共查询到20条相似文献,搜索用时 15 毫秒
1.
A. F. Latypov 《Journal of Applied Mechanics and Technical Physics》2015,56(5):799-812
A functional mathematical model of a hydrogen-driven combustion chamber for a scramjet is described. The model is constructed with the use of one-dimensional steady gas-dynamic equations and parametrization of the channel configuration and the governing parameters (fuel injection into the flow, fuel burnout along the channel, dissipation of kinetic energy, removal of some part of energy generated by gases for modeling cooling of channel walls by the fuel) with allowance for real thermophysical properties of the gases. Through parametric calculations, it is found that fuel injection in three cross sections of the channel consisting of segments with weak and strong expansion ensures a supersonic velocity of combustion products in the range of free-stream Mach numbers M∞ = 6–12. It is demonstrated that the angle between the velocity vectors of the gaseous hydrogen flow and the main gas flow can be fairly large in the case of distributed injection of the fuel. This allows effective control of the mixing process. It is proposed to use the exergy of combustion products as a criterion of the efficiency of heat supply in the combustion chamber. Based on the calculated values of exergy, the critical free-stream Mach number that still allows scramjet operation is estimated. 相似文献
2.
In order to understand the effect of both the new homogeneous charge compression ignition (HCCI) combustion process and the use of biofuel, optical measurements were carried out into a transparent CR diesel engine. Rape seed methyl ester was used and tests with several injection pressures were performed. OH and HCO radical were detected and their evolutions were analyzed during the whole combustion. Moreover, soot concentration was measured by means the two colour pyrometry method. The reduction of particulate emission with biodiesel as compared to the diesel fuel was noted. Moreover, this effect resulted higher increasing the injection pressure. In the case of RME the oxidation of soot depends mainly from O2 content of fuel and OH is responsible of the NO formation in the chamber as it was observed for NOx exhaust emission. Moreover, it was investigated the evolution of HCO and CO into the cylinder. HCO was detected at the start of combustion. During the combustion, HCO oxidizes due to the increasing temperature and it produces CO. Both fuels have similar trend, the highest concentrations are detected for low injection pressure. This effect is more evident for the RME fuel. 相似文献
3.
不同舱室结构内航空油料的燃爆参数存在差异,为了解和掌握不同结构舱室内航空油料的燃爆危害性,运用计算流体动力学(computational fluid dynamics,CFD)方法对不同结构航空油料舱室内的航空油料蒸汽燃爆问题进行了数值模拟。结果表明:密闭航空油料舱中的航空油料蒸汽预混燃爆时,油舱各处压力分布较均匀,无隔板密闭舱室和含不完全分割隔板密闭舱室内航空油料的最大燃爆压力分别为0.76、0.74 MPa,即舱室内的不完全分割隔板对航空油料燃爆时所产生的最大压力无显著影响;隔板等特殊结构的存在使舱室内部产生了气流漩涡,增大了燃料消耗的速率,导致火焰面传播速度及压力上升速率增大,舱室内各处燃料的质量分数由火焰面决定。 相似文献
4.
Particle image velocimetry is applied to measure the vertical (r–z) plane flow structures in a light-duty direct-injection diesel engine with a realistic piston geometry. The measurements are corrected for optical distortions due to the curved piston bowl walls and the cylindrical liner. Mean flow fields are presented and contrasted for operation both with and without fuel injection and combustion. For operation with combustion, the two-dimensional divergence of the measured mean velocity fields is employed as a qualitative indicator of the locations of mean heat release. In agreement with numerical simulations, dual-vortex, vertical plane mean flow structures that may enhance mixing rates are formed approximately mid-way through the combustion event. Late in the cycle a toroidal vortex forms outside the bowl mouth. Imaging studies suggest that soot and partially oxidized fuel trapped within this vortex are slow to mix with surrounding fluid; moreover, the vortex impedes mixing of fluid exiting the bowl with air within the squish volume. 相似文献
5.
6.
Direct-injection spark-ignition (DISI) gasoline engines have been spotlighted due to their high thermal efficiency. Increase in the compression ratio that result from the heat absorption effect of fuel vaporization induces higher thermal efficiency than found in port fuel injection (PFI) engines. Since fuel is injected at the cylinder directly, various fuel injection strategies can be used. In this study, turbulent intensity was improved by a double injection strategy while maintaining mixture homogeneity. To analyze the turbulence enhancement effects using the double injection strategy, a side fuel injected, homogeneous-charge-type DISI gasoline engine with a multi-hole-type injector was utilized. The spray model was evaluated using experimental data for various injection pressures and the combustion model was evaluated for varied ignition timing. First and second injection timing was swept by 20 degree interval. The turbulent kinetic energy and mixture inhomogeneity index were mapped. First injection at the middle of the intake stroke and second injection early in the compression stroke showed improved turbulent characteristics that did not significantly decrease with mixture homogeneity. A double injection case that showed improved turbulent intensity while maintaining an adequate level of mixture homogeneity and another double injection case that showed significantly improved turbulent intensity with a remarkable decrease in mixture homogeneity were considered for combustion simulation. We found that the improved turbulent intensity increased the flame propagation speed. Also, the mixture homogeneity affected the pressure rise rate. 相似文献
7.
Gregory Hannebique Patricia Sierra Eleonore Riber Bénédicte Cuenot 《Flow, Turbulence and Combustion》2013,90(2):449-469
Because of compressibility criteria, fuel used in aeronautical combustors is liquid. Their numerical simulation therefore requires the modeling of two-phase flames, involving key phenomena such as injection, atomization, polydispersion, drag, evaporation and turbulent combustion. In the present work, particular modeling efforts have been made on spray injection and evaporation, and their coupling to turbulent combustion models in the Large Eddy Simulation (LES) approach. The model developed for fuel injection is validated against measurements in a non-evaporating spray in a quiescent atmosphere, while the evaporation model accuracy is discussed from results obtained in the case of evaporating isolated droplets. These models are finally used in reacting LES of a multipoint burner in take-off conditions, showing the complex two-phase flame structure. 相似文献
8.
Combustion of gasoline in a direct injection controlled auto-ignition (CAI) single-cylinder research engine was studied. CAI operation was achieved with the use of the negative valve overlap (NVO) technique and internal exhaust gas re-circulation (EGR). Experiments were performed at single injection and split injection, where some amount of fuel was injected close to top dead centre (TDC) during NVO interval, and the second injection was applied with variable timing. Additionally, combustion at variable fuel-rail pressure was examined.Investigation showed that at fuel injection into recompressed exhaust fuel reforming took place. This process was identified via an analysis of the exhaust-fuel mixture composition after NVO interval. It was found that at single fuel injection in NVO phase, its advance determined the heat release rate and auto-ignition timing, and had a strong influence on NOX emission. However, a delay of single injection to intake stroke resulted in deterioration of cycle-to-cycle variability. Application of split injection showed benefits of this strategy versus single injection. Examinations of different fuel mass split ratios and variable second injection timing resulted in further optimisation of mixture formation. At equal share of the fuel mass injected in the first injection during NVO and in the second injection at the beginning of compression, the lowest emission level and cyclic variability improvement were observed. 相似文献
9.
Mamoru Tanahashi Shohei Inoue Masayasu Shimura Shohei Taka Gyung-Min Choi Toshio Miyauchi 《Experiments in fluids》2008,45(3):447-460
Flame structures of turbulent premixed flames in a noise-controlled, swirl-stabilized combustor are investigated to clarify
the mechanism of combustion noise reduction by the secondary fuel injection. Planar laser-induced fluorescence (PLIF) is conducted
for several cases with different secondary fuel injection, and 3D flame structure is reconstructed from PLIF results on multiple
planes. The secondary fuel injection suppresses the fluctuation of high-temperature gas in the recirculation zone and reduces
Reynolds stress and entropy terms in the acoustic sound source. In the flame zone, effects of the injection frequency are
discussed by introducing mean progress variable. The flame brush is very wide for the no control case, whereas it becomes
thin and is confined to a narrow space for the secondary fuel injection cases. The investigated combustor gives minimum sound
level at a relevant fuel injection frequency, which is very low compared with the natural acoustic mode of the combustor.
The flame brush becomes very thin, and self-induced oscillations of the flame brush disappear at this relevant frequency.
The oscillation of the flame brush represents large-scale fluctuation of the mean heat release rate. The relations between
characteristics of flame brush and combustion noise are discussed by introducing instantaneous and dynamical effects of flame
front on the entropy term of the sound source. The secondary fuel injection works for the control of the entropy term in the
sound source because the thin flame brush represents suppression of the instantaneous and dynamical effects. 相似文献
10.
Juhyeong Seo Ho Young Kim Simsoo Park Scott C. James Sam S. Yoon 《Flow, Turbulence and Combustion》2016,96(2):391-415
Gasoline direct injection (GDI) increases engine power output and reduces emissions. In GDI engines, increasing injection pressure improves atomization, which increases thermal efficiency at the cost of wall wetting. When wall wetting occurs, both soot emissions and fuel consumption increase. Wall wetting in GDI engines under cold driving conditions has rarely been considered. In this study, experimental data characterizing droplet splashing/spreading phenomena were collected to inform numerical simulations of combustion characteristics and wall wetting subject to variable driving conditions and excess air ratio, λ. Fully 3D and unsteady numerical simulations were carried out to predict flow-field, combustion, and spray-impingement characteristics. To simulate a GDI engine, a spray-impingement model was developed using both experimental data and previous modeling efforts. The excess air ratio and driving-condition temperature were the variable parameters considered in this study. When decreasing λ from 1.0 to 0.7 by increasing the fuel-injection rate (fuel rich), the cylinder pressure increases to 61 % of the pressure when λ=1.0. Because of increasing the fuel-injection rate, the increased momentum in the fuel spray increases both wall wetting and soot generation. At low driving-condition temperatures, the cylinder pressure was up to 63 % less than that under warm conditions, but with increased soot generation. Simulations revealed a correlation between wall wetting and the soot emissions. Soot generation was most sensitive to changes in wall wetting. 相似文献
11.
Shock tube studies of thermal radiation of diesel-spray combustion under a range of spray conditions
A tailored interface shock tube and an over-tailored interface shock tube were used to measure the thermal energy radiated
during diesel-spray combustion of light oil, α-methylnaphthalene and cetane by changing the injection pressure. The ignition
delay of methanol and the thermal radiation were also measured. Experiments were performed in a steel shock tube with a 7
m low-pressure section filled with air and a 6 m high-pressure section. Pre-compressed fuel was injected through a throttle
nozzle into air behind a reflected shock wave. Monochromatic emissive power and the power emitted across all infrared wavelengths
were measured with IR-detectors set along the central axis of the tube. Time-dependent radii where soot particles radiated
were also determined, and the results were as follows. For diesel spray combustion with high injection pressures (from 10
to 80 MPa), the thermal radiation energy of light oil per injection increased with injection pressure from 10 to 30 MPa. The
energy was about 2% of the heat of combustion of light oil at P
inj = about 30 MPa. At injection pressure above 30 MPa the thermal radiation decreased with increasing injection pressure. This
profile agreed well with the combustion duration, the flame length, the maximum amount of soot in the flame, the time-integrated
soot volume and the time-integrated flame volume. The ignition delay of light oil was observed to decrease monotonically with
increasing fuel injection pressure. For diesel spray combustion of methanol, the thermal radiation including that due to the
gas phase was 1% of the combustion heat at maximum, and usually lower than 1%. The thermal radiation due to soot was lower
than 0.05% of the combustion heat. The ignition delays were larger (about 50%) than those of light oil. However, these differences
were within experimental error.
An abridged version of this paper was presented at the 18th Int. Symposium on Shock Waves at Sendai, Japan during July 21 to 26, 1991 and at the 19th Int. Symposium on Shock Waves at Marseille, France during July 26 to 30, 1993. 相似文献
An abridged version of this paper was presented at the 18th Int. Symposium on Shock Waves at Sendai, Japan during July 21 to 26, 1991 and at the 19th Int. Symposium on Shock Waves at Marseille, France during July 26 to 30, 1993. 相似文献
12.
Emissions remain a critical issue affecting engine design and operation, while energy conservation is becoming increasingly important. One approach to favorably address these issues is to achieve homogeneous charge combustion and stratified charge combustion at lower peak temperatures with a variable compression ratio, a variable intake temperature and a trapped rate of the EGR using NVO (negative valve overlap). This experiment was attempted to investigate the origins of these lower temperature auto-ignition phenomena with SCCI and CAI using gasoline fuel. In case of SCCI, the combustion and emission characteristics of gasoline-fueled stratified-charge compression ignition (SCCI) engine according to intake temperature and compression ratio was examined. We investigated the effects of air–fuel ratio, residual EGR rate and injection timing on the CAI combustion area. In addition, the effect of injection timing on combustion factors such as the start of combustion, its duration and its heat release rate was also investigated. 相似文献
13.
The industrial combustion chamber designed for burning low-calorific syngas from gasification of waste biomass is presented. For two different gases derived from gasification of waste wood chips and turkey feathers the non-premixed turbulent combustion in the chamber is simulated. It follows from our computations that for stable process the initial temperature of these fuels must be at least 800 K, with comparable influx of air and fuel. The numerical simulations reveal existence of the characteristic frequency of the process which is later observed in high-speed camera recordings from the industrial gasification plant where the combustion chamber operates. The analysis of NO formation and emission shows a difference between wood-derived syngas combustion, where thermal path is prominent, and feathers-derived fuel. In the latter case thermal, prompt and N2O paths of nitric oxides formation are marginal and the dominant source of NO is fuel-bound nitrogen. 相似文献
14.
Performance of supersonic model combustors with staged injections of supercritical aviation kerosene 总被引:1,自引:0,他引:1
Supersonic model combustors using two-stage injections of supercritical kerosene were experimentally investigated in both Mach 2.5 and 3.0 model combustors with stagnation temperatures of approximately 1,750 K. Supercritical kerosene of approximately 760 K was prepared and injected in the overall equivalence ratio range of 0.5-1.46. Two pairs of integrated injector/flameholder cavity modules in tandem were used to facilitate fuel-air mixing and stable combustion. For single-stage fuel injection at an upstream location, it was found that the boundary layer separation could propagate into the isolator with increasing fuel equivalence ratio due to excessive local heat release, which in turns changed the entry airflow conditions. Moving the fuel injection to a further downstream location could alleviate the problem, while it would result in a decrease in combustion efficiency due to shorter fuel residence time. With two-stage fuel injections the overall combustor performance was shown to be improved and kerosene injections at fuel rich conditions could be reached without the upstream propagation of the boundary layer separation into the isolator. Furthermore, effects of the entry Mach number and pilot hydrogen on combustion performance were also studied. 相似文献
15.
A. L. N. Moreira A. S. Moita E. Cossali M. Marengo M. Santini 《Experiments in fluids》2007,43(2-3):297-313
The present paper reports an experimental study aimed at characterizing the effects of heat transfer on the secondary atomization,
which occurs during droplet impact on hot surfaces at conditions reproducing those occurring at fuel injection in internal
combustion engines. The experiments consider single isooctane and water droplets impacting at different angles on a stainless
steel surface with known roughness and encompass a range of Weber numbers from 240 to 600 and heat transfer regimes from the
film-vaporization up to the Leidenfrost regime. The mechanisms of secondary breakup are inferred from the temporal evolution
of the morphology of the impact imaged with a CCD camera, together with instantaneous measurements of droplet size and velocity.
The combination of a technique for image processing with a phase Doppler instrument allows evaluating extended size distributions
from 5.5 μm up to a few millimetres and to cover the full range of secondary droplet sizes observed at all heat transfer regimes
and impaction angles. Temporal evolution of the size and velocity distributions are then determined. The experiments are reported
at impact conditions at which disintegration does not occur at ambient temperature. So, any alteration observed in droplet
impact behavior is thermally induced. The analysis is relevant for port fuel injection systems, where droplets injected to
impact on the back surface of the valves, behave differently depending on fuel properties, particularly when the use of alcohols
is considered, even as an additive to gasoline. 相似文献
16.
Marc Chauvy Bruno Delhom Julien Reveillon Francois-Xavier Demoulin 《Flow, Turbulence and Combustion》2010,84(3):369-396
This work presents a numerical study dedicated to the formation of unburnt hydrocarbon. Two configurations: head-on quenching
(HOQ) on a planar wall and in crevices, are considered. It is well known that they contribute for an important part to the
sources of hydrocarbon (HC) emission in a combustion chamber. The aim of this work is to use laminar flame simulations (LFS)
to understand how the unburnt HC are produced near walls in gasoline engine. A skeletal mechanism (29 species and 48 reactions)
mimicking iso-octane combustion is used. In the HOQ configuration, the flame front propagates toward the cold wall where quenching
occurs. The numerical procedure and the chemical scheme used in this study are first validated by comparisons with literature
results for the 1D case. Several aspects of flame wall quenching such as oxidation of unburnt HC, wall heat flux, quench distances
as well as HC families are investigated by varying parameters like wall temperature and equivalence ratio. In a second part,
crevices are considered to study the impact of wall imperfections in combustion chambers. Configurations with different geometrical
and thermodynamic properties are tested. It leads to a wide range of flame properties and HC production modes. When incomplete
combustion occurs, total HC (fuel + HC) concentration can reach very high levels at the wall. When the crevice is not wide
enough, the flame cannot propagate and the quantity of HC is smaller than in the case where the flame can propagate (but the
fuel is not oxidizing). If the crevice is wide enough for the flame to propagate, HOQ occurs at the bottom of the crevice
and HC accumulate in the corners. The computational results obtained in this work demonstrate the ability of LFS to reproduce
incomplete combustion mechanisms that are responsible for a major part of HC production in gasoline engines. 相似文献
17.
Experimental study on the flow field behind a backward-facing step using a detonation-driven shock tunnel 总被引:1,自引:0,他引:1
The supersonic combustion RAM jet (SCRAM jet) engine is expected to be used in next-generation space planes and hypersonic airliners. To develop the engine, stabilized combustion in a supersonic flow field must be attained even though the residence time of flow is extremely short. A mixing process for breathed air and fuel injected into the supersonic flow field is therefore one of the most important design problems. Because the flow inside the SCRAM jet engine has high enthalpy, an experimental facility is required to produce the high-enthalpy flow field. In this study, a detonation-driven shock tunnel was built to produce a high-enthalpy flow, and a model SCRAM jet engine equipped with a backward-facing step was installed in the test section of the facility to visualize flow fields using a color schlieren technique and high-speed video camera. The fuel was injected perpendicularly to a Mach 3 flow behind the backward-facing step. The height of the step, the injection distance and injection pressure were varied to investigate the effects of the step on air/fuel mixing characteristics. The results show that the recirculation region increases as the fuel injection pressure increases. For injection behind the backward-facing step, mixing efficiency is much higher than with a flat plate. Also, the injection position has a significant influence on the size of the recirculation region generated behind the backward-facing step. The schlieren photograph and pressure histories measured on the bottom wall of the SCRAM jet engine model show that the fuel was ignited behind the step.Communicated by K. Takayama
PACS 47.40.Ki 相似文献
18.
A numerical study was performed to investigate chemically reactive flows with sprays inside a staged turbine combustor (STC) using a modified version of the KIVA-II code. This STC consists of a fuel nozzle (FN), a rich-burn (RB) zone, a converging connecting pipe, a quick-quench (QQ) zone, a diverging connecting pipe and a lean-combustion (LC) zone. From the computational viewpoint, it is more efficient to split the STC into two subsystems, called FN/RB zone and QQ/LC zones, and the numerical solutions were obtained separately for each subsystem. This paper addresses the numerical results of the STC which is equipped with an advanced airblast fuel nozzle. The airblast nozzle has two fuel injection passages and four air flow passages. The input conditions used in this study were chosen similar to those encountered in advanced combustion systems. Preliminary results generated illustrate some of the major features of the flow and temperature fields inside the STC. Velocity, temperature and some critical species information inside the FN/RB zone are given. Formation of the co- and counter-rotating bulk flow and the sandwiched-ring-shaped temperature field, typical of the confined inclined jet-in-cross-flow, can be seen clearly in the QQ/LC zones. The calculations of the mass-weighted standard deviation and the pattern factor of temperature revealed that the mixing performance of the STC is very promising. The temperature of the fluid leaving the LC zone is very uniform. Prediction of the NOx emission shows that there is no excessive thermal NOx produced in the QQ/LC zones for the case studied. From the results obtained so far, it appears that the modified KIVA-II code can be used to guide the low-emission combustion experiments. 相似文献
19.
The effects of magnetic field on the microgravity combustion characteristics of a single methanol droplet in homogeneous flow
are numerically investigated to develop an effective magnetic control method for microgravity droplet combustion and spray
combustion systems. First, governing equations of microgravity single methanol droplet combustion under a homogeneous magnetic
field based on an unsteady two-dimensional, spherically symmetric model including single-step chemistry are presented. Employing
numerical modeling, several combustion behaviors are calculated taking into account the effect of the unsteady magnetic field
profiles at the flame front. It is found that the flame front becomes deformed and is elongated in the direction of the magnetic
field due to the inhomogeneous magnetic pressure distribution at the interface between the fuel vapor phase and the oxidizer
phase. This nonuniformity of magnetic pressure is caused by the transient deformation of the magnetic field with refraction
of magnetic flux at the flame front due to the difference of magnetic susceptibility between the diamagnetic fuel vapor phase
and the paramagnetic oxidizer phase. 相似文献
20.
Joachim Werther Ernst-Ulrich Hartge Lars Ratschow Reiner Wischnewski 《Particuology》2009,7(4):324-331
The concept of simulation-supported measurement is suggested for the elucidation of processes occurring in the combustion chambers of large-scale circulating fluidized bed combustors where the desired information cannot be obtained by direct measurements. The concept is illustrated with the example of secondary air injection where the way the air is released, the penetration depth and the evenness of air distribution over the cross-sectional area of the combustion chamber are of interest. The measured information consists of lateral profiles of oxygen concentrations measured with gas sampling probes at two ports which were located 5 and 9 m, respectively, above the level of secondary air injection. The simulation is carried out on the basis of a 3D semi-empirical fluid-mechanical model of the circulating fluidized bed which is combined with models of gas and solids mixing, fuel distribution, devolatilization and combustion of char and volatiles. The combination of the simulation with the measurements yields a clear picture of the mechanism of secondary air injection, its penetration into the combustion chamber and its effect on the local combustion processes. The results confirm the usefulness of the concept of simulation-supported measurement for this application. 相似文献