Behringer, MK; (2014) Effect of Ethanol and Butanol Content in Future Fuel Blends on Spray and Combustion Characteristics in DISI Engines. Doctoral thesis , UCL (University College London).

Abstract

Direct Injection Spark Ignition has become popular within the automotive industry due to the flexibility in injection strategies. This, along with the introduction of novel fuels such as mixtures of ethanol or butanol with gasoline, requires new understanding of the air-fuel mixture preparation and combustion as fuel properties vary greatly. The motored engine flow field of an optical research engine was characterised using Laser Doppler Velocimetry and Particle Image Velocimetry and analysed regarding turbulence properties at the world wide mapping point. The intake flow effect on the spray of a pressure swirl injector was investigated using the base fuels gasoline, isooctane, ethanol and butanol. Furthermore, low percentage splash blended mixtures of 25 % ethanol and 16 % or 25 % butanol with the reference fuels were created and geometrical spray features were obtained from high speed imaging along with the droplet sizes using Phase Doppler Anemometry. Spray investigations were also under taken in a quiescent environment with a more modern spark eroded multi hole injector and its direct replacement featuring a novel Laser drilled nozzle. The results highlight the strong effect of the fuel type, where especially pure butanol showed largest difference to the baseline fuels in terms of shape along with a significant increase of the droplet size. Ethanol also showed an increase in droplet size but only small differences to gasoline’s spray shape at 80 bar or 120 bar fuel pressure into 0.5 bar or 1 bar ambient air at 20 °C, for fuel temperatures of 20 °C or 80 °C. The ethanol mixture was typically more similar to gasoline than the butanol blends. Thermodynamic parameters were derived using incylinder pressure analysis for stoichiometric (λ=1) and lean (λ=1.2). Additionally, high speed chemiluminescence imaging was used at gasoline’s maximum break torque spark timing, calculating flame radii, radius growth, roundness and centroid development. Further analysis was using flame tomography for better insight into the early stages after ignition and the flame front characteristics for the base fuels only. Overall, the analysis showed little difference between gasoline and the blends, but showed changes for the pure alcohols with typically much faster flame progression of ethanol and issues with the combustion of butanol at low engine temperatures. The tomography analysis returned similar flame structures for the pure fuels, what is confirmed by their location in combustion diagrams.

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