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Experimental investigation of the autoignition properties of ethanol–biodiesel fuel blends
Fuel 235 (2019) 1301–1308
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Full Length Article
Experimental investigation of the autoignition properties of ethanol–biodiesel fuel blends
T
Hubert Kuszewski Faculty of Mechanical Engineering and Aeronautics, Department of Combustion Engines and Transport, Rzeszow University of Technology, 8 Powstancow Warszawy Ave., 35-959 Rzeszow, Poland
A R T I C LE I N FO
A B S T R A C T
Keywords: Ethanol–biodiesel blends Derived cetane number Diesel engine Ignition delay Combustion delay
Growing interest in increasing the market share of renewable fuels results from the increasing consumption of fuels in various industries, especially in road transport. Such fuels include, for example, ethanol and FAME (Fatty Acid Methyl Esters), known as biodiesel. In diesel engines, ethanol, unlike biodiesel, cannot be directly used as a pure fuel due to its very low autoignition propensity. However, due to the good autoignition properties of biodiesel, increasing attention is being paid to the fuel constitution, for example, a blend of biodiesel with ethanol additive. This way, it is possible to obtain fuel for diesel engines that are compositions of only products of plant origin. In this paper, the autoignition properties of RME (Rape Methyl Esters) and ethanol blends, with the ethanol fraction up to 25% (v/v) were examined. A constant volume combustion chamber was used in the study. Under the specified test conditions, the ignition delay period and the combustion delay period, as well as the DCN (Derived Cetane Number), were determined for the individual blends. The average and maximum pressure rise rates in the combustion chamber were also analysed. The study has shown, for example, that with an increase of ethanol fraction in biodiesel, the periods of ignition and combustion delay increase. It was also shown that in the range from 5% (v/v) to 25% (v/v) of the ethanol fraction, for every increase in the fraction of ethanol by 5% (v/v), the DCN of the biodiesel–ethanol blend is reduced by an average of 3.4 units.
1. Introduction Energy security is largely determined by the increase in the renewable fuels market share. In addition, rising prices of fuels derived from crude oil and the limitations resulting from the increasingly stringent standards for exhaust emissions lead to a growing interest in this type of fuel. At the same time, the use of diesel engines in industry and transport is still prevalent. One of the methods of increasing the share of alternative fuels in transport is to use FAME (Fatty Acid Methyl Esters), commonly known as biodiesel. FAME are obtained by catalytic esterification of fatty acids (contained in vegetable oils) with methanol. FAME derived from rapeseed oil are known as RME (Rape Methyl Esters) and are used as biocomponents in diesel or as pure fuel. The results of research on the properties of diesel and biodiesel blends and the effects of such blends on the functioning of diesel engines can be found, for example, in [1–5]. Recently, interest in the use of organic oxygen compounds, especially alcohol, in diesel engines has increased. However, given the low propensity to autoignition and the poor lubricity characteristics of this type of fuel, as indicated, for example, in [6–8], the use of this type of fuel in pure form in diesel engines would require significant design
modifications and the introduction of fuel additives to enhance autoignition and lubricity. Therefore, the blends of oxygen compounds with diesel and biodiesel have a greater practical importance, with such a mutual participation of those fuels, so it is possible to use such blends in typically operated diesel engines, which have been designed to use typical diesel fuel. Several papers have been devoted to this subject, covering various aspects of the use of such fuels. For example, the papers [6–16] concern blends of diesel and alcohol, while the papers [17–26] concern blends of diesel, biodiesel and alcohol. In general, from some of the papers [6–26], it appears that even though the addition of alcohol to diesel or biodiesel may have a beneficial effect on limiting undesired exhaust gas components, it also significantly changes the physicochemical parameters of the base fuels, namely diesel, biodiesel or blends thereof. Changes in those parameters obviously depend on the fraction of alcohol in the blend. This, in turn, implies for example the need to change fuel injection control algorithms. Studies related to the use of blends of biodiesel and alcohol were, among others, the subject matter, for example, of the papers [27–36]. One of the alcohols that is considered as an additive to biodiesel is ethanol. This is because alcohol can be produced from raw materials of plant origin or biomass, and thus can be considered to be a fully
E-mail address: [email protected]. https://doi.org/10.1016/j.fuel.2018.08.146 Received 3 November 2017; Received in revised form 8 February 2018; Accepted 30 August 2018 0016-2361/ © 2018 Elsevier Ltd. All rights reserved.
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Nomenclature FAME RME DCN HC CO NO NOX NO2 PM CN CVCC ID CD MPR APRR MPRR CFPP HHV LHV KOH CID510 pinj tinj
electronic signal that opens the injector), ms chamber static pressure (gauge), MPa chamber wall temperature, °C initial ambient gas temperature, °C injector nozzle coolant jacket temperature, °C maximum pressure rise—the difference between chamber maximum pressure and chamber static pressure, MPa (Δpch/Δt)A average pressure rise rate, MPa/ms pmax maximum chamber pressure (gauge), MPa pID chamber pressure (gauge) at ID, MPa, tpmax time at which the value of pmax is reached, ms (Δpch/Δt)Max maximum pressure rise rate, MPa/ms Δpch/Δt pressure rise rate, MPa/ms Δ(ID)A absolute measurement uncertainty of ID, ms Δ(ID)R relative measurement uncertainty of ID, % Δ(CD)A absolute measurement uncertainty of CD, ms Δ(CD)R relative measurement uncertainty of CD, % Δ(Δpch)A absolute measurement uncertainty of Δpch, MPa Δ(Δpch)R relative measurement uncertainty of Δpch, % Δ(APRR)A absolute measurement uncertainty of APRR, MPa/ms Δ(APRR)R relative measurement uncertainty of APRR, % Δ(MPRR)A absolute measurement uncertainty of MPRR, MPa/ms Δ(MPRR)R relative measurement uncertainty of MPRR, % Δ(DCN)A absolute measurement uncertainty of DCN Δ(DCN)R relative measurement uncertainty of DCN, % p0 tch Ta tco Δpch
fatty acid methyl esters rape methyl esters derived cetane number hydrocarbons carbon monoxide nitrogen monoxide nitrogen oxides nitrogen dioxide particulate matter cetane number constant volume combustion chamber ignition delay (period), ms combustion delay (period), ms maximum pressure rise average pressure rise rate maximum pressure rise rate cold filter plugging point, °C higher heating value, MJ/kg lower heating value, MJ/kg potassium hydroxide name of research device injection pressure, MPa injection period (determined by the length of the
by the CVCC method the concept of DCN is used [40]. In the procedure included in [41,42] to calculate the DCN, not only the ignition delay period but also the so-called combustion delay period is used. Because of the relatively low popularity of the fuel constituting biodiesel and ethanol blends, the previous papers on such blends were mainly focused on the characteristics of the diesel engine powered with such fuel. On the other hand, there are few papers that would directly point to the autoignition properties of ethanol–biodiesel blends. The related data can be found in the papers [28,30]. An et al. [28] have conducted model studies on combustion processes of the ethanol–biodiesel blends, with ethanol fraction of 5%, 10% and 20% (v/v). In general, the simulation of engine operation conducted thereby shows that, with the increase in the fraction of ethanol in the blend, the ignition delay period is extended, which in turn translates into reduction of the peak pressures in the combustion chamber. The longer ignition delay period with the increased ethanol fraction in blends was justified by the authors as due to low CN and higher latent heat of vaporization of ethanol. Lapuerta et al. [30] conducted a study on the effect of the ethanol fraction in blends with biodiesel on the ignition delay period. The researchers used 11 blends of ethanol and biodiesel, with the lowest ethanol content being 2.5% (v/v) and the largest being 75% (v/ v). The authors used the CID510 apparatus with a CVCC in their research. In contrast to the paper [28], the authors of the paper [30] have provided numerical values for the ignition delay period. In addition, the courses of pressure variations in the combustion chamber were shown for the tested blends. From research by Lapuerta et al. [30], it appears that with the increase in the fraction of ethanol in the blend, the ignition delay period is extended, while the increase in the initial temperature and the initial pressure in the combustion chamber clearly shorten that period. This paper focuses on the influence of ethanol fraction on the autoignition properties of ethanol–biodiesel blends. Basically, the assessment of the autoignition properties of biodiesel with specified ethanol fraction was based on the ID (Ignition Delay) period and CD (Combustion Delay) period and the DCN value. However, bearing in mind the specifics of the diesel engine cycle, in the paper the results for APRR (Average Pressure Rise Rate) and MPRR (Maximum Pressure Rise Rate) in the combustion chamber are also included. The higher values of those
renewable fuel. It should also be noted that in the case of biodiesel and ethanol blends, only fuels of plant origin are obtained. It is also important that dehydrated ethanol shows relatively good solubility in biodiesel, as indicated by the papers [26,36,37]. From the engine tests conducted by Yilmaz and Sanchez [27], it appears that adding 15% (v/v) of ethanol to biodiesel, in terms of partial engine loads compared with powering with pure biodiesel, results in an increase in HC (hydrocarbon) and CO (carbon monoxide) concentrations in the exhaust gas, but results in a significant reduction in NO (nitrogen monoxide). In turn, the study conducted by Zhu et al. [29], indicates that an increase in the fraction of ethanol in biodiesel (up to 15% (v/v) ethanol in the test range) results in lower NOX (nitrogen oxides) and NO2 (nitrogen dioxide) specific emission relative to powering with pure biodiesel. Moreover, their study shows that with the increase in the fraction of ethanol in biodiesel, the specific emission of PM (particulate matter) is reduced. In addition, the results of model tests conducted by An et al. [28] show the beneficial effect on NOX emission of adding ethanol to biodiesel, compared with powering with pure biodiesel. The beneficial effects of 20% (v/v) addition of ethanol to biodiesel, in relation to the powering with biodiesel and diesel fuel, on exhaust emission and engine performance are also indicated by the results of the study presented by Aydin and İlkılıç [33]. The potential uses of the ethanol–biodiesel blend in diesel engines are generally indicated also by the papers of Tutak et al. [31,32] and the paper by Torres-Jimenez et al. [36]. Considering the possibility of using ethanol in a diesel engine, when the base fuel is biodiesel or diesel, it should be noted that the addition of ethanol significantly alters the physicochemical and quality parameters of those fuels. Quite extensive results of the study on the physicochemical properties of ethanol–biodiesel blends were included in the paper [36]. From among many physicochemical parameters, particular attention should be paid to the tendency to autoignition and connected with it the ignition delay period. Based on the standard procedures [38,39], the autoignition properties of fuel are determined on the basis of CN (Cetane Number). An alternative method of determining the autoignition properties of fuel is the use of the CVCC (Constant Volume Combustion Chamber) method. To distinguish it from measurements using a test engine, when measured 1302
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combustion chamber, the maximum pressure values and the ID values, the APRR was calculated according to the relation:
parameters in the engine operating conditions translate into a higher load on the crankshaft system components, which usually contributes to reducing its lifetime. The presented data are a supplement to the results of the study included in the paper [36] and to some extent the results of the study presented in [28,30] and in [14], where DCN data for ethanol–diesel fuel blends are presented. The data obtained can be useful, among others, for the optimization of combustion systems of diesel engines fuelled with biodiesel with ethanol additive.
(Δpch /Δt )A = (pmax −pID )/(tpmax−ID) [MPa/ms]
(1)
where pmax – maximum chamber pressure, obtained from the recorded pressure course, MPa; pID – chamber pressure at ID, MPa; tpmax – time after which value of pmax is reached, ms; ID – period of ignition delay, ms. Each of the recorded pressure courses were numerically differentiated using the difference quotient. In this way, the course of the instantaneous pressure rise rate in the combustion chamber was obtained and the maximum value of this parameter was noted. Fig. 1 shows an example of the recorded course of pressure changes in the combustion chamber (fuel BD-ETH-10). The diagram covers 20 ms from the beginning of the recording. Similarly, for the time of 20 ms from the beginning of the recording, the pressure course diagrams presented in Chapter 3 were prepared. Fig. 2 shows the course of the instantaneous pressure rise rate in the combustion chamber obtained from the numerical differentiation of the course shown in Fig. 1. In Fig. 1, the parameters used to calculate the APRR values are marked and Fig. 2 shows the maximum value of the instantaneous pressure rise rate. The calculation of the instantaneous pressure rise rate in the combustion chamber was used only to identify the MPRR of this parameter and therefore no such courses were included in the discussion section of the article. The DCN was determined for each of the fuels shown in Table 2. The measurements were conducted in accordance with the standard requirements contained in [41,42]. The standard measurement uncertainties of type A and their relative values were calculated for each of the analysed parameters. The standard deviation of the mean was assumed to be the standard value of the measurement uncertainty. The values of the calculated absolute and relative measurement uncertainties are presented in the tables in the discussion section. For clarity, the absolute values of the measurement uncertainties were not plotted on the graphs in the form of error bars. The diagrams show the mean values of the parameters, representing the best approximation of the measured values.
2. Experimental methodology 2.1. Samples characterization The study of the autoignition properties was carried out for six samples of fuel. One of them is FAME obtained from rapeseed oil, that is, RME. This fuel, further referred to as biodiesel, meets the requirements of the standard [43] and is a biocomponent commonly used in diesel fuel. The basic parameters of this fuel are included in Table 1. Later herein, the biodiesel has been marked as BD-ETH-0. Further samples are the blends of biodiesel (with the specification shown in Table 1) with ethyl alcohol with proportions of alcohol from 5% to 25%. As pointed out in [26,36,37] the homogeneity and stability of biodiesel and ethanol blends are determined by the ambient temperature and water concentration. Dehydrated ethanol with purity of more than 99.5% was used to avoid turbidity and delamination of the blends, and the blends were prepared at the same temperature of the biodiesel and alcohol of 22 °C ± 1 °C. These are conditions similar to those for which the stability and homogeneity of the blends of ethanol and biodiesel were found in [36]. Fuel samples were stored in sealed glass vessels at their preparation temperature, namely, 22 °C ± 1 °C. The procedures implemented in the preparation and storage of the blends throughout the entire test cycle of autoignition properties ensured the homogeneity and stability of the prepared blends. No signs of turbidity or delamination were observed for any of the samples. The markings of individual fuel samples are presented in Table 2. 2.2. Data acquisition In the study, a commercially available apparatus, CID510, with a CVCC was used. The primary purpose of this test device is to determine the DCN in accordance with the procedure contained in [41,42]. This is the same type of device that Lapuerta et al. [30] as well as Kuszewski et al. [14,16] used in their work. A more detailed description and diagram of the test device structure is presented in [14]. More details on the structure of the device can also be found in [41,42]. Because the determination of DCN was assumed for the individual samples, before performing a series of tests a calibration of the device was carried out according to the procedure specified in the standard [41]. The required reference fuel consisting of a mass blend of hexadecane (40%) and 2,2,4,4,6,8,8-heptamethylnonane (60%) was used for calibration. For each of the 15 fundamental combustion cycles, in addition, the following values were recorded, the ID period, the CD period, the initial pressure in the combustion chamber, p0, MPR (Maximum Pressure Rise) in the chamber, Δpch, in relation to the initial pressure, the temperature of the combustion chamber walls, tch, the temperature of the injector coolant, tco, and the fuel injection pressure, pinj. The temperature of the synthetic air filling the chamber (Ta) (initial ambient gas temperature) corresponds to the recorded wall temperature of the chamber, tch, i.e. tch = Ta. A calibration value of tch was 598 °C. All values of the analysed pressures are the overpressures relative to the ambient pressure (97.8 kPa ± 3 kPa). A detailed description of the measurement of the ID and CD parameters can be found in [14,41,42]. The performance parameters and engine durability are affected by the character of the pressure rise in the combustion chamber. Therefore, using the values of the recorded pressure courses in the
3. Results and discussion Fig. 3 shows the effect of volume fraction of ethanol in a blend with biodiesel on the ID and CD periods. As can be seen from the data provided, under established measurement conditions and for tested blends, the increase in the ethanol fraction in blend results in a second-order polynomial prolongation of the ID. This confirms the data obtained by Table 1 Parameters of biodiesel fuel used in the study.
1303
Property
Method
Value
FAME content (% m/m) Derived cetane number (DCN) Viscosity at 40 °C (mm2/s) Density at 15 °C (g/cm3) Flash-point (°C) HHV (MJ/kg) CFPP (°C) Cloud point (°C) Water content (mg/kg) Sulphur content (mg/kg) Oxidation stability at 110 °C (h) Acid number (mg KOH/g) Methyl alcohol content (% m/m) Monoglycerides content (% m/m) Diglycerides content (% m/m) Linolenic acid methyl ester content (% m/m)
EN 14103 ASTM D7668 EN ISO 3104 EN ISO 12185 EN ISO 2719 PN-C-04375-3 EN 116 ISO 3015 EN ISO 12937 EN ISO 20846 EN 15751 EN 14104 EN 14110 EN 14105 EN 14105 EN 14103
97.6 54.6 4.4767 0.883 174 40.2 −15 −5 195 < 3.0 11.5 0.33 0.01 0.6 0.13 9.1
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similar test conditions and with the same test equipment, in the case of ethanol–diesel blends, the prolongation of the ID was also obtained with an increase in the ethanol fraction [14,16], but it was a linear function. This indicates the different character of the effect of the ethanol additive on the autoignition properties of RME compared with ethanol effects on the autoignition properties of diesel fuel. This is due mainly to the varied chemical structure of the base fuels in the analysed blends. The issues related to the influence of chemical structure on the autoignition properties of FAME are more broadly presented in [49,50]. The CD period can be considered as a complementary assessment factor of the autoignition properties of the fuel. This parameter, defined according to the methodology included in the standards [41,42], along with the ID period is used to calculate the DCN of the fuel. While the ID parameter can be considered as a cool-flame stage, due to the reaction during this stage, namely, the first stage of a two-stage autoignition, the CD period can be used to designate a second, main stage of autoignition. Those issues were highlighted in the study of Lapuerta et al. [30,51], who, in their research, used the same test device with a CVCC as the author of this paper. The heat release in the coolflame stage is determined by the low-temperature reaction of the straight carbon chains in the hydrocarbon radicals forming the esters. This chemical structure also determines the relatively good properties of autoignition of esters, including RME, as in the case of diesel fuel with a high fraction of straight-chain paraffinic hydrocarbons. The relationship between the chemical structure of the fuel and the autoignition properties and the presence of the cool-flame stage was highlighted, for example, in [51]. The second, main stage of autoignition by the CD and the pressure rise rate in the combustion chamber was determined by Lapuerta et al. [51]. According to the methodology adopted by them, the CD period is always slightly longer than the main stage of autoignition. The main stage of the autoignition, directly leading to the combustion propagation, begins when the temperature in the fuel droplets’ environment is high enough to initiate a chain reaction. As can be seen in Fig. 3, in general, the trend of changes in the CD is similar to that of the ID parameter, namely, the increase in the fraction of ethanol in the blend causes the second-order polynomial prolongation of the CD period. However, for the CD period, the difference in absolute CD values between the highest (25% v/v) and lowest (5% v/v) fraction of ethanol is approximately 2.7 ms, and in the case of ID, that difference is approx. 1.2 ms. This is related to the method of determining the CD period. The influence of the ethanol fraction in biodiesel on the changes in the CD parameter is determined by both the MPR in the combustion chamber after autoignition, Δpch, and to an even greater extent, the kind of the course of pressure changes in the combustion chamber from the moment of its recording to the maximum value of pressure, pmax. This was earlier noted by Kuszewski et al. [14], where the effect of ethanol additive on the autoignition properties of diesel fuel was investigated. This is also consistent with the results presented in [30,51]. The effect of ethanol fraction in biodiesel on the MPR, Δpch, in the combustion chamber, is shown in Fig. 4. As can be seen, an increase of the ethanol fraction in biodiesel results in a linear reduction in the MPR parameter. The absolute value of the difference of the MPR value for the highest (25% v/v) and lowest (5% v/v) fraction of ethanol in biodiesel is negligible and amounts to approx. 0.07 MPa. The reduction of MPR with the increase of ethanol fraction in biodiesel is a consequence of the decrease in the LHV (Lower Heating Value) with an increase in ethanol fraction in the tested blends. This, in turn, is a result of a lower HHV (Higher Heating Value) by approx. 26% of the ethanol relative to biodiesel. The HHV of ethanol used in the study, determined before the test, was 29.4 MJ/kg, while the HHV of pure biodiesel used in the study was 40.2 MJ/kg, as indicated in Table 1. The results concerning the MPR in the combustion chamber confirm the data obtained by Lapuerta et al. [30], who in their paper presented the influence of the ethanol fraction in biodiesel on the maximum
Table 2 Symbols of fuel samples. Fuel description
BD-ETH-0 (Biodiesel, RME) BD-ETH-5 BD-ETH-10 BD-ETH-15 BD-ETH-20 BD-ETH-25
Volume fraction [%] RME
Ethanol
100
0
95 90 85 80 75
5 10 15 20 25
Fig. 1. Example pressure course in the combustion chamber (fuel BD-ETH-10).
Fig. 2. Example pressure rise rate in the combustion chamber (fuel BD-ETH10).
Fig. 3. Effect of the ethanol percentage in biodiesel fuel on the ID and CD periods.
Lapuerta et al. [30]. The prolongation of the ID for the ethanol–biodiesel blends with an increase in the ethanol fraction is also indicated in the model study of the engine conducted by An et al. [28]. In general, the prolongation of the ID period for ethanol–biodiesel blend with an increase in the ethanol fraction, as in the case of ethanol–diesel blends, is a consequence of the low autoignition propensity of ethanol [6,9,14,16,23,37,44–48]. However, it should be noted that under 1304
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premixed period of combustion is less intense [52–54], that is, also with smaller (average and maximum) pressure rise rates. Then, the engine emits less noise, also the intensity of the absorption of heat by the working medium is reduced, which translates into a lower concentration of NOX in the exhaust gas. Such dependencies are generally known for diesel fuel. As can be seen in Figs. 6 and 7, with an increase in the ethanol fraction in biodiesel, the APRR parameter is linearly reduced. Because this happens, despite the prolonged period of the ID (Fig. 3), then, under the established CVCC test conditions, as the dominant factor which reduces the APRR parameter (as in the MPR case) the LHV of the ethanol–biodiesel blends, which decreases with increase in ethanol fraction in biodiesel, should be considered. It should also be noted that, for example, the results of the engine tests presented in [31], generally show similarly, as in Fig. 5, the changes of pressure rise from autoignition to peak pressure. In this case, it can be expected that the tendency of changes in APRR and MPRR parameters in engine test conditions is similar to that presented in Figs. 6 and 7. The reduction of APRR and MPRR parameters should result in a reduction in mechanical loads in the crank–piston system of the engine and contribute to its durability. In addition, it cannot be ruled out that the concentration of nitrogen oxides in the exhaust gas will be reduced. Fig. 8 shows the results of the determination of DCN for the analysed ethanol–biodiesel blends. The DCN values have been calculated on the basis of ID and CD periods—according to the methodology contained in [41]. According to this methodology, the calculation of normative DCN values is valid only for ID and CD parameters measured during operation of the test device according to the calibration settings (Table 3). As can be seen in Fig. 8, the increase of the ethanol fraction in biodiesel results in a linear reduction in DCN value, wherein, in the analysed range of ethanol fraction, for every increase in the ethanol fraction by 5%, the DCN of the ethanol–biodiesel blend is reduced by an average of 3.4 units. However, already the addition of 5% (v/v) of ethanol means that the biodiesel does not meet the requirement of the standard [43], according to which the minimum CN number is 51. At the same time, the biodiesel meeting the requirement of the standard [43], with the specification included in Table 1, which contains even 10% (v/v) of ethanol, meets the requirement in terms of CN for both biodiesel grades determined in the standard [55], according to which the minimum CN is 47 (biodiesel No. 1-B and No. 2-B). Considering the use of the ethanol–biodiesel blends in diesel engines, it is justified to refer to the obtained results of the DCN, also to the requirements of diesel fuel. In the Worldwide Fuel Charter [56], the requirement for the five categories of diesel fuel, from 1 to 5 was specified, for which the minimum CN amounts respectively are 48, 51, 53, 55 and 55. The DCN studies indicate that biodiesel with the addition of 5% (v/v) of ethanol meets the requirement for CN specified for the first category of diesel. The addition of 5% (v/v) ethanol to biodiesel means that the ethanol–biodiesel blend does not meet the requirement specified in the standard [43] according to which the minimum value of CN is 51. At the same time, biodiesel with the addition of even 20% (v/v) of
Fig. 4. Effect of the ethanol percentage in biodiesel fuel on the MPR in the combustion chamber, Δpch.
pressures recorded in the combustion chamber of the CID510 test device. They conducted tests for the ambient gas temperature of 602.5 °C and the initial pressure in the combustion chamber of 2.1 MPa. For an ethanol fraction up to 20% (v/v), they noted a slight impact of ethanol fraction on the maximum pressure in the combustion chamber. Only for ethanol fractions above 30% (v/v) did they note a clear reduction in the maximum pressure, and thus also the pressure rise in the combustion chamber. The results obtained for the MPR parameter generally correspond to the results of the model engine tests presented in [28], where the reduction of maximum pressure in the combustion chamber is indicated with an increase in the ethanol fraction in biodiesel, which is justified by the authors of that publication by the delayed start of combustion resulting from the longer ID period and the lower LHV of ethanol. In turn, the results of experimental engine tests presented in [29,31,32] indicate an increase in the maximum pressure in the cylinder with an increase in the ethanol fraction in biodiesel. The authors of these papers essentially justify this phenomenon with the reduction in CN of ethanol, which results in delayed combustion leading to an increase in the amount of fuel combusted in the premixed phase of combustion. Differences in maximum pressure of combustion obtained using the CVCC method and on the basis of engine tests may be justified by different conditions of heat release in the premixed combustion phase. Under engine test conditions, in contrast to tests using the CVCC method, there are several factors, variable in time, that can influence the rate of heat release in the premixed combustion phase. Among other factors, there is difficult evaporation of the injected fuel due to different heat transfer conditions between the working medium and the cylinder walls, determined by the speed and load of the engine, and the fuel injection timing [52]. Fig. 5 shows averaged pressure courses in the combustion chamber for individual fuel samples. As can be seen, with the increase of ethanol fraction in biodiesel, the pressure rise rate in the combustion chamber is reduced in the range from the initial pressure to the peak pressure. From data presented in Fig. 5, it can also be seen that with the increase in the ethanol fraction in biodiesel, not only the peak pressure in the combustion chamber (that is also MPR) is decreasing, as indicated earlier, but also the time after which it occurs is extended. This confirms the results of experiments conducted using the CVCC method presented in [30], as well as the results of the engine tests presented in [31]. A quantitative assessment of the nature of the pressure rise in the combustion chamber was performed for individual fuel samples on the basis of calculations of the APRR values in the combustion chamber (formula (1)). The MPRR parameter was also defined. Values of those parameters are important because, in particular, consideration of parameter ID in the context of fuel applications in a diesel engine should also be conducted in relation to the effects of a long ID period. As indicated by several studies, a shorter ID period (achieved, e.g., by pilot injection or reduction of the injection advance angle for a single fuel injection) in a diesel engine leads to a reduction in the fuel accumulated in the combustion chamber during the ID period, and thus the
Fig. 5. Pressure courses in the combustion chamber for all fuel samples. 1305
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1306
2.5 2.5 2.5 2.5 2.5 2.5 99.9 99.8 99.6 99.5 99.2 99.7 51.1 50.5 50.1 51.2 51.5 51.0 597.7 597.7 597.8 597.8 597.8 597.8 2.00 2.00 2.00 2.00 2.00 2.00 0.3 0.3 0.2 0.2 0.2 0.2 0.2 0.1 0.1 0.1 0.1 0.1 2.8 2.8 3.2 2.6 2.3 1.9 0.1320 0.1237 0.1270 0.0796 0.0476 0.0273 3.6 4.7 3.7 2.0 2.1 1.4 0.0270 0.0307 0.0210 0.0081 0.0062 0.0031 0.2 0.2 0.1 0.1 0.0 0.2 0.0046 0.0030 0.0017 0.0013 0.0009 0.0028 0.3 0.3 0.3 0.2 0.3 0.4 0.0119 0.0143 0.0154 0.0135 0.0193 0.0272 0.5 0.3 0.4 0.3 0.3 0.3 0.0147 0.0111 0.0145 0.0107 0.0135 0.0136
Δ(APRR)A [MPa/ms] Δ(Δpch)R [%] Δ(Δpch)A [MPa] Δ(CD)R [%] Δ(CD)A [ms]
ethanol, meets the requirement in terms of CN for all categories of diesel fuel determined in the standard [39], according to which the minimum cetane number is 40 (all diesel fuels No. 1-D and No. 2-D) or 30 (diesel fuel No. 4-D). In addition, the 25% (v/v) addition of ethanol to the biodiesel means that the blend meets the requirement for diesel fuel No. 4-D. However, it should be noted that DCN values for the analysed blends can slightly differ, depending on the DCN value for the base fuel, that is, biodiesel without ethanol additive. The addition to the results of the ID, CD, DCN, MPR, APRR and MPRR measurements is in Table 3, which summarizes the results of calculation of the absolute and relative measurement uncertainty of the measured parameters. In addition, the average parameters related to fuel injection are also included in the table. The following parameters are included in Table 3, the values of static pressure in the combustion chamber, p0, temperature of the combustion chamber walls, tch, injector nozzle coolant jacket temperature, tco, fuel injection pressure, pinj, as well as the duration of the injection pulse width, tinj. The presented data characterizing parameters associated with fuel injection and operation conditions of the CVCC can be helpful to restore conditions under which the study was conducted,
Δ(ID)R [%]
Fig. 8. Effect of the percentage of ethanol in biodiesel fuel on the DCN.
Δ(ID)A [ms]
Table 3 Absolute and relative measurement uncertainties together with recorded parameters of fuel injection.
Fig. 7. Effect of the percentage of ethanol in biodiesel fuel on the MPRR in the combustion chamber, (Δpch/Δt)Max.
Δ(APRR)R [%]
Δ(MPRR)A [MPa/ms]
Δ(MPRR)R [%]
Δ(DCN)A
Δ(DCN)R [%]
Fig. 6. Effect of the percentage of ethanol in biodiesel fuel on the APRR in the combustion chamber, (Δpch/Δt)A.
BD-ETH-0 BD-ETH-5 BD-ETH-10 BD-ETH-15 BD-ETH-20 BD-ETH-25
p0 [MPa]
tch [°C]
tco [°C]
pinj [MPa]
tinj [ms]
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the results of which are presented in this article.
Bioresour Technol 2006;97:372–8. [6] Chacartegui C, Lopez J, Alfonso F, Aakko P, Hamelinck C, Vossen G, Kattenwinkel H. Blending ethanol in diesel. Final report for Lot 3b of the Biodiesel Improvement On Standards, Coordination of Producers and Ethanol Studies (Bioscopes) project; May 2007. [7] Hansen AC, Lyne PWL, Zhang Q. Ethanol–diesel blends: a step towards a bio-based fuel for diesel engines. ASAE paper 01-6048; 2001. [8] Torres-Jimenez E, Svoljšak Jerman M, Gregorc A, Lisec I, Dorado MP, Kegl B. Physical and chemical properties of ethanol–diesel fuel blends. Fuel 2011;90:795–802. [9] Hansen AC, Zhang Q, Lyne PWL. Ethanol–diesel fuel blends – a review. Bioresour Technol 2005;96:277–85. [10] Taghizadeh-Alisaraei A, Rezaei-Asl A. The effect of added ethanol to diesel fuel on performance, vibration, combustion and knocking of a CI engine. Fuel 2016;185:718–33. [11] Gnanamoorthi V, Devaradjane G. Effect of compression ratio on the performance, combustion and emission of DI diesel engine fueled with ethanol – diesel blend. J Energy Inst 2015;88:19–26. [12] Murcak A, Haşimoğlu C, Çevik İ, Kahraman H. Effect of injection timing to performance of a diesel engine fuelled with different diesel–ethanol mixtures. Fuel 2015;153:569–77. [13] Lapuerta M, Armas O, Herreros JM. Emissions from a diesel–bioethanol blend in an automotive diesel engine. Fuel 2008;87:25–31. [14] Kuszewski H, Jaworski A, Ustrzycki A, Lejda K, Balawender K, Woś P. Use of the constant volume combustion chamber to examine the properties of autoignition and derived cetane number of mixtures of diesel fuel and ethanol. Fuel 2017;200:564–75. [15] Kuszewski H, Jaworski A, Ustrzycki A. Lubricity of ethanol–diesel blends – study with the HFRR method. Fuel 2017;208:491–8. [16] Kuszewski H. Experimental investigation of the effect of ambient gas temperature on the autoignition properties of ethanol–diesel fuel blends. Fuel 2018;214C:26–38. [17] Alviso D, Krauch F, Román R, Maldonado H, Goncalves dos Santos R, Rolón JC, Darabiha N. Development of a diesel-biodiesel-ethanol combined chemical scheme and analysis of reactions pathways. Fuel 2017;191:411–26. [18] Hu N, Tan J, Wang X, Zhang X, Yu P. Volatile organic compound emissions from an engine fueled with an ethanol-biodiesel-diesel blend. J Energy Inst 2017;90:101–9. [19] Aydın F, Öğüt H. Effects of using ethanol-biodiesel-diesel fuel in single cylinder diesel engine to engine performance and emissions. Renewable Energy 2017;103:688–94. [20] Shahir SA, Masjuki HH, Kalam MA, Imran A, Ashraful AM. Performance and emission assessment of diesel–biodiesel–ethanol/bioethanol blend as a fuel in diesel engines: a review. Renew Sustain Energy Rev 2015;48:62–78. [21] Tse H, Leung CW, Cheung CS. Investigation on the combustion characteristics and particulate emissions from a diesel engine fueled with diesel-biodiesel-ethanol blends. Energy 2015;83:343–50. [22] Yilmaz N. Comparative analysis of biodiesel–ethanol–diesel and biodiesel–methanol–diesel blends in a diesel engine. Energy 2012;40:210–3. [23] Yilmaz N, Vigil FM, Donaldson AB, Darabseh T. Investigation of CI engine emissions in biodiesel–ethanol–diesel blends as a function of ethanol concentration. Fuel 2014;115:790–3. [24] Mofijur M, Rasul MG, Hyde J. Recent developments on internal combustion engine performance and emissions fuelled with biodiesel-diesel-ethanol blends. Proc Eng 2015;105:658–64. [25] Labeckas G, Slavinskas S, Mažeika M. The effect of ethanol–diesel–biodiesel blends on combustion, performance and emissions of a direct injection diesel engine. Energy Convers Manage 2014;79:698–720. [26] Shahir SA, Masjuki HH, Kalam MA, Imran A, Rizwanul Fattah IM, Sanjid A. Feasibility of diesel–biodiesel–ethanol/bioethanol blend as existing CI engine fuel: An assessment of properties, material compatibility, safety and combustion. Renew Sustain Energy Rev 2014;32:379–95. [27] Yilmaz N, Sanchez TM. Analysis of operating a diesel engine on biodiesel-ethanol and biodiesel-methanol blends. Energy 2012;46:126–9. [28] An H, Yang WM, Li J. Effects of ethanol addition on biodiesel combustion: a modeling study. Appl Energy 2015;143:176–88. [29] Zhu L, Cheung CS, Zhang WG, Huang Z. Combustion, performance and emission characteristics of a DI diesel engine fueled with ethanol–biodiesel blends. Fuel 2011;90:1743–50. [30] Lapuerta M, Hernández JJ, Fernández-Rodríguez D, Cova-Bonillo A. Autoignition of blends of n-butanol and ethanol with diesel or biodiesel fuels in a constant-volume combustion chamber. Energy 2017;118:613–21. [31] Tutak W, Jamrozik A, Pyrc M. Experimental investigations on combustion, performance and emissions characteristics of compression ignition engine powered by B100/ethanol blend. E3S Web of Conferences 2017;14:02019. https://doi.org/10. 1051/e3sconf/20171402019. [32] Tutak W, Jamrozik A, Pyrc M, Sobiepański M. A comparative study of co-combustion process of diesel-ethanol and biodiesel-ethanol blends in the direct injection diesel engine. Appl Therm Eng 2017;117:155–63. [33] Aydin H, İlkılıç C. Effect of ethanol blending with biodiesel on engine performance and exhaust emissions in a CI engine. Appl Therm Eng 2010;30:1199–204. [34] Torres-Jimenez E, Dorado MP, Kegl B. Experimental investigation on injection characteristics of bioethanol–diesel fuel and bioethanol–biodiesel blends. Fuel 2011;90:1968–79. [35] Su J, Zhu H, Bohac SV. Particulate matter emission comparison from conventional and premixed low temperature combustion with diesel, biodiesel and biodiesel–ethanol fuels. Fuel 2013;113:221–7. [36] Torres-Jimenez E, Svoljšak-Jerman M, Gregorc A, Lisec I, Dorado MP, Kegl B.
4. Conclusions This paper presents the results of a study of the autoignition properties of ethanol–biodiesel blends. The tests were conducted for a typical RME and for several blends of that fuel with ethanol, wherein the maximum ethanol fraction was 25% (v/v). In the study, the test equipment was used with a CVCC, which also allowed determining the DCN according to the valid standard. Essentially, for the assessment of the autoignition properties, the ignition and combustion delay periods were used. Those parameters were determined according to the methodology included in [41,42]. The maximum pressure rise in the combustion chamber was also analysed. Based on the recorded pressure changes, the average and maximum rate of pressure rise in the combustion chamber are also determined. The conducted research allows us to formulate the following conclusions, - Biodiesel with ethanol additive of 5% (v/v) does not meet the requirement of EN 14214 for CN. - Biodiesel with ethanol additive of 10% meets the requirement of ASTM D6751 for biodiesel grade No. 1-B and No. 2-B for CN. - Biodiesel with ethanol additive of 5% (v/v) does not meet the requirement of EN 590 for CN. - Biodiesel with ethanol additive of 5% (v/v) meets the requirement specified in the Worldwide Fuel Charter for the CN defined for the first category of diesel fuel. - Biodiesel with ethanol additive of 20% (v/v) meets the requirement of ASTM D975 for CN for all categories of diesel. - Biodiesel with ethanol additive of 25% (v/v) meets the requirement of ASTM D975 for CN for diesel fuel grade No. 4-D. The data collected as a result of the study provide a supplement to the studies related to the properties of ethanol–biodiesel blends, in particular, their autoignition properties. That data can also be helpful when optimizing combustion systems of diesel engines, for which the powering with ethanol–biodiesel is permitted. The conducted studies also confirmed the usefulness of the measurement system with a CVCC for the tests of the autoignition properties of ethanol–biodiesel blends. The determination in a normative way of the DCN provides a view of the tendency of changes in that parameter for RME as a result of the addition of ethanol. Such data may be helpful in optimizing the composition for ethanol and RME blends. Acknowledgement This work was supported by the Ministry of Infrastructure and Development under the Eastern Poland Development Operational Programme, including the European Regional Development Fund–Belgium, which financed the research instruments. The author wish to acknowledge the Polish Ministry of Science and Higher Education and the Rzeszow University of Technology for supporting this research. References [1] Gülüm M, Bilgin A. Measurements and empirical correlations in predicting biodiesel-diesel blends’ viscosity and density. Fuel 2017;199:567–77. [2] Kanaveli I-P, Atzemi M, Lois E. Predicting the viscosity of diesel/biodiesel blends. Fuel 2017;199:248–63. [3] Hoseini SS, Najafi G, Ghobadian B, Mamat R, Sidik NACh, Azmi WH. The effect of combustion management on diesel engine emissions fueled with biodiesel-diesel blends. Renew Sustain Energy Rev 2017;73:307–31. [4] Hasan MM, Rahman MM. Performance and emission characteristics of biodiesel–diesel blend and environmental and economic impacts of biodiesel production: a review. Renew Sustain Energy Rev 2017;74:938–48. [5] Nurun Nabi Md, Shamim Akhter Md, Zaglul Shahadat Mhia Md. Improvement of engine emissions with conventional diesel fuel and diesel–biodiesel blends.
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[47] Kim H, Choi B. Effect of ethanol–diesel blend fuels on emission and particle size distribution in a common-rail direct injection diesel engine with warm-up catalytic converter. Renewable Energy 2008;33:2222–8. [48] Moon S, Tsujimura T, Oguma M, Chen Z, Huang Z, Saitou T. Mixture condition, combustion and sooting characteristics of ethanol–diesel blends in diffusion flames under various injection and ambient conditions. Fuel 2013;113:128–39. [49] Hoekman KS, Broch A, Robbins C, Ceniceros E, Natarajan M. Review of biodiesel composition, properties, and specifications. Renew Sustain Energy Rev 2012;16:143–69. [50] Wang W, Gowdagiri S, Oehlschlaeger MA. The high-temperature autoignition of biodiesels and biodiesel components. Combust Flame 2014;161:3014–21. [51] Lapuerta M, Sanz-Argent J, Raine RR. Ignition characteristics of diesel fuel in a constant volume bomb under diesel-like conditions. Effect of the operation parameters. Energy Fuels 2014;28:5445–54. [52] Internal combustion engine handbook. Basics, components, system and perspectives. 2nd ed., Richard van Basshuysen, Fred Schäfer, editors, Translated by TechTrans. SAE International; 2016. [53] Yoon SJ, Park B, Park J, Park S. Effect of pilot injection on engine noise in a single cylinder compression ignition engine. Int J Automot Technol 2015;16(4):571–9. https://doi.org/10.1007/s12239-015-0058-6. [54] Kim HM, Cho WJ, Lee KH. Effect of injection condition and swirl on D.I. diesel combustion in a transparent engine system. Int J Automot Technol 2008;9(5):535–41. https://doi.org/10.1007/s12239-008-0063-0. [55] ASTM D6751 – Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels; 2015. [56] Worldwide Fuel Charter 2013 – 5th ed. Prepared by ACEA, AUTO ALLIANCE, EMA and JAMA; September 2013.
Physical and chemical properties of ethanol-biodiesel blends for diesel engines. Energy Fuels 2010;24:2002–9. Kwanchareon P, Luengnaruemitchai A, Jai-In S. Solubility of a diesel–biodiesel–ethanol blend, its fuel properties, and its emission characteristics from diesel engine. Fuel 2007;86:1053–61. EN 590 – Automotive fuels – Diesel – Requirements and test methods; 2013. ASTM D975 – Standard Specification for Diesel Fuel Oils, 2016. Yanowitz J, Ratcliff MA, McCormick RL, Taylor JD, Murphy MJ. Compendium of Experimental Cetane Numbers. Technical Report NREL/TP-5400-61693; August 2014. ASTM D7668 – Standard Test Method for Determination of Derived Cetane Number (DCN) of Diesel Fuel Oils – Ignition Delay and Combustion Delay Using a Constant Volume Combustion Chamber Method; 2014. EN 16715 – Liquid petroleum products – Determination of ignition delay and derived cetane number (DCN) of middle distillate fuels – Ignition delay and combustion delay determination using a constant volume combustion chamber with direct fuel injection; 2015. EN 14214 – Liquid petroleum products – Fatty acid methyl esters (FAME) for use in diesel engines and heating applications – Requirements and test methods; 2014. Can Ö, Ҫelikten İ, Usta N. Effects of ethanol addition on performance and emissions of a turbocharged indirect injection Diesel engine running at different injection pressures. Energy Convers Manage 2004;45:2429–40. Rakopoulos DC, Rakopoulos CD, Giakoumis EG, Papagiannakis RG, Kyritsis DC. Experimental-stochastic investigation of the combustion cyclic variability in HSDI diesel engine using ethanol–diesel fuel blends. Fuel 2008;87:1478–91. Tutak W, Lukács K, Szwaja S, Bereczky Á. Alcohol–diesel fuel combustion in the compression ignition engine. Fuel 2015;154:196–206.
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Fuel journal homepage: www.elsevier.com/locate/fuel
Full Length Article
Experimental investigation of the autoignition properties of ethanol–biodiesel fuel blends
T
Hubert Kuszewski Faculty of Mechanical Engineering and Aeronautics, Department of Combustion Engines and Transport, Rzeszow University of Technology, 8 Powstancow Warszawy Ave., 35-959 Rzeszow, Poland
A R T I C LE I N FO
A B S T R A C T
Keywords: Ethanol–biodiesel blends Derived cetane number Diesel engine Ignition delay Combustion delay
Growing interest in increasing the market share of renewable fuels results from the increasing consumption of fuels in various industries, especially in road transport. Such fuels include, for example, ethanol and FAME (Fatty Acid Methyl Esters), known as biodiesel. In diesel engines, ethanol, unlike biodiesel, cannot be directly used as a pure fuel due to its very low autoignition propensity. However, due to the good autoignition properties of biodiesel, increasing attention is being paid to the fuel constitution, for example, a blend of biodiesel with ethanol additive. This way, it is possible to obtain fuel for diesel engines that are compositions of only products of plant origin. In this paper, the autoignition properties of RME (Rape Methyl Esters) and ethanol blends, with the ethanol fraction up to 25% (v/v) were examined. A constant volume combustion chamber was used in the study. Under the specified test conditions, the ignition delay period and the combustion delay period, as well as the DCN (Derived Cetane Number), were determined for the individual blends. The average and maximum pressure rise rates in the combustion chamber were also analysed. The study has shown, for example, that with an increase of ethanol fraction in biodiesel, the periods of ignition and combustion delay increase. It was also shown that in the range from 5% (v/v) to 25% (v/v) of the ethanol fraction, for every increase in the fraction of ethanol by 5% (v/v), the DCN of the biodiesel–ethanol blend is reduced by an average of 3.4 units.
1. Introduction Energy security is largely determined by the increase in the renewable fuels market share. In addition, rising prices of fuels derived from crude oil and the limitations resulting from the increasingly stringent standards for exhaust emissions lead to a growing interest in this type of fuel. At the same time, the use of diesel engines in industry and transport is still prevalent. One of the methods of increasing the share of alternative fuels in transport is to use FAME (Fatty Acid Methyl Esters), commonly known as biodiesel. FAME are obtained by catalytic esterification of fatty acids (contained in vegetable oils) with methanol. FAME derived from rapeseed oil are known as RME (Rape Methyl Esters) and are used as biocomponents in diesel or as pure fuel. The results of research on the properties of diesel and biodiesel blends and the effects of such blends on the functioning of diesel engines can be found, for example, in [1–5]. Recently, interest in the use of organic oxygen compounds, especially alcohol, in diesel engines has increased. However, given the low propensity to autoignition and the poor lubricity characteristics of this type of fuel, as indicated, for example, in [6–8], the use of this type of fuel in pure form in diesel engines would require significant design
modifications and the introduction of fuel additives to enhance autoignition and lubricity. Therefore, the blends of oxygen compounds with diesel and biodiesel have a greater practical importance, with such a mutual participation of those fuels, so it is possible to use such blends in typically operated diesel engines, which have been designed to use typical diesel fuel. Several papers have been devoted to this subject, covering various aspects of the use of such fuels. For example, the papers [6–16] concern blends of diesel and alcohol, while the papers [17–26] concern blends of diesel, biodiesel and alcohol. In general, from some of the papers [6–26], it appears that even though the addition of alcohol to diesel or biodiesel may have a beneficial effect on limiting undesired exhaust gas components, it also significantly changes the physicochemical parameters of the base fuels, namely diesel, biodiesel or blends thereof. Changes in those parameters obviously depend on the fraction of alcohol in the blend. This, in turn, implies for example the need to change fuel injection control algorithms. Studies related to the use of blends of biodiesel and alcohol were, among others, the subject matter, for example, of the papers [27–36]. One of the alcohols that is considered as an additive to biodiesel is ethanol. This is because alcohol can be produced from raw materials of plant origin or biomass, and thus can be considered to be a fully
E-mail address: [email protected]. https://doi.org/10.1016/j.fuel.2018.08.146 Received 3 November 2017; Received in revised form 8 February 2018; Accepted 30 August 2018 0016-2361/ © 2018 Elsevier Ltd. All rights reserved.
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Nomenclature FAME RME DCN HC CO NO NOX NO2 PM CN CVCC ID CD MPR APRR MPRR CFPP HHV LHV KOH CID510 pinj tinj
electronic signal that opens the injector), ms chamber static pressure (gauge), MPa chamber wall temperature, °C initial ambient gas temperature, °C injector nozzle coolant jacket temperature, °C maximum pressure rise—the difference between chamber maximum pressure and chamber static pressure, MPa (Δpch/Δt)A average pressure rise rate, MPa/ms pmax maximum chamber pressure (gauge), MPa pID chamber pressure (gauge) at ID, MPa, tpmax time at which the value of pmax is reached, ms (Δpch/Δt)Max maximum pressure rise rate, MPa/ms Δpch/Δt pressure rise rate, MPa/ms Δ(ID)A absolute measurement uncertainty of ID, ms Δ(ID)R relative measurement uncertainty of ID, % Δ(CD)A absolute measurement uncertainty of CD, ms Δ(CD)R relative measurement uncertainty of CD, % Δ(Δpch)A absolute measurement uncertainty of Δpch, MPa Δ(Δpch)R relative measurement uncertainty of Δpch, % Δ(APRR)A absolute measurement uncertainty of APRR, MPa/ms Δ(APRR)R relative measurement uncertainty of APRR, % Δ(MPRR)A absolute measurement uncertainty of MPRR, MPa/ms Δ(MPRR)R relative measurement uncertainty of MPRR, % Δ(DCN)A absolute measurement uncertainty of DCN Δ(DCN)R relative measurement uncertainty of DCN, % p0 tch Ta tco Δpch
fatty acid methyl esters rape methyl esters derived cetane number hydrocarbons carbon monoxide nitrogen monoxide nitrogen oxides nitrogen dioxide particulate matter cetane number constant volume combustion chamber ignition delay (period), ms combustion delay (period), ms maximum pressure rise average pressure rise rate maximum pressure rise rate cold filter plugging point, °C higher heating value, MJ/kg lower heating value, MJ/kg potassium hydroxide name of research device injection pressure, MPa injection period (determined by the length of the
by the CVCC method the concept of DCN is used [40]. In the procedure included in [41,42] to calculate the DCN, not only the ignition delay period but also the so-called combustion delay period is used. Because of the relatively low popularity of the fuel constituting biodiesel and ethanol blends, the previous papers on such blends were mainly focused on the characteristics of the diesel engine powered with such fuel. On the other hand, there are few papers that would directly point to the autoignition properties of ethanol–biodiesel blends. The related data can be found in the papers [28,30]. An et al. [28] have conducted model studies on combustion processes of the ethanol–biodiesel blends, with ethanol fraction of 5%, 10% and 20% (v/v). In general, the simulation of engine operation conducted thereby shows that, with the increase in the fraction of ethanol in the blend, the ignition delay period is extended, which in turn translates into reduction of the peak pressures in the combustion chamber. The longer ignition delay period with the increased ethanol fraction in blends was justified by the authors as due to low CN and higher latent heat of vaporization of ethanol. Lapuerta et al. [30] conducted a study on the effect of the ethanol fraction in blends with biodiesel on the ignition delay period. The researchers used 11 blends of ethanol and biodiesel, with the lowest ethanol content being 2.5% (v/v) and the largest being 75% (v/ v). The authors used the CID510 apparatus with a CVCC in their research. In contrast to the paper [28], the authors of the paper [30] have provided numerical values for the ignition delay period. In addition, the courses of pressure variations in the combustion chamber were shown for the tested blends. From research by Lapuerta et al. [30], it appears that with the increase in the fraction of ethanol in the blend, the ignition delay period is extended, while the increase in the initial temperature and the initial pressure in the combustion chamber clearly shorten that period. This paper focuses on the influence of ethanol fraction on the autoignition properties of ethanol–biodiesel blends. Basically, the assessment of the autoignition properties of biodiesel with specified ethanol fraction was based on the ID (Ignition Delay) period and CD (Combustion Delay) period and the DCN value. However, bearing in mind the specifics of the diesel engine cycle, in the paper the results for APRR (Average Pressure Rise Rate) and MPRR (Maximum Pressure Rise Rate) in the combustion chamber are also included. The higher values of those
renewable fuel. It should also be noted that in the case of biodiesel and ethanol blends, only fuels of plant origin are obtained. It is also important that dehydrated ethanol shows relatively good solubility in biodiesel, as indicated by the papers [26,36,37]. From the engine tests conducted by Yilmaz and Sanchez [27], it appears that adding 15% (v/v) of ethanol to biodiesel, in terms of partial engine loads compared with powering with pure biodiesel, results in an increase in HC (hydrocarbon) and CO (carbon monoxide) concentrations in the exhaust gas, but results in a significant reduction in NO (nitrogen monoxide). In turn, the study conducted by Zhu et al. [29], indicates that an increase in the fraction of ethanol in biodiesel (up to 15% (v/v) ethanol in the test range) results in lower NOX (nitrogen oxides) and NO2 (nitrogen dioxide) specific emission relative to powering with pure biodiesel. Moreover, their study shows that with the increase in the fraction of ethanol in biodiesel, the specific emission of PM (particulate matter) is reduced. In addition, the results of model tests conducted by An et al. [28] show the beneficial effect on NOX emission of adding ethanol to biodiesel, compared with powering with pure biodiesel. The beneficial effects of 20% (v/v) addition of ethanol to biodiesel, in relation to the powering with biodiesel and diesel fuel, on exhaust emission and engine performance are also indicated by the results of the study presented by Aydin and İlkılıç [33]. The potential uses of the ethanol–biodiesel blend in diesel engines are generally indicated also by the papers of Tutak et al. [31,32] and the paper by Torres-Jimenez et al. [36]. Considering the possibility of using ethanol in a diesel engine, when the base fuel is biodiesel or diesel, it should be noted that the addition of ethanol significantly alters the physicochemical and quality parameters of those fuels. Quite extensive results of the study on the physicochemical properties of ethanol–biodiesel blends were included in the paper [36]. From among many physicochemical parameters, particular attention should be paid to the tendency to autoignition and connected with it the ignition delay period. Based on the standard procedures [38,39], the autoignition properties of fuel are determined on the basis of CN (Cetane Number). An alternative method of determining the autoignition properties of fuel is the use of the CVCC (Constant Volume Combustion Chamber) method. To distinguish it from measurements using a test engine, when measured 1302
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combustion chamber, the maximum pressure values and the ID values, the APRR was calculated according to the relation:
parameters in the engine operating conditions translate into a higher load on the crankshaft system components, which usually contributes to reducing its lifetime. The presented data are a supplement to the results of the study included in the paper [36] and to some extent the results of the study presented in [28,30] and in [14], where DCN data for ethanol–diesel fuel blends are presented. The data obtained can be useful, among others, for the optimization of combustion systems of diesel engines fuelled with biodiesel with ethanol additive.
(Δpch /Δt )A = (pmax −pID )/(tpmax−ID) [MPa/ms]
(1)
where pmax – maximum chamber pressure, obtained from the recorded pressure course, MPa; pID – chamber pressure at ID, MPa; tpmax – time after which value of pmax is reached, ms; ID – period of ignition delay, ms. Each of the recorded pressure courses were numerically differentiated using the difference quotient. In this way, the course of the instantaneous pressure rise rate in the combustion chamber was obtained and the maximum value of this parameter was noted. Fig. 1 shows an example of the recorded course of pressure changes in the combustion chamber (fuel BD-ETH-10). The diagram covers 20 ms from the beginning of the recording. Similarly, for the time of 20 ms from the beginning of the recording, the pressure course diagrams presented in Chapter 3 were prepared. Fig. 2 shows the course of the instantaneous pressure rise rate in the combustion chamber obtained from the numerical differentiation of the course shown in Fig. 1. In Fig. 1, the parameters used to calculate the APRR values are marked and Fig. 2 shows the maximum value of the instantaneous pressure rise rate. The calculation of the instantaneous pressure rise rate in the combustion chamber was used only to identify the MPRR of this parameter and therefore no such courses were included in the discussion section of the article. The DCN was determined for each of the fuels shown in Table 2. The measurements were conducted in accordance with the standard requirements contained in [41,42]. The standard measurement uncertainties of type A and their relative values were calculated for each of the analysed parameters. The standard deviation of the mean was assumed to be the standard value of the measurement uncertainty. The values of the calculated absolute and relative measurement uncertainties are presented in the tables in the discussion section. For clarity, the absolute values of the measurement uncertainties were not plotted on the graphs in the form of error bars. The diagrams show the mean values of the parameters, representing the best approximation of the measured values.
2. Experimental methodology 2.1. Samples characterization The study of the autoignition properties was carried out for six samples of fuel. One of them is FAME obtained from rapeseed oil, that is, RME. This fuel, further referred to as biodiesel, meets the requirements of the standard [43] and is a biocomponent commonly used in diesel fuel. The basic parameters of this fuel are included in Table 1. Later herein, the biodiesel has been marked as BD-ETH-0. Further samples are the blends of biodiesel (with the specification shown in Table 1) with ethyl alcohol with proportions of alcohol from 5% to 25%. As pointed out in [26,36,37] the homogeneity and stability of biodiesel and ethanol blends are determined by the ambient temperature and water concentration. Dehydrated ethanol with purity of more than 99.5% was used to avoid turbidity and delamination of the blends, and the blends were prepared at the same temperature of the biodiesel and alcohol of 22 °C ± 1 °C. These are conditions similar to those for which the stability and homogeneity of the blends of ethanol and biodiesel were found in [36]. Fuel samples were stored in sealed glass vessels at their preparation temperature, namely, 22 °C ± 1 °C. The procedures implemented in the preparation and storage of the blends throughout the entire test cycle of autoignition properties ensured the homogeneity and stability of the prepared blends. No signs of turbidity or delamination were observed for any of the samples. The markings of individual fuel samples are presented in Table 2. 2.2. Data acquisition In the study, a commercially available apparatus, CID510, with a CVCC was used. The primary purpose of this test device is to determine the DCN in accordance with the procedure contained in [41,42]. This is the same type of device that Lapuerta et al. [30] as well as Kuszewski et al. [14,16] used in their work. A more detailed description and diagram of the test device structure is presented in [14]. More details on the structure of the device can also be found in [41,42]. Because the determination of DCN was assumed for the individual samples, before performing a series of tests a calibration of the device was carried out according to the procedure specified in the standard [41]. The required reference fuel consisting of a mass blend of hexadecane (40%) and 2,2,4,4,6,8,8-heptamethylnonane (60%) was used for calibration. For each of the 15 fundamental combustion cycles, in addition, the following values were recorded, the ID period, the CD period, the initial pressure in the combustion chamber, p0, MPR (Maximum Pressure Rise) in the chamber, Δpch, in relation to the initial pressure, the temperature of the combustion chamber walls, tch, the temperature of the injector coolant, tco, and the fuel injection pressure, pinj. The temperature of the synthetic air filling the chamber (Ta) (initial ambient gas temperature) corresponds to the recorded wall temperature of the chamber, tch, i.e. tch = Ta. A calibration value of tch was 598 °C. All values of the analysed pressures are the overpressures relative to the ambient pressure (97.8 kPa ± 3 kPa). A detailed description of the measurement of the ID and CD parameters can be found in [14,41,42]. The performance parameters and engine durability are affected by the character of the pressure rise in the combustion chamber. Therefore, using the values of the recorded pressure courses in the
3. Results and discussion Fig. 3 shows the effect of volume fraction of ethanol in a blend with biodiesel on the ID and CD periods. As can be seen from the data provided, under established measurement conditions and for tested blends, the increase in the ethanol fraction in blend results in a second-order polynomial prolongation of the ID. This confirms the data obtained by Table 1 Parameters of biodiesel fuel used in the study.
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Property
Method
Value
FAME content (% m/m) Derived cetane number (DCN) Viscosity at 40 °C (mm2/s) Density at 15 °C (g/cm3) Flash-point (°C) HHV (MJ/kg) CFPP (°C) Cloud point (°C) Water content (mg/kg) Sulphur content (mg/kg) Oxidation stability at 110 °C (h) Acid number (mg KOH/g) Methyl alcohol content (% m/m) Monoglycerides content (% m/m) Diglycerides content (% m/m) Linolenic acid methyl ester content (% m/m)
EN 14103 ASTM D7668 EN ISO 3104 EN ISO 12185 EN ISO 2719 PN-C-04375-3 EN 116 ISO 3015 EN ISO 12937 EN ISO 20846 EN 15751 EN 14104 EN 14110 EN 14105 EN 14105 EN 14103
97.6 54.6 4.4767 0.883 174 40.2 −15 −5 195 < 3.0 11.5 0.33 0.01 0.6 0.13 9.1
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similar test conditions and with the same test equipment, in the case of ethanol–diesel blends, the prolongation of the ID was also obtained with an increase in the ethanol fraction [14,16], but it was a linear function. This indicates the different character of the effect of the ethanol additive on the autoignition properties of RME compared with ethanol effects on the autoignition properties of diesel fuel. This is due mainly to the varied chemical structure of the base fuels in the analysed blends. The issues related to the influence of chemical structure on the autoignition properties of FAME are more broadly presented in [49,50]. The CD period can be considered as a complementary assessment factor of the autoignition properties of the fuel. This parameter, defined according to the methodology included in the standards [41,42], along with the ID period is used to calculate the DCN of the fuel. While the ID parameter can be considered as a cool-flame stage, due to the reaction during this stage, namely, the first stage of a two-stage autoignition, the CD period can be used to designate a second, main stage of autoignition. Those issues were highlighted in the study of Lapuerta et al. [30,51], who, in their research, used the same test device with a CVCC as the author of this paper. The heat release in the coolflame stage is determined by the low-temperature reaction of the straight carbon chains in the hydrocarbon radicals forming the esters. This chemical structure also determines the relatively good properties of autoignition of esters, including RME, as in the case of diesel fuel with a high fraction of straight-chain paraffinic hydrocarbons. The relationship between the chemical structure of the fuel and the autoignition properties and the presence of the cool-flame stage was highlighted, for example, in [51]. The second, main stage of autoignition by the CD and the pressure rise rate in the combustion chamber was determined by Lapuerta et al. [51]. According to the methodology adopted by them, the CD period is always slightly longer than the main stage of autoignition. The main stage of the autoignition, directly leading to the combustion propagation, begins when the temperature in the fuel droplets’ environment is high enough to initiate a chain reaction. As can be seen in Fig. 3, in general, the trend of changes in the CD is similar to that of the ID parameter, namely, the increase in the fraction of ethanol in the blend causes the second-order polynomial prolongation of the CD period. However, for the CD period, the difference in absolute CD values between the highest (25% v/v) and lowest (5% v/v) fraction of ethanol is approximately 2.7 ms, and in the case of ID, that difference is approx. 1.2 ms. This is related to the method of determining the CD period. The influence of the ethanol fraction in biodiesel on the changes in the CD parameter is determined by both the MPR in the combustion chamber after autoignition, Δpch, and to an even greater extent, the kind of the course of pressure changes in the combustion chamber from the moment of its recording to the maximum value of pressure, pmax. This was earlier noted by Kuszewski et al. [14], where the effect of ethanol additive on the autoignition properties of diesel fuel was investigated. This is also consistent with the results presented in [30,51]. The effect of ethanol fraction in biodiesel on the MPR, Δpch, in the combustion chamber, is shown in Fig. 4. As can be seen, an increase of the ethanol fraction in biodiesel results in a linear reduction in the MPR parameter. The absolute value of the difference of the MPR value for the highest (25% v/v) and lowest (5% v/v) fraction of ethanol in biodiesel is negligible and amounts to approx. 0.07 MPa. The reduction of MPR with the increase of ethanol fraction in biodiesel is a consequence of the decrease in the LHV (Lower Heating Value) with an increase in ethanol fraction in the tested blends. This, in turn, is a result of a lower HHV (Higher Heating Value) by approx. 26% of the ethanol relative to biodiesel. The HHV of ethanol used in the study, determined before the test, was 29.4 MJ/kg, while the HHV of pure biodiesel used in the study was 40.2 MJ/kg, as indicated in Table 1. The results concerning the MPR in the combustion chamber confirm the data obtained by Lapuerta et al. [30], who in their paper presented the influence of the ethanol fraction in biodiesel on the maximum
Table 2 Symbols of fuel samples. Fuel description
BD-ETH-0 (Biodiesel, RME) BD-ETH-5 BD-ETH-10 BD-ETH-15 BD-ETH-20 BD-ETH-25
Volume fraction [%] RME
Ethanol
100
0
95 90 85 80 75
5 10 15 20 25
Fig. 1. Example pressure course in the combustion chamber (fuel BD-ETH-10).
Fig. 2. Example pressure rise rate in the combustion chamber (fuel BD-ETH10).
Fig. 3. Effect of the ethanol percentage in biodiesel fuel on the ID and CD periods.
Lapuerta et al. [30]. The prolongation of the ID for the ethanol–biodiesel blends with an increase in the ethanol fraction is also indicated in the model study of the engine conducted by An et al. [28]. In general, the prolongation of the ID period for ethanol–biodiesel blend with an increase in the ethanol fraction, as in the case of ethanol–diesel blends, is a consequence of the low autoignition propensity of ethanol [6,9,14,16,23,37,44–48]. However, it should be noted that under 1304
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premixed period of combustion is less intense [52–54], that is, also with smaller (average and maximum) pressure rise rates. Then, the engine emits less noise, also the intensity of the absorption of heat by the working medium is reduced, which translates into a lower concentration of NOX in the exhaust gas. Such dependencies are generally known for diesel fuel. As can be seen in Figs. 6 and 7, with an increase in the ethanol fraction in biodiesel, the APRR parameter is linearly reduced. Because this happens, despite the prolonged period of the ID (Fig. 3), then, under the established CVCC test conditions, as the dominant factor which reduces the APRR parameter (as in the MPR case) the LHV of the ethanol–biodiesel blends, which decreases with increase in ethanol fraction in biodiesel, should be considered. It should also be noted that, for example, the results of the engine tests presented in [31], generally show similarly, as in Fig. 5, the changes of pressure rise from autoignition to peak pressure. In this case, it can be expected that the tendency of changes in APRR and MPRR parameters in engine test conditions is similar to that presented in Figs. 6 and 7. The reduction of APRR and MPRR parameters should result in a reduction in mechanical loads in the crank–piston system of the engine and contribute to its durability. In addition, it cannot be ruled out that the concentration of nitrogen oxides in the exhaust gas will be reduced. Fig. 8 shows the results of the determination of DCN for the analysed ethanol–biodiesel blends. The DCN values have been calculated on the basis of ID and CD periods—according to the methodology contained in [41]. According to this methodology, the calculation of normative DCN values is valid only for ID and CD parameters measured during operation of the test device according to the calibration settings (Table 3). As can be seen in Fig. 8, the increase of the ethanol fraction in biodiesel results in a linear reduction in DCN value, wherein, in the analysed range of ethanol fraction, for every increase in the ethanol fraction by 5%, the DCN of the ethanol–biodiesel blend is reduced by an average of 3.4 units. However, already the addition of 5% (v/v) of ethanol means that the biodiesel does not meet the requirement of the standard [43], according to which the minimum CN number is 51. At the same time, the biodiesel meeting the requirement of the standard [43], with the specification included in Table 1, which contains even 10% (v/v) of ethanol, meets the requirement in terms of CN for both biodiesel grades determined in the standard [55], according to which the minimum CN is 47 (biodiesel No. 1-B and No. 2-B). Considering the use of the ethanol–biodiesel blends in diesel engines, it is justified to refer to the obtained results of the DCN, also to the requirements of diesel fuel. In the Worldwide Fuel Charter [56], the requirement for the five categories of diesel fuel, from 1 to 5 was specified, for which the minimum CN amounts respectively are 48, 51, 53, 55 and 55. The DCN studies indicate that biodiesel with the addition of 5% (v/v) of ethanol meets the requirement for CN specified for the first category of diesel. The addition of 5% (v/v) ethanol to biodiesel means that the ethanol–biodiesel blend does not meet the requirement specified in the standard [43] according to which the minimum value of CN is 51. At the same time, biodiesel with the addition of even 20% (v/v) of
Fig. 4. Effect of the ethanol percentage in biodiesel fuel on the MPR in the combustion chamber, Δpch.
pressures recorded in the combustion chamber of the CID510 test device. They conducted tests for the ambient gas temperature of 602.5 °C and the initial pressure in the combustion chamber of 2.1 MPa. For an ethanol fraction up to 20% (v/v), they noted a slight impact of ethanol fraction on the maximum pressure in the combustion chamber. Only for ethanol fractions above 30% (v/v) did they note a clear reduction in the maximum pressure, and thus also the pressure rise in the combustion chamber. The results obtained for the MPR parameter generally correspond to the results of the model engine tests presented in [28], where the reduction of maximum pressure in the combustion chamber is indicated with an increase in the ethanol fraction in biodiesel, which is justified by the authors of that publication by the delayed start of combustion resulting from the longer ID period and the lower LHV of ethanol. In turn, the results of experimental engine tests presented in [29,31,32] indicate an increase in the maximum pressure in the cylinder with an increase in the ethanol fraction in biodiesel. The authors of these papers essentially justify this phenomenon with the reduction in CN of ethanol, which results in delayed combustion leading to an increase in the amount of fuel combusted in the premixed phase of combustion. Differences in maximum pressure of combustion obtained using the CVCC method and on the basis of engine tests may be justified by different conditions of heat release in the premixed combustion phase. Under engine test conditions, in contrast to tests using the CVCC method, there are several factors, variable in time, that can influence the rate of heat release in the premixed combustion phase. Among other factors, there is difficult evaporation of the injected fuel due to different heat transfer conditions between the working medium and the cylinder walls, determined by the speed and load of the engine, and the fuel injection timing [52]. Fig. 5 shows averaged pressure courses in the combustion chamber for individual fuel samples. As can be seen, with the increase of ethanol fraction in biodiesel, the pressure rise rate in the combustion chamber is reduced in the range from the initial pressure to the peak pressure. From data presented in Fig. 5, it can also be seen that with the increase in the ethanol fraction in biodiesel, not only the peak pressure in the combustion chamber (that is also MPR) is decreasing, as indicated earlier, but also the time after which it occurs is extended. This confirms the results of experiments conducted using the CVCC method presented in [30], as well as the results of the engine tests presented in [31]. A quantitative assessment of the nature of the pressure rise in the combustion chamber was performed for individual fuel samples on the basis of calculations of the APRR values in the combustion chamber (formula (1)). The MPRR parameter was also defined. Values of those parameters are important because, in particular, consideration of parameter ID in the context of fuel applications in a diesel engine should also be conducted in relation to the effects of a long ID period. As indicated by several studies, a shorter ID period (achieved, e.g., by pilot injection or reduction of the injection advance angle for a single fuel injection) in a diesel engine leads to a reduction in the fuel accumulated in the combustion chamber during the ID period, and thus the
Fig. 5. Pressure courses in the combustion chamber for all fuel samples. 1305
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2.5 2.5 2.5 2.5 2.5 2.5 99.9 99.8 99.6 99.5 99.2 99.7 51.1 50.5 50.1 51.2 51.5 51.0 597.7 597.7 597.8 597.8 597.8 597.8 2.00 2.00 2.00 2.00 2.00 2.00 0.3 0.3 0.2 0.2 0.2 0.2 0.2 0.1 0.1 0.1 0.1 0.1 2.8 2.8 3.2 2.6 2.3 1.9 0.1320 0.1237 0.1270 0.0796 0.0476 0.0273 3.6 4.7 3.7 2.0 2.1 1.4 0.0270 0.0307 0.0210 0.0081 0.0062 0.0031 0.2 0.2 0.1 0.1 0.0 0.2 0.0046 0.0030 0.0017 0.0013 0.0009 0.0028 0.3 0.3 0.3 0.2 0.3 0.4 0.0119 0.0143 0.0154 0.0135 0.0193 0.0272 0.5 0.3 0.4 0.3 0.3 0.3 0.0147 0.0111 0.0145 0.0107 0.0135 0.0136
Δ(APRR)A [MPa/ms] Δ(Δpch)R [%] Δ(Δpch)A [MPa] Δ(CD)R [%] Δ(CD)A [ms]
ethanol, meets the requirement in terms of CN for all categories of diesel fuel determined in the standard [39], according to which the minimum cetane number is 40 (all diesel fuels No. 1-D and No. 2-D) or 30 (diesel fuel No. 4-D). In addition, the 25% (v/v) addition of ethanol to the biodiesel means that the blend meets the requirement for diesel fuel No. 4-D. However, it should be noted that DCN values for the analysed blends can slightly differ, depending on the DCN value for the base fuel, that is, biodiesel without ethanol additive. The addition to the results of the ID, CD, DCN, MPR, APRR and MPRR measurements is in Table 3, which summarizes the results of calculation of the absolute and relative measurement uncertainty of the measured parameters. In addition, the average parameters related to fuel injection are also included in the table. The following parameters are included in Table 3, the values of static pressure in the combustion chamber, p0, temperature of the combustion chamber walls, tch, injector nozzle coolant jacket temperature, tco, fuel injection pressure, pinj, as well as the duration of the injection pulse width, tinj. The presented data characterizing parameters associated with fuel injection and operation conditions of the CVCC can be helpful to restore conditions under which the study was conducted,
Δ(ID)R [%]
Fig. 8. Effect of the percentage of ethanol in biodiesel fuel on the DCN.
Δ(ID)A [ms]
Table 3 Absolute and relative measurement uncertainties together with recorded parameters of fuel injection.
Fig. 7. Effect of the percentage of ethanol in biodiesel fuel on the MPRR in the combustion chamber, (Δpch/Δt)Max.
Δ(APRR)R [%]
Δ(MPRR)A [MPa/ms]
Δ(MPRR)R [%]
Δ(DCN)A
Δ(DCN)R [%]
Fig. 6. Effect of the percentage of ethanol in biodiesel fuel on the APRR in the combustion chamber, (Δpch/Δt)A.
BD-ETH-0 BD-ETH-5 BD-ETH-10 BD-ETH-15 BD-ETH-20 BD-ETH-25
p0 [MPa]
tch [°C]
tco [°C]
pinj [MPa]
tinj [ms]
H. Kuszewski
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the results of which are presented in this article.
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4. Conclusions This paper presents the results of a study of the autoignition properties of ethanol–biodiesel blends. The tests were conducted for a typical RME and for several blends of that fuel with ethanol, wherein the maximum ethanol fraction was 25% (v/v). In the study, the test equipment was used with a CVCC, which also allowed determining the DCN according to the valid standard. Essentially, for the assessment of the autoignition properties, the ignition and combustion delay periods were used. Those parameters were determined according to the methodology included in [41,42]. The maximum pressure rise in the combustion chamber was also analysed. Based on the recorded pressure changes, the average and maximum rate of pressure rise in the combustion chamber are also determined. The conducted research allows us to formulate the following conclusions, - Biodiesel with ethanol additive of 5% (v/v) does not meet the requirement of EN 14214 for CN. - Biodiesel with ethanol additive of 10% meets the requirement of ASTM D6751 for biodiesel grade No. 1-B and No. 2-B for CN. - Biodiesel with ethanol additive of 5% (v/v) does not meet the requirement of EN 590 for CN. - Biodiesel with ethanol additive of 5% (v/v) meets the requirement specified in the Worldwide Fuel Charter for the CN defined for the first category of diesel fuel. - Biodiesel with ethanol additive of 20% (v/v) meets the requirement of ASTM D975 for CN for all categories of diesel. - Biodiesel with ethanol additive of 25% (v/v) meets the requirement of ASTM D975 for CN for diesel fuel grade No. 4-D. The data collected as a result of the study provide a supplement to the studies related to the properties of ethanol–biodiesel blends, in particular, their autoignition properties. That data can also be helpful when optimizing combustion systems of diesel engines, for which the powering with ethanol–biodiesel is permitted. The conducted studies also confirmed the usefulness of the measurement system with a CVCC for the tests of the autoignition properties of ethanol–biodiesel blends. The determination in a normative way of the DCN provides a view of the tendency of changes in that parameter for RME as a result of the addition of ethanol. Such data may be helpful in optimizing the composition for ethanol and RME blends. Acknowledgement This work was supported by the Ministry of Infrastructure and Development under the Eastern Poland Development Operational Programme, including the European Regional Development Fund–Belgium, which financed the research instruments. The author wish to acknowledge the Polish Ministry of Science and Higher Education and the Rzeszow University of Technology for supporting this research. References [1] Gülüm M, Bilgin A. Measurements and empirical correlations in predicting biodiesel-diesel blends’ viscosity and density. Fuel 2017;199:567–77. [2] Kanaveli I-P, Atzemi M, Lois E. Predicting the viscosity of diesel/biodiesel blends. Fuel 2017;199:248–63. [3] Hoseini SS, Najafi G, Ghobadian B, Mamat R, Sidik NACh, Azmi WH. The effect of combustion management on diesel engine emissions fueled with biodiesel-diesel blends. Renew Sustain Energy Rev 2017;73:307–31. [4] Hasan MM, Rahman MM. Performance and emission characteristics of biodiesel–diesel blend and environmental and economic impacts of biodiesel production: a review. Renew Sustain Energy Rev 2017;74:938–48. [5] Nurun Nabi Md, Shamim Akhter Md, Zaglul Shahadat Mhia Md. Improvement of engine emissions with conventional diesel fuel and diesel–biodiesel blends.
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