Studies on the combustion of isolated droplets are crucial for gaining insights into the mechanisms of soot formation and destruction in practical combustion devices involving liquid fuels. The light extinction (LE) method is arguably the most popular technique for quantifying soot in laboratory flames and has been used frequently for investigating droplet flames. Fluctuation in the intensity of the background image is one of the primary sources of uncertainties in measuring soot volume fractions during transient combustion events using the LE technique. In the commonly adopted approach, referred to in this paper as the averaged background image (ABI) method, multiple frames of the background image are acquired prior to combustion, and the mean value of intensity computed from these frames is assumed as the best estimate of the true value of the background signal. In this work, a novel post-processing method, referred to as the extrapolated background image (EBI) method is presented, wherein the best estimate of the true value of background intensity for each pixel at a given time instant is calculated based on the measured value of intensity at a reference point in the image, outside the sooty region. Results are presented for a droplet combustion event, analyzed using the ABI and EBI techniques, for various fuels. As compared to the ABI method, the implementation of the EBI method was found to reduce the root mean square errors (RMSE's) by a factor of approximately three, helping significantly to reduce measurement uncertainties, especially for fuels with low sooting propensities.

对孤立液滴燃烧的研究对于深入了解涉及液体燃料的实际燃烧装置中烟灰形成和破坏机理至关重要。消光（LE）方法可以说是量化实验室火焰中烟灰的最流行技术，并且已广泛用于研究液滴火焰。背景图像强度的波动是使用LE技术测量瞬态燃烧事件期间烟尘体积分数时不确定性的主要来源之一。在通常采用的方法（本文中称为平均背景图像（ABI）方法）中，在燃烧之前先获取背景图像的多个帧，从这些帧计算出的强度平均值被假定为背景信号真值的最佳估计。在这项工作中，提出了一种新颖的后处理方法，称为外推背景图像（EBI）方法，其中，根据测量的值，计算给定时刻每个像素的背景强度真实值的最佳估计值煤烟灰区以外图像中参考点的强度值。给出了液滴燃烧事件的结果，并使用ABI和EBI技术对各种燃料进行了分析。与ABI方法相比，发现采用EBI方法可将均方根误差（RMSE）降低大约三倍，从而有助于显着降低测量不确定度，