Experimental and kinetic study of the effects of n-butanol addition on toluene reference fuel auto-ignition

As a renewable bio-alcohol, n-butanol is a promising candidate fuel for the alternative fuels of internal com-bustion engines. In current work, ignition delay times of stoichiometric n-butanol/toluene reference fuel/air mixtures have been measured in a shock tube at different n-butanol blending ratios (0 %, 20 %, 50 %, and 75 % by volume). Experiments were carried out at wide ignition temperatures from 729 to 1518 K and pressures from 1.0 to 20.0 atm. The effects of n-butanol on toluene reference fuel/air auto-ignition were explored, and a pro-moting effect of n-butanol on toluene reference fuel auto-ignition was observed at high temperatures of T > 800 K. However, n-butanol exhibits an inhibiting effect to toluene reference fuel auto-ignition at low temperatures of T < 800 K at 20.0 atm. The addition of n-butanol is able to smooth out the negative temperature coefficient behavior of toluene reference fuel auto-ignition. A reduced n-butanol/toluene reference fuel mechanism with 67 species and 211 reaction steps has been developed. Good agreements between calculations and experiments validate the reliability of mechanism. The sensitivity analysis shows that NC4H9OH + HO2 = C4H8OH-1 + H2O2 and H2O2(+M) = 2OH(+M) are dominant chain propagating reactions, which accelerate auto-ignition of n- butanol/ toluene reference fuel/air at high temperatures. The inhibiting reaction C4H8OH-1O2 = CO + C2H6 + CH2O + OH plays a crucial factor at low temperatures.

Automated summary

In this study, the effects of n-butanol on the auto-ignition of toluene reference fuel have been investigated. It was found that n-butanol promotes the auto-ignition of toluene at high temperatures, but inhibits it at low temperatures. A reliable mechanism for n-butanol/toluene reference fuel has been developed and validated through calculations and experiments. The dominant chain propagating reactions were identified, and an inhibiting reaction at low temperatures was also discovered.