Fuel Droplets Research Articles

Experimental Study on Combustion of O/W Emulsion Droplets of Hydrocarbon Fuels under Zero Gravity

本研究はO/W形エマルジョン燃料滴の燃焼におけるミクロ爆発などの複雑な燃焼機構を解明するために、自由落下する燃焼容器中の無重力状態のもとでC7～C16の一連のパラフィン族炭化水素燃料をもちいて、その実験を行い、落下装置本体に搭載された連続拡大シュリーレン写真および影写真によってその燃料挙動を詳細に観測し、二次微粒化機構、液滴直径の時間的変化、あるいは見かけの燃焼速度定数を調べ、その基本的な燃焼特性を明らかにした。

Two Dimensional Analysis of Combustion of Fuel Droplet or Fuel Sphere under Conditions of Natural Convection

自然対流場における燃料液滴または液球まわりの拡散火炎の二次元解析を行った。薄炎モデルのもとに、Schvab-Zeldovich変換を行い、更に、二次元拡散火炎面を処理するため境界固定法を導入することにより数値解析を行って、液滴まわりの温度場、濃度場および速度場を明らかにし液滴(または球)の燃焼におよぼす自然対流の効果を定量的に明らかにした。また、蒸発係数kの直径依存性について従来の理論および実験の結果と対比した。

Interference Effects on Combustion of Linear Fuel Droplet Streams

Interference Effects on Combustion of Linear Fuel Droplet Streams

The Effect of Fluctuations in Temperature and Oxygen Concentration on the Lifetime of a Fuel Droplet

Abstract Monte-Carlo calculations are undertaken to determine the lifetime of fuel droplets which encounter temperature and oxygen fluctuations along their path through a turbulent flame. Two kinds of ignition and extinction criteria are used: fixed values of Yυ and T for ignition and Yυ for extinction, and size-dependent values based on finite kinetics. It is assumed that ignition and extinetion are instantaneous, and that the behaviour is otherwise quasi-steady, i.e, the droplet either evaporates or burns at the corresponding quasi-steady rate. Droplet dynamics and convective effects are excluded from the model. Ambient temperature and oxygen concentrations take on random values between prescribed limits, and maintain these values for periods of random duration. Each such period is the travel time of the droplet over a random distance of the other of a scale factor times its initial diameter. Calculations are carried out for both uncorrelated and correlated temperature and oxygen concentrations. The out...

Single-droplet combustion of coal slurry fuels

The combustion characteristics of single droplets of coal slurry fuels were experimentally investigated using both spontaneous and forced ignition. Results showed that the combustion is a sequential two-staged process, consisting of gas-phase combusion of the volatiles followed by combusion of the solid residue, which is mostly carbon. A splashing combustion phenomenon, which corresponds to the outgassing of the thermally cracked fuel gas from the droplet interior, occurred during the later period of gas-phase combustion in the same way as for residual heavy fuel oils. However, no disintegration or disruption of the droplet was observed. The duration of combustion of the solid residue agglomerate was several times longer than that of the volatiles, and therefore constituted a major part of the total burning time. The gas-phase burning time as well as the total burning time were found to vary linearly with the square of the initial droplet diameter, thus obeying the “square law of initial droplet diameter.” The overall burning rate coefficients of coal slurry fuels were about 1 2 to 1 4 times those of residual heavy fuel oils because of the long solid combustion time. The overall burning rate coefficient was found to depend mainly on the residual carbon content of the coal slurry fuel.

A Spray Flame Held by a Recirculating Flow : 3rd Report, Behaiviors of Fuel Droplets

循環気流中に噴射された燃焼噴霧によって形成される噴霧火炎内の油滴を光学的な手法を用いてとらえ, 火炎内全域にわたってその空間密度, 粒径分布, 速度, 飛行方向を明らかにした. そしてすでに明らかにされている火炎の温度, ガス成分濃度などのデータと比較して, 火炎の構造を油滴の挙動の面から考察した.

Burning of Distillate Fuel Droplets Containing Alcohol or Water: Effect of Additive Concentration

Previous work on the addition of methanol, ethanol and water to pure n-paraffins is extended to a conventional No. 2 distillate fuel oil. Both the effect of additive content in the fuel oil and oxidizer concentration in the environmental flow on the existence and character of the disruptive behavior of these solutions and emulsions are investigated. For the ethanol in No. 2 oil solution cases it is shown that there is a maximum and a minimum ethanol con-centiation for which disruptive burning occurs, viz. 5% and 90% by volume. The results show an optimal ethanol concentration range within 15% and 55% by volume for which the disruption occurs prior to the consumption of 40% of the initial volume of the solution droplet. It is also shown that emulsions of water-in-No. 2 oil undergo micro-explosive vaporization and combustion and that the role of emulsion water content in promoting the dispersion of mass through micro-explosive phenomena is not highly significant.

Transient Combustion of a Fuel Droplet with Finite Rate of Chemical Reaction

Abstract A numerical analysis for the transient combustion of a single fuel droplet with finite rate of chemical reaction has been performed under the assumptions of spherical symmetry and constant transport properties. Evaporation curves and transient variation of the flame location, temperature profiles, and the ratio of flame to droplet radius were obtained in detail. Moreover, the effects of finiteness of chemical reaction were revealed. It was found that there exists a critical droplet diameter beneath which no stable combustion can be realized. The present results support those of earlier analytical works of Waldman, which were obtained by virtue of an asymptotic expansion method.

Calculation of the Burning Rates of Interacting Fuel Droplets†

Abstract The quasi-steady (QS) burning rates of interacting spherical fuel droplets are calculated by transforming the equations governing the inter-droplet fields to the Laplace equation and then solving the transformed equations by the method of images. The results of this work indicate that QS interactions can significantly reduce the droplet burning rates even for large droplet spacings. Further, the well known D2-law is found to be only approximately correct when applied to interacting droplets.

Experimental Observations on the Disruptive Combustion of Free Droplets of Multicomponent Fuels

Abstract The disruptive burning characteristics of isolated free droplets of binary n-paraffin mixtures have been observed experimentally. For disruptions to occur a minimum difference in the normal boiling points of the components as well as a certain initial concentration of the more volatile component must exist. The initial concentration of the volatile component must be within a limited range defined by the relation of the homogeneous superheat limit of the mixture to the normal boiling point of the less volatile material. Disruptive burning is a result of homogeneous nucleation of the mixture somewhere within the interior of the droplet. Mass diffusion is the limiting liquid transport process which results in superheating of the droplet interior. Comparison with previous studies of micro-explosive atomization of water-in-fuel emulsions shows that the disruptive burning of a binary fuel mixture is a slower and less violent process. It is also concluded that through relieving the requirement for homog...

Theoretical Analysis of the Interaction between Two Burning Fuel Droplets : Part 1, Identical Droplet Case

The effects of the interaction between two burning identical fuel droplets are analyzed exactly in the Schvab-Zeldovich formulation. The expression for the evaporation rate of each droplet is obtained in an explicit form, which shows that the interaction reduces the evaporation rate compared with that of an isolated droplet. The criterion which divides two possible types of flame surfaces, i, e., two separate flames or one coalescent flame, is derived, which will be of interest in connection with the prediction of the combustion modes in spray.

Analysis to Interaction Effects of Burning Droplets : 1st Report, Case of Two Identical Fuel Droplets

Analysis to Interaction Effects of Burning Droplets : 1st Report, Case of Two Identical Fuel Droplets

Soot Formation by Combustion of a Fuel Droplet : 2nd Report, Effect of Air Stream Velocity and Ambient Temperature

Soot Formation by Combustion of a Fuel Droplet : 2nd Report, Effect of Air Stream Velocity and Ambient Temperature

Initial Observations on the Free Droplet Combustion Characteristics of Water-In-Fuel Emulsions†

A new mechanical technique for the production of well characterized small diameter isolated free droplets of multi-component and emulsified liquids is described. The technique is employed in development of an experimental facility to generate, inject, and combust free droplets of liquid fuels in a well defined, hot convective atmosphere. Initial observations of the burning characteristics of isolated free droplets of water in pure n-paraffin emulsions are reported. The existence of free droplet secondary atomization and the importance of fuel physical characteristics, water content, and internal phase structure to optimizing this phenomenon are confirmed. Observations are found to be in agreement with earlier predictions of the required internal phase super heat (Avedisian and Andres, 1978) and results suggest previously published suspended droplet combustion data on emulsified fuels to be of limited quantitative value. Observations are compared with the prediction of and physical models used in recent an...

Interaction of Two Burning Fuel Droplets of Arbitrary Size

The combustion of two interacting droplets of arbitrary size was analyzed by solving Laplace's equation in bispherical coordinates, with the conjecture that multiplication by &(1 + B) converts the diffusion rate in the absence of a flame to the evaporation rate of a burning droplet. Closed-form solutions were obtained both for the burning rate of each droplet and for the shape of the flame. The burning rate of each droplet was found to be smaller than that of an isolated droplet of the same size. The reduction was greatest when the droplets were touching, and was relatively larger for the smaller droplet. Two simple functions, one for the larger droplet and one for the smaller, were found to give good approximations to the burning rate of touching droplets. Free-fall experiments were performed to check the theory. The results available so far have provided qualitative support for the mathematical model in that observed flames of some pairs of burning droplets strongly resemble the calculated flame shape.

Evaporation and Ignition of a Fuel Droplet on Hot Surface : 3rd Report, Effects of initial Droplet Diameter

加熱平板上におけるηセタンの単一燃料液滴の蒸発過程と着火過程を、加熱板表面温度300～550℃の範囲において、初期液滴径約0.7～3.3mmの範囲で変化させて実験的に詳細に調べた。さらに液滴の蒸発形態の観察結果に基づき、液滴が加熱板に接して蒸発する形態がみられなくなる加熱板表面温度に着目し、初期液滴径が蒸発時間や着火遅れ時間に及ぼす影響を検討した。また着火の起こらなくなる臨界液滴径を実測により求めた。

Holographic Particle Sizing for Fuel Droplets

Holographic Particle Sizing for Fuel Droplets

Combustion of Fuel Droplets under Conditions of Forced and Natural Convection

液滴燃焼およぼす強制対流および自然対流の影響を詳細に調べるために、自由落下する燃焼容器中の無重力状態のもので燃焼する燃料液滴に一様な空気流をあてる実験および鉛直方向に一定加速度で上昇する燃焼容器中の過重力状態のもとで燃料液滴の燃焼に関する実験を行い、液滴燃焼の基本的性質、すなわち蒸発係数、火炎形状および高温ガス層などにおよぼすそれらの効果を解明した。

Diesel odor studies in a laboratory spray burner

An air aspirated burner facility has been modified and instrumented for studying diesel odor formation. Odor sampling and analysis techniques, based on the Diesel Odor Analysis System (DOAS), have been developed and refined. Burner stoichiometry, combustion aerodynamics, swirl, wall quenching and fuel composition were investigated for their effect on odor formation. Fuel composition had a negligible influence and swirl had only a small effect except at very high swirl levels. The most significant factor was overall burner stoichiometry. This pronounced stoichiometry effect appears to be the result of the aerodynamic turbulence and wall quenching at lean operating conditions. Fuel droplet diameter, while having no direct effect on odor production, probably has an indirect effect through its influence on both aerodynamics and quenching. The effect of stoichiometry was to increase odor from very low or undetectable levels at equivalence ratios near 0.5 to moderate to strong levels as burner operation becomes very lean and to very strong levels at rich operating conditions. Increasing aerodynamic turbulence caused odor levels to drop by increasing the size and intensity of the recirculation pattern, thereby allowing more complete combustion. Conversely, increased wall quenching removed energy from the reaction zone, resulting in incomplete combustion and higher odor levels. Very high swirl appeared to cause faster reaction rates and lower odor levels.

Transient Heat Flow to a Liquid Fuel Droplet in Combustion Gases

Transient Heat Flow to a Liquid Fuel Droplet in Combustion Gases