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An author's previous studies addressed a combustion system which reduces emissions, noise, and fuel consumption by using PCCI with the split injection of fuel. This concept relies on the premixed combustion of the first injected fuel and accelerated oxidation by the second injected fuel. Although this combustion system requires the optimization of the timing of the second injection, the details of how noise and emissions are reduced have not been elucidated. In this paper, the authors explain the mechanism whereby emissions and noise are reduced by the second injection. In-cylinder visualizations and numerical simulations both showed an increase in smoke and CO as the second injection timing was advanced, as induced by the inhibited oxidation of the rich flame. When the second injection timing is excessively retarded, the amount of soot forming around the near-nozzle increased.

This paper describes a laser-induced fluorescence (LIF) method for quantitative 2-D fuel concentration measurements in an SI engine. The combination of fluorescence tracer and excitation wavelength to lower the temperature and pressure effects on LIF intensity were evaluated. Each kind of fluorescence tracer selected from ketones, aldehydes and aromatics has been excited at 248 nm or 266 nm in a heated and pressurized constant volume vessel. For the promising candidates, further evaluation has been performed using a fired visualization engine. The results show that the optimum combination which gives the lowest effects of temperature and pressure on LIF intensity is acetone with 266 nm excitation. 3-pentanone, which is commonly used fluorescence tracer has been shown to be not suitable for the quantitative measurements, especially in a fired engine.

The set-off length (also referred to as the “lift-off length”) is reduced by the re-entrainment of the burned gas by the backward flow surrounding a diesel spray jet produced by a multi-hole nozzle. In the present study, to estimate the equivalence ratio at the set-off length, a means of estimating the amount of burned gas that is re-entrained into the near-nozzle region of the diesel spray jet was established. The results revealed that the suppression of soot formation in quasi-steady diesel spray flames produced by a multi-hole nozzle and a high injection pressure is not attained by reducing the equivalence ratio at the set-off length. Analysis of the amount of soot along the spray axis using a two-color method revealed that the maximum soot amount position appears in a quasi-steady spray flame, after the collapse of the head vortex in which a dense soot cloud is formed. The maximum soot amount position does not change even if the injection pressure varies.