Shukla, Jaimin; (2021) Characterisation of Spray Development with Hydrous and Anhydrous Ethanol for Direct-Injection Spark-Ignition Engines. Doctoral thesis (Ph.D), UCL (University College London).

Abstract

The aim of this study was to understand spray break up behaviour of hydrous ethanol as a fuel for direct injection spark ignition engines. The motivation of using hydrous ethanol is mainly associated with the removal of the expensive distillation and dehydration processes required to produce anhydrous ethanol, that is commonly used in engines as a renewable additive to gasoline in varying percentages across the world. Anhydrous (E100) and hydrous ethanol used in the form of blends including E96W4 (96% ethanol and 4% water by volume), E94W6 (6% water), E90W10 (10% water), E85W15D (15% water) were sprayed by 6-hole injectors inside an optical injection chamber using 150 bar fuel pressure. Iso-Octane was also used as a reference fuel. The fuel temperature was measured at -15 °C, -10 °C, -5 °C, 20 °C, 50 °C, 90 °C and 110 °C at 1.0 bar and 0.5 bar gas pressures to simulate early homogeneous injection strategies for part-load and wide open throttle engine operation at fully warm and ultra-cold engine conditions. Shadowgraphy and side illuminated Mie scattering spray imaging techniques were used. Phase Doppler Anemometry (PDA) was also used to characterize droplet sizing and velocities. It was found that the increase in water content to ethanol in the range of fuel temperatures between 20-90 °C reduced plume tip penetration in ascending order of water content with E85W15D having the shortest penetration. All forms of anhydrous and hydrous ethanol displayed signs of plume merging and spray collapse at 110 °C, 0.5 bar due to flash boiling effects. In general, E96W4 the fuel closest to the azeotropic point, displayed larger outer spray envelope cone angles across all conditions. To study atomization in the absence of plume to plume interactions, high speed spray imaging techniques were used on an isolated single plume of the multihole injector, along with PDA measurements 25 mm downstream of the nozzle hole. At ambient conditions the differences between fuels were minimal but at 110 °C, 0.5 bar, there was an increase in the single plume’s cone angle with the increase in water content. Iso-Octane consistently exhibited smaller Sauter Mean Diameter (SMD) droplet sizes than the alcohols. For all fuels, increasing the temperature and reducing the pressure decreased SMD values from levels close to 18 µm down to about 10 µm, with E96W4 showing the largest difference between temperatures. Increasing the temperature and reducing the pressure showed an inverse trend of faster mean droplet velocities. At cold conditions, the increase of water content led to narrowing of the plume and reduction in penetration. An increase in SMD was observed for all fuels as the temperature was reduced, with the highest SMD values in excess of 20 µm for E90W10 at -15 °C. For comparison, pure water injection was associated with an SMD of a similar value at 20 °C. This highlights that, in general, hydrous forms of ethanol up to 15% of water level studied here, are not overly detrimental to the atomization process. Future work in optical engines can highlight combustion characteristics to consider these fuels for widespread use.

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