Ameer Randolph
Diesel fuel consumption in tractors is influenced by various factors, including engine load, engine speed, soil type, and row width. The specific volumetric fuel consumption (SVFC) for diesel engines in tractors typically ranges from 0.0476 to 0.1110 gal/hp-h. The Nebraska Tractor Test Laboratory (NTTL) plays a crucial role in testing tractors and disseminating power and fuel consumption data. Tractor-and-wagon hauling generally requires more fuel per acre than a truck of a similar size. Additionally, certain field operations, such as tilling and plowing, demand more diesel fuel than others. The evolution of tractor fuel types over the decades, from gasoline and kerosene to LP gas and eventually diesel, has shaped the industry. Today, diesel engines are the primary power source for large farm tractors, with ongoing efforts to maximize fuel efficiency.
| Characteristics | Values |
|---|---|
| Factors affecting fuel consumption | Engine load, engine speed (rpm), tractor and soil type, row width, yield, and other factors |
| Specific volumetric fuel consumption (SVFC) range for diesel engines | 0.0476–0.1110 gal/hp-h |
| Specific volumetric fuel efficiency (SVFE) range | 12–21 hp-h/gal |
| Fuel consumption estimation methods | "General" and "specific" equations based on tractor test results |
| Example fuel requirements for field operations (in gallons) | Tilling (subsoiling at 14 inches): 2.10 (diesel) |
| Moldboard plowing (8 inches): 1.85 (diesel) | |
| Chisel plowing (8 inches): 1.25 (diesel) | |
| Offset disking: 0.95 (diesel) | |
| Fuel types used in tractors | Gasoline, diesel, kerosene, LP gas, tractor-fuel/distillate/TVO, Power Fuel |
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What You'll Learn
Factors affecting fuel consumption
Fuel consumption in tractors is a critical aspect of farm management and budgeting. The ability to predict tractor fuel consumption helps farmers estimate costs and manage their machinery systems. While specific volumetric fuel consumption (SVFC) is generally not affected by engine size, several factors influence the fuel efficiency and overall consumption of tractors. Here are the key factors affecting fuel consumption in tractors:
Engine Load and Speed
Engine load and engine speed (rpm) are critical factors in determining fuel consumption. The relationship between engine load and speed plays a significant role, and reducing engine load can lead to lower fuel consumption. Additionally, the governor response power curve, which illustrates the relationship between engine speed and fuel consumption, is essential for understanding fuel usage at different throttle levels.
Power Take-off (PTO) Utilisation and Speed Ratio
The power required at the power takeoff (PTO) affects fuel consumption. The PTO power is calculated from the torque and speed, and it influences the draw-bar power, which is determined by the drawbar pull and forward speed. The speed ratio, or the gear setting, also impacts fuel consumption. Gear settings in terms of the speed ratio (peripheral speed of the rotavator to forward speed of the tractor) can lead to variations in fuel usage.
Soil Type and Row Width
Soil type plays a role in fuel consumption. Different soils have varying draft requirements, which impact fuel usage. For instance, low-draft soils like sands and sandy loams generally require less fuel for primary tillage, planting, and secondary tillage. In contrast, high-draft soils like clay loams and clays demand higher fuel consumption. Additionally, row width for planting affects fuel consumption. Wider row spacing, such as 40-inch rows instead of 30-inch rows, can reduce fuel requirements.
Tractor and Implement Matching
Properly matching the tractor to the implement being used is essential for optimising fuel efficiency. Controlled traffic and navigation aids can help improve field efficiency and reduce unnecessary fuel usage. Additionally, ensuring sufficient machine maintenance can also impact fuel consumption, as well-maintained machinery tends to be more fuel-efficient.
Operating Conditions and Loading
Fuel consumption is influenced by the operating conditions and loading of the tractor. Different field operations have varying fuel requirements, and not all tasks require full power. Optimising travel speed and implementing the GUTD practice (reducing speed based on load level) can lead to significant fuel savings.
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Historical context of tractor fuel types
The history of tractor fuel types is a long and varied one, with the quest for efficiency and sustainability driving innovation in the sector. The first successful American tractor, built by Charles W. Hart and Charles H. Parr, used a two-cylinder gasoline engine. This was in 1903, and the internal combustion engine became the power source of choice for tractors from 1900 onwards.
The Early 20th Century
In the early 20th century, gasoline was the predominant fuel for tractors, with kerosene being a common alternative. Kerosene was widely used in farm tractors within a decade of its introduction. It had a higher thermal value than gasoline and was considered to use less fuel. Its popularity may have been due to its precise requirements for combustion, needing a delicate mixture of air, water, and fuel to burn. However, kerosene's popularity diminished with the onset of World War II, as people needed cheaper gasoline.
World War II
During the war, petroleum-based fuel was scarce in Europe, so tractors were often converted to use a wood gas generator or "gasifier". Gasoline was still used in all-fuel engines, which could also burn kerosene or tractor fuel. Tractor fuel was a low-grade fuel produced between gasoline and diesel in the traditional distillation of crude oil. However, new refining techniques developed during the war made it possible to convert it into more useful fuels, causing it to disappear.
Post-World War II
After World War II, diesel engines began to replace gasoline engines as the primary fuel source for tractors. Diesel fuel was first introduced in large agricultural crawlers in the 1930s, but it wasn't until the 1950s that it became a major fuel source for tractors. Early diesel engines were difficult to start, particularly in cold months, but manufacturers worked to solve this issue with spark ignition and gasoline starters. By the 1960s, diesel engines had greatly improved and were used in almost all farm tractors.
Modern Times
Today, diesel is still a common source of fuel for tractors, especially for full-sized tractors. However, there is a growing trend towards alternative fuel types, such as LPG, propane, and biodiesel, which offer better efficiency and less environmental damage. Prototype battery-powered electric tractors are also being developed.
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Estimating fuel requirements for field operations
Estimating the fuel requirements for field operations is a complex task with many variables. The first step is to determine how much fuel is being used for a particular field operation and compare it to average usage. The worth of a tractor is assessed based on work output and the cost associated with completing the task. Drawbar power is defined by pull (or draft) and travel speed, and an ideal tractor would convert all fuel energy into useful work at the drawbar.
However, due to power losses, not all fuel energy is converted into useful work. To improve efficiency, one could consider:
- Maximizing the fuel efficiency of the engine and the mechanical efficiency of the drivetrain
- Maximizing tractive efficiency of the traction devices
- Selecting an optimum travel speed for a given tractor-implement system
- Properly matching tractor and implement
- Optimizing field efficiency with controlled traffic and navigation aids
- Ensuring sufficient machine maintenance
There are two equations for estimating fuel consumption: a "general" and a "specific" one. The "specific" model tends to provide better estimates. These equations are based on PTO power test results from the Nebraska Tractor Test reports during the mid-1970s. The fuel consumption (gal/h) over varying PTO power tests was averaged, then divided by the rated PTO power. This method assumes that the tractor is operated under the same load pattern for an equal amount of time, so it tends to underestimate fuel consumption.
To estimate fuel requirements for field operations, one can refer to tables that provide fuel consumption values for various field operations. These tables include information on the type of field operation, the fuel type, and the amount of fuel required per acre. For example, chisel plowing with diesel fuel requires 1.25 gallons of diesel per acre. By multiplying the number of acres by the gallons per acre, one can estimate the total fuel requirement for a particular field operation.
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Methods to improve fuel efficiency
The worth of a tractor is assessed based on its work output and the cost associated with completing the task. While an ideal tractor would convert all fuel energy into useful work, due to power losses, this is not the case. To improve fuel efficiency, the following methods can be employed:
Maximise Fuel Efficiency and Mechanical Efficiency
Firstly, it is important to maximise the fuel efficiency of the engine and the mechanical efficiency of the drivetrain. This can be achieved through diligent maintenance, including regular cleaning of radiator screens and replacement of air and fuel filters.
Maximise Tractive Efficiency
The second method is to maximise the tractive efficiency of the traction devices. This can be achieved by ensuring proper ballasting, which determines the amount of slip in any given field condition, influencing fuel consumption and tire wear.
Optimum Travel Speed
Thirdly, selecting the optimum travel speed for a given tractor-implement system is crucial. This involves minimising turning, road travel, and opening gates, as these activities increase fuel consumption and reduce productivity. Efficient travel patterns and the use of cattle guards can help reduce idling time.
Proper Tractor and Implement Matching
Another way to improve fuel efficiency is to ensure proper matching between the tractor and the implement. Controlled traffic and navigation aids can help optimise field efficiency.
Store Fuel Correctly
Storing fuel correctly can also save fuel. Painting above-ground fuel tanks a light colour and keeping them shaded prevents fuel loss through evaporation.
Use Quality Products
Using quality oils, lubricants, and fuel can increase fuel efficiency and extend engine life. For example, Cenex offers engine oils, hydraulic fluids, gear lubricants, and greases specifically designed for tractors and agricultural equipment.
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Fuel costs as a percentage of total machine costs
The worth of a tractor is assessed based on its work output and the cost associated with completing a task. The ideal tractor would convert all fuel energy into useful work, but due to power losses, this is not the case. Fuel costs can be estimated in two ways.
Firstly, fuel consumption can be estimated by filling the tractor's fuel tank before and after a field operation and noting the number of acres covered. The number of gallons used, divided by the number of acres covered, gives the fuel consumption in gallons per acre. This can be compared to average values to determine if fuel usage is reasonable.
Secondly, there are three methods for estimating tractor fuel consumption: "general" and "specific" equations, and the "GUTD" (gear-up, throttle-down) practice. The "general" model uses the relationship between engine load and engine speed (RPM) and data from over 500 tractors to estimate fuel consumption. The "specific" model uses data from one specific tractor and can predict fuel consumption when the tractor is fully or partially loaded with reduced engine speed. The "GUTD" practice involves reducing speed by 20%, which can result in significant fuel savings.
Fuel and lubricant costs typically represent at least 16% to over 45% of total machine costs. Surveys indicate that lubrication costs average about 15% of fuel costs. Repair costs also play a role, with total accumulated repair costs equalling about 25% of a tractor's new list price after 6,000 hours of use. Labor costs are also important to consider, as different-sized machines require different amounts of labor for tasks like planting or harvesting. Actual labor hours usually exceed field machine time by 10-20% due to travel and machine servicing.
Other variable costs, such as repairs, maintenance, lubrication, and labor, are included in the variable costs for a tractor. When estimating future costs for a machine already owned for several years, it is best to use the current market value or salvage value instead of the original purchase price. The total cost per hour for a tractor includes ownership costs, operating costs, and variable costs.
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Frequently asked questions
The diesel fuel consumption for field operations varies depending on the type of operation. For example, diesel fuel consumption for tilling (subsoiling at 14 inches) is 2.10 gallons per acre, whereas diesel fuel consumption for harrowing (spring-tooth) is 0.40 gallons per acre.
Diesel fuel consumption for tractors is calculated using equations that consider factors such as engine load and engine speed (rpm). The Nebraska Tractor Test Laboratory (NTTL) has also developed specific volumetric fuel consumption (SVFC) and specific volumetric fuel efficiency (SVFE) metrics to compare energy efficiencies between tractors with different engine sizes and operating conditions.
Several factors can influence diesel fuel consumption in tractors, including soil type, row width, and tractor-implement matching. Soil type can significantly impact fuel use and power requirements for tillage operations, with low-draft soils requiring less fuel and high-draft soils needing more.
To estimate diesel fuel requirements for a particular farm operation, you can refer to tables and equations provided by sources such as Purdue University's extension service. These resources provide values and calculations for various field operations, allowing you to estimate fuel requirements based on the specific operation and tractor characteristics.
Tractors have used various types of fuel throughout their history. Early tractors used gasoline, kerosene, or tractor vapourising oil (TVO). In the 1950s and 1960s, liquified propane (LP) gas became popular due to its low cost. By the 1970s, diesel engines became the primary fuel source for farm tractors due to their improved performance and efficiency. Today, gasoline is mainly used in lawn tractors or small equipment.
