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流入スワ-ル強度可変機構を設けた単流掃気形二サイクルディーゼル機関を使用した実験から、燃焼に最適なスワ-ルの強さは、噴射ノズルの噴口数だけでなく、噴霧の衝突条件や燃焼室形状、また燃焼性状によっても変化することがあきらかとなった。またビストンに設けた皿を深くすることによって、噴口数が少ない場合の排煙濃度を改善でき、皿の形状を変えることによって、さらに燃焼改善をはかる自由度があることも確かめられた。

A recently developed theory of fuel spray burning [1] is applied to the experiments of Nuruzzaman, Hedley and Beer [3] on linear arrays of burning fuel droplets. The calculated burning rates have the right order of magnitude but are too strongly dependent on the initial droplet diameter and on the interdroplet separation as compared to the above mentioned experiments.

The vaporization and transport of a monodisperse fuel spray in a cold, humid environment are analyzed, allowing for the possibility that the water vapor may condense, either heterogeneously at the droplet surface or homogeneously in the gas medium, as the spray interior is chilled through fuel vaporization. Results show that the associated condensation heat release is substantial and can significantly enhance the fuel vaporization rate, especially for the heterogeneous mode. It is further found that after initiation of vaporization the droplet temperature rapidly approaches a characteristic, constant value with heterogeneous condensation; this renders analytical solution possible. Potential complications caused by water condensation during spray experimentation are also discussed.

A simple model of fuel spray burning is considered. The major simplifying feature of this model is that only diffusive and conductive modes of mass and heat transfer are included, while all the effects due to the hydrodynamic flow field are ignored. A self-consistent equation is derived which expresses the dependence of the burning rate of a droplet on the burning rates of all the other droplets in the spray. This equation is solved for the case of a random distribution of droplet locations using common techniques of statistical mechanics. The resulting expression for the average burning rate is compared to experimental data.

デイーゼル機関の燃焼評価因子として,先に提案した燃料噴霧の有効燃焼速度係数Keを用い,異種燃料および燃料噴射圧を変えた場合の燃料噴霧の燃焼現象の違いを示した.またKeどのパターンを仮定してシミュレーション計算を行うことにより,燃料消費率や熱効率の改善を目的とした燃焼改善の目標を明確に定義することができた.

The characteristic time model for lean blowoff [1] has been used to predict extinction of disk-stabilized flames of No. 4 and No. 6 oils, unleaded gasoline, and JP-10. The predictions show good agreement with experimental values of the blowoff equivalence ratio obtained at pressures of 2–6 atm, inlet air temperatures of 500–800K, and 1.5 kg/sec air mass flow. Droplets penetrating the flame-stabilizing shear layer strongly augment the stabilization process at lower combustor loadings, especially with No. 6 oil.

The structures of air blast atomized heavy fuel oil spray flames, in particular, the mechanisms of droplet burning, are examined as functions of initial conditions by using a novel atomizer design. A particle sizing instrument and a spray momentum measurement device are used to calibrate this atomizer so that parametric variations can be made of the initial droplet size distribution, spray momentum, fuel flow rate, and air/fuel ratio. Information is obtained on flame length, droplet burning regime (individual or group combustion of droplets), and combustion chamber wall temperature as a function of initial conditions. Supported by this information, reasoning regarding the physics of the flows is used to propose that the relative values of two parameters, which incorporate initial spray momentum, droplet size distribution, and fuel flow rate, can give a good indication of the likely burning regime and other important features of spray flames.

An experimental verification of the transition from a heterogeneous controlled to a homogeneous gas phase combustion of a monodisperse tetralin-air spray is presented. The fuel sprays are produced by a condensation aerosol generator. The flame tube method, together with multiple-exposure, high speed photography and an in situ electro-optical sensor array, are employed to measure the flame propagation speed. Flat flame fronts are obtained with the aid of suitable acoustic devices. The results show that for relatively large particle sizes, droplets burn in their own flame envelope. As the droplet size is progressively reduced at a constant equivalence ratio, the flame propagation speed first increases to a maximum and then decreases to that of the premixed mixture having the same equivalence ratio. The result is interpreted in terms of the transition from heterogeneous to homogeneous combustion of fuel sprays.

An experimental study was conducted to determine the effects of nozzle orifice size and operating parameters on the cone angle of a liquid fuel spray injected into a gaseous environment. High fuel pressures in the range 55 to 130 MPa and background gas density ranging from atmospheric to 40 kg/m3 were used in the study. The results show the spray cone angle to depend on the orifice dimensions as well as on the operating conditions such as the injection velocity and the background gas density. A correlation is derived to predict spray cone angles in terms of Reynolds and Weber numbers. The predicted results are shown to agree well with the experimental findings of other investigators. On a fait une etude experimentale pour determiner les effets de la dimension de l'orifice du gicleur et des parametres de fonctionnement sur l'angle du cone du jet de pulverisation d'un combustible liquide injecte dans un milieu gazeux. On a employe dans cette etude des pressions du combustible elevees variant entre 55 et 130 MPa et une densite du gaz comprise entre celle des conditions atmospheriques et 40 kg/m3. Les resultats ont indique que l'angle du jet de pulverisation depend de la dimension de l'orifice ainsi que des conditions operatoires telles que la vitesse d'injection et la densite du gaz. On a etabli une correlation pour predire les angles des jets de pulverisation en fonction des nombres de Reynolds et de Weber. Les resultats calcules ont bien concorde avec les resultats experimentaux etablis par differents chercheurs.

A mathematical model for predicting spray–swirl interaction in a direct injection diesel engine combustion chamber is developed using centre-line velocity vector/continuum approach. The model has three-dimensional features in fuel spray motion. The present model responds to the various air swirl, fuel injection and cylinder charge conditions. The predicted results are compared with the analytical and experimental data available from various sources in the two-dimensional case. Very good agreement is achieved over a wide range of data. The three-dimensional predictions are directly possible without any alteration in the computation scheme.

The changing pattern of demand for oil products has required that refining practices be adjusted to maximize yields of premium products from crudes. There has been a concomitant deterioration in the quality of the ‘residual’ or ‘heavy’ fuel oil used in power generation. A major constraint on the burning of such heavy fuel is a restriction on particulate emissions. These emissions largely comprise carbon particles (coke), which form from the individual oil spray droplets and remain unburnt. Poorer quality oils have an increased propensity to form coke, and can give rise to unacceptable emissions. One way of countering these increases is to make the fuel spray finer and hence improve burn-out. Research has been aimed firstly at quantifying the effects of those oil properties that directly influence coke formation and combustion and then at developing improved atomizers and water-in-oil emulsions to reduce droplet sizes.

Publisher Summary This chapter discusses the fundamentals of oil combustion and the nature of the spray combustion of fuel oil. The atomization of fuel oils provides a convenient means of obtaining self-sustaining flames. The way in which the fuel spray and the combustion air are mixed is crucial in determining the way in which the overall combustion proceeds. When the fuel spray is premixed or initially well mixed with the combustion air, two cases of combustion can be identified, these are heterogeneous combustion and homogeneous combustion. In the case of heterogeneous combustion, the droplets burn either as individual droplets each with a surrounding flame or as droplets in a sea of flame. However, in either of the event, the system is essentially heterogeneous in that two phases are present. In homogeneous spray combustion, the droplets evaporate prior to their arrival in the flame zone and the flame front is supported essentially by fuel vapor and air.

A phenomenologic al experimental method for the investigation of fuel spray evaporation is introduced. The method is based on the measurement of pressure decrease resulting from spray evaporation in a closed vessel at high temperature and pressure. If certain physical and thermodynamic properties of the fuel are available, the method gives the average lifetime of the droplets and a mixing characteristic of the spray. If these properties are unavailable, the method can be employed to compare injector designs. A significant advantage of this technique is that it serves as an automatic integrator of all the governing parameters of spray evaporation. Ethyl alcohol and water sprays evaporating in nitrogen gas have been investigated successfully. The initial conditions of these experiments were 400 psig, 450 psig, and 500 psig chamber pressures and 700 F, 800 F, and 900 F chamber temperatures. Fuel injection rates were approximately 30 g/sec. 16-hole and 8-hole self impinging injector-plates were used. The lifetime of the sprays was found to vary between 144 and 550 msec. a b B

This paper deals with the oscillatory combustion occurring in the diffusion flame of liquid fuel spray burning. Main results obtained are as follows. (1) Major part of the fuel burns as the droplet flames. Most of these droplets burn penetrating the surrounding gas and with the flame type of a wake flame. (2) Fluctuation of burning rate that is the driving force of oscillation is brought about by the transition phenomenon of the flame type of droplets. From the above result, the magnitude of the pressure fluctuation can be correlated with the burning condition by using a parameter f. (3) Dependency of the frequency on the combustor length agrees well with the prediction obtained in 1st Report and the dependency of that on the burning condition can be explained quantitatively by examining the relation between the burning condition and the parameters |B| and ∈ which are the synthetic parameters representing the burning condition.

In order to prevent carbon deposits in the combustion chamber of a diesel engine, it is recommended to avoid direct impingement of fuel on the wall of combustion chamber, though it may sometimes be impossible. In this report, the present authors examined how the carbon deposits were dependent on the wall surface temperature of the combustion chamber in the case where fuel spray impinged directly on the wall. For this purpose, a probe on which the spray impinged was set in the prechamber of the testing engine and thereby the relation between deposits and wall temperature was determined. The test results are summarized as follows : The deposits increase with time at a constant rate at first and, when it exceeds a certain limit, the deposit lump is removed off the probe. With the fuel employed in the test, the deposit reached a maximum at 200°C. Above 550°C, the amount of the deposit is only about one thirtieth the quantity at 200°C. This is because inadhesive deposits are produced at a high wall temperature owing to thorough cracking.

The purpose of the present research is to determine the method of injection, injection pressure, starting period of injection and compression ratio, favourable in the manifoldinjection engine, and also to investigate the anti-knock characteristics and to compare them with those in the carburetor system. With the manifold-injection engine, the direction and the shape of the fuel spray, injection pressure, and the start of injection have not too serious effect on performance as in the cylinder injection engine. Especially, when the spray is directed against the air-flow, very low injection pressure (even 10 atm) can be applied. The start of injection of 90-120°after TDC on the suction stroke is optimum. Manifold-injection is superior to carburetion with respect to anti-knock characteristics. In the manifold-injection engine, slightly later spark is favourable than in the carburetor engine.

Regarding the penetrating distance of fuel spray in a diesel engine, the old theory dealing with the motion of a fuel droplet in still air is recognized not to coincide with the actual phenomenon in a diesel engine because of the extremely small size of atomized fuel droplets and the very high density of gas in cylinder. In this paper, the characteristics of spray penetration are discussed from the viewpoint of momentum theory based on the idea that the air induced into a fuel jet stream makes a kind of mixed gas together with fuel droplets. According to the results of experiment, the authors confirmed that the theory was satisfactory, that there existed the simple relations among several dimensionless numbers which indicate the effect of various factors on the spray penetration, that there is a close relationship between the spray cone angle and penetration, and others.

This paper deals with the theoretical analys's of one dimensional steady flow in a combustion chamber of gas turbine. In this study, the following were assumed : (1) The liquid fuel drops and combustion gas stream have a same velocity. (2) The law of combustion of single droplet is adopted to the combustion rate of fuel spray. (3) The combustion is not influenced by the condition of combustion gas stream. By using above three assumptions and the analysis which is analogous to Shapiro and Erickson's method(7), the total heat release rate, the local heat release rate, the temperature- and velocity-distributions in the direction of gas flow were calculated. In this study, it is found that the local heat release rate rapidly increases, but the temperature and velocity of combustion gas do not increase so rapidly as the local heat release rate and these values decrease after they become maximum. And the obtained local heat release rate has a similar form to the assumption that was reported in the previous papers(3)(4).

Spontaneous ignition delay of fuel spray injected into a hot gas stream produced by burning of propane has been measured, using a test rig consisting of 200φ×3 m parallel duct. Results obtained were compared with those by Mullins, who had carried out the same experiment in the range of higher stream temperature and velocity, and with the delay obtained by other methods at atmospheric pressure. Conclusions can be summarized as follows : Controlling factor of ignition delay in a gas stream is considered to be of chemical nature judging from activation energy, 35 to 45 kcal/mol. It depends predominantly on the temperature and less on the physical factors such as velocity or spray condition. This is explained as follows : In spite of rapid formation of uniform mixture, velocity and concentration prevailing is outside the stability range of fuel spray and cannot lead to flame propagation against other ignition processes.

A spray-burning model (based on single-droplet theory) for heat release in a diesel engine is presented. Comparison of computations using this model and experimental data from an operating diesel engine indicate that heat release rates are not adequately represented by single-droplet burning rates. A new concept is proposed, i.e. a burning coefficient for a fuel spray. Comparisons between computations and experimental data indicate that the numerical value of this coefficient is nearly independent of engine speed and combustion-chamber pressure. However, the instantaneous value of the spray burning coefficient is approximately proportional to the instantaneous mass-averaged cylinder gas temperature to the one-third power.

Etude photographique de l'allumage d'un jet pulverise de carburant dans une machine a compression rapide

A study was performed to evaluate the influence of combustion chamber design and fuel spray geometry on cold startability. High-squish toroidal, high-squish bowl, and Mexican hat-type combustion chambers were tested. In each case, the effects of fuel-air mixing process on cold startability was studied at different starting temperatures and injection timings. Cold startability aids, such as additional air for starting purposes and glow plugs, were tested with each of the above combustion chambers. Chamber designs with high squish and swirl and fuel impingement on the walls were found to be undesirable for good cold startability. Improved cold startability resulted from locally non-uniform air-fuel ratios with a well organized air swirl-fuel spray pattern. Glow plugs were found to be desirable for improved cold startability.

A theoretical model for the calculation of the fuel spray behaviour inside a swirl chamber has been developed. The two dimensional momentum equation, the mass and energy equations are derived and solved numerically incorporating the air velocity pattern, the heat transfer by radiation to the wall and the heat transfer by convection to the fuel film. The model can predict the trajectory and shape of the fuel spray, fuel film velocity, fuel film area, and temperature along the path, as well as the fuel evaporation. The comparison of the theoretical and experimental results showed a rather good agreement between them.

Mesure de la taille des gouttelettes et leur evolution dans le temps dans le cas d'un jet pulverise intermittant de carburant a de hautes pressions

This paper examines the spatial distribution characteristics of fuel sprays emanating from simplex pressure swirl atomizers of the type commonly used in the gas turbine engine. Three different atomizers were tested on kerosine at chamber gas pressures up to 1377 KN/m2 and fuel pressure drops up to 3448 KN/m2. A non-intrusive, still photographic technique was developed for recording the spray profiles over the entire range of test conditions. Analysis of the experimental data shows that the closing in of the spray boundaries due to an increase in air pressure is a result of the aerodynamic interaction between the fuel spray and its gaseous environment — the nozzle hydrodynamics apparently exercising no influence. Experimental data collected in the study reveals the influence of gas pressure (Pa) upon the half width (y) of the spray envelope at a downstream distance of 30mm from the nozzle face to be described adequately by the expression y α Display FormulaPa-0.26.Copyright © 1986 by ASME

Presentation et discussion de resultats experimentaux mettant en evidence les effets de variations des proprietes du combustible et de l'air sur les caracteristiques de pulverisation de ce nouveau type d'injecteur

To study diesel fuel spray behavior at high injection pressures, an experimental study was undertaken to investigate spray penetration and spray angles at constant injection pressures. Fuel spray penetration and spray angles were found to depend on the injection pressure, density of the background gas, orifice dimensions, etc. A relation, based on non-dimensional parameters, is derived to predict diesel spray tip penetration. The calculated tip penetration is found to agree well with the experimental results.

Because combustion in direct injection engines is strongly influenced by the details of the fuel spray in these engines, we have begun a broad research effort of jet breakup experiments and modelling of these high pressure sprays. The main objective of this effort is to better understand fuel injection from the study of the spray-jet breakup process and the associated fuel-oxidant mixing. The focus of this paper is the development of specific models for atomization of the spray-jet

A simple calculation method based on an evaporation analysis proposed previously [1] [2] is used to predict the variation of JP-5 fuel spray characteristics (median drop diameter, Dm, and drop-size distribution parameter, n) with time during evaporation in stagnant hot air. The method takes full account of transient effects occurring during the heat-up period. The results show that Dm increases with time, and so also does n, indicating that the drop-size distribution narrows with passage of time. The time to vaporize any given fraction of the spray mass is found to be proportional to D2mo. The effect of the initial value of n, no, is that a spray having a large value of no will reach its 90% evaporation point faster, but a smaller value of no will give a shorter 20% evaporation time. Based on these calculations, a general method for estimating the time required for any liquid fuel to attain any given percentage of spray mass evaporation in stagnant air is proposed.Copyright © 1983 by ASME

Extensive investigations of fuel spray characteristics have been conducted to improve combustion installations. Still much more information is needed to understand the more complicated phenomena, such as the wall impinging fuel jets and swirling jets often seen in combustion equipment. One important parameter is the air entrainment in the fuel jets. Its measurement has been possible only with point by point scanning probes.