Tailoring Simplified Models for the Feeding Performances Prediction of CNG PWM Controlled Single Stage Injectors

In this paper, an orifice-based lumped parametermodel has been developed and tailored to predict thefeeding performances of a single stage, inwardlyopening, PWM controlled gas injector for automotiveapplications.In particular, simplifying the description of injectorrelevant sections, and adopting a “semi-perfect”approach to depict the gas properties dependency onpressure and temperature, the sub-sonic effluxthrough the injector metering section is studiedinvolving both an isentropic and a polytropicexpansion.Then, considering dry air as fluid medium, the injectorfeeding characteristics variations with the duty cycle,with the feeding pressure and with temperature arehighlighted.After, an experimental vs. numerical data comparisonextended to the injector whole operational field is usedto tailor the main corrective parameters of thesimplified numerical model: among others, particularattention is devoted to the efflux coefficient variationwith injector operating conditions.Successively, the parameters setting coming from theadoption of dry air is used to perform computationsinvolving other gases, such as the pure methane andthe Groningen gas (chosen as reference gas forCNG).Finally, through a numerical vs. experimentalcomparison about mass flow-rate, the reliability of thesimplified numerical model, and its design usefulnessto predict the injector feeding performances withdifferent gases of automotive interest, is highlighted.