Combined Effect of Exhaust Gas Recirculation and Partially Premixed Charge on Performance and Emissions of a Direct Injection Diesel Engine

The effects of exhaust gas recirculation (EGR) cooling, in combination with a partially-premixed charge obtained by a very advanced fuel injection (early injection), on the combustion of a Common-Rail Diesel engine, have been experimentally investigated. The combustion behavior, for different injection strategies, has been analyzed as well as the emission levels. Experimental tests have been carried out on a direct injection Fiat 1929 cm 3 Common Rail Diesel engine. Two different injection strategies have been investigated: the first one was obtained performing pilot and main injections only, the second one adding an early injection. The effects on engine combustion of hot and water cooled EGR have been compared with the combustion behavior without EGR, also showing the effect produced by different pilot injection timings and quantities. Results show that cooled EGR can improve both pilot and early injection combustion causing an increase in the peak values of the heat release (GHRR), and a decrease of the NO x emissions. The use of a small early injection in addition to a pilot one contributes to reduce NO x emissions, causing a reduction of the peak heat release of pilot + early injection and an increase of the peak of heat release of main injection. NO x emissions can be reduced by the increase of EGR percentage, more with cooled than with hot EGR.