An engine-relevant kinetic investigation into the anti-knock effect of organometallics through the example of ferrocene

A detailed study on the ignition of ferrocene-containing mixtures has been undertaken in a Rapid Compression Machine (RCM). Two hydrocarbon fuels, isooctane and 3-hexene, were investigated in order to assess the hypothesis of an inhibiting effect of iron oxide particles on HO2 radicals and H2O2. Ignition delays were measured at core gas temperatures of 700 K and 850 K, pressures from 6 to 20 bar, and ferrocene mole fractions in the original fuel from 0 to 900 ppm. These experiments provide insight into the kinetics of the antiknock effect of ferrocene on both the non-octane sensitive (isooctane) and octane sensitive (3-hexene) fuels. Experimental results show that doping reactive mixtures with ferrocene always lengthens the total ignition delay. Also, the increment in auto-ignition delay is monotonic with increasing amount of ferrocene while no loss of effectiveness was noticed, even at the highest mole fractions. On the other hand, in the event of two stage ignition, the first stage delay is not affected by any doping with ferrocene. The kinetic mode of action of ferrocene is investigated, based on these statements, in an effort to better understand the impact of organometallic octane boosters on the combustion of fuels. A kinetic short sub-mechanism was built in order to describe the influence of ferrocene on the reactivity of isooctane and 3-hexene in a RCM, yielding qualitative agreement. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.