Reducing Particulate and NOx Using Multiple Injections and EGR in a D.I. Diesel

An emissions and performance study was conducted to explore the effects of EGR and multiple injections on particulate, NOx, and BSFC. EGR is known to be effective at reducing NOx, but at high loads there is usually a large increase in particulate. Recent work has shown that multiple injections are effective at reducing particulate. Thus, it was of interest to examine the possibility of simultaneously reducing particulate and NOx with the combined use of EGR and multiple injections. The tests were conducted on a fully instrumented single cylinder version of the Caterpillar 3406 heavy duty truck engine. Tests were done at high load (75% of peak torque at 1600 RPM where EGR has been shown to produce unacceptable increases in particulate emissions. The fuel system used was an electronically controlled, common rail injector and supporting hardware. The fuel system was capable of up to four independent injections per cycle. Two nozzle spray angles were used with included spray angles of 125° and 140° (i.e., with and without significant spray wall impingement). Particulate versus NOx trade-off curves were generated over a range of injection timings for each injection scheme and EGR rate studied. The results show that the combined use of EGR and multiple injections is very effective at simultaneously reducing particulate and NOx. For example, by using a 125 degree spray angle, an optimal triple injection, and about a 6% EGR rate, particulate and NOx were simultaneously reduced to 0.07 and 2.2 g/bhp-hr, respectively. There was, however, a significant sacrifice in BSFC due mainly to the retarded injection timing used at that condition.