Experts are scrambling to find suitable replacement energy options, which have grown in importance due to rising energy needs and pollution. . A few environmental issues emerge because of the utilization energy sources in IC engines. Biodiesel is a fuel delivered from vegetable oils utilizing a couple of catalysts. Biodiesel is an alternative solution to the problem faced by most developing countries . Biodiesel has been select by many kinds of research as far as maintainability, financial, and environmentally friendly behavior . To produce sustainable biodiesel on a large scale, it is imperative to understand the advantage of utilizing minimal effort non-edible oil that can cut down the expense of delivering biodiesel . Rudolf diesel, with his engine powered by peanut oil, wrote, “The use of vegetable oil in diesel engine fuel may appear to be inconsequential now, but in the future it might turn out to be just as essential as conventional oil.” . It is notable that non-renewable energy sources are effectively approachable in a few locations around the globe. Several researchers have been making systematic effort to utilize plant oils as engine fuel. This will also lessen the need for fossil fuel and emission of harmful wastes into the atmosphere, because they are organic and emissions-less. The raw vegetable oils have the highest significance and exist as a promising substitute for fossil fuels . They have high viscosity, lower heat capacity, and are well known for gum formation, auto oxidation, and lower engine durability. Without any changes to the engine, the use of these oils may lead to poor performance and engine damage. Contamination forms and adheres to piston rings due to the direct usage of vegetable oil. It will be necessary to put in place some preparatory activities in order to make vegetable oils a viable fuel. Several methods are available for making vegetable oils usable, Among these, transesterification is the most popular method of extracting biodiesel.
In a previous study, the palm and jatropha biodiesel are extracted from the transesterification process. The combination of palm biodiesel and jatropha biodiesel each 5% when mixed with 90% of diesel and palm biodiesel and jatropha biodiesel each 10% when mixed with 80% of diesel gave better performance when compared with other tested fuel. These two fuels blend shows slightly increased brake specific fuel consumption (BSFC) then correlated with diesel. Apart from this the emission characteristics have been reduced mainly because of more injection of fuel through the inlet manifold. The oxides of nitrogen (NOx) and hydrocarbon (HC) emission for blend of palm and jatropha biodiesel each 5% mixed with 90% of diesel were decreased by 9.53% and 3.69%, respectively, when used in conjunction with mineral diesel fuel. The carbon monoxide (CO) and carbon dioxide (CO2) of blend palm and jatropha biodiesel each 5% mixed with 90% of diesel were decreased by 20.49% and 5.69%, respectively, when used in conjunction with mineral diesel fuel due to the proper combustion and shorten ignition delay .
The rape seed oil was separated by transesterification process and mixed with 80% and 90% of base fuel and fuel mixes were prepared, such as B10 and B20, respectively, at a different speed to run the base diesel engine. At 1800 rpm the mix B10 demonstrated the diminished BSFC when contrasted with the diesel fuel due to the lesser heating value and improved the ignition process. The emission of CO and HC were cut down when the fuel blends of B10 were used at 75% of load condition at 3000 rpm, owing to the oxygen concentration of biodiesel and appropriate ignition timing. This is mainly due to proper blending of air–fuel through the ignition procedure .
The rapeseed oil and mahua oil were mixed equally and a new biodiesel was prepared and this biodiesel has been mixed with the various proportion of diesel having varying percentage of 20%, 40%, 60%, and 80%, respectively. The blend B20 gave the superior performance and this value near to the base fuel diesel. The brake thermal efficiency (BTE) was decreased by 2.79%, when used in conjunction with mineral base fuel due to the inferior CV and greater viscosity. The emission of CO, smoke opacity, and HC were decreased by 20.66%, 6.9%, and 8.56%, respectively, individually when contrasted with perfect diesel fuel owing to the full combustion and shortened ignition delay. The concentrations of NOx were found to be more by 3.71% with B20, when contrasted with slick diesel fuel due to higher temperatures produced obtained during the combustion process .
In this investigation, the sunflower and soybean oil were mixed 50% equally and new biodiesel has been prepared. It is mixed with various proportions of diesel preferably 10%, 20%, and 30%, respectively. The blends showed slight decrease in cylinder pressure and HRR by 8.1% and 7.2%, respectively, when compared with neat diesel fuel, because of the lesser CV and lower ID. The CO concentration was decreased by 33.8% when contrasted with flawless diesel fuel due to better combustion and lesser IT. When compared to pure diesel fuel, the HC emission was shown to be reduced using the B30 fuel mix. The NOx and BSFC were increased by 0.98%, 2.5%, and 11.43% with the fuel bend B30 when compared with the neat base fuel. It is owing to the higher ignition delay and lack of oxygen availability of the biodiesel .
Nowadays, many studies have been done focusing on biodiesel with some antioxidant agents like BHT, BHA, n-butanol, n-octanol, and so on, to improvement performance and decreased emission attributes of the diesel engine. When using the antioxidants there is a drastic decrease in NOx and slightly increase in BTE.
In this investigation, Calophyllum inophyllum was chosen as the biodiesel, mixed with antioxidants, preferably BHT 500 ppm of dosage, and nanoadditives of titanium oxide of 100 ppm dosage and was used in the direct ignition diesel engine. The inclusion of nanoparticles and BHT into the fuel showed slight increase in BTE by 4% and 2%, respectively, then correlated to the neat diesel fuel due to the oxygen availability in the nanoparticles and higher the density of the fuel. The CLME with BHT of fuel blend showed increase in emission of HC and CO by 35% and 12.76%, respectively, when compared with pure C100 due to the availability of free radical surface and decreased oxidation of HC. The NOx concentration was drastically reduced by 11.85% when adding the antioxidants (BHT) with the fuel, when compared with other tested fuels due to the oxidation during the combustion process .
In this study mahua oil extracted by transesterification process was mixed with the antioxidants (BHT) in various proportions, such as 5%, 10%, and 15%, and was then used for investigation. The BTE was found to be slightly increased by 3.42% with the blends B85, when contrasted with the raw diesel fuel. The blend B85 showed a decrease in HC and smoke opacity by 37.63% and 2.65%, respectively, when contrasted with the mineral fuel, because of the greater oxygen content available in the fuel and proper combustion. The concentration of NOx and EGT were found to increase in the B85 blend by 45.87% and 27.33%, respectively, when contrasted with diesel fuel, this was mainly because of the high temperature produced during the combustion process .
The coconut biodiesel extracted by the transesterification method is mixed with the antioxidants such as BHT and BHA at a dosage of 2000 ppm and used for investigation. The results showed significant decrease in NOx and slightly increase in BTE. Addition of BHA in B20 blend showed drastic decrease in NOx by 7.78%, when correlated with the base fuel, because of phenolic hydroxyl present in the antioxidant and oxygen availability in the biodiesel. The blend B20 with BHA showed decreased emission of CO and smoke opacity by 18.39% and 32.43%, respectively, when correlated with neat base fuel mainly due to the oxygen availability and also due to increase in the C–C bond. The B20 blend containing BHT showed highest HC emission of 27.65%, when correlated with diesel fuel, mainly due to the free radical formation .
In another study, the Annona biodiesel and three different antioxidants agents like p-phenylenediamine (PPDA), alpha-tocopherol acetate (AT) and l-ascorbic acid (LA)were investigated. The antioxidants were used in a different dosage of 50, 150, 250, 350, and 450 mg and mixed with biodiesel. It was found that all the antioxidants when mixed with the biodiesel showed slight decrease in emission of NOx. Among all the dosage of antioxidants, 250 mg showed a significant decrease in NOx by 24.7%, 22%, and 23.8%, respectively, when compared with base fuel, and this is mainly due to the greater cetane number and lesser ignition delay and oxygen availability in the biodiesel. Finally, the results concluded that biodiesel containing 250 mg of PPDA showed drastic reduction in NOx, when correlated with the other two antioxidants .
The researchers are also focusing on diesel engine parameters like injection timing, injection pressure, and so on. When using antioxidants mixed with B20 during the injection timing there was a significant decrease in NOx improvement in the performance of the engine, and also improvement in combustion, when compared with the normal base engine.
In another study, the Syzygium cumini oil containing biodiesel was used and experiments were performed at different injection timing and pressure. The blends tested were B30, B70, and B100 to operate the diesel engine. The blend B30 and diesel increased the BTE by 16.68% and 17.85%, respectively, when the injection timing was 21oCA bTDC. When the injection timing was increased, the emission of HC and CO in the blend B30 was decreased by 46.15% and 15.9%, respectively, when compared with other test fuels. In advanced injection timing greatly reduced the smoke opacity emission by 28.7% in B30 blend, when compared with other test fuels. During the advanced injection timing NOx emission was high, when compared with the normal diesel engine. There was a remarkable reduction in emission of harmful wastes when the injection timing was increased .
In another study, the idea was to vary injection timing of the base engine to reduce the NOx emission. By delaying injection to 21oCA bTDC from the usual 24oCA bTDC, the hybrid biofuel (jatropha oil and rubber seed oil) was utilized in a single-cylinder base engine. Along with pure diesel fuel, B20 (biodiesel-20 percent), B40 (biodiesel-40 percent), and B60 (biodiesel-60 percent) mixes were utilized. By using this hybrid biofuel, this study article demonstrated the effect of injection time modification in a base engine. The experiments examined the performance and emission characteristics of BSFC, NOx, CO, and unburned hydrocarbon (UHC).It was found from the results that SFC for B20 blend was lesser than for raw base fuel, while B40 and B60 blends had slightly increased values but were similar to the B20 blend. It was also seen that the CO and UHC) emissions were decreased by increasing biodiesel blends in the fuel mixture, but NOx emissions were higher by increasing biodiesel blends in the fuel mixture .
For their study, the authors used mineral oil, gasoline, biodiesels, and various alternative fuels. When the diesel fuel exhibited improved injection timing was seen that BTE was greater with diminished fuel consumption and minimal HC and CO emissions. However, NOx emission was found to be higher. Retarded injection time resulted in a reduction in cylinder pressure, which further led to reduced peak temperature resulting in decreased NOx emission. During the retarded injection timing, the fuel injection happened slowly because of which the duration of combustion and cylinder peak pressure were lowered. Due to this reason fuel efficiency was also reduced. On the contrary, advanced injection timing enhanced the combustion process and the fuel efficiency was also higher. It was also found that oxidation capacity was increased with increased cylinder temperature. It further resulted in a decreased O2, carbon (C), CO, and HC emissions and EGT. Normally, diesel–biodiesel fuel blends gave higher HC and CO emissions. However, in the case of retard injection timing the NOx emissions were minimized .
In this study, the diesel is mixed with n-octanol with various percentages of 10%, 20%, and 30%, respectively. The experiments also used EGR at a rate of 10%, 15%, and 20% with injection timing advanced and retarded conditions. The best position of brake thermal efficiency is obtained by diesel with a blend of 10% n-octanol in 10% EGR at 23oCA bTDC. There is the simultaneous reduction of smoke, NOx, and CO of blend diesel with 10% n-octanol + 10% EGR in advanced injection timing of 47.77%, 21.08%, and 18.76%, respectively, due to the antioxidants agents its react as a catalyst more oxygen content available in the antioxidants proper combustion takes places and shorten ignition delay .
The novelty of work is clear from the above literature review that the various additives added to biodiesel led to improved efficiency and decreased harmful environmental emissions. The modification of the injection timing and the introduction of the fuel additives resulted in the diesel engine with superior output and emission characteristics. The present work was conducted with various injection timings such as 21oCA bTDC for retardation, 23oCA bTDC for standard and 25oCA bTDC for advanced. The mahua biodiesel is mixed with the diesel and additives, they are prepared the three blends for investigation of M100 (mahua raw oil), M20 (mahua oil 20 vol.% + diesel 80 vol.%) and NBM (mahua oil 20 vol.% + diesel 80 vol.% + n-butanol 30 vol.%). These blends are used in the current investigation with varying injection timing (advancing and retardation) and then compared with mineral diesel fuel.
Table 7 shows that the comparison of various ignition timing for different fuel blends from the previous literature survey. The table uses two arrow symbols, one is upward arrows and the other one is downward arrow. The upward arrow symbol indicates increased performance and emission characteristics while the downward arrow symbol indicates decreased performance and emission characteristics.
Table 8 shows the comparison of different antioxidants used in diesel engines with different fuels. The table uses two arrow symbols, one is upward arrow and the other one is downward arrow. The upward arrow symbol indicates increased performance and emission characteristics and downward arrow symbol indicates decreased performance and emission characteristics.