An Experimental Study of the Emission Characteristics and Soot Emission of Fatty Acid Methyl Esters (FAME) in an Industrial Burner

Abstract

The aim of this research is to investigate the environmental emission effects and combustion properties of burning different types of FAME biodiesel fuels in an industrial oil burner. These burner heads are used in many areas of industry for heating various boilers and tube furnaces. The fuels used, the area of use, the emission norm values, and the climatic conditions are key factors in this investigation. In this research, two plant-based oils are examined, the properties of which have been compared to standard commercial heating oil. The raw material of the two tested bio-based components was rapeseed. The main gas emission parameters CO, THC, CO₂, O₂, HC, water content, and consumption data were measured. The measurements were performed in an AVL engine brake platform infrastructure, where gas emissions were measured with an AVL AMA i60 FTIR emission gas analyzer, fuel consumption was meticulously gauged using a fuel flow meter, fuel temperature was monitored using an AVL 745 fuel temperature conditioning system, and air consumption was measured with an AVL Flowsonix intake air flow meter. The measurement results showed that both tested biofuels can be burned stably in industrial oil burners, have favorable properties in terms of ignition and flame extinction tendencies, and there is no significant difference in emission parameters compared to standard fuel oil.

1. Introduction

The use of biodiesel in industrial oil burners is receiving increasing attention because of environmental concerns. Research in recent years has shown that replacing conventional fossil fuels with renewable energy sources, such as fatty acid methyl ester (FAME) biodiesel, can significantly reduce carbon dioxide and other harmful emissions [1,2,3,4]. The combustion properties and environmental impacts of different types of biodiesels used in industrial heating systems have been investigated by many researchers. Zhang et al. showed that the use of biodiesel significantly reduces CO and NOx emissions compared to conventional fuel oil while maintaining thermal efficiency [5]. In contrast, Keskin et al., 2020, highlighted that biodiesels exhibit different combustion behavior, which affects their industrial applicability [6]. In addition, E J Liu and colleagues, 2023, pointed out that the geographic and climatic factors of biodiesel also have a significant impact on their ability to meet emission standards [7,8,9,10]. NOx emissions are of importance in industrial settings because they contribute to the formation of ground-level ozone and fine particulate matter, both of which are harmful to human health and the environment. NOx also plays a key role in the formation of acid rain, which can have detrimental effects on ecosystems, infrastructure, and human health. Studies have shown that the higher oxygen content in biodiesel, while beneficial for reducing CO and PM, can lead to higher combustion temperatures, thereby increasing thermal NOx formation. This trade-off between reducing CO and PM while increasing NOx emissions presents a challenge in optimizing biodiesel combustion for industrial use. To address this issue, various aftertreatment technologies, such as selective catalytic reduction (SCR) and exhaust gas recirculation (EGR), are being explored to mitigate NOx emissions without compromising the other environmental benefits of biodiesel [11,12,13]. Most current research highlights the potential of biodiesel as a more environmentally friendly alternative to traditional diesel fuels, as they offer reductions in harmful emissions without compromising engine performance [14,15,16,17].

To address the identified research gaps, our study explores the less examined area of biodiesel use in industrial oil burners, specifically looking at the performance and emission characteristics of rapeseed-based biodiesel. Previous studies have mainly focused on automotive applications, leaving a need for more understanding of its behavior in industrial contexts. Additionally, the effects of different feedstocks on combustion in these settings are not fully understood. Our research contributes to this area by providing data on the operational feasibility and environmental impact of rapeseed biodiesel in industrial oil burners [1,2]. The aim of the present research is to investigate the combustion properties and environmental impact of two plant-based biodiesels in an industrial oil burner compared to standard fuel oil [14,15,16,17]. The main gas emission parameters, fuel consumption, and other relevant factors were measured to assess industrial applicability.

2. Materials and Methods

The oil burner used in our research is a Ganz N-10-A type industrial burner. The N-10A type oil burner is a forced-air, pressurized atomization system, with two-point control and one-stage fully automatic combustion. The oil burner is an automatic combustion device with a block construction system, mounted on a fan housing with a top discharge system. Its structural elements include the injection-molded aluminum burner housing, which carries the electric motor and has the direct-drive pump and fan impeller mounted on one side. The other side of the fan housing is enclosed by a side plate, which holds the safety and control elements. On the side plate is the automation, the ignition transformer, and the damper that regulates combustion air, as well as the seven-pole connector for electrical connection. The atomizer pump is integrated with the oil solenoid valve. The nozzle and flame tube of the burner atomizer fit centrally in the catch rim, which is ensured by the integrated baffle disc, ignition electrode holder, and nozzle holder. Figure 1 shows the performance diagram of the burner. Performance and oil consumption are shown on the horizontal axis, with combustion chamber pressure on the vertical axis.

The performance and fuel consumption values were influenced by the quality and technical parameters of the fuel used. The values presented in the diagram above refer to commercially available heating oil. The technical parameters of the burner are listed in

Table 1. Technical parameters of the Ganz N10-A oil burner.

Ganz N10-A Oil Burner
Performance (kW)	22–44
Fuel consumption (kg/h)	1.8–3.7
Viscosity required for atomization (cSt)	10
Oil pressure (bar)	0.5
Atomization system	pressurized
Control system	on/off two-point control
Supply voltage (V)	220
Supply frequency (Hz)	50
Electrical power consumption (W)	140
Protection (IP)	20
Ambient temperature (°C)	−5...+50
Noise level (dB)	60
Weight (kg)	10

.

2.1. Materials

The two tested biofuels were produced by Rossi biofuel using its own developed technology. The reference fuel was commercially available heating oil, which had the same parameters as conventional diesel oil. The two investigated FAME fuels were produced from rapeseed through the transesterification of vegetable oils and fats. High molecular weight fats and oils were reacted with lower-chain alcohols, usually in the presence of potassium hydroxide, to produce lower-molecular-weight substances. The chemical process is illustrated in Figure 2.

Vegetable oils are composed of natural glycerides, which are esters of the trivalent alcohol glycerol with different fatty acids. Typically, three fatty acids with different structures are attached to glycerol, and several unsaturated carboxylic acids are involved in their composition. Oleic acid, linoleic acid, and linolenic acid are most often among the molecular constituents in rapeseed oils, which also contain a small amount of erucic acid. Transesterification involves the removal of three alkoxy groups from the triglyceride (oil/fat) backbone. When the substance reacts with alcohol, it breaks down into three lower-molecular-weight esters (FAME), with glycerol produced as a by-product during the separation. Potassium hydroxide acts as a catalyst in the process. During transesterification, the glycerol triester decomposes under the influence of alkali, and the resulting fatty acids are converted into fatty acid methyl ester by reacting with methanol.

The structure of the mixture of fatty acid methyl esters in the final product forms through a multi-stage consecutive reaction. The molecular structure of the target products of transesterification is very similar to the paraffin hydrocarbons that make up diesel fuel oils [17,18,19,20]. The technical parameters of the tested fuel are listed in the

Table 2. Technical parameters of the tested fuels [17,18,19,20].

Parameter	Heating Oil	B1	B2	Standard
Cetane	≥51.0	≥44	≥44	MSZ EN ISO 5165
Sulfur [mg/kg]	≤10	≤10	≤10	MSZ EN ISO 20846
Water [mg/kg]	≤200	≤200	≤250	MSZ EN ISO 12937
Pensky–Martens flash point	˃55	˃50	˃50	MSZ EN 2719
Caloric value [MJ/kg]	42.7	40.5	40	-
Ash [w/w%]	≤0.01	≤0.02	≤0.015	MSZ EN ISO 6245
Viscosity [mm2/s]	2.00–4.50	2.50–5.50	2.70–5.60	MSZ EN ISO 2104
Mechanical impurities [mg/kg]	≤24	≤26	≤26	MSZ EN 12662
Density [kg/m3]	0.83	0.9	0.95	-
Coke residue [w/w%]	≤0.30	≤0.40	≤0.45	EN ISO 10370
Cold Filter Point (CFPP)	≤5	≤5	≤5	MSZ EN 116

.

The vegetable oil was transesterified primarily with methanol or ethanol in the presence of a fatty acid catalyst in a glyceride bond at a temperature of 20–80 °C. During transesterification, the initial two phases merged into one phase as the reaction progressed, and after some time, two phases formed again. Upon completion of transesterification, the product mixture was separated by sedimentation. The heavier, glycerin-containing phase included most of the catalyst, the salts of fatty acids formed with the catalyst (soaps), a portion of the alcohol, other organic compounds in the vegetable oil (polypeptides, phospholipids), a small amount of vegetable oil, and by-products. The lighter ester phase contained vegetable oil methyl ester, alcohol, a small amount of soap, and catalyst residue. The success of the biodiesel production was fundamentally influenced by the quality of the raw material, in this case, rapeseed. The composition of the fatty acids in the triglycerides of the oil made from the seeds, the number of carbon atoms, and the number of double bonds were decisive factors in this regard.

2.2. Methods for Exhaust Gas Measurement

The equipment used during the measurements was an AVL SESAM i60, a Fourier-transform infrared (FTIR) spectrometer. The measurement principle was based on absorption and reflection. A gas scanned with broad-spectrum infrared light absorbed light rays of certain frequencies and transmitted others. The frequency of the absorbed light corresponded to the natural frequency of the vibrational modes of the gas molecules, or the harmonics of these frequencies. The ratio of the absorbed light was proportional to the concentration ratio of the gas being tested. Thus, the spectrum of the absorbed frequencies identified the type of gas, while the amount of absorbed light indicated the concentration of the gas being tested [21,22,23]. Figure 3 schematically illustrates the process by which the infrared light was introduced through a modulator into a cuvette containing the gas to be analyzed.

The modulator modulated the light, splitting it into different wavelengths. As the light passed through the cuvette, the detector measured the amount of light transmitted. From the detected signal, the electronics inferred the degree of absorption and converted this information into the concentration of the analyzed gases using Fourier transformation. The accuracy of the measuring instruments ensured reliable and precise measurements (

Table 3. The accuracy of the measuring instruments.

Measured Components	NO and NOx	THC and CH4	CO2	CO
Reproducibility	≤0.5% of range full scale	≤0.5% of range full scale	≤0.5% of range full scale	≤0.5% of range full scale
Linearity	≤2% of measured value (10–100% of full-scale range) ≤1% of full-scale range, whichever is smaller	≤2% of measured value (10–100% of full-scale range) ≤1% of full-scale range, whichever is smaller	≤2% of measured value (10–100% of full-scale range) ≤1% of full-scale range, whichever is smaller	≤2% of measured value (10–100% of full-scale range) ≤1% of full-scale range, whichever is smaller

).

During the experiment, the oil burner was integrated into the infrastructure of a standard AVL engine testbed platform (Figure 4). The air inlet was connected via an AVL Flowsonix air flow meter. The fuel was supplied to the burner’s own gear pump through a daily tank, an AVL 753C fuel flow meter, and AVL 735 fuel conditioning equipment. During the measurements, the fuel was conditioned to 20 °C. The combustion chamber was connected to the exhaust system. The AVL SESAM i60 emission meter analyzed the sample taken from the exhaust gas. The signals from the measuring instruments were processed by the AVL PUMA system. The burner was connected to a straight exhaust pipe to minimize turbulence. The sampling point was positioned two meters away from the burner, and it was connected to the emission measuring equipment via a heated sample line.

3. Results and Discussion

The water vapor emissions (Figure 5) during the combustion of the tested fuels were examined. The amount of water vapor in the flue gas from the combustion chamber strongly depended on the amount of fuel burned and the hydrogen content formed during the chemical reactions. Significant differences in water vapor content were attributed to varying degrees of fuel oxidation at different operating points. The burner operation parameters differed due to the varying properties of the tested fuels, which resulted in different performance even when the settings were kept constant. The oxidation was significantly influenced by the composition and density of the combustion products. The figure indicates that B2 produced the highest water vapor emissions due to its higher density, whereas B1 exhibited the lowest emissions according to the examined criteria.

Based on the CO₂ measurement data, it was determined that the B2 fuel exhibited the highest emission levels (Figure 6). This outcome was attributed to its composition and the incomplete combustion process, leading to significant environmental pollution and necessitating measures to mitigate emissions. Comparable values were observed between the heating oil and B1 fuel, with B1 demonstrating slightly lower emission levels. In terms of carbon monoxide and carbon dioxide emissions, industrial burners demonstrated advantageous properties, as the flame temperature could be maintained at a high level due to continuous fuel injection.

In terms of carbon monoxide emission, a significant change was observed for both biocomponents examined. As shown in the diagram, the output doubled for B1 and tripled for B2. The CO emission is most influenced by the stoichiometric ratio (Figure 7). The measurements were performed with a stoichiometric value of 1.2. Since the measurements were carried out with the same stoichiometric ratio, it is necessary to carry out further experiments to change the stoichiometric ratio, but this will be part of later research.

NO_x, or oxides of nitrogen, are compounds formed from the combination of nitrogen and oxygen, and they play a significant role in the development of environmental and health problems. Their two most important components, nitrogen monoxide (NO) and nitrogen dioxide (NO₂), are involved in air pollution and environmental effects. The emission of NO_x into the atmosphere often contributes to the formation of acid rain. The formation of NO_x has been attributed to three main factors: acidic combustion, excess air levels, and high combustion temperatures. Among the tested fuels, high combustion temperature played a decisive role in NO_x formation. The fuel burned continuously at a high temperature in the oil burner, favoring the formation of nitrogen oxides. The highest value of NO_x formation was observed with B1 fuel, while the low combustion temperature of B2 resulted in lower NO_x emissions. NO_x emissions were reduced by adjusting the amount of air added to the fuel or by regulating or reducing the combustion temperature. Figure 8 illustrates the evolution of nitrogen oxide emissions.

The measurement of unburned hydrocarbons played an important role in examining the efficiency and environmental effects of the combustion process. Unburned hydrocarbons, a group of organic compounds, did not burn completely during the combustion of fuels and, as a result, were not converted into carbon dioxide (CO₂) and water vapor (H₂O) during the reaction, as they would have been in ideal combustion.

During the combustion of fuels, many factors affected the presence of unburned hydrocarbons, including the combustion temperature and stoichiometric ratio. The concentration of THC was critical from an environmental perspective, as these substances could lead to harmful emissions such as carbon monoxide (CO) and other pollutants.

From the perspective of THC emissions, heating oil exhibited the highest value, which may have resulted from the design of the combustion chamber. For the optimal combustion of heating oil or diesel oil, a special combustion chamber needed to be used under specific conditions to ensure complete combustion. Based on the measurements and the diagrams, it was determined that the most favorable level of unburned hydrocarbons was achieved with the B1 fuel, using a closed combustion chamber. In industrial practice, burners are applied to the combustion chamber of some furnace or boiler, which is considered to be a closed construction. This indicated that proper combustion chamber design and the addition of intake air could improve combustion efficiency, minimizing unburned hydrocarbons and thereby reducing environmental impact. Figure 9 illustrated the evolution of THC.

During the measurements, the evolution of fuel consumption was as follows: heating oil at 2.4 kg/h, B1 fuel at 3.2 kg/h, and B2 fuel at 3.8 kg/h. These results indicated that the biofuels exhibited higher fuel consumption, which can be attributed to their lower calorific value. In terms of combustion temperature, heating oil achieved the highest value of 700 °C, while B1 and B2 burned at 650 °C and 600 °C, respectively. This variation in combustion temperatures is also attributable to the lower heating values of the biofuels.

4. Conclusions

In this paper, two types of FAME fuels (B1, B2) were compared with standard heating oil in terms of combustion and emission properties. Both tested bio-based components showed stable combustion properties in the industrial burner. In terms of ignition and flame emission properties, there was no significant difference compared to conventional fuel, which is a very important feature of these burners. In terms of the measured emission parameters, the B1 fuel was the closest to the properties of the reference fuel, although the NOx emission value was higher, which was due to the continuously high combustion temperature. The CO emission also showed a slightly higher value, which can be improved by controlling the amount of fuel. It outperformed other emission values. The examined B2 component showed worse properties from an emission point of view, but with a suitable emission aftertreatment device, which forms the basis of later research, it can be a good alternative to fossil-based fuels.

Overall, it can be said that the experiments and tests were successfully concluded and represent a decisive step in the research of sustainable energy carriers. The tested materials are all of plant origin and come from waste, which is beneficial from an environmentally friendly point of view. The results indicate that some of these materials may be suitable as fossil fuel substitutes, as their combustion properties are extremely similar, and their stocks suggest sustainable use. This research can contribute to the development of alternative energy carriers and the sustainable satisfaction of future energy needs.