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The droplets and vapor distributions in a fuel spray were imaged by a dual-wavelength laser absorption-scattering technique. 1,3-dimethylnaphthalene, which has physical properties similar to those of Diesel fuel, strongly absorbs the ultraviolet light near the fourth harmonic (266 nm) of a Nd:YAG laser but is nearly transparent to the visible light near the second harmonic (532 nm) of a Nd:YAG laser. Therefore, droplets and vapor distributions in a Diesel spray can be visualized by an imaging system that uses a Nd:YAG laser as the incident light and 1,3-dimethylnaphthalene as the test fuel. For a quantitative application consideration, the absorption coefficients of dimethylnapthalene vapor at different temperatures and pressures were examined with an optical spectrometer. The findings of this study suggest that this imaging technique has great promise for simultaneously obtaining quantitative information of droplet density and vapor concentration in Diesel fuel spray.

Swirling flow in a cylinder of a direct injection diesel engine was investigated under motored and fired conditions. Air flow velocity in a motored engine was measured by a laser doppler velocimeter (LDV). Profiles of tangential and axial velocities of the swirling flow, and a local swirl ratio, which was defined as the ratio of the local tangential velocity to an engine revolving speed, were obtained. The combustion process in a fired engine was observed by high speed photography. Local swirl ratios of a flame during the combustion process were measured by tracing the flame motion on the combustion photographs. The history of the swirl ratio of a flame during the combustion of a small amount of fuel could be considered to be a standard for histories of swirl ratios of a flame inside a cavity radius. The local swirl ratios at various positions in a cylinder show different histories under both motored and fired conditions. The value is larger inside a cavity radius than outside it. Therefore, it can be considered that the swirling flow in a cylinder consists of two regions, that is, the regions inside and outside the cavity radius. The comparison of measured results under motored and fired conditions shows that the swirl motion inside the cavity radius is accelerated by the effect of combustion, especially by the effect of pre-mixed combustion in an early stage of diesel combustion. These experimental results can be utilized to verify the results of mathematical modeling for the swirling flow in a cylinder.

Application of the pulsed laser laser holography technique was made to observe diesel sprays injected into a high pressure and temperature atmosphere in a quiescent bomb. Two different holography techniques, that is, single-pulsed laser holography and double-pulsed holographic interferometry were adopted in this study. Shadowgraphs, schlieren photographs and micrographs of a reconstructed image of the spray were taken. The spray widths and equivalence ratios of fuel droplets were microscopically measured. The fuel droplets and vapor around the spray in a high pressure and temperature atmosphere could be observed by single-pulsed laser holography. By double-pulsed holographic interferometry, interference fringes were observed at the spray edge, and the contrast between the spray edge and the atmosphere was made more striking. The spray width has a tendency to decrease when the atmospheric temperature is increased. Some droplets were observed around the spray up to the pressure 3.1 MPa and the temperature 773K.

Visualization by the liquid injection technique, in which liquid fuel is injected into another liquid, was applied to an investigation of the spray developing processes in a small direct injection diesel engine. The injector was newly designed to obtain spray characteristics similar to a diesel spray in a high-pressure atmosphere. The spray injected into water by this injector has a penetration and break-up length similar to the diesel spray. The behavior of the spray in a swirling water flow was investigated. Sprays with different break-up lengths show different behavior in the same swirling water flow. The spray with a higher injection pressure shows a larger spray angle, a lower dispersion by the swirling flow before impingement with the combustion chamber wall, but wider distribution along the wall after the impingement.

Application of the pulsed laser holography technique was made to observe a diesel spray injected into a high pressure bomb. Two different holography techniques, that is, single-pulsed laser holography and double-pulsed holographic interferometry were adopted in this study. Shadowgraphs, schlieren photographs and micrographs of a reconstructed image of the spray were taken. The spray width and equivalence ratio of fuel droplets were microscopically measured. The fuel droplets and vapor around the spray in a high pressure and temperature atmosphere could be observed by single -pulsed laser holography. Interference fringes were observed along the spray edge by double-pulsed holographic interferometry. double-pulsed holographic interferometry made the image of the evaporating spray at high temperature clearer than the single-pulsed laser holography. The spray width had a tendency to decrease as the atmospheric temperature was increased. Some droplets were observed around the spray up to a pressure of 3.1 MPa and a temperature of 773 K.

A laser doppler velocimeter was allied to a steady-flow test rig to analyze the transition of an intake swirl and a turbulence in a cylinder of a D.I. diesel engine. Three dimensional mean velocity and turbulence were measured with two kinds of intake ports that showed different engine performance. The formation process of the swirling flow in a cylinder was revealed by investigating the angular momentum flux around the intake valve and around the cylinder axis. The transition of the swirl and the turbulence along the cylinder axis showed a remarkable difference between these two ports. From the correlation with engine performance, it was found that the in-cylinder flow near the cylinder head (up to 0.6 ∼0.7 x bore) had more important effect on the engine performance than the swirling flow the swirling flow in the downstream region (1 ∼2 x bore apart from the cylinder head, swirl detectors are often placed).

This paper describes the characteristics of flame motion in the throat of a swirl- chamber diesel engine. Two optical-fiber probes were installed in a cylinder head to transmit the radiant light from a flame passing two halfway locations in the throat. The radiant light intensity from the probe was converted into an electric signal (a flame signal) by a photoelectric transducer. The temporal phase difference between two flame signals was measured at each crank angle by the correlation between feature points on both signals. From these results, transitions of the moving velocity of a flame in the throat were obtained. Immediately after the flame begins to spout into the main chamber, the moving velocity of the flame in the throat gradually decreases to a minimum. Then the velocity increases to a maximum, and decreases again as combustion proceeds. There is a correlation between transitions of the moving velocity of a flame and heat release rate in the middle and final stages of the combustion.

A diesel spray in a high-pressure and high-temperature atmosphere was recorded by pulsed-laser holography. The schlieren and shadow images of the same spray obtained from a reconstructed hologram were analyzed, and the concentrations of fuel vapor and droplets in the spray were measured. The radial distribution of the fuel vapor concentration shows a low value at the center and the edge of the spray, and takes a maximum between them. At the section where a relatively large eddy is produced around the spray, the fuel vapor concentration increases in the whole section, and takes two maximums corresponding to the structure of the eddy flow. The axial distribution of the fuel vapor concentration shows a gradual increase in the upper stream of the spray, whereas in the lower part of the spray it shows sudden increase and decrease repeatedly due to the eddies around the spray. The axial distribution of the total fuel (vapor and droplets) approximately agrees with the calculated result by the momentum theory in the lower part of the spray.

Etude experimentale de la combustion dans la prechambre et la chambre principale d'un moteur diesel a injection indirecte par photographie ultrarapide

Simplified visualization of the fuel spray developing process in a small D.I. diesel engine was made by the liquid injection technique. In this technique, a liquid fuel was injected into another liquid to simulate injection into a high pressure gaseous atmosphere. For obtaining spray characteristics in the liquid similar to a diesel spray in a high-pressure gaseous atmosphere, the similarity principles based on the Reynolds number of the fuel flow at a nozzle hole and empirical equations of the spray penetration including the breakup length were introduced in this study. The behavior of the spray in a swirling flow was investigated

This paper describes a simplified three-dimensional modeling of the mixture formation and combustion processes in a direct injection (D.I.) diesel engine. The fuel-air mixing and combustion processes in the D.I. diesel engine can be characterized by the combined effects of some processes, such as spray trajectory, fuel vaporization, gas motion, combustion, and dispersion of gaseous components and enthalpy. Each process was computed by a simple sub-model based on the experimental results and empirical equations. Reasonable agreement between computed and experimental results for these engine variables demonstrate that, with appropriate adjustments to the empirical coefficients of each model, the model produces qualitatively realistic predictions of the in-cylinder processes and engine performance. (A) For the covering abstract see IRRD 865952.

The trajectory and dispersion of a fuel spray vapourising in a combustion chamber are of importance in the mixture formation and combustion of a direct injection (DI) diesel engine. The paper describes experiments and modelling of the spray, of both swirling gas flow and wall impingement, under simulated conditions. A simplified computational model was developed to describe the spray trajectory and vapour dispersion in the DI diesel combustion chamber. The model includes the effects of the breakup on the trajectory, vapourization, gas flow and dispersion of the fuel vapour. For the covering abstract see IRRD 865952.

Details of air flow in a direct injection diesel engine was investigated with a steady flow test rig. A laser doppler velocimeter was used to characterize the three dimensional air flow generated by two kinds of inlet ports. In order to obtain the distribution of flow velocity in a cylinder section, interpolation was carried out. A stereographic display of the three dimensional velocity vectors in the cylinder space allowed easy comprehension of the flow characteristics. Angular momentum flux and turbulence kinetic energy in the region closer to the cylinder head as well as those in the lower region of the cylinder space are important for the prediction of air flow in an actual engine cylinder. Transition of the angular momentum flux along the cylinder axis is considered to be influenced by three kinds of angular momentum flux which is induced by an air jet around the inlet valve.