur are later for BDM5 and BDM10 than for BD50. At high engine load, the peak cylinder pressure, the peak of pressure rise rate and peak of heat release rate of BDM5 and BDM10 are higher than those of BD50, and the crank angle of peak values for all tested fuels are almost same. The power and torque outputs of BDM5 and BDM10 are slightly lower than those of BD50. BDM5 and BDM10 show dramatic reduction of smoke emissions. CO emissions are slightly lower, and NO_x and HC emissions are almost similar to those of BD50 at speed characteristic of full engine load.     

Study of the combustion efficiency of polymers using a pyrolysis–combustion flow calorimeter

The combustion efficiency of various polymeric materials was studied using a pyrolysis–combustion flow calorimeter (PCFC). Decreasing the combustion temperature in a PCFC leads to partial combustion and lower heat release rates. Combustion efficiency versus combustion temperature was modeled using a phenomenological equation and model parameters were related to the chemical structures of eight pure polymers. The flame inhibition effect was evaluated for two classical approaches in flame retardancy by plotting the combustion efficiency versus the combustion temperature. In the first one (the reactive approach), polystyrenes with different chemical groups substituted on the aromatic ring were studied. In the second one (the additive approach), three well-known flame retardants were incorporated into an ABS matrix: ammonium polyphosphate, tetrabromobisphenol A (TBBA), and a TBBA/antimony trioxide system. Results confirm the flame inhibition effect of halogenated compounds in both approaches. Finally, a correlation between peaks of heat release rate (pHRR) in a cone calorimeter and in a PCFC was attempted. Predicting pHRR in a cone calorimeter using a PCFC appears possible when no barrier effect is expected, if PCFC tests are carried out at a precise combustion temperature, for which the combustion efficiencies in both tests are the same.     

Kalman Filter bank post-processor methodology for the Weather Research and Forecasting Model wind speed grid model output correction

The performance of the Weather Research and Forecasting (WRF) model, coupled with a bank of eight Kalman Filters (KFB) as a post-processor toolbox for the three hourly average WRF wind speed forecasts, is investigated and compared to the output of the WRF model alone. Two model set-ups, WRF and WRF+KFB, have been tested for the period January to December 2008 on nine locations corresponding to gradient wind towers of the Cuban Eolic program. Tests demonstrated that the KFB post-processing technique, using a third-order polynomial, combined with a four-point a priori moving window averager for covariance matrix computation, was the best configuration for improving the WRF grid model day-ahead wind speed forecast output. The WRF+KFB approach investigated has been shown to adapt to changing wind speed patterns and to offer improved wind speed forecasts for each location considered, whilst only requiring a limited data set for training purposes.     

Numerical investigation on combustion characteristics of methane/air in a micro-combustor with a regular triangular pyramid bluff body

Combustion characteristics of methane/air in a micro-combustor with a regular triangular pyramid bluff body were numerically investigated. Results reveal that the blow-off limit of the micro-combustor with a regular triangular pyramid bluff body is 2.4 times of that in the micro-combustor without bluff body. With the increase of inlet velocity, the recirculation zone expands and preferential transport effect behind the bluff body is intensified. Therefore, the local equivalence ratio in the recirculation zone increases when Φ = 0.8, but the growth trend of local equivalence ratio is not obvious when the inlet velocity exceeds 10 m/s. When Φ < 1.0, adding small amount of hydrogen into gas mixture can speed up the significant elementary reaction, leading to an increase of methane conversion. It's found that both the methane conversion rate and the temperature behind the bluff body reaches the highest when blockage ratio increase to 0.22.     

Catalytic combustion of selected hydrocarbon fuels on platinum: Reactivity and hetero–homogeneous interactions

This paper addresses the interactions between homogeneous and heterogeneous reactions for different hydrocarbons namely, compressed natural gas (CNG), liquefied petroleum gas (LPG), butane and dimethyl ether (DME) over platinum. Experiments are performed to study the effects of varying the temperature of the incoming mixture (T_jet), its equivalence ratio (Ø) and the Reynolds number (Re), on the reactivity limits. Computational fluid dynamic (CFD) calculations using detailed chemical kinetics for both the platinum surface and gas phase are completed for a range of methane–air mixtures to resolve the impact of varying T_jet, Ø and Re on the compositional structure of the flow. Comparison between numerical and experimental results is performed where relevant.For flameless conditions (defined by the presence of reactions on the plate without a gaseous flame), it is found for all fuels studied here that the temperature of the platinum plate, resulting from reactions with the co-flowing fuel–air mixture, increases with increasing T_jet and Re. However, with CNG, the temperature of the plate peaks near stoichiometry while for LPG, butane and DME the peak occurred at richer mixtures of Ø ≈ 1.5. The reactive limits for CNG, propane and DME are found to broaden significantly. Numerical simulations show very good agreement with the measured plate temperature at different equivalence ratios. The computed compositional structure confirms the existence of a flame inhibition effect due to the presence of the catalyst and shows interesting trends of some species at different Re, T_jet and Ø. Gas and surface chemistries seem to affect a few species such as CO, CO₂, H₂, and H₂O depending on the conditions of the co-flowing mixture. Minor species such as CH₃, CH₂O, O, HCO, and OH are largely controlled by gas-phase chemistry.     

Influence of injector technology on injection and combustion development – Part 1: Hydraulic characterization

An experimental study of two real multi-hole Diesel injectors is performed under current DI Diesel engine operating conditions. The aim of the investigation is to study the influence of injector technology on the flow at the nozzle exit and to analyse its effect on the spray in evaporative conditions and combustion development. The injectors used are two of the most common technologies used nowadays: solenoid and piezoelectric. The nozzles for both injectors are very similar since the objective of the work is the understanding of the influence of the injector technology on spray characteristics for a given nozzle geometry. In the first part of the study, experimental measurements of hydraulic characterization have been analyzed for both systems. Analysis of spray behaviour in evaporative conditions and combustion development will be carried out in the second part of the work. Important differences between both injectors have been observed, especially in their transient opening and closing of the needle, leading to a more efficient air–fuel mixing and combustion processes for the piezoelectric actuated injector.     

Experimental investigation and combustion analysis of a direct injection dual-fuel diesel–natural gas engine

A single-cylinder diesel engine has been converted into a dual-fuel engine to operate with natural gas together with a pilot injection of diesel fuel used to ignite the CNG–air charge. The CNG was injected into the intake manifold via a gas injector on purpose designed for this application. The main performance of the gas injector, such as flow coefficient, instantaneous mass flow rate, delay time between electrical signal and opening of the injector, have been characterized by testing the injector in a constant-volume optical vessel. The CNG jet structure has also been characterized by means of shadowgraphy technique.     

Synthesis of LiCo1−xNixO2 from a low temperature solution combustion route and characterization

Nickel substituted lithium–cobalt oxides, LiCo_1−xNi_xO₂ (0<x<0.4), have been synthesized in a very short time by a solution combustion method at 350 °C using diformyl hydrazine as a fuel. Pure phases with hexagonal lattice structure have been obtained. These compounds facilitate reversible insertion/extraction of Li⁺ ions with good discharge capacity between 3.0 and 4.4 V versus Li/Li⁺. Results of the studies by powder X-ray diffraction, scanning electron microscopy, cyclic voltammetry, galvanostatic charge–discharge cycling and ac impedance measurements are presented.     

Porous medium based burner for efficient and clean combustion of ammonia–hydrogen–air systems

Due to its high hydrogen density and extensive experience base, ammonia (NH₃) has been gaining special attention as a potential green energy carrier. This study focuses on premixed ammonia–hydrogen–air flames under standard temperature and pressure conditions using an inert silicon-carbide (SiC) porous block as a practical and effective medium for flame stabilization. Combustion experiments conducted using a lab scale burner resulted in stable combustion and high combustion efficiencies at very high ammonia concentration levels over a wide range of equivalence ratios. Noticeable power output densities have also been achieved. Preliminary results of NO_x emission measurements indicate NO_x concentrations as low as 35 ppm under rich conditions. The remarkable capability of this specific burner to operate efficiently and cleanly at high ammonia concentration levels, which can easily be achieved by partial cracking of NH₃, is believed to be a key accomplishment in the development of ammonia fired power generation systems.     

Effects of ion irradiation on H2O and CO2 absorption and desorption characteristics of Li2ZrO3 and Pt-coated Li2ZrO3

The effects of irradiation with 10 keV D₂⁺ ions on the hydrogen and water absorption and desorption characteristics of Li₂ZrO₃ and platinum-coated Li₂ZrO₃ (Pt-Li₂ZrO₃) were investigated by employing elastic recoil detection (ERD), weight gain measurement (WGM), and thermal desorption spectroscopy (TDS). WGM and ERD results indicated that the amounts of H and H₂O absorbed into the ion irradiated bulk Li₂ZrO₃ and Pt-Li₂ZrO₃ samples in air at room temperature increased up to ～2–3 times, as compared with those of the unirradiated ones. TDS examinations revealed that the amounts of hydrogen molecules (H₂) and H₂O released from the unirradiated Pt-Li₂ZrO₃ and ion irradiated Li₂ZrO₃ and Pt-Li₂ZrO₃ were approximately one order of magnitude higher than those of unirradiated Li₂ZrO₃. Li segregation, ion-induced oxygen deficiency, as well as Pt deposition significantly enhance the splitting of H₂O, eventually increasing the amounts of H accumulated in the bulk Li₂ZrO₃ and the H₂ release.     

On-board generation of hydrogen to improve in-cylinder combustion and after-treatment efficiency and emissions performance of a hybrid hydrogen–gasoline engine

Hydrogen on-board fuel reforming has been identified as a waste energy recovery technology with potential to improve Internal combustion engines (ICE) efficiency. Additionally, can help to reduce CO₂, NO_x and particulate matter (PM) emissions. As this thermochemical energy is recovered from the hot exhaust stream and used in an efficient way by endothermic catalytic reforming of petrol mixed with a fraction of the engine exhaust gas. The hydrogen-rich reformate has higher enthalpy than the petrol fed to the reformer and is recirculated to the intake manifold, which will be called reformed exhaust gas recirculation (rEGR).The rEGR system has been simulated by supplying hydrogen (H₂) and carbon monoxide (CO) into a conventional Exhaust Gas Recirculation (EGR) system. The hydrogen and CO concentrations in the rEGR stream were selected to be achievable in practice at typical gasoline exhaust temperatures (temperatures between 300 and 600 °C). A special attention has been paid on comparing rEGR to the baseline ICE, and to conventional EGR. The results demonstrate the potential of rEGR to simultaneously increase thermal efficiency, reduce gaseous emissions and decrease PM formation.Complete fuel reformation can increase the calorific value of the fuel by 28%. This energy can be provided by the waste heat in the exhaust and so it is ideal for combination with a gasoline engine with its high engine-out exhaust temperatures.The aim of this work is to demonstrate that exhaust gas fuel reforming on an engine is possible and is commercially viable. Also, this paper demonstrates how the combustion of reformate in a direct injection gasoline engine via reformed Exhaust Gas Recirculation (rEGR) can be beneficial to engine performance and emissions.     

Feed compositions and gasification potential of several biomasses including a microalgae: A thermodynamic modeling approach

This study presents the relation of the biomass properties with the gasification performance. The potential of microalgae (N. oculta) for gasification also has been investigated. Other biomasses such as palm frond, mangrove, and rice husk were considered as the benchmarks. The performance of a combined gasification process for different biomass was evaluated by developing a thermodynamic model using Aspen Plus. The performance of gasification process was evaluated based on the composition of the producer gas, the cold gas efficiency, and the gasification system efficiency. The effects of biomass composition on the gasification performance was studied by varying the gasification temperature, the oxygen equivalence ratio, and the steam to carbon ratio. It was found that the H/O ratio in the feed biomass has a considerable effect on the H₂/CO ratio of producer gas on the gasification without gasifying agent. The gasification of algae with oxygen exhibited the highest H₂/CO ratio. The highest cold gas efficiency was found during gasification of algae with oxygen, while the highest cold gas efficiency from gasification with steam was exhibited on gasification of palm frond. The highest gasification system efficiency was obtained for palm frond using the oxygen or steam as the gasifying agent.     

Slagging behavior and mechanism of high-sodium–chlorine coal combustion in a full-scale circulating fluidized bed boiler

The contents of chlorine and sodium in Xinjiang Shaerhu (SEH) coal are extremely high, leading to severe slagging. In this paper, the slag was sampled from a circulating fluidized bed (CFB) boiler purely burning SEH coal, to analyze the slagging mechanism based on the characterization of morphology and composition. The results show a three-layer structure for the slag sampled from the buried heat-exchanger in the dense-phase zone of the CFB boiler. The inner layer close to the heat-exchanger is NaCl, which enhances the adhesion of ash particles, while the middle layer and the outer layer are mainly composed of Ca₂Al₂SiO₇ and other Si–Al materials. In comparison, the slag sampled from the refractory wall shows a molten state without a layered structure and mainly composed of NaCl, NaAlSiO₄, Ca₂Al₂SiO₇, and CaSiO₃. The effect of mixing bed material, on the ash melting and release of chlorine and sodium was further conducted, which indicates that the mixing of bed material has no significant effect on the release of chlorine(Cl) and sodium(Na) but highly affects the melting temperature and compositions. The ash fusion temperature reaches the lowest with a 50% mixing ratio of bed material, which is 120 °C lower than that of SEH coal ash. This study can provide better guidance for controlling severe slagging, from the combustion of high Na and Cl coal in industrial furnaces.     

Pressure loss and compensation in the combustion process of Al–CuO nanoenergetics on a microheater chip

This study investigates pressure loss and compensation in the combustion process of Al–CuO metastable intermolecular composite (MIC) on a microheater chip. A ball cell model of pressure change in the combustion process is proposed to show the effects of pressure loss on the reaction rate and efficiency of energy output at microscale. An effective compensation method for pressure loss is then developed by integrating Al–CuO MIC with CL-20 (2,4,6,8,10,12-hexanitrohexaazaisowurtzitane) onto a SiO₂/Cr/Pt/Au microheater chip. The combustion processes of Al–CuO MIC with different weight percentages of fine CL-20 particles on the microheater chips are observed by high-speed video recording. Results indicate that the reaction of Al–CuO MIC is a slow combustion process that turns into intense deflagration after adding fine CL-20 particles to Al–CuO MIC. The pressure–time characteristics indicate higher maximum pressure and pressurization rate for Al–CuO/CL-20 because the pressure loss at microscale is well compensated by the addition of fine CL-20. This study proves the importance of pressure loss in the combustion process of MIC at microscale and provides an efficient compensation strategy for pressure loss to improve the reaction rate and efficiency of energy output at microscale environment.