Investigation of the Radical Nitration of Isooctane Fuel via Nitromethane Propellant

The possible radical nitration reactions of isooctane fuel with nitromethane propellant, which is generally used as an additive in fuel formulations, were thermodynamically investigated both at room temperature and at a higher temperature of 691.15 K. The temperature of 691.15 K was chosen because it is the auto-ignition temperature of isooctane and nitromethane and has the potential to mimic better engine conditions. The computational calculations were performed at the theoretical level of DFT UB3LYP/cc-pVDZ. Four different nitration reactions and nitrated products were considered and interpreted in detail. The most and the least favorable nitrations were observed at the primary and secondary carbons of isooctane at 691.15 K, respectively. Four of the designated reactions were endothermic at this temperature. The other outcome of this study was that there was a direct relationship between the thermodynamic tendencies of the considered reactions and the ballistic performances (detonation velocities, detonation pressures, and specific impulses) of their nitrated products. The thermodynamic properties of heats of combustion and deflagration temperatures were calculated via empirical formulations based on the stoichiometry and some other structural parameters of the energetic materials. The results for nitromethane and the nitroisooctane products were examined.