Effects of Multiple Injections and Flexible Control of Boost and EGR on Emissions and Fuel Consumption of a Heavy-Duty Diesel Engine

A study of the combined use of split injections, EGR, and flexible boosting was conducted. Statistical optimization of the engine operating parameters was accomplished using a new response surface method. The objective of the study was to demonstrate the emissions and fuel consumption capabilities of a state-of-the-art heavy -duty diesel engine when using split injections, EGR, and flexible boosting over a wide range of engine operating conditions. Previous studies have indicated that multiple injections with EGR can provide substantial simultaneous reductions in emissions of particulate and NO_x from heavy-duty diesel engines, but careful optimization of the operating parameters is necessary in order to receive the full benefit of these combustion control techniques. Similarly, boost has been shown to be an important parameter to optimize. During the experiments, an instrumented single-cylinder heavy -duty diesel engine was used. A prototype mechanically actuated (cam driven) fuel injection system was used to provide multiple injections. Flexible control of boost and EGR was accomplished by controlling the pressure of the intake and exhaust surge tanks. The operating conditions studied include operation close to the peak torque condition and at high speed at a medium and at a low load condition. The variables considered in the optimization process included injection pressure, boost pressure, EGR rate, injection timing, and split injection parameters. Using the new response surface optimization scheme, the engine could be optimized rapidly, yielding both reductions in emissions consistent with future heavy -duty standards, and also a substantial reduction in fuel consumption compared to the same engine using an electronic unit injector calibrated for 1998 emissions levels.