The Structure Characteristics of Laminar Premixed Flames of Gasoline-like Fuel Under CI Engine-Relevant Conditions

TL;DR

This study examines how gasoline-like fuel burns under compression ignition engine conditions, focusing on flame structures and chemical reactions.

Contribution

The paper identifies unique combustion behaviors and key chemical reactions in PRF90 flames under CI engine conditions.

Findings

Flame propagation speed depends on unburnt mixture properties and residence time.

Temperature-dependent autoignition chemistry leads to varied combustion behaviors after flame transition.

C0-based flame location better reflects combustion characteristics in stratified mixtures.

Abstract

Gasoline compression ignition characterized by partially
premixed
and long ignition delays typically features complex flame structures
such as deflagration or spontaneous ignition fronts. In this study,
the flame structure and propagation characteristics of PRF90/air mixtures
under compression ignition engine-relevant conditions are investigated
numerically. Similar to other types of fuels, under such conditions,
the propagation speed of PRF90 laminar premixed flames depends not
only on the unburnt mixture properties but also on the residence time,
and the transition of the flame regime depends only on the residence
time. Nevertheless, due to the temperature-dependent autoignition
chemistry of PRF90, flames with excessively high unburnt temperatures
show different combustion behaviors after the transition from deflagration
to autoignition-assisted flames. Sensitivity analysis showed that,
the dominant chain branching reactions in the deflagration mode are
H + O2 = OH + O and CO + OH = CO2 + H, and that
in the autoignition-assisted flames with lower unburnt temperature
are H2O2(+M) = 2OH(+M) and IC8H18 + HO2 = AC8H17 + H2O2, while for higher unburnt temperatures, the
reactions C3H5 + HO2 = C2H3 + CH2O + OH and IC8H18 = IC4H9 + TC4H9 are
more important than the fuel low-temperature oxidation reactions.
In addition, a criterion based on chemical explosive mode analysis
is used to analyze the local combustion mode. The results show that
the difference in diffusion/chemical structure at the crossover progress
variables C0 and crossover temperature allows both C0 and to be used as a flame location for distinguishing
propagation modes in premixed flame. However, the effects of the equivalence
ratio on C0 are different from that on , which means that the selection of C0 and may lead to different discriminant results
for stratified mixtures. Comparing the applicability of C0-based and -based locations in three-dimensional gasoline
compression ignition flame, it is found that the flame location based
on the value of C0 at ϕ = 1.0 can
more completely reflect the flame development characteristics in stratified
premixed combustion.

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