Use of biodiesel

With the increase in population, transport and agriculture, combined with the predictable scarcity of oil and the reduction in gas emissions, the viability of using biodiesel as an alternative source of energy still depends on several factors, among which the proportion mixing biodiesel with diesel and organizing its production chain.

The agricultural tractor's function is to transport, activate and pull machines and implements, being the main source of transformation and supply of energy for the current agricultural production system. For this reason, there is a growing need for studies that can increase yield, reduce the cost per hour worked, minimize environmental impacts, as well as develop alternative fuel for the operation of this machine.

Studies to evaluate the operational performance of engines using biodiesel do not show signs of increased wear, compromised power or reduced durability. Experiments carried out show that the use of mixtures (biodiesel and mineral diesel) up to a limit of 50% does not compromise the tractor's performance. Mixtures above this level can lead to a reduction in engine torque and power.

BIODIESEL X DIESEL MIXES

To evaluate the energy performance of the agricultural tractor, a team of researchers from the Universidade Federal Rural do Semiárido carried out an experiment using mineral diesel (B0) and six proportions of biodiesel/diesel mixtures (B5, B10, B20, B50, B75 and B100) in which the number indicates the volume percentage of biodiesel in the diesel in the scarification operation.

SCARIFICATION OPERATION

To carry out the research, the scarification operation was chosen, which consists of subsurface mobilization of the soil to break compacted layers up to 35cm deep, which requires great traction effort and fuel consumption. The chosen area had been managed in a direct planting system, with a predominantly typical dystrophic red latosol soil, with water content close to field capacity.

The scarifier used was a Jan brand, Jumbo Matic model, trailed, with seven rods spaced 0,40m apart, working width of 2,80m, equipped with cutting discs, de-clogging roller, parabolic rods with narrow tips and lifting system. hydraulic, adjusted to work at a depth of 30cm.

To drive the scarifier, a Massey Ferguson tractor, model MF5285 cab, with auxiliary front-wheel drive (TDA), engine power of 62,5kW (85hp) at 2.200rpm, ISO TR14396 standard, shipping weight of 44,1kN was used. (4.500kgf), with ballast, 18.4-30R1 rear wheels and 12.4-24R1 front wheels. When the tests were carried out, the tractor was at maximum ballast (metallic weights + water in the wheelsets).

MONITORED PARAMETERS AND

ELECTRONIC INSTRUMENTATION

The monitored variables were force requirement on the drawbar in kN, travel speed in km/h, volumetric hourly consumption in L/h, number of rear wheel revolutions, supply fuel temperatures, return in degrees Celsius and engine temperature. engine oil.

Using the monitored data, the slippage of the rear wheels in percentage, the average power required on the drawbar in (kW) and the specific consumption in L/kW/h were calculated.

To monitor the instantaneous force requirement on the drawbar, a load cell was installed between the tractor and the scarifier, leveled horizontally. To monitor hourly fuel consumption, two Oval Corporation – Japan flowmeters, model LSN 40 M-III with 1mL×pulse precision, were used, one installed in the supply line, before the injection pump, and the other in the fuel return line. to the tank. The actual volumetric hourly consumption was calculated by the difference between the volume of fuel that enters the injection pump and the volume that returns to the tank.

Inductive proximity sensors installed on the inside of the rear wheel hubs near the head of the screws that fix the wheel were used to monitor the slipping of the driving wheelsets.

The instantaneous speed was monitored by a Dickey-John radar unit, model DjRVS, with an error of less than 3%. The average displacement speed was determined by calculating the arithmetic mean of all values ​​stored in each experimental plot.

A “Campbell Scientific” computerized data acquisition system, model CR23X, was used to continuously monitor and record, at a frequency of 10Hz, previously defined by programming, the signals generated by the transducers and sensors installed in the motor-mechanized set.

As the objective of the work was to evaluate the energy demand of the tractor depending on the diesel x biodiesel mixtures, we worked under the condition of maximum traction capacity provided by the tractor. In order for the tractor to be able to pull the scarifier at a depth of 30cm, the reduced 1st L gear was used.

TRACTION POWER, SPEED AND SKATING x MIXTURES

The force required by the scarifier on the drawbar showed significant differences, varying from 2.344kgf in treatment B100 to 2.746kgf for B5 (Figure 1), variations occurring due to the non-uniform condition of the soil.

The engine speed was regulated to work at 1.900rpm, this value showed small changes, varying 3,3%, from 1.848 for the B10 to 1.909rpm for the B5. These variations are acceptable depending on the change in load required on the drawbar by the scarifier.

The theoretical travel speed of the tractor depending on the gearshift used (1st L reduced) at 2.200rpm is 2,7km/h. When carrying out the operation, the speed varied from 2,39km/h for the B10 treatment to 2,61km/h for the B100. The speed variations that occurred are justified by the values ​​observed in the slippage of the rear wheels, which varied from 23,4 for the B100 to 35,3% for the B5, this higher value being justified by also presenting the greater force requirement on the brake bar. traction.

The high values ​​for slippage are justified by the load limit imposed on the tractor, since the objective of the work was to evaluate its energy performance in a situation of maximum power demand.

POWER, HOURLY CONSUMPTION AND

SPECIFIC CONSUMPTION x MIXTURES

The power demand on the drawbar varied from 16,5kW for the B10 to 18,1kW for the B5 (Figure 2), variations influenced by the force requirement and travel speed of the assembly.

The lowest and highest hourly fuel consumption were obtained for mixtures B10 and B5, respectively. The highest hourly consumption was observed for B5, which presented the greatest force requirement and the greatest slippage (Figure 1). To evaluate the energy performance of the tractor depending on the mixtures used, the specific consumption variable is more appropriate, as its calculation takes into account the factors force requirement, travel speed and slippage of the driving wheelset, thus representing the amount of energy required to generate 1kW of power in the drawbar. The lowest specific consumption value was obtained for B0, a value justified by the higher calorific value of mineral diesel. For the other mixtures, an increase in specific consumption is observed when compared to B0.

For mixtures B5, B10, B50 and B100, specific consumption showed positive increases with the increase in biodiesel. The B10 and B20 mixtures presented the same value, demonstrating that there was no interference in the power generated with the increase in biodiesel. The lowest specific consumption for the mixtures was verified for B75, demonstrating that this is the most economical among the mixtures used. The use of pure biodiesel (B100) resulted in the highest specific consumption, with an increase of 6,4% and 5% when compared to B0 and B75, respectively.

TEMPERATURES x MIXTURES

An important factor when using high percentages of biodiesel is to evaluate the engine's operating temperature, as this factor may indicate the possibility of contamination of the lubricating oil with biodiesel, causing its dilution and reduced dispersant and detergent capabilities.

As can be seen in Figure 3, the intake air temperature for the tested mixtures ranged from 22ºC to 26,6ºC, while the engine oil temperature remained within standard operating values, below 90ºC.

The exhaust gas temperature ranged from 258ºC to 351ºC, with the highest value being observed for the B5 mixture, which also presented the highest power requirement and hourly fuel consumption.

Figure 1 - Force required on the drawbar (FBT) in kgf, engine rotation (ROT) in rpm, travel speed (VEL) in km/h and rear wheel slip (PAT) in %

Figure 2 - Power required on the drawbar (P_BT) in kW, hourly fuel consumption (Cons. Hor.) in L∙h^-1 and Specific consumption (Special Cons.) in L∙(kW∙h)^-1

Figure 3 - Exhaust gas temperature (Exhaust Temp.), intake air temperature (Adm. Temp.) and engine oil temperature (Engine Temp.) in ºC

This article was published in issue 143 of Cultivar Máquinas magazine. Click here to read the edition.