Over the last years, automotive industries drove a great amount of research in
the field of advanced combustion techniques minimizing carbon dioxide emissions.
The so-called Low-Temperature Combustions (LTC), characterized by the
self-ignition of highly premixed air-fuel mixtures, represent a promising
solution to achieving high efficiency and ultralow emissions of nitrogen oxides
(NOx) and particulate matter. Among these, gasoline Partially Premixed
Combustion (PPC), obtained through the high-pressure direct injections of
gasoline, showed a good potential for the simultaneous reduction of pollutants
and emissions in compression ignited engines. However, when multiple injections
per cycle are performed (with hydraulic-assisted needle opening), combustion
stability might be compromised by the wave effects in the hydraulic system,
which produce incoherence between the requested and injected fuel. This work
presents a model-based pressure waves reconstruction strategy, based on a
control-oriented model of the high-pressure common rail injection system fueled
with gasoline. To determine the hydraulic system’s behavior during the injection
process, a specifically designed flushing bench with a high-frequency
acquisition system has been developed. Experimental activities have been carried
out to highlight fuel pressure fluctuations with single and double injection
patterns. Through the analysis of the acquired data, the key parameters
(characteristic of the system) have been identified and the accuracy of pressure
waves reconstruction has been evaluated, always returning errors lower than 2%
between measured and estimated instantaneous pressures. Different fuel types,
injectors, and rail positions have been tested to highlight the robustness of
the approach. Based on the instantaneous pressure trace estimated with the
control-oriented model, a fuel quantity Fluctuation Correction Strategy (FQC),
implementable on a standard engine Electronic Control Unit (ECU), has been
developed. The obtained results confirm the potential to reduce fuel quantity
oscillations in multiple-injections systems.
