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In the present study, Large Eddy Simulations (LES) have been performed with a 3D model of a step nozzle injector, using n-pentane as the injected fluid, a representative of the high-volatility components in gasoline. The influence of fuel temperature and injection pressure were investigated in conditions that shed light on engine cold-start, a phenomenon prevalent in a number of combustion applications, albeit not extensively studied. The test cases provide an impression of the in-nozzle phase change and the near-nozzle spray structure across different cavitation regimes. Results for the 20oC fuel temperature case (supercavitating regime) depict the formation of a continuous cavitation region that extends to the nozzle outlet. Collapse-induced pressure wave dynamics near the outlet cause a transient entrainment of air from the discharge chamber towards the nozzle.

Carbonaceous deposits can accumulate on various surfaces of the internal combustion engine and affect its performance. The porous nature of these deposits means that they act like a “sponge”, adsorbing fuel components and changing both the composition and the amount of fuel in the combustion chamber. Here we use a previously developed and validated model of engine deposits to predict adsorption of normal heptane, isooctane, toluene and their mixtures in deposits of different origin within a port fuel injected spark ignition engine (Combustion Chamber Deposits, or CCDs, and Intake Valve Deposits, or IVDs) and under different conditions. We explore the influence of molecular structure of adsorbing species, composition of the bulk mixture and temperature on the uptake and selectivity behaviour of the deposits. While deposits generally show high capacity toward all three components, we observe that selectivity behaviour is a more subtle and complex property.

There is widespread evidence in the literature that carbonaceous deposits can accumulate on the rear of intake valves and can adversely affect engine performance. For port fuel injected engines, a number of authors have suggested that the porous nature of these intake valve deposits (IVDs) means that they can act like a “sponge”, thereby preventing the correct amount of fuel from entering the combustion chamber during transient operation, especially when the engine is cold. A combination of experimental gas adsorption measurements and computational molecular simulations were used to characterize the porous structure of a sample of IVD. Molecular simulation was then used to predict the equilibrium adsorption of various hydrocarbons, including isooctane, in IVDs. The results support the theory that adsorption of fuel components in IVDs could perturb the mixture preparation.