Research and Innovation to Improve the Efficiency of Modern Diesel Engines

Abstract

Modern diesel engines are one of the main mobile energy sources and are characterized by a high degree of workflow completeness, design, and manufacturing technology. The chapter summarizes the authors’ experience in improving diesel engines, increasing specific volume power, and reliability, ensuring a low level of environmental pollution emissions. The results of research using industry 4.0 technologies for systematization, choice of directions, and the search for rational ways to improve the efficiency of diesel engines are presented. The application of anergo-exergy method for analyzing the efficiency of the working process of the engine and its systems is considered. Taking into consideration the operating conditions, technical solutions are proposed to improve the reliability of the most heat-stressed parts of high-powered engines. The possibilities for a comprehensive assessment of the fuel efficiency and environmental qualities of diesel engines have been expanded taking into account CO2 emissions when using traditional, alternative, and hybrid diesel fuel.

1. Introduction

Modern diesel engines are the main mobile energy sources, are widely used as stationary power plants, and are distinguished by a high degree of design, working, and technological processes.

The advantages of diesel engines are determined by the high level of fuel efficiency and reliability due to the high level of workflow, all systems, and components refining. But this does not mean that all reserves for further improvement of diesel engine performance have been exhausted.

The main disadvantages of diesel engines include the consumption of natural organic fuels and the contribution to environmental pollution.

Taking into account, the prospects for increasing energy potential in stationary, and especially in transport energy, limited natural resources, deterioration of the environment, today it seems relevant to solve the following problems:

• further improvement of the design of diesel engines in order to boost the liter capacity;

• reduction of operating fuel consumption;

• reduction of toxic emissions into the environment with exhaust gases;

• reduction of emissions (СО₂) into the environment with fuel combustion products.

The solution of these problems seems to be a much more rational direction, in comparison with the proposed solutions for the reduction and possible abandonment of the use of diesel engines in the future, which will invariably lead to the energy crisis, which may turn out to be much more painful for humanity in comparison with the ecological one.

In this chapter of the monograph, in order to systematize, select directions, and search for rational ways to improve the efficiency of diesel engines, the main results of fundamental and applied research carried out in recent years at the Department of Internal Combustion Engines of the National Technical University “KhPI” are considered. The experience of the authors in improving the quality of processes in cylinders of diesel engines, in increasing the reliability of the most loaded parts, in ensuring a reduction in the level of emissions of toxic substances and carbon dioxide, including the use of alternative fuels, is generalized.

It is proposed to evaluate the effectiveness of technical solutions to reduce the operating fuel consumption of transport diesel engines and emissions of toxic substances with exhaust gases, use of alternative and hybrid fuels, which includes green hydrogen, is proposed to be carried out using the fuel-ecological criterion. It is shown that further improvement of this criterion is associated with taking into account the impact of carbon dioxide emissions on the environment.

At the same time, the heat generated by the combustion of fuel in the engine cylinders cannot be completely converted into useful mechanical work. To study the efficiency of thermodynamic processes of diesel engines, it is proposed to use the anergy-energetic method of analysis, and the quality of heat conversion into work is estimated by the exergy efficiency, which makes it possible to identify the mechanisms of formation of internal and external losses and substantiate the ways to achieve optimal heat use.

Along with the improvement of economic and environmental indicators and the technical level, the improvement of diesel engines is associated with an increase in liter power, which requires ensuring reliability, first of all, the most heat-stressed engine parts and using modern industry 4.0 technologies.

2. Comprehensive assessment of the automotive diesel engines efficiency in terms of fuel consumption and exhaust gas toxicity

Improving the efficiency of power plants, preserving natural resources, and improving the quality of the environment are global problems of our time. Diesel engines are the main source of energy for transport, and at the same time, they are one of the main consumers of fuel oil and an active pollutant of the environment.

The level of excellence and technical level of modern diesel engines is largely determined by fuel consumption and exhaust gas emissions (EG). Diesel engines have higher fuel efficiency and lower mass emissions of toxic substances compared to gasoline and other heat engines. However, research data shows that, along with a high level of toxicity of nitrogen oxides emitted into the atmosphere together with EG, particulate matter (PM) poses a great danger to humans and the environment due to the adsorption of carcinogens.

At the same time, it is known that technical solutions aimed at reducing fuel consumption have an impact on the environmental performance of an engine, and fuel consumption can increase with an improvement in its environmental performance. Therefore, a compromise is needed. A targeted search for compromise technical solutions requires a comprehensive approach using a criterion that takes into account the level of fuel consumption indicators, EG emissions, and operating conditions. The solution to this problem is of paramount importance for automobile engines, since, they are used in crowded places in cities, suburbs, industrial areas and, therefore, pose the greatest danger to people and the environment.

2.1 Basics of calculating a comprehensive criterion

At the Department of Internal Combustion Engines of the National Technical University “Kharkiv Polytechnic Institute” (NTU “KhPI”), a dimensionless comprehensive criterion of fuel efficiency and EG toxicity for diesel engines has been developed [1].

This criterion is informative, simple, and user-friendly, takes into account the operating conditions, provides information on the degree of economic and environmental excellence, the effectiveness of the developed measures to improve the work process, engine design, and technology, the use of alternative and mixed fuels, exhaust gas neutralization systems for a specific diesel engine.

The initial data for the criterial comprehensive assessment of diesel engines are obtained with relatively simple, affordable, and minimal bench tests.

To determine the fuel-ecological criterion, it is necessary to know the average operating effective efficiency of the engine (η_e._e.), operating costs for fuel (S_f), and compensation for environmental damage from harmful emissions EG (S_ec) [2].

Then the comprehensive criterion can be represented as:

$$C_{f.\mathit{ec}}={\eta }_{e.e}\cdot \beta$$E1

Here, β is the ratio of relative operating environmental costs

$$\beta =\left(S_{f.\mathit{ec}}-S_{\mathit{ec}}\right)/S_{f.\mathit{ec}}$$E2

where $S_{f.\mathit{ec}}=S_f+S_{\mathit{ec}}$– are total costs fuel and compensation for environmental damage from harmful emissions.

Then, the unit costs for compensation of environmental damage from the harmful effects on the environment of the exhaust gases of a diesel engine during the combustion of 1 kg of fuel, referred to a unit of power for each representative fixed mode of operation of a diesel engine, are equal to:

$$S_{\mathit{eci}}=\left(\raisebox{1ex}{$B_{\mathit{hi}}$}\!\left/ \!\raisebox{-1ex}{$N_{\mathit{ei}}$}\right.\right)\cdot D_{\mathit{eci}}\left(\mathrm{EUR}/\mathrm{kW}·\mathrm{hr}\right),$$E3

And the total unit costs for reimbursement of environmental damage from the harmful effects of toxic emissions of exhaust gases of a diesel engine for all representative fixed modes of the operating model.

$$S_{\mathit{ec}}=\frac{{\sum }_{i=1}^z\left(B_{\mathit{hi}}\cdot D_{\mathit{eci}}\cdot P_i\right)}{{\sum }_{i=1}^z\left(N_{\mathit{ei}}\cdot P_i\right)}\left(\mathrm{EUR}/\mathrm{kW}\cdot \mathrm{hr}\right)$$E4

In formulas (3) and (4): B_hi—the hourly fuel consumption for each engine operating mode (kW hr), N_ei—the effective power for each engine operating mode (kW); D_eci—value damage cost when burning one kg of fuel, in EUR/ kgf; Р_і—partial operating time of the engine at each i-th fixed mode of the diesel engine operation model, z—the number of representative modes.

2.2 Automotive diesel engine operation model

As mentioned above, it is advisable to evaluate the indicators of fuel efficiency and toxicity of exhaust gases of diesel engines under operating conditions during bench tests on typical fixed operating modes, which are selected taking into account the type, purpose, and generalized data on engine operating time. Selected and justified fixed modes of operation, in which bench tests are carried out, represent a model of engine operation.

As a result of the analysis and processing of the operational test data, the authors proposed a generalized model of the operation of a diesel truck in the form of probabilistic distribution of the centers of the operating ranges (Figure 1).

Figure 1.

Probabilistic distribution of ranges of operating modes of a diesel engine of a truck during the aggregate movement in the city and on a suburban highway.

Thus, it is possible, based on the results of bench tests of a diesel engine, to determine the level of fuel costs and compensation for environmental damage from the harmful effects of EG on the human body and the environment, as well as to apply a dimensionless fuel and environmental criterion for comparative assessment.

The disadvantages of the proposed model include the comparative complexity of the procedure for carrying out bench tests of a diesel engine, which provides for the determination of a large number of parameters at 28 modes. In this regard, based on summarizing the results of the research carried out for diesel engines of trucks, a 9 regime test cycle is proposed. The basis for the development of the 9th mode test cycle was ensuring the maximum possible compliance with the comprehensive criterion in comparison with tests for the 28th mode cycle. As a result, the developed cycle with a limited number of load modes and crankshaft speeds of a diesel engine makes it possible to determine a comprehensive criterion of fuel efficiency and exhaust gas toxicity without introducing additional errors.

The proposed 9th mode cycle of bench tests to determine the comprehensive criterion of fuel consumption and toxicity of exhaust gases during the operation of diesel engines of trucks is presented in Table 1. At the rated speed mode, the diesel engine is tested under loads corresponding to Р_n and 0.7 Р_n. Three load modes (1.1, 0.7 and 0.3Р_n) correspond to crankshaft speeds of 0.8 and 0.6 n_n. Another mode takes into account the share of fuel and environmental costs when the diesel engine is operating at the minimum idle crankshaft speed (n_х/х min).

Modes Nos.	n	Р	Significance coefficient, z
1	nn	Рn	0.05
2	nn	0.7 Рn	0.025
3	0.8 nn	1.1 Рn	0.3
4	0.8 nn н	0.7 Рn	0.05
5	0.8 nn	0.3 Рn	0.05
6	0.6 nn	1.1 Рn	0.35
7	0.6 nn	0.7 Рn	0.1
8	0.6 nn	0.3 Рn	0.05
9	nх/х min	0	0.025

Table 1.

Model of operation of a diesel engine of a truck with the combined movement of the city and suburban highway.

For each mode, coefficients were selected that took into account the conditions for the distribution of fuel and environmental costs over the ranges of the diesel engine operating model of a fully loaded truck when driving in the city and on the highway.

Interestingly, if we compare the ESC cycles in accordance with the UNECE rules for diesel engines of trucks and the KhPI cycle, it can be noted that with a smaller number of test modes, the KhPI cycle covers almost equal ranges in terms of load and speed.

Consequently, for a balanced assessment of the environmental hazard of diesel engines for various purposes, it is necessary to take into account the real conditions of their operation and an objective approach to calculating the damage from the harmful effects of exhaust gases. Since the emissions of toxic components of the exhaust gases and the fuel efficiency of a diesel engine are directly related to the organization of mixture formation and combustion, an integrated approach to this problem is required.

The choice of the significant coefficient for each of the modes is based on generalizing the share of costs for fuel consumption and compensation for environmental damage from the harmful effects of exhaust gases in the total costs of the aggregate modes. The proposed dimensionless comprehensive criterion of fuel efficiency and toxicity allows a targeted search and assessment of the effectiveness of the developed measures aimed at reducing fuel consumption and toxicity of exhaust gas emissions under engine operating conditions.

The comprehensive criterion allows:

• to evaluate the efficiency of the internal combustion engine when operating conditions change;

• to determine the operating modes in which S_f, S_e, and S_fe are the most significant;

• to develop measures aimed at increasing the efficiency of the internal combustion engine;

• to evaluate the efficiency of using alternative fuels or EG neutralization systems.

The dimensionless comprehensive criterion of fuel efficiency and toxicity of harmful EG emissions, taking into account the degree of diesel loading and the factor of operating time, makes it possible to evaluate the quality of a diesel engine when used on different vehicles or to assess the fuel and environmental efficiency of various engines when used on the same vehicle. The use of a comprehensive criterion, or, if necessary, the ratio of relative operating environmental costs, in turn, allows an analysis of a compromise situation when a decision is required on the permissible increase in fuel costs provided that the overall level of fuel and environmental costs decreases. In this case, it is necessary to additionally agree on the degree of complexity of the implementation of these solutions, taking into account the potential costs of a significant reconstruction of the diesel engine and the costs of using, for example, electronic control systems or neutralization of EG.

Further improvement of the integrated fuel and environmental criterion is associated with taking into account the compensation for damage caused by diesel engines by СО₂ emissions.

2.3 Efficiency of using alternative fuels in road transport

The most pressing for transport engines are fuel, energy, and environmental problems. These problems are directly related to the limitation of natural resources and environmental degradation. Currently, there are about 1 billion vehicles in the world that run on petroleum engine fuels and actively pollute the environment with hazardous toxic constituents of exhaust gases—carbon oxides (CO), hydrocarbons (CH), nitrogen oxides (NO_x), particulate matter (PM), and also contribute to the expansion of the greenhouse effect by emissions of carbon dioxide (СО₂).

In this regard, along with the further improvement of the power plants of vehicles, including those with diesel engines, the most important task is to expand the use of alternative fuels, as well as to reduce emissions of toxic components of exhaust gases and reduce the level of СО₂ emissions.

It should be noted that the share of the level of СО₂ emissions into the atmosphere by road transport and their average annual increase in relation to the total levels of emissions of СО₂ with fuel combustion products is ∼23% and in relation to the technogenic СО₂ emission into the atmosphere ∼ from 1 to 2%. These data give grounds to assert that vehicles with internal combustion engines, like all heat and power engineering, are not significant at the present stage in terms of the degree of accumulation of СО₂ in the atmosphere, and the corresponding warming of the climate, are not significant. But, on the other hand, vehicles with internal combustion engines negatively affect the change in the natural environment, as a component of the creation of transport systems, their operation and maintenance, including the search, production, transportation, processing of all natural resources, including the oil industry, which has a negative impact on the environment. Under the influence of the above-listed factors, the transformation and destruction of natural massifs, land desertification, pollution of the waters of the World Ocean occurs. All this leads to the degradation and destruction of the planet’s photosynthetic systems, to a decrease in their natural biological productivity, a corresponding decrease in runoff levels of СО₂ and, as a consequence, an increase in the content of СО₂ in the atmosphere and the temperature of the surface air layer [3].

Currently, promising alternative fuels for diesel engines include:

• natural gas, which, in terms of reserves and cost, is currently considered one of the most acceptable energy carriers for vehicles, especially those operating in large cities;

• water-fuel emulsions, which are widely used in water transport, as well as for trucks with diesel engines [4, 5];

• biofuel, which can be used for road transport and especially for self-propelled agricultural vehicles.

“Green” hydrogen is currently being considered as an additional energy carrier for oil and alternative fuels for vehicles. The presence of additives of “green” hydrogen provides a decrease in the energy of ignition of fuels, an increase in the rate of its combustion, and reduces the level of formation of NO_x and PM.

The Department of Internal combustion engines of NTU “KhPI” using a comprehensive fuel and environmental criterion (see Section 2.1 of this Chapter) has made a comparative analysis and a quantitative assessment of the effectiveness of the use of alternative fuels when operating a diesel engine of a truck in comparison with standard diesel fuel on a 6-cylinder diesel engine with a cylinder volume of 9.5 l.

The results of the tests and processing of experimental data are shown in Table 2 and Figure 2. The Figure and the Table show the relative change in the integrated fuel and environmental criterion Cf.ec.

Features of the piston design	Uncoated		Coated
Engine boost level, kW/l	25	29	29
Temperature at a heavier stationary mode (section b), °C	314	343	322
Temperature at idle speed (section d), °С	191	193	188
Stress in a heavier stationary mode (section b), MPa	−36	−42.5	−7.6
No-load stress (section d), MPa	−0.15	0	−2.9
Parameter of the physical reliability of the structure for the resource Р	0.552	< −4	0.574

Table 2.

Parameters of thermal tension of the piston combustion chamber edge.

Figure 2.

Relative change of Cf.ec., when using alternative types of fuel in a 6-cylinder automobile diesel engine with a cylinder capacity of 9.5 l.

The criterion was determined based on the results of bench tests using a model of operation of a truck diesel engine. The engine was tested on diesel fuel, compressed natural gas (CNG) with 15% pilot diesel, rapeseed methyl ester (RME), and water-fuel emulsion (WFE) which contained diesel fuel and 10% water.

The price of natural gas and diesel fuel in the calculations was taken according to the averaged data of filling and gas filling stations in Ukraine.

The costs of water and the preparation of a water-fuel emulsion were not taken into account in the calculations.

The cost of 1 kg of rapeseed oil methyl ester, obtained in pilot plants and in small quantities, exceeds the cost of 1 kg of diesel fuel by 1.4–1.6 times. However, when calculating the comprehensive criterion, the price of rapeseed oil methyl ester was taken to be equal to the price of diesel fuel, taking into account its possible decrease with the expansion of the production of this fuel.

It follows from the above data that any of the investigated alternative fuels in an automotive diesel engine provides an increase in fuel and environmental efficiency. This is mainly due to a decrease in toxic emissions at engine operating modes at maximum load at reduced speeds.

The use of a gas-diesel cycle with CNG allows increasing the value of the comprehensive criterion of fuel efficiency and toxicity of exhaust gases of a truck diesel engine by 11.9%. It should be noted that in this case, as the proportion of partial modes increases, the ratio between the constant doses of ignition diesel fuel supplied to the cylinders and the amount of compressed natural gas increases. Accordingly, fuel costs increase and environmental efficiency from the use of gas fuel decreases.

The complex fuel and environmental criterion increase by almost the same amount when a truck diesel engine runs on rapeseed oil methyl ether. In this case, the deterioration in the average operating efficiency occurs to a large extent when the engine is running at partial conditions, in comparison with the engine running on diesel fuel.

When a truck diesel engine runs on a water-fuel emulsion, the comprehensive criterion of fuel efficiency and toxicity of exhaust gases increases most significantly—by 15%. This is due to the simultaneous reduction in environmental operating costs, and an increase in the average diesel engine operating efficiency.

It should be noted that the presented results were obtained without any changes in the diesel engine settings and without any changes in their design in order to adapt to a specific type of alternative fuel. Consequently, there are reserves for increasing fuel efficiency and improving the environmental performance of diesel engines when using each of the considered alternative fuels. These reserves include the use of alternative hybrid fuels, which contain green hydrogen.

3. Application of the anergo-exergy method for evaluating the efficiency of working processes in diesel engines

The heat generated by the combustion of fuel in the engine cylinders cannot be completely converted into useful mechanical work. In the thermodynamic cycle, the efficiency of converting heat into work is estimated by the thermal efficiency η_t, which is always less than one as a result of the transfer of part of the heat to a cold source. In a real engine, heat losses increase due to friction, heat transfer, incomplete combustion, and other reasons. In this regard, the effective efficiency of η_t cycle is less important than the value of η_t.

Currently, there are two directions in the thermodynamics of investigating the efficiency of diesel processes. The traditional direction is that for the thermodynamic study of motors, a heat balance is used, based on the first principle of thermodynamics, when the criterion for the quality of converting heat into work is the effective efficiency (η_е). The capabilities of the traditional method are limited by the fact that the heat balance only records the final, qualitative result of energy transformations in the internal combustion engine cycle. To implement all the reserves for improving modern internal combustion engines, it is necessary to deeply study the quality of energy transformations in the engine. The anergo-exergetic method of analysis combines the first and second laws of thermodynamics, and the exergy efficiency (η_еx) acts as a criterion for the quality of converting heat into work. Only this method allows to identify the mechanisms of the formation of internal and external ICE losses, assess the possibilities of their reduction, and, therefore, substantiate the ways to achieve optimal heat use in diesel engines.

3.1 Theoretical foundations of the anergo-exergy method

It is known that heat and internal energy, as forms of energy, determined by the first law of thermodynamics, can only be partially converted into work. Accordingly, in a heat engine (Figure 3) it is possible to convert into work only a certain fraction of the energy supplied in the form of heat Q [6].

Figure 3.

Diagram of the circular process of a heat power plant.

In a generalized form, a consequence of the second law of thermodynamics is the statement that there are forms of energy that can be converted into any other form of energy. These forms of energy, covered by the general concept “exergy”, are completely mutually convertible during reversible processes, and by reversible and irreversible processes they can be transformed into limited convertible forms of energy—internal energy and heat. At the same time, limited convertible forms of energy cannot be converted in any quantities into exergy. All forms of energy that are not transformed into exergy are summarized by the term “anergy”.

“Exergy is the maximum possible work that the system can perform in the reversible transition from this state to a state of equilibrium with the environment; anergy is the energy that cannot be converted into exergy” [7].

For all forms of energy, the following general correlation is valid:

$$\text{Energy}=\text{Exergy}+\text{Anergy}.$$

According to the principle of irreversibility, all natural, actually occurring processes are irreversible. Thus, in these processes, the supply of exergy decreases due to its transformation into anergy. Part of the exergy that is converted into anergy during irreversible processes is the loss of exergy in the process.

To use the concept of exergy and anergy, it is necessary to know the proportions of these quantities for various forms of energy. When determining exergy, the heat supplied to the heat-power plant is considered, the working fluid of which performs a circular process. The exergy of heat appears here as useful work, and anergy as the unused heat of a circular process. However, the useful work of the circular process coincides with the exergy of the supplied heat under the following conditions:

• the circular process is reversible (otherwise it turns into anergy and useful work will be less than the applied exergy);

• heat removal is carried out at ambient temperature, so that the removed heat consists only of anergy and corresponds to the anergy of the supplied heat (Figure 3).

Heat supplied to the working fluid

$$\mathit{dQ}={\mathit{dE}}_Q+{\mathit{dA}}_Q$$E5

As a result of the heat supply dQ, perceived at temperature T, the entropy of the working fluid will increase.

${\mathit{dS}}_Q=\mathit{dQ}/T$. Since the entropy is not produced in a reversible process, the given heat ${\mathit{dQ}}_0$should be such that the entropy

$${\mathit{dS}}_{Q_0}={\mathit{dQ}}_0/T_0$$

transferred with it is equal to the perceived entropy ${\mathit{dS}}_Q$. From the balanced equation of entropy

$${\mathit{dS}}_Q+{\mathit{dS}}_{Q_0}=\frac{\mathit{dQ}}{T}+\frac{{\mathit{dQ}}_0}{T_0}$$E6

for the given heat we get

$$-{\mathit{dQ}}_0=\frac{T_0}{T}\mathit{dQ}$$E7

The heat removed to the environment consists only of anergy and represents the desired anergy of heat.

$${\mathit{dA}}_Q=\frac{T_0}{T}\mathit{dQ}$$E8

The exergy of heat is manifested as the work of an imaginary reversible circular process

$${\mathit{dE}}_Q=\mathit{dQ}-{\mathit{dA}}_Q=\left(1-\frac{T_0}{T}\right)\mathit{dQ}$$E9

If heat is perceived or given off by the system in a certain temperature range, then the exergy of heat perceived or given off with heat Q₁₂ is determined by integrating:

$$E_{Q_{12}}=\underset{1}{\overset{2}{\int }}\left(1-\frac{T_0}{T}\right)\mathit{dQ}=Q_{12}-T_0\underset{1}{\overset{2}{\int }}\frac{\mathit{dQ}}{T}$$E10

In a similar way for the anergy of heat

$$A_{Q_{12}}=T_0\underset{1}{\overset{2}{\int }}\frac{\mathit{dQ}}{T}.$$E11

Here T is the temperature of the energy carrier that gives or receives heat.

As well as Q₁₂, exergy of heat and anergy are characteristics of the process, and not parameters of state. The exergy and anergy of heat depend not only on $T_0$, but also on the temperature of the system that receives or gives off heat, which can be seen from expressions (10) and (11). This allows coming to the conclusion that in heat power plants, heat supply to the working fluid must be implemented at the maximum possible temperature for a given installation and to obtain the maximum possible work in the cycle.

3.2 Evaluation of the efficiency of the diesel engine working process based on the anergo-exergy method

According to the theory [8], any heat and enthalpy can be represented as components of exergy and anergy.

$$Q={Е}_Q+A_Q;I=E+A.$$

In addition, the anergy balance equations are valid for any ICE unit

$$\sum D_i=\sum A_{\mathit{\text{out}}}-\sum {А}_{\mathit{\text{in}}}$$

and balance of exergy

$$\sum D_i=\sum E_{\mathit{\text{in}}}-\sum E_{\mathit{\text{out}}}$$

where ΣЕ_in and ΣE_out may include work supplied to the assembly or taken away from it.

From these equations, it can be concluded that the exergy losses ΣD_i arising due to the irreversibility of real processes increase the energy leaving the assembly and decrease the exergy entering the assembly. This allows representing the flows of anergy, exergy, and exergy losses in the form of anergo-exergy scheme of the thermodynamic unit. Based on the above equations and fundamental considerations, which are laid above in the basis for constructing an anergo-exergy scheme of a thermodynamic unit, will make it possible to build an anergo-exergy scheme of a diesel engine, shown in Figure 4.

Figure 4.

Anergo-exergy scheme of the internal combustion engine. SC—supercharger; S—air cooler; C—cylinders; EX—exhaust manifold; T—gas turbine; EM—engine mechanisms; FP—fuel pump; WP—water pump; OP—oil pump; W—water system unit that receives frictional heat transferred to water; O—oil system unit that receives frictional heat transferred to oil; A_i, Е_i respectively, are the flows of anergy and exergy of the working fluid; —respectively, with the cooling agent anergy and exergy; А′_os, a″_os, a′_w, A_w, a″_w, A′_o, A_o, A″_o, A_f, a′_f and E′_os, E″_osЕ′_w, Е_w, Е″_w Е′_o, Е_o, Е″_o Е_f, Е′_f respectively are the flows of anergy and exergy with the cooling agent, of water in the liquid cooling system of the engine, of oil in the engine lubrication system, of the fuel in the fuel supply system.

The bifurcation of the ICE assemblies made it possible to reveal the corresponding losses of exergy: D_sc, D_s, ΣD_i, D_w, D_wp, D_ex, D_t, D_fp, D_o, D_op, D_мн. To determine the listed exergy losses, it is easier to use the following energy balances of the corresponding assemblies. D_sc = А_sc – А₀; D_s = (A″_os - A′_os) – (A_sc – A_s); A_т = A_exh – A_т; A_w = A″_w – A_w – A_qw; D_o = A″_o – А_o; D_op = А_o – А′_o; D_fp = A′_f – А_f.

For a diesel engine cylinder, you can write

$$E_{Q_{\mathit{ch}}}=\left(Q_{\mathit{ch}}-Q_w\right)-A_Q,$$

where $A_Q={Т}_0\int \frac{\delta Q_{\mathit{ch}}}{T}-{Т}_0\int \frac{\delta Q_w}{T}=A_{Q_{\mathit{ch}}}-A_{Q_w}$—heat anergy $Q=Q_{\mathit{ch}}-Q_w.$

At the same time

$$D_f=D_s+D_{В}={А}_{Т}-A_Q-A_s-A_f.$$E12

To find A_Q and D_f, we divide the cycle in the engine cylinder into two parts: section (a–e)—compression, combustion, and expansion and section (e–a)—the gas exchange process.

In general, $\mathit{dA}=\delta A_Q+\delta A_f+\delta A_s-\delta {А}_{Т}+\delta D_s+\delta D_{В}$, so for the process (a—f)

$$A_e-A_a=A_{Q_{\mathit{ch}}}-A_{Q_w}^{\text{'}}+A_f,$$

For process (e–a)

$$A_{а}-A_e=-A_{Q_w}^{\text{'}\text{'}}+A_s-A_{Т}+D_f.$$

If the law of heat transfer in the gas exchange section is known, then

$$A_{Q_w}^{\text{'}\text{'}}={Т}_0\int \frac{\delta Q_w}{T}=\frac{{Т}_0}{{Т}_m^{\text{'}\text{'}}}{Q}_w^{\text{'}\text{'}},$$

where, ${Т}_m^{\text{'}\text{'}}$ average process (e–a) temperature.

Having found $A_{Q_w}^{\text{'}\text{'}}$, we find the total losses of exergy during gas exchange D_f.

According to Eq. (12)), one can find $A_Q=A_T-A_s-A_f-D_f.$

If the law of heat transfer is known in the area of compression, combustion, expansion, then

$$A_{Q_w}^{\text{'}}={Т}_0\int \frac{\delta Q_w}{T}=\frac{{Т}_0}{{Т}_m^{\text{'}}}{Q}_w^{\text{'}},$$

where ${Т}_m^{\text{'}}$ average process (a–f) temperature.

In this case $A_{\mathit{Qch}}=A_{е}-A_{а}-A_f+A_{Q_w}^{\text{'}}.$

The balance of the exergy flows of the internal combustion engine can be obtained by considering the contour E:

$$\begin{array}{l}{Е}_0+L_m+L_{\mathit{op}}+{Е}_o^{\text{'}}+A_o^{\text{'}}+L_{\mathit{fp}}+Q_{\mathit{ch}}+E_f+{А}_w^{\text{'}}+E_w^{\text{'}}+L_{\mathit{wp}}+{Е}_{\mathit{os}}^{\text{'}}+L_{\mathit{cs}}=\\ =L_e+E_o^{\text{'}\text{'}}+A_o^{\text{'}\text{'}}+L_p+D_{\mathit{fp}}+E_w^{\text{'}\text{'}}+A_w^{\text{'}\text{'}}+{Е}_{\mathit{os}}^{\text{'}\text{'}}+D_{\mathit{sc}}+D_s+A_Q+D_w+D_{Т}+E_{\mathit{exh}}+L_{т.}\end{array}$$

Let us take into account that

$$\begin{array}{l}{L}_p=L_{\mathit{op}}+L_{\mathit{wp}}+L_{\mathit{fp}};L_m+L_{\mathit{sc}}=L_{\mathit{ті}};D_{\sum o}=D_o+D_{\mathit{op}}=A_o^{\text{'}\text{'}}-A_o^{\text{'}};\\ D_{\sum w}+A_{\mathit{Qw}}=D_w+D_{\mathit{wp}}+A_{Q_w}=A_w^{\text{'}\text{'}}-A_w^{\text{'}};D_{\mathit{fp}}+D_s+D_{в}=D_f.\end{array}$$

With this in mind, we get

$$\begin{array}{l}{Q}_{\mathit{ch}}=L_e+\left[\left(E_o^{\text{'}\text{'}}-{Е}_o^{\text{'}}\right)+\left(A_o^{\text{'}\text{'}}-A_o^{\text{'}}\right)\right]+\left[\left(E_w^{\text{'}\text{'}}-{Е}_w^{\text{'}}\right)+\left(A_w^{\text{'}\text{'}}-A_w^{\text{'}}\right)\right]+\left({Е}_{\mathit{os}}^{\text{'}\text{'}}-{Е}_{\mathit{os}}^{\text{'}}\right)+\\ +\left({Е}_{\mathit{exh}}-{Е}_0-{Е}_f\right)+D_{\mathit{sc}}+D_s+D_f+A_Q+D_{Т}\end{array}$$

or

$$Q_{\mathit{ch}}=L_e+\mathrm{\Delta }{E}_o+\mathrm{\Delta }{E}_w+\mathrm{\Delta }{Е}_{\mathit{os}}+\mathrm{\Delta }{Е}_{\mathit{exh}}+A_Q+D_{\mathit{ch}}+D_s+D_f+D_{Т}+D_{\sum o}+D_{\sum w}.$$

Note that in this expression

$$\sum E_i+A_{\mathit{Qch}}+\sum D_i=Q_2\text{and}\sum E_i=\sum Q_2.$$

Since $Q_{\mathit{ch}}-A_{Q_{\mathit{ch}}}=E_{Q_{\mathit{ch}}},$ then

$$E_{Q_{\mathit{ch}}}=L_e+\sum E_i+\sum D_i.$$

This dependence is the equation of the energy balance of the engine. It can be seen from it that the exergy $E_{Q_{\mathit{ch}}}$, is supplied to the working fluid with the heat of the fuel Q_ch, is spent on the efficient operation of the engine L_e, covering the losses of exergy $\sum D_i$. Part of the fuel heat energy is removed to the environment with water $\mathrm{\Delta }{E}_w$, with oil $\mathrm{\Delta }{E}_o$, with intermediate air cooling $\mathrm{\Delta }{Е}_{\mathit{os}}$, and with exhaust gases $\mathrm{\Delta }{Е}_{\mathit{exh}}$_. According to the well-known theory [9, 10], exergy supplied to the internal combustion engine

$${Е}_{\sup }=E_{Q_{\mathit{ch}}}-\sum E_i.$$

Then

$${Е}_{\sup }=L_e+\sum D_i.$$

The efficiency of converting exergy supplied to the internal combustion engine into useful work can be estimated by the exergy efficiency

$${\eta }_{е}=\frac{L_e}{{Е}_{\sup }}=1-\frac{\sum D_i}{{Е}_{\sup }}.$$

Let us give an example of determining exergy losses using the proposed anergo-exergy method for a 6ChN12/14 tractor diesel engine with a power of 150 kW in one of its operating modes.

The performed calculation shows that in the diesel cycle, when the heat of the fuel is transferred to the working fluid, 21.3% of the anergy of this heat was formed. In addition, due to the irreversibility of real processes, losses of exergy amounted to 16.75%, that is, 38.05% of inoperable heat was also formed in the cycle. Part of the workable heat (20.95%) is carried away into the environment by heat carriers—oil, water, air, and exhaust gases. The rest of the heat turned into useful work (41.05%).

The largest amount of workable heat is carried away by waste gases (16.84%). The loss of performance in the lubrication and cooling systems is 2.16 and 7.84%, respectively. Attention is drawn to the noticeable total loss of performance during filling and when gases enter the exhaust manifold—1.34%. Noteworthy are D_SC = 1.25% and D_T = 3.83%—losses of exergy in the supercharger and gas turbine. In reducing the indicated losses of exergy, reserves for increasing the efficiency of a diesel engine are laid. Figure 5 shows the items of the exergy balance.

Figure 5.

Exergy balance of a diesel engine.

In the diesel cycle, the exergy of the chemical heat of the fuel is supplied to the working fluid

$$E_{Q_x}=Q_{\mathit{ch}}-A_{Q_{\mathit{ch}}}=3.19\mathit{kJ}/\mathit{\text{cycle}}.$$

However, exergy took part in the process of converting this heat into work.

$$E_{\sup }=E_{Q_{\mathit{ch}}}-\sum E_i-A_{Q_{\mathit{ch}}}=2.34\mathit{kJ}/\mathit{\text{cycle}}.$$_Hlk95741500

Due to the irreversibility of real processes, 29% of E_sup turned into loss of exergy, that is, a third of the exergy has irreversibly disappeared (turned into anergy).

The remaining 71% of exergy turned into effective work. The exergy losses in the exergy balance are “significant”, since the exergy losses in water are 13.58%, that is, almost half of all exergy losses. Turbine losses are less and amount to about 6%. Both should be dealt with at the same time by the researcher in order to reduce them.

So, the use of anergo-exergy method of analysis makes it possible to identify the mechanisms of the formation of internal and external losses of diesel engines and their systems, and to substantiate the ways to achieve their maximum efficiency.

4. Improving the reliability of the most thermally stressed parts of highly accelerated engines, based on the operating conditions

Modernization of existing and creation of new engines of high specific power causes significant difficulties since it is necessary to minimize costs during the life cycle of a structure while ensuring a set of quality indicators during given service life. At the same time, for the most thermally stressed engine parts, the provision of their physical and parametric reliability must be taken into account. The practice of operating engines testifies to cases of failure of the combustion chamber parts due to their cracking during the declared resource and the appearance of chafes and scuffs on the lateral surface of the piston [11]. A substantiated increase in the reliability of heat-stressed parts of an internal combustion engine requires the use at the design stage of mathematical models that take into account a complex of factors affecting the physical and parametric reliability.

Let us consider the process of loss of structural reliability based on the model of material damage accumulation in time d(τ). At the initial moment of operation, it is usually assumed that there is no damage to the material, the reliability factor is d(0) = 1. Then the values d(τ*) = 0 correspond to the limiting state of the material. The dependence of the criterion d(τ) on the level of the engine-specific power is shown in Figure 6. Zone I corresponds to the absence of damage accumulation during the assigned resource P, zone II—to extensive accumulation of damage, zone III—to intensive accumulation of damage, and zone IV—to the loss of reliability during operation, i.e. d(P) < 0. The main factors affecting the accumulation of damage are design features of the concerned part; properties of the part material(s); ICE operating conditions and features of the working process, cooling and lubrication systems. The influence of these factors is associated with the heat-stressed state of structures due to the material creep and fatigue over time.

Figure 6.

Typical zones of change in the reliability factor of the ICE heat-stressed part.

Figure 7a shows a diagram of the part critical zone deformation for the case of possible instantaneous plastic deformations and creep deformations under the conditions of deformations structural limitation. Typical examples of such zones are the edges of the pistons combustion chamber and the cylinder head cross-sections between the valve orifice and the injector bore. Here, sections 1–2–3–4 denote the initial engine load, 4–5—work in a stationary heavy operating mode, 5–6–7–8—load reduction to a certain partial mode, 8–9—work in a stationary partial mode, 9–10—subsequent engine load to previous heavy-duty level. In this case, sections 1–2 and 5–6 correspond to the material elastic deformation, sections 2–3 and 6–7: creep deformation and stress relaxation, in sections 3–4 and 7–8 the creep process is accompanied by instant plastic deformations, and in Section 4–5 and 8–9 are characterized by stress relaxation.

Figure 7.

Typical variants of deformation of the critical zone of ICE heat-stressed part.

In this case, the common condition for ensuring physical reliability during the work of the part material in such zones on the verge of strength are:

$$d_1\left(\mathrm{\Xi },P\right)={\phi }_{\mathit{sf}}\left(\mathrm{\Xi },t\left(\tau \right),\sigma \left(\tau \right)\right)=1-\sum _{k=1}^{N_P}\frac{1}{N_{\mathit{sk}}}-\sum _{k=1}^{N_P}\frac{1}{N_{\mathit{fk}}}>0,$$E13

where Ξ is the operating model of an engine for a specific purpose, $\mathrm{\Xi }=\left\{{\mathit{\zeta }}_1,{\mathit{\zeta }}_2,\dots ,{\mathit{\zeta }}_{\mathit{n}}\right\};\mathit{k}=\left[1,{\mathit{N}}_{\mathit{p}}\right]\mathrm{\Xi }=\left\{{\mathrm{\xi }}_1,{\mathrm{\xi }}_2,\dots ,{\mathrm{\xi }}_{\mathrm{N}}\right\}$—single-engine load cycle; N_p—total number of engine load cycles during a given resource P; t—current temperature state of the part in the investigated area; σ—current tension value; N_sk—number of cycles until material failure due to creep under the conditions of the k-th cycle of loads; N_fk—number of cycles until material failure due to fatigue under the conditions of the k-th load cycle.

In practice, the choice of technical solutions to improve the physical reliability of the high specific power ICE heat-stressed parts corresponds to the solution of the problem of transition of the calculated result in Eq. (13), in accordance with Figure 1, from zone IV to zone III.

Figure 7b presents a variant of the part critical zone deformation with practically no limitation of creep deformations. Side surface of the piston is a typical example of such a zone. Here sections 1–2–3 denote the initial engine load, 3–4—work on the stationary heavy operation mode, 4–5—load reduction to a certain partial mode and work on the stationary partial mode, 5–6-7—subsequent engine load to the level of the previous heavy-duty and 7–8—subsequent work on the stationary mode. In this case, sections 1–2 and 5–6 correspond to the material elastic deformation, and 2–3–4 and 6–7–8 correspond to creep deformation ε_s, which increases with time.

Methods for determining the profile of the piston lateral surface are known. They consist in determining the clearance ΔR_set(h_i, θ_i) when installing a piston in a cylinder that is variable in height h_i in piston circumferential direction θ_i. Subsequently, in the process of friction pair surfaces wear, the real gap increases to the permissible value [ΔR_set]. Accordingly, the structure parametric reliability criterion is represented by the expression [12]:

$$0<\mathrm{\Delta }{R}_{\mathit{set}}\left(h_i,{\theta }_i,\tau \right)\le \left[\mathrm{\Delta }{R}_{\mathit{set}}\left(P\right)\right]$$E14

With an increase in the level of engine boost due to the appearance of creep deformation, in accordance with Figure 7b, the size of the gap along with some coordinates h_i, θ_i may not increase, but decrease until chafing and scuffing occur, that is, the theoretical mutual penetration of the piston and cylinder materials, ΔR_set (h_i, θ_i, τ) < 0. Therefore, to the condition for ensuring parametric reliability in Eq. (14), it is necessary to add the condition for parametric reliability not to exceed the material creep limit:

$$d_2\left(\mathrm{\Xi }\right)=\left\{\begin{array}{l}1,{\phi }_s\left(t,\sigma \right)\ge 1\\ {\phi }_s\left(t,\sigma \right),{\phi }_s\left(t,\sigma \right)<1\end{array}\right.,$$E15

where ${\mathrm{\varphi }}_s$ is the function of bringing the creep threshold to the criterion d₂.

Thus, the choice of technical solutions to improve the parametric reliability of the ICE piston side surface corresponds to the solution of the problem of transition of the calculated result from zone II to zone I (Figure 6).

To obtain a reliable result of the part guaranteed reliability, it is necessary to have input information about the non-stationary low-frequency and high-frequency temperature state of the structure in accordance with the adopted operating model:

$$t_k\left(\tau \right)={\overline{t}}_k\left(\tau \right)+{\tilde{t}}_k\left(\tau \right)$$E16

$${\sigma }_k\left(\tau \right)={\overline{\sigma }}_k\left(\tau \right)+{\tilde{\sigma }}_k\left(\tau \right)$$E17

where the values ${\overline{t}}_k\left(\tau \right)$ and ${\overline{\sigma }}_k\left(\tau \right)$ correspond to the instantaneous averaged values of the low-frequency change in temperatures and thermal stresses in the investigated area of the part under the conditions of a single load cycle of the type k, and ${\tilde{t}}_k\left(\tau \right)$і${\tilde{\sigma }}_k\left(\tau \right)$ correspond to the instantaneous deviation of temperatures and thermal stresses from the average value.

Formulation of the problem in the form Eqs. (16) and (17) with the subsequent use of model Eq. (13) significantly increases the design time. Therefore, a simplification of problem Eqs. (16) and (17) is proposed, which does not contradict the principle of guaranteed ensuring the strength of a part during design [13]. With a load surge and engine operation in a heavy stationary mode, we take:

$$t_k^{\mathit{ab}}\left(\tau \right)={\overline{t}}_k\left(\tau \right)+{\tilde{t}}_k^{bmax}$$E18

$${\sigma }_k^{\mathit{ab}}\left(\tau \right)={\overline{\sigma }}_k\left(\tau \right)+{\tilde{\sigma }}_k^{bmin}$$E19

With a load drop and engine operation in a less heavy stationary mode, we take:

$$t_k^{\mathit{сd}}\left(\tau \right)={\overline{t}}_k\left(\tau \right)+{\tilde{t}}_k^{dmax}$$E20

$${\sigma }_k^{\mathit{сd}}\left(\tau \right)={\overline{\sigma }}_k\left(\tau \right)+{\tilde{\sigma }}_k^{dmax}$$E21

A graphical explanation of the values used is shown in Figure 8.

Figure 8.

Local temperature (left) and thermal stress (right) in a single loading cycle of the studied zone of the piston: a—temperature and b—stress state of the studied area of the part: a—load surge; b—heavily loaded stationary mode; c—load drop; d—less loaded stationary mode.

On the basis of the proposed approaches, we determined the reliability criteria d₁(Ξ, P) and d₂(Ξ) relative to the piston of a tractor diesel engine of the SMD type (the engine cylinder diameter is 120 mm, the piston stroke is 140 mm, and the number of cylinders is 4), the boundary conditions of heat transfer for which are well known. The main piston material is the AK12M2MgN alloy. A piston of traditional design and with a heat-insulating layer on the surface of the combustion chamber is considered. Layer material—Al₂O₃. Layer thickness—0.25 mm. For a piston with a surface layer, the analysis was carried out according to the parameters under the thermal insulation layer. The calculation of the value d₁(Ξ, P) was carried out for the edge of the piston combustion chamber with a liter diesel power of 25 and 29 kW/l using the RESURS program (Pylyov, V.О., Prokopenko, M.V., Shekhovtsov, A.F.: Resurs. UA Computer Software 5915, 16 July 2002). The value of N_sk in Eq. (13) was determined by the energy criterion of Sosnin, the value of N_fk—on the basis of the generalized Neuber principle [14]. The calculated base is taken as P = 10,000 hours. The engine operation model is adopted for an agricultural tractor [14]. The number of calculation cycles N = 80,800. The main calculation results are given in Table 2. It can be seen from the Table that for a given uncoated piston with a liter engine power of 25 kW/l, there is no cracking of the combustion chamber edge during a given resource, d₁(Ξ, P) = 0.552. But with a liter power of 29 kW/l, the resource is not guaranteed, d₁(Ξ, P) < 0. This means that at a power level of 25 kW/l, the piston is practically working on the verge of physical reliability. But with a thermal barrier layer with a liter engine power of 29 kW/l, the parameter of the physical reliability of the piston is 0.574, i.e. the reliability of the structure has been restored.

The calculated data on the structure thermal stress are also sufficient to determine the parametric reliability of the piston lateral surface d₂(Ξ). The piston control points to be analyzed are shown in Figure 9a. The arrangement of the calculation array results for a piston with a thermal barrier layer at a liter engine power level of 29 kW/l is shown in Figure 9b. The data on the reduction of the creep threshold of the alloy to the criterion d₂(Ξ) in Eq. (15) were taken on the basis of work [14], ${\phi }_s=\left(2,5\sigma +t\right)/225$. The figure shows that the parametric reliability of the structure is ensured.

Figure 9.

Control points on the piston: a—Location of control points on the piston for levels a—D; b—Change in the thermally stressed state for control points.

The proposed approach to the analysis of the reliability of structures of heat-stressed parts of highly accelerated engines takes into account the operating model and allows you to search for technical solutions while ensuring the operation of materials of structures on the verge of strength.

For monitoring and predicting the residual life of the most thermally stressed parts under engine operating conditions, the proposed methodology allows using modern 4.0 technologies.

5. Conclusions

The improvement of diesel engines, as the main source of modern energy, is associated with a further increase in fuel efficiency, liter capacity, and reliability, with a significant reduction in emissions of toxic substances and carbon dioxide into the environment.

The proposed systematic approach to a comprehensive assessment of fuel efficiency and emissions toxicity allowed proposing a dimensionless criterion that takes into account the operating conditions of the engine. Using this criterion, an assessment of the efficiency of using alternative fuels is given and the prospect of such an assessment is shown when using hybrid fuels that include green hydrogen.

To identify the mechanisms of the formation of internal and external losses and substantiate the ways to achieve optimal heat use, the use of the anergy-energetic method of analysis is justified.

In order to increase the reliability of the most thermally stressed parts of highly accelerated engines, taking into account the operating conditions, the approach has been proposed, taking into account the complexity of factors affecting the physical and parametric reliability.

The directions for improving diesel engines, considered in the chapter, are only a part of a set of tasks, the solution of which seems to be extremely relevant from the point of view of preventing an energy crisis and, at the same time, are only a part of the possible ones for practical implementation.