The direct injection of liquefied petroleum gas (LPG) in an optical, spark ignition engine
Document TypeMasters Research thesis
Access StatusOpen Access
© 2017 Aditiya Harjon
Given concerns with energy security and the environmental impact of anthropogenic climate change, spark-ignition (SI) engine research is intensely focused on improving fuel efficiency and reducing emissions outputs. The solution requires a synergistic approach that utilises multiple technological innovations, including fuelling strategies (e.g. efficient fuel injection system and engine operation regime) and cleaner, alternative fuels. One promising combination is DI liquefied petroleum gas (LPG); DI and LPG both enable more fuel efficient operation and LPG-fuelled engines produce a lower quantity of harmful emissions than a gasoline equivalent. However, the commercial realisation of DI LPG in an SI engine requires a thorough understanding of the in-cylinder fuel spray behaviour. To this end, an investigation is conducted in a modern, production engine converted for optical access in one cylinder, using propane as a surrogate for LPG. Planar laser Mie-scattering is employed to assess the extent of the liquid phase of the fuel spray over a range of engine operating conditions. These results are compared against those of iso-octane, a common surrogate to approximate gasoline. It was found that DI propane is sensitive to its initial condition in the fuel rail before injection, as well as the in-cylinder pressure at the start of injection. DI propane is also susceptible to severe flash-boiling and spray collapse at all DISI operating conditions. These experimental results are further analysed using a previously developed framework that employs simple thermodynamic and geometric information to predict flash-boiling spray structure in a multi-hole injector. Though this model was validated using spray image data from a quiescent vessel and an experimental injector, it was shown to adequately describe the overall spray structure in the optical engine, which uses a production injector. The overall spray structures predicted by the flash-boiling criterion calculations were consistent with flashing spray structures observed in the engine. Because the time-scales of flash-boiling are significantly faster than those of the flow field in the engine, the formation of flashing fuel sprays is dominated by flash-boiling phenomena, i.e. multi-phase, underexpanded flow, spray collapse due to plume interaction and increased vaporisation rates.
Keywordsdirect injection; spark ignition; LPG; spray studies; mie scattering; optical diagnostics; flash-boiling; thermodynamics
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