Search Results

This paper presents the fuel atomization effect of a fuel supply system on the lean burn characteristics of a spark-ignition engine and its mechanism. The fuel supply system can realize extremely different two state of atomization, i.e., wall-film of fuel flow and ultra-fine spray (less than 7 um S.M.D. by Malvern measurement). For the first step of the study, the atomization effect is examined under steady operation; several operating parameters including cyclic variability are expressed against the A/F over the wide range of operating condition. Within the operation limits, the fuel atomization does not affect any parameters, while it gives pretty much influence on the lean operation limit. Furthermore, this influencing behavior strongly depends on the throttle valve position and its opening.

This paper presents the characteristics of diesel spray with higher and unsteady injection pressure under an elevated pressure and temperature condition. For this purpose, a pneumatically actuated rapid-compression machine was developed, which has 120 mm bore combustion chamber. A Bosch type injection system was used and can realize the maximum injection pressure about 160 MPa. By using high-speed photography, the spray-tip penetration and the spray angle were measured. Under the non-evaporating condition, the penetrations of higher and normal injection pressure are almost the same, whereas, under the evaporating condition, those penetrations are not the same. Thus, the penetration of the normal injection pressure is affected by the ambient temperature, while that of the higher injection pressure is little affected by the evaporation. The same tendency was observed in the behavior of spray angle development.

The swirl and axial components of gas velocity in the disk type combustion chamber of a fired and motored spark ignition engine were measured using a fiber-optic laser Doppler Anemometer (LDA). The engine was operated at a speed of 1500 rpm, a volumetric efficiency of ηυ = 0.5, an equivalence ratio ϕ = 1.4 and with an ignition timing of θig = 30°BTDC (MBT condition). The gas velocities at 9 points on a diameter at mid-height of the combustion chamber were processed by the cycle-resolved frequency discrimination method. The bulk (mean) velocity was determined by frequency components lower than a cut-off frequency of 667Hz. The flame propagation pattern was detected by ionization probes set at 17 points on the piston. The results indicate significant differences in flow characteristics between motored and fired conditions during the combustion period.

By using an inside visible carburettor, effects of high voltage application to the injected fuel on its behaviour and engine performances are investigated. At first five electrode arrangements around the venturi are examined to clearify the charging mechanism on the injected fuel and its effect on the fuel atomization. The experimental results show that when induced charging, corona charging and electrostatic force are effectively applied to the injected fuel, its atomization is remarkably improved. The diameter of fuel droplets monotonously decreases with increase of applied voltage and the effect is more distinct when the induced air velocity is low. Firing engine test is also carried out and it is revealed that when the throttle valve opening is large, the application of voltage considerably spreads the combustible range toward leaner side. Cyclic variation is reduced and startability is improved by the charge under the severe operating condition.

The purpose of this study is to reveal the ignition assistance mechanism in an alcohol fueled diesel engine. A motored two stroke cycle engine with a ceramic hot plug is motored, and one shot of spray is injected into the combustion chamber. Ignition lags are measured and splitted into physical and chemical lags by means of a statistical technique presented by S. Kumagai. High speed direct photographs are also taken. From the experimental results, it has been found that there are three kinds of hot surface temperature regions. In the low temperature region the mean value of ignition lags, the physical and chemical lags decrease exponentially with increasing the hot surface temperature. These decreasing behaviours are expressed by Arrhenius type equation. The activation energies of these three kinds of lags have the same value. In the higher temperature region the ignition lags are not affected by the hot surface temperature. Between these two regions a transient region is recognized.

The purpose of this study is to reveal the effect of use of W/O emulsified fuel without additives on DI diesel combustion. The combustion pattern, which means the ratio of fuel mass burned in the premixed (or the diffusion) combustion period to the overall supplied fuel mass, is varied by changing the injection timing and the intake manifold pressure. The exhaust emissions, such as particulates, NOx and CO, are measured. By analyzing the indicator diagrams, ignition lags are also measured. Contrary to the results of the other studies, NOx is hardly reduced by using the emulsified fuel, although it does not increase. While the particulate emission is considerably affected, remarkable changes in S.F.C. and the exhaust gas temperature are not recognized. With decreasing the fuel mass fraction burned in the prernixed combustion (spontaneous ignition) or the intake manifold pressure, the effect of the emulsification on particulate emission turns from the promotion to the suppression.

In order to improve adaptability of the laser Doppler anemometer (LDA) to measurement of gas flow velocities in an internal combustion engine, an optical fiber system composed of a couple of single mode, polarization-preserving optical fibers has been developed to transmit the incident beams. The overall light transmission efficiency of the system is 24 % and not so high, but the system enables real-time measurements of gas flow velocity in the combustion chamber of a small two-cycle engine during firing operation. The velocity data measured are processed with cycle by cycle analysis by stationary time-averaged method to obtain bulk velocity Ū, turbulence intensity u′ and integral time scale of turbulence Lt.