Kevin P. McDonnell, Shane M. Ward & Paul B. McNulty
University College Dublin, Dept of Agricultural & Food Engineering, Earlsfort Terrace. Dublin 2, Ireland.
ABSTRACT
The renewed interest in environmentally compatible fuels has led to the choice of rapeseed oil as the main alternative to diesel fuel in Europe. The objective of this research was to produce and test an economic and high-quality non-esterified rapeseed oil suitable for use as a diesel fuel extender. This was achieved by acidified hot water degumming combined with filtration to five microns. This rapeseed oil, designated as a Semi Refined Oil (SRO), has a high viscosity in comparison with diesel. Hence SRO fuel can only be used as a diesel fuel extender, with inclusion rates of up to 25 %.
SRO proved to be a suitable diesel fuel extender, at inclusion rates up to 25 %, when used with direct injection combustion systems (viz. tractor type engines). Power output (at 540 rev/min at the power take off shaft) was reduced by c. 0.06% for every 1% increase in SRO inclusion rate, and brake specific fuel consumption (BSFC) increased by c. 0.14% per 1% increase in SRO inclusion rate. These values are in accordance with the lower energy density of rapeseed oil fuels compared with diesel. Chemical and viscosity analysis of engine lubrication oil (after c. 170 hours per fuel tested), including metal contamination as an indicator of engine wear occurring, showed that there was no measurable effect on engine lubricating oil due to SRO inclusion in diesel oil. When SRO was used to fuel IDI engines (viz. light duty commercial vehicles), power was considerably reduced mainly due to inadequate air/fuel mixing.
KEYWORDS
Biodiesel, SRO, Injector Fouling, Engine Tests
INTRODUCTION
In 1900 at the Paris Exposition, Dr. Rudolf Diesel ran a prototype of his engine on groundnut oil. In 1911 he was quoted as saying: "The diesel engine can be fed with vegetable oils and would help considerably in the development of agriculture of the countries which will use it". From the very beginning, the diesel engine concept has been associated with vegetable oils.
Methods and materials
The objective of this research was to produce an economic and high-quality non-esterified rapeseed oil suitable for use as a diesel fuel extender. This was achieved by acidified hot water degumming combined with filtration to five microns. The resultant degummed and filtered oil had a gum content of 0.13% (w/w) compared with 1.4% for unfiltered degummed rapeseed oil. This rapeseed oil, designated as a Semi Refined Oil (SRO), has a high viscosity in comparison with diesel (589 mPa.s v. 22 mPa.s at -12 °C). Tests on fuel pumping systems have shown that, in order to support adequate fuel flow and atomisation, the maximum acceptable viscosity for a fuel is c. 55 mPa.s at -12 °C.
Results and Conclusion
In conclusion, Semi Refined Rapeseed Oil (SRO) proved to be a suitable diesel fuel extender, at inclusion rates up to 25 %, when used with direct injection combustion systems. The only practical difference observed in this study is that the injectors require more frequent servicing compared with diesel operation. The technology for producing SRO is relatively simple and hence offers the possibility of small, locally based production units as well as economic mass production units.
References
- Lowery J.P.A. 1990. Alternative fuels for automotive and stationary engines in developing countries. Institution of Mechanical Engineers Seminar, U.K., November 19-20, pp31-35.
- Seddon R.H., 1942. Vegetable oils in commercial vehicles. Gas Oil Power, August, pp 136-146.
- Barsic N.J. & Humke A.L. 1981a. Performance and emission characteristics of a naturally aspirated diesel engine with vegetable oil fuels. Society of Automotive Engineers 810262 pp95-109.