A Case Study for Evaluation of GUTD on Soil Compaction and Tractor Performance

Machinery traffic on farm and forest caused to problems in environment and economics by Fossil fuel consumption and soil compaction. According to result of investigation, The GUTD (Gear Up and Throttle Down) method was recommended to decrease fuel consumption. But the wide range of machinery applications, soil conditions and experience of drivers or operators need to have index for ensuring the GUTD method is carried out properly. The purpose of this study was evaluation of GUTD method using MF 399 tractor on instantaneous fuel consumption and soil compaction. The tractor was equipped by sensors, a designed electronic circuit and a computer to measure and record parameters such as fuel consumption, forward speed and wheel slip. This field examination was carried out on tilled land with clay-loam soil and then data were analyzed in a randomized complete block design with three replications. Considered factors were included four speed levels (1.6, 3.2, 6.4, 12.8 km·h), three levels of gear (first, second and third) and two levels of wheel drive (2WD and 4WD). Parameters of cone index and bulk density were used to determine soil compaction.Variations in compaction of before and after tractor passage were calculated in each plot. Statistical analysis in each speed showed that factor of gear in variations of soil compaction was significant at all speeds except 12.8 km·h and instantaneous fuel consumption was reduced by GUTD at each of constant speed except the mentioned speed. This research showed that instantaneous fuel consumption can be considered as appropriate index for selecting the best gear and speed in terms of fuel consumption and soil compaction.


Introduction
Agriculture tractors are designed for different conditions in one season farm work.Increasing number of powerful tractors on farm causes to use them sometimes in light works.In cases where operation is required to be less than 75% of total power of tractor (light works), fuel consumption can be considerably reduced by performing GUTD.A number of researchers have studied the GUTD technique as a solution to proportionate load on tractor in field operations to consume fuels more economically.Tewari and Mondal (2011) evaluated GUTD by a digital fuel economizer (DFE) system in laboratory and field experiments conditions and concluded that in laboratory tests fuel consuming decrease from 7.1 to 15.8% in different load conditions.Field experiment with two bottom mould board plough showed maximum 2.6 to 15.8% fuel saving for different depths of operation.Experiments showed that with full load condition scope of DFE is very limited.Lister (1985) performed GUTD on 16 tractors in a limited amount of load which fuel consuming decrease fairly from 9 to 18%.Grogan et al. (1987) developed an instrumented tractor with an on-board microcomputer to measure engine load, engine speed, wheel slip, fuel consumption, draught, and hitch forces.The analysis indicated that farmers could have reduced fuel consumption up to 15-27% by practicing "shift-up, throttle-back"; i.e. by shifting to a higher transmission gear and reducing the engine speed to maintain a nearly constant forward travel speed.Actual fuel consumption dropped in the range of (from) 20 to 11.3%, in controlled field tests.
Whether performing GUTD under any condition results less fuel consumption?With respect to continuous variation in soil, desirable performing of GUTD is difficult.Here there is a need to determine an index to assess the performance.On the other hand there are many older model tractors and even the majority of new models in developing countries, especially Iran that those were not equipped by precision measuring instruments such as slip meter, fuel meter, etc. Moreover majority of them are equipped by manual transmission (gearbox).Generally In this stud investigate compactio

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GUTD Effect on Soil Compaction
Soil compaction was investigated by two parameters, CI and BD.

CI Changes
CI changes were analyzed in four speeds separately.According to ANOVA results, gear effect was significant at the 0.01 level in all speeds except 12.8 km•h -1 .The drive wheel effect was considerable at the 0.01 level, CI changes at 4WD were more than 2WD but this difference decreased by increasing speed.Depth effect was significant in 1.6 km•h -1 and at the 0.05 level while it was at the 0.01 level for other speeds and CI changes in undersurface depth was higher than surface.Comparison test (by Duncan test) between mean of CI changes at three gears in each speed was also performed (Table 4).
Table 3 shows that the effect of GUTD on soil compaction is related to forward travel speed because the variation process in compaction varies in each speed along with increasing such that in speed of 1.6 and 3.2 km•h -1 , soil compaction in third gear is significantly less than first and second gears.But this reduction in 6.4 km•h -1 between third gear and first gear is not significant.Finally, in 12.8 km•h -1 on the contrary, compaction in third gear is more than first.Although it is not considerable but variation process in this speed varies with other ones.
Wheel slip was around 5 to 15% at all of speeds except of in speed of 12.8 km•h -1 at third gear, it reached to more than 20%.In 20% Wheel slip, soil surface remained without changes but soil undersurface was compacted more than twice.High slippage can be a reason for changing in variation process of soil compaction in 12.8 km•h -1 in respect to other speeds.By considering Table 3, in terms of compactness, speed of 6.4 km•h -1 at the third gear was more suitable for drawbar force of the test among the tested speeds.Note.*Average values followed by the same letter and in the same row do not differ by Duncan's test: P < 0.05.

BD
BD was measured in 3 depths and ANOVA of BD variations (after passage than before passage) was done in each speed at three gears (first, second and third).This analysis showed that gear and drive wheel effect at three first speed in 0.01 level and in 12.8 km•h -1 but in 0.05 level were significant.Depth effect in all speeds was significant in 0.01 level, as compaction in second depth (10-20 cm) was more than compaction in first and third depths.
Comparison test (by Duncan test) between mean of BD changes was performed at three gears in each speed (Table 5).The results show that in each constant speed, BD changes for third gear in 0-30 cm depth range was considerably lower than the first and second gear in all speeds except 12.8 km•h -1 .
Regarding to Tables 4 and 5, in terms of compactness, speed of 6.4 km•h -1 at the third gear and 12.8 km•h -1 at the first gear are suitable for drawbar force of the test.Note.*Average values followed by the same letter and in the same row do not differ by Duncan's test: P < 0.05.

GUTD Effect on Instantaneous Fuel Consumption
Instantaneous fuel consumption (IFC) vs. forward gears was illustrated at 24 states (four speeds * three gears * (2WD/4WD)) by Figures 8 and 9, where each solid line in figures shows constant speed at three gears (carry out GUTD method).As it can be seen in the figures two points are worth attention.

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There are two consumption zones: first zone is in 3 first speeds, IFC is in 0.3 to 0.4 liter per minute (L•min -1 ) and second zone is in 12.8 km•h -1 that increase to 0.46-0.53L•min -1 (40 percent more than first zone).

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In three first speeds, when gear up, IFC decreases but in speed of 12.8 km•h -1 there is not decreasing process.
IFC has the sharp rise at 12.8 km•h -1 because some heavy implements, such as a single axle trailer, can exert excessive force on the drawbar.Force increases considerably with speed or on irregular terrain.So the force was exerted by the trailer to the tractor was more than producing tractor power therefor IFC was reaction to unfit exerted force.Tractor engine was lugging (black smoke existed from exhaust) in 12.8 km•h -1 at third gear (tractor gear: 12) while began to run but it was in normal position for the rest of the experiment.

GUTD Effect on Fuel Consumption in 1000 Meters
To better understand the fuel saving, IFC converted to fuel consumption (FC) for 1000 meters direct distance (Figure 10).
Figure 10 shows that GUTD method in 1.6 km•h -1 causes to save nearly 3 liters per 1000 meters (in 2WD more than 3 L and in 4WD less than 3 L), in 3.2 km•h -1 : FC reduction is about 1.5 L and in 6.4 km•h -1 it decreases around 0.4 L, but in 12.8 km•h -1 , FC was increased more than 0.2 L.
As it can be seen in Figure 10, effect on FC by GUTD method is related to travel speed, other hand its effect reduce by increasing forward speed.Therefore the result of prior studies was confirmed (full load condition scope of DFE is very limited (Tewari & Mondal, 2011) Finally based on soil compaction and instantaneous fuel consumption (IFC), speed of 6.4 km•h -1 at gear 9 was more suitable in respect to other experimental speeds and gears.

Conclusion
According to the results, there was immediate reaction between instantaneous fuel consumption (IFC) and the forces that act on the tractor, therefore IFC is proper index for GUTD method performance and choice of suitable forward speed operation.
IFC can be applied to an alarm system programing by two ways: Use of normal zone of IFC: the range of IFC was determined for different agricultural operations on the various soil conditions (local conditions) thus skilled drivers perform common operations (Note 1) in condition of optimum perfomance for types of common tractor.An alarm system can be designed on tractor when IFC rises over the determined range, the system alarms to tractor driver.The system configuration is easy and can be programmed for different local conditions (soil and agricultural operations).
Use of the sharp rise of IFC: it can be applied for unknown conditions, thus the forward speed and gear are gradually risen until the sharp rise in IFC will be occurred and the system alarms to tractor driver, therefore forward speed and gear before the sharp rise are chosen as suitable choice.

Figure 8 .
Figure 8. Tractor IFC in determined speeds at different gears in 4WD

Table 3 .
Evaluation and analysis of data was performed with analysis of variance (ANOVA) and Duncan test by SPSS.Matching tractor gears with named gears (first, second, third) in each speed (km•h -1 )

Table 4 .
Comparison test results of CI changes in GUTD method

Table 5 .
Comparison test result of soil BD changes in GUTD method ).Figure10.GUTD effect on Fuel consumption per 1000 meter in determined speeds at 2WD and 4WD