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An experimental study has been completed which evaluated the effectiveness of using double, triple and rate shaped injections to simultaneously reduce particulate and NOx emissions. The experiments were done using a single cylinder version of a Caterpillar 3406 heavy duty D.I. diesel engine. The fuel system used was a common rail, electronically controlled injector that allowed flexibility in both the number and duration of injections per cycle. Injection timing was varied for each injection scheme to evaluate the particulate vs. NOx tradeoff and fuel consumption. Tests were done at 1600 rpm using engine load conditions of 25% and 75% of maximum torque. The results indicate that a double injection with a significantly long delay between injections reduced particulate by as much as a factor of three over a single injection at 75% load with no increase in NOx. Double injections with a smaller dwell gave less improvement in particulate and NOx at 75% load.

A study was performed to correlate the Sauter Mean Diameter (SMD), NOx and particulate emissions of a direct injection diesel engine with various injection pressures and different nozzle geometry. The spray experiments and engine emission tests were conducted in parallel using the same fuel injection system and same operating conditions. With high speed photography and digital image analysis, a light extinction technique was used to obtain the spray characteristics which included spray tip penetration length, spray angle, and overall average SMD for the entire spray. The NOx and particulate emissions were acquired by running the tests on a fully instrumented Caterpillar 3406 heavy duty engine. Experimental results showed that for higher injection pressures, a smaller SMD was observed, i.e. a finer spray was obtained. For this case, a higher NOx and lower particulate resulted.