Excess Air Research Articles

Insights into syngas-fueled Wankel rotary engine performance from varied CO/H2 ratio

Syngas is a fuel with a huge market and low carbon emission, which has been proven to be well applied to internal combustion engines. WRE with high power density can effectively improve the power characteristic when syngas is employed as fuel in engines, however, which has not been reported publicly. This work aims to provide insights into the performance of syngas-fueled WRE under different CO/H2 ratios and thus gives theoretical guidance for its application. The test is done at 1500 r/min and part load. It is found that with the increase of the volumetric ratio of CO in syngas (CO%), the efficiency, torque and carbon emissions are deteriorated, however, the NO emission is significantly improved and the knock level is also reduced. In addition, on the premise of constant CO%, a high brake thermal efficiency, low NO emission and knock intensity can be achieved at lean combustion. In particular, when CO% is 10%, the combustion efficiency of CO is independent of the excess air ratio, while when CO% is 20%, that is decreased with increasing excess air ratio. In summary, the syngas-fueled WRE is recommended to adopt the qualitative control and the syngas with low CO%.

Numerical study of the effects of excess air ratio on passive pre-chamber jet performance and ignition mechanism

Pre-chamber (PC) ignition is a promising lean-burn technology to improve the efficiency of spark ignition (SI) engines while achieving ultra-low NOx emissions. However, the significant effects of the excess air ratio (λ) on the PC jet performance and ignition mechanism were still not fully unraveled. The current study numerically investigated the jet characteristics and combustion behaviors of a narrow-throat PC with two rows of orifices on a passive PC engine fueled with methane. The numerical model was validated extensively by the pressure, heat release rate, and natural flame luminosity (NFL) imaging of the PC flame jet. A detailed comparison of the NFL images of the jets and the simulated flame iso-faces presented excellent matching in the flame jet penetration and propagation process. The results reveal that the λ = 0.9 case has the best jet performance, but it doesn’t lead in every jet characteristic. For instance, the jet temperature is highest under λ = 1.0, and OH concentration is most under λ = 1.1. The transition from cold jet to flame jet produces noticeable jet non-uniformity, which is reported for the first time. This observation can be remarked as a more accurate indication of the initiation of pre-chamber flame jet discharge. The asymmetrical mixture inflow from the main chamber produces asymmetrical turbulent kinetic energy (TKE) and temperature distributions; these result in different flame propagation in the PC, jet non-uniformity, and varied stages of jet discharge. The upper jets are quenched in every case because of the much higher TKE, while the lower jets don’t present quenching when the λ ranges from 0.9 to 1.3; especially, the λ = 1.1 case has the best ignition performance for its most OH radicals. The “jet ignition regime”, in which flame quenching takes place, results in highly non-uniform flame propagation and low flame propagation speed. The ultra-rich case shows more signs of jet ignition and thus exhibits worse jet performance than the lean cases. This study uncovers the mechanisms and the optimal λ value for the pre-chamber ignition of the main chamber charge, providing valuable guidance for PC design.

The Development and Investigation of the Diffusion-Stabilizing Burner with the Niche

The article presents the results of researches of the development and field tests in bench conditions of the microdiffusion stabilizer burner device of a rectangular slot type with a niche deepening along the entire perimeter of the burner. The air passes through a rectangular slot, gaseous fuel for combustion is supplied to the recirculation zone through a system of holes in the end wall of the stabilizer. On the side of the output end of the stabilizer, there is a niche deepening. As studies have shown, the niche deepening is an additional source of stabilization and intensification of torch burning. The experimental data and calculated dependences on the stabilization of the torch in the modes of “poor” disruption are obtained. It is shown that the stable operation of the burner on the lean limit expands – the coefficient of excess air increases with an increase in the width of the stabilizer, the diameter of the gas distribution holes, the coefficient of shading of the burner and air temperature, as well as with a decrease in the speed of the air flow. The research results showed that “rich” flame failure – flame failure with a gradual increase in gas flow occurs at air excess ratios less than unity. This ensures the reliable operation of the burner at the calculated operating modes with respect to the coefficient of excess air a = 1.15 – 6.0 and the air flow speed Wp = 12.0 m/s. A dependence was obtained that determines the influence of regime and design factors on the characteristics of a rich flare failure. The sustainability of the burner operation on the rich limit increases – the coefficient of excess air decreases, with an increase in the width of the stabilizer, the shading coefficient of the burner, air temperature and a decrease in air velocity. The experimental data and calculated dependences on the length of the combustion zone in the burner device are obtained. It was established that at the calculated coefficient of excess air a = 2.0 and higher coefficients, complete combustion of fuel occurs on the length of the combustion space X = 1000 mm. The relative length of the flame decreases when the shading coefficient of the burner and the air temperature increases. Measurements of harmful nitrogen oxides showed that the maximum content of oxides is observed at the coefficient of excess air a = 1.0 and is 125 mg/m3, which is less than the limit values which allowed by regulatory documents.

Study on mixing and combustion characteristics of solid rocket ramjet with a large angle of attack

Solid rocket ramjet faces the problems of large angle maneuvering and stage transformation in the actual operation. In order to study the effect of the change of angle of attack and excess air coefficient on the performance of boron-containing solid rocket ramjet, the fluid field with different conditions were calculated. The applicability of the numerical model was verified by ground direct-connected experiments. The results showed that as the angle of attack increases, the mixing in the head reflux area and the initial air-gas contact area are enhanced. The combustion ratio of combustible components in the front section is greatly increased, which helps to improve the combustion efficiency of the motor. When the excess air coefficient increases from less than 1 to much greater than 1, the mixing combustion in the head region is also strengthened. However, the radial impact of excess air causes the gas to deflect to the upper side of chamber, and then most of the particles move close to the wall, resulting in a lower level of combustion. The general trend is as follows, under the same mixing-dominated pattern, the average mixing at the outlet decreases with increasing angle of attack, and the combustion efficiency is reversed. Under different mixing-dominated patterns, higher combustion efficiency can be obtained at lower mixing when the head region dominates.

Combustion and emission characteristics of dimethyl ether/gasoline DFSI engine under different excess air coefficients

Dimethyl ether (DME) was a carbon neutral alternative fuel for engines.The combustion and emission characteristics of a DME/gasoline Dual Fuel Spark Ignition (DFSI) engine with various excess air coefficients (λs) at different DME ratios (ΦDME) were investigated experimentally in this study.The in-cylinder pressures along with their relevant crank angle were used for the combustion characteristics calculation. The light five component exhaust gas analyzer and particle analyzer were employed for the gaseous and particulate matter emission measurement, respectively. Results showed that the DME/gasoline dual fuel combustion strategy can enhance the Brake Mean Effective Pressure (BMEP) by up to 12.6% because the high diffusivity, superior LTR and fast LFS of DME. Although adding DME was beneficial for the reduction of gaseous emissions (HC, CO and NOx) from DME/gasoline DFSI engines, the gaseous emissions were mainly determined by the variation of λ s. Particularly, up to 93.4% of the CO emissions at stoichiometric condition can be reduced after increasing λ to 1.3. The fast evaporation rate and superior LTR of DME helped to suppress PN emissions, but larger DME ratio (ΦDME > 5%) was needed for λ >1.2.

Experiment and Numerical Simulation Study of Low-Nitrogen Combustion Technology Inside Small Gas Boiler

Abstract This paper studies different experimental conditions for a 25t/h industrial boiler fueled with nature gas. In the meanwhile, numerical simulation is carried out using the commercial software of fluent. The different excess air coefficients of 1.05, 1.1, 1.15, 1.2, and 1.25 are studied. The different flue gas circulation rates of 5%, 10%, 15%, and 20% are studied compared with that rate of 0. The results show that the maximum temperature of the furnace and NOx emission concentration at the outlet increase first and then decrease with increasing excess air coefficient when flue gas circulation rate is 0, and the peak value of temperature and NOx emission concentration reaches 2071.93 K and 65.21 mg/m3 when excess air coefficient is 1.15, respectively. With increasing flue gas circulation rate, the average temperature of the furnace and the concentration of NOx at the outlet decreased, and the concentration of NOx decreased from 65.21 mg/m3 to 25 mg/m3. The higher the flue gas circulation, the smaller the high-temperature area of the furnace and the lower concentration of O2. However, excessively higher flue gas circulation rate and excess air coefficient can lead to incomplete combustion and lower coefficient. Hence, for optimizing the combustion conditions, the excess air coefficient and the flue gas circulation rate should be within an appropriate range.

Experimental study on combustion and emission of ternary-fuel combined supply SI engine with oxyhydrogen/butanol/gasoline at different excess air ratios

Both oxyhydrogen and butanol are renewable alternative fuels. Based on gasoline/butanol compound injection mode, although the introduction of oxyhydrogen can effectually enhance the optimal BDIr (butanol direct injection ratio), it also leads to an increase in NO emission. Therefore, this paper further studies the influence of lean-burn on the combustion and emission of ternary-fuel combined supply engine with oxyhydrogen/butanol/gasoline. In this paper, three variables are set, namely five BDIr (0–80%), five ONPIv (oxyhydrogen negative pressure inhalation volume) (0–16 L/min) and five λ (1.0–1.4). The results show that the larger the λ, the more significant the impact of oxyhydrogen on improving combustion and thermal transfer inside the cylinder. With the increase of ONPIv, CoVIMEP, CA 10–90 and CA 0-10 decrease, IMEP increases. Under all lean-burn conditions, ONPI can reduce CO and HC emissions. Under the condition of λ = 1.4, when ONPIv = 16 L/min, NO emission is 49.98% lower than the value of the original engine. Moreover, based on BDIr = 40%, 16 L/min ONPIv can elevate the λ limit from 1.41 to 1.83. In summary, “1.1 = λ ≤ 1.2+ONPIv = 16 L/min+60%≤BDIr≤80%” is the excellent control strategy of ONPI + BDI + GPI engine. The synergistic influence of lean-burn and larger BDIr can greatly reduce gasoline consumption and NOx emission caused by oxyhydrogen, but also worsen the mixture combustion atmosphere. ONPI can effectively improve this problem, and further increase energy efficiency. The coupling technology of ternary-fuel combined supply and lean-burn has a positive impact on improving thermal transfer efficiency, optimizing mixture combustion and decreasing gaseous emission.

Computational investigation of NOx emission in biogas combustion.

Landfills and anaerobic digesters in the waste treatment processes generate biogas. Biogas can be used as a fuel and excess biogas is typically burned in a flare to reduce the greenhouse effect. However, burning biogas produces several pollutants, including CO2, NOx, and SO2. To minimize these emissions, the amount of excess air used in the combustion process needs to be considered, which has a significant impact on NOx emissions. This study developed a Computational Fluid Dynamics (CFD) model to simulate a small-scale biogas combustion system and analyses the effect of excess air on heat output and NOx emissions during biogas combustion. The GRI-Mech reaction mechanism was used to simulate reactions, and the model was validated by comparing it to experimental data from the DLR-Stuttgart CH4/H2/N2 Jet Flame. To reduce computational costs, a Tabulation of Dynamic Adaptive Chemistry (TDAC) algorithm was used to dynamically adapt the reaction mechanism in real time. Turbulence in the DLR flame was simulated using Reynolds-Averaged Navier-Stokes (RANS). The CFD model used a co-flow of a natural draft to provide additional air, while the air was premixed with fuel. The CFD model was used to simulate various premixed equivalent ratios, and the resulting emissions and heat outputs were compared. The study found that the optimal premixed equivalent ratio for the studied system was between 0.85 and 1.1, as this range produced the highest temperature and lowest NOx emissions. This model facilitates emission analysis of gas-phase combustion systems.

Analytical study for the comparison between hygroscopic and Rankine cycle. An exergy approach

The Hygroscopic Cycle Technology (HCT) is a proprietary technology that allows producing energy with better performance and more sustainable than traditional Rankine Cycle (RC). The aim of this study is to implement analytical models for comparing the performance of HCT and RC operating at industrial scale conditions. The study focuses on energy and exergy analysis in order to compare the cycles and determine the equipment with the higher irreversibilities for providing a base to improve them. A base case of each cycle has been defined and compared. Also, a sensitivity analysis of the main parameters of the cycles has been done. Grassman diagrams of the base cases have been studied to quantify the exergy distribution and destruction. According to the results obtained exergy efficiency of the HCT can be 2.52% greater than that of the regenerative RC for high cooling temperatures. For cooling, dry coolers can be used with ambient temperatures of up to 46 °C for HCT while for the RC it is limited to 38 °C. The variables with the greatest influence on the exergy efficiency are the condensing pressure and the boiler air–fuel ratio. In the HCT, due to the excess of air required for complete combustion, the exergy destruction rate in the boiler can be increased by 1% and the exergy efficiency of the HCT can be 1.3% lower than the value for the stoichiometric air–fuel ratio. For a 10 MW power plant the exergy of the fuel in absolute terms was lower for the HCT (37.08 MW) than for the RC (37.92 MW).

Investigation of boost pressure and spark timing on combustion and NO emissions under lean mixture operation in hydrogen engines

Hydrogen may become a replacement for liquid fossil fuels, contributing to greenhouse gas emissions reductions by improving the thermal efficiency of boosted lean burn spark ignition engines. Single-zone engine combustion models are simple, but can yield useful results as a step in the design process for developing alternative fuel systems. The single-zone thermodynamic model is advanced by implementing a laminar flame speed sub-model to investigate combustion, an extended Zeldovich mechanism for nitric oxide emissions, and incorporating the Livengood-Wu integral model for knock characteristics. The results were validated using published experiments giving satisfactory predictions between simulation and experiment for spark timing variation, manifold air pressure, and equivalence ratios. A detailed analysis of boosted lean burn strategies showed that nitric oxide emissions increased with boosted pressure, hence emissions can be controlled through optimizing the excess air ratio and the start of combustion. Further techniques to achieve high thermal efficiency and to prevent knock for boosted lean burn hydrogen SI engine are discussed.

Experimental and numerical study on indoor thermal environment of solar Trombe walls with different air-channel thicknesses in plateau

Trombe wall is an effective method for passively absorbing solar energy and providing heat to buildings. This paper conducts a comparative experiment between Trombe wall buildings and glass curtain wall buildings during the winter season in Songpan County, western Sichuan. The climate characteristics of the western Sichuan plateau are analyzed, and the potential applications of these two building types in the region are investigated. To further understand the heat transfer mechanism of Trombe wall buildings, numerical simulations are carried out to analyze the indoor thermal environment of buildings with varying air channel thicknesses. The results show that Trombe wall buildings are more effective at delaying heat loss compared to glass curtain wall buildings, due to the thermal storage of the Trombe wall providing heat at night. This makes Trombe wall buildings well-suited for regions with strong solar radiation and large temperature differences between day and night, such as the alpine region. However, excessively small air channel thickness can lead to excessive air flow speed during the day, causing more heat loss and weaker insulation at night. Conversely, excessively large air channel thickness reduces air flow temperature difference and diminishes the heat brought into the room. Among different air channels, a thickness of 100 mm performs best with a temperature difference between the inlet and outlet of about 45 °C. At 13:00 o ‘clock, the maximum airflow rate of approximately 5.8 L/s is achieved for a thickness of 100 mm, whereas for thicknesses of 150 mm and 50 mm, the corresponding values are 4.9 L/s and 4.1 L/s, respectively. It is important to note that blindly increasing air channel thickness to raise indoor temperature is not a practical or reasonable engineering solution. The measured and numerical results can provide valuable reference value for the improvement and development of Trombe wall buildings in the future.

A method for calculating the moisture load in the tailrace surge tank of underground hydropower station based on field tests

As an important part of a hydropower station, the tailrace surge tank is usually buried deep underground. The indoor air is in contact with a large area of water, resulting in excessive air humidity, especially in the summertime when the hot and humid environment is harsh. Therefore, the moisture exchange process in the tailrace surge tank is first analyzed in this research. Based on this analysis, a method for calculating the moisture load is proposed. After that, the hot and humid environment in the tailrace surge tank at the Xiluodu hydropower station is tested for a year. The test results show that the relative humidity of the air at the tailrace surge tank's entrance is negatively correlated with the amount of moisture dissipation. Meanwhile, the rate of moisture dissipation exhibits a law of low in the summer and high in the winter, with summer lows of −103.2 kg/h and winter highs of 1404.7 kg/h. In addition, the fitting formula for moisture load in the tailrace surge tank is obtained in this paper by combining test data with mass transfer theory, and the relative error between the calculation results and the test results is less than 9.32%. The study's findings can be utilized as a reference when creating a ventilation and mechanical dehumidification plan for the tailrace surge tank's hot and humid environment.

Hydrogen production from an on-board reformer for a natural gas engine: A thermodynamics study

In the present study, for an insight into the optimizing windows of comprehensive energy efficiency for open-loop system of marine NG engine and reformer, a peculiar thermodynamic equilibrium model for simulating the exhaust gas-fuel reforming process is established using equilibrium constant and experimental results. The accuracy of the model is evaluated by comparing numerical simulations with data derived from experiment of the open-loop operation system. Accordingly, the effect of engine loads and excess air (λ) as well as reformer feedstocks on maximum theoretical reforming characteristics are investigated. In addition, the energetic distribution in open-loop operation system can be clarified by the first law of thermodynamic. The results shown that fuel conversion toward H2 is highly selective due to the enhancement of reaction temperature with increasing engine loads. Especially, under 75% engine load, the maximum theoretical H2 yield reaches up to approximately 42.3% when λ = 1.4, CH4/O2 (M/O) = 1.5 and H2O/CH4 (S/M) = 2; The high λ will dilute the feed concentration of the reformer, thereby inhibiting the reforming reaction moving toward H2 production. Hence, an appropriate λ (1.4) can maximize the hydrogen production capacity of the reformer. In addition, according to the energy distribution of the open-loop system, the theoretical reforming energy efficiency of the reformer reaches a peak of 93.5% at S/M = 2 and M/O = 5. However, it can be found that M/O should be maintained above 1.5 to acquire optimal reforming energy utilization efficiency of system. Summarily, the optimal operation conditions for the reformer in open-loop operation system are confirmed: M/O = 1.5–2.5 and S/M = 1.5–2 under 75% engine load, which could fulfill efficient reforming performance.

ИССЛЕДОВАНИЕ ВОЗМОЖНОСТИ СНИЖЕНИЯ ОКИСЛЕНИЯ СТОП ЛИСТОВ ПРИ НАГРЕВЕ ПОД ТЕРМООБРАБОТКУ ЗА СЧЕТ НАНЕСЕНИЯ ЗАЩИТНЫХ ПОКРЫТИЙ

Heating of metal products for heat treatment and metal treatment by pressure is accompanied by a loss of metal mass, called carbon monoxide. To protect the metal surface from oxidation, heating of workpieces is used: in products of incomplete combustion of fuel with an excess air coefficient of less than one; in molten salts; in protective media and by applying protective coatings to the surface of the heated metal, for example, using a spray gun that works well when using large products. When heating the stop sheets, coating each sheet is a difficult task, therefore, in this work, a method was tested to protect the stop sheets from oxidation when they were heated for heat treatment by applying liquid glass with a brush to various stop surfaces: end, upper and lower.

APLIKASI LUBANG RESAPAN BIOPORI BERKOMPOS DI KEBUN KOPI MENINGKATKAN JUMLAH SPORA MIKORIZA ARBUSKULA DAN KOLONI AKAR

Mycorrhizae is a mutualistic symbiotic relationship between fungi and plant roots, and soil characteristics influence the performance of this symbiosis. Biopore Infiltration Hole is a vertical hole into the soil with a diameter of about 10cm and at a depth of ±100 cm in the soil for air infiltration, which is helpful in reducing the occurrence of excessive air puddles. This research was conducted to determine the effect of soil properties such as pH, total N, available P, CEC and texture on the number of spores and root colonies by arbuscular mycorrhizae on the effect of biopore infiltration holes with the addition of organic matter. The results showed that the highest number of arbuscular mycorrhizae spores and root colonies was in the biopore infiltration holes with goat manure, namely 16.3 spores 100 g-1 soil and 66.22% root colonization. The arbuscular mycorrhizal genera found included Glomus, Acaulospora, Scutellospora, and Gigaspora. The number of spores and soil properties that were positively correlated were pH (r=0.45), organic C (r=0.945**), total N (r=0.716**), available P (r=0.922**), dan CEC (r=0.894**).

Performance Analyses of Combined Cycle Power Plants

In this article, different compressor pressure and different excess air rates for a gas turbine based combine cycle power plant with steam Rankine cycle as bottoming cycle were analyzed by using 1. and 2. laws of thermodynamics and exergy analyses methods to obtain the best performances of the cycle. Exergy efficiency of the cycle, net powers of the gas and steam turbines and the overall cycle, exergy loss of the components, the efficiencies of the components are obtained, compared and discussed. It was found that, increasing the compressor pressure increases exergy efficiency of cycle, gas turbine and total plant power, and the combustion chamber, the HRSG and the compressor efficiencies. However, increasing compression rates decreases steam turbine power, combustion chamber, steam turbine, and HRSG exergy losses and the gas turbine efficiency. Also, it is found that, increases in excess air ratios gives an optimum or a maximum exergy efficiency, at 2.5 excess air rate of the cycle.

ENVIRONMENTALLY SAFE OPERATION OF MUNICIPAL WASTE INCINERATION

The technology of waste incineration makes it possible to solve the issue of obtaining an alternative type of fuel and eliminate the problem of the excess waste in landfills. A multi-stage emission cleaning technology has been proposed to protect the environment and service personnel. The chemical processes that take place in the furnace space have been considered.
 The purpose of the research is to develop the concept of control systems for the technological cycle of the installation of thermal disposal of solid household waste to protection of the environment from these toxic substances: dioxins, carcinogenic hydrocarbons, products of incomplete combustion, in particular, polycyclic aromatic hydrocarbons, nitrogen and sulfur oxides. A complex of methods of system analysis and the method of data analysis was applied to achieve the goal of the research. An analysis of modern international literary sources, an analysis of the morphological composition of solid household waste, an analysis of the interaction of chemical substances, and experimental studies at a research and industrial facility were carried out. As a result of the research, the scientific and applied task of improving the system of protection of the environment and service personnel from emissions of thermal disposal of solid household waste was formulated and substantiated.
 Research results might apply to designing equipment for waste incineration, for choosing rational parameters of the furnace, location of fuel supply burners. General recommendations for the use of chemical properties of harmful substances in the design of cleaning equipment have been provided. The effectiveness of the method of supplying an inert medium (flue gases) to the combustion zone at a temperature below the flame temperature was evaluated. Effective thermal destruction of dioxins is possible in modern waste incineration plants, provided high temperatures, excess air and sufficient residence time followed by a catalytic cleaning. Homogeneous and heterogeneous formation of polychlorinated dibenzodioxins and polychlorinated dibenzofurans formed and released in zones with relatively low temperatures.

Investigation on the performance of a by-product hydrogen-fueled spark-ignition engine with Miller cycle under various lean conditions

The direct combustion of by-product hydrogen is a promising way for reducing costs and greenhouse emissions. Coke oven gas (COG) which is mainly composed of H2, CH4 and CO is a major source of by-product hydrogen that is suitable to be adopted by internal combustion engines. This paper investigated the COG combustion in a spark-ignition engine with Miller cycle. To get an overview of by-product hydrogen combustion properties, two kinds of COG compositions with the maximum and minimum hydrogen fractions were tested. The excess air ratio (λ) was raised from stoichiometric to the lean limit to explore the capability of COG on improving the engine performance under a common-driving speed of 1500 rpm and part load conditions. The test results indicated that the engine fueled by COG with higher hydrogen fractions could gain concentrated heat release period, extended lean burn limit, reduced HC and CO2 emissions, and enhanced working capability only at ultra-lean conditions. The properly increased λ availed improving engine efficiency and lowering HC emissions. The peak indicated thermal efficiency of 38.6% was acquired at the λ of 1.2, while the lowest HC emissions of only 32 ppm was gained at the λ of 1.4. Under ultra lean conditions, NO emission dropped to near zero, and CO from the by-product hydrogen-fueled engine was negligible for all tested ranges. An interesting trend of peak pressure correlated crank angle versus λ was also found in this study.

Modification of perforated plate in fluidized-bed combustor chamber through computational fluid dynamics simulation

The combustion of solid fuels in a combustion chamber can be perfect if all the fuel included can burn out, and nothing remains. The combustion chamber requires sufficient air to burn all the fuel; therefore, meeting the air supply requires modifications with various considerations. The perforated plate modeled through computational fluid dynamics (CFD) was modified to investigate the excess air supply into the combustion chamber. The CFD simulation modeled in this study was used to validate the results of the experiments carried out with the previous fluidized-bed combustor technology. The simulation results show that the temperature increased for all fuels tested in geometry-2 compared with geometry-1. The best boiler efficiency from the simulation results is in geometry-1 for 45% oil palm midrib fuel with a mass flow rate of 7.78 kg/s. The maximum radiation was recorded from geometry-2 at a variation of 66.939 W/m2, with a heat loss level of 1.10 W/m2. Overall, the simulation was performed by modifying the fuel floor plate in geometry-2 to increase the temperature and radiation with lower heat loss.

Comparative study of machine learning methods integrated with different optimisation algorithms for prediction of thermal performance and emissions in a pellet stove

ABSTRACT The parameters of thermal power, excess air, and supply air distance at burner pot are critical to obtain low emissions and high combustion efficiency in a pellet stove. The main aim of this study is to predict the performance and gaseous emissions in a pellet stove with four different supply airflow distances of 15, 30, 60, and 75 mm above the burner pot base at different excess air ratios and thermal power inputs. For this purpose, different models, namely, support vector regression, k-nearest neighbors, and deep neural network, are developed to predict the performance and emissions of the pellet stove. The thermal power, excess air ratio, and supply air distance were used as input variables to predict the flue gas temperature, efficiency, carbon monoxide (CO), nitrogen oxides (NOx), and carbon dioxide (CO2) emissions. The hyperparameters of the designed models are tuned using several optimization approaches: grid search, Bayesian optimization, particle swarm, and genetic algorithms. Experiments are conducted to validate the performances of the models with optimized hyperparameters using statistical metrics such as coefficient of determination, mean-squared error, mean absolute error, and mean absolute percentage error. Analysis results indicate that the deep neural network performs the best with the highest correlation coefficient and lowest error metrics in the prediction of output parameters. The coefficient of determination (R2) values of the DNN model were obtained as 0.8875, 0.8464, 0.934, 0.8692, and 0.9992 in the training phase 0.909, 0.8760, 0.9164, 0.9086, and 0.9991 in the testing phase for the efficiency, Tg, CO, NOx, and CO2 parameters, respectively. The results of this study can serve as a guide to help researchers, engineers, and facility owners or operators predict the gaseous emissions levels and to get an idea of the impact of operating conditions on performance and emissions behaviors.