This work presents an application of a reduced chemical kinetic mechanism using computational singular perturbation (CSP) based on the significant indices of the modes on the evolution of species and the degree of participation of reactions. With this approach, the mechanism of Yang and Pope is reduced to 22 reversible reactions (RR22). In this study, the tabulation of ignition delays is made with Yang and Pope mechanism, GRI 3.0, and the reduced mechanism RR22; the results obtained show a good agreement among the three mechanisms. The “Modèle Intermittent Lagrangien” (MIL) necessary to calculate the chemical source term of the transport equation of the species requires the library of ignition delays determined above and a probability density function (PDF) of the mixture fraction presumed by a beta distribution. The scalar variance, one of the key parameters for the determination of the presumed beta function, is obtained by solving its own transport equation with the unclosed scalar dissipation rate modeled using either an algebraic model or a transport equation. All these models are introduced in the computational fluid dynamics “Code-Saturne” to simulate a turbulent CH 4 /H 2 /N 2 jet flame (DLR Flame A) performed at the Deutsches Zentrum für Luft-und Raumfahrt (DLR), or German Aerospace Center. A set of comparisons is made and the results of simulations show a good agreement among the three mechanisms as well with the experimental data.

Two equations are developed to estimate laminar flame speed and ignition delay for different alkane mixtures at a range of engine-relevant conditions. Fuel mixtures of methane, ethane, propane, butane, and pentane were selected by analyzing the natural gas composition in a natural gas pipeline located in the Midwestern United States. The laminar flame speed and ignition delay were calculated for each mixture at each set of conditions using Cantera, a chemical kinetics solver. The range of initial conditions for laminar flame speed includes temperatures from 300 to 700 K, pressures from 1 to 40 bar, equivalence ratios from 0.4 to 1.2, and residual fractions from 0% to 20%. These data were then fit to a non-linear regression. The range of initial conditions for the ignition delay equation includes temperatures from 1100 to 2000 K, pressures from 1 to 40 bar, equivalence ratios from 0.4 to 1.15, and residual fractions from 0% to 20%. These data were fit to a previously developed equation. Sensitivity studies were conducted on each equation to quantify the impact of the independent variables on the target variable. This showed that, for laminar flame speed, the initial pressure, temperature, and equivalence ratio had the largest impact, with fuel composition having a lesser impact. For ignition delay, the temperature and pressure were shown to have the largest impact. There is a room for improvement, namely, increasing the fuel mixture variability and range of initial conditions, and developing a better fit to the data.

This paper presents the results of thermal efficiency of two coal based oxy-combustion thermodynamic cycles that are modeled using aspen plus . The objective of the present study is to perform a parametric analysis, investigating the effect of different recirculation ratios at different pressures on the efficiencies of the cycle named for the company, ENEL, and the thermo energy power system, TIPS, cycles using aspen plus ® software. Variables include the flue gas recycle flow rate, the combustor temperature, and the operational pressure. Five recirculation ratios were investigated, ranging from 20% to 75%. It was determined that as the amount of recycled gas into the combustor increased, the thermal efficiency increased for both the TIPS and ENEL cycles. The highest thermal efficiency for TIPS is 37% and for ENEL is 38%, both occurring at a 75% recirculation ratio. After investigation, since combustion temperature and specific heat capacity decreases at higher recirculation ratios, the mass flow rate was the dominant factor that contributes to the increase in thermal efficiency of the cycle. At each recirculation ratio, the effect of pressure is also determined. For ENEL, the increase in cycle efficiency is 10% over the pressure range of 1–12 bar at a recirculation ratio of 20%, while the increase in cycle efficiency is only 1.5% at a higher recirculation ratio of 75%. For TIPS, the cycle efficiency increases by 4% at the recirculation ratio of 20% and increases by 3% at the recirculation ratio of 75% for a pressure range of 50–80 bar.

As a new energy source with abundant resources, clean combustion and high calorific value, gas hydrates have received much attention in recent years. However, the sampling cost is relatively high because the gas hydrates exist in deep seas and frozen soils. Digital core technology can reconstruct hydrate cores without destroying rock samples. In this paper, the advanced image processing technology is used to process the gas hydrate CT scan image, and a three-dimensional hydrate digital core model is constructed, which can depict the sample's pore structure features. Avizo software is used for filtering and image segmentation, and the porosity is calculated as 35.9%, the hydrate saturation is 36.9%, the pore network model is established; The pore volume is mostly distributed in 0∼1×108µm 3 , the average pore radius is 168.131µm, and the throat radius is mostly distributed in 0.5∼1×102µm; The seepage simulation on the pore scale is carried out and the absolute permeability is calculated to be 76.8µm 2 . Compared with conventional physical experiments, the digital core technology can obtain the true distribution of the pores inside the hydrate core, which is very helpful for analyzing the physical parameters of the hydrate core. Digital core technology is of great significance in the study of hydrate reservoirs. Keywords: gas hydrate, digital core, pore-scale network model, permeability

The use of natural gas (NG) in heavy-duty internal combustion engines can reduce the dependence on petroleum fuels and greenhouse gas emissions. Diesel engines can convert to NG spark-ignition (SI) by installing a high-energy ignition system and a gas injector. The diesel combustion chamber affects the flow inside the cylinder, so some existing SI combustion models will not accurately describe the operation of converted diesels. For example, the single Wiebe function has difficulties in correctly describing the mass fraction burn throughout the combustion process. This study used experiments from a 2L single-cylinder research engine converted to port fuel injection NG SI and operated with methane at 1,300 rpm and equivalence ratio 0.8 (6.2 bar IMEP) to compare the standard Wiebe function to a triple-Wiebe function. Results indicated that lean-burn engine operation at an advanced spark timing produced three peaks in the heat release rate, suggesting a multi-stage combustion process. A “best goodness-of-fit” approach determined the values of the key parameters in the zero-dimensional Wiebe function model. The triple-Wiebe function described the mass fraction burn and combustion phasing more accurately compared to the single Wiebe function. Moreover, it provided the duration and phasing of each individual burning stage that can then characterize the combustion in such converted diesel engines. This suggests that a multiple Wiebe function combustion model would effectively assist in analyzing such a multi-stage combustion process, which is important for engine optimization and development.

This paper presents an exergy-based sustainability analysis of manufacturing roof tiles from plastic waste in Uganda. This work focuses specifically on the developing country context and on utilizing waste material. A summary of the current Ugandan plastic waste situation, environmental and health issues associated with plastic waste, current means of recycling plastic waste into new products, and an analysis of the Ugandan roofing market are presented. The total exergy consumed to produce one batch of seventy-five tiles is over 210 MJ, the potentially recoverable exergy is nearly 17 MJ (8% of consumed exergy), and the realistic recoverable exergy is over 6 MJ (3% of consumed exergy). Recycling plastic waste into roof tiles saves a net 188 kg of CO 2 from entering the atmosphere compared to open burning. If all of Kampala's plastic waste was converted to roofing tiles, nearly 560 tons of CO 2 could be saved per year.

Effects of controllable vortex slotted bluff body parameters (position of a bluff body, slit size, and controllable flow ratio) on the combustion characteristics of hydrogen/air in a micro-combustor with a bluff body were investigated numerically. The results illustrated that the combustion efficiency of hydrogen decreases with increasing distance (L 1 ) between the front edge of the bluff body and the combustor inlet. The combustion characteristics of the micro-combustor are optimum when L 1 is 0 mm. The blow-off limit of the combustor reaches a maximum (564 cm 3 /s) when the slit width (d) is 20% of the bluff body width. The blow-off limit first increases and then decreases when the equivalence ratio (φ) increases and reaches a maximum (732 cm 3 /s) when φ is 1.0, and the controllable flow ratio is 0.2. The combustion efficiency of hydrogen is gradually increased with the increase in the controllable flow ratio. When φ is less than 1.0, the optimal controllable flow ratio gradually decreases with the increase in the premixed gas flow rate, and the optimal controllable flow ratio basically remains at 0.6 when the premixed gas flow rate is less than 360 cm 3 /s.

The combustion kinetics of corn stalk (CS), paper sludge (PS), and their mixture were studied by thermogravimetric analysis (TGA) using one model-fitting method (Coats–Redfern (CR)) and four model-free methods, namely, Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), Starink, and Friedman methods. TGA experiments were carried out at three different heating rates (10, 20, and 30 °C min −1 ) and with different weight percentages of PS in the mixture (0%, 20%, 50%, 80%, and 100%). The comprehensive combustion characteristic index decreases with an increase in the weight percentage of PS in the blends and increases with the increasing heating rate. Significant interactions occur in the co-firing of the blends containing 20% and 50% of PS. The co-firing kinetic parameters determined by the CR method show relatively high reliability due to the high correlation coefficient obtained from the linear fitting. The values of average activation energy determined by the model-fitting method are generally lower than those calculated from model-free methods. The co-firing of the blends containing 20% of PS shows the highest comprehensive combustion characteristic index and the lowest average activation energy based on the model-free methods.

This work presents the effect of specific gravity of coal on its combustion characteristics. Coals with different specific gravity fractions represented by the arithmetic mean specific gravity (MSG) in the range of 1.35 to 2.0 were prepared by sink–float based density separation from run-of-mine (ROM) coal. The characterization of coal with different MSG was done using proximate, ultimate, and gross calorific value (GCV) analysis. Thermogravimetric analysis and differential thermogravimetry (TGA-DTG) studies of coals with different MSG were carried out in oxygen atmosphere to analyze their combustion characteristics. Various burning profile parameters (T i , T p , T f , DTG max ) were assessed to identify the impacts of MSG of coals on their combustion characteristics. Further, different combustion indices (D i , D f , S, H f ) were evaluated to get the insights of combustion. Based on the experimental results, it was observed that, with an increase in coal MSG from 1.35 to 2.0, GCV decreased from 7426 to 3625 kcal/kg, T i varied from 355 to 412 °C, T p varied between 466 and 487 °C, and DTG max decreased from 6.73 to 4.83 wt%/min. The result signifies that with an increase in MSG of coal, its combustion properties weaken. The activation energy for combustion varied between 93 and 119 kJ/mol. Based on the present analysis, it may be observed that lower MSG coals have enhanced combustion characteristics than higher MSG coals.

The results of investigations on solids flow in a cold model of the dual fluidized bed reactor designed for chemical looping combustion of solid fuels (DFB-CLC-SF) are presented in this paper. The constructed unit consists of two interconnected reactors. The first one, so-called fuel reactor (FR), is operated under bubbling fluidized bed (BFB) conditions, whereas the second one, so-called air reactor (AR), is structurally divided into two sections. The bottom part of AR works under BFB while the upper part, i.e., the riser, is operated in the fast fluidized bed (FFB) regime. In these studies, the air was used for fluidization process in all parts of the DFB-CLC-SF reactor. The glass beads with similar parameters to oxygen carriers (OCs) used in the CLC process were utilized as an inventory. The fluidization conditions are controlled by using the sets of pressure sensors installed around the circulation loop. The experimental data acquired in the tests are further employed to the analysis of solids behavior in a cold model of the DFB-CLC-SF reactor. The main goal of these studies was to establish the conditions for smooth fluidization, which concurrently provide the required residence time of solids in both reactors that is one of the most crucial factors in the CLC process. It was found that the fluidizing gas velocity in reactors has a significant impact on solids behavior and the investigated parameters. However, what is the most important, it was confirmed that the operation condition of the DFB-CLC-SF reactor can be adjusted to meet the requirements resulting from the properties of OCs.

During the combustion of solid fuels, the undesired effects of ash transformation include bed agglomeration, slagging, and fouling processes. In particular, a problematic consequence of bed agglomeration is the defluidization process, resulting from the disappearance of gaseous bubbles that are created behind air distributors. Different solutions can be applied against the agglomeration process. One possible method is to apply some additives that influence the ash behavior, thus inhibiting the agglomeration process. This paper presents the results of investigations into ash-related issues in a laboratory-scale bubbling fluidized bed (BFB) reactor. In particular, the impact of additives (kaolin, halloysite, fly ash, and the residuals from wet desulfurization system (IMOS)) on bed agglomeration was investigated. It was found that the addition of these compounds increased the defluidization time from ∼109 min (without additive) to ∼285 min in the BFB (with the addition of 0.1 g/min of kaolin). The morphology of additive (kaolin and halloysite) transformation after their addition into the combustion chamber was discussed. Another interesting phenomenon is that residuals from the IMOS exhibited the ability to be an additive against the agglomeration process. The defluidization time can be also significantly increased by the simultaneous application of the additive and the control of fluidization air velocity. The procedure of periodical bed moving by impulse primary air feeding against defluidization (PADM) is suggested and discussed. The PADM procedure resulted in a 36% reduction of additive, thus reducing the cost of measures against ash-related issues.

In this paper, we aim to develop a comprehensive ignition model for three-dimensional (3D) computational fluid dynamics (CFD) combustion modeling in spark-ignited (SI) engines. In the proposed model, we consider the following aspects separately to model the spark ignition process comprehensively. An electrical circuit is solved for calculation of the energy transferred to the spark plasma channel. The spark itself is represented by computational particles for monitoring its motion and ignitability. Heat diffusion from the spark toward the surrounding mixture is calculated with a one-dimensional (1D) model, resulting in the temperature obtained at the surface of the spark channel. Based on the calculated temperature and interpolated pressure and local mixture composition, an instantaneous ignition delay time is read from tabulated values for every particle representing the spark channel. The final ignitability criterion is defined by a precursor calculated with a zero-dimensional (0D) model, which accounts for the history of changes in spark surface temperature and local mixture properties. As soon as the precursor reaches a threshold value for a given spark channel particle, a flame kernel is introduced at a position of the particle. Flame propagation is generally treated by the G-equation combustion model. Validation is performed by measurements of the spark discharge process in high-velocity flow field and single-cylinder AVL research engine. We demonstrate that the proposed model can correctly reproduce the electrical circuit, spark channel dynamics, and overall engine performance.

Fuel availability, global warming, and energy security are the three main driving forces, which determine suitability and long-term implementation potential of a renewable fuel for internal combustion engines for a variety of applications. Comprehensive engine experiments were conducted in a single-cylinder gasoline direct injection (GDI) engine prototype having a compression ratio of 10.5, for gaining insights into application of mixtures of gasoline and primary alcohols. Performance, emissions, combustion, and particulate characteristics were determined at different engine speeds (1500, 2000, 2500, 3000 rpm), different fuel injection pressures (FIP: 40, 80, 120, 160 bars) and different test fuel blends namely 15% (v/v) butanol, ethanol, and methanol blended with gasoline, respectively (Bu15, E15, and M15) and baseline gasoline at a fixed (optimum) spark timing of 24 deg before top dead center (bTDC). For a majority of operating conditions, gasohols exhibited superior characteristics except minor engine performance penalty. Gasohols therefore emerged as serious candidate as a transitional renewable fuel for utilization in the existing GDI engines, without requirement of any major hardware changes.

This paper aims at developing a novel mesoscale combustion-based thermoelectric power generator as an alternate to the electrochemical batteries. Most of the micro and mesoscale combustors investigated till date are based on external fuel and air supply systems, which may not be beneficial for a practical system. The proposed design is a standalone system which makes use of the heat conducted through the combustor walls, as an energy source to evaporate the liquid fuel stored in a surrounding tank and supply the vaporized fuel to the combustor. The high momentum fuel (vapor) jet is designed to entrain the ambient air in appropriate proportion so as to form a combustible mixture. The fuel/air mixture is fed to a mesoscale combustor and the flame is stabilized by facilitating hot gas recirculation regions. The hot combustion products then flow over a ceramic plate on the other side of which the hot side of a thermoelectric module (TEM) is attached, while ensuring a near uniform temperature, to generate electricity. The cold side of the TEM is maintained at relatively lower temperature and the heat is designed to be rejected using fins to the ambient. The prototype is designed to produce an electrical power output of 12 W with an overall efficiency of about 2.4% (heat load of 500 W) and endurance of 1.5 h in a single fuel refill. The paper presents detailed description of the constituent components and the CFD analysis which evaluates the performance of the system.

High cycle-to-cycle variation (CCV) is detrimental to engine performance, as it leads to poor combustion and high noise and vibration. In this work, CCV in a gasoline engine is studied using large eddy simulation (LES). The engine chosen as the basis of this work is a single-cylinder gasoline direct injection (GDI) research engine. Two stoichiometric part-load engine operating points (6 brake mean effective pressure (BMEP) and 2000 revolutions per minute) were evaluated: a nondilute (0% exhaust gas recirculation (EGR)) case and a dilute (18% EGR) case. The experimental data for both operating conditions had 500 cycles. The measured CCV in indicated mean effective pressure (IMEP) was 1.40% for the nondilute case and 7.78% for the dilute case. To estimate CCV from simulation, perturbed concurrent cycles of engine simulations were compared with consecutively obtained engine cycles. The motivation behind this is that running consecutive cycles to estimate CCV is quite time consuming. For example, running 100 consecutive cycles requires 2–3 months (on a typical cluster); however, by running concurrently, one can potentially run all 100 cycles at the same time and reduce the overall turnaround time for 100 cycles to the time taken for a single cycle (2 days). The goal of this paper is to statistically determine if concurrent cycles, with a perturbation applied to each individual cycle at the start, can be representative of consecutively obtained cycles and accurately estimate CCV. 100 cycles were run for each case to obtain statistically valid results. The concurrent cycles began at different timings before the combustion event, with the motivation to identify the closest time before spark to minimize the run time. Only a single combustion cycle was run for each concurrent case. The calculated standard deviation of peak pressure and coefficient of variance (COV) of IMEP were compared between the consecutive and concurrent methods to quantify CCV. It was found that the concurrent method could be used to predict CCV with either a velocity or numerical perturbation. Both a large and small velocity perturbations were compared, and both produced correct predictions, implying that the type of perturbation is not important to yield a valid realization. Starting the simulation too close to the combustion event, at intake valve close (IVC) or at spark timing, underpredicted the CCV. When concurrent simulations were initiated during or before the intake even, at start of injection (SOI) or earlier, distinct and valid realizations were obtained to accurately predict CCV for both operating points. By simulating CCV with concurrent cycles, the required wall clock time can be reduced from 2–3 months to 1–2 days. In addition, the required core-hours can be reduced up to 41%, since only a portion of each cycle needs to be simulated.

A torrefaction process operating on oxyfuel combustion concept is introduced. The working fluid employed in the process is carbon dioxide captured from the combustion products. The thermodynamic modeling of the process is carried out to determine the energy requirement, recycled CO 2 flow rate, energy yield, and CO 2 production rate at various torrefaction conditions. The total capital investment and production costs of the new system are also estimated. By increasing the torrefaction severity, the CO 2 production rate, recycled gas mass, and the process thermal energy requirement increase, whereas the grinding energy and the energy yield decrease. A comparison made between the performance and economic parameters of the new and a conventional torrefaction processes shows that the proposed process is expected to produce torrefied wood pellet of compatible fuel quality and overall efficiency while eliminating CO 2 and NO x emissions at the expense of 11.5% and 9% increase in the capital and production costs, respectively. The proposed torrefaction process requires 91.8 M$ capital investment and 113.2 $ to produce 1 ton of torrefied wood pellets with 91% energy yield and 88% overall plant efficiency. Sensitivity analysis shows that the reactor type and raw biomass costs have significant impact on cost structures.

Stringent emission legislations, increasing environmental and health issues, have driven extensive research on combustion engines to control pollutants. Modeling of emissions offers a cost-saving alternative to experimental analysis for combustion chamber design and optimization. Soot modeling in diesel engines has evolved over four decades from simple empirical relations to detailed kinetics involving polycyclic aromatic hydrocarbons (PAHs) and complex particle dynamics. Although numerical models have been established for predicting soot mass for parametric variations, there is a lack of modeling studies for predicting soot particle size distribution for parametric variations. This becomes important considering the inclusion of limits on soot particle count in recent emission norms. The current work aims at modeling the soot particle size distribution inside a heavy-duty diesel engine and validating the results for a parametric variation in injection pressure and intake temperature. Closed cycle combustion simulations have been performed using converge , a 3D computational fluid dynamics (CFD) code. A sectional soot model coupled with gas-phase kinetics has been used with source terms for inception, condensation, surface reactions, and coagulation. Numerical predictions for soot mass and particle size distribution at the exhaust show good agreement with experimental data after increasing the transition regime collision frequency by a factor of 100.

A Kalina cycle is coupled to an ejector refrigeration cycle to generate power and refrigeration outputs, simultaneously. Ejector refrigeration cycle is driven by the heat which is extracted from a high-temperature/pressure stream of Kalina cycle working fluid since the energy content of this fluid stream is not directly utilized in power production in the Kalina cycle. Supplied heat to the proposed combined cycle is produced by combustion of biomethane which is obtained from anaerobic digestion of biomass, namely, food waste. System reactions to altering operation conditions (entrainment ratio, condenser pressure, evaporator pressure, and superheating degree) in terms of refrigeration production, power production, energy efficiency, exergy efficiency, and exergy of produced power and refrigeration are analyzed. The results are reported for R290, R134a, and R152a working fluids of the ejector refrigeration cycle and an extensive discussion of the results are provided. It is shown that the entrainment ratio strongly affects the thermal and exergy efficiency results. The highest thermal and exergy efficiency results are performed when R290 and R134a are used, whereas the lowest thermal and exergy efficiencies are obtained when R152a and R290 are used as the refrigerant, respectively.

Fossil fuel consumption provides a negative impact on the human health and environment in parallel with the decreased availability of this valuable natural resource for the future generations to use as a source of chemical energy for all applications in energy, power, and propulsion. The diesel fuel consumption in the transport sector is higher than the gasoline in most developing countries for reasons of cost and economy. Biodiesel fuel offers a good replacement for diesel fuel in compression ignition (CI) diesel engines. Earlier investigations by the authors revealed that a blend of 70% amla seed oil biodiesel and 30% eucalyptus oil (AB70EU30) is the favorable alternative renewable fuel blend that can be used as a fuel in diesel engines. With any fuel, air/fuel mixing and mixture preparation impact efficiency, emissions, and performance in CI engines. Minor adjustments in engine parameters to improve air/fuel mixing and combustion are deployable approaches to achieve good performance with alternative fuel blends in CI engines. This paper provides the role of a minor modification to engine parameters (compression ratio, injection timing, and injection pressure) on improved performance using the above mixture of binary fuel blends (AB70EU30). The results showed that the use of AB70EU30 in modified engine resulted in higher brake thermal efficiency and lower brake specific fuel consumption compared to normal diesel for improved combustion that also resulted in very low tailpipe emissions.

Woody biomasses such as ash tree (AT), hybrid poplar (HP), and rhododendron (RD) were subjected to torrefaction and carbonization at temperatures of 200 °C and 400 °C. Likewise, several lignite samples were carbonized at 750 °C. Various binary fuel blends such as raw lignite/raw biomass, raw lignite/biochar, lignitic char/raw biomass, and lignitic char/biochar were prepared where the fraction of biomass or biochar was 10 wt% in the blends. The cocombustion characteristics of these blends were investigated through a thermal analysis method from the synergetic point of view considering the fuel properties and the combustion performance. Some parameters relevant to the combustion reactivity such as ignition point, maximum rate, peak temperature, and burnout temperature were commented to figure out whether synergistic interaction or additive behavior governs the combustion characteristics of the blends. Also, the combustion performance indices such as ignition index (C i ), burnout index (C b ), comprehensive combustibility index (S), and the burning stability index (D W ) were estimated. It was concluded that the combinations of the additive behavior and the synergistic interactions governs the cocombustion process, and the kind of the fuels and their thermal history determine the reactivity and the interactions during cocombustion.