**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

#### *Research and Innovation to Improve the Efficiency of Modern Diesel Engines DOI: http://dx.doi.org/10.5772/intechopen.102759*

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 (Sf), and compensation for environmental damage from harmful emissions EG (Sec) [2].

Then the comprehensive criterion can be represented as:

$$\mathcal{C}\_{f.\mathcal{ex}} = \eta\_{\mathcal{ex}} \cdot \beta \tag{1}$$

Here, *β* is the ratio of relative operating environmental costs

$$\mathcal{J} = \left( \mathbb{S}\_{f.\text{ac}} - \mathbb{S}\_{\text{cc}} \right) / \mathbb{S}\_{f.\text{ac}} \tag{2}$$

where *S <sup>f</sup>:ec* ¼ *S <sup>f</sup>* þ *Sec*– 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:

$$\mathcal{S}\_{\rm eci} = \left(^{\mathcal{B}\_{\rm bi}}\!/\_{\mathcal{N}\_{\rm ci}}\right) \cdot \mathcal{D}\_{\rm eci} \left(\mathbf{EUK}/\mathbf{kW}\cdot\mathbf{hr}\right),\tag{3}$$

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.

$$\mathbf{S}\_{\text{cc}} = \frac{\sum\_{i=1}^{x} (B\_{hi} \cdot D\_{ci} \cdot P\_i)}{\sum\_{i=1}^{x} (N\_{ci} \cdot P\_i)} \text{ (EUR/kW} \cdot \text{hr)} \tag{4}$$

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; *Рі*—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**).

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<sup>n</sup> and 0.7 Рn. Three load modes (1.1, 0.7 and 0.3Рn) correspond to crankshaft speeds of 0.8 and 0.6 nn. Another mode takes into account the share of fuel and environmental costs when the diesel engine is operating at the minimum idle crankshaft speed (*nх*/*<sup>х</sup>* min).

*Research and Innovation to Improve the Efficiency of Modern Diesel Engines DOI: http://dx.doi.org/10.5772/intechopen.102759*

#### **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.*


#### **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:


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 СО<sup>2</sup> 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

#### *Research and Innovation to Improve the Efficiency of Modern Diesel Engines DOI: http://dx.doi.org/10.5772/intechopen.102759*

hazardous toxic constituents of exhaust gases—carbon oxides (CO), hydrocarbons (CH), nitrogen oxides (NOx), 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 СО<sup>2</sup> emissions.

It should be noted that the share of the level of СО<sup>2</sup> emissions into the atmosphere by road transport and their average annual increase in relation to the total levels of emissions of СО<sup>2</sup> with fuel combustion products is 23% and in relation to the technogenic СО<sup>2</sup> 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 СО<sup>2</sup> 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 СО<sup>2</sup> and, as a consequence, an increase in the content of СО<sup>2</sup> in the atmosphere and the temperature of the surface air layer [3].

Currently, promising alternative fuels for diesel engines include:


"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*<sup>x</sup>* 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.


#### **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

#### *Research and Innovation to Improve the Efficiency of Modern Diesel Engines DOI: http://dx.doi.org/10.5772/intechopen.102759*

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.
