CFD Modeling of Reacting Diesel Sprays with Primary Reference Fuel

Abstract

Computational fluid dynamics (CFD) modeling has many potentials for the design and calibration of modern and future engine concepts, including facilitating the exploration of operation conditions and casting light on the involved physical and chemical phenomena. As more attention is paid to the matching of different fuel types and combustion strategies, the use of detailed chemistry in characterizing auto-ignition, flame stabilization processes and the formation of pollutant emissions is becoming critical, yet computationally intensive. Therefore, there is much interest in using tabulated approaches to account for detailed chemistry with an affordable computational cost. In the present work, the tabulated flamelet progress variable approach (TFPV), based on flamelet assumptions, was investigated and validated by simulating constant-volume Diesel combustion with primary reference fuels -binary mixtures of n-heptane and iso-octane. Simulations were initially carried out to evaluate and compare the performance of two kinetic models in homogeneous reactors and laminar diffusion flames, followed by turbulent reacting spray simulations considering different fuels, ambient temperatures, and oxygen concentrations. The sensitivity study of the turbulent Schmidt number was then conducted, and results in terms of ignition delay and lift-off length were compared with experimental data to determine a more appropriate global constant. Finally, parametric variations of ambient temperature and oxygen concentration were performed for six fuel blends ranging from PRF0 (n-heptane) to PRF100 (iso-octane), confirming the validity of the TFPV model. FIGURE 15 Comparison between radial mixture fraction distributions at (a) 15 mm, (b) 25 mm, (c) 45 mm from the injector and (d) axial mixture fraction distribution for different Sct values at 1.5 ms ASOI).

Model-Based Calibration and Control of Tailpipe Nitrogen Oxide Emissions in a Light-Duty Diesel Engine and Its Assessment through Model-In-The-Loop

“…Therefore, they are typically adopted to simulate specific engine subsystems, such as the combustion chamber, the intake/exhaust pipes, or the ATS system. An example is provided in [30], in which the authors study a flamelet progress variable approach for simulating a reacting diesel spray using a 3D-CFD methodology. Models based on 1D-CFD are instead capable of providing the fluid-dynamic evolution along one selected direction, and are commonly adopted in codes which are capable of simulating the entire engine, with a reasonable computational time.…”