The adiabatic laminar burning velocities of a commercial gasoline and of a model fuel (n-heptane, iso-octane, and toluene mixture) of close research octane number have been measured at 358 K. Non-stretched flames were stabilized on a perforated plate burner at 1 atm. The heat flux method was used to determine burning velocities under conditions for which the net heat loss of the flame is zero. Very similar values of flame velocities have been obtained for the commercial gasoline and for the proposed model fuel. The influence of ethanol as an oxygenated additive has been investigated for these two fuels and has been found to be negligible for values up to 15% (vol). Measurements were also performed for ethanol and the three pure components of the model fuel at 298, 358 and 398 K. The results obtained for the studied mixtures, and for pure n-heptane, iso-octane, toluene and ethanol, have been satisfactorily simulated using a detailed kinetic mechanism.

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International audienceThis paper presents an approch for modeling with one single kinetic mechanism the chemistry of the autoignition and combustion processes inside an internal combustion engine, as well as the chemical kinetics governing the post-oxidation of unburned hydrocarbons in engine exhaust gases. Therefore a new kinetic model was developed, valid over a wide range of temperatures including the negative temperature coefficient regime. The model simulates the autoignition and the oxidation of engine surrogate fuels composed of n-heptane, iso-octane and toluene, which are sensitized by the presence of nitric oxides. The new model was obtained from previously published mechanisms for the oxidation of alkanes and toluene where the coupling reactions describing interactions between hydrocarbons and NOx were added. The mechanism was validated against a wide range of experimental data obtained in jet-stirred reactors, rapid compression machines, shock tubes and homogenous charge compression ignition engines. Flow rate and sensitivity analysis were performed in order to explain the low temperature chemical kinetics, especially the impact of NOx on hydrocarbon oxidation

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This paper presents an experimental and numerical study of the impact of various additives on the oxidation of a typical automotive surrogate fuel blend, i.e. n-heptane and toluene. It examines the impact of engine re-cycled exhaust gas compounds on the control of a Homogeneous Charge Compression Ignition (HCCI) engine. A series of experiments were performed in a highly diluted Jet-Stirred Reactor (JSR) at pressures of 1 and 10atm (1atm = 101325Pa). The chosen thermo-chemical conditions were close to those characteristic of the pre-ignition period in an HCCI-engine. The influence of various additives, namely nitric oxide (NO), ethylene (C 2 H 4 ) and methanol (CH 3 OH), on the oxidation of a n-heptane/toluene blend was studied over a wide range of temperatures (550-1100K), including the zone of the Negative Temperature Coefficient (NTC).A new detailed chemical kinetic reaction mechanism is proposed for the oxidation of the surrogate fuel. It includes reactions of NO, methanol (CH 3 OH) and ethylene (C 2 H 4 ) and is used to explain the obtained experimental data. The mechanism is further used to theoretically study the impact of other Exhaust Gas Recirculation (EGR) compounds on the hydrocarbon oxidation, namely ethane (C 2 H 6 ), formaldehyde (HCHO) and carbon monoxide (CO).

The thermal and kinetic impact of the residual species CO, CO 2 , and H 2 O on hydrocarbon (HC) oxidation chemistry was investigated numerically. The case of pure dilution by N 2 was tested against a dilutant composed of CO, CO 2 , and H 2 O in proportions corresponding to internal combustion (IC)-engine Postoxidation conditions (at the end of the expansion stroke and throughout exhaust). The impact of each residual species was tested individually, as well as in combination with others. Attention was given to the thermal impact, kinetic impact and third-body effects of each residual. In the cases of CO 2 and H 2 O, a negative thermal C p -effect in competition with an accelerating kinetic impact due to third-body reactions was observed. The influence of CO on HC-oxidation is restricted to its direct participation in oxidizing reactions, and its thermal impact is negligible compared to N 2 . CO 2 and H 2 O have a negative thermal impact compared to N 2 , resulting from their increased heat capacities. Kinetically, they interact as collision partners with HC-oxidation through H 2 O 2 -dissociation. Generally, it was shown that the composition of a dilutant strongly impacts HC-oxidation and that the presence of CO 2 and mainly H 2 O may lead to an acceleration of HC-oxidation, in spite of their unfavorable thermal properties compared to N 2 .

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