@article{wang_wu_badra_roberts_fang_2020, title={Soot characteristics of high-reactivity gasoline under compression-ignition conditions using a gasoline direct injection (GDI) piezoelectric fuel injector}, volume={265}, ISSN={["1873-7153"]}, DOI={10.1016/j.fuel.2019.116931}, abstractNote={Gasoline compression ignition (GCI) engine technology has become one of the promising alternative solutions to achieve better fuel economy and meet emission requirement. Higher reactivity gasoline-like fuels are more desirable in GCI engines. This study investigates the soot processes under autoignition combustion of high-reactivity gasoline (HRG) with an outwardly opening piezo gasoline direct injection (GDI) fuel injector. HRG fuels are mixtures of refinery streams with RON of 50–80 and they can potentially yield better fuel economy and emissions in GCI engines. Five ambient oxygen concentrations varying from 10% to 21% and three different ambient temperature combinations were selected to simulate various ambient environments. A two-color pyrometry was applied to measure flame temperature and soot concentration (i.e., KL factor). In general, HRG flame temperatures range from 1500 to 2400 K under selected conditions. HRG flames have relatively low KL factor for all selected experiment conditions. High KL factors are only observed at the flame periphery where flame temperatures are lower than 1800 K. Accumulated KL factor was calculated to evaluate overall soot amount. Flames at 800 K ambient temperature always have the highest accumulated KL factor. The soot and soot temperature trade-off were also discussed. The desired condition needs to approach a moderate soot temperature with a relative low integrated KL factor level. The conditions of 800 K with 15% O2, 1000 K with 10% O2 and 1000 K with 12% O2 shows better results. The findings can help facilitate the application of high reactivity gasoline fuels in next generation clean combustion engines.}, journal={FUEL}, author={Wang, Libing and Wu, Zengyang and Badra, Jihad A. and Roberts, William L. and Fang, Tiegang}, year={2020}, month={Apr} }
 @article{wang_wu_ahmed_badra_sarathy_roberts_fang_2019, title={Auto-ignition of direct injection spray of light naphtha, primary reference fuels, gasoline and gasoline surrogate}, volume={170}, ISSN={["1873-6785"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85059141893&partnerID=MN8TOARS}, DOI={10.1016/j.energy.2018.12.144}, abstractNote={In this work, the spray and auto-ignition characteristics of light naphtha (LN), primary reference fuels (PRF65, PRF95), Haltermann gasoline (CARB LEVIII, 10 vol% ethanol), and a gasoline surrogate were studied in an optically accessible constant volume combustion chamber. An outwardly opening hollow cone piezoelectric gasoline direct injection fuel injector was used. Five ambient temperatures from 650 to 950 K with a 75 K step were selected with a fixed ambient density of 3.5 kg/m3, similar to the Spray G density defined by the engine combustion network (ECN). Fuel auto-ignition was achieved with varying ignition delays for the five investigated fuels depending on the selected experimental conditions. Results show that the auto-ignition locations are randomly distributed in the combustion chamber. Differences in ignition delay times among the five fuels are more significant when the ambient temperature is lower than 750 K. When the ambient temperature is lower than 750 K, PRF95 always has the longest ignition delay and LN has the shortest. Ignition delays of the five fuels are almost identical when the ambient temperature exceeds 750 K. Meanwhile, the five fuels have a similar spray front penetration length and spray angles before the occurrence of auto-ignition under all the investigated conditions.}, journal={ENERGY}, author={Wang, Libing and Wu, Zengyang and Ahmed, Ahfaz and Badra, Jihad A. and Sarathy, S. Mani and Roberts, William L. and Fang, Tiegang}, year={2019}, month={Mar}, pages={375–390} }
 @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={This research was supported in part by the Natural Science Foundation under Grant No. CBET-0854174 and by the Saudi Aramco R&D Center through the Clean Combustion Research Center of the King Abdullah University of Science and Technology. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the funding agencies. The authors also thank Dr. Stephen Kelley for providing the BTL fuel.}, 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{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} }