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This work investigates the effects of ambient conditions on diesel spray combustion in an optically accessible, constant volume chamber using a single-nozzle fuel injector. The ambient O2 concentration was varied between five discrete values from 10% to 21% and three different ambient temperatures (800 K, 1000 K, and 1200 K). These conditions simul...
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Context 1
... order to avoid signal saturation and make full use of the dynamic range of the cameras, neutral density (ND) filters were used for certain conditions. The configuration of the filters is summarized in Tables 3 and 4. The image intensity was corrected based on the optical thickness (D) of the ND filters listed in Table 4. ...
Context 2
... configuration of the filters is summarized in Tables 3 and 4. The image intensity was corrected based on the optical thickness (D) of the ND filters listed in Table 4. The relation between intensity and D is given in Tables 3 and 4. Therefore, the intensity of each spectral region can be compared for all the conditions. ...
Context 3
... the ambient gas to fuel density ratio, d is the diameter of injector nozzle in mm, g þ is a characteristic length scale for the jet, h is the jet spreading angle, g is the axial dis- tance normalized by the nozzle diameter d, C a is the nozzle area-contraction coef- ficient, which is assumed to have a value of 0.86, and the spreading angle constant c is assumed to have a value of 0.265. Both C a and c are based on the interpolation from Table 3 in Siebers (1999) and Pickett et al. (2006), the value of Ca comes from the measurements in Siebers (1999), and the range of Ca is from 0.79 to 0.94 for dif- ferent injection pressures and nozzle diameters. The interpolated value for our appli- cation with an injection pressure of 100 MPa and a nozzle diameter of 150 micrometers is 0.86. ...
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Citations
... It also appears that the ambient temperature and injection pressure do not have a significant impact on both the flame length and height. In previous studies a clear correlation was noted with an increase in ambient temperature correlating to a reduced flame length and height [64]. This relationship indicates that the combustion occurring 6 ms aSOI for the longer wall case is enhanced compared to the reduced wall distance. ...
There is a growing focus on reducing global greenhouse gas emissions. The transportation sector is a significant contributor to these emissions, requiring significant work to reduce its environmental impact. The incorporation of hydrogen using innovative direct-injection technologies into internal combustion engines presents an opportunity to drastically reduce greenhouse gas emissions. This thesis seeks to further the understanding of the hydrogen combustion occurring in direct-injection compression ignition conditions. Specifically, this thesis examines the flame-wall interaction between a high-pressure hydrogen jet and a plane-wall in a simulated compression ignition environment utilising an optically accessible constant volume combustion chamber. The impact of varying the injection pressure (84-140 bar), ambient temperature (985-1145 K) and wall distance (25-45 mm) on the flame-wall interaction is investigated. Measurements are completed utilising a high-speed schlieren setup in conjunction with an ICCD camera to capture the time-averaged spatial distribution of the OH* chemiluminescence during the last millisecond of hydrogen injection. The results indicate that hydrogen is extremely sensitive to the cooling effect arising from the interaction with the wall. This was apparent in the trend of the ignition delay, which is significantly longer than the equivalent free jet case when the extent of the wall interaction was increased. Further, the flame propagation behaviour was also characterised from the captured schlieren images, with significantly varied flame propagation behaviours exhibited based upon the location of the ignition kernel. Increased injection pressure, and similarly reduced ambient temperature resulted in an increased tendency for ignition to initiate in the near-wall region. The OH* chemiluminescence suggests that the wall distance influences the intensity of the quasi-steady reaction most significantly. These findings have significant implications for the further development of the direct-injection compression ignition hydrogen internal combustion engines and optimisation of their thermal efficiency.
... location of high temperature chemical reactions) [4]. Exhaust gas recirculation to achieve low-emissions and low temperature combustion, also leads to reduced O 2 concentration that can significantly increase lift-off length [5]. At the same time, with downsizing trends of engines [6] particularly in the automotive market, the wall is now closer to the injector. ...
... As is noted in previous studies [14], at lower ambient O 2 condition, an increased entrainment of ambient gases into the flame would need to occur to compensate for the reduced O 2 concentration. This can lead to the heating up of more inert gases within the flame during combustion, and hence, the lowering of the overall flame temperature and reaction rate [31,14,5]. All these would combine to result in the observed prolonging of the combustion period of the flames under the more diluted 10 vol% ambient O 2 condition. ...
This work aims to assess the effects of flame-wall impingement on the combustion and soot processes of diesel flames. For this work, experimental measurements were performed in a constant-volume combustion chamber (CVCC) at ambient conditions that are representative of compression-ignition engines. The characteristics of impinging and free flames were compared at two identical ambient and injector conditions (20.8 kg/m3 ambient density, 6 MPa ambient pressure, 1000 K bulk temperature, 15 and 10 vol% ambient O2 concentration, and 100 MPa injection pressure). To simulate flame-wall impingement, a flat plane steel wall, normal to the injector axis, was initially placed at 53 mm from nozzle, but was varied from 53 to 35 mm during the experiments. Under the test conditions of this work, it was found that wall impingement resulted in lower soot temperature and soot content, in addition to a loss of momentum for the wall jet. The results also revealed that decreasing impingement distance from the nozzle resulted in reduced soot temperature and soot level for the wall jet. The reduced soot content observed for the wall jet appeared to be mainly driven by enhanced mixing. Flame transparency modeling was also performed to assess the uncertainties of two-color measurements for flame-plane wall impingement. The analysis indicated that the derived soot temperature and concentration values would be affected by the actual temperature profiles, rendering the technique useful to reveal trends, but not reliable for absolute soot concentration measurements.
... For both the average soot temperature and KL factor plots, it can be seen that the time that is taken for the flames to reach their maximum quasi-steady values increases with decreasing ambient O 2 concentration. Similarly, the combustion periods of the flames are also observed to increase with decreasing O 2 level, which is to be expected, as more mixing would be required for complete combustion to occur under diluted conditions [49]. It is noted, however, that the combustion duration of the diesel flame is similar to that of the biodiesel flames for the 21 vol.% ...
Alternative fuels will come from a variety of feed stocks and refinement processes. Understanding the fundamentals of combustion and pollutants formation processes of these fuels will be useful for their implementation in different combustion systems. In this work, optical diagnostics were performed to waste cooking oil (WCO) and canola oil (CAO) based biodiesel sprays to assess their combustion and soot formation processes. Conventional diesel was used as a reference fuel for comparison with the biodiesels. The experiments were conducted in an optically-accessible constant-volume combustion chamber (CVCC) with simulated compression-ignition engine conditions, with different degree of exhaust gas recirculation. The liquid length and lift-off length results indicate that there was no significant interaction between the liquid phases of the fuels and their combustion regions. The flame lift-off lengths were found to be affected by both the chemical and physical properties of the fuels. It was observed that a larger difference between the lift-off length and the first-luminosity distance was correlated with lesser downstream soot formation, although the molecular structure of the fuel was found to affect the process too. Assessing the sooting and combustion characteristics of the biodiesel and diesel flames across the varied ambient O2 atmospheres revealed that the estimated soot contents of the biodiesel and diesel flames peaked at 15 and 21 vol.% O2 concentration, respectively. The peak soot contents of the WCO and CAO biodiesel flames were found be comparable, but lower than that of diesel, across the various O2 environment. The results also demonstrated that the biodiesels have higher normalized peak pressure values than diesel at all O2 conditions. Two-color pyrometry data demonstrated that the measured soot temperature and soot KL factors of the flames were similar at 15 and 21 vol.% O2, but varied with further reduction of ambient O2 concentration. Variations in the combustion duration and flame area were found to be fuel dependent.
... Experiments were conducted in an optically accessible constant-volume combustion chamber via a quartz window under diesel-like conditions. Details about the combustion chamber, the fuel injector and injection parameters can be found in previous publications [37,38]. The experimental setup for the two-color pyrometry is shown in Fig. 1. ...
Soot formation process was investigated for biomass-based renewable diesel fuel, such as biomass to liquid (BTL), and conventional diesel combustion under varied fuel quantities injected into a constant volume combustion chamber. Soot measurement was implemented by two-color pyrometry under quiescent type diesel engine conditions (1000 K and 21% O2 concentration). Different fuel quantities, which correspond to different injection widths from 0.5 ms to 2 ms under constant injection pressure (1000 bar), were used to simulate different loads in engines. For a given fuel, soot temperature and KL factor show a different trend at initial stage for different fuel quantities, where a higher soot temperature can be found in a small fuel quantity case but a higher KL factor is observed in a large fuel quantity case generally. Another difference occurs at the end of combustion due to the termination of fuel injection. Additionally, BTL flame has a lower soot temperature, especially under a larger fuel quantity (2 ms injection width). Meanwhile, average soot level is lower for BTL flame, especially under a lower fuel quantity (0.5 ms injection width). BTL shows an overall low sooting behavior with low soot temperature compared to diesel, however, trade-off between soot level and soot temperature needs to be carefully selected when different loads are used.
... The lift-off length is a characteristic parameter describing the location of high-temperature reactions. In this study, the method used to calculate the lift-off length is similar to that used by Higgins and Siebers [2] and Jing et al. [36]. Two lines are selected along the nozzle axis, one is a pixel above the nozzle axis and the other is one pixel below the nozzle axis. ...
... In order to find a fundamental basis to explain the difference of the flame structure between dieseline and diesel, some theoretical derivations and analyses are presented. The reaction of a pure hydrocarbon fuel with air dilution can be simplified based on the discussion in [36,37], as shown in Eq. (1): ...
... The constant c in Eq. (4) is an empirical coefficient used to describe the spray spread angle in [37]. Jing et al. [36] used a value of 0.265 for diesel with the same injector and injection pressure employed in this study. Since dieseline has lower density, lower viscosity and lower boiling point than diesel, the value of c for dieseline should be larger than diesel. ...
h i g h l i g h t s Spray combustion of diesel-gasoline blend was tested in constant volume combustion chamber. Multiband flame emission was measured for different ambient conditions. Flames of the two fuels become shorter, thinner and stronger with increased ambient oxygen concentration and temperature. Experimental observations were analyzed by an empirical model. a b s t r a c t In this paper, spray combustion of diesel (No. 2) and diesel-gasoline blend (dieseline: 80% diesel and 20% gasoline by volume) were investigated in an optically accessible constant volume combustion chamber. Effects of ambient conditions on flame emissions were studied. Ambient oxygen concentration was varied from 12% to 21% and three ambient temperatures were selected: 800 K, 1000 K and 1200 K. An intensified CCD camera coupled with bandpass filters was employed to capture the quasi-steady state flame emissions at 430 nm and 470 nm bands. Under non-sooting conditions, the narrow-band flame emissions at 430 nm and 470 nm can be used as indicators of CH ⁄ (methylidyne) and HCHO ⁄ (formaldehyde), respectively. The lift-off length was measured by imaging the OH ⁄ chemiluminescence at 310 nm. Flame emission structure and intensity distribution were compared between dieseline and diesel at wavelength bands. Flame emission images show that both narrow band emissions become shorter, thinner and stronger with higher oxygen concentration and higher ambient temperature for both fuels. Areas of weak intensity are observed at the flame periphery and the upstream for both fuels under all ambient conditions. Average flame emission intensity and area were calculated for 430 nm and 470 nm narrow-band emissions. At a lower ambient temperature the average intensity increases with increasing ambient oxygen concentration. However, at the 1200 K ambient temperature condition, the average intensity is not increasing monotonically for both fuels. For most of the conditions, diesel has a stronger average flame emission intensity than dieseline for the 430 nm band, and similar phenomena can be observed for the 470 nm band with 800 K and 1200 K ambient temperatures. However, for the 1000 K ambient temperature cases, dieseline has stronger average flame emission intensities than diesel for all oxygen concentrations at 470 nm band. Flame emissions for the two bands have a smaller average emission area under higher ambient oxygen concentration and temperature for both fuels, while dieseline has a slightly larger average flame emission area than diesel for most cases. The experimental findings were further analyzed and discussed based on an empirical model of the distributions of air and fuel. Both experiment results and theoretical model show that dieseline has wider 430 nm and 470 nm band emissions than diesel under all conditions.
... Experiments were conducted in an optically accessible constant-volume combustion chamber via a quartz window under diesel-like conditions. Details about the combustion chamber, the fuel injector and injection parameters can be found in previous publications [37,38]. The experimental setup for the two-color pyrometry is shown in Fig. 1. ...
Soot formation process was investigated for biomass-based renewable diesel fuel, such as biomass to liquid (BTL), and conventional diesel combustion under varied fuel quantities injected into a constant volume combustion chamber. Soot measurement was implemented by two-color pyrometry under quiescent type diesel engine conditions (1000 K and 21% O2 concentration). Different fuel quantities, which correspond to different injection widths from 0.5 ms to 2 ms under constant injection pressure (1000 bar), were used to simulate different loads in engines. For a given fuel, soot temperature and KL factor show a different trend at initial stage for different fuel quantities, where a higher soot temperature can be found in a small fuel quantity case but a higher KL factor is observed in a large fuel quantity case generally. Another difference occurs at the end of combustion due to the termination of fuel injection. Additionally, BTL flame has a lower soot temperature, especially under a larger fuel quantity (2 ms injection width). Meanwhile, average soot level is lower for BTL flame, especially under a lower fuel quantity (0.5 ms injection width). BTL shows an overall low sooting behavior with low soot temperature compared to diesel, however, trade-off between soot level and soot temperature needs to be carefully selected when different loads are used.
... A single-hole injector was used with a nozzle diameter of 150 lm. Details about the combustion chamber can be found in previous publications [59,60]. The experimental setup for the multi-band emission measurement and two-color pyrometry is shown in Fig. 1. ...
Effect of a two-injection strategy associated with a pilot injection on the spray combustion process was investigated under conventional diesel combustion conditions (1000 K and 21% O2 concentration) for a biomass-based renewable diesel fuel, i.e., biomass to liquid (BTL), and a regular No. 2 diesel in a constant volume combustion chamber using multiband flame measurement and two-color pyrometry. The spray combustion flame structure was visualized by using multiband flame measurement to show features of soot formation, high temperature and low temperature reactions, which can be characterized by the narrow-band emissions of radicals or intermediate species such as OH, HCHO, and CH. The objective of this study was to identify the details of multiple injection combustion, including a pilot and a main injection, and to provide further insights on how the two injections interact. For comparison, three injection strategies were considered for both fuels including a two-injection strategy (Case TI), single injection strategy A (Case SA), and single injection strategy B (Case SB). Multiband flame results show a strong interaction, indicated by OH∗ emissions between the pilot injection and the main injection for Case TI while very weak connection is found for the narrow-band emissions acquired through filters with centerlines of 430 nm and 470 nm. A faster flame development is found for the main injection of Case TI compared to Cases SA and SB, which could be due to the high temperature environment and large air entrainment from the pilot injection. A lower soot level is observed for the BTL flame compared to the diesel flame for all three injection types. Case TI has a lower soot level compared to Cases SA and SB for the BTL fuel, while the diesel fuel maintains a similar soot level among all three injection strategies. Soot temperature of Case TI is lower for both fuels, especially for diesel. Based on these results, it is expected that the two-injection strategy could be effective in reducing soot and NOx (due to lower combustion temperature) simultaneously compared to either of the single injection strategies.
... Experiments were conducted in a constant-volume combustion vessel with optical access via a quartz window under simulated, quiescent diesel combustion environments. Details about the combustion chamber can be found in previous publications [44,45]. The chamber configuration with a two-color pyrometry setup is shown in Fig. 1. ...
Soot concentration (KL factor) and soot temperature were measured in a constant volume combustion chamber for a new biomass-based biofuel or BTL (biomass to liquid) fuel and regular No.2 diesel. A high-speed camera was employed coupled with two bandpass filters to implement a two-color thermometry method and measure the soot concentration and temperature simultaneously. Ambient conditions were set as follows: three temperatures of 800 K, 1000 K, and 1200 K and four O2 concentrations of 10%, 15%, 18% and 21%. The soot KL factor and temperature spatial distributions are presented for 1000 K ambient temperature. More soot is seen in the near-wall regions under the low ambient oxygen conditions while high level soot is observed in the upstream and midstream for the conventional combustion mode. An analysis was then conducted for the quasi-steady state. The results show that BTL combustion generates a lower integrated KL factor and soot temperature compared to diesel fuel under all the experimental conditions. Additionally, low ambient temperature with a moderate O2 concentration benefits BTL more than diesel due to a larger reduction in the integrated KL factor without increasing soot temperature significantly. Finally, the characteristics of the two-color results were further discussed and analyzed.
... Simultaneous OH and formaldehyde laser induced fluorescence (LIF) measurements were performed in an HCCI engine with a port fuel injection system by Collin et al. [15] and they found that the formaldehyde signal was constant until the main heat-release started, and OH was formed in the areas where the formaldehyde signal disappeared. OH radicals were shown to be effective in oxidizing the soot in the downstream region of a diesel spray combustion plume [16]. The concepts of conventional and low-temperature spray combustion were discussed and compared by Musculus et al. [17]. ...
... During the low-temperature combustion modes with little soot, however, Band A and Band B can show the activities of these two radicals. A comparison was then performed for the current Jet-A results with our previous No. 2 diesel results [16,27,28]. ...
... The chamber volume is 0.95 L. More details are available in our previous publications [47,52,53]. The view of injector from the window side is shown in Fig. 3. Six holes of the injector are located symmetrically around the injector tip. ...
This paper presents the soot temperature and KL factor for biodiesel, namely fatty acid methyl ester (FAME) and diesel fuel combustion in a constant volume chamber using a two-color technique. The KL factor is a parameter for soot concentration, where K is an absorption coefficient and proportional to the number density of soot particles, L is the geometric thickness of the flame along the optical detection axis, and KL factor is proportional to soot volume fraction. The main objective is to explore a combustion regime called high-temperature and highly-diluted combustion (HTHDC) and compare it with the conventional and low-temperature combustion (LTC) modes. The three different combustion regimes are implemented under different ambient temperatures (800 K, 1000 K, and 1400 K) and ambient oxygen concentrations (10%, 15%, and 21%). Results are presented in terms of soot temperature and KL factor images, time-resolved pixel-averaged soot temperature, KL factor, and spatially integrated KL factor over the soot area. The time-averaged results for these three regimes are compared for both diesel and biodiesel fuels. Results show complex combined effects of the ambient temperature and oxygen concentration, and that two-color temperature for the HTHDC mode at the 10% oxygen level can actually be lower than the conventional mode. Increasing ambient oxygen and temperature increases soot temperature. Diesel fuel results in higher soot temperature than biodiesel for all three regimes. Results also show that diesel and biodiesel fuels have very different burning and sooting behavior under the three different combustion regimes. For diesel fuel, the HTHDC regime offers better results in terms of lower soot than the conventional and LTC regimes, and the 10% O2, 1400 K ambient condition shows the lowest soot concentration while maintaining a moderate two-color temperature. For biodiesel, the 15% O2, 800 K ambient condition shows some advantages in terms of reducing soot concentration. Based on these results, the practical implementation of this combustion mode is outlined and a feasible option is proposed.
