Biodiesel and blends with petroleum diesel have shown their potential as renewable alternative fuels for engines, with additional benefits of low particulate matter and low sulfate emissions. In this paper we measure the soot volume fraction produced by three different methyl esters processed biodiesels (extracted from palm (PME), soy (SME) and coconut (CME)), and their blends with petroleum diesel, in a series of co-flow stabilized laminar pool flames, using laser induced-incandescence (LII) and laser extinction optical methods. The soot volume fraction measurement results show that all neat biodiesels produce only up to 33% of the total soot volume compared to pure diesel, and that the total soot volume correlates directly with the degree of unsaturation of the biodiesels. Blending leads to approximately linear behaviour of total soot volume, with a shift in slope with smaller sensitivity towards neat diesel.

Biodiesel and blends with petroleum diesel are promising renewable alternative fuels for engines. In the present study, the soot concentration generated from four biodiesels, two pure methyl esters, and their blends with petroleum diesel are measured in a series of fully pre-vapourised co-flow diffusion flames. The experimental measurements are conducted using laser induced-incandescence (LII) and laser extinction optical methods. The results show that the maximum local soot volume fractions of neat biodiesels are 24.4%-41.2% of pure diesel, whereas the mean soot volume fraction of neat biodiesel cases was measured as 11.3%-21.3% of pure diesel. The addition of biodiesel to diesel not only reduces the number of inception particles,

This is in response to the letter written by Chua and Li (1) regarding our article. (2) We would like to highlight that the Norwegian study by Javo and Sørlie (3) included a representative sample of 3,500 women aged 18-35 years. Therefore, unlike what is suggested by Chua and Li, there was a variation in age and maturity among the subjects in the Norwegian study. (3) In a country like Singapore, where education is almost universal among our youths, it is unfortunately impossible to compare two groups of subjects who are similar in age but have vastly different amount of education. In other words, it is inevitable that in studying Singaporean youths, older age would correspond with a higher level of education. However, we agree that future studies could aim to include a larger and more representative sample of youths. In the meantime, the lack of knowledge on cosmetic procedures even in this select group of youths makes our findings more startling.