The NOx reduction extent is much more significant than the Type 1 piston as shown in the figure. However the deterioration in smoke and fuel consumption at the full load is the problem for this combustion. The CSAC piston resulted in significantly increased smoke. Investigation of the soot deposit distribution on the piston surface indicated that the increased smoke was caused by the fact that CCD jet injected into the air cavity pushed out the smoke cloud from the main cavity to the top clearance space. To realize simultaneous reduction of NOx and smoke, variety trials were made as combining the two-stage combustion with EGR and fumigation, but none of these trials succeeded to accomplish this.

Although the problems still remains, the above results suggests that it is possible to reduce NOx by the two-stage combustion with forming a rich mixture at the initial combustion stage followed by the secondary turbulent mixing.

　

5. ANALYSIS OF NOx FORMATION KINETICS AND JET MOMENTUM ON SMOKE REDUCTION

　

Next, to see the NOx reduction potential of the two-stage combustion and to identify the effective control-factors for the reduction, calculations of the NO reaction kinetics were made based on Extended Zel'dovich Reactions. Calculation method is outlined in Chapter 2, and details of the simulation are shown in Ref. [12].

　

Fig.3 Tested piston coonfigurations for two-stage combustion

Fig.4 Engine performance for various piston configurations in Fig.3 for two-stage combustion

Fig.5 0SKA and CSAC type piston for two-stage combustion

Fig.6 Engine performance With OSKA type piston for two-stage combustion, compared with base piston performance.

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