Experimental investigation of n-Heptane ring fires with varying shape characteristics under sub-atmospheric pressures

ABSTRACT

The influences of shape characteristics and pressure on n-Heptane ring fire were investigated through two groups of experiments. In group A, the ring fire with varying shape characteristics was conducted. In group B, the ring fire was performed under sub-atmospheric pressures including 45 kPa, 60 kPa, 75 kPa, and 90 kPa. The results show that the mass loss rate is determined by combined results of air entrainment and heat dissipation effect. The flame structure is divided into merged flame and separated flame. The axis temperature has no significant difference in growth stage but presents a corresponding relationship in decrease stage.

KEYWORDS:

• n-Heptane
• ring fire
• annular pool
• air entrainment
• mass loss rate

Nomenclature

$C_O$	=	outside circumference (m)
$C_I$	=	inside circumference (m)
${\dot{C}}^{\prime \prime }$	=	outside circumference per unit area (m−1)
$c_p$	=	heat capacity of ambient air (J/kg·K)
$D_O$	=	outside diameter (m)
$D_I$	=	inside diameter (m)
$D_{eq}$	=	equivalent diameter (m)
$d$	=	projection length of oblique flame (m)
$g$	=	gravity acceleration (m/s2)
$h_{ac}$	=	actual flame height (m)
$h_v$	=	vertical flame height (m)
$M$	=	molecular mass of n-heptane (g/mol)
${\dot{m}}^{\prime \prime }$	=	mass loss rate of n-heptane(g/m2·s)
$p$	=	environmental pressure (kPa)
${\dot{Q}}^{\ast }$	=	dimensionless heat release rate
$R$	=	molar gas constant (J/mol·K)
$S$	=	pool area (m2)
$T_{\mathrm{\infty }}$	=	ambient temperature (K)
$\mathrm{\Delta }{H}_c$	=	combustion heat of fuel (kJ/mol)
${\rho }_{\mathrm{\infty }}$	=	density of ambient air (kg/m3)
$\eta$	=	diameter ratio

Additional information

Funding

This work was partially supported by National Key Research & Development (R&D) Plan [Grant No. 2018YFC0809500], the National Natural Science Foundation of China [Grant No. U1633203], and the Fundamental Research Funds for the Central Universities [Grant No. 800015J9].