P.B. McNulty

RESULTS OF ENGINE AND VEHICLE TESTING OF SEMIREFINED RAPESEED OIL

The renewed interest in environmentally compatible fuels has led to the choice of rapeseed oil as the main alternative to diesel fuel in Europe. Transesterified rapeseed oil (viz. rape methyl ester) has been the predominant vegetable oil fuel used because its characteristics are quite similar to diesel. However, it is an expensive product due to high feedstock costs. The objective of this research was to produce and test an economic and high quality nonesterified 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 (589 mPa·s vs 22 mPa·s at –12°C). Hence, SRO fuel can be used only as a diesel fuel extender at inclusion rates up to 25%, the resultant blend having a viscosity of 55 mPa·s at –12°C. When used with direct injection (DI) engines, power output (at 540 rpm 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%/1% increase in SRO inclusion rate (viz. a 25% SRO/diesel blend had a 1.5% decrease in power and a 3.5% increase in BSFC compared with diesel). These values are in accordance with the lower energy density of rapeseed oil fuels compared with diesel. Chemical and viscosity analyses of engine lubrication oil using both diesel and a 15% SRO inclusion rate (after c. 170 h/fuel tested), including metal contamination as an indicator of engine wear, showed that there was no measurable effect on engine lubricating oil due to SRO inclusion in diesel oil. However, the injector fouling results showed that shorter injector service intervals are required. In contrast to the DI results, above, when SRO was used to fuel indirect injection (IDI) engines, power was considerably reduced mainly due to inadequate air/fuel mixing. As most agricultural tractors are DI, SRO has a potential as a diesel fuel extender for agricultural equipment.

Repair Costs of 2 and 4 WD Tractors

ABSTRACT FIELD data on the repair costs of both two and four wheel drive tractors is presented. The tractors were used for general purpose forestry work (viz. trailer transportation, hedge trimming, grass mowing and some miscellaneous tasks); and the repair costs obtained were higher than previous literature estimates. For example, after 6 000 h of work, a two wheel drive tractor has an accumulated repair cost equivalent to 70% of the original purchase price, while the nearest estimate from other sources is 46%. In addition, four wheel drive tractors were found to have marginally higher repair costs than two wheel drive tractors - this is in direct contrast to other sources. It was concluded that the inclusion of this data in system cost models would result in a reduction in the recommended tractor replacement age and an increase in overall system costs.

Power and chop length analyses of trailed forage harvesters

Abstract Field data are presented on the total power requirement of trailed forage harvesters. Results indicate that, while fluctuations occur in the PTO (power take-off shaft of the tractor) power requirement of the harvester, the mean value is the best estimate of the actual tractor PTO power required. No appreciable increase in power requirement was observed as chop length decreased from 55 to 10 mm. For example, the PTO nominal specific energy (MJ per t of wet matter) requirements, at crop lengths of 40 and 10 mm, were 6.18 and 5.84, respectively. A mean draught force of 5.13 kN was obtained for the forage harvesting rig Iviz. tractor/harvester/trailer). This was found to be independent of field speed, over the range 3.8–9.1 km/h, and is equivalent to a coefficient of rolling resistance of 0.052.

Weather dependence of forage harvesting operations

Abstract The weather dependence of forage harvesting operations is discussed, and threshold rainfall values are established for field work interruption. A computer program is developed that evaluates the suitability of a given weather sequence for forage harvesting. Results indicate that almost twice the number of forage harvesting days can be expected in the East vs. West coast of Ireland, in the 2nd half of May. This has major implications for the selection of silage mechanisation systems.

Repair Costs and Reliability of Silage Mechanization Systems

ABSTRACT FIELD data was collected on the repair costs of forage harvesters and rotary mowers; and additional data was obtained on the reliability of silage mechanization systems. The results indicate that, in general, the repair costs of forage harvesters are higher than previous estimates. For example, it was found that a double chop forage harvester, with an accumulated use of 1000 ha, has a total repair cost bill of 83% of the capital cost of the machine, compared with the nearest literature estimate of approximately 67%. In addition, results indicate that self-propelled harvesters are more reliable than trailed units, when compared on an accumulated use basis. For example, the total number of breakdown hours, during the first 1000 ha of use, are 250 and 180 for trailed and self-propelled harvesters, respectively.

ACCELERATED INJECTOR FOULING USING RAPESEED OIL/DIESEL BLENDS IN A DIRECT INJECTION ENGINE

Injector fouling was accelerated by reducing the injector needle opening pressure by 20% in a modified Perkins direct injection diesel engine operated at 75% rated speed and 75% of maximum torque. This resulted in a 20 min test (including 5 min idling pre-check) which produced accelerated injector fouling when using Semi-refined Rapeseed Oil (SRO)/diesel blends ranging from zero to 75% SRO inclusion rates. The extent of fouling, which ranged from approximately 40% to 80% blockage of the total orifice area compared with a clean injector, was determined by measuring the reduction in individual orifice diameters using a novel technique based on image analysis. This was achieved by lighting the individual injector orifices (4 orifices per injector; 100-200 µm diameter) from the inside with a light source thus producing a sharp, easily detectable difference between the now illuminated orifices and the darker background of the nozzle. An injector Fouling Index (FI), based on the ratio between the fouled and clean orifice areas, was developed for direct injection diesel engines. A regression model relating FI to SRO inclusion rates was established. This model, where FI = 0.19156 + 2.8879(10–2) SRO – 5.1472(10–4) SRO2 + 3.1008(10–6) SRO3 (R2 = 0.86; SRO = % SRO in the fuel blend), showed that the injector orifice blocking increased with increasing SRO inclusion rates. For example, a 25% (v/v) SRO/diesel oil blend had a Fouling Index of 0.64 compared with 0.38 for diesel fuel only, i.e., the SRO fuelled nozzle was approximately two thirds more blocked (i.e., 0.64/0.38) than when diesel only was used. Preliminary analysis of conventionally fouled direct injection diesel injectors has shown that this 20 min accelerated injector fouling test using diesel fuel is approximately equivalent to 2500 h of conventional engine use also using diesel fuel (R2 = 0.68). Further work is required to substantiate the predicted capabilities of accelerated injector fouling using longer term engine tests.

Cost model of silage mechanization systems

A cost model of silage mechanization systems is constructed, the algorithms of which are based on both field and literature data. Two computer programs, FORSYS and FORCOST, were developed from this model. The program language is BASIC and both are in a format suitable for use on microcomputers. FORSYS determines the optimum machine and labour requirements for a given situation; FORCOST evaluates the total system cost for private ownership, machinery ring membership and contractor hire. The opportunity cost of crop losses, arising from delayed harvest, are included in this analysis, for different enterprise types, viz. beef or dairy (Autumn or Spring-calving) enterprises.