Application of the Design of Experiments and Objective Functions for the Optimization of Multiple Injection Strategies for Low Emissions in CR Diesel Engines

Design of Experiments (DoE) methodologies have been applied in conjunction with objective functions to the experimental optimization of multiple injection strategies for a small displacement Common Rail (CR) off-road diesel engine.

One operating point, which corresponds to the 5^th mode of the ISO 8178 - C1 test cycle (intermediate speed / full load), was considered during this analysis: this operating condition is one of the most critical as far as exhaust emissions for the considered engine are concerned. Three injections were actuated per engine cycle during the experimental tests, with different strategies characterized by different timings and durations of each injection.

It was found that DoE techniques for the reduction of experimental plans can be very effective in finding the optimum values for the injection parameters, leading to a remarkable reduction in the calibration process time, compared to full factorial designs. It was also pointed out that the formulation of the objective function can greatly influence the optimization process. A new objective function, that also takes the combustion noise level into account, was proposed and was shown to be very effective in detecting the benefits obtained from the introduction of pilot injections, which are essentially related to combustion noise decrease.