Semidetailed Kinetic Model for Gasoline Surrogate Fuel Interactions with the Ignition Enhancer 2-Ethylhexyl Nitrate

Abstract

A semidetailed chemical kinetic model has been developed describing the interaction of gasoline surrogate fuels with the ignition enhancer 2-ethylhexyl nitrate (2EHN). The model, which consists of 788 reactions among 157 species, has been checked for validity using ignition delay data obtained in a shock tube for the fuel n-heptane and rapid compression machine for primary and toluene reference fuels. The validation showed that the model can predict the reactivity trends in the measured data including differences observed between different fuels and operating conditions, which is an improvement compared to previous models for this system in the literature. The kinetic model has been used to study the effect of fuel sensitivity on the ignition delay when 2EHN is added to a gasoline surrogate fuel with a constant research octane number of 95. The efficiency of 2EHN is a nonlinear function of temperature that increases with fuel sensitivity and doping level. This is interpreted by results from a kinetic analysis which shows that, as fuel sensitivity increases, key chain branching reactions become more important. At lower temperatures (<740 K), the efficiency of 2EHN decreases with pressure and fuel sensitivities >2. Results from a brute force sensitivity analysis on the kinetics indicate that this can be related to a lower value of the inverse pressure exponent for the ignition delay time with increasing fuel sensitivity. Moreover, the kinetic analysis shows that reactions involving the 3-heptyl radical become inhibitory or less promoting while increasing the fuel sensitivity. The results presented in this work provide important information for development of advanced combustion engines such as homogeneous charge compression ignition (HCCI).

Autoignition Control Using an Additive with Adaptable Chemical Structure. Part 2. Development of a PRF Kinetic Model Including 1,3-Cyclohexadiene Mechanism and Simulations of Ignition Control

“…This could lead to variation in the ignition enhancing capabilities of the additive. To the best of our knowledge, no study has reported such behaviors, but simulations performed by a reviewer of this article, using Andrae’s model, showed that 2-EHN addition into a PRF90 leads to a similar behavior (under the conditions defined in Figure ).…”

“…They also quantify the effect of two additives on the ignition delay of a PRF90: di- tert -butyl-peroxide (DTBP) and 2-ethylhexyl nitrate (EHN). These two additives are well-known ignition enhancers of conventional fuels , because of their ability to generate free radicals at low temperatures, through a relatively easy initial bond fission. These free radicals promote the hydrocarbon reactivity and contribute to decreasing the ignition delay time of the hydrocarbon fuel/air mixtures.…”

The importance of endothermic pyrolysis reactions in the understanding of diesel spray combustion

“…Both the n-C7H16 and n-C16H34 kinetic models are sourced from the POLIMI library [22,23]. A 2-EHN kinetic model has been added to these models to account for the influence of 2-EHN on the chemical kinetics and thermodynamics which control the fuel oxidation, with kinetic and thermodynamic parameters adopted from the work of Andrae [24]. Sub-mechanisms for NOx and low molecular weight alkyl nitrate species are pre-existing in the POLIMI databases.…”

Development and evaluation of a skeletal mechanism for EHN additized gasoline mixtures in large Eddy simulations of HCCI combustion

“…Reaction chemistry simulations of fuels additized with EHN are generally performed with the two-step chemical-kinetic mechanism shown in Figure 1, [18][19][20] and only few more comprehensive models of EHN decomposition can be found in the literature. 21 Hartmann et al 18 experimentally studied the autoignition and combustion characteristics of n-heptane doped with EHN in both a shock tube and burner apparatus.…”

“…They simulated the experiments using the two-reaction model of Figure 1 to model EHN unimolecular thermal decomposition, concluding that the increased reactivity of the fuel was mainly due to the 3-heptyl radical activity. Andrae 19 studied the impact of EHN additive on the autoignition characteristics of multiple gasoline-like surrogates by numerical simulations, in which EHN decomposition was modeled by a single reaction that forms NO 2 , CH 2 O, and 3-heptyl radical. Goldsborough et al 20 utilized a rapid compression machine testing facility to perform experimental studies of two different gasoline surrogates additized with EHN.…”