Diesel engine control strategies use complex injection patterns which are designed to meet the increasing request for engine-out emissions and fuel consumption reduction. As a result of the large number of tuneable injection parameters in modern injection systems (such as start and duration of each injection), injection patterns can be designed with many degrees of freedom. Each variation of the injection parameters modifies the whole combustion process and, consequently, engine-out emissions.
Aging of the injection system usually affects injection location within the cycle as well as the amount of injected fuel (compared to the target value), especially for small pre-injections. Since Diesel combustion is very sensitive to injection pattern variations, aging of injectors strongly affects engine behavior, both in terms of efficiency and pollutant emissions production. Moreover, such variations greatly affect other quantities related to the effectiveness of the combustion process, such as noise radiated by the engine.
This work analyses the effects of pre-injection variations on combustion, pollutant emissions and noise radiated by the engine. In particular, several experimental tests were run on a 1.3L Common Rail Diesel engine varying the amount of fuel injected in pre-injections. Torque delivered by the engine and center of combustion (MFB50) were kept constant using a specifically designed closed-loop combustion controller. During the tests, noise radiated by the engine was measured by properly processing the signal coming from a microphone faced to the engine block. The investigation of the correlation between the combustion process and engine noise can be used to set up a closed-loop algorithm for detecting and recentering injectors’ drifts over time.