Investigation of the effect of air supply on the effective engine performance of a machine-tractor unit under unsteady load

The article discusses the effect of air supply (excess air coefficient) on the effective performance of the engine of a machine-tractor unit with an unsteady load. The analysis of the influence of unsteady load on the engine performance of the machine-tractor unit (MTU) is given. Theoretical studies are presented to determine the effective performance of the MTU engine under unsteady load and their comparative analysis with the results of experimental data. This is necessary to verify the adequacy of theoretical dependencies with the results of experimental studies.

They determined the negative impact of the transient load on the performance of the MTU engine.
Among these indicators are [1]: 1. Resistive torque on the shaft of the tractor engine.
where Мrthe resistive torque on the shaft of the tractor engine, Nm; Мfthe resistive torque to rolling the tractor, Nm; Мhthe resistive torque on the hook of the tractor, Nm; Мthe resistive torque when lifting (lowering) the tractor, Nm; МJthe resistive torque from inertia forces during acceleration (braking) of the tractor, Nm; Мfrthe resistive torque from friction, Nm.
2. The degree of unevenness of the resistive torque on the motor shaft. (2) where is the degree of non-uniformity of the resistive torque on the motor shaft; Мrmaxthe largest value of the resistive torque on the motor shaft, Nm; Мrminthe smallest value of the resistive torque on the motor shaft, Nm; Мavthe average value of the resistive torque on the motor shaft, Nm.
3. The period of change of the resistive torque -T, seconds.
4. Overload factor. max max r over where Кoveroverload fractor; Меmaxmaximum torque on the crankshaft of the engine, Nm.
The change in engine torque is described by the formula, [2]: During the implementation of agricultural work, scientists recommend under-loading the MTU engine to 20%, and this causes an increased fuel consumption by 10 ... 15% [6][7][8]. Engine life is being reduced [9,10].
As noted in [9], power losses during harrowing are 6.5%, when towing 7.1%, and when plowing 17.5%. Figure 1.1. presents the results of studies of the distribution of resistive torque to MTU during various agricultural operations [2,3].
The works of A.K. Yuldasheva [2,3] studied the change in the indicator indicators of a tractor diesel engine (vortex chamber) with a fixed rail of the fuel pump at an unsteady load. It was observed that with an increase in the amplitude of fluctuations in the frequency of rotation of the engine shaft, the engine filling factor (v) , the excess air coefficient (),the mixture formation and combustion process deteriorate, and this leads to a decrease in the average indicator pressure (Pi) and indicator efficiency (i), which in turn leads to a decrease in the technical and economic indicators of engines.
The works of V. Antipov [5], A. Yuldashev [2,3], V. M. Arkhangelsky [12] and other scientists [13][14][15][16][17], devoted to the study of the influence of operating modes engines of mobile vehicles in operating conditions for fuel efficiency and performance, indicated the drop in power and fuel consumption increase.
In the works of Gabdrafikov, F.Z. [18] and Abramov M.A. [19] the operation of a high-pressure fuel pump (HPFP) of a diesel engine in dynamic modes was widely considered.

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(5) To obtain the transfer functions that describe the change in the cyclic fuel supply under an unsteady load, the authors note that when the load changes, the speed of the pump shaft changes exponentially on the corrector branch, and the rack position on a periodically damped curve on the regulator branch.
The engine fill factor is affected by a change in air flow. The magnitude of the filling ratio depends on structural, operational factors.
With an increase in angular velocity, a decrease is observed, and with a decrease in an increase in angular velocity, an increase in the filling of cylinders is observed [3,5,9].
The mathematical model of MTU engine performance under an unsteady load along the regulatory branch can be described by differential equations of the second, third and higher ranks.

Materials and methods
The processes occurring in the MTU engine within the linear zones can be described by linear differential equations with constant coefficients. These equations allow us to describe the processes occurring in the MTU engine under operating conditions.
The determination of the coefficients of differential equations in an analytical way is difficult and not always possible. Therefore, it is proposed to apply the method of numerical solution of differential equations to determine the coefficients taking into account the obtained experimental dynamic characteristics, which will greatly simplify the problem.
When solving linear differential equations, the following assumptions are made: The study of the dynamic characteristics of the MTU engine is made with allowance for the linear sections of the load characteristic; The effective performance of the MTU engine is growing with allowance for the requirements of the guests: GOST 18509 "Tractor and combine diesel engines, bench test methods"; International Standard 1585-82 "Road vehicles, engine test methods, net power".
When studying the dynamic characteristics of the MTU enginethe in regulatory branch, second-order linear differential equations are described: where Т1i, Т2i, Т3i,inertial coefficients for the engine speed of the MTU engine, hourly air flow rate, and cyclic fuel supply; n0, Ga0, ,gT0the initial value of the rotational speed of the crankshaft of the MTU engine, hourly air flow and cyclic fuel supply; Кn2, Кg2 , Кa2amplification factors of the MTU engine crankshaft rotation, hourly air flow rate and cyclic supply from a change in engine torque according to the regulatory stationary characteristics; Мсload increment, Nm. When solving differential equations, we take into account that the law of change in the resistive torque should most accurately describe the change in the resistive torque of the MTU, which is brought to the crankshaft of the engine.
To find the values of the coefficients of differential equations, it is necessary to solve it taking into account the results of the obtained experimental data. Differential equations were solved numerically using a computer and a special program.

Fig. 2. Mathematical model of ICE
The effective engine power is determined by the formula.
where BNproportionality coefficient, where rrrolling radius of the driving wheel, m; itrransmission gear ratio; ηtrtractor transmission efficiency; Gtr the weight of the tractor, N; fthe rolling resistance coefficient of the tractor; βthe angle of inclination of the field surface, degrees; КVtractor streamlining coefficient, N • s2 / m4; Ftractor crosssectional area, m 2 ; Vtrtractor speed, m / s; Рh0initial force on the hook of the tractor, N.
Icsggear transmission ratio of the change speed gearbox; i0gear transmission ratio of the rear drive; ifgear transmission ratio of the final drive; Кssoil resistivity, Pa; Аworking width of the agricultural implements, m; ВVdepth of penetration of agricultural implements, m / s; t1the time of deepening of agricultural implements, s. Indicators of the efficiency of the MTU engine are: Hourly fuel consumption, kg / hour.
Hourly air consumption, kg / h.
where Gachange in hourly air flow, Ga=f(t, n,). The excess air coefficient for a diesel engine is determined by the formula. 14.5 The delay time of a change in the parameter perturbation is determined experimentally. Theoretical studies of the performance of the MTU engine led us to the following conclusions: The theoretical dependencies describing the influence of the nature of the unsteady load (taking into account the excess air coefficient) on the changes in the MTU engine are considered. This allows us to determine the coefficients of differential equations, the fuel cycle, the change in the engine speed and hourly air flow rate.
Theoretical principles to modernize the air supply regulation system in MTU engines could be applied. 2. The MTU engine power change occurs more intensively at α = 1.23 than at α = 1.43 by 0.8 s, but at the end of the transition process the power becomes 1.2 kW less compared to the base engine.

Results
3. The torque of the crankshaft of the MTU engine at α = 1.23 increases faster intensively (by 0.7 s) than at α = 1.43.
5. The change in hourly fuel consumption is almost the same, but at the end of the transition process at α = 1.23 it is 0.4 kg / h more than at α = 1.43.
6. The change in the hourly air flow occurs more intensively by 0.7 s at α = 1.43 than at α = 1.23.      When testing the adjustment of the coefficient of excess air corresponded to the parameters of the manufacturer.
Analyzing this graph, we can say that the theoretical and experimental values have good convergence, and the slight deviation in the initial period is explained by the fact that during the theoretical calculations the power spent on rolling the MTU across the field was not taken into account.  The initial values of the hourly air flow rate are somewhat lower during field tests compared to theoretical ones, which is due to the lower initial engine speed, which in turn decreases due to the fact that part of the engine power is spent on rolling the tractor. Fig. 11. Graphs of changes in cyclic fuel supply during load surge Graphs of field and theoretical studies have good convergence. The difference in the initial period is due to not a significant difference in the engine speed of the MTU engine.

Conclusion
Improving the working processes of the MTU engine is associated with the air supply system when working with an unsteady load will reduce engine power loss by 3 ... 4% and reduce specific fuel consumption by 4 ... 5%.
Experimental (field) and theoretical studies have confirmed the adequacy of theoretical calculations with experimental data. Deviation in rotational speed of the crankshaft of the MTU engine is not more than 3%; cyclic fuel supply not more than 3%, hourly air consumption not more than 4%.