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Session 2793

ESTIMATION OF LAMINAR BURNING VELOCITIES BY DIRECT DIGITAL PHOTOGRAPHY

J. Uske and R. Barat* Chemical Engineering Department New Jersey Institute of Technology University Heights Newark, NJ 07102

Abstract

By being a function of both transport (diffusion) and chemical reaction rates, the laminar burning velocity (LBV) of a gaseous fuel/oxidant mixture is a window to the complexities of combustion. Direct photography of the inner cone of a Bunsen flame remains a classical measurement technique for estimating LBVs. The availability and utility of the modern digital camera, together with the ease and power of digital photograph computer processing, greatly facilitate the determination of LBVs, especially for the undergraduate laboratory. In this work, the LBVs of hydrocarbon/air mixtures are estimated using direct digital photography. In addition, selected flames doped with ammonia are studied. The estimated precision of this technique illustrates the need for careful measurements.

Introduction

Undergraduate experiments on flame dynamics are rare since actual temperatures are very high, and rates are very fast. However, the most common flame in the laboratory can now be easily studied thanks to modern digital technology economically available to student laboratories. Consider the Bunsen flame in Figure 1. The inner cone is referred to as the premixed region, while the outer region is the diffusion envelope. In a simple interpretation, the flame is stable on the burner because the cold gas velocity at the flame front matches the speed at which the flame propagates upstream (the burning velocity). In this idealized Bunsen flame configuration, the laminar burning velocity (LBV) can be defined as the component of the cold gas velocity passing normal to the flame front (1) as given by:

Su = u g sin(θ 2) (1)

where Su = laminar burning velocity, u g = mean cold gas laminar velocity (gas volumetric flow rate ÷ tube cross section), and θ = cone apex angle. In real Bunsen flames, curvature at the apex makes Equation 1 problematic. Alternative formulations (2) that avoid curvatures at the cone apex and base are useful, as

Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition, Copyright 2003, American Society for Engineering Education

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Uske, J., & Barat, R. (2003, June), Estimation Of Laminar Burning Velocities By Direct Digital Photography Paper presented at 2003 Annual Conference, Nashville, Tennessee. 10.18260/1-2--12604