Experimental Characterisation of Fuel Blends

In the quest to mitigate demand for conventional petroleum derived transportation fuels and reduce their associated CO2 emissions, there are an increasing number of alternative fuels being proposed. Blending of such alternatives necessitates a comprehensive understanding of their combustion behaviour for effective and efficient commercial deployment. Therefore, characterisation of such blends fundamental combustion parameters relative to their constituents, under different operational conditions, is of essential importance. Two key parameters are that of laminar burning velocity and ignition delay time. The present work predominately focused on investigations of the former and the theoretical development of a universal predictive laminar burning velocity blending law, suitable for all commercial fuel types and those from chemically dissimilar families, such as methane and hydrogen. Aiding this development, an array of pure fuel/air mixtures and their blends burning velocities were measured by means of a constant volume combustion vessel, at a temperature of 360K, for pressures of 0.1, 0.5 and 1.0 MPa, at equivalence ratios from 0.8 to 1.3. Blends comprised of pure fuels representative of the major chemical families found within Fischer-Tropsch synthetic gasoline, namely, iso-octane, n-heptane, toluene, 1-hexene, and that of promising bio-derived alcohols, namely, ethanol and n-butanol. A proposed laminar burning velocity blending law was evaluated against existing laws, using the measured blend data, and existing data from other researchers, and on average, outperformed all. The acquired data also allowed investigations into linear and nonlinear flame speed/stretch relationships, and correlations between the critical Peclet and Karlovitz numbers with Markstein numbers, as a function of fuel type, pressure and equivalence ratio. Furthermore, during the present work, considerable efforts were made towards commissioning a rapid compression machine, which served to allow the concurrent collection of ignition delay data for the same blends by other researchers. This gave the opportunity for a conjoint investigation into the comparative effects of ethanol and n-butanol addition to a TRF gasoline surrogates burning velocity and ignition delay behaviour.