Effects of nozzle geometry on direct injection diesel engine combustion process

The aim of the current article is to link nozzle geometry, and its influence on spray characteristics, with combustion characteristics in the chamber. For this purpose, three 6-hole sac nozzles, with different orifices degree of conicity, have been used. These nozzles had been geometrically and hydraulically characterized in a previous publication, where also a study of liquid phase penetration and stabilized liquid length in real engine conditions has been done. In the present work, CH and OH chemiluminescence techniques are used to thoroughly examine combustion process. CH-radicals are directly related to pre-reactions, which take place once the fuel has mixed with air and it has evaporated. On the other hand, OH-radicals data provide information about the location of the flame front once the combustion has begun. The analysis of all the results allows linking nozzle geometry, spray behaviour and combustion development. In particular, CH-radicals have shown to appear together with vapor spray, both temporally and in their location, being directly related to nozzle characteristics. Additionally, analysis of ignition delay is done form OH measurements, including some correlations in terms of chamber properties, injection pressure and nozzle diameter.