Tailoring Simplified Models for the Feeding Performances Prediction of CNG PWM Controlled Single Stage Injectors 2007-01-0022
In this paper, an orifice-based lumped parameter model has been developed and tailored to predict the feeding performances of a single stage, inwardly opening, PWM controlled gas injector for automotive applications.
In particular, simplifying the description of injector relevant sections, and adopting a “semi-perfect” approach to depict the gas properties dependency on pressure and temperature, the sub-sonic efflux through the injector metering section is studied involving both an isentropic and a polytropic expansion.
Then, considering dry air as fluid medium, the injector feeding characteristics variations with the duty cycle, with the feeding pressure and with temperature are highlighted.
After, an experimental vs. numerical data comparison extended to the injector whole operational field is used to tailor the main corrective parameters of the simplified numerical model: among others, particular attention is devoted to the efflux coefficient variation with injector operating conditions.
Successively, the parameters setting coming from the adoption of dry air is used to perform computations involving other gases, such as the pure methane and the Groningen gas (chosen as reference gas for CNG).
Finally, through a numerical vs. experimental comparison about mass flow-rate, the reliability of the simplified numerical model, and its design usefulness to predict the injector feeding performances with different gases of automotive interest, is highlighted.