Sustainable emission reduction in CI engines using cerium nanoparticles and acetylene-cedar wood oil biofuel

Abstract

The rising costs of petroleum-based fuels for internal combustion engines and their detrimental environmental impacts have spurred the search for alternative fuels. This study explores minor modifications to a compression ignition engine, enabling it to operate in dual fuel mode using biofuels as a viable alternative to neat diesel. A novel biofuel was developed using cedar wood oil, and its performance was experimentally investigated in a single-cylinder diesel engine operating at a constant speed. Acetylene was continuously introduced to the engine at a flow rate of 6 L per minute, chosen for its optimal performance, yielding a brake thermal efficiency of over 30.7%. The engine was operated under constant conditions, including a compression ratio of 18, an ignition timing of 23°CA before top dead centre, and an injection pressure of 220 bar. Comparative evaluations were performed by analyzing the combustion characteristics and emission levels of diesel and cedar wood oil-based fuels with and without nanoadditive for diesel, B50 and B100 with a constant acetylene gas supply at 6 Lit/min. The primary objective was to reduce toxic emissions, including smoke, carbon monoxide, hydrocarbons, and nitrogen oxides, released during fuel combustion with the help nanoadditives in fuel. The effects of cerium nanoparticles as an additive were considered in this study due its thermal stability and activation energy which reduce CO and HC emission significantly.The smoke, CO and HC were decreased for B100 + 6L A + 50 ppm blend by 20.21%, 65.52% and 51.42% for 100% load. It is found that cedar wood oil oil with nanoparticle additives could effectively reduce smoke and hydrocarbon emissions while maintaining comparable efficiency to neat diesel and pure biodiesel modes.

Graphical abstract

Introduction

The depletion of petroleum-based fuels and their detrimental environmental impact have raised concerns regarding their future availability (Yu et al. 2010). The escalating demand for energy derived from burning petroleum fuels has necessitated the exploration of alternative options (Zhang et al. 2023; El-Sheekh et al. 2023a, b). Major petroleum fuels such as diesel, gasoline, and compressed natural gas (CNG) are extensively used in internal combustion (IC) engines (Wu et al. 2023; EL-Seesy et al. 2020). Apart from being non-renewable, these fuels contribute to environmental pollution when combusted (Elkelawy et al. 2021a).

To address the need for alternative fuels, researchers have turned their attention to biofuels and their potential utilization in IC engines. Several studies have demonstrated that biodiesel exhibits engine performance characteristics comparable to diesel fuel (Murugapoopathi and Vasudevan 2019b, a; Ilkilic 2009; Lapuerta et al. 2005; Avinash et al. 2014; Pramanik 2003). Engines fuelled by biodiesel emit fewer air pollutants compared to conventional diesel engines (Agarwal and Rajamanoharan 2007; Ahmad et al. 2011; Lapuerta et al. 2008), while also demonstrating similar conversion performance to diesel operation (Gad et al. 2023).

Previous studies have investigated the suitability of biodiesel derived from various organic sources, including cassava, sunflower, soybean, canola, wheat starch, molasses, jatropha, rape, palm, olive, karanja, mahua, and rubber oils (Murugapoopathi and Vasudevan 2021; Leo et al. 2021; Shehata et al. 2015; Murugapoopathi and Vasudevan 2019b, a). In this investigation, we focus on cedar wood, a readily available and widely cultivated crop in South India. Cedar wood is commonly used in the preparation of various snacks, leaving its residual biomass largely unused and wasted in India. Starch, constituting 12.78% of cedar wood, serves as a valuable feedstock for starch extraction and forms the basis for our biofuel production (Nuriana 2015).

Besides biofuels, the viability of gaseous fuels, including compressed natural gas (CNG), liquefied petroleum gas (LPG), hydrogen, acetylene, ethanol, methanol, producer gas, and vegetable fats, has been frequently tested for IC engines (Sai Kiran et al. 2021). Dual-fuel operation, where gaseous fuels partially or fully replace liquid fuels like diesel or petrol, offers advantages as it requires minimal engine modifications. However, gaseous fuels have higher self-ignition temperatures and are unsuitable for automatic operation (Dinesha et al. 2021). Consequently, they are either injected directly into the combustion chamber or introduced through the inlet manifold. The use of acetylene as a dual fuel in IC engines alongside diesel has garnered significant attention, owing to its broader flammability range and high flame speed, which make it a potential substitute fuel (Heidari-Maleni et al. 2020; Lakshmanan and Nagarajan 2011a, 2011b).

Previous studies have revealed that oxidized mixed hydrocarbons and nanoparticle-based compounds can affect brake power during combustion and alter the fuel consumption range. Nanoparticles, due to their higher energy density, improved combustion characteristics, and lower exhaust emissions, have demonstrated superior fuel catalytic properties (Muruganantham et al. 2021).

The properties diesel fuel was enhanced by multi-walled carbon nanotubes (MWCNT) and nitrogen-doped MWCNT in CI engine for various loads. The performance was improved with reduced SFC and CO, NO_x and soot emissions were decreased significantly, using N-doped MWCNT (EL-Seesy et al. 2023a; b, c).

Elkelawy et al. 2021a, b investigated the engine performance by cyclohexane by 5%, 10% and 15% with B60 by varying proportion in diesel by varying injection pressure from 150 and 250 bar respectively. The fuel additive increased the combustion process and CO, HC, NOx and smoke decreased with increase in pressure by 250 bar.

Waly et al. 2023 investigated amino-based MWCNT (25, 50, 75 and 100 ppm) blended with diesel at combination of loads at constant speed in CI engine. The improved cylinder pressure, HRR and BTE were obtained with considerable reduction in emission parameters with 100 ppm blend.

The performance enhancement of diesel engine and fuel characteristics was improved with the addition octane with different nanoparticles (50 ppm) concentration with diesel-methanol-diethyl ether at 5, 10 and 15%. The gaseous emissions like HC, CO and NOx decreased with the addition of nanoparticle (EL-Seesy et al. 2022).

EL-Seesy et al. 2023b examined amino-based nitrogen-doped MWCNT (50 & 75 ppm) in 80% biodiesel with decanol in CI engine at combination of loads. The nanoadditive in fuel blend reduced the CO, NO_x and soot by 61%, 35% and 44% with 10% decline in BTE and 15% raise in SFC with that of diesel fuel.

The diesel fuel was blended with n-hexanol at 10,20,30,40 and 50% for various loading conditions. The performance parameters, HRR and ignition delay improved with 50% hexanol at 100% load. The NO_x and smoke were decreased by 26% and 54% for same condition (Nour et al. 2021).

The 50% biodiesel blended diesel with 200 ppm silver nanoparticle with 4% hydrogen peroxide in diesel engine to evaluate the engine performance. The combustion characteristics improved with nanoadditive in fuel and decreased the CO, HC and NO_x emission significantly (Elkelawy et al. 2021a, b).

In light of these factors, this study aims to evaluate the performance, emission characteristics, and combustion properties of a single cylinder, four-stroke, variable compression ratio (VCR) direct injection diesel engine using different fuel blends, including cedar wood oil, acetylene, and nanoparticle additives. The novelty of this work lies in the comprehensive assessment of the combined effects of cedar wood oil, acetylene injection, and nanoparticle additives on engine performance and emissions. Cerium oxide nanoparticles have good thermal stability and it can withstand high temperatures without undergoing significant changes in their structure. The activation energy of CeO₂ plays a role in preventing the deposits of non-polar compounds on the surface of engine cylinders (El-Sheekh et al. 2023a). This property is crucial in reducing hydrocarbon (HC) and carbon monoxide (CO) emissions. By inhibiting the formation of deposits, cerium oxide helps maintain cleaner engine surfaces and enhances combustion efficiency, leading to lower emissions (Elkelawy et al. 2018). By investigating this novel fuel combination, we contribute to the growing body of research on sustainable energy solutions and the optimization of engine operations.

Materials and methods

Nanoparticle preparation

In this study, cerium oxide (CeO₂) nanoparticles were incorporated into gasoline blends. The preparation of the nanoparticle additive involved the utilization of the solgel combustion method, as described by Chandrasekaran et al. (2016). The size of the ceria nanoadditives was reported to be in the range of 15–30 nm. The morphology and crystal nature of the ceria nanoadditive was studied using SEM. The specific SEM model used was VEGA3 TESCAN, with an applied voltage of 30 kV. The SEM images (Fig. 1) indicate that the particles are aggregated consistently and distributed throughout the sample. The solgel technique stimulated dissimilar diameters and the development of vacancies on the particle surfaces. The morphology of the ceria nanoadditive was studied using a JEM–3010 ultra-high-resolution analytic electron microscope. The TEM images (Fig. 2) show that all the particles are distributed throughout the crystal. These characterization techniques provide insights into the physical characteristics, morphology, and distribution of the ceria nanoadditives at the nanoscale level. It is worth noting that the use of solgel techniques is common in nanoparticle synthesis as it allows for precise control over particle size, shape, and distribution (Thodda et al. 2023a, b). The observed aggregation and variations in diameter mentioned in the SEM analysis could be attributed to the specific conditions and parameters employed during the solgel synthesis (Thodda et al. 2023a; Leo et al. 2023).

Fig. 1

SEM morphological image ceria

Fig. 2

TEM morphological image of ceria

The method consisted of dissolving an appropriate quantity of hexahydrate and glycine in deionized water. Glycine was employed as a reductant, while cerium nitrate acted as an oxidizing catalyst. The mixture was continuously stirred for two hours at 60 °C until a translucent viscous gel was formed. The gel was then transferred to an electric furnace and heated to 100 °C, facilitating the dehydration of excess water and resulting in the formation of a yellow, porous foam comprising nanoparticles. During the combustion process, a significant amount of non-toxic gas, including N₂, CO₂, and H₂O, was released in the form of brown vapor. Subsequently, the produced nanoparticles were subjected to a grinding process to achieve a smooth texture and were further treated by blast heating at 600 °C for three hours to enhance their properties before being utilized for evaluation.

The experimental setup used for the present research work is depicted in Fig. 3 and 4. The investigation was conducted on a single-cylinder, four-stroke, variable compression ratio (VCR) direct injection CI engine with a rated power output of 3.5 kW. Table 1 provides the technical specifications of the engine, while Table 2 shows the comparison of physical and combustion properties of acetylene with other fuels. An eddy current dynamometer equipped with a water cooling system was connected to the engine for load application. To facilitate adjustments to the compression ratio (CR) without interrupting the engine operation, a cylinder block modification was implemented. Piezoelectric sensors were affixed to the engine block and fuel system to measure cylinder pressure and fuel system pressure, respectively. A solenoid gas injector was installed in the engine chamber block beneath the throttle pipe to introduce acetylene gas for combustion. The air flow was precisely measured by monitoring the pressure drop across the radial opening of the air surging chamber using a manometer. Fuel consumption was determined by measuring the fuel drift over a fixed duration. The exhaust gas temperature was measured using a Chromel–alumel K type thermocouple, while the constituents of the exhaust gas (CO, HC, NO_x, CO₂, O₂) and smoke density were analyzed using an AVL gas analyzer and AVL smoke meter, respectively. Table 3 presents the physical and combustion properties of cedar wood oil, which was utilized as the fuel in this study.

Fig. 3

Schematic diagram of experimental set up. 1. Acetylene gas cylinder. 2. Flame trap. 3. Flow meter. 4. Flame arrestor. 5. Proximity sensor. 6. Electronic Control unit. 7. Gas injector. 8. Air intake tank. 9. Engine. 10. Provision for CR adjustment. 11. Provision for injection timing adjustment. 12. Fly wheel. 13. Dynamo meter. 14. Gas analyser and smoke meter. 15. RPM indicator. 16. U—tube Manometer. 17. Fuel Measuring burette. 18. Load Varying knob. 19 Engine cooling water flow measuring rotameter. 20. Calorimeter cooling rotameter. 21. Data Logger

Fig. 4

Photographic image of experimental setup

Table 1 Specifications of the CI engine

Table 2 Comparison of physical and combustion properties of acetylene with other fuels

Table 3 Physical and combustion properties of cedar wood oil

The engine operation commenced with diesel fuel, and subsequently, acetylene gas was introduced into the cylinder during the suction stroke via an electronic gas injector situated at the intake port. The injector's opening and closing were controlled by a proximity sensor, with the voltage signal being processed by the electronic control unit (ECU). Diesel fuel injection occurred at 23° before top dead center (bTDC) at a pressure of 220 bar. Acetylene gas from a high-pressure cylinder was regulated using a double-stage gas regulator at 2 bar. The gas flow was regulated by a ball valve and measured using a gas flow meter. Safety measures, such as a flame trap and flame arrestor, were implemented in the flow line to prevent engine backfire. Experimental data were recorded using a data acquisition device (DAD) from National Instruments and stored in a computer for offline analysis. Crank angle information was obtained using an encoder, and a sensor was mounted on the flywheel. A summary of the methodology and loading details are provided in Tables 4 and 5. The instruments and software were used to find the various parameters are given in Table 6.

Table 4 Load details

Table 5 Experimental methodology

Table 6 Measuring instrument details

Error analysis of the experimental data

Accurate measurement of parameters in the experimental data is crucial for obtaining reliable results. However, various factors can introduce errors, including working conditions, environmental influences, calibration discrepancies, experimental methods, and instrument limitations. Therefore, it is essential to conduct error analysis to assess the accuracy of the measured parameters (El-seesy et al. 2021).

To determine the error in the engine speed, the error in the tach generator was taken into consideration. The fuel mass flow rate was calculated by evaluating the fuel consumed per minute, and the corresponding error was estimated accordingly. Similarly, the error in the measurement of exhaust gas temperature was assessed by accounting for the error in the thermocouple.

Statistical analysis and standard analytical techniques were employed to calculate the errors associated with the measured parameters. The root-mean-square method was utilized for error estimation (Murugapoopathi et.al. 2023) presented in Eq. 1.

$$ \frac{\partial R}{R} = {\left\{ {{{\left( {\partial {x_1}{/}{x_1}} \right)}^2} + {{\left( {\partial {x_2}{/}{x_2}} \right)}^2} \cdots + {{\left( {\partial {x_n}{/}{x_n}} \right)}^2}} \right\}^2}$$

(1)

where $\left( {\partial {x_1}{/}{x_1}} \right)$, $\left( {\partial {x_2}{/}{x_2}} \right)$, etc. are the errors in independent variables.

$$ {U_{{\text{total}}}} = \sqrt {\{ \;({{({U_{{\text{bte}}}})}^2} + {{({U_{{\text{smoke}}}})}^2} + {{({U_{{\text{ROPR}}}})}^2} + {{({U_{{\text{CA}}}})}^2} + {{({U_{{\text{CO}}}})}^2} + {{({U_{{\text{CO2}}}})}^2} + {{({U_{{\text{HC}}}})}^2} + {{({U_{{\text{NOx}}}})}^2}\} } \;$$

(2)

$$ {U_{{\text{total}}}} = \sqrt {\{ \;({{(1.1)}^2} + {{(1)}^2} + {{(1.35)}^2} + {{(1.25)}^2} + {{(0.2)}^2} + {{(0.2)}^2} + {{(0.2)}^2} + {{(0.3)}^2}\} } = 2.41$$

It is important to note that the estimated errors had negligible influence on the final results, ensuring their reliability. Detailed information regarding the maximum uncertainties in the measured and calculated results is provided in Table 7, which summarizes the uncertainty in measurement (Gavaskar et al. 2023) calculated using Eq. 2.

Table 7 Uncertainty in measurement

Results and discussion

Combustion characteristics fuel blends without nanoparticle additive

Cylinder pressure crank angle

In this study, the variation of cylinder pressure with crank angle was analyzed for different fuel combinations. Figure 5 illustrates the cylinder pressure profiles for the following fuel blends: diesel with acetylene injected at a flow rate of 6 LPM (D + A 6L), a blend comprising 50% by volume of biodiesel (B50) derived from diesel and cedar wood oil with acetylene injected at 6 LPM (B50 + A 6L), and 100% biodiesel (B100) derived from diesel and cedar wood oil with acetylene injected at 6 LPM (B100 + A 6L).

Fig. 5

Variations of peak cylinder pressure with crank angle for different fuels modes

During the experiments, a constant acetylene flow rate of 6 LPM, compression ratio of 18, injection timing of 23°CA bTDC, and injection pressure of 220 bar were maintained. The highest peak pressure of 49.20 bar was achieved when the engine was fueled with diesel combined with acetylene (D + A 6L) under full load conditions. For the blend of 50% biodiesel with acetylene (B50 + A 6L), the peak pressure was recorded as 45.57 bar, while for 100% biodiesel with acetylene (B100 + A 6L), the peak pressure was slightly lower at 44.25 bar.

These results indicate that the maximum peak pressure was attained when the engine was fueled with acetylene-enhanced diesel. This advance in peak pressure can be attributed to the instantaneous combustion characteristics of acetylene compared to diesel fuel, leading to higher cylinder pressure (Lakshmanan and Nagarajan 2011a). Acetylene gas exhibits a higher flame speed, resulting in a higher energy release rate, which is a significant factor contributing to the elevated peak pressure (Mohan and Dinesha 2022; Lakshmanan and Nagarajan 2010a).

Heat release rate

The variation of heat release rate with crank angle was analyzed for different fuel blends, namely diesel with acetylene, a 50% biodiesel blend (diesel + cedar wood oil) with acetylene, and 100% biodiesel (diesel + cedar wood oil) with acetylene, as depicted in Fig. 6. The acetylene flow rate was maintained at 6 LPM, while the compression ratio was set to 18, the injection timing to 23°CA bTDC, and the injection pressure to 220 bar throughout the experiment.

Fig. 6

Variations of peak heat release rate with crank angle for different fuels modes

The highest heat release rate of 42.93 J/◦CA was observed for the engine fueled with diesel and acetylene. For the blend of 50% biodiesel with acetylene, the heat release rate was recorded as 38.74 J/◦CA, while for 100% biodiesel with acetylene, it decreased further to 34.97 J/◦CA.

These results highlight that the maximum heat release rate was achieved when the engine was fueled with acetylene-enhanced diesel. The use of acetylene in the diesel fuel mixture increases the heat release rate due to the higher energy density of the acetylene-diesel-air mixture (Lakshmanan and Nagarajan 2011b; Singh et al. 2020). Moreover, the higher viscosity of cedar wood oil compared to diesel affects the flammability characteristics of the biodiesel blend, resulting in a lower heat release rate compared to neat diesel with acetylene (Vijayabalan and Nagarajan 2009).

Performance characteristics

Brake thermal efficiency

The variation of brake thermal efficiency with load was analyzed for different fuel blends, including diesel with acetylene, a 50% biodiesel blend (diesel + cedar wood oil) with acetylene, and 100% biodiesel (diesel + cedar wood oil) with acetylene, as shown in Fig. 7. The acetylene flow rate was maintained at 6 LPM, while the compression ratio was set to 18, the injection timing to 23°CA bTDC, and the injection pressure to 220 bar throughout the experiment.

Fig. 7

Variation of brake thermal efficiency with load for different fuels modes

The highest brake thermal efficiency of 30.66% was achieved when the engine was fueled with diesel and acetylene at full load. For the blend of 50% biodiesel with acetylene, the brake thermal efficiency was recorded as 28.63%, while for 100% biodiesel with acetylene, it decreased further to 27.6%.

These findings indicate that at lower loads, the flame fronts formed during the ignition process fail to propagate across the entire combustion chamber, resulting in the homogeneous dispersion of unburnt acetylene and lower thermal efficiency (Hariram et al. 2017). The injection of acetylene improves thermal efficiency compared to neat diesel and biodiesel operation of the internal combustion engine due to the higher heat release rate, which ultimately leads to higher cylinder pressure and optimal utilization of the heat input (Poonia et al. 2011).

Emissions characteristics

HC emissions

The variation of HC (hydrocarbon) emissions with load was analyzed for different fuel blends, including diesel with acetylene, a 50% biodiesel blend (diesel + cedar wood oil) with acetylene, and 100% biodiesel (diesel + cedar wood oil) with acetylene, as shown in Fig. 8. The acetylene flow rate was maintained at 6 LPM, while the compression ratio was set to 18, the injection timing to 23°CA bTDC, and the injection pressure to 220 bar throughout the experiment.

Fig. 8

Variation of HC emissions with load for different fuels modes

At no load, the highest HC emission of 73 ppm was recorded for the engine fueled with diesel and acetylene. For the blend of 50% biodiesel with acetylene, the HC emission was measured at 65 ppm, and for 100% biodiesel with acetylene, it further reduced to 50 ppm.

Interestingly, it was observed that as the load increased, the HC emissions decreased for all fuel blends. This decrease in HC emissions across the entire load range can be attributed to the wider range of ignition limits, higher burning velocity, leaner operation of the engine, and the higher energy release of acetylene (Khan et al. 2021; El-Sheekh et al. 2022).

NOx emissions

The variation of NO_x (nitrogen oxides) emissions with load was examined for different fuel blends, including diesel with acetylene, a 50% biodiesel blend (diesel + cedar wood oil) with acetylene, and 100% biodiesel (Diesel + Cedar Wood oil) with acetylene, as illustrated in Fig. 9. The acetylene flow rate was maintained at 6 LPM, while the compression ratio was set to 18, the injection timing to 23°CA bTDC, and the injection pressure to 220 bar throughout the experiment.

Fig. 9

Variation of NOx emissions with load for different fuels modes

At full load, the highest NO_x emission of 380 ppm was observed for the engine fueled with 100% biodiesel and acetylene. The combustion of the 50% biodiesel blend with acetylene resulted in NO_x emissions of 340 ppm, while the lowest NO_x emission of 275 ppm was recorded for the diesel and acetylene fuel blend. Furthermore, it was noted that NO_x emissions increased with an increase in load for all fuel blends. This trend indicates that as the engine operates at higher loads, the production of NO_x emissions intensifies (Velmurugan et al. 2023), irrespective of the type of fuel blend used.

CO emissions

The variation of CO (carbon monoxide) emissions with load was analyzed for different fuel blends, namely diesel with acetylene, a 50% biodiesel blend (diesel + cedar wood oil) with acetylene, and 100% biodiesel (Diesel + Cedar Wood oil) with acetylene, as depicted in Fig. 10. The acetylene flow rate was maintained at 6 LPM, while the compression ratio was set to 18, the injection timing to 23°CA bTDC, and the injection pressure to 220 bar throughout the experiment.

Fig. 10

Variation of CO emissions with load for different fuels modes

Under no load conditions, the combustion of the diesel and acetylene fuel blend resulted in the highest CO emission of 0.15 ppm. Similarly, the combustion of the 50% biodiesel blend with acetylene and the 100% biodiesel blend with acetylene produced CO emissions of 0.12 ppm each.

Furthermore, it was observed that as the load increased, the CO emissions decreased for all fuel blends (Thiruselvam et al. 2023). This trend indicates that higher engine loads promote pre-dominant combustion, leading to reduced CO emissions regardless of the fuel blend used (Saravanamuthu et al. 2023).

Smoke emissions

The variation of smoke emissions with load was analyzed for different fuel blends, including diesel with acetylene, a 50% biodiesel blend (diesel + cedar wood oil) with acetylene, and 100% biodiesel (diesel + cedar wood oil) with acetylene, as shown in Fig. 11. The acetylene flow rate was maintained at 6 LPM, while the compression ratio was set to 18, the injection timing to 23°CA bTDC, and the injection pressure to 220 bar throughout the experiment.

Fig. 11

Variation of smoke emissions with load for different fuels modes

At full load conditions, the combustion of the diesel and acetylene fuel blend resulted in the highest smoke emission of 93 ppm. Similarly, the combustion of the 50% biodiesel blend with acetylene generated 91 ppm of smoke emission, while the 100% biodiesel blend with acetylene produced 85 ppm of smoke emissions. Furthermore, it was observed that as the load increased, the smoke emissions also increased for all fuel blends. This trend indicates that higher engine loads contribute to the production of more smoke, regardless of the specific fuel blend used (Murugapoopathi et al. 2022).

Combustion characteristics fuel blends with nanoparticle additives

Cylinder pressure crank angle

In this section, the variation of cylinder pressure with crank angle was examined for different fuel blend combinations as shown in Fig. 12. These blends include diesel with acetylene injected at a flow rate of 6 LPM (D + A 6L), diesel with acetylene and nanoparticle additives injected at 6 LPM (D + N + A 6L), 50% biodiesel blend (diesel + cedar wood oil) with acetylene and nanoparticle additives (B50 + N + A 6L), and 100% biodiesel blend with acetylene and nanoparticle additives (B100 + N + A 6L). The experiment was conducted under constant conditions of acetylene flow rate (6 LPM), compression ratio (18), injection timing (23°CA bTDC), and injection pressure (220 bar).

Fig. 12

Variation of pressure with crank angle for different fuels modes with nanoparticle additives

The peak pressure during the combustion process was observed at a crank angle of 10◦CA. The highest peak pressure of 49.20 bar was obtained when the engine was fueled with a blend of diesel and acetylene. However, when nanoparticle additives were introduced to the blend (D + N + A 6L) at full load, the peak pressure increased to 51.22 bar. Similarly, the peak pressure for the 50% biodiesel blend with acetylene and nanoparticle additives (B50 + N + A 6L) was 47.86 bar, and for the 100% biodiesel blend with acetylene and nanoparticle additives (B100 + N + A 6L), it was 46.59 bar. Thus, the maximum peak pressure was achieved when the engine was fueled with acetylene-aspirated diesel containing nanoparticle additives.

The addition of nanoparticles resulted in a slight reduction in cylinder pressure. This can be attributed to the decreased ignition lag and lower fuel availability during the premixed combustion phase, leading to faster evaporation and atomization. As a result, the overall combustion phase is advanced, leading to a lower rise in cylinder pressure. Furthermore, the introduction of nanoparticles in the blend improves the cetane number and combustion characteristics, leading to a lower premixed combustion phase (PCP) and subsequently reduced cylinder pressure.

Heat release rate

In this section, Fig. 13 shows the variation of heat release rate with crank angle was analyzed for different fuel combinations, including diesel with acetylene, diesel with acetylene and nanoparticle additives, 50% biodiesel with acetylene and nanoparticle additives, and 100% biodiesel with acetylene and nanoparticle additives. The flow rate of acetylene was maintained at 6 LPM, while the compression ratio was 18, injection timing was 23°CA bTDC, and injection pressure was 220 bar, all of which remained constant throughout the experiment.

Fig. 13

Variation of heat release rate with crank angle for different fuels modes with nanoparticle additives

The crank angle of 5°CA was found to correspond to the maximum heat release rate. The highest heat release rate of 41.99 J/°CA was achieved during the combustion of diesel with acetylene and nanoparticle additives. Combustion of diesel with acetylene alone resulted in a heat release rate of 40.77 J/°CA. For the 50% biodiesel blend with acetylene and nanoparticle additives, the maximum heat release rate recorded was 35.71 J/°CA, while for the 100% biodiesel blend with acetylene and nanoparticle additives, it was 32.30 J/°CA. Thus, the engine fueled with acetylene-aspirated diesel containing nanoparticle additives exhibited the highest heat release rate.

The addition of nanoparticles initially caused a slight decrease in the heat release rate. This can be attributed to the reduced ignition delay (Rajesh et al. 2023) and the ability of nanoparticles to promote early initiation of combustion, leading to a lower heat release rate and an advanced peak heat release rate (Seela et al. 2019).

Performance characteristics

Brake thermal efficiency

In this section, the variation of brake thermal efficiency with load was examined for different fuel combinations, including diesel with acetylene, diesel with acetylene and nanoparticle additives, 50% biodiesel with acetylene and nanoparticle additives, and 100% biodiesel with acetylene and nanoparticle additives. The flow rate of acetylene was maintained at 6 LPM, while the compression ratio was 18, injection timing was 23°CA bTDC, and injection pressure was 220 bar, all of which remained constant throughout the experiment.

Figure 14 illustrates the results, showing the relationship between brake thermal efficiency and load for each fuel blend. The highest brake thermal efficiency of 33.3% was achieved when the engine was fueled with diesel containing acetylene and nanoparticle additives at full load. A brake thermal efficiency of 30.663% was obtained for the engine running on diesel with acetylene alone at full load. For the 50% biodiesel blend with acetylene and nanoparticle additives, as well as the diesel with acetylene and nanoparticle additives, a brake thermal efficiency of 29.80% was recorded at full load. Lastly, the engine fueled with 100% biodiesel and acetylene with nanoparticle additives exhibited a brake thermal efficiency of 28.9% at full load.

Fig. 14

Variation of heat brake thermal efficiency with load for different fuels modes with nanoparticle additives

The inclusion of nanoparticle additives in the fuel blend has shown to enhance the combustion rate by preventing the formation of carbon deposits. This improvement in combustion efficiency contributes to the increased brake thermal efficiency observed. Furthermore, the biodiesel blended fuel with nanoparticle additives demonstrated brake thermal efficiency performance comparable to that of neat diesel with acetylene injection operation, indicating its potential as a viable alternative fuel option (Das and Sharma 2018).

Emissions characteristics

HC emissions

The variations in HC emissions with load were analyzed for different fuel blends, namely diesel with acetylene, diesel with acetylene and nanoparticle additives, 50% biodiesel with acetylene and nanoparticle additives, and 100% biodiesel with acetylene and nanoparticle additives. The flow rate of acetylene was maintained at 6 LPM, while the compression ratio, injection timing, and injection pressure remained constant at 18, 23°CA bTDC, and 220 bar, respectively.

Figure 15 presents the results, showcasing the relationship between HC emissions and load for each fuel blend. At no load, the highest HC emission of 73 ppm was observed during the combustion of diesel with acetylene. When diesel was combined with acetylene and nanoparticle additives, the HC emission reduced slightly to 71 ppm. Similarly, the 50% biodiesel blend with acetylene and nanoparticle additives exhibited an HC emission of 68 ppm, while the 100% biodiesel blend with acetylene and nanoparticle additives recorded an HC emission of 65 ppm at no load.

Fig. 15

Variation of HC emissions with load for different fuels modes with nanoparticle additives

As the load increased, it was observed that the HC emissions decreased for all the fuel blends. This reduction in HC emissions can be attributed to the presence of nanoparticles in the fuel blend (Gharehghani et al. 2019). The addition of nanoparticles leads to an excess of oxygen content and facilitates the release of activation energy, resulting in lower HC emissions. Previous studies have also highlighted the role of nanoparticles in reducing HC emissions (Fu et al. 2017).

NOx emissions

The variations in NOx emissions with load were analyzed for different fuel blends, including diesel with acetylene, diesel with acetylene and nanoparticle additives, 50% biodiesel with acetylene and nanoparticle additives, and 100% biodiesel with acetylene and nanoparticle additives. The flow rate of acetylene was maintained at 6 LPM, while the compression ratio, injection timing, and injection pressure were held constant at 18, 23°CA bTDC, and 220 bar, respectively.

Figure 16 illustrates the results, depicting the relationship between NO_x emissions and load for each fuel blend. At full load, the highest NO_x emission of 380 ppm was observed during the combustion of 100% biodiesel with acetylene and nanoparticle additives. Combustion of the 50% biodiesel blend with acetylene and nanoparticle additives produced a peak NO_x emission of 373 ppm, while the combustion of diesel with acetylene and nanoparticle additives resulted in a peak NOx emission of 345 ppm. On the other hand, the lowest peak value of NO_x emissions (275.86 ppm) at full load was obtained from the combustion of diesel with acetylene.

Fig. 16

Variation of NO_x emissions with load for different fuels modes with nanoparticle additives

It was observed that NO_x emissions increased with an increase in load for all fuel blends. The combustion of B100 + N + A 6L exhibited higher NO_x emissions compared to the nanoblended B50 + N + A 6L and nanoblended diesel blends. This difference can be attributed to the availability of oxygen content in the test fuel, which induces a significant temperature rise inside the combustion chamber, leading to excessive nitrogen oxide formation (Shameer 2017; EL-Zohairy et al. 2023).

CO Emissions

The variations in CO emissions with load were examined for different fuel blends, including diesel with acetylene, diesel with acetylene and nanoparticle additives, 50% biodiesel with acetylene and nanoparticle additives, and 100% biodiesel with acetylene and nanoparticle additives. The flow rate of acetylene was maintained at 6 LPM, while the compression ratio, injection timing, and injection pressure were held constant at 18, 23°CA bTDC, and 220 bar, respectively.

Figure 17 displays the results, illustrating the relationship between CO emissions and load for each fuel blend. At no load condition, the maximum CO emission value of 0.15 ppm was observed during the combustion of diesel with acetylene fuel blend. Similarly, the combustion of diesel with acetylene and nanoparticle additives produced a peak CO emission of 0.13 ppm. Combustion of 50% biodiesel with acetylene and nanoparticle additives resulted in a peak CO emission of 0.12 ppm, while 100% biodiesel with acetylene and nanoparticle additives blends exhibited a peak CO emission of 0.11 ppm.

Fig. 17

Variation of CO emissions with load for different fuels modes with nanoparticle additives

The increase in the proportion of biodiesel in the fuel blend led to a reduction in CO emissions due to its lower carbon content, higher cetane number, and delayed formation of fuel-rich zones (Emiro and Mehmet 2018; Xuan et al. 2021). The addition of nanoparticle additives facilitated the oxidation of CO into CO₂, promoting complete combustion and resulting in lower CO emissions in fuel blends containing nanoparticle additives (Lawrence et al. 2011; Gharehghani and Pourrahmani 2019).

Smoke emissions

The variations in smoke emissions with load were analyzed for different fuel blends, namely diesel with acetylene, diesel with acetylene and nanoparticle additives, 50% biodiesel with acetylene and nanoparticle additives, and 100% biodiesel with acetylene and nanoparticle additives. The flow rate of acetylene was maintained at 6 LPM, while the compression ratio, injection timing, and injection pressure were kept constant at 18, 23°CA bTDC, and 220 bar, respectively.

Figure 18 illustrates the results, depicting the relationship between smoke emissions and load for each fuel blend. At full load condition, the maximum smoke emission value of 93.32 ppm was observed during the combustion of diesel with acetylene injection operation. Combustion of diesel with acetylene and nanoparticle additives resulted in a maximum smoke emission of 84.00 ppm at full load. Similarly, combustion of 50% biodiesel with acetylene and nanoparticle additives generated a maximum smoke emission of 82.00 ppm at full load. Finally, combustion of 100% biodiesel with acetylene and nanoparticle additives blends produced a maximum smoke emission of 79.00 ppm.

Fig. 18

Variation of Smoke emissions with load for different fuels modes with nanoparticle additives

It is evident that smoke emissions increase with an increase in load for all fuel blends. However, the results clearly demonstrate that the addition of nanoparticle additives has significantly reduced smoke emissions compared to neat diesel (Kumar and Amirtham 2016; EL-Seesy et al. 2023a).

Conclusion

In this study, we conducted experimental investigations on the performance, emission, and combustion properties of a single cylinder, four-stroke, variable compression ratio (VCR) direct injection diesel engine. Various fuel blends were tested, including neat diesel with acetylene injection, 50% biodiesel with acetylene, 100% biodiesel with acetylene, diesel with acetylene and nanoparticle additives, 50% biodiesel with acetylene and nanoparticle additives, and 100% biodiesel with acetylene and nanoparticle additives. Based on our findings, the following conclusions can be made:

• The addition of cerium oxide nanoparticles to diesel fuel improved brake thermal efficiency (BTE) by enhancing the surface area-to-volume ratio. This resulted in better performance compared to neat diesel operation.

• The combination of cedar wood oil blend, acetylene injection, and nanoparticle additives demonstrated equivalent engine efficiency compared to that diesel.

• The smoke, CO and HC were decreased for B100 + 6L A + 50 ppm blend by 20.21%, 65.52% and 51.42% for 100% load for maximum load.

• Among the tested fuel blends, B50 + 6L A + 50 ppm at 100% load, combustion pressure and BTE improved by 5.31% and 4.09% when compared without nanoparticle for the same fuel blends.

• The NO_x emission was slightly higher than diesel for nanoadditives due to its enhance fuel combustion and thermal stability of blends.

These findings highlight the potential of cerium oxide nanoparticles, biodiesel blends, and acetylene injection in improving engine performance and reducing emissions. Further research in this area could lead to the development of more efficient and environmentally friendly diesel engine technologies.