The autoignition of Heptamethylnonane at moderate-to-high temperatures and elevated pressures: Shock tube study and improved chemical kinetic model

Abstract

Iso-cetane (2,2,4,4,6,8,8-Heptamethylnonane) is used as a reference fuel to define the cetane number rating of diesel fuel and as an important component for diesel and jet fuel surrogates. This experimental study presented the ignition delay measurement of iso-cetane in a heated shock tube at a temperature range of 838–1617 K, pressures of 10, 15, and 20 bar and over equivalence ratios of Φ = 0.5–2.0 with fuel/air mixture and at Φ = 1.5 with diluted fuel mixture. The experimental conditions were designed to study the effect of pressure, equivalence ratio, and oxygen concentration variation on ignition delay times. The ignition delay time was found to be sensitive to all the investigated factors. The experimental data obtained were in good agreement with both low and high-temperature data reported in the previous studies. The comparison with experimental data of iso-alkanes of various chain lengths showed an impact of chain length on reactivity noticeably at intermediate and low temperatures. The onset of the negative temperature coefficient region is also found to be influenced by an increase in the chain length. The mechanism of Yu et al. was revised by incorporating new rate rules. The kinetic modeling predictions of the updated model showed a noticeable improvement in the mechanism performance except under diluted conditions. The reaction flux and sensitivity analyses were conducted to further discuss the mechanism performance and overall kinetic behavior of the fuel.