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Internal combustion engines still play a vital role in realizing the low carbon society. For spark ignition engines, further improvement in thermal efficiency can be achieved by increasing both compression and specific heat ratios. In the current work, the authors developed practical technologies to prevent output power loss due to knocking at full load, which is a critical issue for increasing compression ratio. These new technologies allowed to increase the compression ratio significantly and provide an equivalent torque level as a conventional engine. As a result, thermal efficiency has been improved at partial load.

To get quantitative measurements of liquid and vapor phase concentration distributions in a gasoline spray, a laser-based absorption and scattering (LAS) technique was developed. The LAS technique adopts ultraviolet and visible lasers as light sources and a test fuel, which absorbs the ultraviolet light but does not absorb the visible light, instead of gasoline. The LAS principle is based on the incident light extinction in the ultraviolet band due to both vapor absorption and droplets scattering, whereas in the visible band, the incident light extinction is due only to the droplet scattering. The absorption spectra and molar absorption coefficients of the candidate test fuels including p-xylene, benzene and toluene, all of which have physical properties similar to gasoline, were investigated, and p-xylene was finally selected as a test fuel. Measurement accuracy of the LAS technique was discussed.

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.

Mixture formation processes play a vital role on the performance of a D.I. Gasoline engine. Quantitative measurement of liquid and vapor phase concentration distribution in a D.I. gasoline spray is very important in understanding the mixture formation processes. In this paper, an unique laser absorption scattering (LAS) technique was employed to investigate the mixture formation processes of a fuel spray injected by a D.I. gasoline injector into a high pressure and temperature constant volume vessel. P-xylene, which is quite suitable for the application of the LAS technique, was selected as the test fuel. The temporal variations of the concentration distribution of both the liquid and vapor phases in the spray were quantitatively clarified. Then the effects of injection pressure and quantity on the concentration distributions of both the liquid and vapor phases in the spray were analyzed.

To get a better understanding of the characteristics of the high pressure gasoline sprays impinging on a wall, a fundamental study was conducted in a high-temperature high-pressure constant volume vessel under the simulated engine conditions of in-cylinder pressures, temperatures, and wall temperatures. The injection pressure was varied from 20 to 120 MPa. The spray tip penetration, vapor mass distribution, and vaporization rate were quantitatively measured with the laser absorption-scattering (LAS) technique. The velocity fields of the wall-impinging sprays under vaporizing conditions were measured with the particle image velocimetry (PIV) technique using silicone oil droplets as tracers. The effects of injection pressure and spray/wall interactions on spray characteristics were investigated. The results showed that the increased injection pressure improved penetration, vaporization, and turbulence of the sprays.