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Article

Investigating the Effect of 2-Ethylhexyl Nitrate Cetane Improver (2-EHN) on the Autoignition Characteristics of a 1-Butanol–Diesel Blend

by
Hubert Kuszewski
* and
Artur Jaworski
Faculty of Mechanical Engineering and Aeronautics, Rzeszow University of Technology, 35-959 Rzeszów, Poland
*
Author to whom correspondence should be addressed.
Energies 2024, 17(16), 4085; https://doi.org/10.3390/en17164085
Submission received: 22 July 2024 / Revised: 11 August 2024 / Accepted: 15 August 2024 / Published: 16 August 2024
(This article belongs to the Special Issue Internal Combustion Engine: Research and Application—2nd Edition)
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Abstract

:
One promising oxygenate additive being considered as a fuel component for diesel engines is 1-butanol. However, since 1-butanol is characterized, like many other alcohols, by poor autoignition properties and, consequently, a low cetane number, the introduction of this additive into diesel fuel naturally worsens the autoignition properties of the blend so obtained. It is usual to consider a proportion of 1-butanol no higher than approx. 30% alcohol by volume. Thus, when considering the addition of 1-butanol to diesel fuel, it is necessary to improve the autoignition properties of such a blend. One such additive may be 2-ethylhexyl nitrate (2-EHN). This article determines the effect of the 2-EHN additive on the autoignition properties of a blend of 1-butanol and diesel fuel at an alcohol content of 30% (v/v). The tests were carried out using a constant volume combustion chamber method, which additionally made it possible to determine the effect of ambient gas temperature on the ignition delay (ID), combustion delay (CD) and derived cetane number (DCN), among other factors. The study showed, among other things, that with an increase in the mass proportion of 2-EHN in the 1-butanol–diesel blend (BDB) tested, the ignition and combustion delay were shortened, which resulted in an increase in the value of the derived cetane number.

1. Introduction

The use of diesel engines in industry and transportation has driven the search for alternative fuels for these engines, which have traditionally been powered by diesel fuel combined with plant oil esters. Research on the properties of these blends can be found in sources such as [1,2,3]. The interest in organic oxygen compounds for diesel engines, particularly alcohols, stems from their beneficial ecological effects, including reduced nitrogen oxide (NOX) emissions and lower smoke opacity. Studies have mainly focused on 1-butanol [4,5,6,7], ethanol [8,9] and methanol [10,11,12].
Due to its physicochemical properties, 1-butanol stands out as a particularly appealing oxygen additive for diesel fuel. This alcohol can be produced through the fermentation of lignocellulosic biomass, making it a fully renewable fuel [13]. The appeal of 1-butanol as a diesel biocomponent is attributed to its physicochemical properties, which are closer to those of conventional diesel fuel compared to ethanol and methanol. Although 1-butanol has poorer autoignition properties than diesel fuel, it surpasses ethanol and methanol in this aspect [14]. Additionally, 1-butanol has a lower heat of evaporation [15], higher kinematic viscosity [16], better lubricity, higher density [4], higher flash point [17], and a significantly lower autoignition temperature [16], resulting in a higher cetane number (CN) [4,14]. Another notable advantage of 1-butanol is its significantly lower hygroscopicity compared to ethanol and methanol.
Several studies have explored the potential of using 1-butanol as an additive to diesel fuel. These studies indicate, among other findings, that as the proportion of 1-butanol in the blend increases, the autoignition properties of the 1-butanol–diesel blend worsen due to 1-butanol’s relatively lower tendency for autoignition [4,14,17]. This is evident in the declining CN of the BDB as the 1-butanol fraction rises, as noted in [18,19,20,21]. Low CN values are undesirable because they lead to a longer ignition delay. Generally, a prolonged ID negatively impacts diesel engine performance, as it allows a large amount of fuel to accumulate in the combustion chamber, resulting in higher peak combustion pressures [22,23]. This can make the engine run noisily, increase stress on the crank–piston mechanism, accelerate engine wear and raise NOX emissions. The effects of CN on diesel engine performance parameters have been discussed in various studies, for example in [24,25].
One method of improving the autoignition properties of a blend of diesel and 1-butanol may be to introduce a certain mass fraction of cetane improver. Cetane improvers offer several benefits. Firstly, they substantially lower the initial temperature required for the fuel oxidation reaction. Secondly, they extend the reaction zone at the flame front. Lastly, they decrease the autoignition temperature of the fuel [26].
One commonly used additive that improves the propensity for autoignition and thus increases the cetane number of diesel fuel is 2-EHN. Generally, 2-EHN releases free radicals into the cylinder, accelerating the oxidation process. This enhances combustion characteristics, reduces the burning point and shortens the ignition delay. The mechanism of operation of the cetane improver in the form of 2-EHN is explained in detail, for example, in references [26,27,28,29]. The effectiveness of the 2-EHN additive for different fuels and under different test conditions has been the subject of numerous studies [26,30,31,32].
With the above in mind, it is also important to note the important issue of the effect of 2-EHN additive on NOX emissions in diesel–biofuel blends. This issue has been and still is the subject of many studies [33,34,35,36,37,38,39,40]. To date, however, the research results presented in the literature are not conclusive in this regard. Although some results indicate an increase in NOX emissions (or concentrations) for fuel blends with the addition of 2-EHN [39], more studies indicate the opposite trend, i.e., a positive effect of the addition of 2-EHN on NOX emissions [33,37,38]. The indication of a positive effect of 2-EHN on NOX emissions further justifies the need for studies on the effectiveness of this additive for alternative fuels, including diesel and 1-butanol blends.
Particularly noteworthy is reference [26], which highlighted the mechanism of operation and the effect of 2-EHN on the autoignition process and the course of methanol combustion, which is particularly important in the context of analyzing the possibility of introducing organic oxygenates into diesel fuel. As pointed out in the aforementioned study, the fundamental structure of 2-EHN consists of an ethyl hexane molecule with one hydrogen atom substituted by an NO3 nitrate functional group. When 2-EHN encounters the higher pressure and temperature inside the cylinder, its nitrogen–oxygen bond easily breaks, causing 2-EHN to quickly pyrolyze into NO2, CH2O and other less reactive radicals. The NO2 from 2-EHN reacts with hydrogen from methanol to produce HNO2, which then forms OH and NO. 2-EHN enhances low-temperature reactions primarily through the formation of OH from CH2O and NO2 [26].
In the author’s earlier study [32], the effect of the addition of 2-EHN on the autoignition properties of an ethanol– diesel fuel with 15% (v/v) of alcohol was investigated. The study was conducted using a constant volume combustion chamber (CVCC) and considering different mass fractions of 2-EHN. The tests were conducted considering three different initial temperatures in the combustion chamber. Among other things, the tests showed that as the mass fraction of 2-EHN in the blend increases, the ignition and combustion delay period shortens, leading to a linear increase in the DCN. In addition, the study showed that an increase in the initial temperature of the combustion chamber leads to a noticeable shortening of the ID and CD parameters for all 2-EHN fractions tested.
Previous studies have not presented the results of research on the effect of the mass fraction of 2-EHN on the autoignition properties of a blend of 1-butanol and diesel fuel realized under fixed conditions of fuel injection parameters using the CVCC method. The study presented in this paper significantly fills this gap, providing results obtained for fixed fuel injection conditions in terms of ID and CD parameters, additional DCN and, additionally, three other parameters characterizing the autoignition properties. The study results presented in this article are also an important complement to the authors’ earlier works focused on the study of the autoignition properties of fuels with the addition of organic oxygen compounds, intended for powering diesel engines [32,33,41,42,43,44,45,46].

2. Experimental Methodology

2.1. Sample Characterization

The tests were realized for a blend of typical diesel fuel and 1-butanol at an alcohol content of 30% by volume. The blend of diesel fuel and 1-butanol was prepared at 22 °C ± 1 °C; during all stages of testing the autoignition properties, the blend was maintained at this temperature. The parameters of the diesel fuel are shown in Table 1. Most of the parameters were determined using the OptiFuel instrument (Petroleum Analyzer Company; Houston, TX, USA), which employs Fourier transform infrared spectroscopy (FTIR). The measurements were performed three times, and the average values are presented in Table 1. The value of the DCN was determined using the CID510 instrument, (Petroleum Analyzer Company; Houston, TX, USA) which was used in a later stage of the study to test the autoignition properties. Characteristic points on the distillation curve were determined when studying the fractional composition of diesel fuel. For this purpose, the OptiDist instrument was used. The distillation curve of the diesel used in the study is shown in Figure 1.
Directly before the main measurements, appropriate mass fractions of 2-EHN were added to the blend to obtain concentration values corresponding to those shown in Table 2, which include the fuel determinations used in the Discussion section when presenting the measurement results. The highest of the 2-EHN concentration values used was due to the desire to obtain a DCN value that meets the requirements of EN590 [47].

2.2. Experimental Setup and Data Acquisition

In this study, we used the previously mentioned CID510 instrument, whose primary purpose is to determine the DCN according to standard procedures [48,49]. As shown by the studies of Lapuerta et al. [5,50,51] and Kuszewski et al. [32,41,42,43,44,45,52,53], the instrument can be successfully used to test the autoignition properties of various fuels, including those containing oxygen additives in the form of alcohols and, very importantly, also in the range of fuel injection conditions deviating from the standard conditions required for DCN determination. Detailed data on the instrument’s design, along with a schematic diagram containing its basic functional systems, can be found in [41,42,49,51]. Since it was also the intention of the authors of the present study to provide data on the DCN values for the tested fuel samples, the test instrument was therefore calibrated according to the standard procedure described in [49]. The calibration parameters are summarized in Table 3. In order to verify the performance of the analyzer after the calibration procedure, a DCN determination was carried out using a reference fuel with a DCN of 51.6 ± 0.6. The DCN value after the calibration of the instrument for this fuel was 51.9.
During the main stage of the study, six fuel injections were carried out for the established fuel injection conditions, preceded by five pre-injections, the main purpose of which was to fill the system with the tested fuel. The primary parameter measured was the pressure in the combustion chamber (pch). For this purpose, a special high-frequency dynamic pressure transducer implemented into the test device was used, which enabled pressure recording at a frequency of 25 kHz. Pressure recording was implemented for each of the six test fuel injections, and then the waveforms were averaged. The recorded time waveforms of pressure changes in the combustion chamber formed the basis for quantifying all analyzed parameters characterizing the autoignition of the tested fuel samples.
During the measurements, the following parameters were recorded and stored in the computer memory of the instrument: combustion chamber wall temperature (tch), initial combustion chamber pressure (p0), fuel injection pressure (pinj), maximum pressure rise (MPR) in the combustion chamber from the initial value of p0 and ID and CD parameters, i.e., ignition and combustion delay. During the tests, the ambient pressure at the site of the measuring instrument was 99.4 kPa and varied by no more than 2 kPa. The method of measuring ID, CD and MPR parameters is illustrated in Figure 2.
Figure 3 shows the averaged (based on six recorded waveforms) pressure rise rate and how the maximum pressure rise rate (MPRR) was determined. The recorded and averaged waveforms formed the basis for calculating the average pressure rise rate (APRR). The method of calculating this parameter and recording the other parameters used to analyze autoignition properties was used in the authors’ earlier studies [42,45,46].
In the measurement methodology used, it is assumed that the initial temperature (Ta) (at the start of fuel injection) of the synthetic air in the combustion chamber corresponds to the temperature tch. Two values of this temperature were established during the tests. One of them was Ta = 588 °C and was in accordance with the calibration settings, which made it possible to determine the DCN parameter in accordance with standard procedures [48,49]. The second value of this temperature, for which measurements were made, was Ta = 648 °C, which was the maximum temperature that could be held by the instrument control system.
Table 4 and Table 5 show the averaged values of the parameters describing the fuel injection conditions, which at the same time represented the steady-state conditions. The results are presented for all analyzed fuel samples. In addition, the tables contain values of measurement uncertainties relating to the measured and calculated values, which were calculated as the standard deviation of the mean. Columns containing measurement uncertainties are described using the designations adopted for each measured and calculated parameter, prefixed by the ϕ symbol. Since Table 4 deals with measurements performed at Ta = 588 °C, which corresponds to the calibration value of tch, therefore, unlike Table 5, measurement uncertainties calculated for DCN are also included.

3. Results and Discussion

3.1. Pressure Waveform in a Constant-Volume Combustion Chamber

Figure 4 shows the averaged time-course of combustion chamber pressure waveforms recorded for all the fuel samples analyzed and for the two initial combustion chamber temperatures Ta. Analyzing the curves recorded for both values of Ta temperature, it can be seen that the angle of slope of the curve from the beginning of pressure rise to reaching the maximum value in the case of sample DFBu0-0 is the largest. The addition of 1-butanol to the diesel fuel at a fraction of 30% (v/v) (sample DFBu30-0) resulted in clearly delayed combustion, as evidenced by the apparent later reaching of the maximum pressure value in the combustion chamber. In particular, a large difference in the pressure waveforms recorded for samples DFBu0-0 and DFBu30-0 is evident for the lower initial temperature in the combustion chamber Ta. At a higher temperature Ta, on the other hand, it can be seen that the mentioned difference is noticeably smaller. The addition of 2-EHN to a 1-butanol–diesel blend resulted in intermediate times after which the maximum pressure in the combustion chamber was reached, which was due to a change in the autoignition conditions of the blends, with the smallest differences in this range recorded for Ta = 648 °C for samples DFBu0-0, DFBu30-25 and DFBu30-30. Similar relationships were reported in the work of [32], where the effect of the addition of 2-EHN on the autoignition properties of an ethanol–diesel blend at an alcohol fraction of 15% (v/v) was studied. It should be noted here that the differences in the recorded pressure waveforms for both temperatures Ta were also due to changes in the conditions for the formation of the combustible mixture, which was affected by the rate of fuel evaporation. In turn, the difference in the pressure waveforms for diesel fuel and the 1-butanol–diesel blend also takes into account a certain change in the kinematic viscosity of the fuel, conditioning the secondary break-up of fuel droplets and the lower heating value of the analyzed blends [52].

3.2. Ignition and Combustion Delay

As can be seen from Figure 5, comparing the ID period for diesel fuel and a 1-butanol–diesel blend, the addition of alcohol to diesel fuel at the analyzed 30% (v/v) fraction, resulted in a noticeable prolongation of the ID, particularly for the lower of the Ta values considered. In this case, this increase in length was more than 2 ms. This is a natural consequence of the low autoignition propensity of 1-butanol [44,52]. An increase in the temperature of Ta at the start of fuel injection resulted in a shortening of ID, but did not, of course, reverse the trend of change in ID, and for DFBu30-0, the ID parameter remained longer relative to pure diesel (DFBu0-0). In this case, however, the difference was about 1 ms. The correlations shown in Figure 5 demonstrate that, for both Ta temperatures analyzed, the addition of 2-EHN to the blend resulted in a clear shortening of the ID relative to the DBu30-0. The greatest differences with regard to ID shortening were recorded when comparing the DFBu30-5 and DFBu30-0 blends. Further increases in the mass fraction of 2-EHN in the blend resulted in a further, clear shortening of ID. The addition of 20,000 ppm (m/m) of cetane improver 2-EHN resulted in an ID value for the blend (DFBu30-20) that was similar to the ID value recorded for DFBu0-0. Increasing the mass fraction of 2-EHN in the blends analyzed contributed to further ID shortening, but the changes were relatively small. Finally, however, the effectiveness of the 2-EHN addition with respect to ID shortening was recorded for both analyzed temperatures Ta.
When considering the effect of temperature on the observed ID values for all analyzed fuel samples, it should be noted that, in this case, the shortening of ID was additionally the result of a shortening of the physical part of the ignition delay period caused by the faster evaporation of the fuel in a higher ambient temperature [42,44,54]. The physical part of the ignition delay includes the time from the point of fuel injection until the fuel–air mixture reaches the initiation temperature of pre-ignition chemical reactions. During this time, the primary and secondary break-up of the fuel spray, partial evaporation and diffusion of fuel vapors from the liquid phase occur [55]. The reported tendency of the ID parameter to change by increasing this period with an increase in the mass fraction of 2-EHN in a 1-butanol–diesel blend is the same as in the case of an ethanol–diesel blend [32]. Thus, bearing in mind the desire to shorten the ignition delay, the obtained relationships lead us to consider the use of 2-EHN for diesel fuel containing components in the form of organic oxygenated compounds.
As can be seen from Figure 6, in general, the trend of changes in the CD, defined as shown in Figure 2, is the same as for the ID parameter (Figure 5). The validity of using the CD to evaluate the autoignition properties of a fuel–air mixture was pointed out in reference [50]. As noted later in the article, the values of the CD, together with the ID, are used to calculate the DCN, according to the methodology provided in [48,49]. The method of measuring CD determined the higher values obtained for this parameter relative to ID. For a lower temperature Ta, the CD for the DFBu0-0 sample had a similar value to that achieved at the highest mass fraction of 2-EHN, which corresponded to the DFBu30-30 sample. On the other hand, for a higher value of the initial temperature at the start of fuel injection, i.e., Ta = 648 °C, the CD value for the DFBu0-0 (pure diesel) sample was close to the value recorded for a mass fraction of 2-EHN amounting to 20,000 ppm (DFBu30-20). The shortening of the CD with increasing 2-EHN mass fraction was a consequence of the shorter time followed by the rapid increase in pressure recorded in the combustion chamber after the appearance of autoignition (Figure 4). This, in turn, was due to the longer time followed by the autoignition of the fuel–air mixture, as confirmed by the ID change data presented in Figure 5.

3.3. Average and Maximum Pressure Rise Rate

In Figure 7 and Figure 8, the changes in the APRR and MPRR parameters as a function of the mass fraction of 2-EHN are presented, respectively, as indicators complementing the evaluation of the autoignition properties of the blends analyzed. In line with previous results, results for diesel fuel containing neither 1-butanol nor cetane improver in the form of 2-EHN are also presented for comparison. It should be noted that the evaluation of the combustion course, on the basis of APRR and MPRR parameters using the CVCC method, is much more representative in relation to possible tests carried out on the engine, mainly due to the established and repeatable conditions related to fuel injection. As can be seen from the data presented, it is characteristic that, for the blends analyzed, for the lower temperature Ta, an increasing trend in the APRR and MPRR parameters was observed as the fraction of 2-EHN increased. For a higher initial temperature in the combustion chamber, on the other hand, the opposite trend was observed, i.e., a decrease in the values of these parameters with an increase in the fraction of 2-EHN in the blend.
The course of the combustion process is largely dependent on the premixed combustion phase. It determines the time after which peak pressure is reached in the combustion chamber. In the case analyzed, despite the lower temperature of Ta at the start of fuel injection, as the mass proportion of 2-EHN in the blend increased, the difference between the time of peak combustion chamber pressure and the combustion chamber pressure reached after the time corresponding to ID decreased. This led to an increase in the APRR and MPRR parameters despite an increase in the fraction of 2-EHN in the blends analyzed and, as a result, a shortening of the ID values obtained for them. It is noteworthy that a similar effect of 2-EHN on the timing of peak combustion pressure was observed in studies on ethanol–diesel blends carried out using the CVCC method [32], where the same method of determining APRR and MPRR parameters was used as in this article, and under engine test conditions [56]. In the case of engine tests, the observed relationships were confirmed by recorded waveforms of cylinder pressure changes.
For higher temperature Ta, more favorable conditions prevailed in the combustion chamber determining the improvement of key parameters of the microstructure of the fuel spray resulting from more intensive fuel evaporation. This phenomenon, combined with the intensification of free radical formation caused by the presence of 2-EHN in the blend, resulted in a decrease in the rate of combustion in the premixed combustion phase and implied a reduction in the values of APRR and MPRR parameters.

3.4. Maximum Pressure Rise

Figure 9 presents the values of the MPR parameter, defined according to the method presented in Figure 2. The highest MPR values were obtained for the DFBu0-0 sample. A slight decrease in MPR values was recorded for the DFBu30-0 sample. The addition of 2-EHN and an increase in its mass fraction in the BDB resulted in a further, but slight as far as the absolute value is concerned, decrease in MPR values.
In general, it can also be seen that the values of the MPR parameter correlate with the ID and CD values, i.e., a shortening of these periods for individual blends containing 2-EHN resulted in a slight decrease in the MPR value. This was due to the fact that, in the shorter time corresponding to the lower ID value, less fuel accumulated in the combustion chamber in the premixed combustion phase, which contributed to a reduction in the heat release rate after autoignition occurred and led to a certain decrease in the value of the MPR parameter for both analyzed Ta temperatures.

3.5. Derived Cetane Number

On the basis of the collected data of ID and CD parameters according to the procedure contained in [48,49], the average values of DCN were calculated, which are summarized in Figure 10. Nowadays, as is known, the DCN parameter, which is determined using the CVCC method, is equivalent to CN, which is determined using the engine method. An analysis of the DCN parameter is justified primarily if the purpose of the study is to relate the autoignition properties of the fuel to standard requirements, possibly the requirements included in the Worldwide Fuel Charter [57].
As can be seen from the figure, a value of 51.6 was obtained for the DFBu0-0 (pure diesel) sample, i.e., this fuel met the requirements of [47,57,58] for diesel categories 1 and 2. For the DFBu30-0 sample, the obtained value of 35.9 is well below most of the requirements in this regard. However, as can be seen, as the mass fraction of 2-EHN in the BDB increased, the DCN value clearly increased, but only at the highest mass fraction of 2-EHN amounting to 30,000 ppm was a value close to that for diesel fuel, which was the base fuel in the blends analyzed. It should be noted that a different DCN value for the base fuel, i.e., diesel fuel, would affect the DCN values obtained for BDB containing a 30% volume fraction of 1-butanol and with the mass fractions of 2-EHN taken into account.

4. Conclusions

The data collected in the study complement the results of works on the use of diesel fuels containing organic oxygen compounds. The study of autoignition properties was carried out using the CVCC method, resulting in the collection of data in quantitative terms relating to the autoignition properties of a blend of 1-butanol and typical diesel fuel with different mass fractions of cetane improver in the form of 2-EHN and for two different initial temperatures in the combustion chamber. Several parameters were used to evaluate the autoignition properties, the most significant of which is ignition delay. The conducted tests made it possible to formulate the following specific conclusions:
  • As the mass fraction of 2-EHN in a 1-butanol–diesel blend at 30% (v/v) of 1-butanol increased, the ignition delay and combustion delay shortened, with noticeably lower values of these parameters recorded for the higher initial temperature in the combustion chamber.
  • As the mass fraction of 2-EHN in a 1-butanol–diesel blend at 30% (v/v) of 1-butanol increased, for a lower initial temperature in the combustion chamber, the average pressure rise rate increased, and for the higher of these temperatures, the value of this parameter decreased.
  • As the mass fraction of 2-EHN in a 1-butanol–diesel blend at 30% (v/v) of 1-butanol increased, for a lower initial temperature in the combustion chamber, the maximum pressure rise rate increased, and for the higher of these temperatures, the value of this parameter decreased.
  • As the mass fraction of 2-EHN in a 1-butanol–diesel blend at 30% (v/v) of 1-butanol increased, for both analyzed initial temperatures in the combustion chamber, the value of maximum pressure rise decreased marginally.
  • As the mass fraction of 2-EHN in a 1-butanol–diesel blend at 30% (v/v) of 1-butanol increased, the value of the derived cetane number increased, with a value close to that obtained for the base fuel, which was diesel fuel, achieved only at a mass fraction of 2-EHN amounting to 30,000 ppm.

Author Contributions

Conceptualization, H.K. and A.J.; methodology, H.K. and A.J.; software, H.K.; validation, H.K. and A.J.; formal analysis, H.K. and A.J.; investigation, H.K. and A.J.; resources, H.K. and A.J.; data curation, H.K.; writing—original draft preparation, H.K. and A.J.; writing—review and editing, H.K. and A.J.; visualization, H.K. and A.J.; supervision, H.K. and A.J. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

Nomenclature

2-EHN2-ethylhexyl nitrate
IDIgnition delay
CDCombustion delay
DCNDerived cetane number
BDB1-butanol–diesel blend
NOXNitrogen oxides
CNCetane number
NO3Nitrate
NO2Nitrogen dioxide
CH2OFormaldehyde
OHHydroxyl
CVCCConstant volume combustion chamber
FTIRFourier transform infrared spectroscopy
FAMEFatty acid methyl esters
IBPInitial boiling point
FBPFinal boiling point
tchCombustion chamber wall temperature
tcoTemperature of injector coolant
p0Initial combustion chamber pressure
pinjFuel injection pressure
tinjInjection pulse width (injection period)
pchPressure in the combustion chamber
MPRMaximum pressure rise
MPRRMaximum pressure rise rate
APRRAverage pressure rise rate
TaInitial temperature in the combustion chamber
ϕSymbol prefixed to the parameter indicating the value of the measurement uncertainty

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Figure 1. Distillation curve for pure diesel fuel (DFBu0-0).
Figure 1. Distillation curve for pure diesel fuel (DFBu0-0).
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Figure 2. Determining of the ID, CD and MPR parameters.
Figure 2. Determining of the ID, CD and MPR parameters.
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Figure 3. The MPRR parameter designation on the example waveform of the pressure rise rate.
Figure 3. The MPRR parameter designation on the example waveform of the pressure rise rate.
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Figure 4. Pressure waveforms pch in the combustion chamber at different Ta values.
Figure 4. Pressure waveforms pch in the combustion chamber at different Ta values.
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Figure 5. ID parameter values for the tested fuel samples.
Figure 5. ID parameter values for the tested fuel samples.
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Figure 6. CD parameter values for the tested fuel samples.
Figure 6. CD parameter values for the tested fuel samples.
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Figure 7. APRR parameter values for the tested fuel samples.
Figure 7. APRR parameter values for the tested fuel samples.
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Figure 8. MPRR parameter values for the tested fuel samples.
Figure 8. MPRR parameter values for the tested fuel samples.
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Figure 9. MPR parameter values for the tested fuel samples.
Figure 9. MPR parameter values for the tested fuel samples.
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Figure 10. DCN values for the tested fuel samples.
Figure 10. DCN values for the tested fuel samples.
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Table 1. Diesel fuel parameters.
Table 1. Diesel fuel parameters.
ParameterUnitValue
FAME% (v/v)6.4
DCN-51.6
Cetane index-53.5
IBP°C169.0
T10°C202.9
T50°C274.8
T90°C339.8
E250% (v/v)35.0
E350% (v/v)94.0
FBP°C359.2
Kinematic viscosity at 40 °Cmm2/s2.7
Dynamic viscosity at 40 °CcP2.6
Density at 15 °Cg/cm30.834
2-EHNppm (m/m) 0.0
Mono Aromatics% (m/m)17.6
Di Aromatics% (m/m)2.3
Tri+ Aromatics% (m/m)0.2
Total Aromatics% (m/m)20.1
Polycyclic Aromatics% (m/m)2.5
Table 2. Fuel sample symbols.
Table 2. Fuel sample symbols.
Symbols of Fuel SamplesFraction, % (by Volume)Fraction, ppm (by Mass)
Diesel Fuel1-Butanol2-EHN
DFBu0-010000
DFBu30-070300
DFBu30-570305000
DFBu30-10703010,000
DFBu30-20703020,000
DFBu30-25703025,000
DFBu30-30703030,000
Table 3. Calibration setting of testing device.
Table 3. Calibration setting of testing device.
Calibration ParameterSettingTolerance
tch588.0 °C±0.2 °C
tco50 °C±2 °C
p02.00 MPa±0.02 MPa
pinj100.0 MPa±1.5 MPa
tinj2.5 msnot defined
Table 4. Average values of fuel injection parameters and measurement uncertainties recorded for Ta = 588 °C.
Table 4. Average values of fuel injection parameters and measurement uncertainties recorded for Ta = 588 °C.
Symbols of Fuel
Samples		tinj,
ms		pinj,
MPa		p0,
MPa		tch (Ta),
°C		ϕID,
ms		ϕCD,
ms		ϕDCNϕMPR, MPaϕAPRR,
MPa/ms		ϕMPRR, MPa/ms
DFBu0-02.599.42.00587.60.02260.02540.30.0030.02340.1515
DFBu30-02.599.62.00587.50.04750.09670.20.0060.00440.0287
DFBu30-52.598.92.00587.70.01180.03070.10.0050.01070.1506
DFBu30-102.599.62.00587.70.02390.02390.10.0050.00770.0771
DFBu30-202.599.02.00588.80.01360.02260.20.0060.04080.1579
DFBu30-252.599.12.00588.70.02280.02240.20.0040.01020.1175
DFBu30-302.5100.52.00588.80.03330.03680.40.0020.01600.1580
Table 5. Average values of fuel injection parameters and measurement uncertainties recorded for Ta = 648 °C.
Table 5. Average values of fuel injection parameters and measurement uncertainties recorded for Ta = 648 °C.
Symbols of Fuel
Samples		tinj,
ms		pinj,
MPa		p0,
MPa		tch (Ta),
°C		ϕID,
ms		ϕCD,
ms		ϕMPR, MPaϕAPRR,
MPa/ms		ϕMPRR, MPa/ms
DFBu0-02.5100.22.00648.30.01210.01360.0010.02560.2302
DFBu30-02.5100.02.00648.20.02800.04480.0040.02230.1425
DFBu30-52.599.21.99648.40.01440.02540.0030.05400.1631
DFBu30-102.599.92.00648.30.01580.04130.0030.03230.1701
DFBu30-202.5100.02.00648.30.01190.01630.0020.01960.0857
DFBu30-252.5100.22.00648.30.02130.02660.0040.02060.1126
DFBu30-302.599.92.00648.40.01880.03340.0020.02010.1091
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Kuszewski, H.; Jaworski, A. Investigating the Effect of 2-Ethylhexyl Nitrate Cetane Improver (2-EHN) on the Autoignition Characteristics of a 1-Butanol–Diesel Blend. Energies 2024, 17, 4085. https://doi.org/10.3390/en17164085

AMA Style

Kuszewski H, Jaworski A. Investigating the Effect of 2-Ethylhexyl Nitrate Cetane Improver (2-EHN) on the Autoignition Characteristics of a 1-Butanol–Diesel Blend. Energies. 2024; 17(16):4085. https://doi.org/10.3390/en17164085

Chicago/Turabian Style

Kuszewski, Hubert, and Artur Jaworski. 2024. "Investigating the Effect of 2-Ethylhexyl Nitrate Cetane Improver (2-EHN) on the Autoignition Characteristics of a 1-Butanol–Diesel Blend" Energies 17, no. 16: 4085. https://doi.org/10.3390/en17164085

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