The Nitric monoxide(NO) emission from the combustion of hydro- carbon fuel peaks at stoichiometric condition and becomes a little at either condition of lean or rich combustion. There are lots of studies on 2-stage combustion which making rich condition in the early combustion period and lean condition late period.
But it is difficult to realize 2-stage combustion in diesel engine due to its nature of combustion process such as being closed system. So far, most studies on NO emission control from diesel engine were focussed on exhaust aftertreatment using catalytic method, exhaust gas recirculation(EGR), water injection etc.. But these methods invite either high cost or additional system to control. If it is possible to realize 2-stage combustion in diesel engine combustion chamber without power loss and increase of another emissions like CO or smoke, it might become a better way to control the emission.
In this study, devised was a uniquely shaped combustion chamber with reformed piston crown intended to keep fuel-rich condition during early stage of combustion and fuel-lean condition during next stage. The engine for experiment was direct injection type single cylinder small diesel engine, which has displacement of 631cc. Each spray from 4 hole nozzle is directed to narrow and long cavity and keeps rich condition, and after that unburned fuels are mixed with air in big cavity to make lean combustion. The strong squish and reverse squish from and to top flat position of piston were used to help mixing fuel and air.
It was found that the NO emission decreased significantly at various condition of operation with the 2-stage combustion type diesel engine, but CO and smoke emission and specific fuel consumption increased. It was suggested as conclusion that 2-stage combustion concept could be a potential way to control emissions and fuel consumption in diesel engine.