Reducing Particulate and NOx Emissions by Using Multiple Injections in a Heavy Duty D.I. Diesel Engine 940897

An experimental study has been completed which evaluated the effectiveness of using double, triple and rate shaped injections to simultaneously reduce particulate and NO_x 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. NO_x 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 NO_x. Double injections with a smaller dwell gave less improvement in particulate and NO_x at 75% load. At 25% load, where ignition delays are long, the effect a small dwell between double injections was found to reduce the premix burn fraction and NO_x. Similar results were obtained using a single injection with a ramped injection rate rise, however at 75% load the particulate levels increased as compared to a fast injection rate rise. Triple injections were also found to be effective if the third injection started significantly after the end of the second injection. At 25% load a triple injection reduced particulate by 50% and NO_x by 30%. For the multiple injections strategies investigated in this study, a fast injection rate rise was found to be the most beneficial towards a overall reduction of particulate and NO_x. The effectiveness of a late injection in both triple and double injections strategies appears to be that it promotes particulate oxidation later in the cycle and improves mixing. Triple injections gave greater flexibility in controlling the heat release rate as compared to single and double injections. This flexibility was required for simultaneous reductions in particulate and NO_x at 25% load conditions.