@article{jing_wu_roberts_fang_2017, title={Effects of Fuel Quantity on Soot Formation Process for Biomass-Based Renewable Diesel Fuel Combustion}, volume={139}, ISSN={["1528-8919"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85020430438&partnerID=MN8TOARS}, DOI={10.1115/1.4036292}, abstractNote={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.}, number={10}, journal={JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME}, author={Jing, Wei and Wu, Zengyang and Roberts, William L. and Fang, Tiegang}, year={2017}, month={Oct} }
 @inproceedings{jing_wu_roberts_fang_2016, title={Effects of fuel quantity on soot formation process for biomass-based renewable diesel fuel combustion}, DOI={10.1115/icef2016-9380}, abstractNote={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.}, booktitle={Proceedings of the ASME Internal Combustion Engine Division Fall Technical Conference (ICEF)}, author={Jing, W. and Wu, Z. Y. and Roberts, W. L. and Fang, Tiegang}, year={2016} }
 @article{wu_jing_zhang_roberts_fang_2016, title={Narrow band flame emission from dieseline and diesel spray combustion in a constant volume combustion chamber}, volume={185}, ISSN={["1873-7153"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84982090895&partnerID=MN8TOARS}, DOI={10.1016/j.fuel.2016.08.022}, abstractNote={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.}, journal={FUEL}, author={Wu, Zengyang and Jing, Wei and Zhang, Weibo and Roberts, William L. and Fang, Tiegang}, year={2016}, month={Dec}, pages={829–846} }
 @article{jing_wu_roberts_fang_2016, title={Spray combustion of biomass-based renewable diesel fuel using multiple injection strategy in a constant volume combustion chamber}, volume={181}, ISSN={["1873-7153"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84969269086&partnerID=MN8TOARS}, DOI={10.1016/j.fuel.2016.05.039}, abstractNote={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.}, journal={FUEL}, author={Jing, Wei and Wu, Zengyang and Roberts, William L. and Fang, Tiegang}, year={2016}, month={Oct}, pages={718–728} }
 @article{zhang_jing_roberts_fang_2015, title={Effects of Ambient Oxygen Concentration on Soot Temperature and Concentration for Biodiesel and Diesel Spray Combustion}, volume={141}, ISSN={["1943-7897"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84929628830&partnerID=MN8TOARS}, DOI={10.1061/(asce)ey.1943-7897.0000214}, abstractNote={AbstractAmbient oxygen concentration, a key variable directly related to exhaust gas recirculation (EGR) levels in diesel engines, plays a significant role in particulate matter (PM) and nitrogen oxides (NOx) emissions. The utilization of biodiesel in diesel engines has been investigated over the last decades for its renewable characteristics and lower emissions compared to diesel. In an earlier work, we demonstrated that the soot temperature and concentration of biodiesel were lower than diesel under regular diesel engine conditions without EGR. Soot concentration was quantified by a parameter called KL factor. As a continuous effort, this paper presents an experimental investigation of the ambient oxygen concentration on soot temperature and KL factor during biodiesel and diesel spray combustion. The experiment was implemented in a constant volume chamber system, where the ambient oxygen concentration varied from 21 to 10% and the ambient temperature was kept to 1,000 K. A high speed two-color pyrometry...}, number={2}, journal={JOURNAL OF ENERGY ENGINEERING}, author={Zhang, Ji and Jing, Wei and Roberts, William L. and Fang, Tiegang}, year={2015}, month={Jun} }
 @article{jing_wu_zhang_fang_2015, title={Measurements of soot temperature and KL factor for spray combustion of biomass derived renewable fuels}, volume={91}, ISSN={["1873-6785"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84946083894&partnerID=MN8TOARS}, DOI={10.1016/j.energy.2015.08.069}, abstractNote={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.}, journal={ENERGY}, author={Jing, Wei and Wu, Zengyang and Zhang, Weibo and Fang, Tiegang}, year={2015}, month={Nov}, pages={758–771} }
 @article{jing_roberts_fang_2015, title={Spray combustion of Jet-A and diesel fuels in a constant volume combustion chamber}, volume={89}, ISSN={["1879-2227"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84908374137&partnerID=MN8TOARS}, DOI={10.1016/j.enconman.2014.10.010}, abstractNote={This work investigates the spray combustion of Jet-A fuel in an optical constant-volume combustion chamber under different ambient initial conditions. Ambient temperature was varied at 800 K, 1000 K, and 1200 K and five different ambient O2 concentrations were used, spanning 10–21%. These ambient conditions can be used to mimic practical diesel engine working conditions under different fuel injection timings and exhaust gas recirculation (EGR) levels. Both transient and quasi-steady state analyses were conducted. The transient analysis focused on the flame development from the beginning to the end of the combustion process, illustrating how the flame structure evolves with time. The quasi-steady state analysis concentrated on the stable flame structure and compared the flame emissions in terms of spatially integrated intensity, flame effective area, and intensity per pixel. The transient analysis was based on measurements using high-speed imaging of both OH∗ chemiluminescence and broadband natural luminosity (NL). For the quasi-steady state analysis, three flame narrow-band emissions (OH∗ at 310 nm, Band A at 430 nm and Band B at 470 nm) were captured using an ICCD camera. Based on the current Jet-A data and diesel data obtained from previous experiments, a comparison between Jet-A and diesel was made in terms of flame development during the transient state and spatially integrated intensity, flame effective area, and intensity per pixel during the quasi-steady state. For the transient results, Jet-A shares a similar flame development trend to diesel, but featuring a narrower region of NL and a wider region of OH∗ with the increase of ambient temperature and O2 concentration. The soot cloud is oxidized more quickly for Jet-A than diesel at the end of combustion, evident by comparing the area of NL, especially under high O2 concentration. The quasi-steady state results suggest that soot is oxidized effectively under high O2 concentration conditions by the wider region of OH∗ in the downstream locations where only OH∗ emission is observed. The intensity of OH∗ is higher for Jet-A than diesel under low O2 concentration but lower under high O2 concentration. The intensity of NL is higher for Jet-A for all the conditions investigated. However, the intensities of Band A and Band B are lower for Jet-A for all these conditions. Based on the imaging of multiple-band flame emissions, the spray flame structures were further analyzed for the two fuels under both low temperature and conventional combustion modes. Conceptual flame structures were proposed to complement the previous conceptual models for spray combustion under different combustion modes.}, journal={ENERGY CONVERSION AND MANAGEMENT}, author={Jing, Wei and Roberts, William L. and Fang, Tiegang}, year={2015}, month={Jan}, pages={525–540} }
 @article{fang_jing_2014, title={Flow, heat, and species transfer over a stretching plate considering coupled Stefan blowing effects from species transfer}, volume={19}, ISSN={["1878-7274"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84897073047&partnerID=MN8TOARS}, DOI={10.1016/j.cnsns.2014.02.009}, abstractNote={In this paper, we investigate the flow, heat and mass transfer of a viscous fluid flow over a stretching sheet by including the blowing effects of mass transfer under high flux conditions. Mass transfer in this work means species transfer and is different from mass transpiration for permeable walls. The new contribution from this work is, for the first time, to consider the coupled blowing effects from massive species transfer on flow, heat, and species transfer for a stretching plate. Based on the exact solutions of the momentum equations, which are valid for the whole Navier–Stokes equations, the energy and mass transfer equations are solved exactly and the effects of the blowing parameter, the Schmidt number, and the Prandtl number on the flow, heat and mass transfer are presented and discussed. The solution is given in terms of an incomplete Gamma function. It is found the coupled blowing effects due to mass transfer can have significant influences on velocity profiles, drag, heat flux, as well as temperature and concentration profiles. These solutions provide rare results with closed form analytical expressions and can be used as benchmark problem for numerical code validation.}, number={9}, journal={COMMUNICATIONS IN NONLINEAR SCIENCE AND NUMERICAL SIMULATION}, author={Fang, Tiegang and Jing, Wei}, year={2014}, month={Sep}, pages={3086–3097} }
 @article{zhang_jing_roberts_fang_2014, title={Soot measurements for diesel and biodiesel spray combustion under high temperature highly diluted ambient conditions}, volume={135}, ISSN={["1873-7153"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84904957615&partnerID=MN8TOARS}, DOI={10.1016/j.fuel.2014.06.071}, abstractNote={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.}, journal={FUEL}, author={Zhang, Ji and Jing, Wei and Roberts, William L. and Fang, Tiegang}, year={2014}, month={Nov}, pages={340–351} }
 @article{fang_jing_2013, title={Closed-form analytical solutions of flow and heat transfer for an unsteady rear stagnation-point flow}, volume={62}, ISSN={["0017-9310"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84875443267&partnerID=MN8TOARS}, DOI={10.1016/j.ijheatmasstransfer.2013.02.049}, abstractNote={In this paper, flow and heat transfer characteristics of an unsteady rear stagnation-point flow over a moving wall with transpiration are studied. The flow solution is an exact solution to the unsteady Navier–Stokes equations. By ignoring the viscous dissipation terms, analytical solutions of the boundary layer energy equation are obtained for the cases with a constant wall temperature and a prescribed time-dependent wall heat flux. The effects of the controlling parameters on the solution domain, the velocity distribution and the temperature distribution in the fluids are analyzed. With certain given values of the controlling parameters, two solution branches are found for both the flow and the heat transfer problems. These closed-form solutions are rare and can be used as a benchmark problem for numerical code validation.}, number={1}, journal={INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, author={Fang, Tiegang and Jing, Wei}, year={2013}, month={Jul}, pages={55–62} }
 @article{jing_roberts_fang_2013, title={Effects of Ambient Temperature and Oxygen Concentration on Diesel Spray Combustion Using a Single-Nozzle Injector in a Constant Volume Combustion Chamber}, volume={185}, ISSN={["0010-2202"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84882388541&partnerID=MN8TOARS}, DOI={10.1080/00102202.2013.798315}, abstractNote={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 simulate different exhaust gas recirculation (EGR) levels and ambient temperatures in diesel engines. Both conventional diesel combustion and low temperature combustion (LTC) modes were observed under these conditions. A transient analysis and a quasi-steady state analysis are employed in this article. The transient analysis focuses on the flame development from beginning to the end, illustrating how the flame structure changes during this process; the quasi-steady state analysis focuses on the stable flame structure. The transient analysis was conducted using high-speed imaging of both OH* chemiluminescence and natural luminosity (NL). In addition, three different images were acquired using an ICCD camera, corresponding to OH* chemiluminescence, narrow-band flame emission at 430 nm (Band A) and at 470 nm (Band B), and were used to investigate the quasi-steady state combustion process. From the transient analysis, it was found that the NL signal becomes stronger and confined to narrow regions when the temperature and O2 concentration increase during the development of flame. The OH* intensity is much lower for the 10% ambient O2 and 800 K conditions compared to the higher temperatures and O2 levels. This implies the occurrence of LTC under these conditions. Results from the quasi-steady combustion stage indicate that high-temperature reactions effectively oxidize the soot in the downstream locations where only OH* signal is observed. In addition, an area was calculated for each spectral region, and results show that the area of Band A and Band B emissions in these images is larger than the area of OH* emissions at the lower O2 concentrations while the area of OH* emission is larger than the area of Band A and Band B emissions at higher O2 concentrations, for a given ambient temperature. Moreover, the mixture stoichiometry was analyzed using a reformulated definition of excess air ratio for diluted combustion, and this shows that more mixing is required to achieve complete combustion for low ambient oxygen concentration conditions where longer and wider flames are observed. This observation is also verified by the flame length estimated from the NL images.}, number={9}, journal={COMBUSTION SCIENCE AND TECHNOLOGY}, author={Jing, Wei and Roberts, William L. and Fang, Tiegang}, year={2013}, month={Sep}, pages={1378–1399} }
 @article{zhang_jing_roberts_fang_2013, title={Effects of ambient oxygen concentration on biodiesel and diesel spray combustion under simulated engine conditions}, volume={57}, ISSN={["1873-6785"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84880702414&partnerID=MN8TOARS}, DOI={10.1016/j.energy.2013.05.063}, abstractNote={This study investigates the effect of ambient oxygen concentration on biodiesel and diesel spray combustion under simulated compression-ignition engine conditions in a constant-volume chamber. The apparent heat release rate (AHRR) is calculated based on the measured pressure. High-speed imaging of OH* chemiluminescence and natural luminosity (NL) is employed to visualize the combustion process. Temporally and spatially resolved NL and OH* contour plots are obtained. The result indicates that AHRR depends monotonically on the ambient oxygen concentration for both fuels. A lower oxygen concentration yields a slower AHRR increase rate, a lower peak AHRR value, but a higher AHRR value during the burn-out stage when compared with higher ambient oxygen concentration conditions. OH* chemiluminescence and NL contours indicate that biodiesel may experience a longer premixed-combustion duration. The 18% ambient O2 condition works better for biodiesel than diesel in reducing soot luminosity. With 12% O2, diesel combustion is significantly degraded. However, both fuels experience low temperature combustion at 10% O2. These results may imply that biodiesel is able to achieve the desired lower soot production under a moderate oxygen level with higher combustion efficiency, while diesel needs to be burned under very low ambient oxygen concentration for low soot production.}, journal={ENERGY}, author={Zhang, Ji and Jing, Wei and Roberts, William L. and Fang, Tiegang}, year={2013}, month={Aug}, pages={722–732} }
 @article{jing_fang_2013, title={Note on a New Blackbody Fraction Function Used for Surfaces With a Linear Emissivity in a Wavelength Interval}, volume={135}, ISSN={["1528-8943"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84877622228&partnerID=MN8TOARS}, DOI={10.1115/1.4023393}, abstractNote={In this note, a new blackbody radiation fraction function is proposed for calculating the emissive power or total emissivity of a surface that has an emissivity depending linearly on wavelength in a wavelength interval. This new fraction function is expressed as a function of the product of wavelength and temperature and the numerical values are tabulated. Based on the new defined fraction function, the emissive power in a given wavelength interval can be calculated very conveniently combined with the traditional blackbody radiation fraction function. This new function can be used in many practical applications with good accuracy without numerical integration.}, number={5}, journal={JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME}, author={Jing, Wei and Fang, Tiegang}, year={2013}, month={May} }
 @article{zhang_jing_roberts_fang_2013, title={Soot temperature and KL factor for biodiesel and diesel spray combustion in a constant volume combustion chamber}, volume={107}, ISSN={["1872-9118"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84875117595&partnerID=MN8TOARS}, DOI={10.1016/j.apenergy.2013.02.023}, abstractNote={This paper presents measurements of the soot temperature and KL factor for biodiesel and diesel combustion in a constant volume chamber using a two-color technique. This technique uses a high-speed camera coupled with two narrowband filters (550 nm and 650 nm, 10 nm FWHM). After calibration, statistical analysis shows that the uncertainty of the two-color temperature is less than 5%, while it is about 50% for the KL factor. This technique is then applied to the spray combustion of biodiesel and diesel fuels under an ambient oxygen concentration of 21% and ambient temperatures of 800, 1000 and 1200 K. The heat release result shows higher energy utilization efficiency for biodiesel compared to diesel under all conditions; meanwhile, diesel shows a higher pressure increase due to its higher heating value. Biodiesel yields a lower temperature inside the flame area, a longer soot lift-off length, and a smaller soot area compared to diesel. Both the KL factor and the total soot with biodiesel are lower than with diesel throughout the entire combustion process, and this difference becomes larger as the ambient temperature decreases. Biodiesel shows approximately 50–100 K lower temperatures than diesel at the quasi-steady stage for 1000 and 1200 K ambient temperature, while diesel shows a lower temperature than biodiesel at 800 K ambient. This result may raise the question of how important the flame temperature is in explaining the higher NOx emissions often observed during biodiesel combustion. Other factors may also play an important role in controlling NOx emissions. Both biodiesel and diesel temperature measurements show a monotonic dependence on the ambient temperature. However, the ambient temperature appears to have a more significant effect on the soot formation and oxidation in diesel combustion, while biodiesel combustion soot characteristics shows relative insensitivity to the ambient temperature.}, journal={APPLIED ENERGY}, author={Zhang, Ji and Jing, Wei and Roberts, William L. and Fang, Tiegang}, year={2013}, month={Jul}, pages={52–65} }
 @article{zhang_jing_fang_2012, title={High speed imaging of OH* chemiluminescence and natural luminosity of low temperature diesel spray combustion}, volume={99}, ISSN={["1873-7153"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84862163802&partnerID=MN8TOARS}, DOI={10.1016/j.fuel.2012.04.031}, abstractNote={This study focused on spray combustion of ultra low sulfur diesel (ULSD) fuel under low oxygen conditions with low temperature combustion (LTC) mode in an optically accessible constant volume combustion chamber. The ambient oxygen concentration was configured as 10% and 15% to achieve low flame temperature. The ambient gas temperature varied from 800 K to 1200 K. High speed imaging of OH* chemiluminescence and natural luminosity (NL) was used to visualize the instantaneous spray combustion process. The heat release rate was analyzed using the transient combustion pressure and the flame structure was studied based on the combustion images. Results show that a higher oxygen concentration case features a shorter ignition delay and higher heat release rate. The LTC mode can be realized by decreasing the oxygen concentration and ambient temperature simultaneously and it features a longer ignition delay, a slower reaction rate, and apparently lower soot radiation heat loss. The visualization results of NL and OH* show that the high temperature reaction occurs mainly in the mid-stream and downstream of the spray combustion, but not in the region very close to the chamber wall. This study validates the LTC process by showing very weak OH* chemiluminescence signal. The results also indicate that in order to realize LTC mode, it is important to control the ambient oxygen and ambient temperature at the same time. By only reducing the ambient oxygen concentration it may not be effective to suppress soot generation.}, journal={FUEL}, author={Zhang, Ji and Jing, Wei and Fang, Tiegang}, year={2012}, month={Sep}, pages={226–234} }