Combustion Cycle Research Articles

Numerical and experimental investigation of the influence of various metal-oxide-based nanoparticles on performance, combustion, and emissions of CI engine fuelled with tamarind seed oil methyl ester

The present study aims to experimentally and numerically investigate diesel engine's combustion, performance, and exhaust emission characteristics fuelled with tamarind seed oil methyl ester (TSOME) and nanoparticles as fuel additives. The Diesel-RK, a complete thermodynamic cycle engine analysis tool, is employed to assess the engine characteristics. Cerium Oxide (CeO2) and Aluminium Oxide (Al2O3) nanoparticles are introduced as additives and dispersed in pure TSOME at a concentration of 30 ppm to obtain TSOME + CeO2 and TSOME + Al2O3 blends correspondingly. The tests are conducted when the engine is loaded from 0 to 100% with intervals of 25%. The research reveals that incorporating CeO2 and Al2O3 improves the BTE by 17–18% compared to that of TSOME. TSOME + CeO2 and TSOME + Al2O3 substantially decreased CO2, HC, and smoke emissions compared to those of conventional diesel fuel. Furthermore, when CeO2 and Al2O3 nanoparticles are added into the TSOME fuel, oxides of nitrogen emissions are mitigated by 6–7% compared to TSOME by reducing the fuel consumption. Also, the addition of nanoparticles led to an improvement in combustion characteristics compared to pure TSOME due to the high catalyst role of nanoparticles, which accelerate the chemical reactions during the combustion cycle. Furthermore, the nanoparticles-added test fuels have generally presented the competitive results with each other, but the CeO2 nanoparticle presented slightly better results in terms of exhaust emissions, while Al2O3 added test fuel gave slightly better results in terms of engine performance. Finally, the results of this research show that metal oxide-based nanoparticles such as CeO2 and Al2O3 as a fuel additive can improve the characteristics of diesel engines fuelled by biofuels.

Design and construction of a gas filter system for hospital incinerators

An incinerator is designed to burn combustible waste materials such as municipal solid waste and infectious waste into inert ash. The design reduces waste volumes and subsequently destroys pathogens. A gas filtering unit is designed, constructed, and fitted on an existing incinerator for cleaning the smoke from medical waste treatment. Its main components are a framework whose material is made of galvanized diamond, three wire meshes, made of steel, to serve as filter bed supports, an inlet and 2 sampling holes of diameter 1.5cm beneath the wire meshes, and an outlet and 2 sampling holes of 1.5 cm above the wire meshes. As part of the gas filter design considerations, the amounts of dry volumetric gas discharged during combustion, and of particulate matter produced per cycle of combustion in the chosen incinerator were estimated to be 12,051.86 m3 /cycle, and 2.17 kg PM/cycle of incineration respectively. The novelty in this design consisted in adapting the impingement plate type of wet scrubbing unit for dry adsorption of organic pollutants in smoke using locally-activated charcoal powder. The incorporation of powdered activated charcoal in the filter unit as adsorbent material significantly reduces the emission of harmful pollutants into the atmosphere. As a result, pollution of the environment is minimized. The smoke was sampled before and after filtration, and the samples were later tested in the laboratory for 14 polychlorinated biphenyls, namely PCB 18, PCB 28, PCB 31, PCB 44, PCB 52, PCB 101, PCB 118, PCB 138, PCB 149, PCB 153, PCB 170, PCB 180, PCB 194 and PCB 209. The three charcoal filter beds used in the evaluation study achieved target pollutant reductions in smoke ranging from 2.03 % - 71.85%. An Air Pollution Control Device with such pollutant reductions should justify the continued use of incinerators if they are properly mounted and secured on the incinerators and can curb the problem of air pollution from point sources.

Prediction and control of knock at high load boundary for HCCI engine based on neural network

Homogenous Charge Compression Ignition (HCCI) have drawn lots of attentions due to its high efficiency and low emissions. But HCCI engines are prone to random abnormal combustion phenomena at load boundaries. In this paper, innovatively implement online prediction and control of knock at high load boundary for HCCI utilizing only cylinder pressure as the diagnostic parameter based on neural networks. The results show that the neural network model with previous cycle heat release, previous cycle crank angle at 50 % cumulative heat release (CA50), peak cylinder pressure during previous and current cycle negative valve overlap (NVO) as inputs can realize the prediction of 87.5 % early combustion cycle in the intake phase before the early combustion occurs, and the diagnosis accuracy is 89.4 %. The frequency of early combustion can be reduced from 2.3 % to 0.3 % with the help of prediction model combining water injection and fuel injection reduction control, and no knocking occurs. The high load boundary of the HCCI engine is expanded by 7.1 % from 0.366 MPa to 0.392 MPa at 1500 r/min with the help of this control strategy.

Experimental detection of two-dimensional temperature distribution in Rocket-Based Combined Cycle combustion chamber using multispectral imaging processing

The extremely harsh environment and highly unsteady and transient nature during supersonic combustion bring great challenges for quantitative diagnostics. In the present work, for the first time, we report measurements of two-dimensional distributions of flame temperatures in a Rocket-Based Combined Cycle (RBCC) combustion chamber using a multispectral imaging technique with both spatial and spectral resolutions. The relation between the multispectral radiation intensity images and the flame 2-D temperature distributions was established by combing the Lvevenberg-Marquardt algorithm and the Hottel and Broughton emissivity models. The experimental results revealed that both laser-induced plasma (LIP) and plasma jet (PJ) torches had positive effects on combustion stabilization, and LIP had better effect on combustion enhancement. In the ignition stage of a fuel/air mixture with an equivalence ratio of 1.0, the average temperature of a flame initiated by LIP combustion enhancement was 100 K higher than that by PJ torch combustion enhancement. A recirculation zone was formed inside a cavity, which improved the combustion stability. The injected fuel and inflow were most fully mixed on the slope at the rear of the cavity, where 70 % and 65 % of the peak flame temperature points of LIP and JP were located, respectively. The combustion in the RBCC chamber showed an oscillation phenomenon that peak flame temperature and the flame structure oscillated continuously around the central axis with a horizontal extent of 162 mm. Due to the insufficient fuel blending, the oscillation amplitude was minimal when the equivalence ratio was 1.0. Overall, the results of flame temperature distributions demonstrated that the proposed multispectral thermometry was suitable for measuring temperatures of supersonic combustion flames.

Simulation Tool for the Development of a Staged Combustion Pellet Stove Controller

Optimizing the combustion control concepts on a pellet stove with very low heat output is time-consuming and costly. In order to shorten the required laboratory test time, a 0-D transient tool was developed within the ERA-NET project “LowEmi-MicroStove”, which simulates a 4 kW pellet stove with staged combustion and heat transfer. This approach was chosen in order to greatly simplify the description of the combustion processes and so reduce the computational complexity and simulation time. The combustion of a bed of pellets is modeled as a superposition of the combustion cycles of individual pellets, assuming no interactions between pellets. A test setup was developed and used to determine the ignition and burning cycle of individual pellets. The description of the CO emissions behavior is based upon an empirically grounded relation which is in turn based on the air/fuel ratio and the combustion chamber temperature. For the validation of the 0-D simulation results, a test rig for a 4 kW pellet stove was built. Despite its simplistic approach, good agreement was found between the simulation and 4 kW pellet stove test results for the mean values and temporal fluctuations of flue gas temperature and oxygen and carbon monoxide content during start up, stable operation and load changes. The simulation could thus be used to quantify the effect of air flow rates and distribution as well as load changes on performance and draw conclusions regarding different process control strategies. A control strategy which can operate the stove at high temperatures near the air stoichiometric limit with acceptable CO emissions has been proven to be the most promising. Additionally, the model can be used to quantify the effects of variations in other process parameters, for example the impact of fluctuations in the pellet feed. Due to its effectiveness and simplicity, this model approach can be applied for the development of control strategies for other staged, pellet combustion systems.

Cycling performance of composite hematite and copper ore oxygen carrier in chemical looping combustion

A single natural ore oxygen carrier (OC) has a limited industrial application due to its weak reactivity and cyclic stability. For the composite hematite and copper ore OC prepared by spray drying granulation, long-term chemical looping combustion (CLC) cycle tests were performed on a fluidized bed thermogravimetric analyzer (FB-TGA). The results showed that a substantial mechanical stress and the presence of partially enriched fine particles on the surface of new OC particles caused a high attrition rate of OC at the early stage of fluidization. After 6 min, the attrition rate of the particle was stabilized at 0.28 %/h. The OC was subjected to chemical and thermal stresses during the redox cycle reaction, which decreased the mechanical strength and increased particle attrition and sintering. The particle sintering also hindered the oxidation stage, which led to a deep reduction of OC to a lower valence state, which drove particle agglomeration and eventual defluidization. Therefore, lowering the oxygen transfer capacity and residence time in the fuel reactor is beneficial for the safe operation of OC in industry.

Parallel perturbation analysis of combustion cycle-to-cycle variations and emissions characteristics in a natural gas spark ignition engine with comparison to consecutive cycle method

Severe combustion cycle-to-cycle variations (CCVs) in spark ignition (SI) engines significantly increase partial or incomplete combustion cycles, which may result in combustion instability or even misfire under extreme conditions, thereby seriously affecting the engine performance and increasing the unburned hydrocarbon and carbon monoxide emissions. In this study, the consecutive cycle method (CCM) and parallel perturbation method (PPM) are utilized to simulate the CCVs in a natural-gas (NG) SI engine. Specifically, 25 consecutive and concurrent cycles of the SI engine are simulated, and simulation results are compared with the experimental data. Further, the factors affecting the CCVs and exhaust emissions in the NG SI engine are verified by analyzing the low-pressure (LP) and high-pressure (HP) cycles. The results indicate that the simulated in-cylinder pressures of the NG SI engine based on PPM are basically in agreement with the experimental in-cylinder pressure distribution range, which suggests that the PPM can effectively predict the CCVs in NG SI engines. Furthermore, the required wall clock time for the simulation of CCVs is greatly reduced from 1 to 2 months (using CCM) to 2–3 days by using the PPM, which makes it particularly suitable for the industrial applications. Besides, the velocity field of the HP cycle is obviously stronger than that of the LP cycle. During the early stage of flame development, the flame area and volume of LP and HP cycles do not show much difference. However, the flame front surface-volume ratio of the HP cycle is larger than that of the LP cycle at 15 CA after the spark timing. Furthermore, the emissions formation and oxidation of the NG SI engine are strongly depended on the HP and LP cycles due to the combustion rate and flame propagation in the cylinder.

Effects of injection pressure on the flame front growth in an optical direct injection spark ignition engine

• Optical diagnostics performed at wide open throttle and 1200 rpm conditions. • Elevated injection pressure does not monotonically increase engine output. • Higher spatial variation in turbulence measured for very high injection pressure. • Local overmixing and increased mixture inhomogeneity are likely causes. • Despite decreased power, soot is still lower at very high injection pressure. The fuel injection pressure of direct injection spark ignition (DISI) petrol engines has increased significantly to improve engine efficiency and reduce air-polluting emissions. The present study performs a detailed analysis of spray penetration, burn duration, flame front vectors and turbulence intensity to provide scientific explanations about the optimal injection pressure observed for the maximum power output/efficiency in a single-cylinder optically accessible DISI engine. Five injection pressures of 5, 10, 15, 20 and 25 MPa were tested based on an equal-split double injection strategy using a side-mounted six-hole direct injector. A high-speed camera with a 20 kHz frame rate was used to record spray development, propagating petrol flame and soot luminosity. The Mie-scattering technique was used to image the fuel dispersion under varied injection pressure and to calculate spray penetration. For time-resolved, two-dimensional flame front vector extraction, a newly developed flame image velocimetry (FIV) was applied to high-speed natural combustion luminosity movies. A spatial filtering method was also used for the flow decomposition to acquire flame front turbulence intensity. A total of 100 combustion cycles were FIV processed for each test pressure to tackle the inherent cyclic variations. The spray images showed that higher fuel injection pressure leads to faster spray tip penetration and enhanced spray evaporation for better air/fuel mixing. However, the in-cylinder pressure and power output do not continue to increase with an increase in injection pressure; they peak at 15 MPa and decrease at higher injection pressure. The spatially averaged flame front vector magnitude and turbulence intensity also peak at 15 MPa, indicating the optimal injection pressure was due to the maximum turbulent flame front growth. The distribution of turbulence intensity along the flame boundary shows increased variations at injection pressure higher than 15 MPa, because local over-mixing caused low turbulent flame growth regions. Although the highest turbulent flame front growth was not measured at 25 MPa, the soot luminosity was much lower than that of 15 MPa, which explains the development trend towards higher injection pressure.

Jet Characteristics of a Narrow Throat Pre-Chamber and Influence on the Main-Chamber Combustion

<div class="section abstract"><div class="htmlview paragraph">Lean combustion is one of the most applied methods to increase engine efficiency and maintain a good trade-off with engine emissions. The pre-chamber combustion (PCC) is one of the most promising combustion concepts to extend the lean operating limits of the engine. The Narrow throat pre-chamber has shown better lean limit extension compared to other ignition sources. The pre-chamber jets and the main-chamber combustion were studied in a Heavy-Duty optical engine using methane fuel. The tested conditions covered global excess air ratios (λ), between 1.9 to 2.3. The combustion process was recorded using three collection systems: (a) Natural Flame Luminosity (NFL) with a temporal resolution of 0.1 CAD; (b) OH* Chemiluminescence, and (c) CH* Chemiluminescence with a temporal resolution of 0.2 CAD for both. The propagating velocity of the reacting jets was studied using Combustion Image Velocimetry (CIV) based on bottom view images of the main chamber. After the pre-chamber jets ignite the main-chamber charge, a two-stage heat release rate (HRR) was observed for all the tested conditions. None of the three combustion visualizations exhibited a linear correlation with the HRR. The CIV reported high-speed jets penetrating around 400 m/s into the main chamber. The richest case of λ 1.9 presented a higher axial and radial propagation speed than the other cases. The individual vector fields have significant differences with the ensemble average fields, behavior characteristic of a high turbulent process. Finally, the ultra-lean case showed higher vorticity during the pre-chamber discharge, a synonym of high air-fuel entrainment that generates heavy waviness on the flame front. This heavy waviness generates local/partial or total extinction, resulting in abnormal combustion cycles.</div></div>

The Influence of Flow on Cycle-to-Cycle Variations in a Spark-Ignition Engine: A Parametric Investigation of Increasing Exhaust Gas Recirculation Levels

Cyclic variability is investigated in an optically accessible single-cylinder spark-ignition research engine by introducing artificial exhaust gas in controlled amounts to the homogenous air–fuel mixture before ignition. A skip-fire scheme ensures the absence of internal exhaust gas recirculation (EGR) and allows the engine to be fired continuously for acquisition of large statistics. Four operating conditions ranging from a stable 0% EGR case up to a highly unstable extreme EGR case are analyzed to examine the increasing effects of homogeneous EGR on the cycle performance. To that end, high-speed measurements of the velocity field via particle image velocimetry and flame imaging in the tumble plane allow the determination of phenomena leading to various flame positions and sizes as well as faster and slower combustion cycles. Through extensive conditional statistical and multivariate correlation techniques, flames are found to be heavily influenced by large-scale velocity motion, especially with the presence of greater EGR which leads to lower flame speeds. The greater sensitivity of slower flames to variations in the velocity field manifests itself in an exponential increase in cyclic variability of the maximum in-cylinder pressure and causes misfire cycles where the flame is blown off or quenched at the cylinder roof. In the most extreme cycles at the highest EGR level, the state of the large-scale velocity structures at the time of ignition determines whether the flame propagates towards the center of the cylinder (and is blown off or quenched) or if the flame sustains growth by propagating within the lingering tumble vortex.

Experimental study on combustion and emission characteristics of LIVC Miller cycle with asynchronous intake valves

An experiment was conducted to explore the performance, combustion, and emission characteristics of the Miller cycle by asynchronous late intake valve closing (LIVC) on a direct-injection turbocharged gasoline engine. Asynchronous LIVC Miller cycle uses geometric compression ratio (GCR) of 12.5:1 (Miller-CR12.5), compared with Otto cycle original engine with GCR of 12.5:1 (Otto-CR12.5) and 10:1 (Otto-CR10). The study indicates that one late intake valve closing can not only realize the Miller cycle but also control the load to effectively reduce the pumping loss. When the brake mean effective pressure (BMEP) is below 4 bar, Miller-CR12.5 shows a very short combustion duration and lower combustion cycle variation compared with the Otto cycle, which solves the problem of low combustion efficiency due to the low actual compression ratio of the Miller cycle. In addition, the Miller cycle of asynchronous LIVC is similar to that of synchronous LIVC, which all can improve knock resistance at medium and high loads. Based on the above factors, Miller-CR12.5 reduces fuel consumption, especially at low and heavy loads. Besides, Miller-CR12.5 shows great fuel-saving potential at high speeds. In terms of emissions, Miller-CR12.5 significantly increases CO and THC emissions within the range of tested loads, but the NOx emissions are reduced under low and high loads.

Perhitungan Desain Konsep Reaktor Cepat Berpendingin Karbondioksida Superkritis dan Berbahan Bakar Uranium Metalik Alam

This study discusses the design concept of the fast reactor core with supercritical carbon dioxide as coolant and natural metallic uranium as fuel that has been burnup for one hundred years. Calculations and simulations are performed using the SRAC code. The PIJ-SRAC module is for calculating the fuel cell level, and the CITATION-SRAC module is for calculating the reactor core level. Radial modified CANDLE is applied as a fuel arrangement strategy in the reactor core. The survey parameters were calculated in the form of burnup level, infinite multiplication factor (kinf), the density of fissile and fertile atoms, conversion ratio, and ef ective multiplication factor (kef ). The calculated reactor core thermal power varies from 400 MWt, 450 MWt, and 500 MWt. Based on calculation and simulation results, a reactor with thermal power of 450 MWt with geometry RZ (R = 150 cm and Z = 150 cm) is the best design. The calculation results show that the kef value from the beginning of the combustion cycle is around 1.002662 with a reactivity value of 0.2654%; until the end of the cycle, the kef value is 1.041057 with a reactivity value of 3.9437%.

(Invited) Renewable Hydrogen Systems Enable Deep Energy Decarbonization of Power and Transportation Sectors

Climate change is one of the most preeminent challenges facing the world. Continued fossil fuel energy consumption at the current trajectory will result in a temperature rise of more than 3.5°C by the year 2050. Melting glaciers, rising sea levels, wildfires, floods, and extreme weather events such as heat waves and large storms, are likely to become more frequent or more intense. The Paris Agreement is a legally binding international treaty to reduce carbon emissions which led to keep the global temperature rise well below 2°C [1]. This target cannot be achieved without deeply decarbonized energy production which focuses on three main factors: 1) Reducing energy consumption through improved efficiency (optimize), 2) Shifting energy demand to electricity and away from combustion of fossil fuels (electrify everything), 3) Shifting entirely to zero-carbon technologies such as solar photovoltaic (PV), wind, hydrogen, etc. to generate electricity (decarbonize). According to the United States (U.S.) Environmental Protection Agency (EPA), the largest contributors to anthropogenic U.S. greenhouse gas emissions in the descending order are transportation (29%), electricity (25%), industry (23%), agriculture (10%), commercial (7%), and residential (6%) [2].In our previous research, we focused on decarbonization pathways using utility solar, hydrogen consumption and production (electrolyzer, compressor, storage tank, and stationary fuel cells) for improved utilities operation without considering transportation sector demand [3]. Here the focus is on energy decarbonization for both power and hydrogen fueled transportation sector using hydrogen systems. To this end, a vertically integrated 33-node distribution network which is managed by distribution system operator (DSO) is optimized. The DSO manages all the assets in the network including natural gas power plants (combined cycle units and combustion turbine units), solar PV, distributed energy storage systems, hydrogen systems (including storage and refueling station) with the objective of cost minimization. Besides managing the aforementioned technologies, the DSO ensures safe and reliable operation of these assets by considering the technical and physical constraints of the network including voltage regulation, power flow and line congestion management, etc. The DSO in this study also manages the transportation sector hydrogen demand of fuel cell electric vehicles, medium- and heavy-duty vehicles.Simulation results show that hydrogen demand from the transportation sector is the main driver in sizing of hydrogen system components. Additionally, for the 33-node distribution network to fully supply heavy-duty vehicles demand, natural gas power plants must be operated to supply the required electricity for the electrolyzers to supply hydrogen for these vehicles. Furthermore, different sensitivity analysis for various PV and hydrogen demand penetrations will be presented.

Effects of intake charge temperature and relative air-fuel ratio on the deterministic characteristics of cyclic combustion dynamics of a HCCI engine

Homogenous charge compression ignition (HCCI) combustion can significantly reduce automotive pollution and increase the thermal efficiency of the engine. However, combustion phasing control is a major challenge in HCCI engines due to severe cyclic combustion variations. This study investigates the cyclic combustion dynamics of the HCCI engine using nonlinear dynamic methods such as return maps, recurrence plots (RPs), and recurrence quantitative analysis (RQA). Combustion stability and cyclic variations of HCCI combustion parameters were investigated on a modified four-stroke diesel engine. The experiments were conducted by varying relative air-fuel ratios ([Formula: see text]) and intake air temperatures ([Formula: see text]) at two engine speeds. In-cylinder pressure data of 2000 consecutive engine combustion cycles is logged for each test condition. In this study, deterministic characteristics of combustion phasing (CA50) and crank angle position of maximum cylinder pressure ([Formula: see text]) are investigated and compared by employing nonlinear dynamical methods. Return maps revealed that [Formula: see text] is having distinct and more frequently observed deterministic characteristics in comparison to CA50. Patterns in RPs showed a more persistent and sudden change in the combustion dynamics at higher engine speeds. Recurrence plot-based analysis found the existence of deterministic features in the combustion dynamics irrespective of the operating conditions. It was found using RQA parameters that the deterministic nature becomes stronger with a decrease in [Formula: see text] and any deviation in intermediate values of [Formula: see text]. Additionally, RQA measures advocate that CA50 has more deterministic characteristics at higher engine speed while [Formula: see text] at lower engine speed. Strong coupling and synchronization between [Formula: see text] and CA50 is indicated by cross-recurrence plots and CPR index when engine operated with a comparatively richer mixture.

Synthesis, characterization, and kinetic study of nanostructured copper-based oxygen carrier supported on silica and zirconia aerogels in the cyclic chemical looping combustion process

In this study, copper-based oxygen carriers (OCs) confined in the structure of silica and zirconia aerogels were in situ synthesized by a simple sol–gel method, and the performance of the prepared oxygen carriers was investigated in the chemical looping combustion (CLC) process. The effects of different support types and copper loadings (20–60 wt%) were studied on the physicochemical properties and catalytic behavior of OCs during 15 reduction–oxidation cycles at the temperature of 800 °C. Zirconia-supported oxygen carriers exhibited high reactivity and stability over the cycles. However, the OCs supported on silica showed lower oxygen capacity than the theoretically expected values. This is due to the decomposition of copper oxide (CuO) to Cupric (Cu2O) during the reaction along with the collapse and fuse of mesoporous silica at high calcination and reaction temperatures which leads to a significant loss of oxygen-carrying capacity. The kinetics of reduction/oxidation steps in the CLC process was studied using a modified grain model considering grain size distribution in the OC particles based on their pore size distribution profile and “pore to sphere” factor. The synthesized oxygen carriers were characterized by Brunauer-Emmet-Teller (BET), Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX).

A computational framework combining a basic turbulent combustion model, self-similar chemistry behavior, and a wall thermal law adapted for large-eddy simulations of a cyclically operating constant volume combustion chamber

The development of a computational tool capable of simulating and completing the experimental data obtained on a constant volume cyclic combustion (CV2) bench available at the Pprime Institute is the major objective of this study. The main difficulty is that, no matter how good the models used or the mesh refinement, specifying the boundary and initial conditions for the simulation of a specific cycle independently of the previous cycles requires an unattainable amount and accuracy of experimental data. In addition, high-fidelity simulation of all previous cycles is too costly. Developing a modeling framework compatible with coarse meshes for which the computational cost is reasonable is the first step necessary to simulate multiple cycles. However, the LES of CV2 presents numerous modeling difficulties due to the interactions of turbulent flow with fast and slow chemical reactions, compressible effects, walls and heat losses. Consequently, the wide spectrum of unresolved scales in the presence of so many correlated physical mechanisms leads to the introduction of several modeling parameters. Specific modeling developments are provided in this paper for turbulent combustion in the presence of residual burnt gases and the database takes into account the self-similar nature of the thermochemical properties. A detailed time-function for the inlet and outlet mass flow rates and a new blending function for the wall heat fluxes are also introduced. The sensitivity of the numerical results to the values of key modeling parameters such as injected air mass mair, ejected mass mout, segregation rate S∈[0.7;0.8], wall heat losses parameter κT∈[0.41;2.36] is studied. A quantitative comparison of the results and computational data is performed based on the pressure and heat flux signals in the case of propane-air combustion. The chamber pressure and temperature of air is 1 bar and 307K for the initial cycle. The calculated pressure profiles are in very good agreement with the experimental results. The values obtained for the calculated pressure peaks respectively for the first three reactive cycles are 17.4, 13.1 and 14.4 bars. For the experimental pressure peaks, the values obtained are 17.8, 14 and 14.6 bars which shows the validity of the modeling strategy. A qualitative comparison of the numerical results with other measurements, i.e PIV, flame visualization and MIE tomography, is also presented. The numerical results are then used to describe the flow during the successive phases, i.e injection, combustion and exhaust, of one specific cycle. Finally, the numerical pressure signal and wall heat flux obtained from the simulation of a sequence of ten cycles is compared to the experimental data. This last result demonstrates the ability of the LES tool to study the cycle-to-cycle variability observed in CV2 but further work is now required.

Direct Comparison of Schlieren and Soot Foil Measurements of Detonation Cell Sizes

Detonation-based combustion cycles have the potential to have higher thermodynamic efficiencies than the more common deflagration-based combustion cycles because the pressure of the products is higher than that of the reactants. The geometry to which a detonation is confined can have a strong influence on the detonation’s behavior, or even prevent a detonation from occurring. A key measurement that can be used to design detonation-based engines is the cell size of the mixture. The cell size is a characteristic length scale of a chemical mixture. For the first time, this study compares two methods of collecting cell size measurements within a single tube. This approach controls for the effects of tube geometry and surface roughness, which may confound studies whose schlieren and soot foil measurements have been collected from different tubes. This study indicates that measurements taken using the two measurement techniques agree to within experimental uncertainty (a difference of 1.3 mm, or 7%). Soot foil methods are generally preferable for detonation cell size measurements because soot foils provide larger triple point sample sizes per detonation and lower instrumentation costs relative to schlieren methods. Various sources of uncertainty are extensively analyzed and reported for the two techniques.

Field assessment of straw pellet combustion in improved heating stoves in rural Northeast China

Straw pellets are widely promoted and expected to be a cleaner alternative fuel to unprocessed crop residues and raw coal in rural China. However, the effectiveness of these dissemination programs is not well evaluated. In this field study, emission characteristics of burning straw pellets, raw coal, and unprocessed corn cobs in heating stoves were investigated in a pilot village in Northeast China. Emission measurements covering the whole combustion cycle (ignition, flaming, and smoldering phases) shows the promotion of improved heating stoves and straw pellets could reduce pollutant emissions (e.g., SO2 and CO), but increase NOX and PM2.5 emissions compared to the initial stove-fuel use pattern in the studied area. There is a significant variance in emission characteristics between different combustion phases. The normalized emission concentrations of the different stove-fuel combinations were higher than the limits in the Chinese national standard for heating stoves, indicating that the standard is not met for real-world emissions. Coal consumption was lower than official data. Household surveys were conducted to identify the barriers to fuel and stove access associated with existing promotion strategies, management, and policies. The pilot program was of the typical “subsidy-and-policy-dependence” pattern and was unlikely to be implemented on a large scale. Technological innovation, operational optimization, and proper policies considering the local socioeconomic factors are needed to sustain the promotion of biomass straw pellets and stoves.

Thermo-economic optimization of biomass-fired organic Rankine cycles combined heat and power system coupled CO2 capture with a rated power of 30 kW

Combining organic Rankine cycle (ORC) and biomass direct combustion to form a combined heating and power system (CHP) is a feasible technology to realize small biomass power generation. A small-scale biomass-fired ORC-CHP system with a rated power of 30 kW is proposed and the thermo-economic optimization under two operation strategies is discussed. The effects of key operating parameters on exergy efficiency and levelized energy cost (LEC) are analyzed. Meanwhile, a single-objective optimization for maximum exergy efficiency or minimum LEC is addressed, and a further thermo-economic optimization is examined. The Pareto-optimal solutions using three decision makings are yielded and compared. Research demonstrates that the exergy efficiency of model A increases with condensation temperature, while the exergy efficiency of model B first increases, reaches the peak, and then slightly decreases. The split ratio has a significant effect on model B. The Pareto-optimal solutions from TOPSIS decision making are selected because of its lowest deviation index. The Pareto optimal solution for models A and B in pairs of (exergy efficiency, LEC) are (19.69%, 0.2968) and (19.75%, 0.2975), respectively. Compared to model A, model B presents higher thermodynamic performance and slightly lower economic performance.

Расчетное исследование особенностей рабочего процесса в камере сгорания кислородно-метанового жидкостного ракетного двигателя, работающего по схеме с дожиганием восстановительного генераторного газа

We performed a numerical investigation of cumulative efficiency and the structure in detail concerning the working process in the combustion chamber of a lox/methane liquid-propellant rocket engine operating in steady-state, boosted and throttled modes. In order to do it, we used tools developed by JSC SSC "Center Keldysh", that is, physical and mathematical models, numerical methods and software packages for numerical simulation of two-phase turbulent flows with combustion in liquid-propellant engine combustion chambers. The paper presents numerical simulation and investigation results concerning the specifics of fuel component flows, their mixing and combustion in the combustion chamber of a lox/methane liquid-propellant rocket engine using staged combustion cycle with reductant gas in steady-state, boosted (117 % by thrust) and throttled (30 % by thrust) operation modes. We performed a comparative analysis of work cycle parameters in combustion chambers at different fuel component consumption rates and pressure levels. The paper shows that the boosted mode increases the interaction of fuel jets, which intensifies mixing and burnout processes, while the deep throttling mode decreases the mixing and fuel burnout amplitudes as compared to the steady-state mode. The numerical simulation results may be used to investigate fuel combustion processes in combustion chambers of promising liquid-propellant rocket engines at the stages of development, design and refinement