Combustion Ratio Research Articles

Heat transfer in counter-current two phase flow applied to feasibility study of harvesting natural gas from seabed hydrates

The gas hydrate deposits at seabed fall into a special category of gas hydrate resources. This study investigates the technical feasibility of harvesting natural gas from seabed hydrates using a new thermal method called Moving Riser Method (MRM). A mathematical model for heat transfer along the injection pipe in the MRM system was developed. Heat transfer from the injected hot water to the gas hydrate deposit was analyzed. This study concludes that with today’s pipe insulation technology water temperature drops only a few degrees from sea surface level to the seafloor level in an insulated 800 m deep vertical pipe. The injected water at seafloor level will be hot enough to dissociate gas hydrate at a commercial rate with an affordable gas consumption rate. The gas production to gas combustion ratio (PCR) is greater than 4. The PCR increases slightly with gas combustion rate. Even the gas production ship stays at the same location for over 40 h with continuous injection of hot water, the water-hydrate boundary will still be within 0.9 m of the hot water injection point. Therefore it is possible to use a gas collector of reasonable size (e.g., 2 m in diameter) to gather all dissociated gas from the hydrate deposit. Result of this investigation shows that harvesting natural gas from gas hydrate at seabed with the MRM is technically viable, economically feasible, and environmentally safe.

An investigation for reducing combustion instability under cold-start condition of a direct injection gasoline engine

In order to meet recent stringent emission regulations, the exhaust catalyst should be heated as early as possible to activate the purifying reactions. In a direct injection spark-ignition engine, a combination of late fuel injection during the compression stroke and late ignition in the expansion stroke is a common strategy to quickly raise exhaust gas temperature for subsequent rapid activation of exhaust catalysts. However, this approach under cold start-up of an engine often results in incomplete and unstable combustion. In this study, to explore the conditions of stable ignition and combustion, the effect of injection timing on indicated mean effective pressure and early combustion duration (MBD0.5) are first investigated by an analysis of the pressure indicator diagram. As this analysis shows a strong correlation between indicated mean effective pressure and MBD0.5, the mechanism of initial flame propagation is investigated intensively using optical diagnostics. Namely, mean equivalence ratio of mixtures in the propagating flame front is measured by focusing on the ratio of C2* to CH* emission intensities. The flow velocity and turbulence intensity around the spark electrode are measured by the back-scattering laser Doppler anemometry. Two major conclusions are derived from this study: First, when the injection timing is retarded, the mean equivalence ratio increases as the time for the injected fuel to travel and diffuse is shortened. The most preferable mean equivalence ratio for fast initial combustion is found to lie in a range from 1.2 to 1.4. Second, when the second injection timing is retarded further, the mean equivalence ratio increases exceeding 1.4, and this results in slower and more fluctuated initial flame propagation. But, if the turbulent intensity is increased by means of the spray induced air motion, the slowed initial combustion can be recovered.

ИССЛЕДОВАНИЕ ЭНЕРГОЕМКОСТИ ИЗМЕЛЬЧЕНИЯ ОТХОДОВ ОКОРКИ УСТАНОВКОЙ С НОЖЕВЫМ РАБОЧИМ ОРГАНОМ

Abstract The subject of the proposed study is aimed at studying the process of grinding barking waste. The main tasks of experimental research are to establish general patterns linking the energy intensity of grinding of debarking waste with the degree of grinding and to estimate the energy intensity of the grinding operation of barking waste in prepara-tion for utilization. The article presents the results of experiments on crushing waste from spruce and pine, performed with the Erdwich M600 / 1-400 industrial choppers. For each of the two species, 9 groups of experimental material have been examined at different humidity and degree of grinding. It is shown that the specific energy intensity of grinding waste from spruce and pine barking is associated with the relative humidity of the barking waste and the degree of their grinding by a nonlinear dependence repeating the structure of the Kirpichev-Kick grinding law; corresponding mathematical models are got. It has been established that the ratio of heat combustion of the dry matter contained in the bark crushing product ("energy cost") and the energy expended for its crushing ("energy prime cost") depends on the relative humidity of the bark, and the dependence has a minimum point. The optimum moisture content of the waste products from the spruce, subject to grinding, is 25%, pine - 27%. It is established that the specific energy intensity of grinding waste from debarking spruce and pine with the optimum humidity is proportional to the natural logarithm of the degree of grinding. With optimum humidity for grinding waste, debarking sprues in 5-15 times requires energy consumption of 5-10% of the calorific value. At optimum humidity for pine waste grinding in 5-15 times, energy making 7-14% of a heat of combustion is required

Influence of coke content on sintering process of chromium-containing vanadium-titanium magnetite

The sintering of chromium-containing vanadium-titanium magnetite using different coke contents was studied through the sintering pot tests, X-ray diffraction analysis and mineralogical phase analysis. Results showed that, as the coke content increased from 3.2% to 4.4%, the liquid phase and combustion zone thickness increased while the vertical sintering rate and ratio of sintered product decreased. In addition, the combustion ratio of exhaust gas also increased with increasing the coke content, indicating that combustion zone temperature also increased, and the excessive the coke content in the sintering process of vanadiumtitanium magnetite is harmful. As the coke content increased, the magnetite, silicates, and perovskite contents of the sintered ore increased while the contents of hematite and calcium ferrite of sintered ore decreased; drum strength decreased, and reduction degradation properties increased while reduction ability decreased. We found that the appropriate coke content for the sintering process is 3.6 wt%.

The effect of microalgae biodiesel on combustion, performance and emission characteristics of a diesel power generator

Microalgae oil is expected to be a relevant source of biofuel in the future as it is more favorable to confront the problems of food shortages and greenhouse emission challenges raised by conventional biofuels. Therefore, in this study, a most common kind of microalgae that have a great potential, Chlorella protothecoides, was evaluated as fuel in terms of its combustion and emission characteristics in a Diesel engine-powered generator set at constant engine speed of 1500 rpm under various loads after converting its oil to biodiesel by typical base-catalyzed transesterification process. A biodiesel/diesel blend at the rate of 20% by volume was tested too. According to results obtained, using biodiesel resulted in an increase in fuel consumption, in a slight reduction of efficiency, and in sharp reductions in both unburned hydrocarbon emissions and smoke opacity especially at light loads, despite increasing NOx emissions were observed when compared with conventional petroleum diesel. In addition, premixed combustion ratio was higher for biodiesel than for diesel while total combustion duration took shorter for biodiesel especially at higher loads. The overall results of the study reveals that the combustion parameters of the biodiesel studied here are within the typical ranges of conventional biodiesel fuels.

Stability of Propane-air and oxyfuel diffusion flames in a swirl-stabilized combustor; an experimental study

Emission of greenhouse gases like CO2 is associated with global warming and ultimately climate change. Oxy-fuel combustion as a carbon capture technique is among the most widely recommended means of tackling CO2 emission. The use of oxygen/carbon dioxide (O2/CO2) mixture as oxidizer in place of air will result in distinct combustion characteristics. Flame blowout is one of such characteristics and is one of the critical operational issues in real combustion systems. In this study, blowout characteristics of air and oxyfuel combustion of propane in a non-premixed, swirl-stabilized combustor were studied. The effect of the equivalence ratio on flame blow off for three oxidizer mixtures (air, oxyfuel I, and oxyfuel II) was first studied. Furthermore, the effect of CO2 addition and swirl number on oxyfuel flame blowout was also studied. Results show that the propane–air flame transits from: attached flame - lifted flame - no flame regimes with the lifted flame regime occurring at a critical velocity ratio (ratio of fuel velocity to oxidizer velocity). The oxyfuel I and oxyfuel II flames, however, transit directly from attached flame to no flame regime at all firing rates below 4.5MW/m3 bar. This is due to the fact that oxyfuel I and oxyfuel II could not reach the critical velocity ratio for oxy-flames (Critical velocity ratio observed = 3) before flame blowout. We observed that the critical velocity ratio for propane oxyfuel combustion is six times more than that of propane–air combustion (about 0.5). At 5 MW firing rate, the amount of CO2 required in the oxidizer at the attached flame - lifted flame transition point decreases from 76% to 74% as the equivalence ratio decreases from 1 to 0.9. The velocity ratios at this operating condition are 3.1 and 3.2, respectively and are more than critical velocity ratio for propane oxyfuel combustion. This indicated that attached flame - lifted flame transition is strongly dependent on the critical velocity ratio irrespective of the equivalence ratio. Further studies showed that oxyfuel flames are more stable at stoichiometry conditions and swirl number of unity.

Influence of Coke Ratio on the Sintering Behavior of High-Chromium Vanadium-Titanium Magnetite

High-chromium vanadium and titanium magnetite (HCVTM) sinter has poor properties. The coke ratio has an important effect on the behavior of HCVTM sintering as it affects the mineral phases in the high-chromium vanadium and titanium sinter (HCVTS) via changing the sintering temperature and atmosphere. In this work, the sintering behavior of HCVTM mixed with varying coke ratios was investigated through sintering pot tests, X-ray diffraction (XRD), gas chromatographic analysis, and mineral phase analysis. The results show that, with the increase of the coke ratio from 4.0% to 6.0%, leading to the increase of the combustion ratio of the flue gas, the vertical sintering rate and sinter productivity decrease. Meanwhile, with the change of the coke ratio, the content of magnetite, silicate, and perovskite increase, while the hematite and calcium ferrite decrease. In addition, the tumble strength and reduction ability of HCVTS decrease, and its degradation strength increase. It was found that the appropriate coke ratio for the sintering process was 5.0 wt %.

Spatial and Temporal Variations in Characteristic Ratios of Elemental Carbon to Carbon Monoxide and Nitrogen Oxides across the United States.

A ratio-based method is used to characterize anthropogenic elemental carbon (ECa) using in situ measurements and emissions of carbon monoxide (CO) and nitrogen oxides (NOx). We use long-term records of ground-based measurements from the U.S. Environmental Protection Agency (EPA) Air Quality System and Interagency Monitoring of Protected Visual Environments to assess the patterns in anthropogenic combustion ratios (ΔECa/ΔCO and ΔECa/ΔNOx) across the U.S. Petroleum Administration for Defense Districts (PADD) regions for the years 2000-2015. We investigate the change in these ratios between the periods 2000-2007 and 2008-2015. Overall, ΔECa/ΔCO ratios increase by 0.7-82% and ΔECa/ΔNOx by 6.8-104% across the East and West PADD regions. The urban West showed the largest increase relative to other regions. This is mainly attributed to a 13-23% increase in ΔECa during the winter and fall seasons and significant reductions in urban ΔNOx (except in winter). We also find that emission ratios derived from the EPA's National Emission Inventory (NEI) overestimate (underestimate) the increase in the observed enhancement ratios in the East (West). Analyses of changes in NEI emissions in the West reveal (a) smaller reductions in NEI emissions for NOx from the off-road sector and (b) an increase in PM2.5 (particulate matter 2.5 μm or less in diameter) emissions from commercial/residential combustion and smaller reductions in nonroad emissions.

Increasing the Load Range, Load-to-Boost Ratio, and Efficiency of Low-Temperature Gasoline Combustion (LTGC) Engines

Increasing the Load Range, Load-to-Boost Ratio, and Efficiency of Low-Temperature Gasoline Combustion (LTGC) Engines

Effect of hydrogen gas addition on combustion characteristics of pulverized coal

A promising approach to decrease CO2 emissions from blast furnaces during ironmaking is to blow a reducing gas containing hydrogen into blast furnaces from their tuyeres. However, the combustion behavior of pulverized coal in the presence of a hydrogen-containing gas has not been elucidated. In this work, the combustion experiments of pulverized coal using a drop tube furnace were carried out to investigate the effect of H2 gas addition on the combustibility of pulverized coal. The combustion ratio of char particles in the presence of H2 gas (when introduced at a flow rate of 0.10L/min) was larger than that in the absence of H2 gas. This is because of the enhanced release of volatile matter from coal and the combustion of char due to an increase in the temperature of the coal particles, which was caused by the drastic combustion of H2 gas. The combustion ratio of char particles when H2 gas was added at flow rates higher than 0.21L/min was considerably smaller than that obtained when H2 gas was not added. It was found that the combustibility of coal was enhanced when an optimum H2 gas flow rate was used.

Development and Application of a New PM2.5 Source Apportionment Approach

ABSTRACTDue to the similarity of PM2.5 chemical species profiles of different sources, time synchronization of source contributions and the uncertainties of source-oriented models, it is difficult to get a well-separated and relatively accurate PM2.5 source apportionment result, especially for the secondary components, when only one method was applied. A new PM2.5 source apportionment approach, combining the receptor models, source-oriented models and emission inventory, was developed in this study. The proposed method had following strengths: (1) it could identify the source contributions to secondary components; (2) target (or expected) sources were optional; (3) mixed sources could be avoided. The new approach was then applied in two typical cities in North China – Beijing and Tangshan, based on intensive PM2.5 observation results from 2011 to 2013. The source apportionment result indicated that the annual average contribution to PM2.5 in Tangshan was 7.4%, 21.5%, 7.6%, 18.0%, 14.5%, 10.9% and 20.0% for power, metallurgy, cement, coal combustion, vehicle, dust and other sources, respectively; the annual average contribution ratio for vehicle, industry and industrial coal combustion, residential coal combustion, dust and other sources in Beijing was 31.5%, 22.9%, 10.6%, 14.5% and 20.4%, respectively. Seasonal variation of the source contributions was also analyzed. The demonstration results showed that the combined method was feasible. In addition, the detailed source contribution results could also provide scientific support for making effective PM2.5 mitigation strategy.

Optical study of the use of recirculated gases for adiabatization of combustion process in the SIDI engine

Proper delivery of gaseous components of the charge into the combustion chamber enables controlling of combustion in the aspect of adiabatization of the process. The adiabatization obtained as result of surrounding of combustible mixture by recirculated exhaust gases should contribute to reducing formation of harmful components created during this process. The key issue here is the formation of radicals, which is not sufficiently recognized according fuels surrounded by non-combustible gases. The innovative nature of this work ensues from the experimental confirmation of so defined organizing of combustion process. Currently there are no tests concerning attempts of gas separation in the combustion chamber of engine with external source of ignition. Such separation would contribute to the increase of the adiabatization process while at the same time the combustion rate increases and reduces the combustion duration. This paper presents the next stage of research, which were preceded by simulation and experimental investigations. In the article the results of the impact of the strategy of non-combustible gas injections on combustion ratios for cylinder head with a centrally positioned ignition point have been discussed. The analysis has been based on the photo material for the period from the start of ignition to full coverage of the cylinder by the flame. Authors performed a comparative analysis (against the recorded images) of the thermodynamic indexes of the combustion process obtained from the indicator traces.

Stabilization of diffusion flames of impacting and opposing fuel jets

Stability of diffusion combustion of fuel jets impacting on targets and interaction of two jets (pure propane–butane and the same fuel with addition of carbon dioxide) are experimentally studied. Data on combustion failure are obtained for various variants of jet interaction, as well as information about the composition of combustion products, air-to-fuel ratio, and completeness of combustion before combustion failure. It is shown that the domain of stable combustion of impacting and opposing jets is expanded by more than an order of magnitude as compared to combustion of individual free jets.

Validation of Novel Wobbe Index Sensor for Biogas Cogeneration

Biogas is a fuel made from the anaerobic digestion of organic material to form methane. It can be used to power a stationary engine to generate electricity making it a viable method of decentralised power generation from renewables. However, biogas is a mixture of methane and carbon dioxide, and other trace gases such as hydrogen, hydrogen sulphide and oxygen. As such the quality can vary and setting the air-fuel ratio for efficient combustion can be problematic under these conditions. The Wobbe Index, or Wobbe Number, is a quality of combustible gases that allows the air-fuel requirement to be determined. This work presents a novel type of Wobbe Index sensor based on a miniaturised capillary viscometer that can be used with biogas. The sensor is validated at a biogas cogeneration plant which uses a stationary engine and the results are compared to a methane sensor installed at the plant.

Octane rating effects of direct injection fuels on dual fuel HCCI-DI stratified combustion mode with port injection of n-heptane

Experimental study on dual fuel HCCI-DI stratified combustion mode is investigated with port injection of n-heptane and direct injection of primary reference fuels (PRFs) with different octane numbers from 0 to 100. Firstly, in-cylinder stratifications of mixture concentration, composition, and temperature for this HCCI-DI combustion mode were numerically simulated. The effects of the octane number of the DI fuel, the overall equivalence ratio and the premixed fuel fraction by port injection on the combustion, emissions and performance characteristics are studied. Further, the premixed fuel fraction in this dual fuel HCCI-DI stratified combustion mode is optimized based on the octane rating of the DI fuels. It was found that at lower premixed ratio of HCCI-DI combustion, dual-fuel sequential combustion was observed when high octane number fuels were used as directly injected fuel. And the ignition of the direct injected fuels was mainly determined by the active radicals or thermal energy-active radical. At large premixed ratio, the ignition of direct injected fuels was determined by the thermal-atmosphere but almost not influenced by partial equivalence ratio of DI fuels and their octane number.

Implementation of a Molecular-Level Kinetic Model for Plasma-Arc Municipal Solid Waste Gasification

A molecular-level kinetic model was developed for a plasma-arc municipal solid waste (MSW) gasification unit. The kinetic model included both MSW and foundry coke. The components included in the MSW kinetic model were biomass and four common plastics, detailed in earlier reports. The relative amounts of these components can be optimized for experimental ultimate analyses using an in-house tool, the MSW Bulk Composition Solver. The reaction chemistries included detailed pyrolysis and gasification chemistry, totaling 1628 reactions and 433 molecular species. The kinetic model used Arrhenius rate laws and contained a material balance for each species in the model. The model of coke gasification included 10 reactions of surface atoms with oxygen and carbon dioxide. The reaction rates were modeled using both surface diffusion and intrinsic kinetics. The plasma-arc gasifier was simulated using three zones for MSW, combustion, gasification, and freeboard, and a separate zone for coke gasification. Each bed was simulated using idealized chemical reactors with independent conditions. The simulation of the gasifier was organized in a user-friendly application, organizing measurable inputs and outputs. This application allowed for trending studies, investigating the effects of the equivalence ratio, MSW composition, and relative sizes of combustion and gasification zones. The results provided insight into the effects of these variables on tar production, tar composition, and quality of produced syngas.

Use of stable carbon isotope ratios to determine the source of cypermethrin in so-called natural plant extract formulations used for organic farming

ABSTRACTSome natural plant extract formulations (NPEFs, also referred to as essential oils) used in organic farming have been shown to contain synthetic pesticides. We obtained samples of four NPEFs (Muso, Hekiro, Kensogen-Ten, and Nurse Green) that were contaminated with the synthetic pyrethroid cypermethrin, and we used gas chromatography coupled with combustion, cryofocusing, and isotope ratio mass spectrometry to determine the stable carbon isotope ratios (δ13C) for the cypermethrin in the four NPEF samples, as well as in ten cypermethrin reagents and two commercial pesticide formulations (Agrothrin emulsion and Agrothrin water-dispersible powder). Our goal was to identify the source of the cypermethrin in the NPEFs. Cryofocusing markedly sharpened the cypermethrin peak and thus improved the accuracy and precision of the determined δ13C values. The δ13C values (± SD) of the 16 cypermethrin samples ranged from −28.3 ± 0.2 to −24.5 ± 0.2 ‰. Surprisingly, the four NPEFs showed similar δ13C values (−26.8 to −27.3 ‰), suggesting that the cypermethrin in all the samples came from the same source (either the same chemical reaction or the same primary material). This possibility was supported by previously published results. In addition, the δ13C values of the two commercial pesticides were similar to the values for the NPEFs, suggesting that the commercial pesticides had been diluted and sold as NPEFs.

Experimental Investigation of the Effect of Steam Dilution on the Combustion of Methane for Humidified Micro Gas Turbine Applications

ABSTRACTWater introduction in the micro gas turbine (mGT) cycle is considered the optimal route for waste heat recovery and flexibility increase of such a small-scale combined heat and power (CHP) unit. However, humidification of the combustion air in a mGT affects combustion stability, efficiency, and exhaust gas emissions. This can lead to a non-stable, incomplete combustion, which will affect the global efficiency negatively. Additionally, CO emissions will increase. The non-stable, incomplete combustion might result in an engine shutdown due to a flameout. To study the impact of humidification on the combustion of methane in a humidified mGT, we performed combustion experiments in an atmospheric, variable-swirl, premixed combustion chamber. The results of these experiments are summarized in this article. The effect of the humidification of the combustion air was simulated by adding steam to the combustion air. The impact of the steam injection on methane combustion has been studied at variable swirl number and steam fraction. Experimental results showed a linearly increasing lean blowout (LBO) equivalence ratio for methane combustion with increasing steam fraction. In addition, CO emission levels started to rise at higher equivalence ratio for higher steam fractions compared to combustion under dry conditions. The CO emission levels at stable combustion were however still the same order of magnitude as for the dry combustion. The swirl number has little effect on the LBO limit. Final results indicated the possibility to maintain complete and stable combustion under humidified conditions with low CO emissions at higher equivalence ratio compared to the dry combustion.

Partially premixed combustion based on different injection strategies in a light-duty diesel engine

The performance of partially premixed combustion (PPC) relies heavily on the proper mixing between the fuel and the in–cylinder gas. In this paper, two injection strategies, including single and multiple injection, were investigated to achieve PPC in a four-cylinder light-duty diesel engine, and were evaluated in terms of heat release rate, combustion phase, emissions and thermal efficiencies. The combustion process is dominated by premixed combustion and the diffusion combustion process is quite short at the early single injection mode. It shows the characteristics of both premixed combustion and low temperature combustion. However, the ratio of diffusion combustion increases at high load. NOx and smoke emissions reduce at the same time with late injection mode. For the multiple injection strategy, the cylinder pressure and peak pressure rise rate is lower. As the pilot-main interval increases, the mixture is more homogeneous due to sufficient premixing time. However, diffusion combustion plays the dominant role in the double pilot injection mode. The BSFC (brake specific fuel consumption) and brake thermal efficiency are considerably improved with pilot injection mode at low load condition, compared with late injection mode. The NOx decreases dramatically in double pilot injection PPC, while the smoke and CO increase, compared with single early injection mode.

ディーゼル機関排出ガス加熱用再生加熱蒸発方式バーナの開発

A lab-scale two-stage light-oil burner has been developed to obtain the fundamental data required for designing burners to heat a diesel particulate filter when exhaust gas temperature of the main engine is low. Regenerative-heating and pre-evaporation premixing combustion were adopted to this burner for downsizing and reducing cost. Two-stage combustion was realized in the burner to reduce the heat-load of the combustion chamber for the first stage combustion. The combustion chamber volume is about 66 mL. Observations of flame-holding condition and temperature measurements of the burner and combustion gas were performed with varying the fuel flow rate and air flow rate. Three types of secondary air nozzle and three secondary air nozzle positions were tested to understand the effect of the secondary nozzle on combustion gas temperature and combustion gas compositions. It was found that the burner in the single-stage combustion mode was able to stabilize a flame in the range of 2 to 14 mL/min in fuel flow rate at adequate equivalence ratio in the range of 1.4 to 1.8. Combustion gas temperature of the burner in the two-stage combustion mode is determined by the total equivalence ration and is independent on the equivalence ratio of the first stage combustion. It is possible to suppress CO and NOx emissions when the burner is operated at 0.8 in the total equivalence ratio.