Exploring and Modeling the Chemical Effect of a Cetane Booster Additive in a Low-Octane Gasoline Fuel

Abstract

Recent internal combustion (IC) engine developments focus on gasoline fuel. This requires a better understanding of fuel reactivity at different thermodynamic conditions. Gasoline fuel reactivity control by additives is an efficient method to get better IC engine performances. 2-Ethylhexyl nitrate (EHN) promoting effect (0.1-1% mol.) on combustion has been investigated experimentally and numerically. Rapid compression machine (RCM) experiments were carried out at equivalence ratio 0.5 at 10 bar, from 675 to 995 K. The targeted surrogate fuel is a mixture of toluene and n-heptane in order to capture the additive effect on both cool flame and main ignition. A kinetic model was developed from literature data assembly and validated upon a large set of variations including species profiles and ignition delays of pure compounds as well as mixtures. At the experimental conditions, it was found that the EHN reduces the ignition delay time (IDT) of the surrogate fuel in the whole temperature range. EHN effectiveness tends to be minimum around 705 K and increases with temperature. The results also indicate that EHN effect increases nonlinearly with EHN doping levels. Numerical analyses revealed that the EHN effect is linked to NO2-NO loops, which enhances fuel reactivity. The methodology proposed here enable to simulate the EHN effect with simple compounds rather than the full EHN chemistry set. This strategy could simplify the consideration of additive effect when computational fluid dynamics (CFD) simulations are performed on engine. Finally, the study also highlights the EHN effectiveness on several thermodynamic conditions as well as equivalence ratios. The objective is to assess its performance upon large operating conditions which appears to be of interest with novel combustion systems targeting low temperature as well as lean combustion.

Chemical effects of ferrocene and 2-ethylhexyl nitrate on a low-octane gasoline: An experimental and numerical RCM study

“…The measurement uncertainties of in-cylinder pressure, intake pressure, intake temperatures, and mass flow rate are ±1%, ±1 mbar, ±2 K and ±1%, respectively. Further details of the RCM of the University of Orleans can be accessed elsewhere [13,26].…”

“…and n-heptane (35% vol.). The IDT of this surrogate was experimentally measured at 10 bar, from 675 K to near 950 K at Φ of 0.5 and 1 in previous studies [13,14]. This surrogate fuel is designed to observe the additive effect on specific combustion properties such as two-stage ignition and negative temperature coefficient (NTC).…”

“…To investigate the ferrocene additive effect on the surrogate fuel reactivity, a detailed kinetic model was developed in this work. The surrogate fuel sub-mechanism, based on the kinetic model of Lawrence Livermore National Laboratory (LLNL) [28], was fully adopted from a previous work [13].…”

“…The validation of this sub-mechanism was obtained with a large set of experimental data from literature and for several toluene/ n-heptane mixtures [13,14,29,30].…”

“…EHN is a conventional cetane booster. This additive has been investigated in various fuels under different engine-relevant conditions [11][12][13][14]. A recent study 4 on EHN from our group [14] is dedicated on understanding its chemical effect which mostly relies on the chemistry of nitrogen oxides (NO and NO2).…”