The Concise Latest Report on the Advantages and Disadvantages of Pure Biodiesel (B100) on Engine Performance: Literature Review and Bibliometric Analysis

Currently, many countries are promoting B100 as the main fuel for diesel engines towards the transition to 100% renewable energy applications. However, due to its properties, B100 has both advantages and disadvantages to replace diesel oil. Therefore, a bibliometric analysis was carried out to evaluate the performance and emissions of a diesel engine with the B100 being tested on a multi-cylinder diesel engine for cars. Unfortunately, only 12 of the 127 selected articles are eligible to be reviewed in detail and none of them discusses all the key performance of diesel engines which include Brake Thermal Efficiency (BTE), Specific Fuel Consumption (SFC), Cylinder Pressure (CPs), Heat Release Rate (HRR), NOx, and smoke. Through data synthesis, we found that the use of B100 provides advantages in engine noise, thermal efficiency, specific fuel consumption, and emissions under certain engine loads. On the other hand, it also has the potential to result in poorer performance, if there is no modification to engine components and the addition of additives. As a recommendation, the results of this analysis provide a guide for further research to examine the use of B100 with all diesel engine performance variables. Research paths can be developed with the wider potential to provide new arguments on various diesel engine technologies, engine capacities, B100 raw materials, and test environments.


INTRODUCTION
In the last decade, the issue of global warming and climate change continues to strengthen and it is associated with the use of oil-based fuels (Franta, 2021;Ginanjar Ahmad Zakky, 2020;Sinaga, 2020) which have more environmental risks from exploration, transportation, production, distribution, and consumption (Chettouh et al., 2016).Natural damage in oil drilling areas (Harnani, 2018), cases of oil spills in the Gulf of Mexico and the Atlantic are other examples of environmental threats from fossil fuels (Bhattarai et al., 2011;Soares et al., 2020).In fact, a greater risk is reported in Nigeria, where oil spills are significantly correlated with humanitarian tragedy (Bruederle & Hodler, 2019).
On the other hand, efforts to find and implement alternative energy are also a strong challenge for many countries, regarding availability, prices, environmental balance, and also policies (Hadiyanto et al., 2020;Kaniapan et al., 2021;Panoutsou et al., 2021;Yusoff et al., 2021).The sustainability of the industrial and transportation sectors with renewable fuels continues to be carried out through the substitution of fossil fuels, either with a fully dedicated system or with a bi-fuel system or a hybrid system (Anderhofstadt & Spinler, 2020;Shao & Dessouky, 2020).The transition to the adoption of 100% renewable energy is a complex process, not only on technical issues, but also on political, economic, and social issues.For example, the expansion of the use of bioethanol will face the availability of land for food production (de Souza Ferreira Filho & Horridge, 2014).
The technology for biodiesel production which includes starting materials, pretreatment methods, reactors, and processing methods, catalysts, and testing methods is also developing rapidly (Hariyanto et al., 2021;Mahlia et al., 2020;Zetra et al., 2021;Hidayat et al., 2022).On the other hand, cleaner ethanol (Vohra et al., 2014;Wahyu et al., 2019;Waluyo et al., 2020) with its different properties from gasoline and the relatively large price difference, requires major modifications to the engine components and increases driving operating costs, making it weaker in terms of market acceptance (Mudombi et al., 2018).
As an alternative fuel with all its advantages, biodiesel also has several disadvantages, including a very high flash point causing delayed ignition, cold flow properties, and poor oxidation stability contributing to its disadvantages (Atabani et al., 2012;Bukkarapu, 2019;Firoz, 2017).Therefore, blending biodiesel with diesel oil is widely used to reduce its disadvantage.
Although currently the use of pure biodiesel (B100) is the future target market and is commercially available, B100 research reports on multi-cylinder car engines are still limited, they are dominated by testing on low-speed single-cylinder engines (Ajith et al., 2021;Altaie, 2020;Arun et al., 2020;Kumar & Subramanian, 2020;Örs et al., 2020;Rameshbabu et al., 2020;Singh et al., 2020;Viswanathan et al., 2020;Yatish et al., 2021).Although the working principle is the same, car engines have complexities related to performance.
In addition, the performance of diesel engines is also more complex than gasoline engines, which include Brake Thermal Efficiency (BTE), Specific Fuel Consumption (SFC), Cylinder Pressure (CPs), Heat Release Rate (HRR), NOx, and Smoke.Partial engine testing with some parameters, of course, cannot measure the overall performance of the B100, considering that these parameters influence each other.The reason this parameter is studied in depth is that the parameters of BTE and SFC are part of engine performance which are very important to analyze because they are related to the use of fuel in diesel engines.As it is known that the main purpose of using biodiesel fuel is to replace diesel fuel to reduce fossil fuel consumption.Likewise, parameters of the cylinder pressure and the heat release rate are representations of engine power that describe the combustion process in the cylinder so that knowing these two parameters can describe engine performance.The parameters of NOx and smoke emissions are important reviewed in this article that diesel engines contribute greatly to producing these emissions so that this is a concern in the world by setting thresholds for these emission levels as issued by the Ministry of Environment and Forestry and the European Union.
Therefore, this article presents a concise literature review and bibliometric analysis on the advantages and disadvantages of the B100 which was tested on a multi-cylinder diesel engine with a capacity above 1 liter, which is considered more representative of real application conditions than single or twin cylinder engines.The literature were reviewed from search engine (Azizah et al., 2021).Then, the references and limitations reviewed are presented in detail in Table 1 (see method section).
As the uniqueness of this work, we used VOSviewer to determine the topics studied (bibliometric analysis), as has been practiced by Hamidah et al. (2020) and Husaeni and Nandiyanto (2022).Key performance of diesel engine which includes Brake Thermal Efficiency (BTE), Specific Fuel Consumption (SFC), Cylinder Pressure (CPs), Heat Release Rate (HRR), NOx, and Smoke is used in the search method for articles in the Scopus database.The iteration results by VOSviewer show they have a strong relationship, as presented in Figure 1.Therefore, the specific purpose of this work is to analyze the advantages and disadvantages of B100 in diesel engines by considering the combustion process which includes cylinder pressure, heat release rate, and engine performance including thermal efficiency, specific fuel consumption, and exhaust emissions including nitrogen oxide and smoke emissions.

Searching method and criteria
In the present work, we used Scopus as the single database.Searching on article titles, abstracts, and keywords were chosen because they are more representative of the keywords "B100", "performance", "emission".Therefore, the constraints were determined, only selected articles were continued in the discussion, and articles that were not included in the scope of the review were excluded, including: (i) Articles from discontinued covered journals and from journals that are alleged to have not carried out a rigorous peer-review process; (ii) Articles that are not included in the original research paper; (iii) Inaccessible articles; (iv) Articles that do not discuss engine performance; (v) Articles mentioning B100 in the abstract and body text but not finding B100 testing in the methods and results; and (vi) Articles that present tests on engines with small capacities, generally on single and twin cylinder engines, or the tests are not on vehicle engines.
The limitations of article selection in the Scopus database are presented in Table 1.

Screening for eligibility
Of the 127 articles that we obtained from the Scopus database, we found 26 articles that did not pass the initial screening process,

Data Synthesis
This section describes the data synthesis from previous studies related to engine performance and emissions in diesel engines using B100.The key performance characteristics of diesel engines (Balasubramanian et al., 2021) including Brake Thermal Efficiency (BTE), Specific Fuel Consumption (SFC), Cylinder Pressure (CPs), Heat Release Rate (HRR), NOx, and Smoke were examined in 12 reviewed articles.The results of the synthesis data review are described in Table 2 and Table 3,  respectively.Unfortunately, only 12 of the 127 selected articles are eligible to be reviewed in detail and none of them discusses all the key performance of diesel engines which include Brake Thermal Efficiency (BTE), Specific Fuel Consumption (SFC), Cylinder Pressure (CPs), Heat Release Rate (HRR), NOx, and smoke, all article discusses partially.The data testing scope is presented in

Standard of B100
Like other fuels, biodiesel is not standardized by its material, but it is standardized by its properties.Biodiesel standards were developed in the 1990s to facilitate the growing use of alkyl estersbased biodiesel and its mixes as automobile fuels.In 1999, American Society for Testing and Materials (ASTM) International issued PS121, a preliminary standard for biodiesel.In 2002, the first ASTM standard (ASTM D6751) was adopted.Table 4 shows the selected ASTM International requirements for B100, where these specifications are regularly updated and modified.

Cylinder pressure and heat release
The use of B100 resulted in lower cylinder pressure and heat release rate than diesel oil and blended biodiesel especially at low and medium loads, as shown in previous studies (Aydın, 2020;Hojati & Shirneshan, 2020;Isik, 2021).Although it was tested with different types of B100, it also showed the same trend.Isik (2021) explained that the peak of cylinder pressure and heat release rate with the use of diesel fuel (USLD) reached 80.55 bar and 69.15 J/o respectively at engine load is 75%, while the use of B100 fuel, the value was much lower.Hojati & Shirneshan (2020) also explained that the cylinder pressure drop reached 10.5% with the use of B100 fuel.Research from Aydın (2020) found that the heat release rate using diesel fuel was 73.01 J/CAD and the use of B100 fuel produced a value of 64.767 J/CAD at a load of 10.8 kW.
Aydin (2020) explained that the cylinder pressure drop in the B100 application was caused by poor atomization and mixing due to its high viscosity and density, which resulted in a longer ignition delay and shorter combustion duration.Hojati and Shirneshan 2020) also explained that the cylinder pressure drop was due to the lower LHV of biodiesel than diesel oil.The application of B100 causes the peak cylinder pressure to be closer to the top dead center (TDC) due to the higher cetane number so that the combustion process is more advanced.Therefore, increasing the compression ratio (CR) can increase the cylinder pressure to increase the temperature at the start of the injection, thereby increasing the rate of heat release.Figure 4 shows the compression ratio (18:1) can increase cylinder pressure in the B100 application by 18.3%.1.9-6.01.9-6.01.9-6.01.9-6.0Sulfated ash, % mass, max D874 0.020 0.020 0.020 The use of B100 can lower the noise level than the use of diesel oil under low and medium loads.Balasubramanian et al., (2021) explained that the noise level in the use of diesel fuel is 88 dB[A] and the use of B100 fuel is 86 dB[A] at medium load.However, at high loads, the noise level of B100 is higher than that of a blend of biodiesel and pure diesel oil.It is caused by the high oxygen content in B100 which causes the fire to extinguish, causing incomplete combustion and pressure variations in the cylinder (Balasubramanian et al., 2021).

Thermal Efficiency
The use of B100 resulted in higher thermal efficiency than diesel oil and blended biodiesel at all engine loads (low, medium, and high) as reported in previous studies (Abdalla, 2018;Esonye et al., 2019;Ghadikolaei et al., 2019;Odibi et al., 2019;Thangaraja & Srinivasan, 2019).The use of B100 includes waste cooking oil (Odibi et al., 2019), vegetable (Abdalla, 2018), coconut (Thangaraja & Srinivasan, 2019), waste cooking oil (Ghadikolaei et al., 2019), dan seed oil (Esonye et al., 2019).Odibi et al., (2019) explained that the increase in thermal efficiency in the use of B100 is due to the high input energy being converted into work.Thangraja & Srinivasan (2019) also explained that biodiesel has a high oxygen content thereby increasing combustion efficiency and lower friction losses due to better lubrication of biodiesel thereby increasing thermal efficiency, as shown in the following Figure 5.The same explanation was also reported by Esonye et al., (2019) that the maximum value of BTE is obtained at the use of B100 fuel of 45% while the use of diesel fuel reaches a maximum value of 26% at full load.However, other studies also reported the use of B100 resulted in lower thermal efficiency than diesel oil especially at low and medium loads, as reported by Aydın, (2020), Hojati & Shirneshan (2020), Isik (2021), and Balasubramanian et al., (2021).The decrease in thermal efficiency can be seen in Figures 6  and Figure     Aydın (2020) described the decrease in thermal efficiency with B100 caused by poor combustion efficiency due to spray atomization.Balasubramanian et al., (2021) also explained the decrease in thermal efficiency that occurred in B100 due to its high viscosity and low heating value, as also described by Sudarmanta et al., (2020) However, thermal efficiency in B100 applications can be improved through; (1) increasing the compression ratio (CR) (Hojati & Shirneshan, 2020), (2) adding ethyl proxitol and methyl proxitol catalysts to B100 (Aydın, 2020), and adding alcohols such as pentanol, butanol, and octanol to B100 (Isik, 2021).One of the results of efforts made to improve thermal efficiency is shown in Figure 8.
Based on Figure 8, the addition of alcohol pentanol (PE20) and Octanol (OC20) into B100 can increase thermal efficiency.The average thermal efficiency increase is 7% with the addition of OC20 to the B100.The inclusion of alcohol in B100 improves evaporation properties and mixing characteristics (Isik, 2021).
However, other studies also reported that the use of B100 resulted in lower SFC than diesel oil, as reported by Abdalla (2018), Thangaraja & Srinivasan, (2019), Isik (2021), and Esonye et al., (2019).Thangaraja & Srinivasan (2019) explained that the specific fuel consumption of B100 application is lower than that of pure diesel oil, it is related to basic energy, where biodiesel performs better than diesel oil, as shown in Figure 11.

Nitrogen oxide (NOx)
Diesel engines have high NOx emissions due to their high combustion temperature (1800 K), thus accelerating the reaction between nitrogen (N2) and oxygen (O2) (Aydın, 2020;Isik, 2021).The use of B100 resulted in higher NOx levels compared to diesel oil in all engine loads, as shown in previous studies (Aydın, 2020;Esonye et al., 2019;García-Martín et al., 2018;Ge et al., 2020;Ghadikolaei et al., 2019;Hojati & Shirneshan, 2020;Isik, 2021;Santos et al., 2017;Thangaraja & Srinivasan, 2019).The increase in NOx emission is shown in Figure 12 and Figure 13.García-Martín et al., (2018) attributed the increase in NOx emission in B100 application to the high oxygen content.The authors further stressed that the increase in NOx emission in B100 application was due to the high oxygen content and low calorific value, leading to higher fuel consumption compared to diesel fuel.Hojati & Shirneshan (2020) also explained that the high NOx content in the B100 application was caused by the high viscosity and higher cetane number which caused a lower autoignition time which increased the temperature inside the cylinder.Meanwhile, Ghadikolaei et al., (2019) explained that biodiesel produces quite high temperatures because there are many oxygen-rich areas in the combustion chamber.Furthermore, Santos et al., (2017) also explained that high oxygen content accelerates the rate of formation of NOx emissions.Esonye et al., (2019) described the high oxygen content of B100 resulting in high temperatures that favor NOx formation.However, other studies also revealed that the use of B100 resulted in lower NOx levels than the use of diesel oil, as reported by Abdalla (2018) and Balasubramanian et al., (2021).Abdalla (2018) explained that the decrease in NOx with B100, as shown in Figure 14.This is caused by the high-water content, thereby lowering the combustion temperature.

Smoke
Diesel engines have high levels of smoke emissions because diesel belongs to the paraffin family with a long carbon chain.The use of B100 produces lower levels of smoke emissions compared to diesel oil at all engine loads, as revealed by Ghadikolaei et al., (2019).He explained that the reduction in smoke emissions of 57.1% with B100 is due to the high oxygen content and shorter carbon chain of biodiesel fuel.
However, another study also revealed that the use of B100 produces high levels of smoke at low and medium loads as reported by Abdalla (2018) and Balasubramanian et al., (2021).The increase in smoke emission is shown in Figure 15.
Furthermore, Balasubramanian et al., (2021) explained that the increase in smoke emissions at low and medium loads due to the rich air-fuel ratio and poor atomization so that the potential for smoke emission was greater, while at high loads, less smoke due to the availability of more oxygen, it resulted in the fuel-air ratio can be streamlined for lower smoke formation.

CONCLUSION
The use of B100 in diesel engines provides advantages and disadvantages to engine performance and emissions.After a schematic literature review has been carried out, several advantages and disadvantages can be reported as follows: (i) Advantages-the use of B100 results in lower noise levels compared to diesel oil.Thermal efficiency with B100 in diesel engines can be increased due to the high oxygen content to improve the combustion process and the rate of combustion speed, although some literature describes a decrease in thermal efficiency at low and medium loads.In terms of fuel consumption, the implementation of B100 can reduce the specific fuel consumption (SFC), although some literature describes an increase in SFC.Finally, the use of B100 can reduce smoke due to its high oxygen content and short carbon chain, although some literature describes an increase in smoke values at low and medium loads.(ii) Disadvantages-the use of B100 can decrease cylinder pressure and heat release rate compared to diesel oil, but the pressure drop can be improved by increasing the compression ratio, adding alcohol, and adding a catalyst to B100.On the emission side, the use of B100 increases NOx emissions due to the increase in combustion temperature.
That's because of the high oxygen content, although some literature also describes a decrease in NOx.
In general, of the 12 articles that were reviewed in depth, none of them fully discussed the key performance characteristics of diesel engines which include BTE, SFC, CPSs, HRR, NOx, and smoke.Therefore, this review provides guidance for further research to examine the use of B100 in diesel engines with all diesel engine performance variables.The research path can be developed with a wider potential to provide new arguments for different variations of diesel engine technology, variations in diesel engine dimensions, variations in B100 raw materials, and variations in test environments.In conclusion, with its weaknesses that can be covered, the B100 becomes a promising diesel engine fuel for now and the future.Besides its superior characteristics in engine performance and emissions, the use of B100 as renewable energy is an effort to realize sustainability in the transportation and industrial sectors.

Figure 2 .
Figure 2. Content selection process and criteria.

Figure 3 .
Figure 3. Testing scope comparison of the selected reviewed articles.

Table 1 .
Limitations of searching criteria.

Table 2 .
Review of data synthesis from engine performance characteristics and emissions using pure biodiesel (B100).

Table 2 (
Continue).Review of data synthesis from engine perfomance characteristics and emissions using pure biodiesel (B100).

Table 3 (
Continue).Testing scope of the selected reviewed articles.