This paper presents a study on the effect of injection rate on the performance and emissions of a direct-injection gasoline engine operated with seven kinds of DI injection and a port-injection. The injection pressures were set at 0.3 and 7 MPa for port injection and DI operation modes respectively. The spray characteristics of DI injectors were obtained by measuring the SMD, droplet concentration and spray angle. The engine was run at a constant speed and load of 1000 rpm and 0.22 MPa of BMEP. The BSFC reduction of DI from port injection was 13% at most in which 4% was derived from the decrease in pumping loss and the remaining 9% was due to the improvement of the cycle efficiency. As for the injection rate effect in DI operation, the BSFC takes the minimum at a value of the injection rate where the maximum difference reached to 7%. It was revealed that this is due to the variation of the combustion efficiency and then corresponds to the behavior of droplet concentration. Soot emission correlated well with the SMD. Thus the performance and emissions were mostly explained by the spray characteristics.

To realize the pre-mixed combustion type Diesel engine, analyses of the wide-angle conical spray flow and its application to the direct injection Diesel engine have been made. In the present work, the spray was evaluated by high speed flow visualization, particle image velocimetry (PTV) measurement, phase Doppler anemometer (PDA) measurement and numerical simulation by KTVA-3V code, and finally the combustion and exhaust characteristics of the proposed engine are examined. The penetration and the shape of the conical sprays under different ambient pressures (0.1, 1.0 and 2.0 MPa) are obtained experimentally and with numerical simulations. Generally, good agreements between them are achieved. It is also cleared that the spray formation is strongly influenced by the surrounding pressure. PIV measurements show the initial development of the spray. The maximum velocity is about 80 m/s, which is almost in the same range as that obtained by the PDA measurements. For the combustion experiment, the excess air ratio was set at 3.1 and 2.5. The engine speed was varied from 1000 to 2000 rpm. Expected premixed combustion region is realized at around the fuel injection timing prior to 65 degree BTDC, where NOx and soot emissions are almost zero at the excess air ratio of 3.1.

A cooling suction air with water spray has been used for the gas turbine. The cooling efficiency depends on spray properties and surrounding conditions. The aim of this study is to know spray properties and to clarity an influence of spray nozzle type on the cooling efficiency. A Phase Doppler Anemometry (PDA) is used for measurements. This measurement system is able to measure size and velocity of each droplet. A pin type nozzle, two different hole type nozzles are tested. The distribution of spray properties for the pin type nozzle becomes asymmetry due to the existence of pin. Its spray spreads widely and has broad size distribution in all spray area. Spray spreading area of hole type nozzles is narrow. Small particles gather on the spray center and large particles gather in the spray outer edge. Properties of each nozzle are also discussed for evaluating the cooling efficiency.

The structure, droplet characteristics and instantaneous fuel injection rate of two stage injection spray designed for direct injection gasoline engine were analyzed experimentally. A particle image velocimetry (PIV) to evaluate the instantaneous two-dimensional velocity field, a phase Doppler anemometer (PDA) and an instantaneous fuel flow rate meter based on a laser Doppler anemometer (LDA flow rate meter) were applied for the measurements. A swirl nozzle injector was used and injection conditions were 25 Hz of spray frequency, 2 ms and 1ms of the first and the second injection durations and 2.4, 3.3 and 9.1 ms of valve opening intervals. The initial jet of the second stage injection can overtook the main spray body of the first stage injection under the valve opening interval of 2.4 and 3.3 ms. The LDA flow rate meter made the injection rate measurement with sufficient accuracy in the two stage injection and showed the unstable second injection due to remaining pressure oscillation in the injection pipe. Both time averaged and time resolved PDA results were compared in the intermittent spray. The interaction between the first and the second sprays was also demonstrated in vector map obtained by the PIV measurement.

Characteristics on particle motion in a liquid-solid two-phase jet flow were studied in the paper. The water jet including glass particle of 389 μm in mean diameter was injected into water bath. The experimental conditions were 0.21% of initial particle volume ratio, 5mm in pipe diameter and 1.84 m/s of mean velocity on outlet of the jet. A laser Doppler anemometer (LDA) with size discrimination was applied for measuring the time serious velocities of the single-phase flow, particle and water phase flow. A particle image velocimetry (PIV) was also applied in the two-phase flow. The normal PIV method can hardly measure the particle size and perform the particle size discrimination. In the experiment, using the gray scales related with the scattering light intensity, measuring method with size discrimination in two-phase flow was carried out. The experimental results show less difference between velocities of single-phase flow and water-phase flow under this low particle volume ratio condition. Particles have the relative motion with the water-phase and large rms velocity. The PIV used in this experiment, which is called multi-intensity-layer-PIV: MILP, can measure water-phase velocity with good accuracy.

This paper presents further investigation into the effect of over-expansion cycle with late-closing of intake valves on the engine performance in gasoline engines. A larger single-cylinder test engine with the stroke volume of 650 cc was used with four kinds of expansion ratio (geometrical compression ratio) from 10 to 25 and four sets of intake valve closure (I.V.C.) timings from 0 to 110 deg C.A. ABDC. Late-closing has an effect of decreasing the pumping work due to the reduction of intake vacuum, althogh higher expansion ratio increases the friction work due to the average cylinder pressure level. Combining the higher expansion ratio with the late-closing determines the mechanical efficiency on the basis of these two contrastive effects. The indicated thermal efficiency is mostly determined by the expansion ratio and little affected by the nominal compression ratio. The value of the indicated thermal efficiency reaches to 48% at most which is almost comparable with the value of diesel engines. The improvement of both indicated and brake thermal efficiency reaches to 16% which is much higher than ever reported by the authors. A simple thermodynamic calculation could successfully explain the behavior of the indicated thermal efficiency. The brake thermal efficiency could also be improved due to the increase in both mechanical and indicated efficiencies.