Turbocharged tractor engines

Turbocharging a tractor engine is certainly a temptation for many producers. However, to obtain the desired effect, one must go beyond simply supercharging air into the combustion system.

Furthermore, many farmers, when purchasing, take into account the engine of agricultural tractors as a reference for comparisons, where the main specifications observed relate to the brand and model of the engine, the number of cylinders, the displaced internal volume (displacement) , suction and torque and power values. These values ​​represent the main characteristics of the engine's performance and are known through dynamometric tests.

The research group at the Agrotechnology Laboratory (Agrotec), linked to the Agricultural Machine Testing Center (Nema) at UFSM, is working on consolidating a broad work proposal, aiming to create a test routine that better characterizes the tractors used in the region. . By carrying out this type of assessment on tractors, it is possible to obtain, for example, the reality encountered when carrying out an agricultural operation.

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In order to increase the power of an aspirated engine, generally below 80 hp, some farmers hire specialized companies that provide air supercharging kits, which can be installed in new or used tractor engines. This practice provides an increase in engine power at a low cost, which results in a good cost-benefit ratio, as these kits serve to introduce a volume of air into the cylinder greater than that corresponding to natural aspiration.

The centrifugal compressor, of the turbocharger type, popularly called turbo, is a system that uses the energy of exhaust gases to move a turbine, installed at the inlet of the engine's air intake system. This turbine sucks in atmospheric air (oxygen) and drives it, under pressure, into the cylinder, thus obtaining greater power for the same displaced internal volume.

According to some researchers, the greater quantity of air allows the diesel engine to function better, and this offers, among others, the advantage of being able to use lower quality fuels to increase engine power, as the greater the air volume admitted, the easier it is to achieve total combustion of the fuel load.

However, to achieve significant gains in engine power, in addition to the increase in air volume, obtained through the addition of the kit, it is also necessary to increase the volume of fuel injected into the combustion chamber. These modifications reduce specific fuel consumption, due to the better stoichiometric ratio (air/fuel mixture), providing an increase in the engine's thermal efficiency.

Due to the need to quantify the effect of adding a turbo on the performance of an agricultural engine, work was developed to determine the values ​​of torque, power and fuel consumption, with different configurations of the air supply system and engine fuel.

DATA COLLECT

The experiment was carried out using a Massey Ferguson tractor, model MF 4275, equipped with a Perkins engine, four-cylinder model 1104A-44, 4,4L displacement volume, natural aspiration with maximum power and torque of 75hp and 275Nm, respectively. under the ISO TR 14396 standard, according to information from the manufacturer. The fuel injection pump that equips the engine is a rotary type mechanical pump, from the Delphi brand.

For the tests, a mobile dynamometric eddy current brake, EGGERS brand, model PT 301 MES, was used. Through this, the torque and maximum power values ​​of the engine were collected. Fuel consumption was measured using an Eggers flowmeter, model FM3-100. For data collection, the with Eggers Power Control, which manages the use of the dynamometer and flowmeter.

Before starting the evaluations, with the objective of reaching the optimal operating temperature, using the dynamometric brake, a load was imposed on the engine for a period of 20 minutes. As the measurements were carried out at the tractor's TDP, and considering that according to the Asae EP496.2 (2003) standard, there are power losses from the engine transmission up to the TDP (10%), this percentage was added to the observed torque and power values. .

Interventions were carried out on the engine to establish the configuration factor of the air and fuel supply system: C1. The engine was evaluated in its original manufacturing configuration; C2. The injection pump was adjusted on a test bench, where the diesel oil load went from 67ml at 800rpm of the injection pump to 74ml (10% increase); C3. An air supercharging kit, from the Master Power brand, model APL 240, with an intake pressure of 1 bar, was installed after the service carried out on the injection pump; C4. With the turbo installed, the original charge of diesel oil injected by the pump was returned.

The average values ​​of the engine performance variables (Table 2) were subjected to statistical analysis to verify the significance of the differences between the four configurations evaluated (C1, C2, C3 and C4), in a completely randomized experimental design, with three replications.

TORQUE RESULTS

The increase in engine torque is directly related to the volume of fuel injected into the combustion chamber. As can be seen in Figure 1a, the highest torque obtained was at 1.200rpm, for the four configurations evaluated.

Furthermore, it is possible to see that the lowest and highest torques, respectively, were obtained in the original engine configuration (295,90Nm) and in the turbo + pump configuration (361,17Nm). In this sense, it is possible to infer that by increasing the diesel oil flow from the injection pump and adding the turbo, there was a 22% increase in the engine's maximum torque.

It is important to highlight that the addition of turbo without increasing the injection pump output volume (C4) does not present a significant gain in torque when compared to the C2 configuration (aspirated + pump). However, when only these two configurations are analyzed, using Figure 1d, specific fuel consumption is lower in configuration C4. That is, with the addition of turbo without increasing the pump output, the engine works economically, and its reaction capacity in the face of a momentary overload will be similar for both configurations (C2 and C4).

POWER RESULTS

For the correct dimensioning of the mechanized set (tractor + implement), it is extremely important to know the type of soil on which the agricultural operations will be carried out, the implement to be pulled and the engine power. In this sense, there is the possibility of obtaining gains in power when using appropriate techniques in mechanical intervention such as: adding a turbo and/or increasing the fuel flow of the injection pump.

However, it can often be observed that in the vast majority of tractors on which turbo kits are installed, there is no adjustment of the injection pump, meaning that the air/fuel mixture (stoichiometric ratio) is not adequate, implying, thus, zero or very small gain in the nominal power of the engine.

When analyzing Figure 1b, it is possible to see that the maximum power was obtained at 2.100 rpm of the engine, for all configurations used. Similar to what was observed for torque, the lowest and highest power occurred in configurations C1 and C3, respectively. Thus, the importance of properly configuring the injection pump after adding the turbo is justified.

It is important to highlight that just the addition of the turbo, without intervention in the injection pump, represents an insignificant gain in power compared to the original engine configuration, resulting in an increase of 5,93%, as a greater volume of air is injected into the combustion chamber. , for the same amount of fuel.

When considering the average values, presented in Table 2, the power gain in relation to the original configuration (66,38 hp), for the C2 configuration represents 1,13 times greater (75,38 hp), for the C3 configuration it is 1,23. 82,08 times greater (4 hp), for the C1,07 configuration, only 70,82 times greater (92,93 hp). Remembering that these are average values, referring to the entire engine speed range evaluated. The maximum power value (2.100 hp at 3 rpm) was obtained for the CXNUMX configuration (turbo + pump).

Fuel consumption

When analyzing Figure 1c, it is clear that with the increase in injection pump output, with or without the addition of the turbo, there is greater fuel consumption, as can be seen in Table 2, since in both configurations ( C2 and C3) hourly consumption was greater than 16L/h. However, for the sake of comparison, the power generated by the engine must be taken into account. Therefore, due to the fact that configurations C2 and C3 present the highest average values ​​of nominal power, 75,38 hp and 82,08 hp, respectively, these higher values ​​of hourly fuel consumption represent better energy conversion, when compared to configurations C1 and C4. .

In short, to evaluate and compare the fuel consumption of an agricultural engine, it is important to take into account the specific consumption (Figure 1d), as it considers the fuel consumption to generate 1 hp per hour. Therefore, as can be seen in Table 2, the lowest specific fuel consumption was obtained in the C3 configuration (turbo + pump), which delivers greater power from the evaluated engine.

Final considerations

It is concluded that the engine's air and fuel supercharging, in relation to the original configuration, provides a significant increase in torque and power. Adding a turbo alone does not have a significant effect on engine performance.

It is important to exercise caution, preferably following each manufacturer's recommendation, to avoid damage to the chassis, tractor transmission components and engine cooling system.

Marcelo Silveira de Farias, José Fernando Schlosser, Alfran Tellechea Martini, Juan Paulo Barbieri, Nema – UFSM

Article published in issue 175 of Cultivar Máquina