Impact of Chainsaw Power on Fuel and Oil Consumption

Abstract

This research was carried out in a selection stand of beech and fir, where logging was performed with chainsaws of different powers. Two chainsaws of 3.9 kW were used for work on one area, while on the other one the applied tools were a combination of a smaller and a larger saw (2.5 kW and 3.9 kW). After logging, the consumption of energy products (fuel (gasoline and motor oil mix ratio 50:1) and chainsaw oil) was measured for each individual chainsaw by the method of refueling. It was found that the power of the chainsaw, i.e., the combination of chainsaws of different powers, significantly influences the consumption of energy products in a beech–fir mixed stand. By using a combination of one larger and one smaller chainsaw instead of two larger chainsaws, savings of about 26% for fuel and 24% for oil were achieved. The prediction analysis found that by using two chainsaws (of lower and higher power) instead of two higher power chainsaws (currently common mode of work) in beech stands for an estimated volume of about 1 million m³ year⁻¹, the savings could be about 54,000 L of fuel and about 19,000 L of oil. In monetary value, this is a saving of about EUR 120,000 year⁻¹, i.e., of about 2,500,000 MJ year⁻¹ of energy.

1. Introduction

It is estimated that a volume of about 3.7 billion m³ of timber is felled around the globe annually, of which about 824 million m³ is felled in Europe [1]. In developed countries, a large part of the wood volume is cut by machinery. For example, in Scandinavian countries, machine felling accounts for about 90% of the wood volume (Latvia, Finland and Sweden), in Germany about 50%, Belarus 41%, the Czech Republic 29% and Poland 20% [2]. However, in some countries this percentage is far lower. For example, in Slovakia it is only 5% [2] and in Croatia 3–4% [3], while in less developed countries these values are even lower (e.g., Ukraine 1%, Romania 2%) [2].

According to the research of [4], about 98.5% of the total amount of logged wood in Serbia is cut with chainsaws, while only about 1.5% is logged with a harvester. However, in the period since 2011, several harvesters have been procured in Serbia, so the assumption is that now the ratio is 90:10, in favor of chainsaws. That means that about 4.5 million m³/year of wood volume from state and private forests are cut by chainsaws, which speaks volumes about their high importance.

Although the number of engaged harvesters is on the rise, chainsaws are still dominant. The reasons for their use are a number of advantages over machinery which are, in essence, reflected in lower unit costs. These costs are directly affected by daily operating costs, which include, but are not limited to, the purchase value of the asset (which directly affects depreciation), fuel and oil costs, replacement of spare parts, maintenance costs, etc. In addition, chainsaws are sometimes the only tools for logging and tree felling, as well as for the cutting of assortments in some specific conditions, such as on steep slopes, or in case of a large tree diameter [5,6,7]. The main reasons for the limited use of harvesters are the specifics of natural conditions, different ways of forest management as well as the financial capacity of companies to procure funding for that purpose.

While efficiency has increased through mechanization [8], forest operations are still the major producer of emissions in the wood value chain. In that regard, harvesting is the most critical phase, due to high consumption of fossil fuels [9,10,11,12]. Felling and processing alone require over 1.1 L diesel per m³ of roundwood [13] and when this amount is multiplied by the volume harvested in industrialized countries, consumption soars to over 1 billion liters of diesel per year [11].

Fuel consumption of cut-to-length (CTL) harvesters accounts for 38% of the total 61 fuel used in the technological cycle, which is higher than the amount consumed during 62 forwarding (35%) and transportation (27%) [11]. As with most production systems, logging assumes energy input that is largely provided by fossil fuels, thus contributing to greenhouse gas emissions (GHG) [14,15,16].

Author [17] state that determining the consumption of energy and energy carriers (fuel and oils) for chainsaws is of great importance for work in practice. Several researchers were involved in the research of energy consumption of chainsaws in logging [17,18,19,20,21,22].

However, [23] states that fuel consumption in logging is still not sufficiently researched (unlike in transport) and that the existing measurement technologies are mostly untested, because although several studies have been conducted, more comprehensive research is needed to investigate how to manage forests in a more efficient way while reducing fuel consumption.

The aim of this paper is to determine the consumption of energy products and determine the economic benefit in logging and wood assortment production in a mixed beech and fir stand for different combinations of chainsaws, which primarily differ in power, i.e., to determine which combination of chainsaws is more efficient from the aspect of fuel consumption (two saws of the same power—Husqvarna XP 372—versus two saws of which one has lower and the other one higher power—Husqvarna XP 372 and Husqvarna H 545).

2. Materials and Methods

2.1. Object of Research

Data collection was performed in a hilly mountainous area, in a selection forest of beech (Fagus silvatica L.) and fir (Abies alba Mill.), while the conditions for sample plot 1 (hereinafter: SP1) and for sample plot 2 (SP2) were the same. The ratio of beech to fir was approximately 45:55. Recording of data for the purposes of this paper was performed in the period of winter logging (November–March), at the teaching base Goč of the University of Belgrade, Faculty of Forestry, Serbia.

Characteristics of the sample plots (tree species, average tree volume, average diameter of the felled tree at breast height and the percentage share of roundwood in the total volume) are shown in

Table 1. Basic characteristics of the sample plots.

Sample plot	Altitude (m)	Terrain Slope (%)	Species	Processed Number of Trees	Average Tree Volume (m3 Tree−1)	Average Diameter of Felled Tree at Breast Height (D1,3) (cm)	The Percentage Share of Firewood in the Total Volume (%)
SP1	1150	10−20	Beech	9	6.41	67	9
			Fir	23	4.75	56	15
SP2			Beech	16	5.63	73	17
			Fir	24	3.52	62	10

. The percentage share of firewood in the total volume ranged from 9–17%, but in addition to technical roundwood, long firewood was also produced (their sum value makes a supplement up to 100%).

2.2. Chainsaw Characteristics

In Serbia, in over 90% of cases, trees are logged by chainsaw. In most cases, two workers with chainsaws work together, most often both of them have chainsaws of the same power and size, and they are mostly chainsaws with a power of over 4 kW. A combination of a lower and higher power saw is very rare in practice.

The chainsaws used in this study are Husqvarna XP 372 (3.9 kW) and Husqvarna H 545 (2.5 kW) (Husqvarna, Stockholm, Sweden) with X-Torq^® technology (higher fuel efficiency and lower exhaust emissions compared to conventional engines). As can be seen from

Table 2. Basic technical characteristics of the applied Husqvarna chainsaws.

Technical Characteristics	Husqvarna 372 XP	Husqvarna H 545
Cylinder capacity (cm3)	70.7	50.1
Output power (kW)	3.9	2.5
Recommended guide bar length (cm)	70	50
Chainsaw weight without the cutting assembly (kg)	6.3	4.9
Special characteristic	-	X-Torq® technology

, the Husqvarna 372 XP chainsaw is larger in size and has a higher power than the Husqvarna H 545 chainsaw.

The Husqvarna 372 XP chainsaws were used in SP1 (both saws were the same). They were 3 months old, while the Husqvarna H 545 chainsaw was 1 month old (applied in SP2), along with the Husqvarna 372 XP. New guides and chains were mounted on all saws. Chainsaws used a gasoline and motor oil mix in the ratio 50:1.

2.3. Work Methods

Two workers operated the saws in each sample plot. In SP1, both workers operated the same chainsaws (two chainsaws Husqvarna 372 XP), while in SP2, one worker operated a higher power saw (Husqvarna 372 XP), and the other one operated a lower power saw (Husqvarna H545). Workers were different for both sample plots, but they worked at the same time on both sample plots.

In SP1, both workers took turns in all work operations (felling, bucking, delimbing technical roundwood and firewood processing), while in SP2, the worker with the larger chainsaw performed work operations of tree felling, technical roundwood and firewood bucking, while the worker who operated the smaller saw mainly performed the delimbing of technical roundwood, firewood processing and firewood bucking (which was produced on this surface as long firewood and as a classic one-meter firewood).

2.4. Energy Consumption Measurement

Fuel consumption was measured for each tree individually by the method of energy products refueling the tank. Measuring cylinders of 250 and 500 mL with a 10 mL accuracy of reading, with engraved values of 10 to 250 (for oil) and 500 mL (for fuel), respectively, were used for the refueling of fuel and oil into tanks. The workers would start their workday with full tanks, and then after each felled and cut tree, they would refill the fuel and oils. The amount of refilled fuel or oil represents the amount of fuel or oil consumed for the previously cut tree. The data on fuel and oil consumption were entered in the corresponding manual. The manual also contains data on the tree (tree species and diameter at breast height), as well as data on the processed wood logs (diameter in the middle of length), from which the volume of logs was calculated according to the Huber formula.

$$V = \frac{{D_s}^2·\pi }{4}·L$$

V—volume of log (m³), D_s—diameter in the middle of the log (cm), L—length of log (m).

2.5. Data Analysis

The data were analyzed using descriptive statistics and Student’s t-test to determine differences in mean values. Regression analysis was used to analyze fuel and lubricant consumption by diameter classes. All analyses were performed in Microsoft Excel 2013.

3. Results

3.1. Consumption of Energy

The average consumption of energy products per individual sample plot is shown in Figure 1 and Figure 2. As can be seen, the average consumption of both fuel and oil was higher in SP1, where two saws of higher power were used, compared to SP2, where one saw had higher (3.9 kW) and the other one lower power (2.5 kW).

The t-test established that at the 0.05 level of significance, there are statistically significant differences in fuel consumption between SP1 and SP2 for beech (t = 2.200, df = 11, p = 0.025), as well as for oil consumption (t = 2.178, df = 12, p = 0.020). However, there are no statistically significant differences between SP1 and SP2 for fir in terms of both fuel consumption (t = 2.021, df = 40, p = 0.178) and oil consumption (t = 2.026, df = 37, p = 0.261).

For further analyses, only the consumption of energy products for beech was taken into account, because there are obvious differences, but also due to the fact that beech is the most common species in Serbia.

With the increase in diameter at breast height, fuel and oil consumption logically grows. However, as can be seen from the figure, differences in energy product consumption between SP1 and SP2 make a drastic difference in higher diameter classes (from 67.5 cm upwards), while in lower diameter classes these differences are smaller (Figure 3 and Figure 4). By applying two higher power saws (in SP1) and by applying one higher and one lower power saw (SP2), an obvious difference can be observed. This difference in energy product consumption reaches over 40% in the highest diameter classes (on average about 26% for fuel and 24% for oil).

The increase in the consumption of energy products expressed in mL tree⁻¹ with an increasing diameter at breast height is shown by exponential functions, which are given below.

• SP1—fuel consumption y = 83.03e^0.04x
• SP1—oil consumption y = 23.98e^0.04x
• SP2—fuel consumption y = 192.30e^0.02x
• SP2—oil consumption y = 59.22e^0.03x

where

• y—fuel consumption is expressed in mL tree⁻¹
• x—diameter at breast height (cm).

This is also shown in the figures of the average consumption of energy products expressed in mL m⁻³ (Figure 5 and Figure 6), whose balancing functions are linear, where the consumption of energy products is correlated with the diameter class, i.e., with the increase in diameter class, the average consumption expressed in ml m⁻³ of processed wood decreases.

However, the correlation coefficient in SP2 for fuel and oil (R² = 0.84; R² = 0.78) shows that diameter is affected on fuel and oil consumption. Nevertheless, there is a clear difference in the consumption of energy products in SP1 and SP2, which is shown by dependency functions, where y, fuel consumption, is expressed in ml m⁻³ and x is diameter at breast height (cm).

The functions that show fuel consumption in the individual sample plots are given below:

• SP1—fuel consumption y = −1.36x + 305.77
• SP1—oil consumption y = −0.90x + 155.63
• SP2—fuel consumption y = −1.68x + 252.57
• SP2—oil consumption y = −0.59x + 98.77

where

• y—fuel consumption is expressed in mL m⁻³.
• x—diameter at breast height (cm).

3.2. Economic Benefit

Beech accounts for about 50% of the total felled wood volume in state forests in Serbia [24]. Beech (Fagus sylvatica L.) is the most widespread broadleaf species in Europe and it plays a key role in the European forest sector, covering more than 11 million hectares throughout Europe [25]. Beech is predominantly widespread in mountain conditions. Fuel consumption in the selection stand of beech found in this study is on average 26% higher for fuel and 24% higher for oil in SP1 (two higher power saws) than in SP2 (one higher power saw and one lower power saw). If we make a prediction, according to which all the wood volume from state beech forests in Serbia (estimated at about 1 million m³ year⁻¹) [24] would be cut down by two saws of higher and lower power compared to two saws of higher power (as is normally done), then the annual savings in absolute value would be about EUR 120,000 year⁻¹ (

Table 3. Predictive analysis of energy carriers’ consumption for different combinations of use of chainsaws in beech forests in Serbia.

Combination of Applied Chainsaws	Estimated Wood Volume of High Beech Forests (m3 Year−1) *	Average Fuel Consumption (L m−3)	Average Oil Consumption (L m−3)	Fuel Price by Volume (EUR m−3) **	Price of Oil by Volume (EUR m−3) **	Total Fuel Cost (EUR Year−1)	Total Cost of Oils (EUR Year−1)	Total Cost of Energy Carriers (EUR Year−1)
Two saws Husqvarna 372 XP	1,000,000	0.19	0.08	0.31	0.17	310,000	170,000	480,000
Husqvarna 372 XP and Husqvarna H 545	1,000,000	0.14	0.06	0.23	0.13	230,000	130,000	360,000
Absolute difference		0.05	0.01	0.08	0.04	80,000	40,000	120,000
Percentage difference (%)						26	24	25

* Estimated value based on data from the monofigure “Beech in Serbia” (2005) [24]. ** The value of fuel was EUR 1.57 L⁻¹, while the value of oils was EUR 2.13 L⁻¹.

) (in 2022). Calculated as energy savings, that would be about 54,000 L of fuel and about 19,000 L of oil per year. Especially in times of energy crises, these seemingly small savings would be reflected in the reduction of energy product consumption, i.e., the reduction of dependence on the imports of energy products, but also in the emission of harmful gases. The wood volume from private forests, which is assumed to have approximately the same value, was not included in this analysis.

It should also be noted that the chainsaws that are currently in use mostly have a power of over 4 kW, so the difference in the consumption of energy products is probably even greater.

If the amount of potentially saved energy was recalculated according to [26] as the energy value of fuel, which is 33.75 MJ L⁻¹, this would also mean a lower consumption of energy products in beech stands in the total value of about 2,463,750 MJ year⁻¹. This issue is very important in times of the great worldwide energy crisis. Of course, this would consequently mean a significantly lower emission of harmful gases, to which special attention should be paid.

4. Discussion

Forest mechanization plays an important role in increasing labor productivity and reducing production costs. Chainsaws are the most commonly used tool for tree felling and can have both positive and negative environmental impacts on the forest ecosystem [27].

As already mentioned, in Serbia, trees are logged by chainsaw in over 90% of cases, where two workers with chainsaws work together (a power of saws over 4 kW). Very rarely, combinations of larger and smaller saws are used, assuming that this would lead to savings not only in the initial investment, but also in the consumption of energy products and also in lower emissions of harmful gases, etc., as already shown in the results.

The average fuel consumption for beech was 198 mL m⁻³ in SP1, and in SP2 it was almost 30% lower (0.144 L m⁻³), while the average fuel consumption of fir in SP1 was 153 mL m⁻³ and in SP2 it was 0.136 L m⁻³. The situation is similar for oil consumption—0.082 L m⁻³ and 0.063 L m⁻³ for beech (SP1 and SP2) and 0.066 L m⁻³ and 0.061 L m⁻³ for fir (SP1 and SP2).

When comparing the average fuel consumption expressed in L m⁻³ for beech with the results obtained by [18], it can be noted that it is higher than in the case of fuel consumption in our research for the same organizational form of work (2+0—two workers with chainsaw, without assistant) (0.295 L m⁻³ compared to 0.198 L m⁻³ in SP1 and 0.163 L m⁻³ in SP2). Converted into percentage values, this consumption in [18] is higher by about 32% compared to SP1, or about 44% compared to SP2.

Comparing the data of [21] for a fir and spruce stand, where the chainsaw Husqvarna 372 XP (3.9 kW) was used in the organizational form of work 1+0, and the data of this research, where the same chainsaw was used in the organizational form 2+0, we can conclude that a higher consumption of energy products was achieved in this research (SP1), where the fuel consumption was 0.153 L m⁻³ and the oil consumption reached 0.066 L m⁻³, while in the research of [21] these values were 0.104 L m⁻³ for fuel and 0.023 L m⁻³ for oil. Calculated as a percentage, in terms of fuel consumption, this amount is slightly higher than 30%, while for oil this value is as high as over 60%. However, the factor with the highest impact on fuel consumption, i.e., diameter at breast height, was not taken into account, so these data are only partially comparable. The values obtained by other researchers [17,28,29] are almost completely incomparable with the data of this research study, both due to missing data and the incomparability of the existing data.

The problem with comparing the consumption of energy products in different studies is that the works often do not specify all the conditions (factors) that can have an impact on fuel consumption, as well as the fact that very rarely can comparable data regarding most impact factors be found. For this reason, the data obtained by other researchers can only serve for orientation, and in order to determine the norms, it is necessary to conduct research under specific conditions.

The consumption of energy products increased with an increase in diameter at breast height, i.e., with an increase in diameter class, which is logical. However, for larger diameter classes, the difference in consumption between SP1 and SP2 increases significantly, and in the highest diameter classes it reaches up to 40%. This can be explained by the fact that the worker who operates the lower power chainsaw (SP2) mainly performs the delimbing and firewood processing, thus saving energy. Unlike that, in SP1, these work operations are performed by a worker with a larger chainsaw, which can be considered irrational, since mostly diameters below 20 cm are dealt with in this case. This means that the application of one smaller and one larger saw is particularly significant for trees of large dimensions. The correlation coefficient in SP2 for fuel and oil shows that, in addition to diameter, other factors such as crown size probably influence fuel consumption, which were not taken into account in this study.

The manufacturer’s website (Husqvarna) states that the Husqvarna H 545 chainsaw has a fuel consumption which is reduced by 20%, but it is not specified in relation to which type of chainsaw. Therefore, these studies have shown that this consumption is even lower, but in relation to the Husqvarna 372 XP chainsaw (almost 30% perceived as total average consumption). The Husqvarna H 545 chainsaw has X-Torq^® technology (this technology uses pure air, instead of air mixed with fuel, to flush out exhaust fumes).

When the values from SP2 are compared with the data from SP1, where the data are recorded in the same conditions, it can be concluded that the organizational form of work in which one worker operates a higher power saw and the other operates a lower power saw is more efficient compared to the form of work in which both workers work with larger saws, if beech logging is performed.

The average oil consumption in relation to the fuel consumption in this study, observed by diameter classes, ranged from 0.42 to 0.45 of fuel consumption regardless of the tree species.

Currently, in Serbia, there are norms, which were researched by [20], which can serve as a basis for the orientation on energy product consumption for different tree species. However, in order to achieve any savings, and also to reduce the emission of harmful gases, a more detailed analysis is needed. This can only be achieved by determining the consumption of energy products in a specific situation, their analysis and possible comparisons, in order to improve the process while saving energy, but also by getting an overview of other aspects (efficiency and ergonomics).

Authors [21] state that fuel and oil savings could be achieved primarily by regular inspections of chainsaw working order, proper storage and distribution of energy products, the use of adequate accessories for fuel manipulation, as well as education and stimulation of workers. It is necessary to continue to pay a lot of attention to the rationalization of fuel and oil consumption, as well as to the reduction of their harmful effects on man and the environment (introduction and use of biodegradable fuels and oils).

In this research, it was found that by using the appropriate type of chainsaw, there can be a reduction in the consumption of energy products, and consequently a reduction in the emission of harmful gases. Fuel consumption in the selection beech stand is 27% higher for fuel and 23% for oil in SP1 (two higher power saws) compared to SP2 (one higher power saw and one lower power saw). If the wood volume from state beech forests in Serbia were cut down by two saws (about 1 million m³) of higher and lower power compared to two saws of higher power, then the annual savings in absolute value would be about EUR 122,000 year⁻¹ and about 2.5 million MJ year⁻¹, i.e., about 54,000 L of fuel and about 19,000 L of oil.

Despite the fact that these savings cannot be compared to those stated by [11], which refers to savings in fuel consumption in mechanized logging in the Nordic and Baltic regions alone (potential savings may amount to almost 50 million L diesel year⁻¹), they are still not negligible. This is primarily due to the fact that the global production of roundwood amounts to approximately 3.7 billion m³ year⁻¹ [1], of which over 1 billion originates from industrialized regions such as Europe, North America and Russia [30]. Thus, almost three-quarters of the total wood cut in the world comes from forests from less developed environments, which in a large number of cases are not able to afford cutting machines, so logging is performed with chainsaws and sometimes with hand saws. This fact should further motivate researchers to pay more attention to chainsaws, i.e., their consumption of energy products in other countries.

Although there is a tendency in Serbia to procure new machinery such as harvesters, it is certain that in the coming period logging with chainsaws will still take precedence over harvesters. As already stated, the investment in the supply of chainsaws is several hundred times lower than the investment in the supply of harvesters, and this is the main reason for the relatively small share of the use of harvesters. The consumption of energy products observed per unit of product (m³ of processed wood) is sometimes even more than five times higher for harvesters than for chainsaws.

It is also a fact that there are currently no special regulations in Serbian forestry in which at least recommendations/obligations are made regarding the use of fuels and oils that are environmentally friendly, as well as regarding the type and quality of fuel and oils to be used (except those given in the commercial leaflets and on the website of chainsaw manufacturers). One way to reduce greenhouse gas emissions when using chainsaws is to use biofuels and bio-oil. This is due to the fact that there are no significant changes in the performance of the chainsaw when using mineral and bio-oil [31,32,33], while biofuels and oils have an advantage of rapid degradation in soil and lower ecotoxicity [31]. In addition, as an alternative to the use of petrol saws, electrically powered saws (battery powered) are available. Electric chainsaws are a good alternative to petrol chainsaws for use in small-scale forestry, since their use can be compared to petrol chainsaws in terms of efficiency; they provide a lower level of energy product consumption, as well as lower noise and vibration exposure in the hand–arm area [34,35]. Similarly to the situation in other fields, the results confirmed a positive impact of electrification on man and the environment. The development of electric tools for forestry is expected to intensify with the development of more powerful batteries, which are still considered the biggest bottleneck [35]. However, these saws are still under development and are almost unusable for commercial purposes, especially for larger diameter trees.

5. Conclusions

In this study, it was confirmed that the some of the factors with the highest impact on the consumption of energy products of a chainsaw are diameter at breast height and chainsaw power.

In the selection stand of beech and fir, it was found that lower energy product consumption is achieved with a combination of two chainsaws (one of higher and one of lower power—Husqvarna 372 XP 3.9 kW and Husqvarna H 545 2.5 kW), by on average 26% for fuel and 24% for oil.

If, theoretically, a wood volume of 1 million m³ from Serbian state forests, dominated by beech, were cut down by two saws of higher and lower power compared to two saws of higher power, then the annual savings in absolute value would be about EUR 120,000 year⁻¹, i.e., about 2,500,000 MJ year⁻¹ in terms of energy products.

Potential savings by using two saws (one of lower and one of higher power instead of two higher power saws) in beech stands would be 54,000 L year⁻¹ for fuel and 19,000 L year⁻¹ for oil.

Although there are seemingly small differences in the consumption of energy products (fuel consumption of 0.144 L m⁻³ versus 0.198 L m⁻³), they make a big difference. These values are proportionally higher in countries where the use of chainsaws continues to dominate, which is estimated to be about three-quarters of the total wood cut in the world that comes from the forests of less developed environments. Apart from Northern Europe, Russia, North America and part of Western Europe, the rest of the world is dominated by logging with chainsaws, which speaks in favor of the importance of research studies such as this one and changes that should consequently be put into practice.