Experimental study on fuel consumption and smoke opacity of defective coffee-bean-based biodiesel fuel engines

This experimental study aims to analyse the performance of sorted coffee beans-based biodiesel. This study is carried out in three main stages; (a) the preparation process of coffee beans raw material, (b) the biodiesel formation process, and (c) biodiesel performance analysis. In manufacturing process, the coffee bean powder is added with two chemical treatments sequentially; extraction-distillation and esterification/transesterification. Parameters of analysis in this study are the characteristics of the biodiesel and the performance of the biodiesel-diesel mixture in terms of fuel consumption efficiency and engine smoke opacity. Measurements of Engine Running Time (ERT) and smoke opacity were carried out on a single-piston diesel engine. There were five biodiesel-diesel mixture specimens; B0, B5, B10, B15, and B20 (20% biodiesel fraction). The experimental results show that mixing biodiesel with diesel fuel provides two main advantages; extending engine running time which means fuel consumption efficiency, and lowering the smoke opacity level. Therefore, it is more environmentally friendly. The efficiency of fuel consumption and smoke opacity depends on the biodiesel fraction in the fuel mixture. The results and methodology of this research are expected to be an additional reference in the development of biodiesel as an alternative fuel.


Introduction
The important issues in Indonesia today are energy security and environmental impacts [1,2].Most of the national energy needs are from fossil energy sources [3].Statistical data released by the Indonesian National Energy Council in 2020 shows that Indonesia's energy needs are from various energy sources.The sources include petroleum, gas, coal, electrical energy, and renewable energy [3].Of all energy sources, the main supply is dominated by almost 40 % by petroleum [3].The dominant use of oil and natural gas as energy sources causes two main problems.They are reserves depletion that could result in price spikes and environmental damage due to CO2 gas emissions from combustion [3].With a high energy consumption per year, Indonesia's oil and natural gas supplies in 2021 are predicted to only last for the next 9.5 and 19.9 years [4].In the environmental aspect, the impact of CO2 emissions from fossil burning, on the other hand, affects climate change which in turn will disrupt the ecosystem as a whole [5].For this reason, it is necessary to save energy use and control environmental impacts in various fields with various methods, such as in the transportation sector [6], the industrial sector [7,8], and the building sector [9][10][11], etc.In addition to the commercial and residential sectors, the transportation sector is the three largest energy consumption sectors in Indonesia.The consumption is more than 574,795 thousand BOE.It is equivalent to 46.58 % of the national energy consumption [12].This consumption continues to cause a significant spike in line with the growth of Indonesia's population, which is estimated to rise by 0.7 % per year [3,12].The increase in public welfare and economy in Indonesia has triggered significant growth in automotive industries and sales by 17.82 % in 2021 [13].Official data from the government in 2021 states that the production capacity of the national automotive industry consisting of 21 companies, reaches 2.35 million units per year, respectively [13].In addition, the high consumption of energy and the environmental impact caused by the transportation sector is one of the problems faced by developing countries [14].The government has made many efforts to minimize energy consumption problems and the environmental impact of transportation.The efforts include shifting the use of private vehicles to public mass vehicles, limiting tolerable exhaust emissions, developing electric vehicles, integrating renewable energy in the transportation sector, etc [15][16][17].
Indonesia has a lot of potential renewable energy sources with an estimated capacity of 94.3 GW of hydro energy, 28.5 GW of geothermal energy, 32.6 GW of bioenergy, 207.8 GW of solar energy, 60.6 GW of wind energy, and 17.9 of Ocean energy [3].Unfortunately, the number of potential energy sources is not proportional to the number of products produced.In 2020, the latest national renewable energy mix was only 14.71 % of the national energy production [18].For the transportation sector, especially in diesel vehicles, an alternative solution is developing biodiesel as a mixture/substitute for diesel.The shift from diesel use to biodiesel in Indonesia is carried out in stages, both in terms of production capacity and quality of the fuel mixture [19].The Indonesian government has initiated the use of biodiesel since 2006.Several regulations issued by the government related to EBT include Presidential Decree No. 5 of 2006 regarding the use of Biodiesel and Act no. 30 of 2007 on new renewable energy [20,21].Diesel fuel is widely available in the Indonesian national market with various biodiesel fraction compositions such as B10, B20, B30, etc. [19,22].Bio Solar B20, for example, is a mixture of 20 % volume fraction of biodiesel and 80 % volume fraction of diesel.Biodiesel production can be done with various natural raw materials: peanuts, soybeans, palm oil, castor oil, coffee, etc. [23][24][25][26].Biodiesel has several advantages compared to Petro diesel (diesel).They are (a).renewable energy sources, (b).has a better combustion efficiency with a high Cetane Number, (c).applicable to all types of engines, (d) biodegradable, (e) able to lubricate pistons and clean injectors, and (e) low content of SOX and other harmful particulates [27,28].This study aims to produce and experimentally analyse the characteristics and performance of biodiesel manufactured from sorted coffee beans.Manufacturing coffee beans into biodiesel oil is carried out in three stages.The stages are the preparation and formation process with two main treatments.They are extraction-distillation and esterification/ transesterification.This experiment analyses several parameters.The parameters are the density and viscosity of the biodiesel produced, the engine running time (ERT) during the combustion test, and the opacity value of the exhaust emissions of the dieselbiodiesel mixture.The combustion test was carried out on a Dong Feng R175 single-piston diesel engine with a large combustion chamber volume of 353 cc.Biodiesel oil from coffee bean processing is mixed into pure diesel fuel with five different volume fractions.It is hoped this research can expand insight into the development of environmentally friendly biofuel technology in the future.

Coffee and Biodiesel
Biodiesel is a promising alternative energy produced from various basic materials such as vegetable fat, animal fat, or leftover cooking oil through several processes [24,29].Biodiesel is a mono-alkyl ester material consisting of long-chain fatty acids that can be either Methyl Esters or Ethyl Esters [30].This methyl/ethyl ester is a relatively stable compound, in the form of a liquid at room temperature, non-corrosive, with a low boiling point.Some plants that can be used as raw materials for biodiesel include peanuts, soybeans, palm oil, jatropha leaves, coffee, etc.However, biodiesel is still less economical when compared to petroleum diesel [31,32].One of the raw materials for making biodiesel in Indonesia is coffee beans [33].Indonesia is the fourth largest coffee producing country, after Brazil, Vietnam, and Columbia [34].However, since coffee is a popular beverage commodity with high economic value, the coffee beans selected as raw material for biodiesel are the defective product.In Indonesia in 2021, due to poor post-harvest handling, around 21.4 % of coffee bean harvested was damaged ( [35]).These faulty coffee beans with a low selling value will be processed into biodiesel.Similar to soybean, coffee beans contain vegetable oil that can be processed into biodiesel [31].This processed coffee oil composed of 81 % triglycerides are essential compounds in the formation of biodiesel [36].Other ingredients contained in coffee oil are linoleic and palmitic acids [31].

Materials and Method
This experimental study aims to process and test the performance of biodiesel made from defective coffee beans.In this research, there are three main processes.(1) The preparation process to select coffee beans to be further processed into coffee powder, (2) biodiesel formation processes, and (3) the process of testing the combustion performance of the diesel-biodiesel mixture.The main raw material is defective coffee beans with low selling value collected from the centre of the Kepahiang coffee plantation in Bengkulu, Indonesia.The preparation process is traditionally done using a roasting furnace and grinding machine.The chemical formation of coffee oil and biodiesel needed several other supporting materials.The supporting material are n-Hexane (C6H14) as a solvent in the coffee bean oil extraction process, methanol (CH3OH) as a coffee oil reactant, aquadest (H2O) as a washing fluid, Phenolphthalein (C20H14O4) as an indicator for acid-base titration, and Sulfuric Acid (H2SO4) as an esterification catalyst or Sodium Hydroxide (NaOH) as a catalyst for the transesterification process.Other supporting equipment used in making biodiesel include; a heating mantle and hot plate, measuring cup, extraction-Erlenmeyer flask, magnetic stirrer, thermometer, reflux condenser, Liebig cooler, etc.The combustion test was carried out using a 353 cc Dong Feng R175 single-piston diesel engine.Measurement of fuel consumption using a burette and thickness of smoke was measured using a smoke tester Opabox Autopower.

Preparation process
The preparation process aims to select damaged coffee beans for chemical processing.The preparation process consists of several main steps, namely: separation of the defective coffee beans (Figure 1.a), drying/roasting (Figure 1.b) and grinding (Figure 1.c).The first step is to sort the coffee beans by shape and size.Coffee beans are defective if the beans are small, cracked, or wrinkled (Figure 1.a).After being sorted, the beans are then roasted to remove the moisture content in the coffee beans (Figure 1.b).The lower the moisture content, the better the oil product.After the moisture content of the coffee beans decreases significantly, the final step in the preparation process is the grinding process.This process aims to refine the size of the coffee beans so that they are easier to extract (Figure 1.c).The expected particle size of the coffee beans is 100 mesh.Extraction-distillation is separating the elements present in solid-phase coffee beans using a solvent.The choice of solvent must be done properly so that the separation of the elements is as expected.In this study, the solvent used was n-Hexane.50 grams ground coffee bean extraction/distillation is done with five-volume variations of n-hexane: 0 ml (case-1), 200 ml (case-2), 300 ml (case-3), 400 ml (case-4), and 500 ml (case-5).The dried coffee bean powder is wrapped in a dry paper.The solvent is heated to a temperature of 70-75 °C.Then, it is flowed to wet the coffee grounds wrapped in paper.The extraction-distillation process was carried out for two hours to obtain pure coffee oil with a clear colour.
a. b. c.   c. esterification / transesterification.The next process is esterification/transesterification.This process aims to convert the free fatty acids in coffee beans into ester compounds.If the Free Fat Acid (FFA) in coffee oil is low enough (< 2 %), then the esterification process (reduction of fat content) can be skipped.The transesterification process is carried out immediately.The transesterification process is carried out by reacting coffee bean oil with methanol with the help of a NaOH catalyst.In the transesterification process, 200 ml of coffee oil was mixed with 100 ml of methanol with a catalyst concentration of 2 % NaOH.The coffee oilmethanol solution was heated to 60 °C and stirred at 600 rpm.After 2 hours of transesterification, then the unreacted methanol was evaporated.The separation process between biodiesel and glycerol (a byproduct of the transesterification process) is carried out with different densities.The separated biodiesel was then washed using 80 °C distilled water.

Performance Test and Indicators
Parameters that become indicators of this experimental research can be classified into three classifications, namely: (a) coffee oil extraction, (b) physical characteristics, including specific gravity, viscosity, and FFA content of coffee oil and biodiesel, and (c) combustion performance which includes consumption of fuel (equivalent to ERT) and the opacity value of exhaust gas emissions from combustion.The specific gravity of the biodiesel and coffee oil is calculated by comparing the specimen density with water density.The device for density measurement is a pycnometer.Meanwhile, the specimen viscosity calculation (η) is carried out by measuring the velocity of a free-falling spherical object in a falling ball viscometer containing the fluid of the specimen, as written in Eq. 1. Measurement of FFA levels was carried out by mixing the specimen with methanol added with NaOH as a catalyst and phenolphthalein as an indicator.Besides that, another important indicator in the biodiesel formation process is the yield from the extraction.The yield is calculated by comparing the mass of coffee oil produced to the coffee beans used.
Where r (m) is the radius of the measuring ball, g is the coefficient of gravity (9.81 m. s -2 ), v is the velocity of the ball dropping (m.s -1 ), ρb and ρf is the density of the ball, and fluid (kg.m -3 ), consecutively.

Rendement of Extraction Process
The extraction-distillation process was carried out on 50 grams of fine coffee powder using n-Hexane as a solvent with four solvent mass variations: 200 grams, 300 grams, 400 grams, and 500 grams.From the measurement results, the yield value of the formation of coffee oil was different for the four solvent mass variations, as shown in Table 1.The data in Table 1 shows that, with the same amount of coffee powder raw material (50 grams), the rendement (extract) of coffee oil production increased with the addition of the mass of solvent catalyst.By dissolving 50 grams of coffee grounds in 200 grams of hhexane catalyst (mass fraction 1:4), it can produce 6.3 grams of coffee oil, equivalent to 12.6 % of the rendement from the extraction process.Meanwhile, when dissolved in 500 grams of catalyst, the resulting coffee oil is 7.6 grams, equivalent to 15.2 % rendement.The increase in extraction yields for the four fractions of catalyst mass in detail can be seen in Table 1 and Figure 4.In Figure 4, the total solvent mass ratio affects the extraction rendement of coffee oil.The greater the amount of solvent mass, the higher the rendement.A significant increase in rendement occurred when the amount of solvent mass was still small.When the total solvent mass ratio is high (about 1:8), the increase in extraction rendement becomes less significant.If the mass ratio of the solvent is too large, then saturation occurs in the solution.Therefore, the increase in rendement becomes stagnant.Besides, the amount of solvent mass used affects the manufacturing cost.The more solvent used, the higher the required cost.Therefore, the mass ratio of coffee and solvent suitable for the extraction process, in this case, is 1:8.

Formation process and characteristics of biodiesel
The other parameter to be analysed is the characteristics of coffee oil and biodiesel produced during the formation process.Analysis of these characteristics is significant for determining the quality of coffee oil and biodiesel from coffee bean extraction.There are three parameters of coffee oil analysed: density, viscosity, and FFA content.These three parameters also determine the quality and effectiveness of combustion.The test results for coffee oil and biodiesel are shown in Table 2.The coffee oil produced has good density and viscosity, and is within the tolerable value range.Free Fatty Acids (%) 0,917 Based on the measurement results, the level of FFA in coffee bean oil is quite low at 0.917 %.Based on the research 0.917 %.In another research [37], coffee oil with a low FFA content (< 2 %) can be directly processed by transesterification without having to go through the esterification process (reducing fat content) because the fat content is already below the required threshold.High levels of FFA in an oil can cause high glycerol production during the biodiesel formation process.The transesterification process in coffee oil was carried out between methanol and coffee oil at a molar ratio of 1:2 with a 2 % NaOH catalyst.Transesterification produces two main elements, namely biodiesel, and glycerol.Furthermore, biodiesel must be separated from glycerol to produce fuel.The separated biodiesel is then washed using heated aquadest.Based on Table 2, this coffee bean biodiesel has 862 kg.m-3 density and 5.41 CSt.This value has fulfilled the biodiesel quality standards in Indonesia stipulated in SNI 7182:2015 [38].The moderate density of biodiesel has a positive impact on combustion effectiveness.When biodiesel density is too high, it can cause low atomization of the fuel.Therefore, it is hard to run the engine.On the other hand, if the biodiesel density is too low, it can accelerate the wear of the injection pump components.

Engine running time and smoke opacity
The cleaned biodiesel is then mixed into diesel to get the fuel for the Dong Feng R175 engine.The performance test uses five variations of the fuel mixture, as described in the methodology section.Fuel consumption is represented by the duration of ERT obtained by burning the diesel-biodiesel mixture.In Table 3 it can be seen that the ERT duration for burning 25 ml of diesel-biodiesel fuel mixture ranges from 391.3 to 442.3 seconds for all cases.It shows that the ERT time of the diesel-biodiesel-fuel mixture engine is slightly longer than that of pure diesel combustion.Although not significant, the addition of biodiesel can increase engine start time for the same volume of fuel.This ERT is equivalent to fuel consumption.The longer the ERT, the more efficient the engine combustion process.In this case, the longest engine running time was obtained for the combustion using B15 fuel with an increase in ignition time of 13 % compared to diesel fuel (Table 3).
In addition, the engine smoke opacity in various diesel-biodiesel mixtures was also analysed in this study.The smoke opacity level is closely related to the air pollution caused by combustion.The measurement results in Table 3 and Figure 5 show an inverse relationship between smoke opacity and the amount of biodiesel fraction in the diesel mixture.The higher the volume percent of biodiesel, the lower the smoke opacity.It happened because biodiesel contains fatty acids that are more prone to oxidation reactions.Therefore, combustion becomes more effective.In addition, coffee biodiesel has a very low sulfur content, so the smoke is clearer and more environmentally friendly.Biodiesel also contains methyl ester that can bind more oxygen atoms in its particles which diesel does not have.The lowest smoke thickness occurs in the B20 mixture, with a decrease of 40.3 % compared to pure diesel combustion.The addition of biodiesel into diesel fuel can increase engine running time and reduce smoke opacity in exhaust gases.These results indicate that biodiesel extracted from coffee beans is an alternative solution to overcome the fossil energy crisis.In addition, biodiesel is a renewable energy source and has the potential to be used as a substitute for diesel fuel.

Conclusion
Experimental research on the formation and performance test of mixing biodiesel from coffee beans with diesel fuel showed significant results in the development of biofuels.The biodiesel formation process is carried out in two stages: the preparation process to grind defective coffee beans into a fine powder and a formation process to produce the biodiesel with three chemical reactions: extractiondistillation and esterification/transesterification.In the extraction-distillation process, the rendement of the resulting coffee oil is highly dependent on the mass of the solvent catalyst used.The addition of solvent can increase the production capacity of the resulting coffee oil.The extracted coffee bean oil is then reacted with methanol.This process is known as transesterification to produce biodiesel.The test results show that the biodiesel produced has good characteristics and meets the specified quality standards.The performance test for the combustion of the diesel-biodiesel mixture has shown good results.(a) An increase in fuel consumption efficiency as an increase in the engine running time, and (b)

Figure 1 .
Figure 1.Traditional preparation process in manufacturing coffee beans as biodiesel material; a. the coffee beans sorting process, b.The roasting process, c.The grinding process

Figure 2 .
Figure 2. Biodiesel formation process; a. extraction, b. distillation, c. esterification /transesterification.The next process is esterification/transesterification.This process aims to convert the free fatty acids in coffee beans into ester compounds.If the Free Fat Acid (FFA) in coffee oil is low enough (< 2 %), then the esterification process (reduction of fat content) can be skipped.The transesterification process is carried out immediately.The transesterification process is carried out by reacting coffee bean oil with methanol with the help of a NaOH catalyst.In the transesterification process, 200 ml of coffee oil was mixed with 100 ml of methanol with a catalyst concentration of 2 % NaOH.The coffee oilmethanol solution was heated to 60 °C and stirred at 600 rpm.After 2 hours of transesterification, then the unreacted methanol was evaporated.The separation process between biodiesel and glycerol (a byproduct of the transesterification process) is carried out with different densities.The separated biodiesel was then washed using 80 °C distilled water.

Figure 3 .
Figure 3. Engine performance test; a. the process of mixing biodiesel and diesel, b. engine starting and c. measurement process

Figure 4 .
Figure 4.The value of coffee oil rendement extraction for several different mass ratios of solvents.

Figure 5 .
Figure 5. Engine Running Time (ERT) and smoke opacity for various biodiesel mixture fractions.

Table 1 .
Extraction rendement of coffee oil from 50 grams of dry coffee powder using n-Hexane solvent with different mass fractions

Table 2 .
Characteristics of coffee oil when measured at room temperature of 25 °C and biodiesel measured at 40 °C

Table 3 .
Measurement of engine running time and smoke opacity of a diesel-biodiesel-fuelled engine