Introduction

Petroleum being the most dependable and potent energy source for both industries and the transportation sector, is being extensively used1,2,3. Due to over-dependency on fossil fuels and population explosion, rapid industrialization, and urbanization, there is fear of its extinction. Additionally, the burning of fossil fuels emits harmful toxic gases which are hazardous to the environment, resulting in the greenhouse gas effect, global warming, and depletion of the ozone layer. Thus, it has become essential to develop alternate fuels that are environmentally benign, cheaper, and minimize energy usage4. The dwindling oil and gas reservoirs and rise in pollution due to population explosion have compelled the humankind to look for alternative, renewable clean fuel. With the current “sustainable development” concept advanced as well as emergent nations have focused on utilizing sustainable fuel resources for environmental protection. Coal, oil, and natural gas—fossil fuels—have long been vital to the development of industrial society in the modern world. However, their widespread use has given rise to a growing concern: the depletion of these finite energy resources. Fossil fuel depletion refers to the gradual exhaustion of these invaluable energy reserves, a process accelerated by escalating global energy demands. As we delve into the challenges and consequences of this depletion, it becomes clear that sustainable alternatives are not merely an option but a necessity for an assured and environment-friendly energy future. Embracing a clean and renewable energy prospect has prompted for exploration of diverse renewable sources5,6,7. Biodiesel has emerged as potential replacement for conventional diesel fuel due to its non-hazardous and biodegradable properties. Moreover, biodiesel is a renewable and eco-friendly option that could help counteract the adverse effects of various industries on the ecology8. Therefore, the development of biodiesel is essential to meet the growing energy demand in a sustainable manner9. Biodiesel, made from plant oils or animal fats (glycerides), in the form of methyl esters of fatty acids is gaining recognition as an environmentally friendly substitute, for traditional fossil diesel fuel10,11. This is due to its ability to partially replace the latter while maintaining similar performance characteristics12. The United Nations Development Programme (UNDP) considers Goal 7 which focuses on “ Clean Energy “ as one of the Sustainable Development Goals (SDGs). This objective is to solve environmental issues and strive towards reducing greenhouse gas emissions while simultaneously guaranteeing that dependable, sustainable, and contemporary energy is accessible to everyone. The efforts to mitigate climate change and advance inclusive development are aligned with Goal 7, which is a component of the larger 2030 agenda for a sustainable future13. One potential alternative is the utilization of fuels sourced from plants, such as mahua biodiesel. Utilizing these kinds of biofuels can lead to a long-term and environmentally friendly energy solution while also offering the benefit of decreasing carbon discharge. Prabu14 found BTE increased by 12% for the B20 nanoparticle blend and 9% for the B100 nanoparticle blend in comparison to B100. CO decreased by 60%. HC decreased by 44%. NO decrease by 30%. Smoke decreased by 38% in comparison to B100 for all parameters. Abdulfatah et al.15 observed that HC and CO decrease for 60-ppm blends. NOx increases for 40 ppm blends in comparison to 20 and 60 ppm blends. Abdulfatah et al.16 found PCP increases and NHRR improves with the B10C15 blend. For CeO2-enriched biodiesel, exhaust gases like carbon monoxide and unburnt hydrocarbon emission levels drop in comparison to diesel. NOx increases for biodiesel-CeO2 blend fuels (B0C15 increased by 6.11%, B10C15 increased by 21.55%, and B15C15 increased by 25.61%) B15C15 fuel produced the lowest smoke at 44.68%. Yusuf et al.17 observed that PCP increases and NHRR improves by enrichment of CeO2 in biodiesels. Carbon monoxide and unburnt hydrocarbon emission levels decrease by 32.16% and 45.59% for B15C20 blend fuels in comparison to diesel. NOx increases for B15C20 blend fuel by 5.97%. The emission of harmful gases drops as the biodiesel percentage is raised in the nanoparticle blends. Yasar et al.18 observed that calorific value increased due to the addition of nanoparticles. Ahmed et al.19 calculated the optimal doses of nanometal additives. BTE increased by 3% for diesel-ferrocene blends and 8% for B30-ferrocene blends. Ahmed et al.20 evaluated that PCP increases by 4.5%, when 40 mg/L of Al2O3 is dosed in JB20D. Alex et al.21 found CO decreased up to 60% load and increased beyond 60% load. The decrease in CO emission level is due to enhancement in the burning properties of the nanoparticles blended biodiesel. Chen et al.22 tested nanoparticles of blended diesel at 0%, 25%, 50%, 75%, and 100% ELs. Due to the lower thermal conductivity of Al2O3 and SiO2 blends, PCP decreased by 8.5% for Al2O3 blends and by 3.25% for SiO2 blends, and ignition delay decreased by 2°/deg CA for Al2O3 blends and by 5 °C for SiO2 blends. Tuan23 found that CeO2-added biodiesel is stable at concentrations below 100 ppm. Tuan et al.24 conducted a study to examine how fuel additives made of metal nanoparticles affect the performance of diesel and biodiesel blends. Performance, as well as combustion efficiencies of the engine, improves for all concentrations of nanoparticles. Metal oxide nanoparticles play a role, in fuel zones by acting as an oxygen buffer facilitating the efficient and thorough combustion of the fuel. Anish et al.25 investigated the impact of nanoparticles additives in mixtures of diesel and biodiesel. The result indicated a significant improvement in the performance of diesel engines promoted by the catalytic activity of nanoparticles. Aram et al.26 found B10 + E4 + GQD60 to be the best fuel at engine revolutions of 1800 rpm, 2100 rpm, and 2400 rpm respectively. Maleni et al.27 examined that, the horsepower and rotational power of the fuel enriched with GQD nanoparticles enhanced by 28.18% and 12.42%. Additionally, the drop in specific fuel consumption is found to be 14.35% and fall in emission levels of carbon monoxide and hydrocarbons are 29.54% and 31.12% respectively. Maleni et al.28 found that the inclusion of GQD + E, in B10 resulted in enhanced horsepower and rotational power while decreasing SFC, CO, UHC and NOx emissions. Dewangan et al.29 researched using biodiesel with metal oxide improves performance while lowering engine emissions. The usage of oxygenated additives, such as n-butanol and DEE, improves BTE and BSFC and lowers engine emissions overall, except NOx. The majority of studies revealed an improvement in BTE along with an increase in operating parameters including CR, IT, and IP. Selvanayagam et al.30 identified that nano additives not only improve the performance of the engines but also contribute to reducing the emission levels of various pollutants. Bitire et al.31 showed BTE, for samples tested, namely the B20, BC50 and BC100 showed values of 32.5%, 33.0% and 32.9% respectively under the highest engine load condition. It appeared that BC50 have a greater BTE than the other fuel samples that were put through testing. In addition, BSFC for BC50 was significantly lower than for the B0 fuel sample, at 3.28%. Ettefaghi et al.32 demonstrated that adding water and quantum dot nano additive particles in B15 fuel raises rotational power and horsepower of the engine while lowering BSFC. This is because there is more oxygen available for combustion in the air–fuel mixture. Polat33 compared diesel with P10 in a separate study. The study indicated that the inclusion of alumina nanometal particles increased efficiency. The BSFC value showed an improvement of 4.29%, with the 10% blended biodiesel, however when using the P10 + 1 g Al2O3 test fuel, 2% drop in BSFC is noticed. When the author included pyrolysis oil, drop in pollutants emittance levels of CO, NOx and unburnt HC by 17.5%, 5.69% and 18.6% respectively are observed. The addition of Al2O3 nanoparticles resulted in improvements of 10%, 6.82% and 13.95%, for these reduced characteristics respectively. Dhahad et al.34 found that with increasing doses of the nanoparticles in the mixed fuel, this condition causes full combustion as well as increased BTE and decreased BSFC. Wei et al.35 found that the inclusion of nano SiO2, in methanol resulted in an increase of 8.6% in the peak pressure and a 4.3% rise, in the peak heat release rate. All of SiO2 nanoparticle dosages evaluated in the fuel resulted in increases to the BTE and BSFC, particularly at maximum EL, where the authors achieved improvements of 5.1%, for efficiency and 6.2% for rate of fuel intake. Wei et al.36 demonstrated that while using methanol in place of diesel fuel, the outcome was a delay, in ignition that was longer. The duration of combustion was shorter. The ignition delay under 10% load circumstances was marginally decreased by the inclusion of Al2O3, CeO2, and SiO2 nano metal particles in each amount as well as silica nanoparticles in the 100-ppm dosage into M10. All three nanoparticles, in varying doses, reduced the ignition delay at engine loads between 10 and 50% when added to M50 fuel. Wei et al.37 indicated enrichment of methanol blended diesel with Alumina nano metal particles resulted a 2.5% increase in peak in cylinder pressure, Young et al.38 indicate that gas fuels increased hydrocarbon emissions, slightly changed NOx emissions, and decreased opacity. Udayakumar et al.39 studied coated engines have higher efficiency and power with less fuel intake. There were also no appreciable differences in emittance of carbon monoxide as well as carbon di oxide for coated as well as uncoated engines, for ceria–zirconia nanoparticle added lemon peel biodiesel. Mani et al.40 found that at a nanoparticle dosing of 160 parts, per million (ppm) and speed of engine of 1000 revolutions, per minute (rpm) the maximum brake horsepower and rotational power reached are 42.82 kilowatts, 403 Newton meters. Additionally, the minimal values for BSFC are 207.21 gm/kWh, carbon monoxide emission levels are 1.15% and unburnt hydrocarbons emission levels is 9%. At a nanoparticle dosing of 160 parts, per million (ppm) and speed of engine of 1000 revolutions, per minute (rpm), CO2 and NOx emission levels of 11.76% and 1899 ppm were obtained. Bidir et al.41 found that, inclusion of nanoparticles resulted in 20% to 23% drop-in fuel intake rate. The brake power enhanced by 2.5% to 4% with nano particles enrichment, in addition to the fact that they have great thermal conductivity. Significant drop in emission levels of carbon monoxide, unburnt hydrocarbons and particulate matters have been observed, however 55% rise in emission levels of oxides of nitrogen have been reported. Khan et al.42 examined for engines running at high loads and high compression ratios, BSEC decreased. Brake thermal efficiency of 33.57% has been achieved with 28.68% hydrogen injection in air at EL of 87.9%, CR of 19 and injection pressure of 194.54 bar along with 80 ppm of nanoparticle dosing. Emission levels of unburnt hydrocarbons of 0.2550 ppm, oxides of nitrogen of 461.3 ppm and particulate matters of 22.1% have been obtained. Rastogi et al.43 observed that increased brake thermal efficiency has been recorded for JB20CN50 in contrast to other blends of jojoba biodiesel dosed with copper oxides nano metal particles. Elumalai et al.44 determined PTO20CuZnO50P10 to be the best choice for reduction in exhaust gas emission levels at 100% load. These reductions were 12% in NOx level, 37% in CO level, 10% in UHC level, and 23% in soot level respectively. However, it was found that when employing PTO20CuZnO50P10 in PCCI mode in contrast to a standard diesel engine, BTE decreased and brake specific fuel consumption increased. Atarod et al.45 studied the results of combined blending of water and nanoparticles with diesel. Brake thermal efficiency of 34% has been achieved with 2.49 wt.% water injection in diesel at EL of 74%, fuel injection timing of 39°BTDC along with 112 ppm of nanoparticle dosing. Emission levels of carbon dioxide of 7.26%, carbon monoxide of 0.46%, unburnt hydrocarbons of 36.2 ppm and oxides of nitrogen of 95.7 ppm have been obtained. Krupakaran et al.46 recorded 5.12% rise in BTE of CIBD20MC80 fuel in contrast with CIBD20, whereas 16.12% drop-in fuel intake rate of CIBD20MC80 is observed in contrast with CIBD20 fuel. Tripathi et al.47 reported that CO and NO emissions are also reduced as a result of nanoparticles converting CO to CO2 and NO to N2. Reddy et al.48 found that nanoparticle enriched B20COTO fuel demonstrated increased BTE, whereas drop in in fuel intake rate is also observed. Also, fall in emission levels of oxides of nitrogen, carbon monoxide and unburnt hydrocarbons were noticed. Santhosh et al.49 used ANN model to draw the conclusion that the enrichment of nano metal oxides significantly improved the engine’s BTE, Agbulut et al.50 conducted a study by exergoeconomic research, D100 had the lowest cost of crankshaft work after D90E10Al2O3. The exergoeconomic performance of D90E10Al2O3 is higher than that of D90E10 and D90E10TiO2, while its exergoeconomic performance is low. The fuel cost raised significantly due to blending of ethanol in diesel. Kul et al.51 revealed that boron dosing @ 50 ppm and 100 ppm showed 2.92% and 2.11% rise in BTE. Zhang et al.52 evaluated that nanoparticles and hydrogen addition improved performance in terms of BTE and torque. Average BTE levels increased by 1.8%. Anupong et al.53 observed that diesel (32%), DN (32.5%), H1 (35.1%), H1N (36.05%), H2 (35.7%), and H2N (37%), all had the highest BTE values. H2N and H2 showed maximum efficiencies of 11% and 14% greater than diesel, respectively. H1 and H2 revealed 9% and 11% increased BTE in comparison to diesel. Table 1 depicts the efficiencies and emission properties of nano particles blended biodiesel fuelled diesel engines.

Table 1 Efficiencies and emission properties of nano particles blended biodiesel fuelled diesel engines.
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Objective

The operating parameters such as compression ratio (CR), engine load (EL), fuel injection timing (FIT) and fuel injection pressure have notable impact on the performance of a diesel engine. Achieving diesel-like efficiency when using alternative fuels in a diesel engine necessitates proper adjustment of operational parameters. Further, the study on variation of CR, EL and FIT for nanoparticle-enriched biodiesel diesel blends on performance and emission characteristic of a diesel engine are very rare. In this regard, the literature survey unravels that the influence of the operating parameters along with the usage of nanoparticles particularly for Mahua biodiesel (MBD) is limited. Taking this into account, the present study investigates the influence of nanoparticle-enriched biodiesel diesel blends on the performance, combustion, and emission characteristics of a diesel engine at varying CR, EL and FIT. The biodiesel and nanoparticles considered for this study are MBD and Titanium oxide nanoparticles. The test fuel is prepared by blending diesel and MBD along with TiO2 nanoparticles. In this study, CR is varied from 17.5 to 18, whereas FIT and EL of 20°, 23°, 25° BTDCs and 20%, 40%, 60%, 80% 100% are considered. The novelty of the present study to investigate the variation of CR, EL and FIT for TiO2 nanoparticle-enriched MBD diesel blends on performance and emission characteristic of a diesel engine.

Materials and methods

Test fuels

Initially, Mahua seeds are sun dried which is collected locally from the Mahua trees present in the RGIPT, Assam Campus, India. Then, mahua seeds are fed to the automatic oil expeller and subsequently mahua oil is obtained as shown in Fig. 1. The maximum capacity of the automatic oil expeller is 10 L. Then, MBD is obtained by mixing the mahua oil and methanol along with the catalyst KOH inside the reactor of the biodiesel production unit through transesterification process as depicted in Fig. 2. The stirring rate is maintained at 150 RPM with the help of a stirrer inside the reactor. A temperature of 55 °C is maintained during the transesterification process. The reactor is heated with a specially designed jacketed circular electrical heater using PID controllers. The reaction time taken for this transesterification process is 1.5 h. The nanoparticles were subjected to X-ray diffraction (XRD) analysis, which confirmed that the sample contained Titanium oxide as shown in Fig. 3 (c). The XRD analysis revealed that the peaks observed aligned with the lattice planes of Titanium oxide. These peaks also provided insights, into the characteristics of the nano particles. In order to gather information, about the surface characteristics, composition and dimensions of the nanoparticles a study was conducted using a Scanning Electron Microscopy technique called field emission-based SEM (FESEM). The process is illustrated in Fig. 3d. The XRD as well as FESEM analysis have been conducted in the Central Instrument facility of RGIPT, Jais, Amethi. For preparing MBD-based nano-blended biodiesel, 20% MBD was mixed with 80% neat diesel using a magnetic stirrer which was termed B20 as shown in Fig. 3. For this study, Titanium Oxide (TiO2) nanoparticles is used because it has the potential to enhance the combustion activity by acting as a catalyst. Titanium naturally combines with oxygen to form oxides making it a suitable choice. To create nanoparticle-based biodiesel, Titanium oxide nanoparticles have been incorporated into the 20% MBD blend. The procedure is started by mixing 200 mg/L of Titanium oxide nanoparticles into the 20% MBD blend. To ensure proper blending, stirring process is followed with ultrasonification with the aid of ultrasonicator. The resulting blend consisting of a combination of TiO2 nanoparticles and B20 biodiesel is referred to as TNPMBB. The characteristics of the TNPMBB biodiesel, viz, density, lower heating value, flash and fire points, and cetane number are given in the Table 2. The experiments are performed as per experimental matrix as given in Table 3.

Fig. 1
Fig. 1
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Automatic oil expeller.

Fig. 2
Fig. 2
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Biodiesel production unit.

Fig. 3
Fig. 3
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Test fuel.

Table 2 Properties of fuel.
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Table 3 Experimental matrix for running the nanoparticles enriched biodiesels.
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Multifuel variable compression ratio test engine rig setup

The multifuel variable compression ratio test engine rig setup consists of a single cylinder having a power rating of 3.5 kW as shown in Fig. 4a and b. The Testo gas emission analyser is used for measuring the emission parameters as depicted in Fig. 4c, which consist of six sensors. Once, the emission analyser is switched on, the pump purges out the residual gases and self-calibration of the sensors take place. Then, the emission analyser is ready for measurement. The tail pipe of the engine test rig is connected to the probe of emission analyser for 30 secs. The values of the different emission parameters are displayed in the screen of the emission analyser. Initially, the engine test rig is first run with neat diesel fuel at operational parameter settings, IT of 23° bTDC and CR of 17.5 and EL is varied from 20 to 100% in steps of 20%. The performance and combustion parameters are recorded as well the emission parameters are also measured. For nano particles biodiesel diesel blend for same range of EL, ITs of 20°, 23° and 25° bTDC along with CR of 17.5 and 18 were considered as indicated in Table 3.

Fig. 4
Fig. 4
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Test engine rig setup and emission analyser.

Uncertainty analysis

The uncertainty analysis is especially done for experiments for estimating the range within which true value lies. For uncertainty estimation, the perturbation technique is adopted54,55. The uncertainty associated and relative errors are shown in Fig. 5a and b.

Fig. 5
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Relative errors and uncertainty analysis associated with experiments.

Results and discussion

Performance analysis of TNPMBB fuel

The BTE rises with the operation with high EL, high CR along with the advancement or retard of FIT as indicated in Fig. 6. At full loading conditions, the BTE is found to increase by 2.11%, 0.35%, and 2.23% for FIT 20°, 23° and 25° BTDCs, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same range of loading conditions and FITs, the BTE is found to rise by 2.95%, 1.24%, and 2.35% at CR of 18 for nanoparticle-blended Mahua biodiesel as compared to DM. The enhancement in BTE for TiO2 enriched biodiesel diesel blend fuel is because TiO2 provides a more reactive surface for combustion reaction due to the high surface-to-volume ratio. Thus, more fuel comes in contact with the oxidizer, thereby, improving the probability of complete combustion. Further, TiO2 lowers the activation energy of the combustion reaction, thereby lowering the ignition temperature and promoting rapid combustion. Furthermore, TiO2 absorbs the thermal radiation and thus, maintains a higher combustion chamber temperature. With the increase in CR, the clearance volume reduces which increases combustion chamber temperature as air-fuel charge is compressed to a comparatively smaller volume. This leads to the possibility of a better combustion. With the retard of IT, the fuel droplets are injected into a relatively high-temperature air within the combustion chamber. This enhances the probability of complete combustion.

Fig. 6
Fig. 6
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Variation of BTE with EL, CR, and FIT.

The EGT rises with EL whereas falls with the use of high CR along with advancement or retard of FIT as shown in Fig. 7. The average drop of EGT is found to be 8.09%, 4.45%, and 6.44% for FIT 20°, 23° and 25° BTDCs, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same setting of FIT at CR of 18, the average fall of EGT is 11.81%, 6.61%, and 9.41%, respectively for TNPMBB in comparison to DM. The EGT is related to the completion of the combustion process. The catalyzing effect of TiO2 particles in biodiesel diesel blend to complete the combustion reaction at a faster rate in combination with the high temperature generated with the use of high CR along with the advancement or retard of FIT leads to favorable conditions towards complete combustion. Similar findings on the variation of CR, IT and EL on the performance characteristics of diesel engine has been reported earlier51,52,53,54,55,56.

Fig. 7
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Variation of EGT with EL, CR, and FIT.

Combustion analysis of TNPMBB fuel

The ID decreases for high ELs, use of high CR along with the advancement or retard of FIT as found in Fig. 8. The average drop of ID is found to be 10%, 14%, and 19.33% for FIT 20°, 23° and 25° BTDCs, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same setting of FIT at CR of 18, the average fall of ID is 21.33%, 26%, and 30%, respectively for TNPMBB in comparison to DM. The synergetic effect of the use of TiO2 nanoparticles in the Mahua biodiesel diesel blend in combination with the use of high CR along with the advancement and retard of FIT lower the time taken for initiation of the combustion reactions and thereby resulting in low ID. The PCP rises with the increase of EL and use of high CR along with the advancement or retard of FIT as given in Fig. 9. The decrement in peak cylinder pressure obtained is 6.21%, 10.41%, and 9.49% for FIT 20°, 23° and 25° BTDCs, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same setting of FIT at CR of 18, the average fall of PCP is 1.92%, 6.52%, and 4.14%, respectively for TNPMBB in comparison to DM. The variation of NHRR and PCP with crank angle is depicted in Figs. 10 and 11.

Fig. 8
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Variation of ID with EL, CR and FIT.

Fig. 9
Fig. 9
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Variation of PCP with EL, CR and FIT.

Fig. 10
Fig. 10
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Variation of NHRR with CR and FIT at 100% EL.

Fig. 11
Fig. 11
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Variation of PCP with CR and FIT at 100% EL.

The presence of TiO2 in Mahua biodiesel diesel blends results in the rapid release of the heat in the early stage of the combustion phase thereby, resulting in a higher and slender peak of the heat release rate curve at various combinations of CRs and FITs compared to DM. However, due to the fast burning of the charge, the PCP of TiO2-enriched Mahua biodiesel diesel blends at various combinations of CRs and FITs is lower as compared to DM. Similar trends on the variation of CR, IT and EL on the combustion characteristics of diesel engine has been reported in previous studies54,55,56.

Emission analysis of TNPMBB fuel

CO and HC emissions drop progressively with an increase of EL up to 80% and then increase as depicted in Figs. 12 and 13. CO and HC emissions are found to drop with an increase of CR along with advancement or retard in FIT. The drop in emittance level of carbon monoxide obtained are 25.42%, 13.98%, and 20.76%, for FIT 20°, 23° and 25° BTDCs, respectively at CR of 17.5 for TNPMBB in contrast with DM. For the same setting of FIT at CR of 18, the average fall of CO is 45.34%, 33.47 and 38.98%, respectively for TNPMBB in comparison to DM. The average drop of HC for FIT 20°, 23° and 25° BTDCs is found 27.2%, 12.8%, and 19.6%, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same setting of FIT at CR of 18, the average drop of HC is found to be 40%, 22.4%, and 31.6%, respectively for TNPMBB in comparison to DM. The emissions of CO2 and NOx increase with the increase of EL, the use of high CR along with the advancement or retard of FIT as shown in Figs. 14 and 15. The average rise of CO2 is found to be 42.05%, 19.95%, and 32.80% for FIT 20°, 23°, and 25° BTDCs, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same setting of FIT, the average increase of CO2 emission is found to be 48.96%, 27.55%, 34.87%, respectively at CR of 18 for TNPMBB in comparison to DM. The average increase of NOx is found to be 40.41%, 28.63%, and 34.6% for FIT 20° BTDC, 23° BTDC and 25° BTDC, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same setting of FIT, the average increase of NOx emission is found to be 24.24%, 12.93%, and 19.05%, respectively at CR of 18 for TNPMBB in comparison to DM. The presence of TiO2 in the biodiesel diesel blends as well as the presence of oxygen in biodiesel leads to complete combustions57,58, thereby, lowering the CO and HC emissions while enhancing the CO2 and NOX emissions. The operational parameters, CR and FIT, also contribute to and affect the emission.

Fig. 12
Fig. 12
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Variation of CO emission with EL, CR and FIT.

Fig. 13
Fig. 13
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Variation of HC emission with EL, CR and FIT.

Fig. 14
Fig. 14
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Variation of CO2 emission with EL, CR and FIT.

Fig. 15
Fig. 15
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Variation of NOx emission with EL, CR and FIT.

The increase in CR results minimization of clearance volume causing a rise in the combustion chamber temperature and thereby increasing the chances of complete combustion. It is seen that the advancement of IT gives ample time for better mixing of fuel and air hereby lowering the CO and HC emissions. However, the maximum drop in emission is recorded with the retard of the FIT. The reason behind this phenomenon is that the fuel droplets enter into the combustion chamber at a higher temperature and thereby, increase the possibility of a proper combustion process. It can be well understood in this study that the combustion phenomena are influenced by the following factors namely; TiO2 enriched biodiesel diesel blend, high CR, and advance or retard of FIT leads to the generation of high in cylinder temperature causing generation of higher NOX emission in comparison to DM. Similar findings on the variation of CR, IT and EL on the emission characteristics of diesel engine has been reported earlier studies59,60,61.

Conclusions

An experimental study was conducted to evaluate the impact of operating parameters on the performance of a diesel engine powered by a nanoparticle-enriched biodiesel-diesel blend. Titanium dioxide (TiO₂) nanoparticles and mahua biodiesel were used to prepare the test fuel, consisting of 20% mahua biodiesel, 80% diesel, and 200 mg/L of TiO₂. The study considered two compression ratios (17.5 and 18), three fuel injection timings (20°, 23°, and 25° BTDC), and five engine load levels (20%, 40%, 60%, 80%, and 100%).The main outcome of the study is discussed below:

  • Brake thermal efficiency (BTE) improves when operating at high ELs, high CRs, and with either advanced or retarded FIT. At full EL conditions, the BTE is found to increase by 2.11%, 0.35%, and 2.23% for FIT 20° BTDC, 23° BTDC and 25° BTDC, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same range of EL conditions and FITs, the BTE is found to rise by 2.95%, 1.24% and 2.35% at CR of 18 for nanoparticle blended Mahua biodiesel as compared to DM.

  • EGT increases with high ELs but decreases when CR is increased or when FIT is advanced or retarded. The average drop of EGT is found to be 8.09%, 4.45% and 6.44% for FIT 20° BTDC, 23° BTDC and 25° BTDC, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same setting of FIT at CR of 18, the average fall of EGT is 11.81%, 6.61% and 9.41%, respectively for TNPMBB in comparison to DM.

  • The ID decreases for high ELs, use of high CR along with advancement or retard of FIT. The fall in ignition delay obtained are 10%, 14% and 19.33% for FIT 20° BTDC, 23° BTDC and 25° BTDC, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same setting of FIT at CR of 18, the average fall of ID is 21.33%, 26% and 30%, respectively for TNPMBB in comparison to DM.

  • The TNPMBB blends exhibit lower PCP compared to DM due to the faster combustion of the charge across various combinations of CRs and FITs. The average drop in PCP is found 6.21%, 10.41% and 9.49% for FIT 20° BTDC, 23° BTDC and 25° BTDC, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same setting of FIT at CR of 18, the average fall of PCP is 1.92%, 6.52% and 4.14%, respectively for TNPMBB in contrast to DM.

  • The presence of TiO2 in Mahua biodiesel diesel blends results in the rapid release of heat in the early stage of the combustion phase and thereby, resulting in a higher and slender peak of the heat release rate curve at various combinations of CRs and FITs compared to DM.

  • The average drop of CO is found to be 25.42%, 13.98% and 20.76%, for FIT 20° BTDC, 23° BTDC and 25° BTDC, respectively at CR of 17.5 for TNPMBB in contrast to DM. For the same setting of FIT at CR of 18, the average fall of CO is 45.34%, 33.47 and 38.98%, respectively for TNPMBB in comparison to DM.

  • The average fall of HC for FIT 20° BTDC, 23° BTDC and 25° BTDC is found 27.2%, 12.8% and 19.6%, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same setting of FIT at CR of 18, the average drop of HC is found to be 40%, 22.4% and 31.6%, respectively for TNPMBB in comparison to DM.

  • The average rise of CO2 is found to be 42.05%, 19.95%, 32.80% for FIT 20° BTDC, 23° BTDC and 25° BTDC, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same setting of FIT, the average increase of CO2 emission is found to be 48.96%, 27.55%, 34.87%, respectively at CR of 18 for TNPMBB in comparison to DM.

  • The average increase of NOx is found to be 40.41%, 28.63% and 34.6% for FIT 20° BTDC, 23° BTDC and 25° BTDC, respectively at CR of 17.5 for TNPMBB in comparison to DM. For the same setting of FIT, the average increase of NOx emission is found to be 24.24%, 12.93% and 19.05%, respectively at CR of 18 for TNPMBB in comparison to DM.

The present study unravels that the efficiency of the diesel engine can be raised through the use of nanoparticle-enriched biodiesel diesel blends as well as with adjustment of operating parameters i.e., compression ratio and injection timing. Further investigation can be carried out on the optimization of the fuel injection pressure as well as use of various nanoparticles enriched biodiesel diesel blends in diesel engine a scope of future research.