Evaluation of the Environmental and Operating Parameters of a Modern Compression-Ignition Engine Running on Vegetable Fuels with a Catalytic Additive

Abstract

This article discusses the possibility of using a liquid catalyst in selected vegetable fuels. The fuels selected for study are rapeseed oil methyl ester and hemp oil methyl ester. The aim of the research presented in this paper is to evaluate the operating and environmental performance of an engine fueled with selected fuels with a catalytic additive. The tests were carried out on a dynamometer bench using a Fiat 1.3 JTD common rail engine. During the tests, parameters such as engine torque and power, specific fuel consumption, and the emission of nitrogen oxides, hydrocarbons, carbon dioxide, and soot were measured. The tests were carried out on fuels with and without a catalytic converter. The results show that the use of a catalytic additive reduces nitrogen oxides and hydrocarbon emissions for all fuels tested.

1. Introduction

The main direction of development of reciprocating internal combustion engines is to reduce the emission of toxic substances in the exhaust gas into the atmosphere. Some limits have already been reached in the design of engines and their systems in terms of maximizing the parameters of working processes and controlling their course. Nevertheless, forecasts for future standards of toxic exhaust emissions and fuel consumption lead to further tightening. The drive to meet these requirements is observed primarily using electronic control systems for fuel injection characteristics, obtaining fuel–air mixtures of stoichiometric composition, as well as through the implementation of exhaust after-treatment devices such as catalytic reactors in exhaust systems. Research is also being conducted on the use of catalysts directly in combustion chambers. Particular attention is being paid to technological solutions implemented in those engine components that directly affect the combustion process, and the reduction in toxic compounds formed—primarily in the injection apparatus, combustion chamber, and exhaust systems. It is worth emphasizing that the approach to the ecological and economic aspects of the operation of internal combustion engines must include both what we burn and what we reduce later. The most important stage in the entire process of engine operation is combustion and its proper organization, which significantly determines both the efficiency of the power unit and the level of harmful emissions. The second key factor influencing the za-value of toxins in the exhaust gases is the process of their reduction and oxidation, i.e., exhaust gas cleaning. It is worth noting, however, that the effectiveness of both the combustion process and the subsequent neutralization of by-products largely depends on the composition of the mixture entering the combustion chamber—that is, on the physical–chemical properties of the fuel and air used.

The subject of this study is a modern compression-ignition engine running on modified fuels of vegetable origin. The fuels used in the work are rapeseed oil methyl ester and hemp oil methyl ester. The modification of the fuels consisted of adding a liquid catalyst to them. The function of the liquid catalyzer is to trigger the reduction and oxidation reaction of toxic compounds formed during the combustion process itself.

Catalytic reactors are widely used in automotive vehicles, mainly in exhaust systems. Their task is to oxidize and reduce toxic substances in the exhaust gas, such as nitrogen oxides, hydrocarbons, and soot [1]. The catalytic materials are platinum or palladium. The catalyst can also be used in the engine injection system in the fuel injector [2,3]. Research in this direction involves the application of catalytic coating to the non-working part of the fuel injector needle. To increase the contact surface area of the fuel with the catalyst, the authors of the work proposed various solutions by making additional helical or spiral elliptical channels on the non-working part of the firing pin. In addition, model tests have shown [3] that the proposed channels induce additional turbulence in the fuel flow through the nozzle which improves the parameters of the injected fuel jet in the engine combustion chamber. The proposed catalyst material is platinum. Analytical studies have been performed in the Solid Works environment, with which flow and temperature fluctuation modeling can be performed [4,5]. The catalytic coating can also be applied in the engine combustion chamber on piston, head, or valve components [6]. Studies show that the use of heterogeneous catalysis during combustion reduces toxic substances at the very stage of their formation and improves the combustion process. However, most research is devoted to the use of various alternative fuels or additives to improve the organization of the combustion process and eliminate toxic substances in the exhaust gases. In article [7], the authors presented the results of a study on the use of micro-emulsification in diesel, vegetable oil, and alcohol-based fuels. The research showed that due to the water content, the calorific value of all fuels improved with a reduction in nitrogen oxides and soot. Carbon dioxide and diazotium oxide are responsible for the greenhouse effect. The fuel injection strategy of a CI engine can be programmed to optimize the combination of injection times to improve the combustion process and reduce emissions of these pollutants [8]. The authors proposed a compression-ignition engine operating on a dual fuel injection strategy. The chosen analytical simulation showed the best injection timing combination to optimize the engine’s combustion and emissions. The engine was fueled with mixed diesel with ammonia and hydrogen. The study showed that ammonia with hydrogen resulted in reduced emissions of carbon dioxide, diazotide, hydrocarbons, and carbon monoxide. Nitrogen oxide emissions were increased but were within the tier III standard. Similar results were obtained in another study [9]. The authors used a hybrid powertrain with a spark-ignition engine running on a Miller circuit for the study. This circuit allows the use of variable valve timing to analyze the gas–air mixture strategy for filling the cylinders: ammonia with hydrogen and a standard fuel–air mixture. Studies have shown that the addition of hydrogen and ammonia improves cold starting. However, the engine achieves the highest efficiency on the standard air–fuel mixture. The electric motor assists the internal combustion engine by making up for the energy shortfall when using an ammonia–hydrogen mixture. In papers [10,11], the authors presented the concept of using nanoparticles as a fuel additive for a compression-ignition engine. The study showed that the fuel additive resulted in a reduction in soot and hydrocarbon emissions at lower engine loads and a reduction in nitrogen oxides at maximum loads. In addition, engine duty cycle analysis showed lower exergy losses for the engine running on nanoparticles. The nanoparticles consisted of cerium, silver, and titanium. The disadvantage of this solution is their high price. An analysis of the research results presented by the authors of the paper [12,13] showed that it is possible to produce oil from non-biodegradable plastic bags (PGB). The authors then proposed to make a water–oil mixture with the addition of 10% diesel fuel from the produced oil. The study showed that this type of fuel resulted in lower emissions of soot and nitrogen oxides in the exhaust gas. However, the specific fuel consumption increased. The authors did not investigate how the proposed mixture affects one of engine components. Paper [14] published the results of a study on the effect of the addition of t-butyl peroxide to diesel fuel and biofuel derived from Mahua oil and palm oil waste. The experiment showed that the engine running at 100% load had lower emissions of carbon monoxide, unburned hydrocarbons, and soot by about 4% for the diesel with the additive, but higher emissions of nitrogen oxides by about 1% compared to the biofuel with the additive. The results of an experiment on a single-cylinder, four-stroke CI engine fueled with ON with hydrogen (as base fuel) and ON with hydrogen with ditertbutyl peroxide (DTBP) additive are presented in [15]. The 3.50 kW engine operated at a constant speed of 1500 rpm. The study compared the auto-ignition delay period for the given mixtures. The study showed that the ignition delay decreases with increasing hydrogen and DTBP in diesel. Ethanol can be used as a fuel additive to reduce nitrogen oxide emissions [16,17]. Ethanol lowers the temperature in the cylinder headspace, but the authors of this paper did not report what the emissions of the other toxic substances in the exhaust gas looked like. Research presented in paper [18] showed that hydrogen as an additive to standard fuel and biofuel for CI engines lowers the temperature in the combustion chamber but also changes the physico-chemical parameters of fuels, especially those of plant origin. A fuel additive that can improve toxic emissions in the exhaust gas may be hydrogen peroxide. The authors of [19] described the effect of 10% hydrogen peroxide as a 5%, 10%, and 15% additive to diesel fuel and Calophyllum Inophyllum methyl ester. The study showed that an engine fueled with biodiesel with the additive showed lower carbon monoxide and nitrogen oxide emissions. Similar results were presented by the authors of [20]. The use of 30% hydrogen peroxide in biofuel from Jatropha oil at 5%, 10%, and 15% improved engine parameters such as cylinder pressure, ignition delay, ignition duration, heat release, and environmental parameters. The analysis showed that the engine achieved the best rates when hydrogen peroxide was mixed into the fuel at a ratio of 15%. Another fuel additive that influences the organization of processes in the cylinder workspace is nanoparticles. Paper [21] describes the results of laboratory tests carried out on a direct-injection diesel engine running on a mixture of sunflower and soybean oil (50-50) catalytically trans-esterified. Silver thiocyanate nanoparticles were additionally added to the fuel. The biodiesel was blended in a ratio of (50-50) with standard diesel. Analysis showed that there was a reduction in carbon monoxide, hydrocarbon, and nitrogen oxide emissions in the exhaust gas for the engine running on the modified fuel. According to the authors of the study, the presence of nanoparticles improved the combustion process due to the occurrence of a micro-explosion phenomenon of the atomized fuel, which increases the pressure and heat release rate in the cylinder. The fuel modifications also resulted in a decrease in specific fuel consumption. The use of nanoparticles as a fuel additive is also presented in works [22,23,24,25,26,27,28]. According to the authors of paper [24], micro explosions of the fuel during evaporation during the auto-ignition delay period resulted in faster formation of the combustible mixture, which generally improved the combustion process. Other work has analyzed how the addition of nanoparticles affects the emission of toxic substances in the exhaust gas. The results showed that they reduced soot, hydrocarbon, carbon monoxide, and nitrogen oxide emissions with both conventional and alternative fuels. The authors of paper [29] proposed a mixture of water and diesel fuel with a suitable emulsifier. The study showed that the use of such a mixture reduced the nitrogen oxide and soot content of the exhaust gas. The authors proposed stearyl ether and propylene glycol stearate as emulsifiers. Paper [30] presents the results of tests carried out on a compression-ignition engine using a mixture of lemongrass and rapeseed oils with pure diesel. Titanium dioxide, which contributes to the reduction of nitrogen oxide and carbon monoxide in exhaust gas due to its catalytic properties, and aluminum oxide, which improves the atomization process in the combustion chamber due to its properties, were added to the fuel. Analysis of the experimental results showed that the emission of toxic substances in the exhaust gas for the engine running on the modified fuel was reduced. Research published in paper [31] analyses the possibility of using a nickel catalyst with a cerium addition as a fuel additive for a compression-ignition engine. Ni/Ce catalysts are used in chemical processes to trigger oxidation and reduction reactions. Research conducted by the authors of this paper [32] has shown that the use of a liquid catalyst in the fuel of a compression-ignition engine to induce oxidation and reduction reactions of toxic substances in the exhaust gas during the combustion process reduces the toxicity of the engine exhaust gas. The authors used the catalyst as an additive to standard fuel. The results showed that the active substance significantly eliminates nitrogen oxides and hydrocarbons from the exhaust gas. Redox reactions are used to perform oxidation and a reduction in harmful gases.

Very similar test results were obtained by the authors of paper [33]. In the paper, a Euro-European driving cycle (NEDC) was performed on a car with a compression-ignition engine. The fuel tested was standard diesel, to which hydrogenated vegetable oil, cerium dioxide, and ferrocene were added. The results of the tests showed that each of the additives caused a reduction in toxic substances in the exhaust gas. The greatest reduction in nitrogen oxides was obtained when 30% hydrogenated vegetable oil and ferrocene nanoparticles were used as an additive to the standard fuel.

The purpose of this paper is to analyze the possibility of reducing toxic emissions in a modern compression-ignition engine with a common rail system running on modified biofuels. Analyzing the literature related to the matter of the paper, it can be noted that a lot of research work is carried out in terms of fuel modification. This is because nowadays there is an emphasis on moving away from traditional fossil fuels and replacing them with alternative fuels. One way to improve the environmental performance of a CI engine is to use a catalytic substance in plant-based fuels. The genesis of the following paper comes from the research presented in paper [32]. In that paper, the author performed tests and analyzed the performance of a liquid catalyst on standard diesel fuel. The research showed that the catalyst reduces and oxidizes toxic substances in exhaust gas by up to 50%, especially nitrogen oxides and carbon. Following the directions of the research, the author expanded the scope of research and modified two types of vegetable fuels: rapeseed and hemp oil methyl ester. The first biofuel is very popular in Europe due to the availability of rapeseed oil and its physical and chemical properties like diesel after esterification. The second biofuel tested and modified is hemp oil methyl ester. It is not a popular fuel, but it also has physical and chemical properties like standard diesel. The novelty of this work is the concept of using a catalytic substance on general-purpose vegetable fuels using a modern CI engine with a common rail system, specifically canola oil methyl ester. The research process was carried out on a standard common rail engine on a dynamometer bench under laboratory conditions.

2. Results

The eco fuel shot homogeneous catalyst is an active substance. Its action is to reduce and oxidize toxins in the exhaust gas during the combustion process. The catalyst contains an active substance that reduces the surface tension of carbon, resulting in the complete combustion of soot and naphthalene. Its action affects the rate of the combustion chain reaction by changing the activation energy of the chemically inert particles that react with each other. Eco fuel shot is a selective catalyst with the approximate empirical formula of C₅H₅FeC₅H₄COC_mH_n. The chemical composition of the catalyst is shown in

Table 1. Chemical composition of catalyst [32].

No.	Identification	Concentration [%]
1	3-Methylbutane-1-ol (Isoamyl alcohol)	50
2	Isopropyl alcohol (2-Propanol)	28
3	1-Butanol	12
4	Acetic acid	10

[32].

The proportion with which the catalytic substance was added to the tested fuels is 1 L of catalyst per 50,000 L of catalyst.

Eco fuel shot is a homogeneous catalyst based on ferrocene. These types of chemicals can act as a reducing and oxidizing catalyst. This type of catalytic substance mainly reduces nitrogen oxides and oxidizes unburned hydrocarbons during the combustion process in the working space of the cylinder.

Engine tests were carried out on a Fiat 1.3 JTD test bench with a common rail system, an Automex AMX 100 brake, an Automex fuel gauge, a MDO Maha smoke meter, and a Capelec exhaust analyzer. For the tests, rapeseed oil ester and hemp oil methyl ester were used. Tests were carried out on these fuels with and without catalytic additives. Exhaust emissions were measured in accordance with the Polish standard PN-EN ISO 8178-1. The following concentrations of toxic substances in exhaust gases were measured during the tests and nitrogen oxides, hydrocarbons, soot, and specific fuel consumption were calculated.

The results of the motor tests are shown in Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7 and Figure 8.

During the engine tests, the engine torque was measured directly (Figure 2). The engine power was calculated from relation (1), which is as follows:

$$N={\displaystyle \frac{Mx}{9554.14}}$$

(1)

The specific fuel consumption (Figure 3) was calculated from relation (2). Engine power and instantaneous fuel consumption are needed to determine this value.

$$g_e={\displaystyle \frac{3600x{G}_e}{N}}$$

(2)

Nitrogen oxides are formed during combustion in a compression-ignition engine at high temperature and pressure (Figure 4). Nitrogen reacts with oxygen to form nitrogen oxide (NO) and nitrogen dioxide (NO₂). Generally, during measurements the exhaust gas analyzer measures the total oxides of nitrogen and records them as NO_x. The mechanism for the formation of nitrogen oxide is shown in the Formulas (3) and (4):

$$N_2+O_2\to 2NO$$

(3)

Further oxidation of NO to NO₂ is shown by the following relation (6):

$$2\mathrm{N}\mathrm{O}+{\mathrm{O}}_2\to 2{\mathrm{N}\mathrm{O}}_2$$

(4)

Unburned hydrocarbons (UHCs) are formed as a result of the incomplete combustion of the combustible mixture in the cylinder (Figure 5). They form in oxygen-poor areas of the engine compartment where low temperatures are present. The reason for the increased UHCs content may be the poor mixing of the fuel and air. Polycyclic aromatic hydrocarbons are one of the most harmful pollutants found in exhaust gases. The hydrocarbons in the fuel undergo pyrolysis and oxidation, giving off light hydrocarbons. They participate in secondary reactions leading to the formation of monocyclic aromatic compounds. These are formed by the addition of C₂H₂ molecules and ring cyclization. The hydrocarbons leave the combustion chamber as gases, vapors, and aerosol condensed and absorbed in soot particles. The mechanism for the formation of these compounds can generally be written using relation (5), which is as follows:

$$C_n{H}_m\to UHC$$

(5)

Exhaust gas smoke was measured in the Hartridge scale as a function of the k-factor of light transmission in the measuring chamber of the smoke meter, the unit of which is [^m−1]. The main components of soot are carbon and hydrogen (0.5–3%). The mechanism of soot formation during combustion is complex, as the chemical processes of soot nucleation and the physical processes of soot particle formation are involved (Figure 6). The factors in the formation of soot are as follows: oil droplets burn in a diffusive manner, where pyrolysis of hydrocarbons and dehydrogenation of aromatic hydrocarbons takes place by expanding their structure with increasing carbon atoms. General relationship for soot formation in exhaust gas is as follows (6):

$$C_n{H}_m+O_2\to C+H_{2}O+CO+UHC$$

(6)

Carbon dioxide is produced in the engine compartment by the oxidation of hydrocarbons (7) and carbon monoxide (8) during the combustion process, which can be shown as follows:

$$C_n{H}_m+O_2\to {CO}_2+H_2$$

(7)

$$CO+OH\to {CO}_2+H$$

(8)

The results of cetane number measurements and ignition delay value calculations are shown in Figure 8.

The cetane number determines the self-ignition capability of fuels. The higher the cetane number, the better the self-ignition behavior of the fuel. Its magnitude influences the activation energy of fuels and the auto-ignition delay period.

The auto-ignition delay period is the first stage of the combustion process in CI engines (Figure 9). It is sought to keep the delay period as short as possible because it affects the subsequent stages and the formation of toxic compounds in the exhaust gas.

3. Discussion

The combustion of a combustible mixture in the working space of a cylinder is a complex fast-moving chemical reaction accompanied by significant heat release. The heat of combustion of the air–fuel mixture is the result of the oxidation of the particles contained in the fuel with the oxidizer and the formation of the corresponding combustion products such as nitrogen oxides, soot, unburned hydrocarbons, carbon dioxide, and carbon monoxide. However, in the following work, carbon monoxide emissions were not considered due to their very low content in the exhaust gas. The combustion process in a CI engine is influenced by the physical and chemical properties of the fuel. The physical ones include viscosity, density, and surface tension. These parameters affect the flow of the liquid through the atomizer and the formation of the fuel jet in the engine combustion chamber. The chemical properties of the fuel describe the composition and structure of the particles. They influence the auto-ignition delay period through the activation energy value E_a, which can be shown as follows (9):

$$E_a={\displaystyle \frac{618.840}{LC+25}}$$

(9)

An analysis of Equation (9) reveals that energy activation is closely related to the cetane number of the fuel. The cetane number represents the percentage of cetane (C₆H₃₄) in a mixture with α-methylnaphthalene (C₁₁H₁₀) in a reference fuel that exhibits combustion characteristics equivalent to those of the tested fuel. Cetane molecules, characterized by long carbon chains with relatively weak bonds, are prone to rapid decomposition and early participation in pre-ignition reactions. In contrast, α-methylnaphthalene possesses a compact molecular structure with strong carbon–carbon bonds, rendering it less reactive and requiring higher activation energy and having a longer ignition delay for spontaneous combustion to initiate [33]. The concept of activation energy in the context of reciprocating internal combustion engines is crucial for understanding reaction kinetics. For a chemical reaction to occur, molecular collisions must possess sufficient energy. However, not all collisions result in a reaction; if they did, all reactions would occur instantaneously. Chemical reactions proceed at finite rates, indicating that only a fraction of effective collisions have enough energy to overcome the activation barrier. Energy activation represents the minimum energy required for reactant molecules to undergo successful chemical transformation. Lower activation energy corresponds to a higher rate constant, thereby accelerating the overall reaction rate. Analyzing relation (10), the auto-ignition delay depends on parameters such as c_m engine speed, temperature T₂, and pressure P₂ in the combustion chamber and the value of the activation energy. Decreasing the value of E_a shortens the auto-ignition delay period. This stage significantly influences the combustion characteristics, velocity, and pressure temperature build-up in the cylinder working space, which directly affects the operating and environmental performance of the compression-ignition engine. The aim is to keep the ignition delay as short as possible. This is represented as follows:

$${\tau }_s=(0.36+0.22\cdot c_m)\cdot \exp [E_a({\displaystyle \frac{1}{R{T}_2}}-{\displaystyle \frac{1}{17.19}})\cdot {({\displaystyle \frac{21.2}{P_2-12.4}})}^{0.63}]$$

(10)

The exact course and stages of combustion have been described by the author in paper [32] and monograph [33]. A simplified combustion scheme in internal combustion engines can be represented by the diagram in Figure 10.

The phenomenon of catalysis and the action of the catalyst involve the conversion of one higher activation energy (without the catalyst) into two, or more, lower activation energies. This means that the pathway from substrates to products is converted into a catalyst-mediated sequence of elementary reactions with low activation energies of the individual steps, resulting in an acceleration of the chemical reaction and a shorter self-ignition delay period [34].

The homogeneous eco fuel shot catalyst is a chemical based on the empirical formula C₅H₅FeC₅H₄COC_mH_n. Engine tests showed that the engine behind-powered with modified vegetable fuels showed significantly lower emissions of nitrogen oxides and hydrocarbons over the entire speed range. The catalyst in the fuel is decomposed into active iron forms because of high temperatures, which trigger reduction and oxidation reactions during the combustion process. The nitrogen oxide reduction process consists of the following three steps: the reduction of nitrogen dioxide to nitrogen oxide, the reduction of nitrogen oxide to the nitrogen molecule N₂, and the catalyst regeneration process. The post-reduction products during the reduction reaction are nitrogen, carbon dioxide, and water. Carbon dioxides are the products formed by incomplete combustion of a combustible mixture. The catalyst oxidizes them to compounds such as carbon dioxide and water. Under the influence of the temperature prevailing in the combustion chamber, ferrocene undergoes partial decomposition and oxidation. Free radicals that are formed from ferrocene particles cause chain reactions with unburned hydrocarbons. These reactions result in the formation of carbon monoxide and carbon dioxide. Iron is an oxygen carrier, so it supports the oxidation of carbon monoxide to carbon dioxide. The catalytic substance causes faster oxidation and lowers the ignition temperature of hydrocarbons. Similar chemical reactions occur during the oxidation of soot, which is oxidized to carbon dioxide [35,36].

According to the manufacturer, eco fuel shot contains an active ingredient that reduces the surface tension of carbon, resulting in complete combustion of soot and naphthalene. However, studies have shown that the soot and carbon monoxide content of the exhaust gas is at similar levels for fuels with and without a catalyst. The combustion process of the combustible mixture is influenced by the physico-chemical properties of the fuel. Addition in the form of a catalyst mainly changes the chemical properties of the fuels (LCs). When analyzing the course of the combustion process, these properties mainly affect the formation of mainly nitrogen oxides and partly hydrocarbons and carbon oxides in the exhaust gas. In contrast, the formation of particulate matter is influenced by the physical properties of fuels such as surface tension, viscosity, and density. These parameters improve the properties of the fuel injection process into the engine compartment, such as the velocity, opening angle, width, atomization, range, homogeneity, and temperature of the injected fuel jet. It is these properties that influence the processes of evaporation and the mixing of fuel vapor with oxidant that take place during the auto-ignition delay period. The formation of soot particles in the flame is preceded by complex chemical processes. Hydrocarbon fuels burn at a temperature of around 2000 K. Under these conditions, the rate of reaction exceeds the rate at which the substrates, i.e., fuel and oxygen, enter the flame. The burning rate of the fuel droplet, which is equal to the evaporation rate of the fuel, depends on the diffusion of oxygen into the flame. The parameters of the flame depend on the stoichiometry of the reaction and the proportion of oxygen in the gas medium surrounding the droplet. Research has shown that the fragmentation of the liquid jet and the size of the injected droplet affect the particulate content of the exhaust gas.

4. Materials and Methods

The tests presented in the paper were carried out in several stages. Preparation of the rapeseed oil methyl ester (Figure 11A) and hemp oil methyl ester (Figure 11B) used as fuels can be seen. In the next step, a mixture of hemp oil methyl ester and rapeseed oil fuels was prepared with a catalyst additive. The proportion of catalysts in the fuel is the same as for standard diesel: 1 L of catalyst per 50,000 L of biofuel.

The next stage of the laboratory tests was to measure the cetane number of the vegetable fuels and the same fuels with the catalytic additive (Figure 12). The laboratory analysis was carried out as follows. The test fuel is compared with a reference fuel using a special single-cylinder reference engine, the compression ratio of which is varied during operation until a specific auto-ignition propensity expressed by the ignition delay is reached.

The final stage of testing involved engine testing (Figure 13).

The engine tests were carried out exactly as in the paper [32]. The engine tests were conducted at the measurement station equipped with a Fiat 1.3 JTD engine featuring a common rail system, an Automex AMX 100 brake (ODIUT Automex Sp z o. o., Gdańsk, Poland) (Figure 10), an Automex fuel meter (ODIUT Automex Sp z o. o., Gdańsk, Poland), a MDO Maha smoke meter (MAHA, Haldenwang, Germany), and a Capelec exhaust gas analyzer (Capelec Group, Montpellier, France), which meets the latest European requirements for MID (Measuring Instruments Directive) with the highest accuracy class of 0. External characteristics were conducted at full engine load for each rotational speed. During the studies, the parameters of the engine running on standard and modified fuels were compared. The results of measurements with the catalyst fuel were referenced to the measurements on standard fuel under the same conditions.

5. Conclusions

Analyzing the results of the tests carried out, it can be concluded that the catalytic additive mainly reduces toxic substances such as nitrogen oxides and hydrocarbons and, in the low- to medium-speed ranges, carbon dioxide. In contrast, it has no effect on soot emissions in the exhaust gas or engine operating parameters. Laboratory results showed that the catalytic additive increases the cetane number of the fuel, which reduces the auto-ignition delay period. Analyzing the results of the tests carried out to reduce soot emissions in exhaust gas, further research will be directed towards performing modifications to the fuel injectors. In the next stage, brake tests will be performed on an engine with modified injectors and fuel with a catalyst.