Analysis of rapid compression machine facility effects on the auto-ignition of ethanol

Ignition delay measurements are frequently carried out in Rapid Compression Machines (RCMs), which require a means to prepare mixtures of fuel, oxidizer and diluent gases. In RCMs, the same compressed conditions can be achieved by various combinations of compression ratio, initial temperature, initial pressure, diluent gas composition, etc. Since it has been previously assumed that the value of ignition delay for a given fuel and at a given set of compressed conditions is independent of the choice of initial conditions, there have been limited studies on understanding the effect that these parameters have on low-temperature reactions and the subsequent ignition of the fuel; and any discrepancy in data is attributed to experimental uncertainties and/or facility effects. Therefore, the objective of this work is to determine the effects of different initial conditions on the measured ignition delay. Experiments and simulations were carried out at two compression ratios of 17.1 and 11.7, for stoichiometric mixtures of ethanol and air that consisted of nitrogen and argon as diluent gases. This study also examines the effect of two mixture preparation methods; (1) directly injecting the fuel in the combustion chamber and allowing it to mix before compressing it and (2) using a mixing tank in which the fuel and air is pre-mixed and then supplied to the combustion chamber for compression. With the help of optical images, in addition to the pressure traces, the effects that both of these mixture preparation methods have on the ignition delay characteristics for the above-mentioned conditions are investigated.