Combustion studies of biodiesel fuel from moringa, jatropha and restaurant oil.

Abstract

Biodiesel is a renewable alternative to finite diesel and, has the capacity to reduce emission and broaden energy access particularly in sub-Saharan Africa where economic growth has been, to some extent, constrained by global warming and a lack of universal access to sustainable source of energy. In the transport sector, a niche exist for biodiesel derived from non-edible feedstock such as waste oil, jatropha and moringa in sub-Saharan Africa. Extraction of oil from jatopha and moringa were achieved via manual as well as soxhlet method using normal hexane, petroleum ether and distilled gasoline. A numerical property prediction scheme was implemented (and validated with experimental data) to obtain the thermo- physical as well as the transport properties of the resulting fuel for the various samples. This prediction scheme reduced the number of experimentation for property determination from nine to one per sample. The pure fuel samples were evaluated in a 3.5kw diesel engine to determine their performance and emissions. The Brake Specific (BS in g/kWh) emissions across the full load spectrum were benchmarked against the United State Environmental Protection Agency (US, EPA) and the European Union (EU) emission caps. This study is a follow-up to an earlier work by Eloka Eboka which focused on the determination of optimal production process for biodiesel using different technique and catalyst. In that work, the engine test was a qualitative evaluation of different mixture ratio forming new hybrids and the engine test protocol did not follow the ISO 8178-4:2006 test cycle categorization nor was the emission benchmarked against the EPA/EU emission caps (both of which were implemented in this study). The extraction results not only confirmed normal hexane solvent and soxhlet method as the optimal means of extraction (with a 37.1% and 51.8% yield for moringa and jatropha respectively) but, gave hint of the potential of distilled Gasoline as a viable solvent (with a 40.2% and 34.1% yield for moringa and jatropha respectively). The validated numerical prediction scheme reduce research cost and time without compromising accuracy. The performance and emission revealed that the Brake specific fuel consumption (BSFC) and brake thermal efficiencies for both diesel and the biodiesels only differ marginally (±4% and ±5 respectively at peak load). Carbon monoxide (CO), unburnt hydrocarbon (UHC) and particulate matter (PM) emissions (in part per million-ppm) showed decreasing trend with load increase and were lower than those of diesel. Oxides of nitrogen (NOX) emission for the biodiesel were lower than those of diesel. The Brake Specific (BS) emission results in comparison to the EU and EPA regulation showed various level of compliance and non-compliance to the emission limits. The result also showed that samples with higher proportion of unsaturated FAME have poorer engine performance and results in higher unwanted emission than saturated FAME. In broad terms, engine retrofitting and novel design could effectively bridge the performance and emission gaps observed between diesel and biodiesel. A multi-blend (saturated and unsaturated FAME) and multi-strategy (Modular kinetic and premix/DI) was recommended as a remediation strategy. For numerical prediction purpose, a 3D CFD with multi zone and detailed chemistryusing KIVA-3V code was proposed.