Assessment of increased energy efficiency of vehicles with a rational reduction of engine capacity

.


Introduction
The tendency to reduce the capacity of internal combustion engines, which has been observed in recent years in the global automobile industry, is due to the need to improve the environmental conditions and energy efficiency of vehicles. In the paper authors presents the results of the research, which allowed them to prove the possibility of reducing the capacity of the internal combustion engine while maintaining the specified maximum speed and the specified level of indicators of the vehicles dynamic properties. The relationship between the increase in the degree of use of the nominal internal combustion engine capacity and the change in the effective specific fuel consumption for a carburetor gasoline engine, an engine with direct gasoline injection, and a diesel engine is determined.

Analysis of publications
Energy efficiency is an operational property that characterizes the rational use of engine energy (or another source of mechanical energy) in the process of vehicle operation. The energy consumption of limited and high cross-country vehicles during operation, on paved roads and off-road, was determined in [1]. In the paper [2] it is shown that the energy efficiency of a car is largely determined by the degree of its aerodynamics, which has become an attribute of almost all recognized design solutions. From this, we can come to the disappointing conclusion that aerodynamic drag indicators are decisive in evaluating the energy efficiency of vehicles. The work [3] presents scientific and technical developments dedicated to improving the energy efficiency of vehicles.
In the paper [4] research is devoted to the development of new indicators and criteria of energy efficiency of vehicles. The need for a new approach to energy efficiency assessment is due to the appearance of vehicles with alternative energy sources. In the paper [4], it is proposed to consider not fuel consumption, but energy consumption as indicators of the economy of vehicles.
In the paper [5][6][7] studies are devoted to the energy efficiency of vehicles using the indicators and criteria proposed in [4], in which vehicles with a mechanical drive, as well as hybrid vehicles and electric vehicles are considered.

Автомобільний транспорт, Вип. 51, 2022
At the beginning of the creation of automobile theory [8] by experts in the field of aviation, a calculation formula for aerodynamic drag was proposed 2 ρ 2 x Wa where Cx is the coefficient of frontal aerodynamic resistance;  is air density; F is the midel (frontal area) of the vehicle; Va is vehicle speed.
Since that time, when calculating the aerodynamic drag, engineers, taking the value of the index degree at Va equals 2, believed that the value of Cx should be chosen in the calculations depending on the speed of the vehicle. But then, everyone forgot about this and began to accept Cx at some constant value of speed, spreading the use of the specified value of Cx throughout the entire speed range of the vehicle.
The well-known German scientist Alfred Jante [9], who studied vehicles in detail in the wind tunnel, recommended determining the Cx coefficient at an air blowing speed equal to 10 m/s. The papers [10][11][12][13][14][15] are devoted to the method of experimental investigation of vehicles aerodynamics. A huge amount of material was accumulated to determine the constant value of Cx for various vehicles.
The use of the method of partial accelerations, implemented in a mobile registration and measurement complex, allowed the authors of [16] to obtain an improved equation to calculate the force of aerodynamic drag, which has the form 2 ρ 2 n w Wa where Aw is the coefficient of regression corresponding to the value of the coefficient of frontal aerodynamic drag at Va=1 m/s. The equation (2) under consideration corresponds to the law of change of the coefficient of frontal aerodynamic drag, which has form where n is the index of degree (regression coefficient).
In the paper [18], using the method of partial accelerations and a mobile registration and measurement complex, conducted experimental studies of 9 models of passenger cars. As a result, the coefficients Aw and n were determined (Tabl. 1). Graphs of dependence (3) for 9 passenger car models studied in [17] are presented in Fig. 1 By the co-authors of the article Podrigalo M.A. and Tkachenko A.S. were previously obtained equations to determin the maximum power of the engine with the traditional calculation of the force of aerodynamic drag according to equation (1) and with the refined calculation according to equation (2). The ratio between the calculated maximum effective power of the engine, calculated according to the traditional method using equation (1) where ' max e N is the maximum effective engine capacity, which is determined by the traditional calculation of the force of aerodynamic drag according to equation (1); '' max e N the maximum effective engine capacity, which is determined by the refined calculation of the force of aerodynamic drag according to equation (2); η ,η mgn mgn tr k are instantaneous efficiency of the transmission and wheels of the vehicle; N  is the ratio of the effective power of the engine ne developed at a given speed Va to Ne max.
By the co-authors of the article Podrigalo M.A. and Tkachenko A.S. were previously obtained equations to determin the maximum power of the engine with the traditional calculation of the force of aerodynamic drag according to equation (1) and with the refined calculation according to equation (2).

Motor vehicles
Automobile transport, Vol. 51, 2022 The ratio between the calculated maximum effective power of the engine, calculated according to the traditional method using equation (1) where ' max e N is the maximum effective engine capacity, which is determined by the traditional calculation of the force of aerodynamic drag according to equation (1); '' max e N the maximum effective engine capacity, which is determined by the refined calculation of the force of aerodynamic drag according to equation (2); , mgn mgn tr k  are instantaneous efficiency of the transmission and wheels of the vehicle; N  is the ratio of the effective power of the engine ne developed at a given speed Va to Ne max.
Regardless of whether the calculation of the necessary maximum engine capacity was carried out using the traditional or refined method of determining the force of aerodynamic drag, the actual consumption of engine capacity when the vehicle is moving at maximum speed will be the same. Only the degree of utilization of the maximum effective capacity of the engine will differ. Suppose that in the case of a refined calculation of the maximum effective power of the engine, an increase in the degree of its use at the maximum speed of the vehicle, a decrease in fuel consumption will occur.

Purpose and Tasks
The aim of the study is to increase the energy efficiency of vehicles by rationally reducing the maximum effective capacity of the engine.
To achieve the goal, the following tasks must be solved: to determine the relationship between the degree of use of the maximum effective engine capacity and the effective specific fuel consumption; -to evaluate the reduction of fuel consumption of the vehicle with a rational reduction of the maximum effective engine capacity.

Determination of the relationship between the degree of use of engine capacity and effective partial fuel consumption
To solve the problem, let us use the load characteristics of carburetor gasoline and diesel engines given in [18]. In Table 2 shows the main indicators of a carburetor engine at throttling [18].
Analysis of the data in Table 2 [18] shows that throttling of a carburetor gasoline engine (CGE) leads to a decrease in the indicator and effective capacity. At the same time, the capacity of mechanical losses remains unchanged, and the specific fuel consumption increases. Let us enter the notation: In Table 3 shows the calculation of parameters Ne and ge for the CGE presented in the Table 2 In Figure 2 shows the graph of the dependence of the relative change in the effective specific fuel consumption on the degree of utilization of the maximum effective capacity of the CGE.
Using the method of least squares, the optimal regression coefficient n1=0.453 was determined.
In Table 4 shows the results of the estimation approximation error.
In Figure 3 shows diesel engine load characteristics at the angular speed of the crankshaft е = 136 s -1 [18].
In Table 5 shows the main parameters of the tractor diesel under different cyclic fuel supplies.  The results of the processing load characteristics for diesel engine, taken from the work [18], made it possible to obtain the dependence ge (Ne) (Table 6, Figure 4).  Table 6 shows the results of estimation of the approximation error. The average error of approximation for 5 points is 5.47%, which is acceptable. Figure 4 shows the dependences of ge (Ne) and for diesel engine presented in [18].
For engine with direct gasoline injection, we use the load characteristic obtained by professor A.A. Prokhorenko and associate professor O.P. Kuzmenko.
In Table 7 shows the results of the calculation of the parameter ge at the angular crankshaft velocity е =419 s -1 In Figure 5 shows the dependence graph of ge (Ne), made according to the calculation results given in Table 7.
The analysis of the course of the curve presented in Figure 5 shows that with Ne=1 point of the curve falls out and the curve ge (Ne) has a break. And here a partial-linear approximation is proposed, i.e.
Construction of the response function by selecting one nodal point Ne =0.982 (see Table 7) and selecting the degree n allowed to obtain A=0.882 and n1=0.3, i.e. for different values of Ne are given in table 7. There is also an estimate of the calculation error based on the approximating dependence. Table 7 shows that the maximum error of calculation exceeds 6.44%. A comparative analysis of the course of the ge (Ne) curves for different types of internal combustion engines shows (see Tables 3,6,7) that for the CGE, a decrease in the degree of utilization of the maximum effective engine capacity Ne causes an increase in the effective specific fuel consumption ge. A different situation with diesel engine and the engine with direct gasoline injection. In a diesel engine at Ne = 0.3-0.96. Value Ne<1. In an engine with direct gasoline injection, Ne<1 at ge =0.653-0.982.

Estimation of fuel consumption reduction with a rational reduction of the maximum effective engine capacity
Given that with a rational reduction of engine capacity "' max max ee NN  , let us determine Ne from equation (4).
Let us evaluate the fuel consumption reduction for the car ZAZ-1103 "Slavuta" with a rational reduction of engine capacity. The initial data for the calculation are given in Table 8. When the car ZAZ-1103 "Slavuta" moves, the power consumption both with installed engine with '  Automobile transport, Vol. 51, 2022 The analysis of the calculation results shows that with a carburetor gasoline engine, a rational reduction of the maximum effective capacity allows to reduce the effective specific fuel consumption by 9.5%. This value is proportional to the absolute fuel consumption (if the effective capacity of the engine is equal). It follows that the expected reduction in fuel consumption will also be 9.5%.
When using engines with direct gasoline injection, on the contrary, a decrease in the maximum effective capacity of the engine will lead to an increase in the effective specific fuel consumption. This increase will amount to 11 1 0.937 1 0.067 e g −− − = − = that is, on 6.7%. A similar situation occurs to ZAZ-1103 "Slavuta" car with diesel engine. In this case, a decrease in the maximum effective power of the engine will lead to an increase in the effective specific fuel consumption by 11 1 0.831 1 0.203 e g −− − = − = that is, on 20.3%.

Conclusions
The results of well-known scientific investigations allowed us to draw a conclusion about the possibility of a rational reduction of the maximum effective capacity of the engine while maintaining the specified maximum speed and level of dynamic properties of the vehicle. Since when installing a serial engine and an engine with a reduced value of effective capacity, the realized power is the same, the degree of realization of the maximum capacity is higher in the latter case. The relationship between the degree of use of the maximum engine capacity and the relative change in the effective specific fuel consumption of a carbureted gasoline engine with direct injection of gasoline and diesel is determined.