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Experimental results of a diesel engine have shown that using split-injection can reduce the NOx and particulate emissions. For understanding the mechanism of emissions reduction, mixture formation in split-injection diesel sprays was characterized in the present paper. A dual-wavelength laser absorption-scattering (LAS) technique was developed by use of the second harmonic (532nm) and the fourth harmonic (266nm) of a pulsed Nd:YAG laser as the incident light and dimethylnaphthalene (DMN) as the test fuel. By applying this technique, imaging was made of DMN sprays injected into a high-temperature and high-pressure constant volume vessel by a single-hole nozzle incorporated in a common rail injection system for D.I. diesel engine. The line-of-sight optical thickness of both fuel vapor and droplets in the sprays was yielded from the sprays images.

Three-dimensional behaviors of direct injection (D.I.) gasoline sprays were investigated using 2-D and 3-D particle image velocimetry (PIV) techniques. The fuel was injected with a swirl type injector for D.I. gasoline engines into a constant volume chamber in which ambient pressure was varied from 0.1 to 0.4 MPa at room temperature. The spray was illuminated by a laser light sheet generated by a double-pulsed Nd:YAG laser (wave length: 532 nm) and the succeeding two tomograms of the spray were taken by a high-resolution CCD camera. The 2-D and 3-D velocity distributions of the droplet cloud in the spray were calculated from these tomograms by using the PIV technique. The effects of the swirl groove flows in the injector and the ambient pressure on the structural behavior of the droplet cloud in the spray were also examined.

In order to measure the droplets and vapor concentration inside a fuel spray, a dual-wavelength laser absorption-scattering technique was developed using the second harmonic (532nm) and the fourth harmonic (266nm) of a Nd:YAG laser and using dimethylnaphthalene as the test fuel. The investigation results show that dimethylnaphthalene, which has physical properties similar to diesel fuel, is almost transparent to visible light near 532nm and is a strong absorber of ultraviolet light near 266nm. Based on this result, the vapor concentration in a fuel spray can be determined by the two separate measurements: a transmission measurement at a non-absorbing wavelength to detect the droplets optical thickness and a transmission measurement at an absorbing wavelength to detect the joint vapor and droplets optical thickness. The droplets density can be determined by extinction imaging through the transmission at the non-absorbing wavelength.

The internal flow of a diesel injection nozzle was studied by using transparent model nozzles to clarify the effects of the flows in the sac chamber and the discharge hole on the spray behaviors. The geometry of the model nozzle was scaled up 10 times the actual nozzle and the injection pressure for the model nozzle was adjusted so as to achieve a Reynolds number at the discharge hole which was the same as an actual nozzle. Aluminium oxide (Al2O3) tracers were used to visualize the flow patterns in the sac chamber. Sequential photographs of the internal flow and the issuing spray plume during the opening process of the needle valve were taken by a high-speed video camera. By locating the discharge hole on the upper side of the sac chamber, the turbulence intensity in the sac chamber increases and the spread angle of the spray plume becomes large.

Three-Dimensional visualization technique based on volume rendering method has been developed in order to translate a calculated result of diesel combustion simulation into an realistically spray and flame image. This paper presents an overview of diesel combustion model which has been developed at Hiroshima University, a description of the three-dimensional visualization technique, and some examples of spray and flame image generated by this visualization technique.

Planar laser-induced fluorescence (PLIF) technique was employed to perform the quantitative measurements of the cyclic variation of mixture concentration in the combustion chamber of a spark ignition (SI) engine. Nitrogen dioxide was used as the fluorescence tracer to simulate the fuel vapor. A Nd:YAG laser operated at its second harmonic wavelength was employed as the light source. The original engine was modified to introduce laser sheet light into the combustion chamber and the induced fluorescence was captured by a CCD camera fitted with a gated image intensifier. The measurements were done at the engine crank angles of 180° ∼ 300° ATDC with the engine speeds of 200 ∼ 400 rpm and the injection timings of -70 °, 50° and 100° ATDC. A theoretical analysis was made to describe the cyclically varying characteristics of the mixture concentration.

Quantitative imaging of the fuel concentration distribution was made in the combustion chamber of a propane-fueled spark ignition (SI) engine with the employment of laser-sheet-induced Rayleigh scattering technique for realizing the remote, nonintrusive and highly space- and time-resolved measurement. The original engine was modified to introduce YAG laser-induced sheet light into the combustion chamber and the scattered light was captured by a CCD camera fitted with a gated double-micro- channel plate image intensifier. The measurements were done at the crank angle of 270°ATDC in the combustion chamber of the engine motored at 200rpm with an air fuel ratio of 13 for various injection timing, injection direction and intake flow. The results show that with an appropriate matching of fuel injection timing, injection direction and intake flow, a stratified distribution of the fuel concentration can be realized.

A new technique was proposed for the simultaneous measurement of the concentration of fuel vapor and liquid in an evaporating diesel spray injected into a high temperature and high pressure environment. This technique was based on the principle of the absorption of ultraviolet laser light by fuel vapor and the scattering of visible laser light by fuel droplets in the diesel spray. For this principle, α-methylnaphthalene was used as a test fuel. Measuring the transmissivity of ultraviolet and visible laser lights absorbed and scattered by β-methylnaphthalene spray made it possible to analyze the fuel vapor concentration, droplets density and the mixture temperature in the diesel spray. A computerized tomographic transfer technique was also adopted to analyze three-dimensional fuel concentration distribution in the spray.

Spray penetration for Diesel injectors, where injection pressure varies with time during the injection period, was calculated. In order to carry out this calculation, the discharge coefficients of the needle-seat opening passage and discharge hole in orifice-type Diesel nozzles were investigated separately. Simple empirical correlations were obtained between these coefficients and needle lift. Then, by introducing these correlations, the injection pressure, which is defined as the pressure in the sac chamber just upstream of the discharge hole, was either derived from measured fuel supply line pressure, or predicted by means of an injection system simulation. Finally, based on the transient injection pressure, spray tip penetration was calculated by taking the overall line which covers the trajectories of all fuel elements ejected during the injection period.