The reduction in IC engine particle emissions requires a detailed knowledge of the physicochemical processes at work during combustion. While fuels have long since been considered as a constant for each engine type, the gradual introduction of biofuels and research conducted in the field of innovative combustion modes have made it necessary to take greater account of the impact of
fuel variability on pollutant formation.
The task is painstaking since fuels are made up of thousands of hydrocarbon compounds and accurately reproducing their behavior is beyond the scope of chemical modeling. Moreover, standard characterization tests (for example, cetane number) are not sufficiently descriptive. In order to understand the relationship between fuel properties and soot formation in a diesel-type combustion scenario, an innovative characterization model was set up by IFPEN’s researchers. The model is hinged around a high-pressure and high-temperature chamber and employs advanced optical measurement techniques with a view to obtaining a simultaneous picture of (figure):
• reaction zones, by chemiluminescencea;
• the quantitative distribution of soot in the flame, via 2D extinctionb measurement.
The use of these techniques demonstrated that fuel composition acted independently on several aspects of combustion, including
the two principal factors influencing soot formation in the flame: equivalence ratio in the pre-mix zone and local chemistry. The impact of different families of hydrocarbonsc was characterized in representative engine operating conditions(1) and this new method could
also be used either to evaluate new fuels or to validate surrogate fuels used in computational simulation tools.
a - Measurement of light emitted by a chemical reaction.
b - Light absorption measurement.
c - Such as long-chain aliphatic alkanes (n-dodecane) or aromatics (n-propylbenzene).
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