Fig.5 Change in trade-off due to nozzle orifice size

Fig.6 Flow-chart of NOx calculation

Fig.7 Flow-chart of soot calculation

　

4. COMBUSTION ANALYSIS BY TWO-ZONE MODEL

　

4.1 Soot Formation and Oxidation Model

In order to estimate the rate of net soot-formation, models proposed by Morel and Keribar [10] are used in the present analysis, which are quite similar to the ones proposed by Hiroyasu & Kadota [6], and are convenient to apply to the present two-zone model in comparison with the multistep model suggested by Kazakov & Foster [7]. The soot-formation rate (dS/dt)_f is calculated using the following Eq.(1). The soot-oxidation rate (dS/dt)_b using Eq.(2) and the net soot-formation rate (dS/dt)_n using Eq.(3) respectively.

　

(dS/dt)_f = A₁ ・ m_d ・ exp(-A₂/T_b) (1)

(dS/dt)_b = (B₁ S/p_sd_s) ・ exp(-B₂/T_rad) ・ √P₀₂ (2)

(dS/dt)_n = (dS/dt)_f - (dS/dt) _b (3)

　

S (kg) denotes the cumulative soot quantity. m_d (kg/s) is the mass rate of diffusion combustion given by the Wiebe's function [11], which is the least square curve of the experimental heat release during the diffusion combustion period.

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