1. Introduction
Today, manufacturers can meet the requirements for oils and lubricants used in industry thanks to modern additives. Currently used base oils are only the main component, while additives that improve the lubricating properties of greases are chemical compounds involved in tribochemical reactions. They can be divided into anti-seize, anti-wear and friction modifiers [
1,
2,
3]. Lubricating oils are being subjected to increasingly stringent requirements, as less oil is now used in machinery and equipment, but at higher pressures and higher thermal loads. Therefore, modern equipment requires only the highest-quality oils. One way to meet these requirements is to use nanoparticles, which are of great significance to control friction and wear [
4,
5,
6,
7].
Otherwise, oil additives improving the properties of lubricants have been used for a long time, and despite this, research is still being carried out to improve the new additives being used [
8,
9]. Despite the addition of a number of different enriching agents, the problem of preventing or slowing down the microbiological decomposition of petroleum products is still an ongoing one. This is because many species of bacteria or fungi have the ability to grow in petroleum products, which are a source of carbon and energy. Therefore, the vital activity of microorganisms breaks down hydrocarbons and oil additives and releases water, sulfur compounds and surfactants into fuels as well aslubricating oils [
10,
11]. The result is changes in the chemical composition of petroleum products and the values of certain physical parameters, such as the flash point, acid number and viscosity.
With the proper operation of an internal combustion piston engine, the deterioration of its technical condition is mainly caused by all kinds of mechanical and chemical contaminants, i.e., foreign solids and chemically active substances that cause corrosion.
Such contaminants are partly a natural residue of petrochemical processes, and they partly get into oils during distribution (transport, storage and transfer). The harmfulness of mechanical impurities in lubricants is mainly due to their hardness and compressive strength [
12,
13,
14]. Microbial contamination is a serious problem in petroleum products, which include automotive, aviation and marine fuels; transformer and engine oils; as well as lubricants and oil emulsions. With the development of industry and the broader automotive industry, including aviation and ships, it has become apparent that the problem of microbial contamination is still relevant and becoming more widespread. Studies have shown that microbial life activity can lead to disruption and even damage to internal combustion engines [
3,
15].
Good-quality oil must be clear and transparent. Microbial growth can often contribute to clouding and darkening. The most obvious and easily recognizable consequence of microbial activity is the formation of sludge visible in the form of particulate matter, which are a mixture of living and dead cells and inorganic by-products [
8,
16].
In addition to environmentally friendly lubricating oil additives, there is parallel research into alternative fuels. One way is to use oxygenated alternative fuels in diesel engines. According to the authors [
17], they are an effective way to solve the energy crisis and environmental pollution. Higher alcohols (butanol and pentanol), as oxygenated and renewable fuels, are considered promising new alternative fuels for diesel engines due to their good physicochemical properties and excellent combustion and emission characteristics in engines.
Dimethyl ether (DME, H3C-O-CH3) is another solution being researched to find alternative fuels that are expected to have a positive impact on the environment. It has a comparably high energy density and can be easily stored in vehicles. In addition, it can be produced on a variety of renewable paths, has a high cetane number and is therefore suitable for use in efficient and durable compression ignition engines [
18].
Continuous research is being carried out to develop engines and fuels in such a way that very few harmful emissions can be generated and released into the environment without significant environmental impact. Accordingly, researchers are testing promising components for the production of environmentally friendly high-octane motor gasoline. Gasoline octane enhancers include bioethanol, prenol, furan blends, dimate and isooctene (diisobutylene) [
19].
In addition, the effects of diesel/ethanol/n-butanol blends on combustion and emission parameters such as cylinder pressure, cylinder temperature, brake power, brake thermal efficiency, specific fuel consumption, NO
x emissions, CO emissions and soot emissions were examined [
20].
Other researchers [
21] are conducting research to achieve the best performance, combustion and emissions of a marine engine fueled by hydrogen (5%, 10% and 15% energy fractions), water (2, 4 and 6% by weight) and a blend of rapeseed methyl esters (RMEs) through multi-objective optimization.
Current oil problems, rapidly rising oil costs and uncertainty about the availability of petroleum-based fuels threaten the renewable and sustainable challenge of the global economy. Both environmental considerations and the availability of fuels have a major impact on the directions of fuels for transportation vehicles. Therefore, the authors of [
22] analyzed the prospects for biodiesel production from hydrotreated vegetable oil (HVO) and fatty acid methyl esters (FAMEs) and their applications. They explored the potential for supplying biodiesel feedstock, including sunflower oil, soybean oil, canola oil, tall oil and used cooking oil. The results indicate that rapeseed oil is the most promising feedstock for biodiesel production, as rapeseed retains a higher yield growth potential, and oil hydrotreating is the most preferred option.
One of the methods currently used to control microorganisms in petroleum products is the use of biocides, which are pesticides used to, among other things, control or reduce the growth of microorganisms in petroleum products. Unfortunately, most biocides also destroy beneficial organisms and cause adverse changes in the composition of microorganisms. Despite a number of benefits from the use of biocides, there are currently strong trends limiting their use. This is due to concerns about the harmful effects of these highly concentrated substances on the environment [
23,
24,
25]. Therefore, one method of combating microorganisms, taking into account environmental aspects, is the use of effective microorganisms (EMs). EMs are used in horticulture, environmental protection, medicine, industry and many other fields with positive results.
The principle of EMs is based solely on natural processes; they are not genetically modified and are completely environmentally friendly. Effective microorganisms are most commonly used in water treatment, wastewater treatment and water reservoirs.
This technology is also used in garbage incinerators, which significantly reduces emissions of dangerous dioxins. In addition, another solution may be silver, which has long been used for protective and therapeutic purposes [
26,
27,
28,
29,
30,
31]. These additives were added in the form of non-ionic and ionic silver. Non-ionic silver, or colloidal silver, has a yellow color because silver particles dispersed in water block the light passing through it. Ionic silver is a solution of silver. Ionic silver is transparent, like water.
So far, the focus has been on chemical and physical tests of lubricating oil without and with these additives. Tests have been conducted on new and used oil. The most favorable results were obtained with effective microorganisms in the form of ceramic tubes, mainly due to the fact that in this case, the additive in this form does not contain water. In further studies, it is planned to test the oils for microbiology, which will allow a full evaluation of the possibility of replacing harmful biocides with these additives.
The purpose of this study was to determine the effect of ecological agents added to lubricating oil on selected performance parameters of an internal combustion engine. The idea was to check whether oils with ecological additives, as a result of improper lubrication, can have a negative impact on the operation and performance of a reciprocating engine. Further research is expected to answer the question of whether it will be possible to replace harmful biocides, such as ecologically effective microorganisms. Oil with these additives may have a beneficial effect on slowing microbial decomposition in lubricating oils used in internal combustion engines.
3. Results and Discussion
Before testing the internal combustion engine parameters and exhaust gas composition, each oil, starting with pure and then with each additive, was run in the engine under the same conditions. Each test lasted 100 h of engine operation not counting breaks, of which, 80 h were at idle and the remaining 20 h at 50% of the total load, which was 20 kW. After the oil was consumed over the assumed period, measurements were made of the engine operating parameters and exhaust gas composition. The obtained results were used to draw charts and then to evaluate the impact of environmental additives to lubricating oil on the technical condition of the studied engine. Each measurement of operating parameters and exhaust gas composition was performed three times. However, this article presents the average results for each case. They are presented in the form of tables and graphs.
In addition, in order to better illustrate the results obtained, the measured parameters and their values are summarized in
Table 4. The results of this work were read using a control and measurement system working with the running engine (
Figure 5) and a schematic of the test stand with the corresponding instrumentation.
The test stand does not reflect the conditions that occur during the operation of an internal combustion engine that is equipment for marine- and land-based transportation. There, the oil operates under a variety of conditions, the most difficult being those of urban and, in the case of marine vessels, maneuvering sailing conditions.
There is also no previous research on the topic discussed in the article, since the agents used in the oils under study are used, for example, in wastewater treatment (effective microorganisms) or the elimination of certain bacteria (silver ions). This may be a limitation, but this research was undertaken on the assumption that it is possible to reduce microbial growth in other liquids, such as water or wastewater, using effective microorganisms or silver ions. This assumes that such an effect can also occur in petroleum products.
Statistical analysis was performed for a significance level of 98%. The results obtained for the adopted significance level do not show significant errors, as they fall within the lower and upper confidence intervals.
Analyzing the results obtained, it can be seen in
Figure 6 that the lubricating oil temperatures for both the 0 kW and 20 kW load for pure oil and oil with additives are very close to each other. A temperature of 77 °C was obtained for idling and pure lubricating oil, with the same temperature obtained after using effective microorganisms in liquid form and colloidal silver. A lower temperature of 76 °C was obtained for effective microorganisms in ceramic tube form and silver solution. Increasing the load to 20 kW increased the temperature of the lubricating oil and, as for idling, the temperatures for pure oil, effective liquid microorganisms and colloidal silver were similar at 80 °C. In contrast, effective microorganisms in ceramic form and silver solution reduced this temperature to 78 °C.
Figure 7 shows the lubricating oil pressure for idle, that is, 0 kW and a load of 20 kW. For pure oil and idling, a pressure value of 4.05 bar could be read; for oil with additives, slightly higher values were obtained. For effective microorganisms in ceramic form and silver solution, 4.07 bar was obtained, and for silver solution—4.08, and the highest value was obtained for liquid effective microorganisms of 4.13 bar.
As for temperature, increasing the load resulted in an increase in system pressure. The same pressure value was obtained for pure oil and silver solution, which was 4.27 bar. For effective microorganisms in the form of ceramic tubes and colloidal silver, 4.25 bar was obtained, while the lowest pressure reading was 4.23 bar. The values obtained are similar enough for this load to conclude that they show a significant effect on lubricating oil pressure, neither positive nor negative.
The temperature of oil rises when its parameters are inappropriate for the engine or when the engine is overloaded. In this case, there were no such effects. The oil pressure values also confirm that the oil additives did not adversely affect the engine’s operation, as the absence of excessive pressure increases means that the oil filter was working properly and the oil parameters were within normal limits.
Only the addition of effective microorganisms in liquid form, due to their composition (mainly water and molasses), slightly affected the resistance of the filter, which may have contributed to a slight increase in oil pressure.
This occurred at idle, which was no longer observed when the engine was loaded. It is likely that engine load made the oil filter work more efficiently and had less effect on oil pressure. Other additives did not show such effects.
The graph in
Figure 8 for cooling water temperature also shows that additives, regardless of their type, have no negative effect on the engine’s cooling performance at idle (0 kW) and under load (20 kW).
Their presence in the oil did not cause overheating of the walls, as the effects were very similar to engine operation on oil without these additives.
The resulting temperature oscillated around the value of 76 °C. Each result did not differ by more than 2% compared to running the engine on pure oil. The largest increase occurred with the addition of effective microorganisms and colloidal nanosilver, but it was still not large enough to have a detrimental effect on the tested internal combustion engine.
Figure 9 shows, as with the previously presented parameters, that the additives did not adversely affect the engine’s condition. All the exhaust gas temperatures obtained were similar to each other, and the resulting differences were also within the previously accepted confidence interval.
The exhaust gas temperature was read for idling, with pure oil and silver solution at 325 °C. The use of effective microorganisms in liquid form and colloidal silver increased the exhaust gas temperature compared to pure oil to values of 332 and 330 °C, respectively. The lowest value was obtained for the effective microorganisms in the ceramic form, which was 318 °C. Of the additives used, in addition to the effective microorganisms in the ceramic form, they have water in their composition, which can somehow affect the performance of the lubricating oil. By doing so, it can affect the operating conditions of the internal combustion engine, which result in higher exhaust gas temperatures.
Because the other parameters were in the typical common confidence range, no negative effect on exhaust gas temperature, which is one of the carriers of diagnostic information of the internal combustion engine, was also noted.
As for instantaneous fuel consumption, this is shown in
Figure 10. It is also clear from this graph that the engine was running properly. All the results obtained confirm that each additive had a small effect on fuel consumption, as each result did not exceed 2% compared to the reading obtained for pure oil. For idling, it oscillated around a value of 9.7 L/h, while for a 20 kW load, the value was 9.9 L/h.
In addition to the selected performance parameters presented above, the effect of oil additives on exhaust gas composition was additionally measured. Due to the fact that the engine dates back to the last century (the production of this series of engines began in 1966), exhaust gas composition can be an important source of information about the engine’s technical condition [
40,
41,
42].
Figure 11,
Figure 12,
Figure 13 and
Figure 14 show the most important components of the exhaust gas in terms of toxicity. The tests were carried out at a load of 20 kW, after 90 h of engine operation. Each measurement was taken three times and, as with the performance parameters, the average of these measurements is presented in the article.
The diagrams shown are only supplementary, as oil combustion should not occur in a fully operational engine. In this particular engine, this phenomenon most likely occurred, hence the different behavior of the exhaust components when mixed with the additives.
Figure 11 shows the NO
x content in the exhaust gas. For pure oil, a NO
x content of approx. 717 ppm was obtained, while for the effective microorganisms, both in liquid and ceramic form, the amount of NO
x, stopped at approx. 715 ppm. After the silver solution was applied, the NO
x content dropped to 702 ppm, and colloidal silver caused a further drop in NO
x to 694 ppm.
Effective microorganisms have a negligible effect on NO
x reduction, while silver solution and colloidal nanosilver significantly reduce the amount of NO
x in the flue gas. This is particularly important and worthy of further research because NO
x gases react with oxygen in the atmosphere and ground-level ozone (O
3) to form corrosive nitric acid and toxic organic nitrates. The presence of these substances in the air causes serious human health problems and contributes to acid rain and the deterioration of water and air quality. In addition, these impaired environmental conditions negatively affect agriculture by killing plant tissues and reducing plant growth rates [
42]. If these results are confirmed in tests after the addition of silver to the fuel, the chemical reactions that may take place between silver ions and nitrogen oxides should be examined in order to reduce the emission of nitrogen oxides into the atmosphere.
Unfortunately, for other exhaust gas components, i.e., O2, CO and CO2, the obtained results are more different compared to NOx.
Figure 12 shows the carbon monoxide (CO) content for pure oil and oil with additives. For pure oil, the CO content was 294 ppm, while the amount of carbon monoxide increased slightly to 295 ppm when effective microorganisms were used. Colloidal silver resulted in the highest CO value of almost 296 ppm. The most beneficial addition was the addition of silver solution, which resulted in a decrease in carbon monoxide to 293 ppm.
Figure 13 shows the carbon dioxide content for lubricating oil without additives and with microbial and silver additives. The dependence of the content of this compound is similar to that obtained for carbon monoxide. For pure lubricating oil and silver solution, the carbon dioxide content was 4.94%, and effective microorganisms increased the content of this compound, for the ceramic form to 5.01% and for the liquid form to 5.06%. The most unfavorable result was obtained after the use of colloidal silver, for which the carbon dioxide content was 5.1%.
These results also confirm that the additives used do not cause engine deterioration, excessive fuel consumption or significantly increase exhaust gas toxicity. Further research is planned to add these environmentally friendly agents to fuel and investigate their direct effects on exhaust gas composition and engine fuel consumption.
To complement the results obtained, the article also presents a comparison of the kinematic viscosity of new and used oil with and without additives in
Figure 14 and
Figure 15. These graphs show the effect of each additive on the kinematic viscosity of the engine oil samples. Each sample of pure oil and oil with additives was tested three times from 40 °C to 100 °C. To determine the kinematic viscosity, the dynamic viscosity was read first. In addition, the density curve of the new oil over the same range is also shown. This density allowed the kinematic density to be determined. Analyzing the obtained results, it can be observed in
Figure 15 that the kinematic viscosity ofpure fresh oil was 77.42 mm
2/s at 40 °C and 12.95 mm
2/s at 100 °C.
The addition of effective microorganisms to oil in liquid and ceramic form followed a similar course, except that for the microorganisms in liquid form, the viscosity value washigher in the lower temperature range compared to the course with the addition of ceramic tubes.
The effective microorganisms caused a slight increase in kinematic viscosity in oil compared to oil without such an additive and wereequal for liquid effective microorganisms to 89.56 mm2/s at 40 °C and for ceramic tubes to 90.15 mm2/s at 40 °C. At 100 °C, we obtained, respectively: 15.75 mm2/s and 15.68 mm2/s.
As for the results obtained for colloidal nanosilver and silver solution, the courses werevery similar to each other, while the higher number of effective microorganisms resulted in an even higher value of kinematic viscosity than that obtained for pure new oil.
The value of the determined viscosity for the additive of colloidal nanosilver and silver solution at 40 °C was 92.65 mm2/s and 93.17 mm2/s, respectively, while for 100 °C—16.56 mm2/s and 15.43 mm2/s.
In addition, it can be seen from the graph that the kinematic viscosity closest to that of pure oil was obtained when ceramic micelles were added, so the behavior of the oil with ceramic tubes should be checked in further tests.
Figure 15 shows the variation inkinematic viscosity with temperature for the reworked and used oil samples, and also after the addition of microorganisms effective in liquid form, in the form of ceramic tubes and colloidal nanosilver and silver solution. To better visualize the results obtained, the density curve of the used oil was also shown. This density enabled the kinematic density to be determined. The viscosity curves are shown over a temperature range of 40–100 °C. The viscosity curve of the new oil has been added to better illustrate the results obtained. The kinematic viscosity value of the used oil without additives was 70.52 mm
2/s at 40 °C and 6.75 mm
2/s at 100 °C. The lowest viscosity value was obtained for the EM additive in liquid form, which means that this form of microorganisms does not have a beneficial effect on oil performance. For this additive, the kinematic viscosity was57.16 mm
2/s at 40 °C and 6.58 mm
2/s at 100 °C.
Similar values to those for used oil can be observed for ceramic tube oil and were 75.42 mm2/s at 40 °C and 6.43 mm2/s at 100 °C, respectively. The situation wasdifferent for the addition of colloidal nanosilver and silver solution. The values obtained for colloidal nanosilver were higher for both used oil and new oil without additives.
The following results were obtained for this addition: 85.08 mm2/s at 40 °C and 5.82 mm2/s at 100 °C. Meanwhile, for silver solution, the results were different and wereas follows: 63.92 mm2/s at 40 °C and 5.39 mm2/s at 100 °C. The results obtained for used oil confirm that the additives of effective microorganisms, colloidal nanosilver and silver solution affect the parameters of used oil. The best results were obtained for effective microorganisms in the form of ceramic tubes.
In order to confirm the obtained results, this article also presents selected other oil parameters, which are presented in
Table 5 and
Table 6. The tables compare the parameters of fresh and used oil without additives with oils in which effective microorganisms and silver compounds have been added. Also, analyzing the data from the tables, it can be concluded that ceramic effective microorganisms are the best additive for new oil. As for silver, they adversely affect the parameters of both new and used oil.
Further tests will also examine, among other things, the effect of additives on the elemental composition of the oil and whether there is rheological dilution under shear. These tests will verify whether molasses has a negative effect on engine oil performance.
4. Conclusions
This article presents a study of the effect of environmental agents added to lubricating oil on selected performance parameters of an internal combustion engine. In addition, some of the chemical compounds present in the composition of the exhaust gas are presented to supplement the results obtained.
Analyzing the results, it was found that the temperatures of pure and additive lubricating oil were very close to each other. A temperature of 77 °C was obtained for idle and pure lubricating oil, oil with the addition of effective microorganisms in liquid form and colloidal silver. A lower temperature of 76 °C was obtained for effective microorganisms in ceramic tube form and silver solution. Increasing the load to 20 kW raised the temperature of the lubricating oil and, as for idling, the temperatures for pure oil, effective microorganisms in liquid form and colloidal silver weresimilar at 80 °C. In contrast, effective microorganisms in ceramic form and silver solution lowered this temperature to 78 °C.
As for the lubricating oil pressure for idling, a pressure value of 4.05 bar could be read for clean oil and idling. Only the highest value was obtained for liquid effective microorganisms of 4.13 bar.
The oil pressure values also confirm that the oil additives do not adversely affect the engine’s operation, as the absence of excessive pressure increases means that the oil filter is working properly and the oil parameters are within normal limits.
Only the addition of effective microorganisms in liquid form, due to their composition (mainly water and molasses), slightly affected the resistance of the filter, which may have contributed to a slight increase in oil pressure. The other additives had no significant effect on oil pressure.
Regardless of the type of additives, it can be concluded that they did not have a negative effect on the cooling performance of the engine, both at idle and under load. Their presence in the oil did not cause overheating of the walls, as the results were very close to the operation of the engine with oil without these additives. The cooling water temperatures for each case were at a similar level, settling around values at 76 °C.
Additives also did not adversely affect the technical condition of the engine, as all obtained exhaust gas temperatures were similar, which are one of the carriers of diagnostic information of the internal combustion engine. These temperatures were close to each other, with idling temperatures oscillating around 325 °C and load temperatures around 500 °C.
As for instantaneous fuel consumption, the results confirm that the engine was running properly. Each of the additives had a slight effect on fuel consumption, as each result did not exceed 2% compared to the reading obtained for pure oil. For idling, it oscillated around a value of 9.7 L/h, while for a 20 kW load, the value was 9.9 L/h.
Effective microorganisms had a negligible effect on NOx reduction, while silver solution and colloidal nano silver significantly reduced the amount of NOx in the exhaust gas. This is particularly important and worthy of further research. For pure oil and effective microorganisms, both in liquid and ceramic form, NOx content was obtained, within the range of about 715 ppm. After the silver solution was applied, the NOx content dropped to 702 ppm; colloidal silver further reduced NOx to 694 ppm.
For pure oil, the CO content was 294 ppm, while the amount of CO increased slightly to 295 ppm after using effective microorganisms. Colloidal silver caused the highest CO value, which was almost 296 ppm. The most beneficial addition was the addition of silver solution, which caused the carbon monoxide content to drop to 293 ppm.
The carbon dioxide content relationship was similar to that obtained for carbon monoxide. For pure lubricating oil and silver solution, the carbon dioxide content was 4.94%; effective microorganisms caused an increase in the content of this compound, for the ceramic mold to the level of 5.01% and for the liquid mold to 5.06%. The most unfavorable result was obtained after using colloidal silver, for which the carbon dioxide content was 5.1%.
In conclusion, it can be said that the best additive is ceramic effective microorganisms for new oil. As for silver, itadversely affected the parameters of both new and used oil.
Based on the results, it can be concluded that the additives used, especially ceramic effective microbes, can be a good alternative to some of the current additives, which can contribute to environmental protection.
The results of the study are satisfactory and will continue, as they confirm that the additives used do not cause engine deterioration or excessive fuel consumption and do not significantly increase exhaust toxicity.
In the future, it is planned to add these environmentally friendly agents to fuel and study their direct effects on exhaust gas composition and engine fuel consumption. Further research will also include physical, chemical and microbiological tests of lubricating and diesel oils.
In addition to this, further studies will need to examine the effect of this additive on the combustion process in the engine and the wear of its components and confirm the results obtained under actual operating conditions.