Compared with petroleum fuel, liquefied petroleum gas (LPG)
demonstrates advantages in low CO₂ emission. This is because of
propane (C₃H₈), n-butane (n-C₄H₁₀) and i-butane (i-C₄H₁₀), which
are the main components of LPG, making H/C ratio higher. In
addition, LPG is suitable for high efficient operation of a spark
ignition (SI) engine due to its higher research octane number
(RON). Because of these advantages, that is, diversity of energy
source and reduction of CO₂, in the past several years, LPG
vehicles have widely been used as the alternate gasoline vehicles
all over the world. Consequently, it is absolutely essential for
the performance increase in LPG vehicles to comprehend combustion
characteristics of LPG.
In this study, the differences of laminar burning velocity
between C₃H₈, n-C4H10, i-C₄H₁₀ and regular gasoline were evaluated
experimentally with the use of a constant volume combustion chamber
(CVCC). Similar comparisons were numerically conducted with
one-dimensional premixed laminar flame simulation to examine
combustion mechanisms of these fuels. The result showed that C₃H₈
and n-C₄H₁₀, which were the normal paraffin in LPG, had the
characteristics that the laminar burning velocity was faster than
those of gasoline and i-C₄H₁₀. It was also showed that the factor
was increase in O, H, OH and C₂ radicals in the flame zone. This
radical formation mechanism was also analyzed in this study.
Furthermore, the effect of above differences in burning velocity
of SI combustion was investigated with an engine bench test and
two-zone model analysis. In the results, it was showed that burning
velocity of SI combustion was affected by the difference of laminar
burning velocity between fuels. Especially, this effect was
significant under the condition of low engine speed, because SI
combustion in early phase of burning period is under laminar state.
Therefore, burning velocity of SI combustion with LPG which is
containing propane and n-butane is faster than that with
gasoline.