Development of a Predictive Pressure Waves Model for High-Pressure Common Rail Injection Systems

Abstract

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.

Experimental characterization of the injected mass variation in a high-pressure GDI injector operating with a multiple injection strategy

“…The experimental campaign has been conducted using a specifically designed hydraulic flow test bench for high-pressure injection system. 21 In this case, the layout has been slightly modified to test a high-pressure fuel system with GDI injectors provided by Marelli Europe SpA. A schematic of the hydraulic flow test bench system is shown in Figure 1.…”

Development of a Control-Oriented Ignition Delay Model for GCI Combustion

“…The chemical-physical variable of the ID model (M eq ) aims to quantify the chemical characteristics of the mixture prior to the pilot injection. Considering the dependencies of the ID highlighted during the sensitivity analysis and summarized in Table 7, the chemical potential of the mixture can be expressed by Equation (14), in which M O 2 is the oxygen content of the fresh air entering the cylinder (reactive part of the mixture, direct consequence of the boost pressure), M H 2 O is the amount of water vapor in the fresh air (φ), M RG represents the mass of residual gases and M RG the amount of external EGR. The model parameters k iRG and k EGR , which will be discussed later, are used to consider the impacts of the residuals and EGR on the mixture chemistry trying to summarize the internal mixing phenomena which affect the ID.…”

“…As a matter of fact, the rise of in-cylinder pressure and temperature generated by the fuel injected with pilot injections strongly affects the auto-ignition mechanisms, reducing the ignition delay of the following injection, which burns in less homogeneous conditions, thus generating smoother combustion [10,11]. Many works have shown that the wrong positioning and dosing of pilot injections could compromise GCI combustion stability [12][13][14]. Therefore, the design of the injection pattern (especially pilot injections) plays a key role to maximize the benefits of this LTC methodology over a wide range of operating conditions.…”

Accelerometer-based SOC estimation methodology for combustion control applied to Gasoline Compression Ignition

“…As a result, an extremely accurate injection management, particularly pilot injections, represents the key factor to assure stable GCI combustion over the whole engine operating range. Several works in literature show that it is possible to increase the GCI operating range by using a model-based injection strategy management aimed to predict the ignition delay of the pilot injections [27][28][29][30][31][32]. However, an accurate feed-forward prediction of the angular position at which the fuel introduced with the first injection starts burning (SOC) still represents the main challenge in the field of developing robust control strategies.…”