
==== Front
Heliyon
Heliyon
Heliyon
2405-8440
Elsevier

S2405-8440(24)12414-0
10.1016/j.heliyon.2024.e36383
e36383
Research Article
Performance and emission profiles of petroleum nut (Pittosporum resineferum Hemsl.) biodiesel in combustion ignition engine-generator for power generation☆
Taguiling Shawn Zedrick G. sgtaguiling@up.edu.ph
a⁎
Manegdeg Ferdinand G. ab
Rollon Analiza P. ac
a Energy Engineering Program, National Graduate School of Engineering, University of the Philippines Diliman, Quezon City, 1101, Philippines
b Department of Mechanical Engineering, College of Engineering, University of the Philippines Diliman, Quezon City, 1101, Philippines
c Department of Chemical Engineering, College of Engineering, University of the Philippines Diliman, Quezon City, 1101, Philippines
⁎ Corresponding author. Energy Engineering Program, National Graduate School of Engineering, University of Philippines Diliman, Quezon City, 1101, Philippines. sgtaguiling@up.edu.ph
15 8 2024
15 9 2024
15 8 2024
10 17 e3638313 12 2023
21 7 2024
14 8 2024
© 2024 Published by Elsevier Ltd.
2024

https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
One of the traditional fuels for power generation in the Philippines is the petroleum diesel (PD). However, its extensive usage contributes to environmental degradation, health risks and climate change concerns. Alternative fuels such as petroleum nut biodiesel (PNB) may address the increasing consumption of PD amidst depleting fossil reserves and related issues. This study aimed to produce, characterize, and observe the behavior of PNB as a fuel in a compression ignition (CI) engine-power generation system at various loads of 0 %, 25 %, 50 %, 75 % and 100 %. Petroleum nut fruits were collected, extracted of oil then transesterified to produce PNB. The performance and emission profiles of the latter were determined. Degumming increased the PNB yield by 24.28 %. Additional refining decreased colorants and impurities. Majority of the chemical and physical properties of the PNB showed comparable values with those of PD. Various blends of PNB-PD were prepared and tested in terms of their performance and emissions. The 20 % PNB mixed with 80 % PD (B20) showed the most efficient performance after 100 % PD with at least 3.95 % decrease, whereas PNB for specific fuel consumption (SFC) showed at most 30.78 % higher than all fuels for all loads. The heat release rate (HRR) increases with increasing %PNB in the PNB-PD blend. PNB generally showed the highest CO2 and NOx emissions with at least 16.67 % and 80.52 % lower with PD respectively, but the lowest for CO emission with at least 13.42 % difference compared with PD. Finally, the study confirms that CI engine-generator can be operated with 100 % PNB and its blends without engine modification.

Keywords

Biodiesel
CI engine-generator performance and exhaust emission
Power generation
Petroleum nut
Transesterification process
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pmc1 Introduction

Non-renewable petroleum products which include diesel are the conventional fuel source in the power generation sector. However, it is a scarce resource with increasing prices due to fast post-pandemic demand recovery and effects of global geopolitical conditions. To lessen the reliance on diesel, a comparable alternative fuel can be used. It should perform efficiently on CI engine-generator and be competitive in terms of characteristics, performance, and emissions. As an alternative, biodiesel is used with advantageous higher cetane number, better lubrication property and the presence of about 10 % oxygen in its elemental composition. The presence of oxygen reduces carbon monoxide (CO), hydrocarbon (HC) and smoke emissions compared to those using PD [1]. Edible oils such as soybean oil, rapeseed oil, castor oil, etc. are the main resources for worldwide biodiesel production. However, their use has direct and indirect influences on global imbalance to the market demand and the food and the growth of commercial plant capacities [2]. Thus, focus was shifted to non-edible resources, which are not commonly used and applicable in many parameters. Aside from low cost and impossibility for human consumption due to toxic components, non-edible oil plants can be cultivated in barren lands at a lower cost, and CO2 concentrations can be reduced in the process [2]. The advantageous properties also include: liquid portability, availability, higher combustion efficiency, lower sulfur and aromatic contents and higher biodegradability of non-edible oil based biodiesel compared to those of PD [3]. The main disadvantage of non-edible oils is the high free fatty acids (FFAs) content which increases the production cost of the biodiesel [2]. Despite these drawbacks, there are several research in non-edible oil seed crops such as jatropha tree (Jatropha curcas), karanja (Pongamia pinnata), castor bean seed (Ricinus communis), and neem (Azadirachta indica), among others. The studies have proven importance of non-edible oils for the future of biodiesel production.

Generally, for biodiesel using non-edible oils and their blends, there is minimal reduction in engine power and increase in fuel consumption and NOx emission, but reduced other emissions such as particulate matter (PM), hydrocarbon compounds (HC), CO and polycyclic aromatic hydrocarbons (PAHs) [4]. How non-edible oil based biodiesel properties compare with those of standard PD vary depending on the oil source. Jatropha biodiesel blends at 5 %, 10 %, 20 % and 30 % lowers break thermal efficiency (BTE), HC, CO, CO2 and smoke density but higher brake-specific fuel consumption (BSFC) and NOx emission compared to diesel fuel [3]. Using pure Jatropha biodiesel and preheated jatropha biodiesel produces lower power but gives higher NOx emission than those when using diesel fuel [5]. For karanja biodiesel and its blends, the BTE and emissions of CO, HC and smoke are reduced whereas NOx and CO2 is increased as compared to diesel fuel [6]. Castor biodiesel at 5 %,10 %, 25 %, 50 %, and 100 % showed higher BSFC and NOx emission and lower brake power output and emissions of CO and CO2 [7]. Neem biodiesel blends at 10 %, 20 % and 30 %, showed higher brake thermal efficiency and lower CO, HC and NOx emissions as compared to diesel fuel [8].

One application for biodiesel is for power generation. Pure dephosphorized jatropha oil can be used in diesel engine generators under normal functional conditions but with modifications of engine cooling system [9]. The study of Pan et al. (2011) further showed that the exhaust nitrogen (NOx) and CO concentrations of biodiesel were lower compared to those of PD but higher as compared to light oil. The combustion has been enhanced with increasing the fuel injection pressure; and it has standard operations after 300 h of durability test [9]. Using either jatropha biodiesel and jatropha seed based producer gas to generate electricity in dual and single fuel modes have been shown to be successful in producing electricity with 48 % savings of jatropha biodiesel, 25–32 % reduction in system and brake thermal efficiency, lower NOx but higher CO and CO2 emissions for dual fuel mode compared to single fuel mode [10]. In a study using biodiesel-PD blends from jatropha, soybean, and waste cooking fuel at an engine-generator with rating of 3.5 kW, it was found that B20 blends, i.e., 20 % biodiesel, gave BTE values similar to that of PD at loading but has predominantly decreasing CO with increasing percent biodiesel up to 80 %, and then sharply increases from 80 to 100 % biodiesel [11]. And using high purity biodiesel blends in diesel engine, the maximum increase in BTE for 5 % biodiesel is found to be 2.09 % with reduction in CO and HCs emissions as compared to diesel [12].

In the Philippines, the biofuel production in the country is currently limited to methyl esters from transesterification of coconut oil [13] as the present national standard for biodiesel is based on this feedstock. Over the years, price trends of the biodiesel would be higher than PD with the increased blend from 2 % biodiesel. As of 2022, the price of coco methyl ester (CME) from coconut ranges from Php 68–96/L and there is a 14 percent increase in biodiesel consumption to 230 million liters in 2023 [13]. Due to economic growth, conflict over food usage, and increasing prices, there is a need for alternative feedstock to alleviate the strain on coconut oil and ensure sustainable supply chains.

Relative to use, a non-edible oil can be extracted from an endemic petroleum nut plant (Pittosporum resiniferum Hemsl.) in the Cordillera Administrative Region (CAR), Philippines specifically in Ifugao and Benguet. It is an evergreen aromatic tree resembling a young grafted mango tree with leaves arranged into whorls that grows from 5 to 30 m in open or forest habitats [14]. A single fruit from the tree can produce 0.1–3.3 ml oil with estimated 1000 trees to produce 1 MT of oil per hectare [15]. The extracted oil is commonly used for cooking, lighting, drying, heating and running small engines [14]. While it is rarely used in small gasoline engines locally, it is not regularly employed due to its arduous traditional production and processing, decreasing number due to deforestation, unavailability due to seasonal fruits and impurities and non-homogeneity in oil extraction. The farmers in CAR extract the petroleum nut oil through cold press or distillation methods [16]. Relatively, solid-liquid extraction method or leaching can be used with the ethanol, isopropanol, hexane, and cyclohexane as solvents for extracting its oil [17]. However, findings in comparisons with commercial fuels of the raw petroleum nut oil suggested that its direct substitution for transport fuel is not suitable, but can be used as a burner or lamp oil [18]. Upon refining and processing for a change, an integrated method of sustainable production of biodiesel from the fruit pulp of petroleum nut was developed. The extracted oil from cold press and boiling was converted to biodiesel by transesterification using acid and base catalysts [19]. The results indicated that after the conversion of petroleum nut oil into fatty acid methyl ester (FAME), good quality of biodiesel can be produced which could be used as an alternative for PD.

Although petroleum nut oil has been proven to be a feasible feedstock for biodiesel production, direct application to diesel engines has not been done before. Furthermore, there is a knowledge gap on the use of PNB in power generation, its emission profiles, and its related energy characteristics and analysis. There is currently limited information on PNB. The objectives of this study are to (a) determine the efficiency of transesterification of petroleum nut oil with methyl alcohol (methanol) and the effect of degumming and refining, (b) determine the composition of the PNB, (c) determine the physical and chemical properties of the PNB, (d) determine the performance of the PNB and its blends with PD at varying load settings and compare them with those of 100%PD and (e) determine the emission profiles of the PNB and its blends with PD at varying load settings and compare them with those of PD.

2 Methodology

2.1 Sampling and fruits collection

Petroleum nut fruits were collected in the different areas in Tinoc, Ifugao (16° 41′ North, 120° 56′ E, and 1483.4 m elevation), Mayoyao, Ifugao (N 16.9513°, E 121.2168° E and 977.28 m elevation) and in Kabayan, Benguet (N 16°37′24″, E 120°50′17″ and 1320 m elevation) Philippines, during the harvest in February to April 2022 and February 2023. Using Geographic Information System, stratified sampling with strata of trees that are located at not less than 900 m elevation were considered. All the ripe fruits per tree were collected and mixed thoroughly.

2.2 Oil extraction

Oil was extracted from 218.20 kg petroleum nut fruits using mechanical extraction method. The fruits were deseeded, boiled, cooled, grounded and pressed using manual hydraulic pressing system. The extracted crude oil was filtered twice to remove impurities and allowed to stand for 2 days. The floating oil was then separated from the fluid by decantation. The detailed flow chart of extracting oil, using a modified method in the province [16] is shown in Fig. 1. The degumming step for 36 % of the sample was not conducted to determine its effect.Fig. 1 Flowchart of the petroleum nut oil extraction process (a) with degumming and (b) without degumming.

Fig. 1

2.3 Transesterification process

Alkali base catalyzed (NaOH) transesterification was conducted for methyl ester (biodiesel) production process from petroleum nut oil. Prior to transesterification, the acid value was determined. The sodium methoxide solution was prepared by dissolving slowly the 5g of sodium hydroxide in 250g of methanol and then constantly stirred. The weighed 1 kg of oil was placed inside the 3-neck round bottom flask and pre-heated to 45–50oC with stirring. The sodium methoxide solution was then added slowly to the pre-heated oil in the flask with constant stirring. The temperature was increased to 65oC and heated for 1 h. After heating, it was cooled using a water-cooling system for at least 1–2 h then transferred to a separatory funnel. The mixture was settled for 8 h and then the methyl ester was collected. The collected PNB was washed with hot deionized water until pH 7 was reached and then dried in an oven. A flow chart of the process as adopted from the work manual in transesterification and Waidee et al. [19,20] is shown in Fig. 2. The percent yield of biodiesel was calculated using Eq. (1).(1) Biodieselyieldpergrampetroleumnut(%)=gramofPNBproducedgramofpetroleumnutoilused×100

Fig. 2 Flowchart of transesterification process [19,20].

Fig. 2

To know the effect of refining for the PNB produced, 2 times washing and drying with vacuum filtration was conducted for a 350 ml sample. The resulting sample was characterized by its cetane number (CN) and observed color.

2.4 Physical and chemical properties

Standard methods were employed to determine the properties of the PNB and PD at Energy Research and Testing Laboratory Services (ERTLS), Department of Energy, Philippines.

2.5 Experimental set-up for determining the performance of PNB:PD blends

The experimental flow chart of the system for determining the performance of the PNB: PD blends is shown in Fig. 3. For each blend, load and time combination, the process was repeated three times. After allowing the engine to reach the steady state conditions with an initial run of 5–10 min, the required readings were measured with each time. The electrical output current, voltage and power were observed using the installed power meter, voltmeter and ammeter of the CI engine-generator and water rheostat. Using a graduated cylinder of volume 250 cm3 and a timer, the fuel consumption was measured by gravimetric method for a period of 180 s. The exhaust gas emission was directly sampled with equipment with each time schedule and analyzed by the Factory Services and Research Division (FSRD) of the Sugar Regulatory Administration (SRA). The procedure was repeated for diesel and biodiesel blends. The electricity generating system is an engine-generator connected to a water rheostat and sensors. The CI engine-generator used was an ANMAX ADG-10800E with a rated power of 8600W and a max power of 10800W.Fig. 3 Experimental flow chart.

Fig. 3

The schematic diagram and actual electricity generating system can be seen in Fig. 4a, Fig. 4ba and 4b. It is a one-cylinder, direct injection one stroke water cooled diesel generator having a capacity of 10 kVA. The technical specifications of the engine-generator used are shown in Table 1.Fig. 4a Schematic diagram of the experimental setup for generating bioelectricity: (1) Engine-generator; (2) Sensors; (3) Water rheostat.

Fig. 4a

Fig. 4b Actual experimental set-up of diesel engine-generator (a) with sensors connected to a water rheostat (b).

Fig. 4b

Table 1 Technical specifications of diesel engine-generator used in the electricity generating system.

Table 1Particulars	Details	
Make	ANMAX	
Model	ADG-10800E	
Rated Power	8600W	
Max Power	10800W	
Fuel Tank Capacity	12.5L	
Number of Cylinder	1	
Displacement	531 ml	
Voltage	220V	
Frequency	60Hz	

2.6 Performance evaluation

The performance of the electricity generating system was evaluated by analyzing the fuel consumption, overall efficiency, and emissions of the system using PNB and its blends with PD. The overall efficiency was divided into calculating the production efficiency and the engine generator efficiency. The transesterification process was assumed for the production efficiency for the PNB whereas literature information for refinery efficiency was used for the PD. The transesterification process as basis for the reaction material balance is shown in Fig. 5.Fig. 5 Transesterification process.

Fig. 5

Eq. (2) uses the correspondence of fatty acid (FA) with the FAME wherein 1 M mass was added to comply with the mass balance for the added hydrogen in the reaction. The individual mass of FA in oil was calculated by multiplying the mass percentage of PNB with the result from the molecular weight (MW) of FA divided by the MW of FAME. Eq. (4) then was used to calculate the division of the analyzed PNB component for mass PNB and Eq. (3). The theoretical mass of the biodiesel yield was calculated using Eq. (6), which was obtained by multiplying Eq. (4) and Eq. (5). The actual mass of the biodiesel produced was calculated using its volume and its density as shown in Eq. (7). The production efficiency was calculated using Eq. (8). The engine-generator efficiency was calculated by the electrical output per fuel used divided by fuel power as shown in Eq. (9). The overall efficiency was then calculated by multiplying the production efficiency and the engine-generator efficiency as shown in Eq. (10). The following equations were used:(2) MWFAME(g/mol)=MWFA+1

(3) massFAinoil(%)=massPNB(%)xMWFAMWFAME

(4) massFame/massFAinoil=∑massPNB(%)∑massFAinoil(%)

(5) masspetroleumnutoil(g)=Vpetroleumnutoilxρpetroleumnutoil

(6) masstheoreticalbiodiesel(g)=massFAMEmassFAinoilxmasspetroleumnutoil

(7) massactualbiodiesel(g)=VPNBxρPNB

(8) ηPNBproduction=massactualbiodieselmasstheoreticalbiodieselx100

(9) Fuelpower(kW)=Heatingvalueoffuel(kJkg)xρfuel(kg()xfuelconsumption(m3/h)3600

(10) OverallEfficiency(%)=ProductionEfficiency(np)xEngine‐GeneratorEfficiency(ne)

(10a) =ηPNB=ηPNBproductionxElectricalOutputTotalFuelPowerInput

(10b) =ηPD=ηPDproductionxElectricalOutputTotalFuelPowerInput

Relatively for insights into the combustion process, the heat release rate (HRR) was calculated using the burning rate from the heating value of fuel. The mass loss method [21] was employed using Eq. (11).(11) HeatReleaseRate(kJ/s)=Heatingvalueoffuel(kJkg)xMassflowrate(kg/s)

2.7 Emission properties

Grab sampling was conducted by the FSRD Sampling team of the Environmental Laboratory, SRA for the emission properties during experimentation. The testing methods for obtaining the emissions used were US EPA CFR 40 Test, Method 7 with Sampling train and post-test calibrations for NOx, Method 10 with Luft-type nondispersive infrared analyzer for CO and Method 3 with Fyrite analyzer for CO2.

3 Results and discussion

3.1 Petroleum nut biodiesel yield

Majority of the fruits collected as seen in Fig. 6 were of type I classification with yellow orange flesh that is rounded. After processing, the resulting biodiesel yield of 78.94 % from the 218.20 kg sample was calculated using Eq. (1). Based on the reaction of transesterification with an acid value of 1.91 from the oil, saponification was observed at one batch without degumming, which reduced the ester conversion for the overall yield. However, the obtained oil conforms with the range of yield per fruit [15].Fig. 6 The (a) petroleum nut tree and its (b) type I fruit, (c) pulp and (d) seed.

Fig. 6

3.1.1 Effect of degumming

Degumming was used to remove phosphatides from oil prior to transesterification. Based on the results of one batch sample without degumming, only 63.56 % biodiesel was obtained. Contrary with degumming for the rest of the batches, an increase of 24.28 % in the biodiesel production was achieved.

3.1.2 Effect of refining

The refining process was done to remove unwanted components like colorants, phosphatides, tocopherols, and FFAs [22]. It was observed that after mixing all biodiesel samples, the resulting color is light yellow orange which was dependent on the procedure used for transesterification and reddish coloration from ground fruits. Although further processing and purification was possible, it would be costly, limiting chemicals, laborious at high quantity and reduction in the overall yield can be expected.

Apart from decreasing impurities and reddish colorants from the sample, further purification of 350 ml sample as seen in Fig. 7 of the PNB can increase the CN to 54.4. There was also significant change in the color from light yellow orange to light yellow color.Fig. 7 PNB before (a) and after additional 2 times washing with vacuum filtration (b).

Fig. 7

3.2 Composition of petroleum nut biodiesel

Using the DPNS/DOE TM 01:2015, a FAME content of 69.23 % was measured. Fig. 8 shows the gas chromatogram of the PNB. Table 2 shows the fatty acid compositions of the PNB with an average molecular weight of 799.06 g/mol.Fig. 8 Gas chromatogram of the fatty acid content of PNB.

Fig. 8

Table 2 Fatty acid composition of petroleum nut biodiesel.

Table 2Fatty Acid	Compound Name	Mass (%)	
Caprylic	C8	0.627	
Capric	C10	0.527	
Lauric	C12	4.323	
Myristic	C14	2.590	
Palmitic	C16	37.501	
Palmitoleic	C16:1	0.149	
Stearic	C18	3.736	
Oleic	C18:1	39.951	
Linoleic	C18:2	9.927	
Linolenic	C18:3	0.092	
Arachidic	C20	0.308	
Gadoleic	C20:1	0.129	
Behenic	C22	0.064	
Lignoceric	C24	0.075	

3.3 Physical and chemical properties of petroleum nut biodiesel

The information for the ASTM 6751 and ASTM 7467 is the detailed requirements for testing the fuel property for checking specifications for use and does not include the values for density, pour point, sulfated ash (for ASTM 7467) and heating value. The chemical and physical properties of the PNB relative to the diesel fuel based on ASTM standards is shown in Table 3. Based on their sulfur content, the pure PNB is Grade S15 based on ASTM 6751 and B20 is Grade S500 based on ASTM 7467. Both the PNB and B20 have lesser sulfur content as compared to the PD. This lower sulfur content would reduce the engine wear and sulfur deposits upon usage. Although there are other byproducts and dissolved metals in the fuels which can also lead to engine corrosion, loss of power, increase fuel degradation and induce carbon deposits, results from the copper strip corrosion, kinematic viscosity and acid number conforms the required ASTM standards. While B20 with a flashpoint of 57 °C satisfies ASTM 7467, the PNB of a flashpoint of 40 °C must be mixed with an additive for fuel handling safety and storage as compared to the PD with 64 °C. The heating value of PNB and B20 are 5.98 MJ/kg and 1.34 MJ/kg less than that of PD respectively. This was because of the presence of more oxygen in biodiesel which generally lowers the heating value. The other heating values of individual biodiesel blends include 43.09 MJ/kg for 40 % PNB and 60 % PD (B40), 41.81 MJ/kg for 60 % PNB and 40 % PD (B60) and 40.81 MJ/kg for 80 % PNB and 20 % PD (B80). In terms of CN, B20 with 51.1 satisfies the minimum requirements of the ASTM 7467. Although the PNB with CN of 32.5 was relatively low as compared to the ASTM 6751 minimum CN of 40, further refining increased the CN value to 54.4.Table 3 Chemical and physical properties of PNB and B20 relative to diesel fuel.

Table 3Property	Method	Fuel/Standard	
PD	B20	PNB	ASTM Standard
6751
Grade S15	ASTM Standard
D7467	
Calculated Cetane number, min	ASTM D4737 Proc. B	54.0	51.1	32.5	47.0	40.0	
Density at 15 °C, kg/m3	ASTM D4052	844.40	852.50	889.80	–	–	
Copper strip corrosion, 3h at 50oC, max	ASTM D130	1a	1a	1b	3	3	
Water, % v/v	ASTM D6304- Proc. A	0.02	0.14	0.52	0.05	0.05	
Total Sulfur, ppm	ASTM D7039	38.70	30.00	<3.2	≤15	≤500	
Flash point, (PMMC), °C, min	ASTM D93- Proc. A	64	57	40	93	52	
Kinematic viscosity @
40 °C, mm2/s	ASTM D445	3.375	3.621	4.714	1.9–6.0	1.9–4.1	
Pour point, °C	ASTM D97	+3	0	+9	–	–	
Acid number, mg KOH/g, max	ASTM D664-Proc. A	0.01	0.20	0.84	0.50	0.30	
Sulfated Ash, %m/m	ASTM D874	<0.001	0.01	0.03	0.02	–	
Heating Value, MJ/kg	ASTM D4809	45.56	44.22	39.59	–	–	
Distillation Temperature @ 90 % recovery, oC, max	ASTM D86	355.60	345.70	324.70	360.00	343.00	

3.4 Performance of petroleum nut biodiesel and its blends

For the performance of the fuels, the refinery efficiency for ηPDproduction of a straight run diesel of 95.90 % produced from crude distillation unit and Ultra-low sulfur diesel hydrotreater was used [23]. Using an average of 908.50 kg/m3 [18] and measured volume of 18,252.40 ml petroleum nut oil, the theoretical biodiesel mass obtained was 16,645.19 g. Based on an actual mass of biodiesel of 12,822.02 g, the ηPNBproduction was 77.03 %. Ratio and proportion procedure was used for the production efficiency for the other blends corresponding to the mixture proportions.

As shown in Fig. 9, with corresponding values shown in Table 4, there was an increasing overall efficiency of the np and ne with load up to 70–75 %, most probably due to a reduction in friction loss. The decrease in efficiency beyond 75 % loading may be caused by mechanical losses, increasing resistance in windings, and energy lost as heat. At all loadings and blends, the most efficient is the 100%PD, followed by a reduction of at least 3.95 % for B20, 7.56 % for B40, 17.15 % for B60, 20.24 % for B80 and 30.46 % for PNB, respectively. This decrease in efficiency can be attributed to the high np and heating value of PD as compared to PNB.Fig. 9 Variation of overall efficiency with engine-generator load for different fuels.

Fig. 9

Table 4 Overall efficiency per engine-generator loading.

Table 4Fuel	Engine-Generator Load (%)	
0	25	50	75	100	
100 % PD	13.87	16.37	21.65	23.87	12.68	
20 % PNB-80%PD	12.28	14.06	20.80	22.88	11.21	
40 % PNB-60%PD	11.99	13.43	20.02	21.38	10.35	
60 % PNB-40%PD	11.49	13.11	17.05	19.75	9.86	
80 % PNB-20%PD	9.75	12.28	16.35	19.04	7.88	
100 % PNB	8.61	10.61	15.06	17.68	7.17	

The SFC of varying fuels with increasing load is shown in Fig. 10 and the corresponding values shown in Table 5. The decreasing SFC curves with loading are caused by the increasing efficiency which decreases fuel consumption per power produced. Relatively, the increasing SFC from 70 to 100 % loading may be attributed to losses which decreased the efficiency. This then required more fuel to attain corresponding power output for the load. It can be observed that the SFC of PD and B20 curves are relatively close to each other by at least 2.08 % difference. As compared with PD, the SFC of PNB is higher by at most 36.92 % at 100 % loading. All curves have decreasing SFC in the order of PNB, B80, B60, B40, B20 and PD respectively.Fig. 10 Variation of specific fuel consumption with engine-generator load for different fuels.

Fig. 10

Table 5 Specific fuel consumption per engine-generator loading.

Table 5Fuel	Engine-Generator Load (%)	
0	25	50	75	100	
100 % PD	644.963	546.541	413.079	374.672	705.663	
20 % PNB-80%PD	714.441	624.089	421.870	383.496	782.460	
40 % PNB-60%PD	722.123	644.803	432.664	405.080	837.119	
60 % PNB-40%PD	745.993	653.963	502.673	434.014	869.724	
80 % PNB-20%PD	863.405	685.129	514.712	441.877	1068.120	
100 % PNB	931.795	756.530	532.967	454.033	1118.756	

3.5 Heat release rate

The variation in HRR with respect to the system load is shown in Fig. 11. The cylinder pressure and crank angle were not measured due to limitation of equipment. As shown in Table 6, the obtained HRR values increased with the engine-generator load. The higher HRR at higher proportion of PNB in the blends must be due to the excess oxygen present and probably due to shorter ignition delay [24]. However, a minor reduction in HRR values was observed in some higher biodiesel blends as compared to increasing trend of values. This may be caused by left over oxygen constituents from a previous complete combustion, and continue to burn in the late combustion phase [24]. And there may be a slight delay in the flow rate of fuel, thereby reducing the peak cool flame at higher load conditions [25], thus, resulting in lower HRR values.Fig. 11 Variation of heat release rate with engine-generator load for different fuels.

Fig. 11

Table 6 Heat release rate per engine-generator loading.

Table 6Fuel	Engine-Generator Load (%)	
0	25	50	75	100	
100 % PD	10.775	16.357	22.007	29.229	73.404	
20 % PNB-80%PD	11.584	17.017	21.629	28.991	79.052	
40 % PNB-60%PD	11.410	16.798	21.241	29.786	80.630	
60 % PNB-40%PD	11.436	16.607	24.469	31.173	79.222	
80 % PNB-20%PD	12.920	16.407	24.409	30.774	94.502	
100 % PNB	13.437	17.695	24.359	30.764	99.421	

3.6 Emission profiles of petroleum nut biodiesel and its blends

For all fuels, 25 %–100 % loading was only considered for the determination of emission profiles since the PNB and its blends are limited in quantity. Furthermore, the HC, PM, PAHs, smoke, and aldehydes emissions were not conducted due to unavailability of equipment for measuring. It was assumed that the emission profiles obtained using grab sampling have data deviations mainly from human and equipment error, and environmental susceptibility from the laboratory. Sampling technicians may also be slightly inaccurate in each sample during a small amount of time. In addition, grab sampling procedure was proven to lead to non-detection of compounds or overlooking and underestimation of data as in the experiment for varying sampling methodologies and high-resolution mass spectrometry-based non-target screening workflows in water [26].

The variations of CO emission obtained from the power generation system at different loading conditions is shown in Fig. 12. The B60 at 75 % loading was omitted due to spurious value observed which may be caused by human error during grab sampling. The CO emissions generally decrease with the addition of PNB blend with the highest value of 28,296.40 mg/Ncm from PD and 24,500 mg/Ncm from PNB at 100 % loading. This reduced CO may be attributed to the higher cetane number of PNB and the presence of more oxygen molecule in biodiesel [27]. The slightly higher values for B20 at 25 % loading, B60 at 100 % loading and PNB at 75 % loading observed, can be attributed to incomplete combustion of the excess fuel injected into the combustion chamber which results in increased fuel-air ratio. The latter may have resulted in insufficient air and prevented the complete oxidation of CO to CO2. At all loads, there was an observed 13.42–53.87 % reduction in CO emissions when using PNB as compared to PD. The least reduction of CO emission of 0.81 % at 100 % loading is using the B20 as compared to PD. A similar decrease in emissions with increasing percent of biodiesel in blends with PD has been reported in literature [3,4,[6], [7], [8]]. A similar behavior was also found in another study for high purity biodiesel blends in diesel engine [12].Fig. 12 Variation of CO emissions with engine-generator load for different fuels.

Fig. 12

The variation of CO2 emission with fuel blends at different loadings is shown in Fig. 13. Apart from the omitted B80 values due to spurious data, the other data points at 100 % loading were not plotted because of low values which may be attributed to human error on manual pumping of emissions and direct reading on the Fyrite analyzer used. Repetition for the 100 % load was not conducted due to unavailable fuel. At higher loading, there was better combustion of fuel and increased performance of the engine which resulted in higher CO2 emission. At all fuel blends, as the proportion of biodiesel increases, the CO2 generally increases. This increased emission with higher blend has been found in other studies on biodiesel-PD blends [6,10]. The CO2 emissions increases with biodiesel portion by at most 16.67 % for B20, 28.57 % for both B40, and B60 and 25 % for PNB as compared to PD. The PD has the lowest CO2 values whereas the PNB with the highest readings has inbuilt oxygen which resulted in better combustion. However, these CO2 emissions are not a major issue with their direct absorption of lipid feedstocks [1].Fig. 13 Variation of CO2 emissions with engine-generator load for different fuels.

Fig. 13

The NOx emissions with respect to varying load is presented in Fig. 14. Due to limited amount of fuel which is reliant on seasonal cropping of petroleum nut tree, repetition of the spurious data points was not conducted. The lower values obtained at 100 % loading and slightly higher values can be explained by the inaccurate entry of the probe of sampling train equipment during the short collection time span and insufficient oxygen on the evacuate flask during sample recovery. In addition, the measured zero and very low values by the sampling team were rejected as outliers. For the conforming data points, it can be observed that the values generally increase with the added biodiesel content mixed from majority of the points. This increased emission can be explained with the higher oxygen content and combustion temperature [1] with higher percentages of PNB mixed. Another contributor to higher NOx emission with increased blend is the presence of burnt amines which bonds into the nitrogen [12]. As compared to PD, the NOx for other fuels increases in the following order by at least 18.86 % for B20, 56.29 % for B40, and 64.32 % for B60, 88.01 % for B80 and 80.52 % for PNB. This increasing trend of NOx with higher blend also conforms with literature [[4], [5], [6],11,23].Fig. 14 Variation of NOx emissions with engine-generator load for different fuels.

Fig. 14

4 Conclusion and recommendations

The study was limited to the seasonal availability of petroleum nut fruits to produce PNB. The experimentation was constrained to the use of the available one-cylinder, 10 kVA CI engine-generator and water rheostat, which would supply the variable loads. Another constraint is the use of grab sampling during experimentation for the emission profiles for carbon monoxide (CO), carbon dioxide (CO2) and nitrous oxides (NOx). Based on the results, as an alternative fuel, the PNB, which showed comparable performance with PD, can be used for power generation in a CI engine-generator without modifications. The following conclusions were drawn from the results.• After transesterification, the overall biodiesel yield was 78.94 %. There was 24.28 % increase in yield if degumming procedure is applied and an improvement in the PNB coloration and CN to 54.4 with additional refining.

• The PNB has a FAME content of 69.23 % and with predominant compositions of palmitic and oleic acids.

• Physical and chemical characteristics revealed that the PNB and B20 conform with most ASTM standards and their values to PD.

• The HRR of at most 99.421 kJ/s generally increases with the increased PNB blend at increasing load settings.

• PNB at varying load settings has reduced overall efficiency of at least 25.95 % and at least 17.38 % SFC as compared to PD.

• PNB has lower CO emission of at least 13.42 % but higher CO2 and NOx emissions of at least 16.67 % and 80.52 % as compared to PD at varying loadings.

It is highly recommended that further research and investigation be conducted on CI engine-generator using non-edible resources of oils such as PNB. The emphasis of the future work should include using complete emission equipment with additional emission profiles for analysis. Performance and durability tests be conducted at increased engine-generator rating for long term usage. Further studies on complete combustion analysis and the use of higher purity PNB for improved performance and emissions may be conducted.

CRediT authorship contribution statement

Shawn Zedrick G. Taguiling: Writing – review & editing, Writing – original draft, Visualization, Validation, Software, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation. Ferdinand G. Manegdeg: Writing – review & editing, Supervision, Project administration, Methodology, Formal analysis, Conceptualization. Analiza P. Rollon: Writing – review & editing, Validation, Supervision, Methodology, Conceptualization.

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Shawn Zedrick G. Taguiling reports financial support was provided by Department of Science and Technology- Engineering Research and Development for Technology for the experimentation. The main author requests that the publication fee of $2100 USD be waived or discounted with Elsevier policy due to financial constraints and country of origin. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

The authors would like to express their appreciation to the Engineering Research and Development for Technology of the 10.13039/501100010218 Department of Science and Technology, Philippines for providing funds for this study. And the authors would like to thank Dr. Florencio C. Ballesteros Jr. and Dr. Juvy A. Balbarona for the suggestions in the analysis and methodology.

☆ ➢The paper has been presented at the 4th International Conference on Biofuels and Bioenergy, October 12–13, 2023, London, United Kingdom.
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