Biodiesel-biodiesel mixtures to upgrade fuel properties and lower exhaust gas emissions

Abstract

Biodiesels are considered as promising alternatives to fossil diesel. Biodiesels produced from various resources can have different fuel properties; hence they do not always comply with the BS EN 14214 standard. This could lead to engine operation and emission challenges. This thesis aims to optimise fuel properties by biodiesel-biodiesel blending in order to improve the fuel properties, combustion and emission characteristics. In this study, biodiesels were produced from different resources such as sheep fat, chicken fat and waste cooking oils; it was found that they do not comply with the BS EN 14214 biodiesel standard. Waste cooking oil-sheep fat biodiesels and cottonseed-chicken fat biodiesels were blended separately at varying proportions and observed that blends of animal fat biodiesels with waste cooking oil or inedible vegetable biodiesels gave promising fuel properties. Waste cooking oil biodiesel-sheep fat biodiesel at 60/40 and 50/50 volume fractions meet the BS EN 14214 standard. Waste cooking oil biodiesel, sheep fat biodiesel and their blends at 60/40, 50/50 and 30/70 ratios were tested in a three cylinder diesel engine and results were compared to fossil diesel. Moreover, effect of degree of unsaturation was also investigated. It was found that decreasing degree of unsaturation resulted in shortened combustion duration, higher heat release at the pre-mix combustion phase, reduced CO and increased NOx emissions. Moreover, 50/50 blend gave the highest in-cylinder pressure around 5% higher than respective neat biodiesels. The 50/50 waste cooking oil biodiesel sheep fat biodiesel blend gave 3.3% lower CO2, 74% lower CO and 2.5% higher NOx than fossil diesel. The engine tests were also conducted using the cottonseed biodiesel, chicken fat biodiesel and their blends at 60/40, 50/50 and 30/70 ratios. Cottonseed biodiesel-chicken fat biodiesel blends at 60/40 and 50/50 ratios gave 4.2% higher in-cylinder pressure than diesel; furthermore, the CO2, CO and NO emissions were reduced by 5.8%, 15% and 6.5% compared to fossil diesel respectively. In order to further improve the emission characteristics of the biomixture fuels, 2-Butoxyethanol was tested as a novel biodiesel additive. Both 50/50 biomixtures doped with the additive (15% by volume) led to further increase in in-cylinder pressure and slight decrease in combustion duration by 5% and 2o CA, respectively when compared to the same without additive. A 5% increase in the brake specific fuel consumption and 2.6% decrease in brake thermal efficiency were observed when additive was used. However, 5% reduction in NO gas emission was achieved. In addition, the biomixtures were tested in a novel SNCR after-treatment design which reduced the NO emissions of the 50/50 biomixtures by 6% with distilled water injection and 15% with urea-water solution injection. The research study concluded that waste cooking oil biodiesel-sheep fat biodiesel and cottonseed biodiesel chicken fat biodiesel blends at 50/50 ratios are recommended for compression ignition engine application.