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Showing papers in "Combustion Science and Technology in 1983"


Journal ArticleDOI
TL;DR: In this paper, a turbulent non-premixed burning mixture is considered at a state close to extinction, expressed by an instantaneous scalar dissipation rate, and the extinction condition of the whole turbulent flame is derived on the basis of the percolation theory.
Abstract: A turbulent non-premixed burning mixture is considered at a state close to extinction. The turbulent flame is conceived as an ensemble of thin laminar diffusion flamelets that are highly distorted and stretched such that they may be quenched locally. The structure of the laminar diffusion flamelets is analysed in the limit of a large activation energy and the results of Linan's analysis of counterflow diffusion flames are used to derive the quenching condition. This condition is expressed by an instantaneous scalar dissipation rate. Statistics of the scalar dissipation rate are discussed on the basis of Kolmogoroff's third hypothesis. Extinction condition of the whole turbulent flame are derived on the basis of the percolation theory.

356 citations


Journal ArticleDOI
TL;DR: In this paper, a general invariant expression for the stretch experienced by a flame due either to its motion or to the nonuniform flow of the gas through it is derived in terms of the local fluid velocity and the shape of the flame front.
Abstract: A general invariant expression is derived for the stretch experienced by a flame due either to its motion or to the nonuniform flow of the gas through it. This expression is given in terms of the local fluid velocity and the shape of the flame front. Specific examples in which the flame stretch takes a simplified form are discussed. Some remarks are made regarding the relation between the three distinct properties of flames: stretch, speed and temperature.

296 citations


Journal ArticleDOI
TL;DR: In this paper, heat transfer and gas phase chemical kinetic aspects of the flame spread process are addressed separately for the spread of flames in oxidizing flows that oppose or concur with the direction of propagation.
Abstract: Recent advances in the experimental study of the mechanisms controlling the spread of flames over the surface of combustible solids are summarized in this work. The heat transfer and gas phase chemical kinetic aspects of the flame spread process are addressed separately for the spread of flames in oxidizing flows that oppose or concur with the direction of propagation. The realization that, in most practical situations, the spread of fire in opposed gas flows occurs at near extinction or non-propagating conditions is particularly significant. Under these circumstances, gas phase chemical kinetics plays a critical role and it must be considered if realistic descriptions of the flame spread process are attempted. In the concurrent mode of flame spread, heat transfer from the flame to the unburnt fuel appears to be the primary controlling mechanism. Although gas phase chemcial kinetics is unimportant in the flame spreading process, it is important in the establishment and extension of the diffusion ...

266 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated a variety of burner-stabilized and freely propagating NH3/2 and NH 3/H2/2 flames and found that the most important pyrolysis steps for NO and N2 formation are the reaction with NH2 or NH, forming NNH or N2.
Abstract: We have investigated theoretically a variety of burner-stabilized and freely propagating NH3/2 and NH3/H2/2. flames. The agreement between theory and experiment is generally good except, perhaps, for very rich flames, where it appears that the kinetic model may be missing important pyrolysis steps. Nevertheless, the important NO and N2 formation reactions can be identified. In lean flames, nitric oxide is produced primarily through the nitroxyl (HNO intermediate, formed either by the reaction of NH2. with oxygen atoms or NH with hydroxyl and oxygen molecules. Similarly, in lcan flames conversion of NO to N2. is by reaction with NH2 or NH, forming NNH or N2.O as intermediates. Under richer conditions NH2.and NH are rapidly converted to nitrogen atoms, and the extended Zel'dovich mechanism becomes responsible for NO formation and the conversion of NO to N2. In addition to our analysis of the nitric oxide production and destruction paths, we find from a sensitivity analysis that the most important r...

258 citations


Journal ArticleDOI
TL;DR: In this article, the surface growth rate of soot increases steeply with increasing equivalence ratio, and the increased growth rate is accounted for primarily by the increased surface area available for growth rather than by increased concentrations of surface growth species.
Abstract: The surface growth rate of soot increases steeply with increasing equivalence ratio. We have found that the increased growth rate is accounted for primarily by the increased surface area available for growth rather than by increased concentrations of surface growth species. We have shown that the surface growth species are not depleted by the process of surface growth. Our data suggest that the surface growth seen in our flames can be accounted for primarily by reaction of acetylene with the soot particles.

214 citations


Journal ArticleDOI
TL;DR: In this article, a general reaction scheme was developed for the simulation of lean and rich high-temperature combustion of hydrocarbons up to C4 -species, and some consequences of this reaction scheme are discussed with respect to future experimental work on rich flames of propane and butane.
Abstract: By combination of a mechanism describing lean and moderately rich combustion of alkanes and alkenes with a mechanism describing rich combustion and formation of soot pre-cursors in acetylene flames, a general reaction scheme is developed for the simulation of lean and rich high-temperature combustion of hydrocarbons up to C4 - species. Results of these simulations are compared to experimental data, and some consequences of this reaction scheme are discussed with respect to future experimental work on rich flames of propane and butane.

167 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that the propagation velocity of a spherical flame is a rich propane-air mixture which exceeds that of a plane flame in a mixture of the same composition, and that this surface may constitute a discontinuity not only in energy flow but also in mass flow and momentum flow.
Abstract: With a freely propagating spherical flame as an example, it is shown that, in the approximation that considers the flame as a geometric surface, this surface may constitute a discontinuity not only in energy flow but also in mass flow and momentum flow. A theoretical account is given of the experimental observation that the propagation velocity of a spherical flame is a rich propane-air mixture which exceeds that of a plane flame in a mixture of the same composition.

152 citations


Journal ArticleDOI
TL;DR: In this paper, a numerical model was used to investigate the properties of laminar flames inhibite d by CF3Br, and the effects of variations in pressure, unburned gas temperature, and equivalence ratio on inhibition efficiency were examined.
Abstract: A numerical model is used to investigate the properties of laminar flames inhibite d by CF3Br. Fuels include hydrogen, methane, methanol, and ethylene, with both oxygen and air as the oxidizers. A detailed chemical kinetic reaction mechanism for the fuel oxidation is combined with a mechanism describing reactions of CF3Br and its halogenated products. The effects of CF3Br on the flammability limits and burning velocity of laminar flames are predicted by the model, and the effects of variations in pressure, unburned gas temperature, and equivalence ratio on inhibition efficiency are examined.

146 citations


Journal ArticleDOI
TL;DR: In this article, the activation energy asymptotics method was used to study the effects of Lewis numbers different from unity on nonadiabatic flamelets in counterflowing streams of reactants and products.
Abstract: The method of activation energy asymptotics is used to study the effects of Lewis numbers different from unity on nonadiabatic flamelets in counterflowing streams of reactants and products. A sequence of analyses parallels those reported earlier for such flamelets having Lewis number unity. Thus initial results relate to nearly adiabatic flows with Lewis numbers close to unity. It is found that the effect of nonunity Lewis numbers is accentuated in flamelets subjected to low rates of strain and that Lewis numbers greater than unity tend to promote extinction. Thus abrupt extinction and ignition events can occur even under adiabatic conditions. Next fully nonadiabatic flamelets with Lewis numbers near unity are treated in order to consider cases involving relatively large degrees of product heating and cooling. These results relate to reaction zones as they arise under conditions of low-to-moderate rates of strain with the customary diffusive-reactive balance. We also treat flamelets subjected to ...

143 citations


Journal ArticleDOI
TL;DR: In this article, the surface growth rate of a premixed flat flame is shown to be first order in the acetylene concentration, and the apparent first order rate is constant with respect to the C/H ratio.
Abstract: The total mass of soot in a premixed flat flame increases steeply with time through a process known as surface growth. In this paper we show that the surface growth rate is first order in the acetylene concentration, and we measure the apparent first order rate constant. We also show that the surface growth rate is not strongly temperature dependent, It is suggested that the C/H ratio of the soot may be important in determining its reactivity.

137 citations


Journal ArticleDOI
TL;DR: In this paper, a numerical method for determining the flame speed and the structure of freely propagating, adiabatic flames is discussed. But the method is computationally faster than other methods, and it is potentially more accurate because it employs an adaptive gridding strategy.
Abstract: Abstract–We discuss a numerical method for determining the flame speed and the structure of freely propagating, adiabatic flames. The method uses a finite difference procedure in which the nonlinear difference equations are solved by a damped, modified, Newton method. This approach is in contrast to the traditional approach of solving a related transient problem until a steady-state solution i5 achieved. Our method is computationally faster than other methods, and it is potentially more accurate because it employs an adaptive gridding strategy. We demonstrate its use for the determination of hydrogen-air flame speeds.

Journal ArticleDOI
TL;DR: In this paper, the activation energy asymptotics was used to describe the behavior and characteristics of nonadiabatic flamelets involving counterflowing reactants and products under the assumption of a unity Lewis number.
Abstract: The method of activation energy asymptotics is used to describe the behavior and characteristics of nonadiabatic flamelets involving counterflowing reactants and products under the assumption of a unity Lewis number. For moderate and low rates of strain the results are analogous to those obtained in earlier applications of the method, namely reaction zones which are maintained in a first approximation by a diffusive-reactive balance. Indeed for low rates of strain many features of flamelet behavior are independent of the extent of the nonadiabaticity since the reaction zone is insulated from the stream of altered enthalpy by a diffusive-convective zone near the stagnation point. Two limiting processes are considered. One pertains to nearly adiabatic flamelets and exposes the principal qualitative results of this study. The second pertains to the full, nonadiabatic case. Flamelets with product streams having elevated enthalpies are shown to possess essentially the same features as the adiabatic fl...

Journal ArticleDOI
TL;DR: In this paper, the motion of a strong line thermal in an unstratified atmosphere is modeled to estimate a bound for its capability to lift firebrand particles, and it is found that the maximum height of a viable firebrand is roughly proportional to the square root of thermal strength.
Abstract: The motion of a strong line thermal in an unstratified atmosphere is modeled to estimate a bound for its capability to lift firebrand particles. It is found that the maximum height of a viable firebrand is roughly proportional to the square root of thermal strength. The horizontal distance traveled from the point of origin to the point where free descent begins is calculated for two wind-speed profiles with height, assuming the transporting thermal to be embedded in the windfield. This downwind drift distance is shown to be both significant and sensitive to the windspeed profile.

Journal ArticleDOI
TL;DR: In this article, the growth of soot particles in rich premixed flames was measured using the diffusion broadening particle-sizing technique, which reduced the dependence of size measurements on particle complex index of refraction.
Abstract: The growth of soot particles in rich premixed flames was measured using the diffusion broadening particle-sizing technique. This dynamic-light-scattering technique reduces the dependence of size measurements on particle complex index of refraction which is a problem with most light-scattering size measurements. Size measurements were made in fuel-rich premixed methaneoxygen flat flames with fuel-oxidizer ratios ranging from 2.2to 2.9 times sloichiometric values,and in propane-oxygen flames at an equivalence ratio of 2.6. Particles as small as 23nm in diameter were observed 5 mm above the burner surface (within about a millimeter of the flame front), growing t0 60-120nm (depending on the equivalence ratio) 14mm above Ihe burner. Measurements of the intensity of scattered light were used in conjunction with the size measurements to determine the soot number density in the methane-oxygen flames, which was found to be decreasing with height above the burner at positions 5 mm above the burner and high...

Journal ArticleDOI
TL;DR: In this paper, scaling laws for pool and crib fire experiments were proposed to predict that the burning time and the irradiance measured at geometrically similar points in pool fires will not depend on the size, while those in crib fires will be proportional to the square root of the length.
Abstract: The general objective of the work on which this paper is based was to improve scaling laws in fire research. Pool and crib fires experimentally exhibit different characteristics. Scaling laws are proposed that reflect these differences. The scaling laws predict that the burning time and the irradiance measured at geometrically similar points in pool fires will not depend on the size, while those in crib fires will be proportional to the square root of the length. Results of experiments done by the authors and other researchers were collected, and some of the results were reinterpreted and replotted. These results support the validity of the proposed scaling.

Journal ArticleDOI
TL;DR: In this paper, a transition from laminar to turbulent premixed Rame propagation is studied and the authors exploit the fact that the overall activation energy is large to derive dynamical flame sheet models, which are then used to predict instability thresholds as functions of the various parameters in the problem.
Abstract: Abstract–We review recent analytical results in the theory of transition from laminar to turbulent premixed Rame propagation. We exploit the fact that the overall activation energy is large to formally derive dynamical flame sheet models, which are then used to predict instability thresholds as functions of the various parameters in the problem, at which steps in the transition occur. Employing perturbation techniques, we then describe bifurcations from a steady, planar flame to both pulsating and cellular modes of propagation. These nonsteady, nonplanar propagation modes represent intermediate stages in the evolution from laminar to turbulent combustion.

Journal ArticleDOI
TL;DR: In this article, a global and a semi-detailed chemical kinetic model of C2HCl3 and CO oxidation is presented to explain the observed flame zone characteristics of chlorinated hydrocarbons.
Abstract: Premixed flames of highly chlorinated hydrocarbons (CHCs), such as trichloroethylene, possess two widely separated flame zones at I atm. In the first zone, the CHCs undergo fast oxidative decomposition reactions, with the formation of mainly CO, HCI and Cl2, as the principal intermediate combustion products, followed by the HCl and Cl2, inhibited, slow combustion of CO, which finally leads to the establishment of the second flame zone. The extent of flame zone separation depends on the degree of dilution present, as well as the chlorine content of the system. A global and a semi-detailed chemical kinetic model of C2HCl3 and CO oxidation are presented to explain the observed flame zone characteristics of chlorinated hydrocarbons

Journal ArticleDOI
TL;DR: In this article, a flame-spread model is analyzed in which heat release occurs at the planar interface of two media, each of which moves with a different but constant velocity, subject to a prescribed temperature distribution on the downstream half of the interface and continuity of the normal heat flux on the upstream half.
Abstract: A flame-spread model is analyzed in which heat release occurs at the planar interface of two media, each of which moves with a different but constant velocity. The steady-state, two-dimensional equations for conservation of energy in each medium are solved subject to a prescribed temperature distribution on the downstream half of the interface and continuity of the normal heat flux on the upstream half. Differing thermal conductivities in normal and streamwise directions are allowed in each medium. The approach involves introduction of Fourier transforms in the streamwise coordinate and use of the Wiener-Hopf technique. The model is shown to be equivalent to that of de Ris with radiant transfer neglected and also may be interpreted in terms of distributed electrical or radiant heating without combustion. Parametric results are obtained for various heat fluxes and for spread rates. The study helps to improve understanding of mechanisms of flame spread under conditions controlled by heat transfer.

Journal ArticleDOI
TL;DR: In this article, a Lagrangian-calculated velocity field is combined with Eulerian scalar transport to describe premixed flame propagation in two dimensions and the interaction between time dependent turbulent flow structure and an irreversible one-step decomposition reaction is explored.
Abstract: This paper explores the interaction between time dependent turbulent flow structure and an irreversible one-step decomposition reaction. A Lagrangian-calculated velocity field is combined with Eulerian scalar transport to describe premixed flame propagation in two dimensions. The time dependent flow structure is calculated by the discrete vortex dynamics method. The flow is two-dimensional and is confined to a unit square through the use of either periodic or non-equilibrium boundary conditions. The velocity field from the known vortex locations is used to describe the convection of a reacting scalar on a fixed Eulerian mesh. By variation of the numerical vortex parameters, the flow field length scale and root-mean-square (RMS) velocity can be changed. For this study, unit Lewis number with temperature-independent transport coefficients has been assumed. Some of the work also assumed a constant density flame model. In addition to calculating reacting scalar transport, calculations have also been ...

Journal ArticleDOI
TL;DR: In this article, the structure of a steady, planar premixed flame in a slowly expanding gas flow is analyzed and the reaction kinetics are represented by a mechanism consisting of a chain branching reaction and a chain breaking reaction.
Abstract: The structure of a steady, planar. premixed flame in a slowly expanding gas flow is analyzed. The reaction kinetics are represented by a mechanism consisting of a chain branching reaction and a chain breaking reaction. An asymptotic analysis is performed in the limit of a large value for the activation energy of the chain branching reaction, with the activation energy for the chain breaking reaction presumed to be zero. The analysis is valid for cases where the mass fraction of the intermediate species is of order unity, An analytical expression is obtained for the change of the mass burning rate with the Karlovitz number, the parameter characterizing flame stretch. This expression shows the role of differential diffusion of heat and the reactant, of differential diffusion of reactant and intermediate species and of enhanced diffusion of intermediates on flame propagation. It is seen that these three different effects may cancel each other. Depending on the parameter range the mass burning rate m...

Journal ArticleDOI
TL;DR: In this paper, a gas sampling valve mounted in the combustion chamber wall of an IC engine was used to sample the wall quench layer with minimum leakage and crevice contributions to measured hydrocarbon concentrations.
Abstract: The hydrocarbon emissions process for the conventional, spark ignited, IC engine has been studied experimentally using a rapid acting gas sampling valve mounted in the combustion chamber wall. The sampling valve was electrohydraulically actuated. Design of the valve specifically allowed sampling in the vicinity of the wall quench layer with minimum leakage and crevice contributions to the measured hydrocarbon concentrations. Experimental results presented give substantial evidence that hydrocarbons remaining in a wall quench layer are not a major source of exhaust hydrocarbon emissions. Measurements of species concentrations as a function of time in the cycle and sample flow rate indicate that after flame arrival and quenching at the cold walls, hydrocarbons in the quench layer are rapidly and extensively oxidized within 2 msec. By use of an analytical model for the gas flow profile into the sampling valve, conservative upper limit calculations have been made of the quench layer contribution to t...

Journal ArticleDOI
TL;DR: In this paper, the authors measured the burning velocities of isooctane, methanol, 90 percent isoxctane/methanol blends, and 80 percent isoxide/20 percent methanols in air using a constant volume bomb.
Abstract: Laminar burning velocities of isooctane, methanol, 90 percent isooctane/l0 percent methanol and 80 percent isooctane/20 percent methanol (by liquid volume) in air have been determined over wide ranges of mixture strength and initial mixture temperature using a constant volume bomb Measurements were made during the constant pressure combustion period and a density correction scheme was employed for calculation of burning rates from measured data It was found that isooctane/methanol blends yield slower burning velocities than those of methanol and isooctane alone in air Causes of this inhibition mechanism are discussed Variation of burning velocity of methanol and isooctane with unburned mixture temperature was compared to the data of previous investigators Measured results were correlated and expressions, for the fuels considered, presented for the ranges of φ = 07-14 and Tu –300-600K at 100 kPa pressure

Journal ArticleDOI
TL;DR: In this paper, a model including the effects of flame structure is derived in coordinate invariant form, which consists of the fluid equations, to be solved on either side of the flame, an evolution equation describing the deformation of the front, and jump conditions for the fluid variables across the front.
Abstract: Viewed on a hydrodynamical scale, a flame may be considered as a surface of discontinuity, separating burned from unburned gas. Unlike earlier treatments, the present study accounts for flame structure, i.e., accounts for the details of chemical reactions and transport processes, and their interaction with the fluid flow. A model, including the effects of flame structure, is derived in coordinate invariant form. It consists of the fluid equations, to be solved on either side of the flame, an evolution equation describing the deformation of the front, and jump conditions for the fluid variables across the front. The model describes the dynamics of flame fronts including their stability. In particular, we study the stability of both plane and curved flames, and discuss the effect on stability of flame front curvature, heat release, Lewis number and Prandtl number.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the concentrations of individual exhaust hydrocarbon species as a function of engine operating variables (φ, rpm, EGR, spark timing, and coolant temperature) in a 2·3-liter fourcylinder engine.
Abstract: Measurements of the concentrations of individual exhaust hydrocarbon species have been made as a function of engine operating variables (φ, rpm, EGR, spark timing, and coolant temperature) in a 2·3-liter four-cylinder engine. Three fuels were used in these experiments: propane, isooctane (2,2,4-trimethylpentane), and an unleaded gasoline (indolene clear). The results show that a change in operating variable can change not only the total hydrocarbon concentration but also the distribution of species in the exhaust. All three fuels show similar trends when an operating variable is changed. Fuel-air equivalence ratio is a critical parameter in controlling exhaust hydrocarbon emissions. Beginning near stoichiometric, the total hydrocarbon concentration and the percentage contributions of methane and acetylene to the exhaust increase as the mixture becomes richer. These species contribute less than 2 percent to the total hydrocarbon emissions at <0.95. Their contribution rises to 15–25 percent at φ...

Journal ArticleDOI
TL;DR: In this article, a thermal theory is developed to explain the experimentally observed effect of pressure changes on the propagation velocity of premixed flames using a one-step reaction and large activation energy asymptotics in the framework of a slowly varying flame analysis.
Abstract: A thermal theory is developed to explain the experimentally observed effect of pressure changes on the propagation velocity of premixed flames. The theory uses a one-step reaction and large activation energy asymptotics in the framework of a slowly varying flame analysis. A one-dimensional unsteady flame with Lewis number ℒ equal or unequal to unity is considered. The Mach number is assumed to be low enough such that spatial pressure gradients can be neglected. The asymptotic analysis requires a small temperature variation of the unburnt gas due to pressure changes-this condition is satisfied in the limit of large heat release. The analysis shows that pressure changes affect the flame velocity in two direrent ways, through the change of the enthalpy balance in the preheat zone and through the change of flame temperature. An ordinary differential equation for the time variation of the normalized mass burning rate is derived. This equation is analysed for ℒ=l and constant relative pressure decrease...

Journal ArticleDOI
TL;DR: In this paper, the authors study the dynamics of a nearly-extinguished and weakly unstable non-adiabalic flame and derive a non-linear partial differential evolution equation for the changes of front shape and velocity.
Abstract: We study the dynamics of a nearly-extinguished and weakly unstable non-adiabalic flame For simplicity sake, the analysis is conducted in the framework of a thermal-diffusional flame model Using high activation energy techniques and bifurcation methods, we derive a non-linear partial differential evolution equation for the changes of front shape and velocity By solving it approximately in a particular case, we show that the spontaneously growing front corrugations, due to diffusive instability, are sufficient to prevent flame quenching: a diffusively unstable flame front can still propagate with heat-loss intensities that would quench a planar one.

Journal ArticleDOI
TL;DR: In this article, a Lagragian finite difference procedure is used for modelling spherically expanding hydrogen-air flames such as are obtained during the early, pre-pressure period of constant volume bomb explosions with single spark ignition at the centre.
Abstract: Abstract–A Lagragian finite difference procedure is outlined for the modelling of constant pressure, spherically summetric, laminar flames, with detailed chemistry and transport property representation. The procedure is used for modelling spherically expanding hydrogen-air flames such as are obtained during the early, pre-pressure period of constant volume bomb explosions with single spark ignition at the centre. For modelling purposes, such explosions have the advantage over hurning velocity measurements on stationary flames that the speeds of radial advance of the flames in space can be measured in a purely objective manner, and they thus provide a calibration standard for the other overall rate processes (such as key reaction rate or diffusion parameters, or indirectly, the burning velocity itself) in the flames. Sensitivity analyses on the hydrogen-air flame system took full account (a) of published data on the hydrogen-oxygen reaction from a variety of sources, including studies of radical r...

Journal ArticleDOI
TL;DR: In this paper, a gas turbine combustion chamber with high purity gaseous propane and high power conditions was used to measure the temperature and CO, CO2 and NO2 at various planes within a can-type model combustion chamber and showed that the measured temperatures and those calculated using the measured composition with assumed adiabatic flow are in agreement only in the combustor nozzle and at the exit plane.
Abstract: Profiles of temperature and concentrations of CO, CO2. O2 UHC and NO2 have been measured at various planes within a can-type model gas turbine combustion chamber. The com-bustor is fuelled by high purity gaseous propane and was operated at air inlet temperatures of 313 K. and 523 K and atmospheric pressure simulating high power conditions. The results show that chemical equilibrium conditions prevail only for locally fuel-lean conditions and there is strong evidence that both fuel breakdown and CO to CO2 oxidation rates are partly controlled by finite rate chemical kinetic mechanisms. The measured temperatures and those calculated using the measured composition with assumed adiabatic flow are in agreement only in the combustor nozzle and at the exit plane. In the primary zone large differences arise and it is postulated that these occur because of the neglect of important correlations, involving the fluctuating density and composition. in the calculated temperatures. The data presented is also su...

Journal ArticleDOI
TL;DR: In this article, the effects of the velocity gradient on the premixed flame in the stagnation flow field have been studied theoretically considering general Lewis number and the steady two-dimensional stagnation flow and the uni-molecular reaction were assumed.
Abstract: The effects of the velocity gradient on the premixed flame in the stagnation flow field have been studied theoretically considering general Lewis number The steady two-dimensional stagnation flow and the uni-molecular reaction were assumed, and the governing equations were solved numerically The influence of the velocity gradient and the Lewis number on the flame temperature were discussed There are two effects of the velocity gradient on the flame One effect is that the velocity gradient causes the flame temperature to increase or to decrease due to the imbalance between the excess heat flow from the reaction zone to the unburned gas and the excess diffusion flow of the reactant from the unburned gas to the reaction zone, and this effect largely depends on the Lewis number By the velocity gradient, the flame temperature increases when Le>1 and decreases when Le< 1 When Le= 1, the velocity gradient has no effect on the flame temperature Another effect is tha velocity gradient causes the fl

Journal ArticleDOI
TL;DR: In this paper, two combustion bombs manufactured from a Ford 1.6L Escort production engine were used to determine the effects of engine crevice volumes on hydrocarbon emissions, and the results cannot directly apply to an operating engine but they focus attention on the major hydrocarbon-producing crevices in an actual engine geometry.
Abstract: Two combustion bombs manufactured from a Ford 1.6L Escort production engine were used to determine the effects of engine crevice volumes on hydrocarbon emissions. Since these combustion bombs were used as static reactors, the results cannot be directly applied to an operating engine but they focus attention on the major hydrocarbon-producing crevices in an actual engine geometry. During Ihis propane-fueled experiment, the crevices were sequentially filled with epoxy or viton rubber, and after filling each crevice, the exhaust hydrocarbon emission was measured by gas chromatography. This provided a quantitative measurement of the hydrocarbon emission from each crevice. For these reactors, the ring-pack crevices produced approximately 80.5 percent of the total scaled hydrocarbon emission, while the head gasket and spark plug threads produced approximately 12.5 percent and 5 percent, respectively. All other hydrocarbon sources produced less than 2 percent of the total scaled hydrocarbon emissionfrom...