Combustion studies of hybrid nanoadditive doped waste cooking oil biodiesel and its blends in compression ignition engine.

Abstract

South Africa, among the developing nations in sub-Saharan Africa lacks technologies for converting crude biooil into biodiesel to run fuel CI engines. The country has also struggled to identify a suitable feedstock that can be used for biodiesel production. This research was therefore aimed at analysing the suitability of mixed waste cooking oil (WCO) biodiesel doped with hybrid nano particles as a viable fuel for diesel engines. The utilization of WCO as feedstock for biodiesel is garnering attention since it does not impact on the food supply chain and provides a solution to the challenges associated with its disposal. Biodiesel acceptance has been hampered by three main issues. These are related to higher production costs linked to feedstock, higher nitrogen dioxide emissions, and a lack of economic evaluation of technologies incorporating different alcohols and catalysts. This research performed investigations to develop solutions to circumvent all these challenges. Regarding high feedstock cost, WCO was identified to present an easily available solution since it is acquired at a low cost and its usage helps to solve the disposal problem. Manufacture, assessment, and engine testing of biodiesel from WCO was conducted to evaluate its viability as a potential feedstock for biodiesel. From the derived results, WCO oil has higher oil yields and excellent fuel properties and therefore is a viable feedstock to create biodiesel. Transesterification, a biodiesel creation measure, was performed utilizing methanol and NaOH or KOH as catalysts. This feedstock showed some favourable engine exhaust emission behaviour, but on engine performance considerable shortfalls were noted when evaluated against fossil diesel (FD) fuels. Lower brake thermal efficiency and higher fuel consumption were noted when the neat fuel blends with fossil diesel were tested in two-cylinder compression ignition engines. Higher NOx emissions were also noted with WCO and its blends when evaluated against FD. Three options are available to dealt with the above problems, namely, engine modification, exhaust after-treatment, and fuel reformulation. Fuel reformulation is the most promising due to its easy implementation and cheaper cost. The researcher’s search for the most relevant solution resulted in identification of hybrid nanoparticles consisting of cerium oxide and aluminium oxide as the most appropriate solutions. WCO biodiesel and its blends were doped with nanoparticles and tested in two-cylinder compression ignition (CI) engines and results compared with those of FD. From the experimental analysis, addition of hybridized nano additives improved BTE by a maximum value of 6.22 % compared to FD fuel when evaluated against load. A maximum decrease in BSFC of 10.20 % was noted with hybrid nano fuel WCO20A50C50 compared to FD fuel. A significant reduction in NOX of 25.62 % was found compared to FD. CO, unburnt hydrocarbons (UBHC) and smoke opacity were reduced by 36.8 %, 27.8 % and 17.68 % respectively compared to FD. WCO20A50C50 produced the most superior characteristics of all the fuels tested in this research. To understand the combined impact of hybrid nanoparticles and other engine conditions on performance and emissions, design of experiments (DOE) using the response surface method (RSM) was performed to model and optimize WCO20 performance and emissions parameters. This was accomplished by utilizing a variable compression engine and selecting three variables, namely, hybrid nanoparticle blends (fuel blend), compression ratio (CR) and load as input parameters, while the analyzed responses were brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), nitrogen oxides (NOX), unburnt hydrocarbons (UBHC), carbon monoxide (CO) and smoke. The outcomes from this investigation showed that RSM is a viable technique for improvement of the parameters of biodiesel blends doped with nanoparticles in diesel engines. Considering the intricacy of biodiesel production measures, process development, technical assessment, and advancement of biodiesel according to the entire chain, is fundamental for improving its performance and increasing its global adoption. A detailed biodiesel process flow design was developed and economic assessment incorporating material performed. The designed plant is expected to produce 16.88 tons per annum. The cost of biodiesel was evaluated based on researched cost variables and plant data which resulted in a biodiesel production cost of ZAR10.10 per kg giving a total production cost of ZAR10,100.00 (US$673.33) per ton. A CaO ethanolysis catalysed process was shown to be the most appropriate process for WCO production – the reaction was faster and produced a high yield. South Africa, among the developing nations in sub-Saharan Africa, has a huge capacity to produce its own renewable fuels but at present there is an absence of localized and effective applicable techniques for converting crude bio-oil into biodiesel to run fuel CI engines. Therefore, the discoveries of the present doctoral study are important because they demonstrate that it is viable to convert WCO to biodiesel and that its properties can be enhanced with the addition of nano particles, thereby demonstrating that its performance is even better than that of FD. Furthermore, a more sustainable CaO catalysed ethanolysis, with superior yields and locally produced in comparison to methanolysis, has been effectively developed and evaluated, as per the objectives of the thesis.