Rate Shape Design for Gasoline-Like Fuels at High Injection Pressures Using One-Dimensional Hydraulic Models

Recent research has demonstrated that gasoline compression ignition (GCI) can improve the soot-oxides of nitrogen (NOx) trade-off of conventional diesel engines due to the beneficial properties of light distillate fuels. In addition to air handling and aftertreatment, fuel systems also require further development to realize the potential efficiency and emissions benefits of GCI. Injector one-dimensional (1-D) hydraulic modeling is an important design tool used for this purpose. The current study is a continuation of prior work that used computed physical fuel properties and hydraulic models to accurately simulate high-pressure injection behavior relevant to GCI. With respect to fuel characteristics for the model, physical properties were validated by direct comparison to measurements at temperatures and pressures reaching 150°C and 2500 bar, respectively. Calibration of the injector model discharge coefficients for gasoline-like fuel was automated with various multi-objective optimization approaches coupled to a genetic search algorithm. However, Pareto optimization showed the best closure with an experimental rate of injection (ROI) and total injected quantity compared to other current and previous manual methods. The validated model was then used to determine the injector specifications needed to approach an idealized, slowly opening rate shape that could enable low-NOx combustion. Initial parametric studies of key parameters affecting rate shape showed that changing a combination of nozzle exit, control chamber (or servo) outlet, and needle orifice diameters could produce the desired single injection fueling profile. A transient targeting (TT) optimization technique coupled to a genetic search algorithm was compared to a full-factorial design of experiments (DoE) and showed that both approaches could reasonably achieve the target rate shape. However, TT required a significantly reduced computational runtime. In general, this study provides a robust methodology for accurately simulating gasoline-like fuels in high-pressure injectors and demonstrates a conceptual rate shape targeting process for GCI using 1-D hydraulic models. This tool could potentially be integrated with predictive computational fluid dynamics (CFD) models to achieve a simulation-led combustion system design process that includes rate shaping as an additional avenue for optimization.