In recent years, it is stated that the emission of pollutant emissions due to the increasing use of fossil fuel resources has increased, moreover, this situation has reached levels that will lead to a global climate change [1]. It is thought that most of the global air pollution is caused by machines using internal combustion engines [2]. Machines using internal combustion engines are used in many areas from the transport sector to the agriculture and health sector [3]. For this reason, countries impose certain limitations in order to reduce exhaust emissions from motor vehicles. Most researchers believe that these limitations can be overcome with the use of renewable energy sources. Therefore, they are working on the reduction of exhaust emissions by using vegetable or animal origin oils and alcohols in internal combustion engines [4–7].
Biodiesel has an important place in biomass-based fuels. It is an important alternative to petroleum, which can be produced by reacting a raw material with a biomass source with oil characteristics with alcohol. Biodiesel fuel is not dependent on a geography unlike petrol [8]. Biodiesel can be produced by growing plants such as soya beans, canola and safflower as raw materials [9]. In addition, biodiesel can be mixed with diesel fuel at any ratio [10]. The use of biodiesel is increasing with its high cetane number and low emission values. However, researchers mention the low emission values of biodiesel. Although this is considered to be a significant disadvantage, the improvement in exhaust emissions can compensate for the amount of fuel consumption [11].
In addition, as a result of the difference in the type of raw material used in biodiesel production, sometimes viscosity and density values are higher than diesel fuel [12]. In addition, the fact that biodiesel has a clouding and freezing point at higher temperatures than diesel fuel causes clogging of the flits of vehicles [13]. These reasons have led to increased research on the use of additives to improve the viscosity, density, cloud and freezing points of biodiesel. In addition, some researchers have stated that oxygen-containing additives improve the combustion characteristics of biodiesel and increase the combustion efficiency [14]. Xiao et al. [3] investigated the effects of 10%, 20% and 30% iso-butanol addition to pure biodiesel on engine performance and exhaust gas emissions. They reported that with the increase in the amount of iso-butanol added to biodiesel, the amount of evaporation and atomisation of fuel mixtures increased and this improved combustion. They stated that ignition delay and combustion time decreased with the increase in iso-butanol content in biodiesel. Compared to diesel fuel, in-cylinder pressure values increased with the addition of isobutanol. While NOx emissions increased, particulate emissions decreased with isobutanol addition. Huang et al. [2] investigated the effects of 10% and 20% methanol addition in pure soybean oil biodiesel to improve combustion efficiency. An increase in in-cylinder pressure values and heat dissipation rates were observed with methanol addition to biodiesel. An increase in HC emissions and a decrease in CO emissions were determined with methanol addition. Kumar et al. [15] investigated the effects of the addition of di ethyl ether and Cerium oxide (CeO2), a nano particle, to biodiesel obtained from waste oils on engine performance and exhaust gas emission values. They reported that the additives added to biodiesel increased thermal efficiency, reduced HC and soot emissions and partially increased NOx emissions. Kumar et al. [16] conducted a study to reduce the exhaust gases of biodiesel by adding solketal to biodiesel. For this purpose, 9%, 10%, 12% and 15% solketal was added to biodiesel by volume. They reported that solketal addition increased specific fuel consumption, increased NOx and CO2 emissions and decreased HC, CO and soot emissions. Chang et al. [17] added ABE (acetone-butanol-ethanol) to the fuel mixture to improve the combustion efficiency of the fuel mixture with biodiesel added to diesel fuel. It was reported that ABE addition to diesel/biodiesel fuel blend improved combustion efficiency and reduced NOx and polycyclic aromatic hydrocarbons (PAH) emissions. Şimşek and Çolak [18] investigated exhaust gas emission values and engine performance values by adding 10%, 20% propanol alcohol into biodiesel. They reported that propanol addition had a positive effect on engine power and fuel consumption values. They also reported that CO, NOx and soot emissions decreased and HC emissions increased with the increase of propanol ratio in fuel mixtures. Masera et al. [19] investigated the effect of 15% by volume addition of 2-Butoxyethanol into biodiesel produced from waste frying oil and rapeseed oil to improve the high viscosity and combustion properties of biodiesel on fuel properties, engine performance and exhaust gas emissions. They stated that the addition of 2-Butoxyethanol increased combustion efficiency and reduced exhaust gas emissions.
Nabi and Resul [20] carried out an exergy analysis using fuel blends obtained by blending pure diesel with waste cooking and macadamia (Macadamia integrifolia) biodiesel. They reported that total unburnt hydrocarbon (THC), carbon monoxide (CO), and particulate matter (PM) emissions decreased and NOX emissions increased in biodiesel/diesel fuel blends compared to pure diesel. In the study, it was explained that the highest exergy efficiency was obtained as 30%. Sekmen and Yılbaşı [21] conducted an experimental study on an engine using biodiesel and pure diesel fuels and compared these fuels by exergy analysis. They reported that the exergy efficiencies of biodiesel and diesel fuel were obtained as 28.94% and 27.52%, respectively. When the energy distribution in biodiesel was analysed, it was explained that exergy destruction was 47%, useful work 28.95%, exergy loss due to heat transfer 7.3% and exhaust exergy 16.7%. Odibi et al. [22] evaluated waste cooking biodiesel and diesel fuels by exergy analysis. It was explained that waste cooking biodiesel showed the lowest exhaust loss rate and 6% higher thermal efficiency than pure diesel fuel. It was reported that a very high exergy destruction of 55% occurred as a result of the use of waste cooking biodiesel. Yeşilyurt and Arslan [13] produced biodiesel from a mixture of waste cooking oil and canola oil and performed exergy analysis. It was reported that the maximum exergy efficiency was 20.52% when biodiesel was used as fuel in the engine. In addition, the exergy destruction of biodiesel fuel was calculated between 58.9% and 62.8%.
In their study, Paul et al. [23] used ternary fuel blends obtained by using diesel, ethanol and pongamia pinata methyl ester (PPME) fuels in different ratios. It was stated that exergy efficiency increased with increasing engine load in all fuel blends. It was explained that the highest exergy efficiency was obtained as 31% in D35E15B50 fuel. It was stated that D35E15B50 fuel showed 22.02% reduction in exergy destruction rate and 21.06% reduction in entropy production rate compared to pure diesel fuel. Madheshiya and Vedrtnam [24] conducted an experimental study using biodiesel obtained from waste cooking oil/mustard oil and pure diesel fuels. Exergetic evaluation of these fuel blends was carried out using the results obtained in the experimental study. It is reported that biodiesel fuels show significant energy performance when used as an alternative to diesel fuel. It is stated that the cooling water exergy of WCO30 fuel is 5% higher than that of pure diesel fuel. Kul and Kahraman [25] conducted experimental studies using diesel, biodiesel and bioethanol fuels in different ratios in a compression ignition engine. Exergy analysis was performed using the results obtained in the experimental study. At 1400 rpm engine speed, the maximum thermal efficiency was 31.42% for D100 fuel and 28.68% for D92B3E5 fuel. Hoseinpour et al. [26] carried out an exergy analysis with the data obtained from tests on a compression ignition engine using waste cooking oil biodiesel and diesel blends. It was reported that thermal and exergy efficiencies increased with increasing engine load for all fuel blends. The highest exergy efficiency was calculated as 42% for B20 fuel at 6 bar pressure. Sanli and Uludamar [27] carried out an exergy analysis in a diesel engine using pure diesel, biodiesel obtained from hazelnut oil and biodiesel obtained from canola oil. The lowest exergy destruction in canola biodiesel was 47.41% at 1800 rpm engine speed. At the same engine speed, the lowest entropy production was 0.15 kW/K in canola biodiesel. Khoobbakht et al. [28] investigated the exergy efficiency at different engine speeds using triple fuel blends using diesel, biodiesel and ethanol fuels. According to the results of the energy and exergy analyses obtained in the study, it was reported that 43.09% of the fuel exergy was destroyed and the average thermal efficiency was approximately 36.61% and the exergy efficiency was approximately 33.81%.
In the literature summary, it was observed that researchers have focused on the effects of additives added to the fuel in order to improve the fuel properties of biodiesel. In addition, it has been determined that the mixing of oxygen-rich (butanol, ethanol, methanol, etc.) or solvent (heptane, hexane, di ethyl ether) chemicals into biodiesel is effective on exhaust gas emissions and engine performance characteristics. Solketal is an oxygen-rich fuel and butyl diglycol is a solvent with high calorific value and cetane number. Limited research has been conducted on the effect of solketal and butyl diglycol addition to biodiesel fuel on performance, combustion and emission characteristics.
In addition, studies on biodiesel have reported that 20% biodiesel blend to diesel fuel (D80B20) produces the most favourable results in terms of engine performance, fuel consumption or exhaust gas emissions [29, 30, 31]. In this study, it is aimed to increase combustion efficiency and reduce harmful exhaust emissions by adding various additives to the D50B50 fuel obtained by adding a higher ratio (50%) of biodiesel to diesel fuel. In addition, it has been determined that energy and exergy analysis studies have not been carried out to evaluate the effects of solketal and butyl diglycol additives on engine performance characteristics as alternative fuels in internal combustion engines. For this purpose, in the present study, fuel blends were prepared using diesel, canola biodiesel, solketal and butyl diglycol at different ratios (D100, D80B20, D50B50, D30B50S20 and D30B50G20) and their effects on engine performance characteristics were investigated in detail. The engine experiments were repeated for each fuel blend in a single cylinder compression ignition direct injection engine at 3000 rpm engine speed under engine loads of 1.6 Nm, 3.2 Nm, 4.8 Nm, 6.4 Nm, 7.9 Nm, 9.5 Nm and 11.1 Nm. During the engine experiments, in-cylinder and fuel line pressure values, exhaust emission values, brake specific fuel consumption and exhaust gas temperature values were recorded. In addition, energy and exergy analyses were performed using the data obtained from the experimental studies.