Combustion Period Research Articles

Study on three droplet sequential burning characteristics of coal direct liquefied diesel

Coal direct liquefied diesel (DDCL) is a new alternative fuel with high cleanliness and quality. Its hydrocarbon composition and physicochemical properties are quite different from those of petrochemical diesel. In order to study the difference in evaporative burning characteristics between DDCL and diesel during the sequential burning of multiple droplets, three fuel droplets are suspended on fibers in order by a micro-injector. The first droplet was ignited by an electrode igniter, and then the sequential burning process of three droplets was captured by a high-speed camera. An automatic processing program is written based on Matlab software to calculate the equivalent diameter of each fuel droplet. The result shows that the burning process of the DDCL droplet can be divided into three stages: initial thermal expansion, steady burning, and late micro-explosion burning. DDCL is much easier to form the burning mixture and has better flammability than diesel. The droplet spacing and fuel type have significant effects on ignition delay. The square of the normalized diameter of droplets decreases linearly with time during the steady burning period, which follows the D2 law. The reduction rates of normalized squared diameter for DDCL droplets are higher than that for diesel. The pyrolysis of macromolecular components at high temperature produces many small molecules and low boiling point components, which induce the micro-explosions in the late burning stage. The micro-explosion intensity of DDCL droplets is obviously lower than that of diesel.

Calculation of Combustion Phases in a Diesel Engine Based on the Difference between Motoring and Combustion Pressures

AbstractTo analyze the combustion and exhaust characteristics of internal combustion engines, it is important to analyze combustion phases, such as ignition delay, premixed combustion period, and d...

On Certain Applications of the Hyperbolic Heat Transfer Equation and Methods for Its Solution

When creating new technological processes based on the use of high-intensity energy flows, it is necessary to take into account the finite speed of heat transfer. This can be done using the hyperbolic heat transfer equation obtained by A. V. Lykov within the framework of nonequilibrium phenomenological thermodynamics as a consequence of a generalization of the Fourier law for flows and the equation of thermal balance. In previous works, V. N. Khankhasaev modeled the process of switching off an electric arc in a gas flow using this equation. In this paper, we present a mathematical model of this process including the period of stable burning of an electric arc until the shutdown moment, which consists of the replacement of the strongly hyperbolic heat transfer equation by a hyperbolicparabolic equation. For the mixed heat transfer equation obtained, we state certain boundary-value problems, solve them by numerical algorithms, and obtain temperature fields that are consistent with the available experimental data.

Experimental study on combustion, performance, and emission behaviours of diesel /WCO biodiesel/Cyclohexane blends in DI-CI engine

Waste cooking oil biodiesel is considered a common way to generate clean energy in all countries. It can be used efficiently, like fossil fuel quality. To overcome the problem of poor combustion, an increase in the NOx and unburned hydrocarbon emissions, liquid, or solid additives were commonly used to improve combustion and emissions properties. In this study, the Cyclohexane (C6H12) as volatile organic and the flammable liquid compound has been applied as a micro additive for B60D40 fuel blends. Its effect on diesel engine combustion, performance, and emissions has been experimentally investigated. The C6H12 added into the diesel/biodiesel blends at different concentrations of 5, 10, and 15 % by volume basis. Two values of injection pressure have tested experimentally at different Cyclohexane concentrations. The experiment activity changed the fuel injection pressure of 150 and 250 bar, respectively, while the WCOB blends of B60D35c5, B60D30c10, and B60D25c15 have been used. The obtained results have been compared with the commercial diesel#1 and B60D40 fuel blends, respectively. The measured data show that the Cyclohexane additives dramatically improve engine emissions as well as engine performance. The CO, HC, and smoke density have decreased by increasing the Cyclohexane dose as a flammable additive. The NOx emission was reduced by increasing the C6H12 due to the fast combustion process and enhancing the premixed combustion period. Moreover, the increased injection pressure from 150 bars to 250 bars reduces the engine BSFC, HC, CO, NOx, smoke density, increasing engine BTE, CO2 emissions, and exhaust gas temperature.

Measurement report: Chemical characteristics of PM<sub>2.5</sub> during typical biomass burning season at an agricultural site of the North China Plain

Abstract. Biomass burning activities are ubiquitous in China, especially in northern China, where there is a large rural population and winter heating custom. Biomass burning tracers (i.e., levoglucosan, mannosan and potassium (K+)), as well as other chemical components, were quantified at a rural site (Gucheng, GC) in northern China from 15 October to 30 November, during a transition heating season, when the field burning of agricultural residue was becoming intense. The measured daily average concentrations of levoglucosan, mannosan and K+ in PM2.5 (particulate matter with aerodynamic diameters less than 2.5 µm) during this study were 0.79 ± 0.75, 0.03 ± 0.03 and 1.52 ± 0.62 µg m−3, respectively. Carbonaceous components and biomass burning tracers showed higher levels during nighttime than daytime, while secondary inorganic ions were enhanced during daytime. An episode with high levels of biomass burning tracers was encountered at the end of October 2016, with high levoglucosan at 4.37 µg m−3. Based on the comparison of chemical components during different biomass burning pollution periods, it appeared that biomass combustion can obviously elevate carbonaceous component levels, whereas there was essentially no effect on secondary inorganic aerosols in the ambient air. Moreover, the levoglucosan / mannosan ratios during different biomass burning pollution periods remained at high values (in the range of 18.3–24.9); however, the levoglucosan / K+ ratio was significantly elevated during the intensive biomass burning pollution period (1.67) when air temperatures were decreasing, which was substantially higher than in other biomass burning periods (averaged at 0.47).

Emissions of ultrafine particles from five types of candles during steady burn conditions.

Emissions from candles are of concern for indoor air quality. In this work, five different types of pillar candles were burned under steady burn conditions in a new laboratory scale system for repeatable and controlled comparison of candle emissions (temperature ~25°C, relative humidity ~13%, O2 >18%, air exchange rate 1.9h-1 ). Burn rate, particle number concentrations, mass concentrations, and mode diameters varied between candle types. Based on the results, the burning period was divided in two phases: initial (0-1h) and stable (1-6h). Burn rates were in the range 4.4-7.3 and 4.7-7.1g/h during initial and stable phase, respectively. Relative particle number emissions, mode diameters, and mass concentrations were higher during the initial phase compared to the stable phase for a majority of the candles. We hypothesize that this is due to elevated emissions of wick additives upon ignition of the candle together with a slightly higher burn rate in the initial phase. Experiments at higher relative humidity (~40%) gave similar results with a tendency toward larger particle sizes at the higher relative humidity. Chemical composition with respect to inorganic salts was similar in the emitted particles (dry conditions) compared to the candlewicks, but with variations between different candles.

The statistical properties of raw knock signal time histories

Traditional processing of knock signals reduces each recorded time history to a single scalar knock intensity metric for each engine firing, thereby losing all information relating to the phasing and evolution of knock over the combustion period. In this work, a statistical analysis of raw knock cylinder pressure and accelerometer signal time histories has been performed showing how the nonstationary stochastic characteristics of these signals evolve as a function of crank angle, and as a function of spark timing. The data are shown to closely approximate a cyclically independent process whose 2-dimensional covariance function captures both the non-stationary deterministic processes taking place within a cycle as well as the stationary random variations from one cycle to the next. A (time-varying) dual-Gaussian model for the distribution of these cyclic variations was fitted to the data, thereby enabling them to be characterized as the sum of knocking and non-knocking populations. The parameters of the model, which describe these populations separately, provide further empirical insight into the knock process.

Severe haze events in the Indo-Gangetic Plain during post-monsoon: Synergetic effect of synoptic meteorology and crop residue burning emission

In recent years, the frequent occurrence of haze events in the Indo-Gangetic Plain (IGP) during crop residue burning period has caused a serious reduction in atmospheric visibility and deteriorated air quality. The present study is carried out to investigate the haze event observed in IGP in Nov 2017 using ground-based observations, satellite data and synoptic meteorology to understand the possible factors responsible for haze formation. PM2.5 (particulate matter with aerodynamic diameter ≤ 2.5 μm) concentrations and Air Quality Index (AQI) at two sites (Agra and Delhi) situated in the central Indo-Gangetic Plain (CIGP) showed a sudden increase in PM2.5 concentrations and deteriorated air quality during 7–14 Nov. To monitor the variation of particulate matter (PM) in IGP, PM2.5 and PM10 (particulate matter with aerodynamic diameter ≤ 10 μm) concentrations were monitored at 22 stations in 12 cities of IGP during 1–15 Nov which also showed an increase in PM concentrations during haze event (7–14 Nov). Crop residue burning activities in north-west Indo-Gangetic Plain (NW-IGP) were observed during haze event. Synoptic weather conditions of IGP identified using geopotential height and wind at 700 hPa showed high-pressure systems and low winds in IGP favoring stagnant conditions during haze event. A detailed analysis of the variation of pollutants and meteorology was carried out at Agra. Ozone (O3), carbon monoxide (CO), sulphur dioxide (SO2) and nitrogen oxides (NOx) showed higher concentrations during haze event along with lower temperature, low wind speed and high relative humidity. Aerosol ionic composition showed a higher contribution (~84%) of Cl−, NO3−, SO42− and NH4+ to total soluble ions suggesting secondary aerosol formation during haze event.

Effects of biomass burning and photochemical oxidation on the black carbon mixing state and light absorption in summer season

To investigate the effects of biomass burning and photochemical oxidation on the black carbon (BC) mixing state and light absorption, a tandem centrifugal particle mass analyzer (CPMA) and single-particle soot photometer (SP2) system was used to measure ambient fine particulate BC during EXPLORE-YRD 2018 campaign (EXPeriment on the eLucidation of the atmospheric Oxidation capacity and aerosol foRmation, and their Effects in Yangtze River Delta). The mass ratio (MR) of the non-BC coating to BC core, a morphology-independent parameter to quantify the mixing state of BC-containing aerosols, is derived. Two types of periods were identified, namely non-significant biomass-burning period (NB), and enhanced biomass burning period (EB). The MR was higher during EB (2.3 ± 0.5), compared with during the NB (2.0 ± 0.5). MR showed bimodal diurnal variation with peaks in the early morning and early afternoon, mainly due to the biomass burning and photochemical processes, respectively. The light-absorbing enhancement ranged from 1.0 to 1.19 when MR was from 1.4 to 3.4. The relationship of rBC mixing state and its optical properties was parameterized, which can further be used in the regional model.

Emission factors of metals bound with PM2.5 and ashes from biomass burning simulated in an open-system combustion chamber for estimation of open burning emissions

Emission Factors (EFs) of metals bound with PM2.5 along with ashes from biomass burning were obtained using an open-system combustion chamber. The burning of agricultural residue (AR) (rice straw (RS) and maize residue (MR)) and forest leaf litter (FLL) collected from dry dipterocarp forests (DDF) and mixed deciduous forests (MDF) were performed. The EFs of PM2.5 of all biomass burning were 2.15–4.38 g kg−1. The order of the EFs of PM2.5-bound metals were K, Na, Mg, Cr and Zn. The EFs values were used to estimate the emissions of PM2.5 and the metals from open burning in Upper Northern Thailand (UNT) in 2019. About 66,990 km2 and 27,060 km2 of the UNT are covered by forests and agriculture areas, respectively. In 2019, 80% of the total burned area was identified in forest areas (8,344 km2) and only 16% (1,647 km2) was identified in agriculture areas. Emissions of PM2.5 recorded during the smoke haze episode of 2019 were from burnings of forests (11 kilotons) and agricultural fields (0.4 kilotons). The major metals present in ash samples were Ca, K, Mg, Al, Fe and Mn. About 0.86 kilotons of total metals were emitted into the atmosphere. Ash resulting from the burning of AR was rich in K, while that of FLL has high in Ca content. After the burning period, about 78 kilotons of metals remained on the ground and/or were found to have accumulated in the environment.

Combustion of Torrefied Pellets of Furniture Work Dusts as Blends With Lignite

Abstract In this study, torrefaction of pellets formed from furniture work dusts collected as a part of space cleaning actions in the industry has been examined. Burning behavior of torrefied dusts and lignite blends was studied. Torrefaction experiments were done under a nitrogen atmosphere for 1 h at temperatures of 220, 260, and 300 °C which corresponded to light, mild, and severe torrefaction, respectively. Combustion of blend pellets prepared by adding lignite in specific ratios to powders of torrefied pellets was carried out at 700 °C initial temperature using a vertical furnace system through which air was flowing in natural convection. Ignition times of blend pellets were affected by volatile matter and moisture contents. Volatile matter combustion rates were lower than those of raw waste, and accordingly, combustion times were higher. However, no relation between volatile matter combustion rates and times was observed. Blending raw or torrefied furniture work dusts with lignite have significantly influenced volatile matter and carbon combustion periods. There was no relation between carbon combustion rates and times. It was concluded that blend pellets of mild or severe torrefaction products of furniture work dusts and lignite behaved similarly to lignite during combustion.

Contrasting the size-resolved nature of particulate arsenic, cadmium, and lead among diverse regions

This study examines the mass size distributions and crustal enrichment factors (EFs) of arsenic (As), cadmium (Cd), and lead (Pb) for diverse regions: coastal marine (Marina, California), arid mining facility (Hayden, Arizona), arid urban (Tucson, Arizona), free troposphere (Mt. Lemmon, Arizona), and coastal urban (Manila, Philippines). Micro-orifice uniform deposit impactor (MOUDI) measurements revealed several notable features. All sites showed a bimodal profile with a peak in the submicrometer and supermicrometer diameter range except for Manila, which peculiarly lacked a peak above 1 μm. Enrichment factor analysis revealed contaminated dust at all sites, even the free tropospheric site, with greater contamination in the submicrometer range. The most extensive dataset in Manila allowed for seasonal analysis, which revealed differences among the same species based on seasonally-dependent transport patterns. Sites experiencing biomass burning influence (Manila and Marina) generally exhibited suppressed concentrations and crustal EFs during burning periods presumably because soil emitted from fires is fresh without extensive processing time to become contaminated. These results have important implications for a variety of aerosol effects dependent on aerosol size (e.g., public health, biogeochemical cycling, heterogeneous chemistry) and underscore the importance of accounting for the coarse aerosol mode as more dust emissions are expected in warmer climate scenarios.

Emission estimates of trace gases (VOCs and NOx) and their reactivity during biomass burning period (2003–2017) over Northeast India

Emission estimates of trace gases (VOCs and NOx) and their reactivity during biomass burning period (2003–2017) over Northeast India

Online Education: Understanding Technological, Socio-Economic and Emotional Challenges

This paper looks at the challenges faced by teachers and students across the globe and Saudi Arabia in particular due to the sudden transition from face-to-face classes to online classes. The pandemic due to Covid 19 brings out the already existing digital/social divide in societies across the world. Amidst such a situation, schools and colleges grappled with new ed-technology, traversing with its non-video or voice only features due to cultural issues and data-cost and network related issues. Since most courses were partly completed by the time the lockdowns happened, students and teachers were exposed to the new methods of assessment. Teachers were not prepared for presenting lectures on a virtual platform which requires different strategies and preparation.<br/> All of a sudden LMSes, like Blackboard experienced tremendous load and the experience was bad due to poor net connection, low quality data packs and phone incompatibility. As every cloud has a silver lining, the teachers found solutions to improve learning and teaching, and engage students inspite of the digital/social divide becoming wider due to the pandemic. The prediction that ELearning is going to be the future mode of learning and teaching came true with all hiccups. Teachers are forced to re-look at their teaching strategies, re-write lessons plans. Unfortunately, it was a period of burn out – emotional and mental.

Spatiotemporal evolution of coal spontaneous combustion in longwall gobs: A case study from mining discontinuation to resumption

AbstractCoal mining is frequently halted for long periods of time due to geological faults, and the process of resuming mining is often fraught with danger. To address this issue, in this study, the previously developed COMBUSS‐3D software was optimized to simulate the process between mining discontinuation and resumption, based on the multi‐field coupling theory. The optimized software takes the temperature distribution in gobs when coal mining ends as the initial condition, and it considers the condition of spontaneous coal combustion after remining. The actual advance distance of the working face is introduced into the program compilation and solved by linear interpolation. These improvements ensure that the calculation results are more realistic. The results demonstrate that the high‐temperature zone is distributed on the air intake side of the gob, and its final location largely depends on the remining advance rate. The hazardous area of spontaneous ignition gradually moves to a deep suffocation zone of the gob when the mining of the coal wall resumes, the residual coal is no longer oxidized, and CO formation is gradually decreased, which is verified by the theoretical expectations and on‐site observations. The spontaneous combustion period can be effectively prolonged by reducing the thickness of crushed coal during the mining stage or by increasing the longwall advance rate after resuming mining. This study can provide significant guidance and suggestion on locating the hazardous area in gobs and suppressing the spontaneous coal ignition.

Investigations on Biogas Fueled Dual Fuel DIesel Engine Employing Dimethyl Carbonate as a Fuel Blend

ABSTRACT In this experimental study, the center point of our work is to evaluate the impact of dimethyl carbonate (DMC) fuel blended with diesel with regard to the engine performance, emissions, and combustion characteristics in dual fuel engine fueled by biogas at various DMC proportions and biogas flow rates. A water-cooled, four stroke, single cylinder Compression Ignition (CI) engine is adjusted to run in dual fuel mode. A simulated biogas is obtained by mixing CH4 and CO2 that are kept in red and black cylinders, respectively. Throughout the experimental process the engine is run at a constant speed of 1800 rpm. Three proportions of DMC are taken which are 10, 20, and 30% by volume and blended with pure diesel. Biogas flow rates taken are 12 lpm and 16 lpm. An experimental study was performed and it is found that a maximum of 3% drop in brake thermal efficiency at high DMC proportions but at low biogas flow rates, the efficiency increased up to 2.7%. NOx emissions were observed to be low on addition of DMC and further decreased at high biogas flow rates. The maximum reduction of 57.5% is observed when compared to diesel-only mode. CO emissions increased upto 28% at high DMC fractions. In combustion characteristics, the Maximum Heat Release Rate (MHRR) decreased at high DMC fractions and high biogas flow rates but decreased, at high loads. The maximum cylinder pressure also decreased at high DMC fractions and at high biogas flow rates. The period of combustion increases when DMC fraction is increased.

Combustion phase of a diesel/natural gas dual fuel engine under various pilot diesel injection timings

Although the brake thermal efficiency and exhaust emissions performance of the engine have been improved significantly in recent years, these issues are still not fully-resolved. Natural gas (NG) engine has been widely concerned because of its extensive resources and relatively clean. To better understand the effect of the pilot diesel injection timing on the combustion phases of the pilot diesel and the natural gas, a detailed study was conducted by experiment and numerical simulation. A 6-cylinder turbocharged intercooler diesel/natural gas dual fuel heavy-duty engine was used in this study, and the pilot diesel injection timing was controlled over a very wide range at a constant engine speed of 1335 r/min. The results show that the injection timing has an obvious effect on the engine combustion process including combustion phases of the pilot diesel and the natural gas, and which decide the engine thermal efficiency and exhaust emissions level. The chemical reaction of diesel and natural gas before combustion start at the same time, however, the combustion duration of natural gas lags behind that of diesel. In addition, during the combustion overlap period, the in-cylinder combustion is good and the working ability is strong. To advance the pilot diesel injection timing from 5 °CA BTDC to 35 °CA BTDC, the chemical ignition delay of diesel shows a lengthening trend, and the combustion duration shows a shortened trend. With advancing the pilot diesel injection, the natural gas combustion duration shows a shortened trend, and the shortest is near to 16.5 °CA. There is a clear correspondence between the lengths of combustion period of two fuels. Either the combustion duration or the combustion overlap period shows a shortened trend, but the ratio of the combustion overlap period to the combustion duration is increasing with advancing the pilot diesel injection. The shortest combustion duration corresponds to the lower brake specific energy consumption and emissions.

Role of meteorological regime in mitigating biomass induced extreme air pollution events

India is an agriculture-based economy; a large fraction of crop residue is being burned directly on fields that are one of the major sources of air pollution. As the autumn edges towards the cooler winter in mega city Delhi, the fear of smog looms, frequently leading to extreme pollution events caused by burn paddy straw under the hostile weather. The Kharif crop stubble burning starts around the first week of October and lasts up to the end of November. We hereby propose that if the burning period is advanced backward by about a month then the severity of its impact in deteriorating the air quality of Delhi would be significantly reduced due to less hostile meteorological regime. The current work is based on 2018 and generalization of current findings would require a much more comprehensive simulation and protocols. In the present work, an interactive high resolution WRF-Chem model forced with newly developed synergized gridded stubble burning emission inventory of PM2.5 for 2018 is used along with normal emissions. Results indicate that emergency episodes significantly reduced from 12 to nil, under proposed scenario that may help minimizing adverse health impacts. Such effort, however, requires a feasibility study and policy level intervention.

Indoor Air Pollution from Residential Stoves: Examining the Flooding of Particulate Matter into Homes during Real-World Use

This study concerns the levels of particulate matter (PM2.5 and PM1) released by residential stoves inside the home during ‘real world’ use. Focusing on stoves that were certified by the UK’s Department of Environment, Food, and Rural Affairs (DEFRA), PM sensors were placed in the vicinity of 20 different stoves over four weeks, recording 260 uses. The participants completed a research diary in order to provide information on time lit, amount and type of fuel used, and duration of use, among other details. Multivariate statistical tools were used in order to analyse indoor PM concentrations, averages, intensities, and their relationship to aspects of stove management. The study has four core findings. First, the daily average indoor PM concentrations when a stove was used were higher for PM2.5 by 196.23% and PM1 by 227.80% than those of the non-use control group. Second, hourly peak averages are higher for PM2.5 by 123.91% and for PM1 by 133.09% than daily averages, showing that PM is ‘flooding’ into indoor areas through normal use. Third, the peaks that are derived from these ’flooding’ incidents are associated with the number of fuel pieces used and length of the burn period. This points to the opening of the stove door as a primary mechanism for introducing PM into the home. Finally, it demonstrates that the indoor air pollution being witnessed is not originating from outside the home. Taken together, the study demonstrates that people inside homes with a residential stove are at risk of exposure to high intensities of PM2.5 and PM1 within a short period of time through normal use. It is recommended that this risk be reflected in the testing and regulation of residential stoves.

Numerical Analysis for Hydrogen Flame Acceleration during a Severe Accident in the APR1400 Containment Using a Multi-Dimensional Hydrogen Analysis System

Korea Atomic Energy Research Institute (KAERI) established a multi-dimensional hydrogen analysis system to evaluate hydrogen release, distribution, and combustion in the containment of a Nuclear Power Plant (NPP), using MAAP, GASFLOW, and COM3D. In particular, KAERI developed an analysis methodology for a hydrogen flame acceleration, on the basis of the COM3D validation results against measured data of the hydrogen combustion tests in the ENACCEF and THAI facilities. The proposed analysis methodology accurately predicted the peak overpressure with an error range of approximately ±10%, using the Kawanabe model used for a turbulent flame speed in the COM3D. KAERI performed a hydrogen flame acceleration analysis using the multi-dimensional hydrogen analysis system for a severe accident initiated by a station blackout (SBO), under the assumption of 100% metal–water reaction in the Reactor Pressure Vessel (RPV), to evaluate an overpressure buildup in the containment of the Advanced Power Reactor 1400 MWe (APR1400). The magnitude of the overpressure buildup in the APR1400 containment might be used as a criterion to judge whether the containment integrity is maintained or not, when the hydrogen combustion occurs during a severe accident. The COM3D calculation results using the established analysis methodology showed that the calculated peak pressure in the containment was lower than the fracture pressure of the APR1400 containment. This calculation result might have resulted from a large air volume of the containment, a reduced hydrogen concentration owing to passive auto-catalytic recombiners installed in the containment during the hydrogen release from the RPV, and a lot of stem presence during the hydrogen combustion period in the containment. Therefore, we found that the current design of the APR1400 containment maintained its integrity when the flame acceleration occurred during the severe accident initiated by the SBO accident.