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International audience; The reduction of particulate emissions is one of the most important challenges facing the development of future gasoline engines. Several studies have demonstrated the impact of fuel chemical composition on the emissions of particulate matter, more particularly, the detrimental effect of high boiling point components such as heavy aromatics. Fuel contamination is likely to become a critical issue as new regulations such as Real Driving Emissions RDE involves the use of market fuel. The objective of this study is to investigate several experimental approaches to detect the presence of Diesel contamination in Gasoline which is likely to alter pollutant emissions. To achieve this, a fuel matrix composed of 12 fuels was built presenting diesel fuel in varying concentrations from 0.1 to 2% v/v. The fuel matrix was characterized using several original techniques developed in this study. These are Near Infrared spectroscopy (NIR) associated to Principal Component Analysis (PCA) and Partial Least Square (PLS) modelling, filtration. Their capacity to identify diesel fuel was compared to standard methods, such as, distillation, washed and unwashed gums, high boiling components by gas chromatography (EN16270 and VDA265). Furthermore, vehicle tests were conducted to evaluate the impact of Diesel contamination on tailpipe particle emissions on Worldwide harmonised Light vehicle Test Procedure WLTP. Vehicle test results suggest a significant impact of Diesel contamination on Particle emissions. A good detection of Diesel fuel (down to 0.5% v/v) is accomplished using filtration, NIR and high boiling components. Filtration and NIR have the added benefit of availability, ease of use and small test duration. This work highlights the critical impact of Diesel fuel contamination on pollutant emissions from future Gasoline engines. It proposes a novel practical approach of measuring Diesel contamination in market gasoline fuels.

Toluene is an important compound in the chemical industry as well as an often chosen simple surrogate compound for aromatic components in transport fuels. As a result, an improved understanding of the liquid phase oxidation of toluene is of interest to both the chemical industry and the transportation sector. In this work, a detailed autoxidation mechanism for the liquid phase oxidation of toluene is developed using an automated mechanism generation tool. The resultant mechanism is significantly improved using quantum chemistry calculations to update the thermodynamic parameters of key species in solution. Comparisons are made between the predicted and experimentally measured induction period and the obtained mechanism. The agreement between both is found to be within 1 order of magnitude. Rate of production analysis and sensitivity analysis are carried out to explain and understand the reactions paths present in the mechanism. The behavior of the mechanism is commented upon qualitatively; however, no qua...

International audience; Modern societies require cleaner and more efficient internal combustion engines. Low-temperature combustion (LTC) has been proved to be a good step toward this goal. This study aims at investigating the promoting effect of a cetane booster additive named 2-ethylhexyl nitrate (EHN) on the reactivity of a low-octane gasoline at LTC-relevant conditions. Rapid compression machine experiments were conducted at 10 bar, from 675 to 960 K for stoichiometric mixtures. The neat fuel was a mixture of toluene and n-heptane whose research octane number is 84. The doping levels of the additive were set at 0.1 and 1% molar basis. At the experimental conditions, it is found that EHN provides a promoting effect on the surrogate reactivity over all the whole temperature range. This effect increases with EHN doping levels. The negative temperature coefficient (NTC) behavior of the surrogate fuel is mitigated by the presence of the additive. The EHN reactivity promoting effect is lowest around 710 K and then increases with temperature. Under some conditions, heat releases are observed during the compression process. The chemical reactivity of the fuel gas mixture during the piston movement has to be considered to get reliable simulations. Kinetic modeling works show a good agreement with experiments. The model of this study reproduces properly the EHN promoting effect over the whole range of investigated temperatures and doping levels. Numerical analyses were conducted. EHN can totally decompose during the compression process resulting in heat releases. EHN is less effective at low Tc (< 800 K) at lean condition than at stoichiometric condition. It is found that the EHN effect links to the OH radical formation and the NO2single bondNO loop. The reactions between NO and n-heptyl peroxy radicals are found to be the main reason for the EHN effect in NTC region of the surrogate fuel oxidation.

International audience; 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.

International audience; Liquid phase stability is a major concern in the transportation and the energy field where fuels, lubricants and additives have to be stable from their production site to their application (engine, combustors). Although alkanes are major constituents of commercial fuels and well-documented solvents, their respective reactivities and selectivities in autoxida-tion are poorly understood. This experimental and modeling study aims at (i) enhancing the current knowledge on alkane autoxidation and (ii) reviewing and correcting the previously established structure reactivity relationships in alkane autox-idation. Experimentally, this study investigates the influence of branching [0-3] and temperature [373-433 K] on the autox-idation of alkanes using four octane isomers: n-octane (C8), 2-methylheptane (MH), 2,5-dimethylhexane (DMH) and the 2,2,4-trimethylpentane(TMP). Induction Period (IP) and qualitative species identification are used to characterize the au-toxidation processes of alkanes. The present study also presents new detailed liquid-phase chemical mechanisms obtained with an automated reaction mechanism generator. Experimental results highlight a non-linear effect of the paraffins branching on IP according to compound structure and similar oxidation products for both normal and branched paraffins. The four iso-octanes mechanisms reproduce fairly well the temperature and the branching effects on IP within a factor of 4 for high temperature range (T>403 K). From rate-of-reaction and sensibility analyses, similarities in alkane autoxidation have been evidenced with notably the key role of peroxy radicals in both normal and branched alkane autoxidation. The origin of the structure-reactivity relations was confirmed from a kinetic point of view with the main role of the hydrogen type on the molecule. Finally, based on experimental results available in literature, an empirical relation involving simple descriptors (number of carbons, type of carbons, temperature) is proposed to estimate alkane stability.

In the present work, the oxidation stability of diesel, rapeseed (RME), and soybean (SME) fatty acid methyl esters (FAME) and a blend of diesel with 10% (v/v) RME (B10–RME) was studied. Fuel samples were aged in the PetroOxy test device from 383 to 423 K at 7 bar. Experiments were conducted in oxygen excess, and the global kinetic constants were determined. The global kinetic constants for diesel, B10–RME, and RME at 383 K were 7.92 × 10–6, 2.78 × 10–5, and 8.87 × 10–5 s–1, respectively. The oxidation products formed at different stages of the oxidation were monitored by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis–differential thermal analysis (TGA–DTA), and gas chromatography/mass spectrometry (GC/MS). The impact of the FAME nature and level of blending on the kinetic rate constant and the oxidation products was investigated. Results show that RME oxidation forms C19 epoxy as the main oxidation product, in addition to a methyl ester FAME derivative and short-chain oxidation...

Because of the recent changes in the formulation and handling of middle-distillate fuels, oxidation stability is becoming an increasingly important issue. However, liquid-phase oxidation kinetics of middle-distillate fuels remains poorly understood. The purpose of this study was to gain an in-depth understanding of the impact of fatty acid methyl ester (FAME) addition on autoxidation kinetics. A detailed kinetic mechanism for the autoxidation of a n-dodecane/methyl oleate (MO) surrogate mixture was generated and validated against original well-controlled accelerated oxidation experiments. Results emphasize the nonlinear oxidation promoting effect of MO on n-dodecane autoxidation. Pathway analyses reveal that HO2 and OH propagation steps as well as the duration of initiation and propagation phases strongly affected sensitivity analysis by MO addition. On the basis of these analyses and the detailed mechanism, an analytical model was derived and validated against experiments on binary surrogate mixtures as ...

The study of fuel oxidation stability is an important issue for the development of future fuels. Diesel and kerosene fuel systems have undergone several technological changes to fulfill environmental and economic requirements. These developments have resulted in increasingly severe operating conditions whose suitability for conventional and alternative fuels needs to be addressed. For example, fatty acid methyl esters (FAMEs) introduced as biodiesel are more prone to oxidation and may lead to deposit formation. Although several methods exist to evaluate fuel stability (induction period, peroxides, acids, and insolubles), no technique allows one to monitor the real-time oxidation mechanism and to measure the formation of oxidation intermediates that may lead to deposit formation. In this article, we developed an advanced oxidation procedure (AOP) based on two existing reactors. This procedure allows the simulation of different oxidation conditions and the monitoring of the oxidation progress by the means of macroscopic parameters, such as total acid number (TAN) and advanced analytical methods like gas chromatography coupled to mass spectrometry (GC-MS) and Fourier Transform Infrared - Attenuated Total Reflection (FTIR-ATR). We successfully applied AOP to gain an in-depth understanding of the oxidation kinetics of a model molecule (methyl oleate) and commercial diesel and biodiesel fuels. These developments represent a key strategy for fuel quality monitoring during logistics and on-board utilization.

The control of deposit precursors formation resulting from the oxidative degradation of alternative fuels relies strongly on the understanding of the underlying chemical pathways. Although C8–C16 n-alkanes are major constituents of commercial fuels and well-documented solvents, their respective reactivities and selectivities in autoxidation are poorly understood. This study experimentally investigates the influence of chain length, temperature (393–433 K), purity, and blending on n-alkanes autoxidation kinetics under concentrated oxygen conditions, using both Induction Period (IP) and speciation analysis. It also numerically constructs new detailed liquid-phase chemical mechanisms for n-C8–C14 obtained with an automated mechanism generator. Macroscopic reactivity descriptors such as IP, combined to microscopic ones, obtained from GC-MS analyses, are herein used to emphasize similarities and discrepancies in n-alkanes autoxidation processes. Experimental results highlight a nonlinear IP evolution with n-al...

International audience; Oxidation and thermal stability (OTS) are key concerns for the development of alternative jet fuels, as they imply complex physical and chemical phenomena such as autoxidation, pyrolysis, cooxidation reactions and transfer-limitation. The OTSof an alternative aviation fuel was characterized using PetroOxy test from 120-160°C and JFTOT test at 325°C. The alternative jet fuel is a Synthetic Paraffinic Keroseneproduced from Hydroprocessed Esters and Fatty Acids (HEFA-SPK). Results showed a high thermal stability of HEFA-SPK. However, a low oxidation stability was also observed. The oxidation stability of8model cyclicmolecules was evaluated. Results allowed to estimate the influence of the molecular structure of cyclic molecules on liquid phase reactivity involving the number and the hydrogenation of the aromatic rings and the number and chain-length of the aromatic alkyl groups.The addition of several alkylbenzenes increased almost linearly the induction period of HEFA-SPK. Tetralin and decalin acted as inhibitors of the radical chain mechanism at low concentration, although having inherently low oxidation stability. Besides offering a better oxidation stability, the addition of specific low fractions of several alkylbenzenes, tetralin and decalin to HEFA-SPK allowed to achieve a good thermal stability as well. These molecules represent good candidates to improve OTS of HEFA-SPK. This work opens the way for the development of future fit-for-purpose formulations of alternative jet fuels with an increased fraction of renewables.

The share of diesel fuel in European transport sector, which currently represents over 50% of total demand, is increasing, requiring massive imports of this product, while at the same time, gasoline fuels are today in surplus. In terms of air pollutant emissions, gasoline and kerosene streams have shown potential in achieving lower emissions in Compression Ignition (CI) engines, particularly nitrogen oxides (NOx) and particulates. A new fuel formulation approach through the use of light fractions within diesel technology could consequently address both questions of energy demand balance and reduction of diesel engines pollution footprint. In this study, a fuel formulation for a Diesel engine is optimized to achieve lower pollutants emissions and higher engine efficiency. The fuel matrix is based on seven refinery streams representative of gasoline (Hydrotreated Straight-Run Gasoline HSRG, Hydrotreated Fluid Catalytic Cracking HFCC and Reformate REF), kerosene (Hydrotreated Straight-Run Kerosene HSRK and Hydrocracked Kerosene HCKK) and diesel cuts (Hydrotreated Straight-Run Diesel HSRD and Hydrocracked Light Diesel HCKLD). A D-Optimal mixture design is applied to build, a 12-run, 7-factor fuel matrix and the fuels are thoroughly optimized on two engine conditions at light and mid-load representative of typical vehicle running conditions. The results show a high sensitivity and a good correlation of the engine efficiency and pollutants emissions with the volumetric contribution of each refinery stream to the fuel composition. The optimum fuel composition varies across the range of engine operating points. At light load for example, the addition of up to 50 vol% of gasoline streams (HSRG and HFCC) to diesel streams demonstrates a good potential to simultaneously reduce NOx and particulate emissions and an overall good engine performance. Reformate, a highly aromatic gasoline stream, did not offer an advantage at any of the tested conditions due to high particulate emissions. The two kerosene streams perform similarly to diesel streams in terms of engine efficiency and pollutants emissions. A compromise fuel, composed of 50 vol% HSRG and 50 vol% HSRD, is proposed that allowed halving NOx and particulate emissions and reducing the fuel consumption by 5 wt% compared to reference diesel HSRD. The optimized fuel represents an alternative for balancing diesel and gasoline demand and for pollutant emissions reduction.