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Title: Numerical study of transient in-nozzle fuel flow phenomena and near-nozzle effects during and after the end of injection for Diesel engines
Author: Papadopoulos, N.
ISNI:       0000 0004 7227 6436
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2017
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The design of a Diesel injector is a key factor in achieving higher engine efficiency. The injector's fuel atomisation characteristics are also critical for minimising toxic emissions such as unburnt Hydrocarbons (HC). However, when developing injection systems, the small dimensions of the nozzle render optical experimental investigations very challenging under realistic engine conditions. For the present work, Computational Fluid Dynamics (CFD) was employed and transient, Volume Of Fluid (VOF), multiphase simulations of the flow inside and immediately downstream of a real-size multi-hole nozzle were performed, during and after the injection event with a small air chamber coupled to the injector downstream of the nozzle exit. A Reynolds Averaged Navier-Stokes (RANS) approach was used to account for turbulence. A moving mesh approach was followed for the movement of the needle. Models that can provide an accurate prediction of the liquid-gas interface and also capture the vapour-air mixing were used. Moreover, an evaporation model was developed. The code was validated against experimental data and data from the literature. 9 different injections were simulated for injection pressures equal to 400 bar and 900 bar, ambient pressure that varied from 60 bar to 1 bar and fuel temperature that varied from 300 K to 353 K. A high chamber temperature case and a high nozzle wall temperature case were also investigated. The results showed that the flow during the injection cannot be considered steady state and that hysteresis exists. After the end of injection, the state of the nozzle varied from being filled with liquid to being filled with air. Some form of dribble existed in all the injections while in one of them a late cycle mass expulsion was predicted. The effect of evaporation was found to be very small but it can contribute towards late cycle mass expulsion. In addition, the pressure drop due to the engine cycle could also have a similar effect.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available