Air-fuel Combustion Research Articles

Estimated electric conductivities of thermal plasma for air-fuel combustion and oxy-fuel combustion with potassium or cesium seeding

A complete model for estimating the electric conductivity of combustion product gases, with added cesium (Cs) or potassium (K) vapor for ionization, is presented. Neutral carrier gases serve as the bulk fluid that carries the seed material, as well as the electrons generated by the partial thermal (equilibrium) ionization of the seed alkali metal. The model accounts for electron-neutral scattering, as well as electron-ion and electron-electron scattering. The model is tested through comparison with published data. The model is aimed at being utilized for the plasma within magnetohydrodynamic (MHD) channels, where direct power extraction from passing electrically conducting plasma gas enables electric power generation.The thermal ionization model is then used to estimate the electric conductivity of seeded combustion gases under complete combustion of three selected fuels, namely: hydrogen (H2), methane (CH4), and carbon (C). For each of these three fuels, two options for the oxidizer were applied, namely: air (21 % molecular oxygen, 79 % molecular nitrogen by mole), and pure oxygen (oxy-combustion). Two types of seeds (with 1 % mole fraction, based on the composition before ionization) were also applied for each of the six combinations of (fuel-oxidizer), leading to a total of 12 different MHD plasma cases. For each of these cases, the electric conductivity was computed for a range of temperatures from 2000 K to 3000 K.The smallest estimated electric conductivity was 0.35 S/m for oxy-hydrogen combustion at 2000 K, with potassium seeding. The largest estimated electric conductivity was 180.30 S/m for oxy-carbon combustion at 3000 K, with cesium seeding. At 2000 K, replacing potassium with cesium causes a gain in the electric conductivity by a multiplicative gain factor of about 3.6 regardless of the fuel and oxidizer. This gain factor declines to between 1.77 and 2.07 at 3000 K.Based on the findings of this research study, the four analyzed factors to increase the electric conductivity of MHD plasma can be listed by their significance (descending order) as (1) type of additive seed type (cesium is better than potassium), (2) temperature (the higher the better), (3) carbon-to-hydrogen ratio of the fuel (the higher the better), and finally (4) the oxidizer type (air is generally better than pure oxygen).The relative size of the two electric conductivity components (due to neutrals scattering and Coulomb scattering) at various plasma conditions are discussed, and a threshold of 10−5 (0.001 %) electrons mole fraction is suggested to safely neglect Coulomb scattering.

A review on comparative analysis of different types of burners for oxy-fuel SCO2 recirculation and air-fuel combustion systems

Due to the global warming and strict environmental regulations encourages researchers to develop efficient combustion system that produce low level of harmful gases. This article focuses on review of different studies and experiment carried out in the sphere of oxy-fuel and air fuel combustion. In order to compare the results of oxy-fuel and air fuel combustion and find a suitable and efficient combustion system.

0/1 and 3 - dimensional cold flow analysis of a diesel engine: A case study

Gas motion in the engine cylinder plays a critical role in diesel engines' air-fuel mixing and combustion processes. Moreover, it influences the engine's performance, emissions, and heat transfer. The intake air motion regulates the main phases of the flow in the cylinder, which is characterized by swirl, squish, and turbulence. Inducing swirl and tumble in the intake process provides high turbulence levels at ignition, resulting in more effective flame speeds and better combustion for lean air-fuel ratios or with EGR. Computational fluid dynamics (CFD) software is used to enhance in-cylinder flow characteristics. In this study, a cold flow simulation of a naturally aspirated, direct injection diesel engine was conducted with different piston bowls using AVL Fire M R2022.2. Swirl, tumble, and TKE parameters were investigated to make a detailed analysis of the in-cylinder flow for the relevant engine. Contrary to the expectation, the swirl ratio for the Piston B configuration is less than that for the original piston configuration. It causes a decrement of swirl ratio compared to the initial piston geometry and the maximum decrement is about 19%. In both cases, the second peak of TKE corresponding to the reverse-squish is around at the -30 CA and the difference between the curves is about ±8%.

Comparison of the flame stabilities during oxy-methane and air-methane combustion in a two-layer porous burner

The development of the oxy-fuel porous media combustion technique not only takes advantage of the characteristics of porous media combustion, such as a relatively low lean-burn limit and small volume, but also dramatically facilitates carbon capture and storage. In this paper, a two-layer porous burner model is established, in which a two-temperature equation model is adopted for calculation purposes. Differences in combustion behaviour between oxy-fuel and air-fuel conditions are compared. The results show that the difference in physical properties between CO2 and air is the main reason for the significant variation of combustion behaviours under the conditions of oxy-fuel compared to air-fuel. The specific performance is lower combustion temperature and flame propagation speed. The temperature under oxy-fuel combustion conditions is 300 K lower than that under air-fuel combustion conditions at an equivalence ratio of 0.6, and the stable range of oxy-fuel combustion is only approximately 50% of air-fuel combustion. The impact of porous media material parameters on combustion behavior has been investigated. These variables include the equivalence ratio, material thermal conductivity, volume heat transfer coefficient, and extinction coefficient, while the ratio of O2/CO2 remains fixed at 0.21/0.79. The influence of these variables on the stable velocity range and temperature field is consistent, but a large difference in values occurs. Reducing the thermal resistance of the burner by adjusting the properties of the porous matrix can increase the velocity limit of stable combustion. However, even if the thermal conductivity and extinction coefficient are increased by 5 times, there will be no significant impact on the stable range. Reducing the pore size of the combustion zone by 50% will increase the stable range by over 100%.

NO emission characteristics for the HTC and MILD combustion regimes with N2, N2/CO2 and CO2 diluents: effect of H2 addition to CH4

In this paper, the effect of H2 addition to CH4 on the NO emission of oxy-fuel, oxygen-enriched, and air-fuel MILD combustion is studied by numerical and chemical calculations. In the CFD section, the University of Lisbon MILD furnace is modeled. The results show that H2 added to CH4 is associated with a higher NO emission in the same oxidant composition. It is due to higher NO formation by NNH and thermal mechanisms. It can be found that by transformation from air-fuel to oxy-fuel MILD regimes, NO emission is reduced significantly. Moreover, the addition of H2 prevents flame extinction that often occurs under MILD conditions when CO2 replaces N2. Reaction pathway analysis displays that dominant routes of NO emission in the H2-lean are N2O-intermediate for the air-fuel and oxygen-enriched conditions and NNH for the oxy-fuel MILD regime. In the H2-rich condition, the NNH mechanism plays the most important role in the NO production.

MODIFICATION OF AMULTIHOLE INJECTOR TO A SINGLE-HOLE INJECTOR AND SPRAY CHARACTERISTICS OF THE MODIFIED INJECTOR BY TWO DIFFERENT IMAGING TECHNIQUES

In the present days, almost all the diesel engines are fitted with multihole injectors. Spray characterization of the injectors by different optical measurement techniques is very important to under-stand the air-fuel mixing and combustion procedure inside the cylinder. Instead of characterization of the dense sprays from a real multihole diesel injector, often a single plume is used to study the spray parameters. In the present work, spray characteristics are studied for a multihole injector with all nozzle holes open and with a single hole open conditions. Experiments have been conducted in a constant-volume, high-pressure, and high-temperature chamber with various injection pressures and at various ambient conditions. A high-pressure common rail injector with six holes is considered for the study. The penetration and cone angle of the spray from each hole are measured, and the hole-to-hole variation is studied. It has been observed that hole-to-hole variations with respect to spray penetration are prominent in low chamber pressures and injection pressures at the initial stage of injection, though they are minimal at later stages of injection. After that, five holes of the injector are blocked by microwelding, and the remaining single plume was studied and the results compared with the original multiplume spray. The study shows that the penetration length and cone angle of the single plume match well with that of the multiplumes at all chamber pressures and injection pressures. Later, the spray from the modified single-hole injector was characterized by two different imaging techniques, Mie scattering and diffused backlit imaging (DBI), to compare the penetration length and cone angle measured by the two imaging techniques. It is seen that the differences in penetration lengths by two imaging techniques are negligible, whereas the cone angles are greater in the case of backlit shadow imaging, particularly at higher temperatures.

Influence of wall thermal conditions on the ignition, flame structure, and temperature behaviors in air-fuel, oxygen-enhanced, and oxy-fuel combustion under the MILD and high-temperature regimes

In this work, variations of wall thermal conditions and oxidant compositions are considered to investigate the temperature distribution, ignition process, and flame structure under MILD and high-temperature combustion (HTC) regimes. Studies are performed by the computational fluid dynamics (CFD) approach with OpenFOAM open-source code. Also, kinetic calculations by well-stirred-reactor (WSR) is used to quantitatively describe results. Results show that by the transition from HTC to the MILD regime, Tmax and Tave have intense (more than 15%) and uniform (less than 3%) drops, respectively. This indicates that moving from HTC to the MILD regime can be considered as an effective way to maintain the thermal conditions while reducing the emission of pollutants. The MILD regime is formed at Tw = 1500 K and Tw = 1700 K under air-fuel and oxy-fuel combustion, respectively, indicating that oxy-fuel MILD combustion is associated with fewer heat losses. Enhancement of heat loss creates an intense variation of reaction pathways under the MILD regime, while it is constant for HTC regime. Higher heat loss leads to diminishing the role of reactions O + H2O ⇌ 2OH and O2+CH2OH ⇌ HO2+CH2O on the ignition delay time (IDT) under insulation reactor and increases the contribution of reactions H + OH + M ⇌ H2O + M and O + CH3 ⇌ H + CH2O.

Exhaust emission characteristics of stoichiometric combustion applying to diesel particulate filter(DPF) and three-way catalytic converter(TWC)

Various researchers study after-treatment system (DPF, SCR, LNT, TWC) to meet the recent strengthening regulation. In this study, we consider the intake air applying to the simulated-EGR which is composed of synthetic constituents (e.g. air, N2, and CO2 gas). Intake air excessively used to simulated-EGR, proceeds with the stoichiometric air-fuel ratio combustion in the cylinder. This stoichiometric exhaust emission was passed through and converted in TWC as well as DPF after-treatment system. We discuss exhaust emission characteristics of stoichiometric combustion applying to DPF and TWC in compression ignition diesel engine. The maximum of the conversion efficiency of NOx is 85.7% at SOI of −18.2° CA. aTDC with simulated-EGR the smoke reduction efficiency of soot is high and is provided over 99% reduction under the stoichiometric condition with reduced O2 mole fraction by adding only N2 and with EGR.

Investigation of air-MILD and oxy-MILD combustion characteristics of semicoke and bituminous coal mixtures in a 0.3 MW fuel-rich/lean fired furnace

To study the combination of fuel-rich/lean combustion with oxy-MILD (moderate and intense low-oxygen dilution) combustion for the reduction of NOx emissions by adopting carbon capture and storage, this paper numerically investigates the turbulence−chemistry interactions and NOx emission behaviours of semicoke mixtures under different secondary velocities Vsec (from air-fuel combustion to air-MILD combustion) and under different CO2 dilution levels (oxy-MILD combustion). The bias concentration ratio (BCR) hardly affects the establishment of air-MILD combustion, which is obtained at Vsec = 158.6 m/s. The oxy-MILD combustion, which is composed of small flamelets diffusing in large-scale eddies (turbulent Damköhler number Dat = 0.1–1), is enhanced, and the ignition and char burnout times are prolonged by increasing CO2 from 0 vol% to 79 vol%. The char oxidation reaction in the diffusion/kinetics-controlled regime and the char gasification reactions in the kinetics-controlled regime both shift towards the kinetics-controlled regime with increasing velocities and CO2 dilution, thus leading to lower burnout rates. The heterogeneous MILD regime of the fuel-lean side is more easily established for the air-MILD combustion, while that of the fuel-rich side is more easily established for oxy-MILD combustion. This is because the intensive turbulence increases the O2 dilution level in the fuel-lean jet, while a high concentration of CO2 reduces the oxygen diffusivity in the fuel-rich jet, which also leads to a larger XNO in the fuel-lean jet compared to the fuel-lean jet. The NOx concentration at the furnace outlet decreases significantly from air-fuel combustion to air-MILD combustion and further decreases as the oxy-MILD combustion is enhanced, along with relatively lower homogeneous and heterogeneous Da.

Spray characteristics of biofuels for advance combustion engines

This study investigates spray characteristics, flashing and non-flashing, of unsaturated neem biodiesel (BD), biodiesel-ethanol (BDE50) blend, and diesel for application in advanced combustion engines. Fuel properties, injection pressure, nozzle geometry, and the surrounding ambient gas conditions govern the spray breakup and air-fuel mixing. The spray characteristics of fuel is studied at various injection pressure and ambient gas densities using the high-speed shadowgraphy technique. BDE50 shows improved spray dispersion with distinct tree-shaped spray morphology at ambient density of 1.14 kg/m 3 and injection pressure of 50 MPa. Theoretical analysis confirms occurrence of cavitation due to high volatile component (ethanol) in biofuel mixture and throttling conditions. At high ambient gas density and injection pressure, diesel and BDE50 exhibit high spray cone angle. Neem biodiesel maintains high tip penetration and low cone angle due to poor atomization. The study recommends use of BDE50 blend for achieving improved mixture formation in engines. • Dual (reactivity) biofuels spray atomization strongly controls the air-fuel mixing and combustion. • Cavitation induced flashing with BDE50 spray shows improved spray dispersion with distinct tree shaped spray morphology. • Theoretical analysis confirms cavitation (in BDE50) by throttling conditions. • Recommended to use the BDE50 instead of biodiesel for achieving the improved mixture formation.

Numerical Analysis of the Effects of Oxygen-Enriched and Different Inlet Conditions on Performance of an Indirect Reheating Furnace with Pulse Combustion.

The requirement of improving efficiency and performance leads to the continuous development of furnaces and burners. For this purpose, it is necessary to establish a model suitable for industrial production and adjust it according to industrial demand. In this paper, a comprehensive numerical model is developed to characterize the combustion, heat transfer, and slab heating in an indirect reheating furnace with pulse combustion. To realize the pulse combustion process, a pulse control approach based on a user-defined function (UDF) was proposed to control the radiant tube burner state. Indirect heat transfer in the furnace was realized by coupling the radiant tubes and the furnace as a whole. In a simulation with the eddy dissipation concept (EDC) model, results from the four-step mechanism were in close accordance with those of the GRI 3.0 mechanism, and both mechanisms could describe the combustion process in detail. However, the calculation time of the EDC model with the four-step mechanism was reduced significantly. Thus, the EDC model with the four-step mechanism was selected as the ideal combustion model used for further simulation research. Through experimental validation, the simulation results of the developed model using the EDC model with the four-step mechanism showed a good agreement with the experimental results. Additionally, with this model, the effects of oxygen-enriched combustion with 74 vol % N2 and 26 vol % O2 in the oxidizer and inlet-change case with a fuel inlet and a primary air inlet on the performance of an indirect reheating furnace with pulse combustion were specially studied. The maximum flame temperature and the average temperature of the furnace atmosphere increased from 2046 to 2175 K and from 1241 to 1279 K for increased oxygen concentration, respectively. Compared with air-fuel combustion, the discharging slab temperature reached a growth of 2.9% in oxygen-enriched combustion. After changing the inlet boundary of the radiant tube burners, since the excessive combustion in the burner’s combustion chamber was avoided and the full combustion of fuel in the radiant tubes was promoted, the flame intensity in the radiant tubes was enhanced and the maximum flame temperature reached 2196 K. At the same time, the mole fraction of CO at the outlet became smaller and the slab temperature in all zones of the furnace increased by more than 3.5%. This study showed that higher efficiency of an indirect reheating furnace with pulse combustion can be achieved by oxygen-enriched combustion and changing the inlet boundary of the burners.

Real-world evaluation of driving behaviour and emission performance of motorcycle transportation in developing countries: A case study of Isfahan, Iran

The present study aims at a real-world assessment of the driving behaviour and exhaustive emission performance of motorcycle (MC) driving in a middle-sized city of a developing country, i.e. Isfahan, Iran. We developed the Isfahan Motorcycle Driving Cycle (IMDC) using comprehensive data collection and then compared it with the available overseas MCDCs and DC of local LDVs. Onboard experiments were also conducted on 20 test motorcycles to analyze emission performance, emission characteristics, and combustion quality of motorcycles under real-world conditions. IVE model was used to estimate the MC emission factors (EFs) according to the real-urban conditions, but it was first adjusted to the real-world measurements. Results show that MC EFs steadily decrease with vehicle speeds. Apparent discrepancies were observed between IMDC and the MC DCs overseas, while local DCs of motorcycles and LDVs follow a prevailing trend determined by the new factors of public culture and urban development. CO was the major criteria pollutant of the MCs exhaust, and formaldehyde and benzene were ranked as the first and second principal toxic gases, respectively. The air-fuel mixture control system and combustion quality of 150 and 200 cc MCs were impaired with the vehicle speed, but the same is not true for the 125 cc MCs.

Feasibility of biogas and oxy-fuel combustion in steam cracking furnaces: Experimental and computational study

This work evaluates the feasibility of biogas air-fuel combustion and natural gas oxy-fuel in steam cracking furnaces. Four cases, namely air-fuel combustion of pure natural gas, 20% CO2, 40% CO2 diluted natural gas, and oxy-fuel combustion of natural gas are investigated both experimentally and numerically. The John Zink Hamworthy Combustion test furnace, representing a section of a steam cracking furnace, is used for experimental studies. A three-dimensional steady-state CFD model is also developed to simulate the test furnace. The simulation results of the air-fuel combustion scenarios are in good agreement with the experimental data, with the maximum and average relative errors of furnace temperature of 3.86% and 1.78%, respectively. The reduction of flame length with increasing CO2 mole fraction in the fuel is observed in both experiments and simulations. It is shown that CO2 dilution has minor effect on the overall heat flux profile, which is beneficial for retrofitting existing furnaces. On the other hand, the oxy-fuel combustion simulation using default EDC model predicts a significant flame lift-off and incident radiative heat flux shift towards the higher elevations which was not observed in the experiments. This can be mainly attributed to the reduced reaction rate in a CO2 and H2O enriched combustion environment. Adjusting the EDC model parameters helps to achieve better agreement between simulation results and experimental data, while additional lab-scale experiments are essential for further validation of the numerical model. Moreover, it is of particular interest to study the optimal mole fraction of O2 in oxy-fuel combustion scenario.

Time Dependent Effect of flow properties on addition of heat to the air flow at Compressible Subsonic Speeds

Heat addition process is a governing phenomenon in turbojet and ramjet burners, where heat is added to the flow during the fuel-air combustion process. In the present work, an analytical study has been performed to investigate the effect of heat addition on the basic flow properties based on compressible Rayleigh flow model between the subsonic and sonic flow regime. The unsteady nature of flow properties in these regimes have been evaluated analytically by adding heat through the walls of a constant area, frictionless duct in which air flow occurs over different periods of time. Sudden variation of temperature, pressure, velocity and kinetic energy of the flow were found at flow Mach number M = 0.94. Flow velocity and kinetic energy increases until the flow approaches M = 0.94, afterwards there is a rapid increase in the flow velocity and kinetic energy until it reaches sonic conditions. Conversely, pressure decreased till the flow reaches M = 0.94, there after a sudden drop was observed. Flow enthalpy increased initially, reached maximum at flow M = 0.845 and then reduced till sonic conditions. Based on the observations, it has been concluded that the heat energy contributed to increase the kinetic energy thereby reducing the temperature of the flow.

Starting to Unpick the Unique Air–Fuel Mixing Dynamics in the Recuperated Split Cycle Engine

In this work air fuel mixing and combustion dynamics in the recuperated split cycle engine (RSCE) are investigated through new theoretical analysis and complementary optical experiments of the flow field. First, a brief introduction to the basic working principles of the RSCE cycle will be presented, followed by recent test bed results relevant to pressure traces and soot emissions. These results prompted fundamental questioning of the air-fuel mixing and combustion dynamics taking place. Hypotheses of the mixing process are then presented, with differences to that of a conventional Diesel engine highlighted. Moreover, the links of the reduced emissions, air transfer processes and enhanced atomisation are explored. Initial experimental results and Schlieren images of the air flow through the poppet valves in a flow rig are reported. The Schlieren images display shockwave and Mach disk phenomena. Demonstrating supersonic air flow in the chamber is consistent with complementary CFD work. The results from the initial experiment alone are inconclusive to suggest which of the three suggested mixing mechanism hypotheses are dominating the air–fuel dynamics in the RSCE. However, one major conclusion of this work is the proof for the presence of shockwave phenomena which are atypical of conventional engines.

A modeling approach for soot formation in non-premixed flames with elevated stoichiometric mixture fraction

Most soot formation models have been developed with particular applications in mind and as such, are valid only for the range of fuel-air combustion conditions representative of the target application. This limits the applicability and versatility of most models, especially for combustion processes wherein the stoichiometric mixture fraction, Zst, could vary widely. A soot-producing flame could become non-sooting (blue) with an increase in Zst even while maintaining constant flame temperature. This paper presents a novel modeling approach to account for the unique flame characteristics at elevated-Zst environments and their effect on soot formation. This modeling approach is designed to capture both the formation and the reversible processes that occur on the fuel-side of a diffusion flame in a way which is robust, simple, and can be utilized in diverse applications. Additionally, a new semi-empirical model is developed for extending two widely-used models–Leung-Lindstedt and Moss-Brookes–both of which render inaccurate predictions under varying Zst conditions. When applied to the counterflow flame system, the soot volume fraction profiles predicted by incorporation of our new and modified models agree well with experimental observations reported in the literature for low Zst. Using this modeling approach also resulted in the prediction of blue (soot-free) limit condition in a non-premixed counterflow flame for the first time. We show that this result cannot be obtained by considering formation processes alone and that the performance of semi-empirical soot formation models can be dramatically improved when applied to higher-Zst flames if the reversible nature of soot formation at high temperature is considered.

An improved water electrolysis and oxy-fuel combustion coupled tri-reforming process for methanol production and CO2 valorization

CO2 containing emissions from electric power plants are major contributors to the consistent rise of atmospheric CO2 concentration. The tri-reforming process has significant relevance as it converts non-inert components (CO2, H2O, O2) of the flue gas (with co-feed as methane) to synthesis gas without the intervention of an energy intensive CO2 separation step. Subsequent synthesis gas conversion to methanol is an important consideration. The conventional process employed air-fuel combustion based power plant generated flue gas in the tri-reforming coupled methanol production process to valorize CO2. Subsequently, the oxy-fuel combustion and water electrolysis coupled tri-reforming based methanol production process was developed as an improvement over it. In this paper, further advancements have been made to this coupled process. The following contributions have been made: (i) modification of the coupled process to increase the throughput of the water electrolysis unit to provide an inlet oxygen stream to the tri-reforming process to supplement an oxygen deficient flue gas stream, (ii) analysis of the synergistic role of simultaneous oxygen and hydrogen inputs from the water electrolysis unit on the performance of the overall process, and (iii) proposition of limiting the oxygen input to the tri-reformer to thermoneutrality to avoid exothermicity related issues. The above propositions have been implemented and compared with the base case coupled process via simulation runs in Aspen Plus V11. The results demonstrated a substantial improvement in both CO2 valorization potential (by 13.40%) and profitability (by 31.59%) of the process.

Numerical Study of NOx Formation Characteristics on the 35 MW Staged Oxy-Coal Combustion

In this study, the NOx formation has been numerically investigated on a 35 MW large-pilot oxy-fuel combustion boiler by employing an improved gas phase reaction mechanism and radiation property models. The fuel is sub-bituminous coal. After verifying the prediction with experimental data, the in-furnace flow patterns, temperature distribution, and NOx formation characteristics are analyzed in detail in the conditions of air-fuel combustion, oxy-fuel and staged oxy-fuel combustion. The results show that aerodynamic and temperature field in staged oxy-fuel combustion are similar to those in air-fuel combustion, which ensures the smoothly transition and similar heat transform characteristics between oxy-fuel combustion and air-fuel combustion. Staged oxy-fuel combustion can effectively reduce the NOx formation. More precisely, fuel staged combustion and fuel-oxygen two-way staged combustion can reduce 16% and 22-30% NOx emission, respectively. With the increase of the equivalent ratio in the burner zone, the reduction of NO becomes more significant. The fuel-oxygen two-way staged combustion can effectively reduce NOx, and the maximum NOx reduction ratio can reach 30%, then, the NOx emission in this condition is 69% lower than that in air-fuel combustion. The results in this study could provide a reference for low NOx operation of oxy-fuel combustion.

Computational Study of 16 kWth Furnace Cofired Using Pulverized Bituminous Coal and Liquified Petroleum Gas Operated in Un-Staged and Air-Staged Conditions

Abstract This paper presents a computational study on air-fuel combustion of bituminous coal and liquified petroleum gas (LPG) in a 16 kWth test facility with a coflow-swirl burner. The performance of three turbulence models is investigated for the furnace operated under both air-staged and un-staged conditions by comparing their predictions with the reported measurements of temperature and species concentrations. This comparison shows that the shear stress transport (SST) k–ω model and SST k–ω model with low-Re correction predict the profiles of temperature and species concentrations reasonably well, but significantly underpredict the temperature in the furnace core at axial locations away from the burner. On the other hand, the transition SST k–ω model provides better overall congruency with the measured temperature and species concentrations when compared with the other turbulence models used, as indicated by relatively higher values of the Pearson correlation coefficient at locations away from the burner. The present high-fidelity computational model developed is also capable of accurately simulating the effect of coal particle size on the furnace environment, which is verified by the match between the computational predictions and the experimental results for two different sized coal samples. The model is also used to investigate the effect of coal particle size on the internal recirculation zone (IRZ) and the reattachment length (LR) for the same inlet swirl number (SN). A decrease of nearly 50% in the coal sample size results in the increase of LR and IRZ length by 20% and 82.6%, respectively.

Experimental and Numerical Validation of In-Cylinder Combustion Analysis of DI Diesel Engine

The major factors affecting the process of combustion in a single cylinder diesel engine is in-cylinder fluid flow characteristics. Better fuel-air mixing and combustion rates in diesel engine are primarily enhanced by the fluid flow. The fluid flow prior to combustion process in DI diesel engines travel through induction process and further gets improvised during the compression process. Therefore, it is compulsory to understand the fluid flow motion inside the cylinder in designing the different bowl-in-piston geometries with the most appropriate operating and emission characteristics. A better spatial distribution is required for the injected fuel throughout the entire space of combustion geometry in DI diesel engine, to obtain a better combustion with lesser emission. In order to effectively make use of gas flows it is mandatory to match the piston bowl geometry with fuel spray characteristics. For obtaining better combustion, matching of combustion chamber geometry, fuel injection and gas flows plays prominent role. But it is evident that piston bowl geometry plays a significant role on flow of compressed air when piston moves from BDC to TDC i.e., before the start of combustion, resulting in proper mixing, better vaporization and atomization of fluid particles. When compared with other combustion chambers, Off-set bowl in the absence of central projection with sharp edges provide higher swirl number. Higher these whirl number lesser will be the soot emission at the expense of higher NOx level.