Flame regime estimations of gasoline explosion in a tubeby Peili Zhang, Yang Du, Songlin Wu, Jiafeng Xu, Guoqing Li, Peng Xu

Journal of Loss Prevention in the Process Industries

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Text

Accepted Manuscript

Flame regime estimations of gasoline explosion in a tube

Peili Zhang, Yang Du, Songlin Wu, Jiafeng Xu, Guoqing Li, Peng Xu

PII: S0950-4230(15)00011-X

DOI: 10.1016/j.jlp.2015.01.010

Reference: JLPP 2901

To appear in: Journal of Loss Prevention in the Process Industries

Received Date: 13 July 2014

Revised Date: 8 January 2015

Accepted Date: 11 January 2015

Please cite this article as: Zhang, P., Du, Y., Wu, S., Xu, J., Li, G., Xu, P., Flame regime estimations of gasoline explosion in a tube, Journal of Loss Prevention in the Process Industries (2015), doi: 10.1016/ j.jlp.2015.01.010.

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Flame regime estimations of gasoline explosion in a tube

Peili Zhang a,* , Yang Du a,*, Songlin Wu a, Jiafeng Xu a, Guoqing Li a, Peng Xu b a Department of Military Petroleum Supply Engineering, Logistical Engineering University, Chongqing 401311,

China b Department of Architecture & Engineering, Logistics University of CAPF, Tianjin 300309, China

Abstract: Flame regime of gasoline-air mixture explosion is related to chemical reaction, turbulent flow and heat and mass transfer. Experimental data of gas velocity, pressure and flame temperature of gasoline-air mixture explosion in a tube at the equivalence ratio of 0.72, 1.00 and 1.28 were preliminarily acquired. Then, fluctuating velocities, overpressures, and burned and unburned gas temperatures at early stage (50ms), intermediate stage (150ms) and last stage (250ms) in three explosions were determined through the analysis of the experimental data.

Finally, the Damköhler number and Reynolds number of the early, intermediate and late stage were calculated respectively, and the flame regimes for each stage were estimated through the

Damköhler number vs. Reynolds number diagram. Results show that all the flames at early, intermediate and late stage of the three explosions have the same regime of flamelets-in-eddies.

The conclusions can provide some useful references for further study of the flame regime and the numerical analysis model selection of gasoline-air mixture explosion.

Keywords: gasoline-air mixture explosion; flame regime; pressure; laminar flame speed;

Damköhler number

Nomenclature lk kolmogorov microscale, m l0 turbulence integral scale, m δ laminar flame thickness, m

Da Damköhler number, dimensionless

Re Reynolds number, dimensionless  flow characteristic time, s τ  chemical characteristic time, s ν′ gas turbulent fluctuating velocity, m/s S laminar flame speed, m/s ,  laminar flame speed under the reference state, m/s ρ density of the combustion flame, m3/kg µ dynamic viscosity of the combustible gas, kg/m2·s ∅ equivalence ratio, dimensionless vt instantaneous gas velocity at a time of t, m/s v average gas velocity, m/s

Tu unburned gas temperature, K

Tb burned gas temperature, K

P,   pressure (overpressure) and reference pressure, Pa *

Corresponding author. Tel.: +86 15826074096; Fax: +86 86731199.

E-mail address: zpl612323@163.com (P. Zhang), duyang58@163.com (Y. Du).

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ACCEPTED MANUSCRIPT γ temperature index, dimensionless β pressure index, dimensionless

BM, B2, ∅ constants determined by fuel type α thermal diffusivity rate, m2/s 1. Introduction

Flames of gasoline-air mixture explosion in confined space behave as typical premixed turbulent flames whose regime also depends on chemical reactivity, heat and mass transfer.

Generally speaking, different flame combustion regimes lead to different explosion characteristics, such as overpressure, pressure rise rate and flame speed. Turbulence makes the flame front surface wrinkled and twisted (Steinberg & Driscoll, 2009; Steinberg et al., 2009; Zhang et al., 2014), resulting in influences on heat and mass transfer (Shin & Lieuwen, 2012; Wang et al., 2013; Yi et al., 2012), and on the chemical reaction (Nishimura et al., 2013; Zhang et al., 2013; Won et al., 2014; Zhang et al., 2014b; Du et al., 2014). Therefore, identifying the flame regime is of great significance to understand and to model the system.

Study on flame combustion regime is the hotspot and difficulty point in combustible gas combustion and explosion field (Bell et al., 2007; Mansour & Chen, 2008; Mukaiyama et al., 2013;

Yuen & Gülder, 2013; Zhang et al., 2014a). Williams (1986) and Abraham et al. (1985) divided turbulent premixed flame into three modes: wrinkled laminar-flame regime, flamelets-in-eddies regime and distributed-reaction regime, according to a criterion composed of kolmogorov microscale lk, turbulence integral scale l0 and laminar flame thickness δ . In this model,

Damköhler number (Da) and Reynolds number (Re) are firstly calculated, and then the regime of the turbulent flame can be determined by a chart of Da vs. Re, as shown in Fig. 1.

Fig. 1. Regime distribution of the turbulent premixed flame based on values of Da and Re (Williams, 1986)

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In the Fig. 1, region above the thick solid line (lk/δ=1) represents the regime of wrinkled laminar-flame, which meets Williams-Klimov criterion (Williams, 1986), and region below the thick solid line (l0/δ=1) represents the regime of distributed-reaction, which meets the Damköhler criterion (Abraham et al., 1985). The region between these two thick solid lines represents flamelets-in-eddies regime. So the flame regime can be judged by Fig. 1 as long as the Da and

Re are identified.

Da (Abraham et al., 1985) is a dimensionless parameter defined as,