Influence of innovative hydrogen multi strut injector with different spacing on cavity-based scramjet combustor

In this study, the flow dynamics with finite volume approach on commercial software Ansys-Fluent 20.0 to solve the compressible two-dimensional fluid flow with Reynolds Average Navier Stokes equation (RANS) equation by considering the density-based solver with Shaer stress transport model (SST) k- ω turbulent model. The species transport model with volumetric reaction and finite rate/eddy dissipation turbulence chemistry interaction is adopted to study the combustion phenomena. Additionally, the effect of spacing between the struts on the flow characters and performance of the combustor is studied by increasing the spacing of struts from 1 mm to 4 mm for each increment of 1 mm. It is found that the multi strut improves the mixing and combustion efficiency compared with that of the single strut owing to the formation of a significant separation layer, resulting in multiple shocks, vortices, and a larger recirculation zone. However, when the spacing of struts is increased further, the performance of the combustor is found to be deteriorating owing to the formation of larger separation layers. The recirculation zone is significant when the strut spacing is minimal and shrinks and restricts itself within the cavity when spacing is increased. So, for better performance of combustor, multi strut with minimum spacing is preferable.

Towards sector-based attribution using intra-city variations in satellite-based emission ratios between CO₂ and CO

Carbon dioxide (CO2) and air pollutants such as carbon monoxide (CO) are co-emitted by many combustion sources. Previous efforts have combined satellite-based observations of multiple tracers to calculate their emission ratio (ER) for inferring combustion efficiency at regional to city scale. Very few studies have focused on burning efficiency at the sub-city scale or related it to emission sectors using space-based observations. Several factors are important for deriving spatially-resolved ERs from asynchronous satellite measurements including 1) variations in meteorological conditions induced by different overpass times, 2) differences in vertical sensitivity of the retrievals (i.e., averaging kernel profiles), and 3) interferences from the biosphere and biomass burning. In this study, we extended an established emission estimate approach to arrive at spatially-resolved ERs based on retrieved column-averaged CO2 (XCO2) from the Snapshot Area Mapping (SAM) mode of the Orbiting Carbon Observatory-3 (OCO-3) and column-averaged CO from the TROPOspheric Monitoring Instrument (TROPOMI). To evaluate the influence of the confounding factors listed above and further explain the intra-urban variations in ERs, we leveraged a Lagrangian atmospheric transport model and an urban land cover classification dataset and reported ERCO from the sounding level to the overpass- and city- levels. We found that the difference in the overpass times and averaging kernels between OCO and TROPOMI strongly affect the estimated spatially-resolved ERCO. Specifically, a time difference of > 3 hours typically led to dramatic changes in the wind direction and shape of urban plumes and thereby making the calculation of accurate sounding-specific ERCO difficult. After removing those cases from consideration and applying a simple plume shift method when necessary, we discovered significant contrasts in combustion efficiencies between 1) two megacities versus two industry-oriented cities and 2) different regions within a city, based on six to seven nearly-coincident overpasses per city. Results suggest that the combustion efficiency for heavy industry in Los Angeles is slightly lower than its overall city-wide value (< 10 ppb-CO / ppm-CO2). In contrast, ERs related to the heavy industry in Shanghai are found to be much higher than Shanghai’s city-mean and more aligned with city-means of the two industry-oriented Chinese cities (approaching 20 ppb-CO / ppm-CO2). Although investigations based on a larger number of satellite overpasses are needed, our first analysis provides guidance for estimating intra-city gradients in combustion efficiency from future missions, such as those that will map column CO2 and CO concentration simultaneously with high spatiotemporal resolutions.

Metals and Alloys Additives as Enhancer for Rocket Propulsion: A Review

A rocket's engine usually uses fuel and oxygen as propellants to increase the rocket's projection during launch. Nowadays, metallic ingredients are commonly used in the rocket’s operation to increase its performance. Metallic ingredients have a high energy density, flame temperature, and regression rate that are important factors in the propulsion process. There is a wide range of additives have been reported so far as catalysts for rocket propulsion. The studies show that the presence of metal additives improves the regression rate, specific impulse and combustion efficiency. Herein, the common energetic additives for rocket propulsion such as metal and light metals are reviewed. Besides the effect of these energetic particles on the regression behaviors of base (hybrid) fuel has been exclusively discussed. This paper also proposed a new alloy namely high entropy alloys (HEAs) as a new energetic additive that can potentially increase the performance of the rocket propellant system.

Thermogravimetric Analysis and Kinetic Calculation on the Combustion Characteristics of Two Typical Shenhua Chars

Recently, a new ultra-low nitrogen combustion technology, pyrolysis and gasification coupling combustion, was proposed. The dependence on SCR or SNCR was reduced measurably with this technology. However, given the lower content of volatile matter in semi-chars, the burn-up ratio and combustion efficiency seemed to become lower. Thus, in this study, the combustion characteristics of the Shenhun and Carboniferous char were investigated under combustion conditions with the thermogravimetric method; meantime, kinetic calculation on the combustion characteristics were evaluated with Coats–Redfern method. Experiments indicated that Shenhun char showed good ignition and burnout characteristics when the pyrolysis temperature ranged from 973.15 K to1073.15 K; meanwhile, Carboniferous char showed good ignition and burnout characteristics when the pyrolysis temperature ranged from 873.15 K to 973.15 K. Besides, both the calculations and experiments indicated that Shenhun char showed better combustion characteristics than Carboniferous char.

Numerical Behaviour of Primary Air Flow Field of a Swirl Injector Under High Pressure and High Temperature Condition

Injector plays pivotal role to meet better combustion performances requirements in terms of combustion efficiency, flame stability, ignition, lower emissions etc. In a multi-swirler injector, the primary swirler mainly dictates the airflow field inside and some extend outside the injector. Present CFD studies have been attempted to characterize the flow field of a swirl injector consisting of conical nozzle fitted with single radial swirler at its upstream. Studies are performed at high pressure and high temperature resulting to high density (increased by around 9 times compared to atmospheric condition) and its impact on the flow field in terms of location of energetic zones useful for fuel atomization. Since direct effect of increase in density lead to increase in turbulence which is helpful for mixing and atomization, this study is helpful to capture the same. Embedded LES based hybrid model has been used where the computational domain divided into 3 zones which are seamlessly connected by capturing the interface fluid dynamics. In LES zone, both the time and spatial scales have been resolved by suitably refining the grids. Analysis is carried out with CFL no. around 2, fixed time step of 1 micro second. The analysis is reasonably able to capture various unsteadiness (PVC, CTRZ, frequencies etc. useful for the atomization of the liquid fuel) which are not available beforehand.

A review on the effects of ethanol/gasoline fuel blends on NOX emissions in spark-ignition engines

Ethanol can be used as an alternative fuel for spark-ignition (SI) engines to increase the octane number and oxygen content of ethanol/gasoline blends, thereby reducing dependence on fossil fuels and the exhaust emissions of incomplete combustion products. Although it is widely agreed that ethanol can reduce CO and HC exhaust emissions, the literature on ethanol and NOX emissions is far from conclusive; hence there is a need for an in-depth, updated review of ethanol/gasoline blends in SI engines and the relative production of NOX emissions. In light of that, the present work aims to provide a comprehensive literature review on the current state of ethanol combustion in SI engines to shed definitive light on the potential changes in NOX emissions under various operating conditions. The first part of this paper discusses the feasibility of ethanol as an alternative transportation fuel, including world production and ethanol production processes. The physicochemical properties of ethanol and gasoline are then compared to analyze their effects on combustion efficiency and exhaust emissions. Then, the pathways of NOX formation inside the cylinder of SI engines are discussed in depth. Finally, we review and critically discuss the effects of ethanol concentration in blends and different engine parameters on NOX formation.

Polymer waste safe disposal by incineration in electrostatic field

Polymer waste disposal of is one of the most pressing problems of our time. The incineration method is widespread, but it has its drawbacks. Problems during the polymer waste combustion, which include low combustion efficiency, combustion products toxicity, significantly reduce the possibility of waste disposal incinerators using. In this regard, the work considers the use of an electrostatic field to optimize the combustion process. Experimental studies of the electrostatic field influence on the substances difficult for disposal (polyethylene, polypropylene, polystyrene, rubber) combustion have been carried out. The possibility of increasing the polymer waste combustion rate, flame temperature, and combustion efficiency is shown.

Thermochemical Recuperation to Enable Efficient Ammonia-Diesel Dual-Fuel Combustion in a Compression Ignition Engine

A thermochemical recuperation (TCR) reactor was developed and experimentally evaluated with the objective to improve dual-fuel diesel–ammonia compression ignition engines. The novel system simultaneously decomposed ammonia into a hydrogen-containing mixture to allow high diesel fuel replacement ratios and oxidized unburned ammonia emissions in the exhaust, overcoming two key shortcomings of ammonia combustion in engines from the previous literature. In the experimental work, a multi-cylinder compression ignition engine was operated in dual-fuel mode using intake-fumigated ammonia and hydrogen mixtures as the secondary fuel. A full-scale catalytic TCR reactor was constructed and generated the fuel used in the engine experiments. The results show that up to 55% of the total fuel energy was provided by ammonia on a lower heating value basis. Overall engine brake thermal efficiency increased for modes with a high exhaust temperature where ammonia decomposition conversion in the TCR reactor was high but decreased for all other modes due to poor combustion efficiency. Hydrocarbon and soot emissions were shown to increase with the replacement ratio for all modes due to lower combustion temperatures and in-cylinder oxidation processes in the late part of heat release. Engine-out oxides of nitrogen (NOx) emissions decreased with increasing diesel replacement levels for all engine modes. A higher concentration of unburned ammonia was measured in the exhaust with increasing replacement ratios. This unburned ammonia predominantly oxidized to NOx species over the oxidation catalyst used within the TCR reactor. Ammonia substitution thus increased post-TCR reactor ammonia and NOx emissions in this work. The results show, however, that engine-out NH3-to-NOx ratios were suitable for passive selective catalytic reduction, thus demonstrating that both ammonia and NOx from the engine could be readily converted to N2 if the appropriate catalyst were used in the TCR reactor.

Numerical investigation on implication of innovative hydrogen strut injector on performance and combustion characteristics in a scramjet combustor

A detailed numerical analysis on a scramjet combustor is carried out by introducing an innovative shaped strut in place of the conventional strut. The design of newly added strut aids in generating intense vorticity which helps in efficient mixing of fuel and oxidizer. The air from the isolator enters the combustor at Mach 2.0, whereas fuel enters from the trailing edge of the strut sonically. In this study the flow dynamics with finite volume approach on commercial software Ansys-Fluent 20.0 to solve the two-dimensional Reynolds average Navier Stokes equation (RANS) with compressible fluid flow by considering the density-based solver with SST k-ε turbulent model. The species transport model with volumetric reaction and finite rate/eddy dissipation turbulence chemistry interaction is adopted to study the combustion phenomena and validated with the experimental results, and it is found that the interaction of the shear shock layer enhances the mixing rate by intensifying turbulence. The modified strut injector’s mixing efficiency is compared to the base strut and observed that with a 40% reduction in length, the modified strut injection technique exhibited a mixing efficiency of >95%. The combustion efficiency is then estimated streamwise, and the plot follows the same pattern as the mixing efficiency with fuel burns down completely when x = 150 mm for the modified strut whereas x = 200 mm for the base strut. This can compact the combustion chamber and increases the thrust-to-weight ratio. So, the innovative strut adopted can improvise the combustion efficiency.