Recently the environment of the world has been exposed to the severe air pollution emitted from the rapid developing industries. And the necessity of controlling the emission from the diesel engines such as NOx, PM, SOx, COx also has been raised up gradually. Among them the NOx emission from the oceangoing vessels has been layed under regulation from international convention of MARPOL Annex Ⅵ of IMO, dated from 1st January, 2000.
Various measures have been tried to reduce the NOx emission from diesel engine but with partial success, because the mechanisms of NOx formation and PM formation appear to have trade-off relation between each other. Therefore it has been known to be difficult to reduce NOx emission and PM emission simultaneously.
Two stage combustion method ie. a combustion process which has rich combustion stage and lean combustion stage one by one, has been developed successfully to reduce NOx formation in continuous combustion chambers such as in the boilers. But until yet it is not successful to apply the same method in intermittent combustion chamber like in the diesel engine cylinder, as it was, only several research works were carried out.
In this study the various modification of configurations of piston crown and spray impingement was attempted to attain a geometry that realize the two stage combustion in the diesel engine cylinder and to acquire a simultaneous reduction of NOx and PM.
It was found that the NOx emission decreased significantly at various condition of operation both with the two stage combustion type engines & impinge swirl type engines of this series of configuration, but other values such as smoke, CO and specific fuel consumption deteriorated as usual. And it was suggested that the weakening of swirl intensity due to the existence of radial division of rich-lean combustion region and reduction of penetrating momentum due to the spray impingement act as a reason of ineffectiveness of this series of combustion chamber geometry.