Modeling the tightness of the valve closing cone of diesel engine fuel injectors when operating on highly concentrated mixtures of diesel fuel with rapeseed oil

Abstract

The relevance is due to the strategic necessity of substituting petroleum fuels with renewable bio-components in diesel engines, which requires revised methods for calculating the tightness of precision fuel injection components at high rapeseed oil concentrations. The aim of the study is the development and experimental verification of a theoretical model of the tightness of the valve closing cone of diesel fuel injectors at rapeseed oil content of 40–100%. The methodology integrates the Reynolds equation to describe hydrodynamic pressure in a tapered conical clearance and the Young-Laplace equation to account for capillary sealing forces. Physicochemical properties of mixtures are described using the Grunberg-Nissan model (viscosity), the additivity of reciprocal specific volumes (density), linear mixing (surface tension), and the Vogel, API, Brock-Bird temperature dependencies. Experimental verification was performed on three production FD-22.455.1112010-50 injectors at 20±2°C with high-frequency strain-gauge transducers recording dynamic pressure parameters. The results showed that within the verified 40–60% range, the tightness coefficient increases by a factor of 2.5–4.1 relative to baseline diesel fuel, while the relative modelling error does not exceed 0.5%. At concentrations below 40%, deviations of experimental data from calculated values were observed, due to increased elastic deformations and the manifestation of non-Newtonian rheological effects. The scientific novelty lies in the delineation of concentration zones of applicability of hydrodynamic lubrication theory for high-viscosity mixtures. Practical significance lies in the possibility of predicting tightness parameters of the valve closing cone without conducting a full set of costly bench tests, as well as in the justified selection of spray tip geometry to compensate for excessive viscosity loads when transitioning to high-concentration fuel mixtures, ensuring a reduction in the carbon footprint without compromising engine reliability.