Abstract
An experimental study was carried out on a large stationary compression ignition engine to evaluate the long-term compatibility and durability issues associated with the use of crude palm oil as fuel. Two different preheating temperatures (60 and 80 °C) were adopted to assess the potential improvements related to lower fuel viscosity. The results obtained, in terms of in-cylinder carbon deposits and engine wear, were compared with the results obtained using ordinary diesel fuel. For each fuel and preheating temperature, the engine was operated for 300 consecutive h, during which several engine lubricant samples were collected and analysed to determine soot and fuel contaminations, viscosity alterations, and the presence of different wear-related metals (measured by atomic absorption spectroscopy). At the end of each 300 h endurance test, the carbon deposits were scraped from engine cylinders and examined through thermogravimetric analysis (TGA). It was found that the use of crude palm oil caused a remarkable increment of in-cylinder deposits formation compared with ordinary diesel. The lubricant analysis also revealed a faster viscosity degradation and consequent stronger engine wear, above all with the lower preheating temperature. The results obtained confirmed that continuous engine operation (i.e., without a complete lubricant change) should be carefully reduced when fuelling with crude palm oil. Moreover, the findings obtained herein confirmed the favourable impacts of fuel preheating at 80 °C compared to 60 °C, i.e., reduced carbon deposits by 27% and extended engine operation time by 30%.
Highlights
The fluctuating price of petroleum-derived fuels and the adoption of more and more severe pollutant emission regulations induced to look at biofuels as a promising alternative to conventional fossil fuels
Addition to that, engine lubricants act as heat transfer agents between combustion-heated parts and heat-dissipating system, sealant between pistons and cylinders, and as cleaning agent removing deposits and Incomplete combustion of fuel and thermal cracking of both fuel and lubricant are regarded as the main reason behind the formation of carbon deposits
Considering that the entire lubricant charge was substituted before each fuel test, the considerable carbon deposits increment recorded using CPO60 could be entirely ascribed to the high viscosity of the fuel
Summary
The fluctuating price of petroleum-derived fuels and the adoption of more and more severe pollutant emission regulations induced to look at biofuels as a promising alternative to conventional fossil fuels. Vegetable oils are directly derived from crops through simple mechanical and thermal processes (Sidibé et al, 2010), while biodiesel is obtained by the transesterification reaction, i.e., the reaction of a fat or oil (fresh or recycled) with a short-chain alcohol to form esters and glycerol (Srivastava and Prasad, 2000; Agarwal, 2007; Ong et al, 2011; Sharon et al, 2012a) Both vegetable oils and biodiesel are biodegradable, non-toxic, and essentially free from sulphur (Srivastava and Prasad, 2000; Agarwal, 2007), they constitute a valuable and environmentally friendly substitute to fossil fuels. In order to be successfully employed in the current CI engines, their viscosity (which affects both jet atomization and penetration and strongly influences both combustion process and pollutant formation) and auto-ignition characteristics (represented by cetane number and affects the rate of heat released by combustion) should be as near as possible to those of the ordinary diesel (OD) fuel
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