Heat Release Pattern Research Articles

Numerical Investigations on Reducing Unburned Hydrocarbon and Carbon Monoxide Emissions in Reactivity-Controlled Compression Ignition Using Partial Reactivity Stratification with Alternative Fuels and Additive

<div>A numerical investigation has been performed in the current work on reactivity-controlled compression ignition (RCCI), a low-temperature combustion (LTC) strategy that is beneficial for achieving lower oxides of nitrogen (NO<sub>x</sub>) and soot emission. A light-duty diesel engine was modified to run in RCCI mode. Experimental data were acquired using diesel as HRF (high-reactivity fuel) and gasoline as LRF (low reactivity fuel) to check the accuracy and fidelity of predicted results. Blends of ethanol and gasoline with DTBP (di-tert-butyl peroxide) addition in a small fraction on an energy basis were used in numerical simulations to promote ignitability and reactivity enhancement of PFI charge. Achieving stable, smooth, and gradual combustion in RCCI is challenging at low loads, especially in light-duty engines, due to misfiring and poor combustion stability. DTBP is known for enhancing cetane number and accelerating combustion, and it is mixed in a PFI blend to avoid combustion deterioration. The factors governing reactivity stratification to achieve optimal combustion phasing were investigated in the present study. DTBP decomposition and its low-temperature oxidation chemistry were found to be responsible for affecting combustion phasing, heat release patterns, and emission trends. DTBP additive and different in-cylinder strategies were applied and studied to reduce unburned emissions. Adopting a multiple injection approach utilizing dual-pulse assisted in reducing HC and CO levels. It enhances combustion quality by providing adequate control over combustion phasing. Altering operating parameters like intake temperatures reduced HC, CO, and soot emissions by 97.6%, 57.6%, and 52.8%, respectively, compared to baseline gasoline/diesel RCCI data. Optimizing the injection timings of the first and second pulse helps achieve optimal combustion phasing and a 72.95% reduction in NO<sub>x</sub> emissions. The higher injection pressure of DI helped lower the CO and soot emissions by 53.33% and 51.84%, respectively.</div>

Intermittency transition to azimuthal instability in a turbulent annular combustor

We experimentally study the transition from a state of combustion noise to azimuthal thermoacoustic instability in a laboratory-scale turbulent annular combustor. This combustor has sixteen swirl-stabilized burners to facilitate continuous and spatially distributed combustion along the annular region. Our approach involves simultaneous measurement of CH* chemiluminescence emission of the flame using two high-speed cameras and the acoustic pressure fluctuations using eight piezoelectric pressure transducers mounted on the backplane of combustor. We observe that the transition from combustion noise to azimuthal instability occurs through mode shifting, where the system switches from a longitudinal mode to an azimuthal mode as the equivalence ratio is decreased. Throughout this progression, the combustor exhibits various dynamical behaviors, including intermittency, dual-mode instability, standing azimuthal instability, and beating azimuthal instability. These dynamical states are determined from the acquired pressure signals by decomposing the acoustic pressure fluctuations into clockwise (CW) and counterclockwise (CCW) waves, enabling a reconstruction of the amplitude of acoustic pressure fluctuations, nature angle, (anti-)nodal line location, and spin ratio. The global heat release response is then examined during various dynamical states, contrasting their behavior at different non-dimensional time steps by phase-averaging the fluctuations of the heat release rate over the acoustic pressure cycle. Distinctive flame behaviors were observed based on the direction of pressure wave propagation, showcasing characteristic CCW spinning, standing, and CW spinning heat release patterns. Moreover, our examination of relative phase distributions during various dynamical states, computed by analyzing the phase of heat release rate fluctuations across all burners with respect to one burner, reveals the emergence of diverse patterns in the interaction of neighboring flames influenced by acoustic field.

Алкилмен алмастырылған фенолдар негізіндегі түрлендіргіш қоспа

This article explores the utilization of mixtures in the production of cellular concrete, leveraging alkyl-substituting phenols to attenuate the wetting impact of cement. Incorporating alkyl-substituting phenols enables the preservation of cement with low alkali and aluminum content for extended durations compared to those with higher levels of tricalcium and alkali additives. Investigation into the heat release patterns during the wetting of various cements revealed additional alternative effects: high alkali content cements diminish calcium impurities in aqueous acid within the liquid phase, while high aluminum content cements exhibit reduced moistening of aluminates. Both of these alternative effects collectively demonstrate that tricalcium aluminates and tricalcium silicates mitigate the influence of humectant carbonate acid on the hydration process.

Analyzing Burner Performance and Combustion Phenomenon in an Olefin Plant's Industrial Furnace: A CFD Study.

This work presents a comprehensive study of the combustion performance of an industrial furnace in an olefin plant using computational fluid dynamics (CFD) simulations. The focus was on analyzing the heat release pattern of bottom burners to optimize the furnace efficiency in steam-cracking processes. The study developed an accurate computational fluid dynamics (CFD) model for predicting combustion behavior in a cracking furnace. The computational model was validated by comparing the simulation results with industrial data and was used to investigate the impact of burner clogging and the importance of small holes in the body of burners in the furnace. The results also provided insights into the influence of excess air, temperature distribution, fluid behavior, composition of combustion products, and thermal efficiency of the furnace. The presented results contributed to a better understanding of parameters controlling combustion performance in steam-cracking furnaces.

Influence of fuel characteristics on the alternative jet fuel atomization at non-reacting conditions

Synthetic paraffinic kerosene jet fuel derived from natural gas (NG-SPK) is gaining importance as a low-emission alternative fuel for aviation combustors. In this context, the influence of fuel properties on the atomization of NG-SPK jet fuel at non-reacting, evaporating conditions is investigated. The spray results of NG-SPK jet fuel are compared with the reference, Jet A-1 fuel. This study considers a simplex atomizer, commonly deployed as a pilot injector in aviation gas turbine combustors for ignition at sea level and in high-altitude relight conditions. The local atomization characteristics like droplet concentration, mean diameters, and mean axial droplet velocity is obtained experimentally using phase Doppler anemometry technique at different ambient gas pressures of 100, 500, and 900 kPa while maintaining the ambient temperature at 400 K. The fuel dispersion parameters are measured at two nozzle pressure differentials of 300 and 900 kPa. The NG-SPK jet fuel exhibited higher droplet concentrations for the conditions studied than conventional fuel. Furthermore, the droplet size distribution of NG-SPK jet fuel revealed a higher percentage of smaller droplet diameters than Jet A-1 fuel. This difference in droplet characteristics can positively influence the heat release patterns under reacting conditions.

Quality of moxa from Artemisia argyi and A. stolonifera in different storage years based on simultaneous thermal analysis

The quality of moxa is an important factor affecting moxibustion therapy, and traditionally, 3-year moxa is considered optimal, although scientific data are lacking. This study focused on 1-year and 3-year moxa from Artemisia stolonifera and A. argyi(leaf-to-moxa ratio of 10∶1) as research objects. Scanning electron microscopy(SEM), Van Soest method, and simultaneous thermal analysis were used to investigate the differences in the combustion heat quality of 1-year and 3-year moxa and their influencing factors. The results showed that the combustion of A. stolonifera moxa exhibited a balanced heat release pattern. The 3-year moxa released a concentrated heat of 9 998.84 mJ·mg~(-1)(accounting for 54% of the total heat release) in the temperature range of 140-302 ℃, with a heat production efficiency of 122 mW·mg~(-1). It further released 7 512.51 mJ·mg~(-1)(accounting for 41% of the total heat release) in the temperature range of 302-519 ℃. The combustion of A. argyi moxa showed a rapid heat release pattern. The 3-year moxa released a heat of 16 695.28 mJ·mg~(-1)(accounting for 70% of the total heat release) in the temperature range of 140-311 ℃, with an instantaneous power output of 218 mW·mg~(-1). It further released 5 996.95 mJ·mg~(-1)(accounting for 25% of the total heat release) in the temperature range of 311-483 ℃. Combustion parameters such as-R_p,-R_v, D_i, C, and D_b indicated that the combustion heat quality of 3-year moxa was superior to that of 1-year moxa. It exhibited greater combustion heat, heat production efficiency, flammability, mild and sustained burning, and higher instantaneous combustion efficiency. This study utilized scientific data to demonstrate that A. stolonifera could be used as excellent moxa, and the quality of 3-year moxa surpassed that of 1-year moxa. The research results provide a scientific basis for the in-depth development of A. stolonifera moxa and the improvement of moxa quality standards.

Observation of reactive shear layer modulation associated with high-frequency transverse thermoacoustic oscillations in a gas turbine reheat combustor experiment

This paper presents the investigation of high-frequency thermoacoustic oscillations and associated flame dynamics in an experimental gas turbine reheat combustor at atmospheric pressure. Examination of dynamic pressure measurements reveals bursts of high-frequency periodic oscillations which appear randomly amidst stochastic fluctuations in the reheat combustor. Analysis of the flame dynamics during these bursts of periodic behaviour reveals that increased heat release in the reactive shear layers of the reheat flame is associated with greater thermoacoustic driving potential. This redistribution of heat release is likely due to the stochastic nature of auto-ignition kernel formation. To determine the underlying flame-acoustic coupling mechanism behind the driving potential, phase-resolved flame dynamics over the acoustic cycle are investigated which reveal the presence of an oscillatory heat release pattern associated with the first transverse eigenmode. An in-phase interaction between the acoustic field and these heat release oscillations in the shear layer regions indicates that this phenomenon likely constitutes a thermoacoustic driving mechanism. This is an important step towards the development of models for high-frequency thermoacoustic driving mechanisms relevant to reheat combustion systems, which will allow accurate prediction and mitigation of thermoacoustic instabilities in future designs.

Adjacent combustion heat release and emissions over various load ranges in a premixed direct injection diesel engine: A comparison between gasoline and ethanol port injection

In a premixed diesel engine, supplementary fuels (gasoline and ethanol) are individually premixed by port fuel injection prior to induction and combustion in the main diesel-injected combustion chamber. This study compared emissions and heat release patterns adjacent to the combustion stroke of a premixed diesel engine. A single-cylinder direct injection diesel engine was examined by varying the ratios of the supplementary fuel to diesel quantity to meet the set loads. The engine's target speed was 1600 rpm, and the brake mean effective pressures of 2, 5, and 7 bar were loads representing low-, medium-, and high-load operations, respectively. Results show that the gasoline premixture yielded higher thermal efficiency than the ethanol premixture. When the quantity of gasoline supplementary fuel increased, the thermal efficiency increased, whereas the opposite trend was observed with ethanol. The combustion phasing was delayed by increasing both supplementary fuel ratios. Quantities of nitrogen oxides, smoke, and total unburned hydrocarbon were reduced, and carbon monoxide increased with the elevated quantity of port-injected fuel. The ethanol–diesel dual fuel is advantageous regarding smoke opacity, but it suffers from nitrogen oxides trade-off.

Expansion heat release and thermal efficiency of acetone-butanol-ethanol-diesel blended fuel (ABE20) combustion in piston engine

The intermediate product of the butanol production process, acetone-butanol-ethanol (ABE) mixture, is a promising alternative fuel for diesel engine as its physical properties are resemble to diesel fuel. This study explores heat release pattern and thermal efficiency as a consequence of combustion of the 20% v/v ABE blended with diesel (ABE20) in a stock single-cylinder diesel engine. All parameters were studied in steady-state condition of medium and full loads at a constant engine speed of 1400 rpm. ABE20 presents a slightly lower thermal efficiency with comparable energy consumption compared to diesel fuel. A longer ignition delay was observed for ABE20 and the diffusion combustion regime was shortened in duration. The cylinder pressure-derived heat release in the expansion stroke discloses a different specific heat ratio during ABE20 combustion.

Experimental analysis of effective combustion heat release rate for improving the performance of synthetic biogas-diesel dual-fuel engine

ABSTRACT To analyze the effect of combustion mode on performance and emission characteristics of dual-fuel engines, an experimental study of heat release rate is conducted for biogas as main fuel. Parametric investigations are needed to establish the effect of heat release rate on performance of dual-fuel engines. A new parameter, Combustion Time Coefficient (CTC), is defined to quantify the combustion timing and heat release patterns to study its effect on the performance parameters. It is used along with a heat release rate (HRR) related coefficient, called as HRR-Balanced Coefficient (HBC). These combustion indicators are used for experimental analysis of reactivity-controlled compression ignition (RCCI) strategies for biogas diesel dual-fuel engine. Experiments were performed on a variable compression ratio, single-cylinder compression ignition (CI) engine run on dual-fuel mode. Synthetic biogas energy shares of 0%, 20%, 40%, 60%, and 80% are provided for RCCI at various compression ratios of 18, 17, 16 ,and 15. The results show that an increase in CTC and a reduction in HBC have a positive effect on BTE, HC, and CO emission, while emissions of NOx increase. The ranges of CTC and HBC are found for low- and high-load conditions to reduce emissions and enhance the performance of the engine. A set of working and design parameters like compression ratio (CR), percentage energy share (PES) of biogas and load are identified to maintain the CTC and HBC within these ranges. For low-load operations, PES of 60% with 18 CR and for full load operations PES of 40% with 17 CR give the favorable performance. For the full range of the loads, CTC and HBC are good parameters to identify the operating range of PES and CR for dual-fuel engines.

Microscopic spray measurements of non-reacting alternative jet fuel: Effect of ambient gas temperature

The volatile characteristics of alternative Gas-to-Liquid (GTL) jet fuel and conventional Jet A-1 fuel are significantly different due to their chemical composition variations. This difference can have a strong influence on the atomization performance at elevated ambient gas temperature conditions. Because the atomization process plays a vital role in fuel distribution inside the combustor, which ultimately affects heat release and emission patterns. The objective of the present work is to investigate the effects of ambient gas temperature and nozzle pressure differential on the non-reacting, microscopic spray performance of the alternative jet fuel using a pressure-swirl nozzle, and then, compare these effects to those of Jet A-1 fuel. Specifically, this study investigates the droplet size, velocity and distribution, by employing the Phase Doppler Anemometry technique to measure these parameters at several radial and axial locations downstream of the nozzle exit. The effect of ambient gas temperatures is studied at 300, 350, and 400 K at two nozzle pressure differentials, 300 and 900 kPa, while maintaining a constant ambient gas pressure and fuel temperature. Results show that, in the region investigated, there is a significant difference between the spray performances of GTL and Jet A-1 at elevated operating conditions. The outcomes of this study will add new knowledge to the limited scientific literature on the effect of ambient gas conditions on the local spray parameters of alternative jet fuel.

Numerical investigation of the local and global supersonic combustion characteristics of ethylene fuel

In supersonic combustors, cavities play an active role in the process of fuel injection and flameholding. This study numerically investigates the influence of chemical kinetics on the local and global heat release predictions of supersonic combustion of ethylene. To this end, three-dimensional compressible, turbulent, Favre-averaged Navier-Strokes reacting-flow calculations have been carried out with a single-step chemistry model and a multi-step chemistry model. The reacting flow calculations have been performed with and without the presence of an inclined cavity in a model supersonic combustor. The heat release patterns obtained using the single-step and multi-step chemistry are compared. Furthermore, the heat release patterns are correlated with the variation of reaction rates involved in different chemistry models. In addition, the overall performance metrics such as mixing efficiency and combustion efficiency are used to draw inferences on the nature (whether mixing- or kinetic-controlled) and the completeness of the combustion process. The predicted values of the dimensionless wall static pressure are compared with experimental data reported in the literature. The calculations show that not only the multi-step chemistry model predicts the heat release better than single step chemistry, but also, the intricate details of the combustion process inside the combustor configurations.

Experimental insight into co-combustion characteristics of oxygenated biofuels in modified DICI engine

The co-combustion of fuel has substantial advantages when compared to normal combustion and it requires very little modification. In this perspective, ethanol supplement co-combustion with biodiesel is proposed. The co-combustion characteristics were studied by manifold induction of vaporized ethanol and direct injection of waste cooking oil biodiesel. A vaporizer system was fabricated to produce vaporized ethanol in a volumetric basis (10% and 20%, respectively). It was revealed from the experiments that with co-combustion of oxygenated biofuels, the combustion advanced and peak pressure shifted to TDC. The pressure rise rate decreased with the increase of vaporized ethanol induction and the maximum rate of pressure rise reduction was noted with biodiesel-20% ethanol induction which was 4% lower than biodiesel-10% vaporized ethanol induction. On the other hand, the maximum rate of heat release rate (60.24 J/°CA) was seen in biodiesel with 20% ethanol induction. Furthermore, the co-combustion studies disclosed a two-stage heat release pattern (low temperature and high temperature reactions). It was observed that the increase in ethanol concentration extended low temperature region by 1° crank angle and retarded high temperature region by 3° crank angle.

Isothermal Microcalorimetry of Tumor Cells: Enhanced Thermogenesis by Metastatic Cells.

Tumor cells exhibit rewired metabolism. We carried out comparative analyses attempting to investigate whether metabolic reprograming could be measured by isothermal microcalorimetry. Intact metastatic cell lines of tongue cell carcinoma, human and murine melanoma, lung, and breast tumors consistently released more heat than non-metastatic cells or cells displaying lower metastatic potential. In tongue squamous carcinoma cells mitochondrial enriched extract reproduced the heat release pattern of intact cells. Cytochalasin D, an actin filament inhibitor, and suppression of metastasis marker Melanoma associated gene 10 (MAGEA10) decreased heat release. Uncoupling protein 2 was highly expressed in metastatic cells, but not in non-metastatic cells. Carnitine palmitoyl transferase-1 inhibitor, Etomoxir strongly inhibited heat release by metastatic cells, thus linking lipid metabolism to thermogenesis. We propose that heat release may be a quantifiable trait of the metastatic process.

An investigation into the heat release and emissions from counterflow diffusion flames of methane/dimethyl ether/hydrogen blends in air

In the present work, the effects of blending dimethyl ether (DME) and hydrogen (H2) with methane (CH4) have been numerically studied in the context of counterflow diffusion flames. In order to do so, a reaction mechanism consisting of 974 reaction steps among 146 species with updated thermodynamic and transport properties has been developed. This mechanism has been validated against the experimental data on laminar burning velocity, ignition delay time and species profiles in counterflow diffusion flames. The present study suggests that the heat release pattern of the CH4 counter flow diffusion flame shows major changes when DME and H2 are present in the fuel stream. Furthermore, the results show that the presence of low volume fractions of DME in CH4 increases the formation of benzene (C6H6) in the flame. This fact can be negated by the presence of H2 together with CH4 and DME in the fuel stream. Moreover, the present study suggests that H2 mitigates the C6H6 formation in the CH4 diffusion flame with greater effectiveness compared to DME. Contrary to the popular belief, the main reason behind such efficacy of H2 has been found to be physical rather than chemical. On the other hand, the NO production routes are primarily dominated by the Zeldovich mechanism in the flames involving CH4, DME and H2 blends. In this regard, the present analysis suggests that the simultaneous presence of DME and H2 in CH4 effectively prevents the formation of NO in the flame.

Effect of aeration and agitation on yeast inulinase production: a biocalorimetric investigation.

Air flow rate and agitation speed for inulinase production by Kluyveromyces marxianus were optimized based on metabolic heat release profiles. Shear stress and oxygen transfer (kLa) values were compared to assess the effects of aeration and agitation. At agitation rates of ≤ 100rpm, the oxygen mass transfer rates were small and eventually led to less inulinase production, but at agitation rates > 150rpm, loss of biomass resulted in less inulinase activity. Bio-reaction calorimeter (BioRc1e) experiment with aeration rates ≤ 0.5 lpm showed low kLa while at 1.5 lpm frothing of reactor contents caused loss of biomass and inulinase activity. The optimum conditions for aeration and agitation rate for K. marxianus in BioRc1e were 1 lpm and 150rpm. Heat yield values obtained for the substrate, product and biomass reinstated the ongoing metabolic process. The heat release pattern could be a promising tool for optimization of bioprocess and in situ monitoring, with a possibility of interventions during the biotransformation process. At optimized aeration and agitation conditions, a two-fold increase in inulinase activity could be noticed.

Flame dynamics of azimuthal forced spinning and standing modes in an annular combustor

Azimuthal forcing has been applied to flames in a laboratory scale annular combustor in order to accurately control the azimuthal mode of excitation. A new forcing configuration permitted not only the pressure amplitude, but also the spin ratio and mode orientation to be accurately controlled, in order to generate standing modes and for the first time strong spinning modes in both a clockwise (CW) and anti-clockwise (ACW) direction. The phase averaged heat release dynamics of these modes was compared and a number of differences observed depending on the direction of pressure wave propagation, demonstrating characteristic ACW and CW heat release patterns. A new spin compensating averaging method was then introduced to analyse the flame dynamics, and it was shown that through the application of this method the dynamics of standing wave oscillations could be decomposed to recover the characteristic ACW and CW heat release responses. The global heat release response was also assessed during strongly spinning modes, and the magnitude of the response was shown to depend strongly on the direction of propagation, demonstrating the importance of the local swirl direction on the global heat release response, with important implications for the modelling of such flows.

Combustion Variation Feedback Control Approach for Multi-cylinder Spark Ignition Engines

Lean-burn is an important advanced technology that is of benefit to the efficiency improvement of spark ignition (SI) engines. However, the combustion variation is a major barrier to achieving leaner air/fuel ratio. This paper presents an in-cylinder pressure-based multi-cylinder multi-variable combustion variation control strategy for SI engines, aims at controlling the combustion to the target heat release pattern (HRP). The combustion phase and total heat release are chosen as the control parameters which are controlled by adjusting spark advance (SA) and fuel injection mass, respectively. Two separate closed-loop statistical controllers are designed for SA and fuel injection control of single cylinder. The designed controllers are then applied to every individual cylinder. The effectiveness of the presented combustion variation control strategy is finally validated on a production four-cylinder SI gasoline engine at lean-burn mode.

Metabolic pathway and role of individual species in the bacterial consortium for biodegradation of azo dye: A biocalorimetric investigation

In this study, an attempt was made to investigate the functional role and metabolic behaviour of the monoculture (Staphylococcus lentus (SL), Bacillus flexus (BF) and Pseudomonas aeruginosa (PA)) in the bacterial biocenosis for biotransformation of an azo dye. The power-time profile obtained from consortia depicted three distinct peaks, which correlated well with the individual bacterial growth (PA > SL > BF), indicating the synergistic relation and division of labour in the biocenosis. The heat release pattern was used to identify the sequential behaviour of microbial consortia in real time. Yield calculation based on total heat liberated to the complete substrate utilization Y (Q/S) for PA, SL, and BF were 15.99, 16.68, 7.32 kJ/L respectively. Similarly, the oxy calorific values Y (Q/O) for the above species are respectively 386, 375, 440 kJ/mol and indicates the aerobic nature of microorganism employed. Further, the metabolome produced during the biotransformation were identified using Gas Chromatography-Mass Spectrometry (GC-MS), based on which a plausible pathway was predicted. The abundant metabolites were palmitic acid (m/z = 256) and diethyl phthalate (m/z = 222.2). The abundance of diethyl phthalate was much lesser in the consortia compared to the monoculture. Thus, the biocalorimetric heat yield calculation along with the stoichiometry and plausible pathway based biochemical elucidation provides a mechanistic basis for understanding the azo-dye biotransformation by the monocultures in consortia.

Effect of Heat Release Pattern during Flame Propagation on Auto-ignition Process of End-gas

Effect of Heat Release Pattern during Flame Propagation on Auto-ignition Process of End-gas