Royal Poinciana Biodiesel Blends with 1-Butanol as a Potential Alternative Fuel for Unmodified Research Engines

Abstract

This research work investigates the experimental work of a single-cylinder diesel engine operated with royal poinciana biodiesel blends with various proportions of 10, 20, and 30% volume with 1-butanol as an effective ignition-improving additive. The test blends were indicated as D90RP7B3 (90% diesel + 7% royal poinciana biodiesel + 3% butanol), D80RP14B6 (80% diesel + 14% royal poinciana biodiesel + 6% butanol), D70RP21B9 (70% diesel + 21% royal poinciana biodiesel + 9% butanol), and pure royal poinciana biodiesel (RP100) and diesel. The significant findings or results obtained during the experimentation are that BTE is suitable for blend D90RP7B3, and the least BSFC is found for blend D90RP7B3 in the 0.24 kg/kWh range. The inline cylinder pressures are found to be suitable for the blend D90RP7B3 in the range of 7 MPa; HRR is ideal for both the blends D90RP7B3 and D80RP14B6 in the range of 90 and 88 kJ; D90RP7B3 possesses adequate ignition delay at full load conditions 16° in crank angle advance; maximum A/F ratios are well suitable for the blend D90RP7B3 in the ratio 11:1 at higher loads. Volumetric efficiency is achieved well for all the blends and diesel; the emissions released from the royal poinciana blends, such as CO, CO₂, HC, and NO_X, were reduced by 14.12, 8.33, 11.1, and 18.8% compared to standard diesel. Hence, royal poinciana blends with 1-butanol can be considered the best fuels in the automobile sector.

1. Introduction

Energy demand has been increasing rapidly over the last 5 years due to the 6% increase in vehicle usage compared to the last 5 years. The natural resources were depleting continuously due to the demand for increased vehicles and power production.¹ People are looking into alternative sources of energy to generate power or drive propulsion because of savings in costs and fewer emissions compared to diesel.² Although there were certain limitations to the diesel engine’s performance, the important factors such as fuel economy and emissions possess thrust areas that remain inconsistent and act as challenging parameters in the transportation sector.³ The emissions released from diesel engines are quite high, which may have a high impact on the environment and living organisms. Hence, people want to move to alternative energy resources instead of diesel. Though various investigations have been done on some additives, based on past research studies, alternative fuels possess a 10% increase in advantage and a 5% better reduction in emissions than diesel.⁴ Hence, it was necessary to conduct investigations on a trial basis to overcome the emissions difficulties and improve the engine performance without any modifications to the diesel engine. An in-depth analysis was carried out to extract the maximum quantity of oil from royal poinciana seeds by the pyrolysis process at 625 °C, and the results proved that the maximum content of royal poinciana oil by 50 vol % can be extracted by using the pyrolysis method; the residue formation was compared with the copyrolysis method.⁵ A characterization study was conducted, which reported that the synthesis of oil through royal poinciana seeds by the process pyrolysis method yields a maximum content of 48% at the reaction temperature of 400–650 °C; the residues formed during this process were quite low at the average levels of 7 wt % as compared to other methods of yielding.⁶ The source of royal poinciana powder utilized a special type of kinetic approach in addition to some percentage of the machaca indica oil to evaluate the thermal stability analysis of blended fuels by the Taguchi method; it was observed that the maximum yield of 85% content of oil can be extracted through this method. The performance and emission of the diesel engine were investigated using royal poinciana biodiesel blends with different blends B25, B50, B75, and B100;⁷ from this study, it was understood that the B25 blend shows the best results. Hence, several researchers evaluated alternative sources of energy such as sunflower seeds, banana leaves, soya bean seeds, palm munja seeds, and other seeds;⁸⁻¹⁰ various investigations have proved that the addition of additives to the different types of biodiesel blends such as lotus biodiesel blends and sunflower blends with different proportions ranging from 5 to 20% has shown significant improvement in the engine performance by 3.5% and reduced the consumption of fuel by 2.5% compared to the diesel.^11,12 The addition of butanol beyond the limits ranging from 20 to 50% leads to excess noise formations inside the engine, causing detonation.¹³ The addition of butanol to the palm oil with proportions of 10% gives the least emissions in terms of NO_X by 2%, CO₂ by 1.6%, and CO by 1.5%. However, adding butanol above 15% leads to preignition, which reduces performance compared to diesel.¹⁴ Adding 1-butanol and 1-pentanol to the collypolium biodiesel proportion up to 50% reduces the emissions of CO and HC in all load cases, followed by 2.2 and 3.1%. Still, a drastic increase in NO_X emissions in the range of 6.2% compared to diesel because of higher additions above 20% proportions leads to incomplete combustion, which tends to cause inadequate combustion and produces more NO_X emissions than diesel.¹⁵ Adding 5% 1-butanol in the tamarind biodiesel reduces regulated emissions such as CO, HC, and smoke opacity by 7.2, 6.2, and 6.1% compared to diesel. However, the NO_X emissions were significantly increased by 11% compared to diesel.¹⁶ It was proved that adding 10, 20, and 30% of 1-butanol to the vegetable oil acts as a homogeneous mixture for achieving the appropriate combustion to reduce the controllable emissions such as CO, CO₂, and HC emissions by 2.2, 3.1, and 2.45%, respectively.¹⁷ However, uncontrollable emissions, such as triglycerides, were increased by 2.3% compared to controllable emissions. This study gives researchers deep knowledge on achieving the least emissions with the latest additives. The properties of palm oil blend proportionated with 1-butanol are tested in the research lab according to the standard EN 590 for calculating the viscosities, flashpoint, and calorific values. However, the 1-butanol blends with 5% 1-butanol have significant properties compared to diesel. The regulated emissions of CO, CO₂, and HC are quite low (3, 5.2, and 6.1%, respectively) compared to standard diesel, whereas uncontrolled emissions during peak loads are very high at 3.2%, higher than diesel.¹⁸ Adding 1-butanol to the lotus biodiesel up to 5% gives the best combustion phenomenon compared to diesel, and fewer emissions were formed at peak loads, followed by 3.1, 4.1, and 7.2% for CO, HC, and CO₂ compared to diesel.¹⁹ 1-butanol acts as an autoignition improver, reducing starting problems in cold conditions. Adding 10% of 1-butanol with algae biodiesel reduces regulated emissions of CO, CO₂, and HC by 3.1, 4.2, and 5.1%, respectively. Further, the addition leads to knocking, which tends to permanent engine failure.²⁰ Hence, from the various research studies, the maximum possible performance achieved with the help of butanol is limited to 20 mL of butanol in definite atmospheric situations. Hence, in this research, adding 1-butanol is limited to 10% to achieve the engine’s best performance. Hence, the motivation of this research is to investigate and evaluate the performance of the single-cylinder diesel engine for four cases, D90RP7B3, D80RP14B6, D70RP24B6, and RP100, and compare the results with diesel (D100).

Although various potential biodiesels were investigated concerning 1-butanol and 1-pentanol, the studies were limited to royal poinciana biodiesel blends. The royal poinciana seeds are available in coastal regions all over India. Many researchers have researched biodiesel blends, which are limited due to plenty of seeds available in the winter season; apart from that, the cost of the seeds per kg is moderate (Rs 600–700 per kg).²¹ However, many researchers have proved that maximum oil has been derived from this type of seed because it is edible and easy to use.²² Few researchers have proved that a maximum of 85% of oil can be obtained in the temperature zone of 500 °C with the help of a reactor, and 350 mL from 6 kg of royal poinciana seeds was crushed with the help of a mechanical expeller.²³ A recent study proved that more oxygenated items in the royal poinciana blends tend to operate the engine in a smoother way when the engine is operating at the maximum pressure of 9 MPa and a temperature of 1200 °C; the least HC, CO, and CO₂ emissions were produced in the range of 1.2, 1.8, and 1.9%; they result in good emission characteristics compared to diesel and other biodiesel blends extracted from other seeds.^24,25 Implementing the oil derived from the royal poinciana has huge potential benefits, fewer emissions, and superior BTE, BSFC, and other main parameters. Recent studies proved that oil derived from the royal poinciana seeds has less regulated and unregulated emissions than other biodiesels, and plenty of seeds are available in the coastal regions of Tamil Nadu. Hence, we chose these oils to analyze and for further study.

The kinematics models were developed for the thermal decomposition of Oleifera and royal poinciana seeds; the two models, namely, Starink Friedman and Flynn Wall Ozawa, were used; from the analysis, the profiles show that the minor activation energy to decompose the seeds into oil is attained with R² > 9. The maximum amount of oil obtained is 85% by weight for the Oleifera seeds and 80% by weight for royal poinciana seeds for Flynn Wall Ozawa models, compared to other models.²⁶ In a study on royal poinciana seeds, the syngas extracted from these seeds with a composition of 27% H₂, 21% CO, and 38.2% CH₄ was mixed with pyrolysis blends directly with a dual-mode combination of 20% pyrolysis oil and 80% diesel + syngas derived from royal poinciana seeds with 8 lpm, which improved the engine performance by 1.6% and reduced the CO and HC emissions and opacity by 15.1, 25.2, and 32.1%, respectively, at peak loads compared to diesel.²⁷ The improvement in results was observed using the diesel engine operated with royal poinciana seeds with a combination of 80% Royal Poicinia blends and 20% diesel with slight modifications in the engine cylinder coated with thermal barrier coatings, followed by 50% Al2O3 + 50% YSZ, which improved the engine performance by 2–3%; the least BSFC was achieved for this blend—80% Royal Poicinia blends and 20% diesel—which was in the range of 0.016 kg/kWh (2.2% compared to diesel). However, the lowest emissions are achieved for this same blend, followed by CO emissions by 5.3%, and smoke opacity is reduced by 7.1% compared to diesel.²⁸ The Royal Poicinia oil is extracted with the help of a solar-assisted pyrolysis reactor and mechanical expeller using a biochemical and hydrocracking process; 80% of the oil is obtained by this combined extraction process. The blend combinations of B20 give optimal results; they improved BTE by 1% and reduced BSFC by 1.2% compared to diesel. The formation of emissions is very low in the range of 2.1% for CO emissions, and the lowest emissions are found for this same blend B20 order of 25 ppm, which is 3.2% less than diesel.²⁹ The best fuel, D30B60EPB10, leads to the dynamic performance of the engine with combustion characteristics. The BTE is increased by 7.3%, the minimum BSFC achieved is 3.9%, and CO, CO₂, and NO_X emissions and smoke opacity are reduced by 8.74, 31.21, 38.55, and 60.2%, respectively.³⁰ Recently, research on the extraction of oil from royal poinciana seeds with the bamboo stem as a catalyst was conducted; RSM and ANN were effectively utilized to estimate the extraction of oil; and from ANN method the oil estimation is found by 97% by weight. From this study, it is understood that the bamboo stem acts as a powerful catalyst to melt and vaporize the royal poinciana seeds for 90 min to attain the maximum content of oil.³¹ The performance of the engine operated with mahua oil and 1-butanol is gradually increased by 2.2%, and the fuel consumption is decreased by 1.3%; emissions of CO₂, CO, and NO_X are reduced by 5.21, 6.12, and 7.32% compared to diesel. 1-butanol acts as a very good ignition improver to boost the overall engine performance and combustion. The researchers tried using lanthanum oxide as a coating material with a thickness of 0.6 mm and ascorbic acid as the base material, which improved the engine heat dissipation compared to conventional engines.³² The increase in BTE is found for the blends operated on WCO combined with Al₂O₃ nanoadditives; with the help of the ANN method and regression analysis with the most petite fit of R² = 1, the usage of WCO blends with 1-butanol significantly improves the cylinder pressures to achieve maximum combustion to reach BTE and least BSFC for the HCCI- DI Engine.³³ The research studies proved that higher injection pressures are obtained for the blends operated on 1-butanol with 100 °CA BTDC or 125 °CA BTDC crank angles; this will improve the engine performance by 4.2% compared to diesel.³⁴ The NO_X emissions were reduced by 4%. Adding 40% of 1-butanol to the biodiesel tends to improve the acceleration of OH radicals at a much faster rate to achieve fine BTE, lower the BSFC, and lower NO_X emissions compared to diesel.³⁵

This study investigates the diesel engine performance, combustion, and emission parameters of the various test blends RP100, D90RP7B3, D80RP14B6, and D70RP21B9. Most of the literature that used 1-butanol with different biodiesel reported that it gives predetermined performance and minor emissions. Hence, the main aim of this study is to add the proportions of 1-butanol to improve the ignition characteristics owing to peak cylinder pressures and HRR parameters. The performance parameters, such as BTE and BSFC, and combustion parameters, such as cylinder pressure, HRR, ignition delay, air to fuel ratio, MFB, and volumetric efficiency, are to be measured. In addition, an emission analysis is to be conducted to determine the emission released from the engine when it operates at part load and full load conditions. The CO, CO₂, HC, and NO_X emissions were investigated with the help of an exhaust gas analyzer to predict the minor emission characteristics. All of the parameters examined by the test fuels are to be compared with pure diesel to measure the blends suitable for replacing diesel fuel in automotive and irrigation applications. In this work, it was found that adding 1-butanol to royal poinciana seeds achieves good ignition qualities and the engine is operated under smoother conditions. Many researchers tried using 1-butanol in various alternative biodiesels such as palm biodiesel, soya biodiesel, lotus biodiesel, and so forth, with higher proportions, but no researchers have tried using 1-butanol with royal poinciana blends with a definite proportion varying from 3 to 9%. Hence, this innovation in the proportion of 1-butanol gives the best results in smoother engine operating conditions compared to diesel fuel. The variance between the current and previous studies is that many of the researchers worked on 1-butanol, which is concerned with royal poinciana, and it is significantly less. Many researchers have used 1-butanol with various biodiesels such as palm oil, algae oil, sunflower oil, and capylum oil, but they focused on specific parameters such as performance and emissions. We tried using 1-butanol with royal poinciana for definite percentages from 3 to 9% and evaluated parameters such as performance, combustion, and emission. However, the results show that all of the parameters have potential merits equal to pure diesel; significantly, the emissions were reduced compared to diesel. The inline cylinder pressures, HRR, ignition delay, A/F ratios, volumetric efficiency, and CO, CO₂, HC, and NO_X emissions are substantially studied in this analysis.

2. Materials and Methods

2.1. Materials

The royal poinciana seeds were dried for 10 h, and the oil was extracted with the help of a mechanical expeller; the oil content removed from the seeds was found to be 70 mg/kg.³⁶ Hence, the extracted oil was used for the transesterification process, with a mixture of methanol as a catalyst. The proportions added for this process were estimated at 20% of methanal with 5% of KOH as the catalyst to form methyl esters.³⁷ After this process, the oil was heated in the temperature range of 120 °C and kept under the action of gravitational settlement for 24–48 h to separate the glycerine. The physical observation shows that the blend is filtered well with 100% purity and is suitable for experiments at different testing atmospheres.

2.2. Filtration of Oil

The contaminants present in the oil are in the form of minute particles in size varying from 1 to 40 μm. This is due to the average cooling rate accompanied by the transesterification process to achieve fabric oil. Hence, it was necessary to filter the minute size foreign particles with the help of well-equipped filters designed by fabric materials or ceramic materials, which resist the flow and filter the oil, resulting in the purified biodiesel for easy operation of the engine for achieving good thermodynamic results in terms of brake thermal efficiency, specific fuel consumption, smoke opacity, CO₂ emissions, and NO_X emissions. In addition, the purified oil results in a better combustion rate, leading to a better ignition delay and a high viscous flow rate. The filtration of oil by the fabric phenomenon will improve the diesel engine’s performance and life span in various aspects that prevent less engine maintenance, which saves cost.

3. Testing Procedure

The selection of the engine is the significant and crucial factor that leads to results with fewer possible errors in terms of efficiency and emissions; Before starting the test procedure, the engine. Figure 1 represents a schematic representation of the system with its technical parameters.

Figure 1.

Schematic setup.

The engine should be cleaned, made dry, and trial run-tested, which ensure that the engine is free from dust, debris, and contaminants. A single-cylinder diesel engine with the abovementioned factors is taken for this analysis, and the engine specifications are tabulated in Table 1. Table 2 provides ASTM standards and properties of royal poinciana, 1-butanol blends, and diesel. The dynamometer is a device used for applying loads by the rotation of a mechanical impeller; the loads that can be given with the help of the dynamometer were applied [0, 25, 50, 75, and 100% (full load conditions)] to evaluate the performance. This method of testing the engine gives accurate results, and many scientists and engineers have suggested applying the load gradually, improving the engine’s span and leading to less maintenance. The data acquisition system is set up with special transducers and analog controllers to acquire the data from the engine to emissions. The engine is running at a constant rpm of 1500 rpm for test trials.

Table 1. Specifications of the Engine.

sno	description	specifications
1	compression ratio (r)	18
2	crank radius	90 mm
3	rated power	5.19 KW at 1500 rpm
4	injection type	DI
5	start of fuel injection	23° BTDC
5	length of the connecting rod	240 mm
6	stroke length (L) and bore (d)	120 and 90 mm
7	no of strokes	4

Table 2. Properties of Royal Poinciana–Butanol Blends and Diesel.

sno	property of fuel	units	ASTM diesel standards	ASTM biodiesel standards	D100	D90RP7B3	D80RP14B6	D70RP21B9	RP100
1	hydrogen	wt %	D3343	14	11	10	9.8	8	4
2	carbon	wt %	D1603	90	77	68	60	50	20
3	pour point	°C	D93	16–34	12	10	8	6	4
4	kinematic viscosity at 40 °C	CST	D445	1.2–4.2	5	4.06	3.72	2.98	1.87
5	flashpoint	C	D93	45–60	45	48	50	52	55
6	cetane number		D4737	41–60	55	47	46	40	38
7	cloud point	°C	D2500	6–16	7	6	5	4	2
8	oxygen	wt %	D5622	2%	1.9	1.2	0.9	0.8	0.7
9	sulfur	ppm	D6751	600		0.8	0.6	0.4	0.2
10	fire point	°C	D93	55-100	55	58	60	63	65
11	calorific value -HHV	MJ/kg	D240	43–44	44.12	43.23	40.11	39.21	38.22

4. Uncertainty Analysis

The uncertainty analysis is essential to determine or evaluate the accuracy of experiments in different trials. It represents the accuracies of each instrument and the errors that occurred during the experiment. The deviations that happened during the experimentation are calibrated by three or more trials using the Gaussian distribution method as the reference sampling analysis method. According to the Gaussian distribution,³⁸ 98.3% accuracy is found in the instruments, and the remaining 1.7% were errors and deviations that occurred from the instruments and calibrated data. The errors may be scientific errors or atmospheric errors.

Table 3 represents the uncertainty analysis of this experiment and the constraints as follows; the actual experimental readings and calibrated readings concerned the preliminary data with the experimental setup are given by eq 1(39)

1

Table 3. Uncertainties in the Experiment.

sno	type of instrument used	measurements	range	accuracy	uncertainties (%)
1	sensor	speed of the engine	rpm	±8 rpm	±0.15
2	buret meter	quality of fuel	0–1200 cc	±0.13 cc ±1.5%	±1.2
3	stopwatch	time in seconds		±0.13 s	±0.22
4	manometer	air measurements	0–500 mm	±3.1 mm	±1.2
5	AVL gas analyzer	HC	0–11,000 ppm	±14 ppm	±0.4
		NOX	0–5600 ppm	±12 ppm	±0.5
		CO	0–14 vol %	±0.05%	±0.5
		CO2	0–10 vol %	±0.05%	±0.4

The calibrated variables are expressed from eq 2(24)

2

The actual number of readings is expressed by eq 3(40)

3

5. Results and Discussion

5.1. Measurement of BTE

The performance of any thermodynamic engine depends upon the important factor termed BTE. The maximum amount of heat energy is liberated from the fuel; thermodynamically, it expands the piston and cylinder to rotate the crankshaft to attain the maximum possible, scientifically called BTE.⁴¹ BTE indicates the predominant performance to express the thermal capacity of the engine, and it is scientifically defined as the ratio of the “BP” to the actual heat transferred from the available fuel,⁴² in other words, the ratio of the maximum heat transfer with actual losses in heat during transmission or generation of power at the crankshaft to the actual heat about the predominant attainment of a lower heating value during fuel supply.⁴³ The BTE is calculated by eqs4–7⁴⁴

4

5

6

7

Figure 2 represents the attainment of “BTE” concerning the increase in load conditions. At initial load conditions (25% load), the BTE is in the order of 10.5%, but at the part load conditions (50% load), the BTE is in the range of 20%, which is significantly closer to the diesel efficiency (21%). However, at 75% load conditions, the efficiency is found to be in the range of 25%, which is closer to diesel fuel efficiency (26%). At full load conditions (100% load), BTE suitable for the diesel is in the range of 32%; and for the blend D90RP7B3, the “BTE” is found to be in the range of 31%, which is much closer to the efficiency of diesel. In all the load conditions, the best thermal efficiency is found for blend D90RP7B3 with an average percentage difference of 1% drop in thermal efficiency for fuel D90RP7B3. It is scientifically understood that the calorific value of D90RP7B3 is good and closer to that of diesel;⁴⁵ this gives a better BTE as compared to other blends.⁴⁶

Figure 2.

BTE.

5.2. Measurement Of BSFC

BSFC is defined as the very least fuel to be consumed concerned with the attainment of per kg of fuel pertained to release the thermodynamic heat to attain per “kWh” power.⁴⁷ In other words, the BSFC predicts the predomination of the slow acceleration of the fuels consumed concerning load conditions; the amount of fuel consumed depicts the losses due to friction and heat.⁴⁸ Mathematically, BSFC is expressed by eq 8(49)

8

The common factor that can be used for indicating the BSFC of an engine is given in eq9, which is expressed in (g/kWh)⁵⁰

9

The mass flow rate of air per gram distribution is converted into grams per joules multiplying the factor 3.61 × 10⁶ for measuring the BSFC.

Figure 3 depicts the BSFC attainment for various blends and diesel. At 25% load conditions, the consumption of fuels is very high for all the blends (D90RP7B3, D80RP14B6, D70RP21B9, and Diesel D100). At initial loads of 25% load conditions, the maximum consumption is found for the fuel RP100 in the 0.8 kg/range. Because of the low viscosity and less oxygenated items in RP 100, they tend to consume more fuel per “kg/kWh”.⁵¹ At 25% load conditions, a minor consumption is observed for the blend D90RP7B3 (0.55 kg/kWh); the BSFC is found to be in the range of 0.5 kg/kWh for diesel, which is much nearer to that of the D90RP7B3 blend.

Figure 3.

Specific fuel consumption vs load.

When the load is increased from 25 to 50, 50 to 75, and 75 to 100% conditions, a substantial increase in consumption is observed for all the blends (D90RP7B3, D80RP14B6, and D70RP21B9). At full load conditions and 100% load conditions, a minor consumption is observed for blend D90RP7B3 in the range of 0.24 kg/kWh; for diesel, the consumption is 0.21 kg/kWh. Diesel BSFC is close to the D90RP7B3 blends. The presence of good oxygenated items, better viscosity, and good calorific value tends to consume the least fuel at full load conditions compared to other blends.⁵² The different blends, such as D80RP14B6 and D70RP21B9, have lower viscosity and higher density difference, causing them to consume more fuel compared to diesel fuel and D90RP7B3 blends.⁵³

6. Combustion Characteristics

6.1. Cylinder Pressures

The adequate amount of pressure required to ignite the combustion process is measured or calculated with the help of cylinder pressures.⁵⁴ The pressure inside the cylinder depends upon the crank angle movement and the blend properties.⁵⁵ The minimum pressure developed from the engine varies at the rotation of the crank angles starting from 20° in advance when the piston is subjected to movement from BDC to TDC. The mathematical correlations required to determine the cylinder pressures inside the cylinder expressed in eq 10(56)

10

Eq 10 defines the correlations that are derived with respect to the cylinder pressures subjected to variations of the piston movements. During the piston movements of BDC to TDC, minimum pressures were developed. The starting pressure or initial pressure of these crank movements from BDC to TDC is measured as 1.8–2.0 MPa, at which the nozzle lifts at 5–6°, and at the end of the combustion, it reaches 7 MPa. The parameter r depends upon the gas constants, which are technically defined by ratios of specific heats of the gases or blends inside the combustion chamber.

Figure 4 represents the pressures developed inside the cylinder that is subjected to different crank angle rotations. From the figure, it is clearly understood that the maximum pressure rise inside the engine cylinder is 7 MPa for blend D90RP7B3. This pressure rise is due to good ignition characteristics owing to the presence of 1-butanol as an ignition improver.⁵⁷ The lower pressure rise occurred for the blends D80RP14B6 and D70RP21B9 compared to D90RP7B3. Because increasing in proportions beyond the limits of 1-butanol decreases the ignition capabilities, it tends to reduce the pressure variations and causes the lack of ignition, owing to the inadequate oxygen supply compared to D90RP7B3 blends. A few researchers have scientifically justified that 1-butanol significantly boosts ignition. However, 1-butanol is limited to 10%, because if it exceeds 10%, it tends to decrease the ignition capacities.²⁷ The pressure rise in the cylinder for the RP100 blends is very poor, on the order of 6 MPa. The lower cetane number tends to reduce the ignition delay too much, causing the cylinder pressure to rise compared with other blends. Another reason for the lower cylinder pressure rise is the lack of oxygen formations during combustion due to reduced flash and firepoint and reduced calorific value, causing the lower cylinder pressure to form an inadequate combustion process compared to other blends.⁵⁷

Figure 4.

Cylinder pressures.

6.2. Heat Release Rate

The total amount of heat released from the chemical fuels owing to different chemical reactions during the combustion of the fuel is determined by a technical factor called HRR. In other words, the energy released from the fuels per unit of time is considered for evaluating these technical parameters. The term “HRR” can be measured by eq 11(58)

11

The main parameters that affect the performance of the engine owing to these technical parameters (HRR) are the area of the cylinder and geometric conditions of the definite engine arrangements and definite mass particle size, injection pressures considering the droplet parameters that were to be considered to get adequate combustion efficiency, and reduced emission particles considering the HRR terminology. The following factors were to be considered for achieving the HRR during the rotation of crank angles represented in eqs 12 –14⁵⁹

12

13

14

Figure 5 represents HRR for royal poinciana blends and diesel. It is keenly observed that for all the blends except RP100, HRR is nearly equal and more than diesel. The blends such as D90RP7B3 and D80RP14B6 achieved good heat release, owing to maximum combustion temperatures with an adequate heat release rate of 90 kJ/CA deg for the D80RP14B6 blend and 88 kJ/CA deg for the D90RP7B3 blend. The reason is that the oxidation capacities of these blends, owing to the mixing proportions of 1-butanol with definite percentages limited to 3–6%, tend to accelerate the maximum liberation of chemical heat release rate for achieving the improvised heat combustion compared to diesel. A few pieces of literature proved that adding up to 10% butanol has significant merits on improved HRR, and this additive acts as a high ignition improver compared with other additives. It works as a good heat-releasing agent with proper combustion, especially for cold starting problems to ignite and produce maximum heat during combustion.⁶⁰ The lowest HRR is achieved for the blend at 60 kJ/CA deg. This lowest formation of oxygen results in reduced viscosity and reduced cetane number, it tends to the improper premixing stage and causes less HRR compared to Diesel and other blends.⁶¹

Figure 5.

Heat Release Rate.

6.3. Ignition Delay

The period that occurs at the starting point of injection and the starting period to attain the combustion phase is called ignition delay. It will happen before the BTDC of 14–21° during the crank. It means that the starting point for this ignition delay ranges from 14° and the end point is 21°. The gap concerning lagging of time relates to the spark is expressed as a technical word during combustion called ignition delay.⁶² This can be split into two ways: physical and chemical delays. The delay that occurs due to the property of self-ignition at self-ignition temperatures occurring during the preignition combustion phase is called physical delay.⁶³ The delay that occurs due to a lack of proper flame travel from the starting ignition point to the final ignition favored at different injection pressures is the chemical ignition delay. The rapid transformation of chemical ignition drives improper combustion in the engine. Figure 6 shows the ignition delay. All the blends possess the lowest ignition delay than diesel. The addition of 1-butanol to diesel makes the engine run in fine conditions in the rich mode.⁶⁴ Despite the cetane number of RP100, its other properties, such as kinematic viscosities, result in poor ignition delays compared to different blends. One more critical factor for the significantly lower ignition delay of RP100 is the insufficient density attained during the combustion, which results in inadequate oxygen supply for the blend RP100, resulting in very poor ignition.⁶⁵

Figure 6.

Ignition delay.

6.4. Air–Fuel Ratio

The required amount of mass of air and adequate amount of fuel by volume required for proper combustion of the fuel are represented by the technical factor called air-to-fuel ratios.⁶⁶ This factor is especially used to determine the engine combustion efficiency by varying the different proportions of the fuels at other loads concerned with different masses of fuels and air. Mathematically, the A/F is expressed in eq 15(67)

15

The mixtures of the masses concerned with different properties of air and its fuel are expressed by the following three technical factors: (a) lean mixtures, (b) rich mixtures, and (c) stochiometric mixtures. The lower proportion of the fuel at lower loads tends to slow the operation of the engine, which affects the engine efficiency slowly; this factor is called a lean mixture. In other words, the proportions of fuel are too low, and the proportions of air are excessive in this lean mixture zone.⁶⁸ Usually, the lean mixtures for diesel fuel are in the range of 1:14. The fuel proportions are very low, and the proportions of the mass are very excessive at lower loads, causing an inadequate combustion efficiency, which leads to the total engine displacements and extreme damage to the valves, and the replacement cost is significantly higher.⁶⁹ A rich mixture is technically expressed as an adequate excess supply of proportionated fuel with less air for aiding combustion at peak loads with different operating pressures. Usually, the rich mixtures for diesel are given in the ratios of 22:1 to 26:1.⁷⁰ The drawback persisting in the zone of rich mixtures is that the vibrational characteristics and noise formations were higher. The mixture proportionated with an equal amount of air and an equal amount of fuel under balanced conditions for achieving the proper combustion efficiency is called a stochiometric air–fuel ratio; the standard stoichiometric air-to-fuel ratio for diesel is 14.5:1. In these stochiometric conditions, the engine will be run under smoother conditions with balanced vibrations and less noise compared to lean and rich mixtures. Figure 7 presents the A/F ratios of the diesel and royal poinciana blends. It is keenly observed that the air/fuel ratio is very high for diesel at all loads. Next to the diesel, the air–fuel ratio is good for the D90RP7B3 blend under partial and complete load conditions. The maximum air–fuel ratio is attained for the 48:1, 33:1,22:1, and 11:1 ratios, followed by different loads such as 25, 50, 75, and 100% load conditions. The main reason behind the achievement of these good ratios for blend D90RP7B3 compared to other blends is that this blend offers suitable or improvised viscosity, which leads to proper mixing of air and fuels with negligible resistances, and also good surface tension offered by this blend causes the split of the particle size of the fuel in finer droplets, which leads to good air to fuel proportions and adequate combustion phenomenon compared to other blends and diesel.⁷¹

Figure 7.

Air–fuel ratio.

6.5. Mass Fraction Burnt

The critical factor that predominantly determines the amount of heat released from the fuel concerned with the movement of crank angle rotation is called MFB.⁷² Technically, it is defined as the ratio of the net amount of HRR to the total amount of heat released, concerning the rotation of crank angles. To evaluate the number of gases and their soots during the combustion stage, the term was introduced by Rassweiler and Withrow in 1938 to assess the performance of the various types of fuels during the evaluation of the combustion process and its releasing soot particles.⁷³ The mathematical correlations that are required to determine the MFB are given in eq 16(74)

16

Figure 8 presents the obtained MFB for the royal poinciana blends and diesel. From Figure 8, it is clearly understood that soot and its byproducts released from the diesel are gradually increased when the crank angles start to rotate, and at initial stage BDC, the soots and the amount of the burnt gases that are produced for all the blends concerned with diesel and royal poinciana blends are low, and when the crank angle rotates to reach TDC, the volume of the burnt gases inside the cylinder is increased. It will reach 60% owing to peak pressures and temperatures of nearly 1200 °C. The blends such as D70RP21B9 have a maximum burnt fraction capacity of 75%. This is because of the higher unbalanced state of the stochiometric factor raised inside the engine cylinder, owing to the higher vibrations and higher number of burnt fractions caused by the engine when the blends are operated by D70RP21B9 and RP100.⁷⁵ One more factor of concern is that the more the MFB causes these blends to have poor oxidation, and the lower the cetane number causes the higher formation of these fuel burnt characteristics and affects the engine’s performance. Another factor also affects the performance, and the higher the fuel burnt characteristics, the shorter the ignition delay for these blends when the engine is operating in rich mode conditions. Hence, the higher the MFB, the more elevated the formations of particularly NO_X emissions compared to other emissions in diesel and all royal poinciana blends.

Figure 8.

Mass fraction burnt.

6.6. Volumetric Efficiency

One more important term that represents the densities of air and the densities of fluid for evaluating power’s transmission capacities is called volumetric efficiency.⁷⁶ In other words, it is the ratio of the drawn volume, called an actual volume (in m³), to the theoretical volume of the working fluid (in m³) during the suction or intake portion of the piston movements inside the cylinder. It is scientifically proven that the greater the densities of the working fluid, the more the intake of the working fluid will improve the thermodynamic engine to operate quietly and smoothly.⁷⁷ Stage by stage, if this phenomenon continues, the maximum volumetric efficiency of up to 90% can be achieved, and the remaining 10% can be considered as losses due to the unavailability of clean air and reduced pressures causing these negligible losses. Mathematically, the formula can be written as shown in eq 17(78)

17

Figure 9 presents the volumetric efficiency of diesel fuel and royal poinciana blends. From Figure 9, it is understood that the volumetric efficiency of diesel and royal poinciana blends is relatively high at initial stage conditions, followed by 25% load conditions. This is because the inhalation of fresh air or admission of fresh air to the engine with optimized pressures is relatively high and quite good compared to other load conditions. Hence, the maximum volumetric efficiency is achieved for diesel fuels in the 83% range. Next to diesel, the D90RP7B3 blend possesses better volumetric efficiency in the range of 82%, which is 1% lower than that of diesel. This is due to the better natural densities of the D90RP7B3 blends due to the higher viscosities for the blend D90RP7B3 compared to other blends.⁷⁹ At load, it gradually increased from 25 to 50%; this efficiency significantly decreased for the diesel and royal poinciana blends. Because of the load increases, the surface tensions offered by the fuel are also reduced, and this causes the lower induction of mass of the working fluids and air to lower the volumetric efficiency compared to 25% load conditions.⁸⁰ At full load conditions, 100% of the maximum volumetric efficiency is obtained for the fuel diesel and the D70RP21B9. Because the D70RP21B9 blend causes a higher oxidation capacity, the MFB attainments at the peak level cause attainment of the maximum volumetric range of 82%; but for the diesel fuel, the volumetric efficiency of up to 80% is achieved. The drop in volumetric efficiency is found for diesel compared to D70RP21B9 blends because the higher release of MFB causes a drop in its volumetric efficiency compared to diesel and other royal poinciana blends. The reason why the filling efficiency is high for D90RP7B3 fuel is that more fuel is required at peak load conditions when the engine is operated at full loads. This causes adequate fuel supply due to the easy flow of D90RP7B3 because of better viscosity and better HHV compared to other blends, causing the engine to operate in a high-efficiency mode. The cylinder has better densities and mass charges for blend D90RP7B3 compared with other blends. However, in the case of 50 and 70%, the A/F mixture required is significantly less, which tends to record less efficiency, and less intake system of the densities of the mass in the cylinder causes less volumetric efficiency compared to 100% load conditions.

Figure 9.

Volumetric efficiency.

7. Emissions

7.1. Emissions of CO

The harmful gas released from the engine results in severe issues for the environment and human beings. One type of emission identified as having no color and no taste in the form of toxic gas is implicated by several scientists, and this type of poisonous gas is named carbon monoxide, one among the harmful toxic emissions released from the engine.⁸¹ The lack of an inadequate supply of oxygen will slow down the combustion rate, releasing this dangerous poisonous gas into the atmosphere, which will result in several effects on human beings and the atmosphere.⁸²Figure 10 indicates the carbon monoxide emissions when the engine is subjected to different loads varying from 0, 25, 50, 75, and 100% load conditions. There is a gradual increase in emissions as the load increases, and it was found that the lowest emission was 0.081% for fuel RP100. The main reason for achieving this lower emission rate at full load conditions is the insufficient quality of hydrocarbons during the combustion at higher temperatures ranging from 1500 and 2000 °C.

Figure 10.

CO emissions

7.2. Emissions of CO₂

CO₂ emissions are indicated by the visual observation of noncolor, nontoxic, which will cause severe issues for human beings, leading to respiration problems. Hence, emissions are considered a negative cause of emissions.⁸³ In other words, it was scientifically expressed as the splitting of carbon atoms by volume due to an insufficient oxygen supply during combustion at the peak pressures at the end of compression, resulting in CO₂ emissions. Figure 11 presents the CO₂ emissions when the engine is subjected to different loads operated at different loads. The emission level for the fuel D100 possesses a much higher emission rate in terms of 6%, but the royal poinciana blend D90RP7B3 has significantly lower emissions in the range of 4.9%. The main reason behind this higher secondary emission for D90RP7B3 fuel was the very low ignition delay, which caused better ignition pressures and higher ignition timing quality for the fuel compared to D100.⁸⁴

Figure 11.

CO₂ emissions.

7.3. Emissions Of HC

Hydrocarbon emissions were categorized as nonvolatile emissions due to the presence of organic contents that will affect the environment, causing stomach and severe headache issues; it was considered a slow, poisonous emission compared to other emissions, and the appearance of heavily polluted engines will appear light brownish. Figure 12 presents the emissions of hydrocarbons; it was noted that the release of emissions for Diesel D100 was 44 ppm, that for blend D90RP7B3 was 35 ppm, that for D80RP14B6 was 30 ppm, and that for D70RP21B9 was 28 ppm; the least amount of ppm was observed for the fuel RP100 (25 ppm). This was due to the fact that adequate oxygen supply dominates the lower release rate of hydrocarbon emissions.⁸⁵

Figure 12.

Hydrocarbon emissions.

7.4. Emissions of NO_X

Emissions that categorized as more harmful to the environment, which appeared in the form of a brownish color physical in nature subjected to high temperatures in the range of 2000 °C, are mentioned by the scientists and named nitrogen gas (NO_X).⁸⁶ In other words, the emission rate of NO_X is exactly defined by the nature of temperature distributions at very high combustion rates due to improper combustion, and an excess amount of oxygen supply predominates the abnormal combustion, leading to the NO_X emissions at peak pressures and elevated temperatures in the range of 1500–2000 °C at higher load conditions. The chemical equations or correlations derived by Zeldovich’s mechanism are given in eqs 18–20^87,88

18

19

20

NO_X emissions have harmful effects on the environment and result in lung failure, asthma, eye irritation, nausea, and permanent kidney failure.⁸⁹Figure 13 presents NO_X emissions when the DI engine is operated on various loads ranging from 0, 25, 75, and 100% full load conditions.⁹⁰ It was observed that the emission release rate of RP100 is nearly 1995 ppm, and that of Diesel D100 is 1680 ppm; fuel RP100 was found to have a higher emission rate compared to diesel; due to the higher intake of oxygen at peak pressures and peak temperatures in the range of 2000 °C during combustion, the most occurrences of emission for the blend RP100 as compared to other blends were observed.

Figure 13.

NO_X emissions.

8. Conclusions

The oil obtained from Royal poinciana seeds is transesterified and filtered well to test engine performance, combustion, and emission properties. Thus, Royal Poinciana blends with different proportions were added with butanol with definite percentages of 3, 6, and 9 for carrying out the experimental trials. In this exploratory analysis, the various performance factors affecting the engine, such as BTE, BSFC, and combustion parameters such as cylinder pressure, HRR, ignition delay, MFB, A/F ratios, and CO, CO₂, HC, and NO_X emissions for multiple fuels such as D90RP7B3, D80RP14B6, D70RP21B9, and D100 were scientifically investigated. From the recent research studies on oil extraction from Royal poinciana seeds, the maximum amount of oil obtained was found to be 88% by weight by different expelling processes like using a mechanical expeller and thermodecomposition process. A significant improvement in engine performance is observed for the blends operated with 1-butanol with different biodiesel blends derived from soybean biodiesel, palm biodiesel, and pyrolysis oil blends. From various research studies conducted in the past, it can be found that the maximum possible performance was achieved with the help of 20 mL of butanol in definite atmospheric situations. Hence, the results from this study suggest that adding 10% of 1-butanol is enough to achieve the best engine performance. Hence, the motivation of this research is to investigate and evaluate the performance of the single-cylinder diesel engine for four cases, D90RP7B3, D80RP14B6, D70RP24B6, and RP100, and compare the results with diesel; the following results were obtained.

• 1.Next to the diesel, BTE suitable for the blend D90RP7B3 is in the range of 31%, which is very close to the diesel efficiency. This excellent calorific value is obtained for the blend D90RP7B3 because lower proportions of 1-butanol improve the oxidation stability of the blends, and diesel fuel tends to achieve an excellent calorific value.
• 2.Next to the diesel, the very least BSFC is achieved for the blend D90RP7B3 in the range of 0.24 kg/kWh, and for the diesel, the consumption is found to be 0.21 kg/kWh. Diesel BSFC is close to that for the D90RP7B3 blend.
• 3.The presence of good oxygenated items, better viscosity, and good calorific value generally lead to the least fuel consumption at full load conditions compared to other blends. The different blends, such as D80RP14B6 and D70RP21B, have lower viscosity and higher density differences, causing them to consume more fuel than D90RP7B3 blends.
• 4.The maximum pressure rise inside the engine cylinder is 7 MPa for the blend D90RP7B3. This pressure rise is due to the good ignition characteristics owing to the presence of 1-butanol as an ignition improver.
• 5.The blends such as D90RP7B3 and D80RP14B6 achieved good heat release owing to maximum combustion temperatures with an adequate heat release rate of 90 kJ for the D80RP14B6 blend and 88 kJ for the D90RP7B3 blends.
• 6.The lowest HRR is achieved for the blend: 60 kJ. Because of the lower oxygen formation due to reduced viscosity and reduced cetane number, it tends to the improper premixing stage and causes less HRR compared to diesel and other blends.
• 7.All the blends possess the lowest ignition delay compared to D100. This is due to the addition of 1-butanol to diesel to operate the engine in the cleanest condition in the rich mode.
• 8.The maximum air–fuel ratio is attained for the D90RP7B3 blend at full load conditions in the ratio of 11:1. The main reason behind the achievement of these good ratios for the blend D90RP7B3 compared to other blends is that this blend offers good or improvised viscosity, which leads to proper mixing of air and fuels with negligible resistances and good surface tensions.
• 9.The maximum volumetric efficiency is achieved for the fuel diesel in the range of 83%, and next to the diesel, the D90RP7B3 blend possesses a better volumetric efficiency in the range of 82%, which is 1% lower than that of diesel. This is due to the better natural densities of the D90RP7B3 blends due to the higher viscosities for the blend D90RP7B3 compared to other blends.
• 10.The emissions released from the Royal Poinciana blends, such as CO, CO₂, HC, and NO_X, were reduced by 14.12, 8.33, 11.1, and 18.8% compared to standard diesel. Hence, Royal Poinciana blends with 1-butanol can be considered the best fuel in the automobile sector.

Glossary

Nomenclature

ASTM

Americal Society for Testing and Evaluation

A/F

Air to fuel ratio.

ATDC

After top dead center.

ANN

Artifical neural network

BTE

Brake thermal Efficiency

BDC

Bottom dead center

B25

25% neem biodiesel + 75% pure diesel.

B50

50% neem biodiesel + 50% pure diesel.

B75

75% neem biodiesel + 25% pure diesel.

B100

100% pure neem biodiesel.

BP

Brake power.

BTDC

Before top dead center

IP

Indicated power.

IT

Ignition timing

ID

Ignition delay

BSFC

Brake specific fuel consumption

CO

Carbon monoxide

CO₂

Carbon dioxide

C

Mass fraction burnt gas constant

CH₄

Methane gas

D100

Pure diesel

D90RP7B3

90% diesel 7% Royal Poinciana biodiesel and 3% butanol

D80RP14B6

80% diesel 14% Royal poinciana biodiesel and 6% butanol

D70RP21B9

70% diesel 22% Royal poinciana biodiesel and 8% butanol

D30B60EPB10

30% diesel + 60% biodiesel + 10% esterified pyrolysis Biooil

g

Grams

EGT

Exhaust gas temperatures in °C

FP

Fuel power

HC

Hydro carbons

HCCI

Homogeneous charge compression ignition

H₂

Hydrogen dioxide

HRR

Heat release rate

kWh

Kilowatt-hour

kg

Kilograms.

HHV

Higher heating value

MFB

Mass fraction burnt

mL

Milli liters.

mg

Milligrams

Mfbc

Mass of burnt fraction of working fluids in kg/s

m_f

Mass of the fuel in kg

Mpa

Mega Pascal

NO_X

Nitrogen oxide

PPM

Parts per minute

P

Pressures of blends in Mpa.

RP100

Royal Poinciana biodiesel

RSM

Response surface methods.

wt

Weight

T

Temperatures in °C

TDC

Top dead center

V_xi

Starting volume of the working fluid in m³

V_(xi+1)

Ending volume of the working fluid opposed by piston in m³

N

Speed in revolutions per minute.

OH

Oxy hydrogen

T_crank

Torque of the crank in N-m

λ_i

Heat transfer rate on walls between piston and cylinder

It

Ignition timing of the blends.

N

Speed of the crank in revolution per minute

λ

Heat release measure rate parameter

Φ

Heat release measure rate parameter considering equivalence mixing

Δθ

Net heat transfer rate of heat evolved

T

Temperatures of the blends during crank rotations in C.

P

Pressures of the blends during crank rotations in Mpa.

EGT

Exhaust gas temperatures of the blends in in K

θ

Individual heat transfer parameters in degree rotations of crank.

Δθ

Net crank rotations concerned all the heat transfer parameters

Δp_cr

Net pressure rise inside the cylinder in bar

p_(xi+1)

Starting and ending pressures subjected to rotation of crank angles

r

Polytropic constant

X_k

Actual readings from scientific experiments

σ_k

Occurred deviation in data

Δp^e_r

Pressure rise at the ending stage of the cylinder in bar

Δpⁿ_xi

Initial pressure rise during evolution of heat in bar

Initial combustion and final combustion stage summations.

V_act

Actual volume developed inside the cylinder in m³

V_max

Maximum volume developed inside the cylinder in m³

M_f

Mass of the proportionated in kg

M_a

Adequate mass of air in kg

Q_HR

Amount of heat released during rapid combustion in kJ/kg

Δ_HCR

Reactants heat release rate of the combustable fuel in kJ/kg

m_fr

Mass of reference fuel in kg/s

C_vfuel

Calorific value of the fuel in MJ/kg

x̅_n

Calibrated data related to concerned variables.

F crank pin

Forces of the crank pin in N.

R crank pin

Radius of the crank pin in m

YSZ

Ytria-stabilized zirconia

R_ms

Measured readings

f(x)

Function of variables data to be calibrated

x_1,x_2,x₃

Individual calibrated data concerned with individual parameters.

Degree of accuracy of the readings with uncertainties.

ΔR

Overall deviated data

Δx_1,Δx₂, Δx₃

Measured data concerned to set of uncertainities.

WCO

Waste cooking oil

Author Contributions

The corresponding author Mr.K. Sunil Kumar is currently pursuing doctoral research in the area of pyrolysis oil from waste plastics and working as an Assistant Professor in the Department of Mechanical Engineering at Mohamad Sathak A.J College of Engineering, IT Park, Siruseri, India. He has published more than 40 research papers in SCI and Scopus indexed journals in the fields of biofuels, the renewable energy sector, and the automobile sector. Recently, he published one pyrolysis work in a high impact factor journal of 11.1 SCI Quartile 1. He was awarded a Best Researcher Award from the 13th Edition of the International Young Scientist Awards from ScienceFather, which is a trademark of Scifax Company Registered Number 130116, approved by Ministry of Corporate Affairs (MCA), Government of India. The Award Certified Number is10885. He received the Certificate and Momentum on 16 November 2023. He has a wide area of interest in biofuels and thermal engineering projects. The author Mohd Asif Shah is working as Associate Professor, Kabridahar University, PO Box: 250, Ethiopia.

The authors declare no competing financial interest.

Notes

The experimentation was carried out with 1-butanol in limited proportions to determine the engine performance, combustion, and emission characteristics. In the future, the authors recommend adding titanium and cerium oxide nanoadditives to enhance or boost the engine performance parameters and comparing it with the predicted results of this research. The authors also have a wide interest in carrying out the analysis of the latest additives, such as graphene additives in combination with Royal Poinciana blends and HHO combinations operating in dual mode at varying injection pressure strategies.