Fuel Mass Fraction Research Articles

Influence of fuel inhomogeneity on detonation wave propagation in a rotating detonation combustor

Rotating detonation combustor (RDC) is a form of pressure gain combustion, which is thermodynamically more efficient than the traditional constant-pressure combustors. In most RDCs, the fuel–air mixture is not perfectly premixed and results in inhomogeneous mixing within the domain. Due to discrete fuel injection locations, local pockets of rich and lean mixtures are formed in the refill region. The objective of the present work is to gain an understanding of the effects of reactant mixture inhomogeneity on detonation wave structure, wave velocity, and pressure profile. To study the effect of mixture inhomogeneity, probability density functions of fuel mass fractions are generated with varying standard deviations. These distributions of fuel mass fractions are incorporated in 2D reacting simulations as a spatially/temporally varying inlet boundary condition. Using this methodology, the effect of mixture inhomogeneity is independently investigated to determine the effects on detonation wave propagation and RDC performance. As mixture inhomogeneity is increased, detonation wave speed, detonation efficiency, and potential for pressure gain all decrease, ultimately leading to the separation of the reaction zone from the shock wave.

Numerical Study On the Effect of Channel Configuration On Mixture Formation of an Axial Flow Wave Rotor Combustor

Abstract Wave rotor combustor technology is a new technical means to improve the thermal efficiency of aero-engine by using unsteady flow and constant volume combustion. In this article, the influence of wave rotor combustor channel structure on the mixture formation in the channel was studied by numerical simulation. The results showed that the internal flow field structure and change of any structure channel are similar. Flow separation will occur in all channels, and wake regions will be formed in the channels. The turbulence kinetic energy in the wake region was increased, and the velocity and pressure were decreased, resulted in the vortex in the channel. When the channel width was reduced to half of the original design, the Relative Standard Deviation (RSD) of the mixture was reduced by at least 54.92% compared to the original design, and the global fuel mass fraction in the channel was increased by at least 27.32%. In addition, the fluctuation of discharge pressure was also reduced. The reduction of the channel height does not lead to a significant improvement in the aforementioned results. This study can provide guidance for the structural design of wave rotor combustor channel.

On the Definition of Reaction Progress Variable in Exhaust Gas Recirculation Type Turbulent MILD Combustion of Methane and n-Heptane

Three-dimensional Direct Numerical Simulations of Exhaust Gas Recirculation (EGR)-type Moderate or Intense Low Oxygen Dilution (MILD) combustion of homogeneous mixtures of methane- and n-heptane–air have been conducted with skeletal chemical mechanisms. The suitability of different choices of reaction progress variable (which is supposed to increase monotonically from zero in the unburned gas to one in fully burned products) based on the mass fractions of different major species and non-dimensional temperature have been analysed in detail. It has been found that reaction progress variable definitions based on oxygen mass fraction, and linear combination of CO, CO2, H2 and H2O mass fractions (i.e. cO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${c}_{O2}$$\\end{document} and cc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${c}_{c}$$\\end{document}) capture all the extreme values of the major species in the range between zero and one under MILD conditions. A reaction progress variable based on fuel mass fraction is found to be unsuitable for heavy hydrocarbons, such as n-heptane, since the fuel breaks down to smaller molecules before the major reactants (products) are completely consumed (formed). Moreover, it has been found that the reaction rates of cO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${c}_{O2}$$\\end{document} and cc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${c}_{c}$$\\end{document} exhibit approximate linear behaviours with the heat release rate in both methane and n-heptane MILD combustion. The interdependence of different mass fractions in the EGR-type homogeneous mixture combustion is considerably different from the corresponding 1D unstretched premixed flames. The current findings indicate that the tabulated chemistry approach based on premixed laminar flames may need to be modified to account for EGR-type MILD combustion. Furthermore, both the reaction rate and scalar dissipation rate of cO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${c}_{O2}$$\\end{document} and cc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${c}_{c}$$\\end{document} are found to be non-linearly related in both methane and n-heptane MILD combustion cases but the qualitative nature of this correlation for n-heptane is different from that in methane. This suggests that the range of validity of SDR-based turbulent combustion models can be different for homogeneous MILD combustion of different fuels.

Experiment investigation on Momordica Charantia biodiesel in CRDI engine with cerium oxide (CeO2) nanoadditives

Most of the transportation fuel is diesel. This type of fuel is widely used and helps the economy by providing high combustion efficiency and affordability. The goal of this study was to analyse the performance and characteristics of a multi-cylinder diesel engine utilising a rail direct injection system and fuel that's composed of 20% momordica. The addition of cerium oxide nanoparticles in the fuel mass fractions of 20 and 40 ppm was performed using an ultrasonicator and a mechanical homogeniser. These small particles help improve fuel stability and prevent injector blockages. By adding cerium oxide nanoparticles to the biodiesel–diesel blend, brake thermal efficiency and heat release rate were also improved. At full load, the MC20 emits 12.341 g/kW h of HC and 84 HSU of smoke, compared to 9.021 g/kW h and 52 HSU for the CONP 40 blended MC20. It is recommended to use cerium oxide nanoparticles at a concentration of 40 ppm for optimal performance, emission combustion, and characteristic enhancement.

Modeling the impact of the fuel injection strategy on the combustion and performance characteristics of a heavy-duty GCI engine

Gasoline compression ignition (GCI) is a promising strategy to achieve high thermal efficiency and low emissions with limited modifications to the conventional diesel engine hardware. It is a partially premixed concept, which derives its superiority from higher volatility and longer ignition delay of gasoline-like fuels combined with higher compression ratio typical of diesel engines. The present study investigates the combustion process in a GCI engine operating with different injection strategies using computational fluid dynamics (CFD). Simulations are carried out on a single cylinder of a multi cylinder heavy-duty compression ignition engine, which operates at a compression ratio of 17:1 and an engine speed of 1038 rev/min. Two different injection strategies viz., late injection (LI), and early pilot injection (EP) are investigated to understand their impact on combustion and performance of the engine. Renormalized group (RNG) k-ε model is used to describe in-cylinder turbulence and KH RT model is used to simulate the fuel spray breakup. The developed CFD methodology is validated against relevant experimental data under a wide range of operating conditions for each injection strategy. The developed CFD methodology was found to capture the engine combustion behavior quite well. Based on the validated CFD model, the differences in the progress of combustion event for the two injection strategies is highlighted. It was found that a larger pilot fuel mass fraction results in a steeper rise in the initial heat release rate which in turn influences the transition to mixing controlled combustion. In line with the experimental data, the study showed that the late pilot injection strategy with three injection pulses, results in higher performance compared to the other conditions.

Modeling study of the ignition characteristics of directly injected 1,3-Cyclohexadiene in surrogate Gasoline/Air under RCCI combustion conditions

In this work a validated chemical kinetic model of the combustion of multicomponent gasoline surrogate fuels containing 680 reactions of 152 species has been used to simulate conditions reminiscent of those of Reactivity Controlled Compression Ignition (RCCI) in order to evaluate 1,3-cyclohexadiene (CYC6H8) as the high reactivity directly injected fuel and a gasoline surrogate fuel as the low reactivity premixed fuel. A single-zone modeling approach was adopted using a modified Cantera example describing the simulation of a gaseous Diesel-type internal combustion engine. The adaptable chemical structure of CYC6H8 to cis-1,3,5-hexatriene (lC6H8), load, start of injection and premixed fuel mass fraction were varied in order to analyze the potential of CYC6H8 as an ignition enhancer. Results have been compared to n-heptane and show that CYC6H8 and its isomer lC6H8 have the potential to be used as the high reactivity directly injected fuel in dual-fuel RCCI combustion, especially at high load conditions. For increased load, the ignition promoting effect is more pronounced at lower premixed fuel mass fractions and less affected by a delayed start of injection. The ignition promoting effect of lC6H8 is more pronounced than CYC6H8 for a decreasing premixed fuel mass fraction. Results from the kinetic analysis indicate that at increased concentrations of lC6H8, the thermal effects are becoming more significant.

Experimental investigation on the electrospray counterflow flame in a small combustor with a porous media as the grounding electrode

An experimental study on electrospray counterflow combustion of ethanol in a new type combustor with a porous media as the grounding electrode is carried out. The electrospray process of ethanol is separated from the combustion system for visualization and four typical spraying modes are identified. The characteristics of electrospray counterflow combustion are discussed. Four flame shapes are classified and the distribution region is determined. The results demonstrate that the double-layer flame and dromedary flame are easier to be observed. The change of fuel mass fraction can significantly affect the flame diameter and temperature. When the fuel mass fraction YF > 0.075, the increase of carrier gas flow rate promotes the fuel evaporation. Ethanol vapor is carried into the porous media, and the flame diameter and temperature are incrensed. When YF < 0.075, the dilution of ethanol vapor by carrier gas is dominant, resulting in the decrease of fuel concentration. The combustion efficiency and ratio of CO2/CO is highest at the dromedary flame, and the maximum combustion efficiency and ratio of CO2/CO are 95.25% and 7.78 for Φ = 0.76 respectively, which means a very efficient conversation of fuel. The results gained insights for the design and operation of electrospray counterflow combustors.

Analysis of knock onset based on two-dimensional direct numerical simulation and theory of explosive transition of deflagration

In this study, we analyzed data from a two-dimensional (2D) direct numerical simulation (DNS) that reproduced the knocking experiment in order to elucidate the knocking phenomenon. First, it was confirmed that the reaction front behavior in 2D DNS could be reproduced as a one-dimensional (1D) laminar premixed flame simulation at extreme conditions. Furthermore, a detailed study using a 1D laminar premixed flame revealed a strong relation between the timing of knock onset and the flame propagation limit of the 1D laminar premixed flame at elevated temperature and pressure conditions. To clarify this relation, we introduced the theory of “explosive transition of deflagration.” This theory shows that when the Lewis number is unity, the time evolution of the normalized fuel mass fraction and temperature in a 0D homogeneous ignition is equal to the temporal evolution observed in a 1D laminar premixed flame, if the spatiotemporal transformation is properly applied. Furthermore, the rate at which the normalized fuel mass fraction decreases in the preheat zone was found to depend on the Lewis number, and when the Lewis number is greater than unity, no flame structure exists above a certain threshold temperature. Finally, the mechanism of knock onset was explained by considering the theory of explosive transition of deflagration and explosive transition boundary plotted on a pressure-temporal diagram.

The exhaust total exergy analysis of compressed natural gas used in an indirect injection diesel engine in different working conditions

Deficiencies of energy resources, air pollution, and climate change have led to some threats to energy security and human health, making natural gas to be offered as one of the most widespread alternative fuels. The novelties of this experimental study are (i) injecting the Compressed Natural Gas (CNG) into the indirect injection diesel engine and measuring the exhaust total exergy, and 2nd law efficiency of a dual-fuel engine via considering the physical and chemical exergy of emissions. (ii) Injecting the CNG with a reduced mole fraction of byproducts decreases the chemical exergy of exhaust emissions that are considered to be wasted in the atmosphere which means the destruction of exhaust exergy that cannot be recycled is declined, and the 2nd law efficiency has been increased. The testbed is provided in the internal combustion engine laboratory of the Ferdowsi University of Mashhad. Replacing 20% diesel fuel mass fraction with natural gas showed that, by the CNG enhancement, the exhaust total exergy has an upward trend which faces maximum variation at 1200 rpm. Also, assuming that excess CO and unburned hydrocarbon can be recovered to reach the level observed in the absence of CNG, the maximum decline in exhaust chemical exergy is related to the speed of 3000 rpm, 25% torque, and 10% exhaust gas recirculation (EGR) by 11.7% between 0% and 20% CNG. Also, the most significant increase in second-law efficiency is reported for 3000 rpm, 25% torque, and 10% EGR with a 4.5% increase.

From molecular to sub-μm scale: The interplay of precursor concentrations, primary particle size, and carbon nanostructure during soot formation in counter-flow diffusion flames

The focus of this work is on counter-flow diffusion flames of C2H4/air near the sooting limit (fV < 500 ppb) to shed light on the transition of precursor molecules to primary soot particles and their nanostructure. The applied experimental techniques cover non-intrusive methods based on laser-induced incandescence (LII) for determination of soot volume fractions, primary particle sizes, and ratios of refractive indices for absorption at different wavelengths. The methods are complemented by intrusive methods such as sampling with microprobes and analysis of gas composition by gas chromatography and mass spectrometry, particle sizing by differential mobility analysis, and determining carbon nanostructures of particles by high-resolution transmission electron microscopy (HRTEM). For numerical simulation, the well-known ABF-model is applied.The experimentally determined structures of the counter-flow flames could be well reproduced within the experimental uncertainties by the ABF-model for varying fuel mass fractions and strain rates. The numerical simulations identify the different processes during particle formation and the main variation can be attributed to variation of surface growth rates when applying strain rates and fuel mass fractions leading to higher soot volume fractions. Particle size distributions detected in the fuel flow near and below the stagnation plane appear bimodal with distinct maxima at particles sizes about 5 nm and 20 nm. The nanostructure of the primary particles exhibits basic structural units (BSUs), that increase up to the size of 7 Å to 10 Å at increasing soot volume fractions from about 100 ppb to 300 ppb. This coincides with the increase of the mole fractions of the detectable soot precursors with increasing soot volume fraction. The ratios of refractive index functions for absorption E(m,λ532)/E(m,λ1064) and E(m,λ266)/E(m,λ1064) decrease approximately linearly with increasing soot volume fractions. This is corroborated by the analyses of HRTEM-images that clearly bring about increasing sized BSUs with increasing soot volume fractions causing a shift of the absorption to larger wavelengths.

Numerical analysis of combustion noise in an atmospheric swirl-stabilized LDI burner through modal decomposition techniques

Combustion noise in gas turbine engines has recently become a relevant source of noise in the aircraft due to the appearance of new burner architectures that are intrinsically more unstable, and the optimization of other conventional noise sources in this mean of transport (e.g., jet, fan, airframe). In this work, a simulation setup for reactive conditions was prepared in the CONVERGE finite-volume package using the detailed chemistry SAGE solver to model the combustion of a benchmark case, which was solved using a LES approach with three different cell base sizes: 8,10,12 mm. A confined liquid-fueled swirl-stabilized burner located at the CORIA Laboratory, France, was used to validate the numerical results with the experimental measurements obtained at this facility. OH-PLIF measurements and PDA results for both phases were used to guarantee the accuracy of the numerical OH contours and the velocity profiles of both phases. These experimental measurements were collected at CORIA. After ensuring the stabilization of the numerical flame, the reactive simulations were extended with some adjustments in the time step to capture the acoustic motion. Several techniques like Fast Fourier Transform (FFT), Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) were used to analyze these results and confirm the presence of a Precessing Vortex Core (PVC) and a Vortex Breakdown Bubble (VBB) during the coupling of pressure, axial velocity and fuel mass fraction in reactive conditions. Furthermore, the acoustic analysis performed with a Helmholtz solver proved that the second longitudinal mode of the chamber (310 Hz) was present in the pressure signal (300 Hz in the LES calculations) and resonated with the Vortex Breakdown Bubble (VBB). However, this dominant frequency did not appear in the frequency distribution of the OH mass fraction and no feedback interaction between the acoustic and the combustion happened. Thus, only combustion noise was obtained.

Оценка возможности применения композитного материала в конструкции криогенного конического бака ракетного блока

Reducing mass of the launch vehicle components structure to increase the payload mass launched into orbit is one of the main areas in developing the space services market. Modern designs of the launch vehicles require extremely high fuel mass fraction, which necessitates introduction of the low-density materials. Fuel tanks could count for 70...80% of the total product volume, which results in the development of tanks for the cryogenic fuel obtaining decisive importance in design and development of the new type of launch vehicles. Introduction of the composite materials in designing a cryogenic fuel tank makes it possible to lower its mass by 30% compared to a reference aluminum tank, which, accordingly, allows increasing the inserted payload mass. Review of the methods used in manufacturing the cryogenic composite fuel tanks is presented. Liner manufacturing technology and its material are proposed, taking into account the temperature difference during shaping and its interaction with the cryogenic fuel. Composite material and method for manufacturing the composite tank are selected. Design calculation of the composite cryogenic tank was carried out.

Computational fluid dynamics study of Y3+-doped Ba(Ce,Zr)O3 based single channel proton ceramic fuel cell

Theoretical studies using Computational Fluid Dynamics (CFD) modeling have been established in the field of polymer electrolyte membrane fuel cells (PEMFCs) and oxygen ion solid oxide fuel cells (O2-SOFCs). However, its implementation in the proton ceramic fuel cell (PCFC) development is still in progress and very limited literature can be found. Thus, in this simulation study, ANSYS 2022 CFD software has been employed to predict hydrogen mass fraction distribution and power density of a single-channel PCFC operating in 100 % hydrogen fuel. This simulation utilized input data based on previously published experimental works. The mass fraction of H2 was 0.0 at the cathode area indicating that the electrolyte layer is fully dense and no leakage of H2 from the anode area into the cathode area. The maximum power density in 100 % H2 was 0.34 W/cm2 at 800° C. This is in agreement with the power density produced by the in-house fabricated button cell with the configuration of NiO-BCZY|BCZY|LSCF (BCZY=BaCe0.54Zr0.36Y0.1O2.95, LSCF=La0.6Sr0.4Co0.2Fe0.8O3-δ.) that showed a maximum power density of 0.33W/cm2 in 100 % H2. This analysis will contribute to insight information on the relationship between fuel mass fraction distribution and fuel cell performance for future improvements in the field of PCFC.

Estimation of Wiebe Function Parameters for Syngas and Anode Off-Gas Combustion in Spark-Ignition Engines

Abstract Wiebe functions, analytical equations that estimate the fuel mass fraction burned (MFB) during combustion, have been effective at describing spark-ignition (SI) engine combustion using gasoline fuels. This study explores if the same methodology can be extended for SI combustion with syngas, a gaseous fuel mixture composed of H2, CO, and CO2, and anode-off gas; the latter is an exhaust gas mixture emitted from the anode of a Solid Oxide Fuel Cell, containing H2, CO, H2O, and CO2. For this study, anode off-gas is treated as a syngas fuel diluted with CO2 and vaporized water. Combustion experiments were run on a single-cylinder, research engine using syngas and anode-off gas as fuels. One single Wiebe function and three double Wiebe functions were fitted and compared with the MFB profile calculated from the experimental data. It was determined that the SI combustion process of both the syngas and the anode-off gas could be estimated using a governing Wiebe function. While the detailed double Wiebe function had the highest accuracy, a reduced double Wiebe function is capable of achieving comparable accuracy. On the other hand, a single Wiebe function is not able to fully capture the combustion process of a SI engine using syngas and anode off-gas.

Soot nanoparticle sizing in counterflow flames using in-situ particle sampling and differential mobility analysis verified with two-colour time-resolved laser-induced incandescence

The emphasis of this work is on the development of an intrusive particle sampling system to track the evolution of soot nanoparticles in ethylene counterflow diffusion flames. The overarching objective is to determine the mobility size distributions in a spatially resolved manner using the developed probe system coupled with differential mobility analysis, i.e., a scanning mobility particle sizer (SMPS). The probe system involves a tailor-made quartz probe, gas supply, pressure control periphery, and a traverse system enabling a precise positioning along the flame axis. In preliminary experiments, the dilution ratio of the quartz probe as function of boundary conditions as well as particle losses during intrusive particle sampling are studied. To demonstrate the capability of the developed particle sampling system, results from ethylene counterflow diffusion flames with different fuel mass fractions and strain rates are presented and compared with results derived by non-intrusive laser-based diagnostics, i.e., two-colour time-resolved laser induced incandescence (2C-TiRe-LII). Results of these experiments indicate that the particle sampling system is capable of tracking the development of particle size distributions – independent of the distribution function, i.e., mono-, bi- or multimodal shape – in counterflow flames. Likewise, the agreement between soot volume fractions and particle size distributions measured via intrusive particle sampling coupled with differential mobility analysis and non-intrusive laser-based 2C-TiRe-LII is excellent at varying the fuel mass fractions and strain rates of the ethylene counterflow flames.

Study of Diffusion Cool Flames of Dimethyl Ether in a Counterflow Burner under a Wide Range of Pressures.

Cool flames have been studied for more than three centuries since the first observation. However, there are few achievements on the effects of the pressure on cool flames. In this work, a diffusion cool flame has been for the first time established using a counterflow configuration under a wide range of pressures. Dimethyl ether is used as the fuel because its low-temperature chemistry has been well tested. The pressure range of the experiments is from 0.05 to 0.15 MPa. The extinction limits, flame temperatures, and combustion products have been measured and simulated. In general, the reactivity of cool flames is stronger with increasing pressure. Specifically, at a fixed fuel mass fraction, the cool flame has a higher extinction strain rate, temperature, and concentration of products under higher pressure. However, the enhancement effect decreases with the increase of pressure. Interestingly, it was observed that the flame became thicker when the pressure increased. Moreover, the cool flame would deflagrate and transform to a hot flame when the pressure exceeds a certain value. The model captures the trends well but underpredicts the extinction limits and overpredicts the flame temperatures and product concentration. Path flux analyses and heat release rate analyses were carried out. It was found that the main heat release reactions are the reactions with CH3OCH2 radicals under low pressure, and CO prefers to form CO2 indirectly through HOCHO radicals. The study advances the understanding of cool flames in a wide range of pressures and provides experimental data for the improvement of the models.

Comparison between sonic jets with one jet orifice and two opposite orifices into a Ma-3.0 supersonic crossflow through circular ducts

Large-eddy simulations and nanoparticle-based planar laser scattering experiments are conducted to investigate various physical aspects of transverse sonic jets injected into a Ma-3.0 supersonic crossflow through a circular pipe. Configurations with one jet and two opposite jets are compared. For the single jet, a separation shock is generated by the recirculation zone on the opposite wall, and this intersects with the jet shear layer to push several jet plumes into the near-wall region. For the two jets, the bow shocks interact with each other, forming an oblique shock train. All of the shocks promote vortex breakage in jet wakes. A counter-rotating vortex pair is generated in the jet near-field region, enhancing the local mixing. A near-wall region in the jet lee between the counter-rotating vortex pair branches exhibits a low fuel mass fraction. The jet fluid in the downstream near-wall region is entrained by the crossflow upstream of the jet. The interaction between the bow shocks and shear layers of the two jets induces recirculation zones in the lee of the jet, which enhance the fuel mixing. This explains the phenomenon whereby the total pressure recovery coefficient and mixing efficiency of two jets are higher than those of the single jet.

박용고속엔진의 프로판 개조를 위한 점화시기 분석

Regulations on exhaust emissions of marine engines are being strengthened, and many related technologies are being developed. In this study, the combustion characteristics of the engine were analyzed for the propane conversion of a 225 kW high-speed engine. The movement of the piston was simulated using a variable grid from 120 degrees before TDC to 120 degrees after TDC, and the ignition timing was analyzed by changing the ignition timing from 20 degrees before TDC to five degrees after TDC at intervals of five degrees. Residual fuel mass fraction was rapidly reduced to 80% during ten degrees of crank angle after ignition, and then decreased slowly thereafter. After combustion, the amount of residual fuel increased significantly when the ignition timing was later than five degrees before TDC. Nitrogen oxide was greatly reduced as the ignition timing was delayed. The engine output was highest at five degree before TDC and decreased when the ignition timing was earlier or later. Considering performance and exhaust emissions, the optimal ignition timing is five degrees before TDC under this engine operating condition.

Effect of spark ignition location on the turbulent jet ignition characteristics in a lean burning natural gas engine

The Turbulent Jet Ignition is an effective concept to achieve stable lean burning for natural gas engines due to the multiple ignition sources, high ignition energy, and fast combustion rate. A variation of the ignition location has a non-negligible effect on the ignition performance of the TJI system. The present work aims to provide more details on this effect by numerical simulations. Both factors of the additional fuel supply to the pre-chamber and the in-cylinder flow field are taken into consideration in this study. A numerical model is built based on a lean burning natural gas engine and validated by experimental results. Five different spark ignition sources are equally arranged on the vertical axis of the pre-chamber, with different distances from the connecting orifices. Simulations are carried out under the same initial and boundary conditions except for the location of the ignition source. Combustion pressure, in-cylinder flow field, fuel mass fraction distribution, and heat release rate are analyzed to study the in-cylinder ignition and combustion process. The results show that a rotational flow and a non-uniform fuel distribution are formed in the pre-chamber during the compression stroke. The turbulent jet characteristics are significantly influenced by the coupling of two factors: the combustion rate inside the pre-chamber as well as the flame propagation distance from the ignition source to the connecting orifices. Rapid combustion rate and shorter flame propagation distance both lead to the earlier ejection of cold jets and hot jets. Among five ignition sources, the one located closest to the connecting orifices generates earlier hot jets with the highest mean velocity. The jets are more effective to ignite the lean mixture and could decrease the combustion duration of the main chamber.

Numerical prediction of the spray from an air-assisted fuel injection system via Eulerian–Lagrangian approach

Air-assisted fuel injection (AAFI) systems may be installed in aviation piston engines for atomization of heavy fuels. However, there are few studies on the in-cylinder air-assisted spray characteristics, which affects the improvement of AAFI engine performance. In this study, an improved air-assisted spray simulation method based on ANSYS FLUENT was proposed to predict the changes in air-assisted spray characteristics alongside spray development, compared with previous simulations, the simulation in this paper was extended in both temporal and spatial domains and more accurate boundary conditions were given. The Eulerian–Lagrangian approach was used to represent the two-phase spray flow and a dynamic mesh model was used to simulate the movement of injector needle valve. The improved method was validated by comparison against experimental results in terms of spray shape, spray volume, spray penetration, spray droplet size spatial distribution, and overall Sauter mean diameter (SMD). By using the improved method, the average relative errors of the simulation results in spray volume and spray penetration were reduced by 13.5% and 10.2%, respectively. Additionally, some typical spray field parameters (gas phase pressure, gasified fuel mass fraction, etc.) were analyzed. The improved method can be used to study the in-cylinder air-assisted spray characteristics, which is beneficial for the fuel injection parameter optimization and the combustion chamber design of the AAFI engine.