• Quantification of carbon particulates produced under open liquid pool and prevaporised flame conditions: Waste cooking oil biodiesel and diesel blends

      Chong, Cheng Tung; Tian, Bo; Jo-Han, Ng; Fan, Luming; Wong, Kang Yao; Hochgreb, Simone; Shanghai Jiao Tong University; University of Derby; University of Southampton Malaysia; University of Cambridge (Elsevier, 2020-03-13)
      The soot volume fraction (SVF) of waste cooking oil (WCO) biodiesel and blends was quantified and compared under the same total carbon flow rate via two experimental setups, namely prevaporised diffusion jet flames and pool flames using extinction calibrated laser induced-incandescence (LII). The spatial SVF distribution shows that for diesel-rich fuels, soot formation peaks near the flame and is convected downstream, whereas biodiesel flames show a more evenly distributed SVF at the flame center region. An increase in biodiesel fraction in diesel results in a reduced propensity for soot, as evident in both pool and vapour flames. Comparison of the radial profiles of SVF along the centerline shows broader SVF profiles for pool flames, reflecting the longer residence times for soot diffusion and growth compared to vapour flames, which reflected the lower mass flux for the pool burner. The total soot produced from pool flames was found to be higher than vapour flame by a factor of two for the same fuel mass consumption rate. WCO biodiesel exhibited the lowest total SVF value regardless of flame type owing to the combined effects of lack of aromatic compounds and fuel chemistry. The soot primary particle sizes produced by WCO biodiesel show lower mean diameter values by a factor of approximately 1.5 compared to diesel-produced soot. The pool flames produced carbon particulates of larger mean diameter by around 22% and 8% for diesel and WCO biodiesel, respectively, relative to the counterpart vapour flames, as a result of extended soot surface growth period.
    • Dual-fuel operation of biodiesel and natural gas in a model gas turbine combustor

      Chong, Cheng Tung; Chiong, Meng-Choung; Ng, Jo-Han; Tran, Manh-Vu; Medina, Agustin Valera; Józsa, Viktor; Tian, Bo; Shanghai Jiao Tong University; Meng-Choung Chiong; University of Southampton Malaysia; et al. (ACS Publications, 2020-02-17)
      The dual-fuel combustion characteristics of palm biodiesel/methyl esters (PME) and natural gas (NG) in a model gas turbine swirl flame burner are investigated at a thermal power of 9.3 kW. The PME is atomized into a spray, while the gaseous NG is premixed with the main bulk swirling air before entering the combustion chamber. The dual-fuel PME/NG flame structure is similar to the single-fuel PME, where the sooty flame brush is noticeably absent. The PME and PME/NG flames emit higher peak intensity of OH* and CH* radicals as compared to diesel at the same equivalence ratio. Dual-fuel operation results in lower NO but higher CO at ϕ = 0.9 as compared to pure diesel and PME spray flames. The higher CO emission level for dual-fuel is attributed to poor mixing and incomplete combustion as a result of reduced air flow. At a leaner operation of ϕ = 0.65, enhanced turbulence due to higher bulk air flow results in improved mixing, lowering the overall CO but increasing the NO emissions because of the more intense flame core. The study shows that optimization of the multiphase dual-fuel injection system is needed to achieve low emissions in a gas turbine combustor.
    • Development of a beam optimization method for absorption-based tomography

      Yu, Tao; Tian, Bo; Cai, Weiwei; Shanghai Jiao Tong University, Shanghai, China; University of Cambridge (The Optical Society, 2017-03-07)
      Absorption tomography is an imaging technique that has been used simultaneously to image multiple scalar parameters, such as temperature and species concentration for combustion diagnostics. Practical combustors, such as internal combustion engines and gas turbine engines, only allow limited optical access, and typically a few (ca. 20-40) beams are available to probe the domain of interest. With such limited spatial sampling, it is non-trivial to optimize beam arrangement for a faithful reconstruction. Previous efforts on beam optimization rely on either heuristic/empirical methods lacking rigorous mathematical derivation or were derived by assuming certain prior information in the tomographic inversion. This paper aims to develop an approach that is expected to be especially useful when prior information is not easily available or intended to be included in the inversion processes. We demonstrate that the orthogonality between rows of the weight matrix directly correlates with reconstruction fidelity and can be used as an effective predictor for beam optimization. A systematic comparison between our method and the existing ones in the literature suggests the validity of our method. We expect this method to be valuable for not only the absorption tomography but also other tomographic modalities.
    • Planar 2-color time-resolved laser-induced incandescence measurements of soot in a diffusion flame

      Tian, Bo; Zhang, C.; Gao, Y.; Hochgreb, S.; University of Cambridge (Taylor and Francis, 2017-09-22)
      Planar two-dimensional two-color time-resolved laser-induced incandescence (2D-2C-TiRe-LII) is employed to investigate soot formation in a standard ethylene laminar diffusion flame. The time resolution of the 2D LII signal is realized by shifting the delay time of ICCD cameras. The two-color configuration is applied to measure the peak temperature of soot particles immediately after the laser pulse rather than using the energy balance to compute . The Sauter mean diameter D32 and the corresponding distribution width parameter σ of the measured soot particles is extracted by using an error minimization method. The method shows that a range of possible geometry mean particle diameters and corresponding distribution width parameters are also possible solutions, and further information on realizable particle size distribution widths is necessary to narrow down the extracted diameter.
    • Concept of laser-based in-situ measurements of TiO2 particles in hydrocarbon flames

      Tian, Bo; Zhang, C; Gao, Y; Hochgreb, S; University of Cambridge; Shanghai Jiao Tong University, China (2017)
      Nano-sized titanium dioxide (TiO2) particles are widely used in industry. In this study, we investigate how laser-based techniques may be candidates for non-intrusive measurements of TiO2 nanoparticles in flame. The TiO2 nanoparticles are strong optical absorbers in the ultraviolet (UV) region, thus extinction/scattering and laser induced incandescence (LII) techniques can be used to evaluate both the volume concentration and the size of TiO2 nanoparticles. The theory of light absorption and scattering of TiO2 nanoparticles is analysed, and a preliminary heat transfer model of time-resolved LII (TiRe-LII) for TiO2 nanoparticles sizing is also presented.
    • Soot reduction effects of dibutyl ether (DBE) addition to a biodiesel surrogate in laminar coflow diffusion flames

      Gao, Zhan; Zhu, Lei; Zou, Xinyao; Liu, Chunpeng; Tian, Bo; Huang, Zhen; Shanghai Jiao Tong University, Shanghai, China; University of Cambridge (Elsevier BV, 2018-06-25)
      The dibutyl ether (DBE) has been recently identified as an alternative biofuel produced from lignocellulosic biomass. In the present study, experimental and chemical kinetics studies were carried out to investigate the effects of dibutyl ether addition to a biodiesel surrogate (methyl decanoate) on soot formation in laminar coflow diffusion flames. The mole fraction of DBE in the fuel stream varies from 0 to 40 mol%. Laser-induced incandescence (LII) technique was applied to obtain the 2D soot volume fraction distribution and a combined methyl decanoate-dibutyl ether-PAH kinetic model was constructed to analyze chemical effects of DBE addition on the concentration of key species for soot inception and growth. The experimental results show that DBE addition can indeed reduce the soot yielding and the suppressive effect is nonlinear with the mole fraction of DBE in the fuel mixture. It is found that in the flame centerline, soot reduction with more DBE addition is a combined effect of lower nucleation rate and decreasing PAHs condensation, while soot reduction effect is somewhat moderate in flame wings as the result of the competition between decreasing inception rate and enhanced surface growth caused by higher acetylene concentration. Reaction path analysis suggests that DBE addition can markedly suppress C3 + C3 pathways to the first aromatic ring, lead to lower A1 yield and consequently limit the aromatic growth to larger PAHs. DBE is found to be remarkably promising in terms of suppressing soot formation and reducing particle emission.
    • Soot measurement in diluted methane diffusion flames by multi-pass extinction and laser-induced incandescence

      Tian, Bo; Gao, Yi; Zhang, Cen; Hochgreb, Simone; University of Cambridge (Elsevier BV, 2018-03-20)
      Multi-pass cavity line-of-sight extinction (MPC-LOSE) and laser-induced incandescence (LII) techniques are deployed to measure the soot volume fraction in a series of nitrogen-diluted flames, which produce only ppm volume mass fractions of soot. The separate suppression effects on soot formation of direct fuel dilution and indirect effects of temperature and residence time are interpreted by using a numerically calculated flow velocity and temperature field using a one-step fast chemistry model. The experimentally determined rate of soot formation is shown to obey approximately the same function of the local temperature for all dilution cases. The results show that a simple one-step reaction model using previously measured activation energies can account for the dilution effect with good accuracy. The results show that the direct effect of dilution on concentration is comparable to the effects of changing the temperature estimated local temperature and residence time.
    • Soot volume fraction measurements over laminar pool flames of biofuels, diesel and blends

      Tian, Bo; Chong, C.T.; Fan, L.; Ng, J.-H.; Zhang, C.; Hochgreb, S.; University of Cambridge; UTM Centre for Low Carbon Transport in cooperation with Imperial College London, Universiti Teknologi Malaysia, Malaysia; University of Southampton Malaysia Campus (USMC), Iskandar Puteri, Johor, Malaysia (Elsevier BV, 2018-06-25)
      Biodiesel and blends with petroleum diesel have shown their potential as renewable alternative fuels for engines, with additional benefits of low particulate matter and low sulfate emissions. In this paper we measure the soot volume fraction produced by three different methyl esters processed biodiesels (extracted from palm (PME), soy (SME) and coconut (CME)), and their blends with petroleum diesel, in a series of co-flow stabilized laminar pool flames, using laser induced-incandescence (LII) and laser extinction optical methods. The soot volume fraction measurement results show that all neat biodiesels produce only up to 33% of the total soot volume compared to pure diesel, and that the total soot volume correlates directly with the degree of unsaturation of the biodiesels. Blending leads to approximately linear behaviour of total soot volume, with a shift in slope with smaller sensitivity towards neat diesel.
    • Chemical mechanism of exhaust gas recirculation on polycyclic aromatic hydrocarbons formation based on laser-induced fluorescence measurement

      Liu, Peng; Zhang, Yiran; Wang, Lijun; Tian, Bo; Guan, Bin; Han, Dong; Huang, Zhen; Lin, He; Shanghai Jiao Tong University, Shanghai, China; University of Cambridge (American Chemical Society (ACS), 2018-05-14)
      Exhaust gas recirculation (EGR) has been widely used in engines to meet current emission regulations. Investigating the chemical mechanism of EGR on polycyclic aromatic hydrocarbons (PAHs, the precursor of soot) formation in premixed flames contributes to understanding the EGR dependence on soot formation in engines. In this study, the influence of flame temperature, equivalence ratio, and CO2 addition on the formation of PAHs was systematically investigated in premixed C2H4/O2/Ar/CO2 flames using laser-induced fluorescence (LIF) technology. The temperature dependence of PAHs formation was studied at a fixed equivalence ratio and dilution ratio. It was found that the LIF signal of PAH reaches the maximum value around 1730 K and decreases at a lower or higher temperature in this study. The LIF signal of PAHs almost increases linearly with the equivalence ratio, as the maximum flame temperature and dilution ratio are kept constant. The experimental results show that the CO2 addition in the inlet gas suppresses PAHs formation due to the chemical inhibition effect. The thermal effect of CO2 addition on PAHs formation is highly sensitive to flame temperature. The PAHs reaction mechanisms proposed by Appel et al. and Wang et al. are used to clarify the experimental results. The first-order temperature sensitivity analysis showed that the hydrogen-abstraction–carbon-addition pathway with high reaction reversibility should account for temperature effects on PAHs formation. The pathway sensitivity analysis showed that the CO2 inhibition chemical effect is realized through the route CO2 (+H) → OH → C3H3 (C2H2) → A1 → PAHs with the assistance of the entrance reaction CO2 + H = CO + OH.
    • Soot measurements over a series of laminar pool flames of biofuels, methyl esters and blends with diesel

      Tian, Bo; Chong, C.T.; Fan, L; Ni, S; Hochgreb, S; University of Cambridge; Shanghai Jiao Tong University, 200240, Shanghai, China (2019-04)
      Biofuel combustion results in lower soot compared with petroleum fuels. There have been several studies of soot formation measurement in flames of biodiesel surrogates (methyl esters), but few quantitative measurements from real biodiesels. In this study, we use laser induced incandescence and extinction measurements to obtain soot volume fraction in co-flow stabilised pool flames fueled with four different real biodiesels and two methyl esters. The results show that the degree of unsaturation plays an important role in the soot yield of fuels. A SEM analysis shows that the biofuels with lower degree of unsaturation produce a lower amount and smaller soot particles comparing the more saturated fuel.
    • The effect of droplets on laminar propagation speed of an acetone-methane flame

      Fan, L; Tian, Bo; Chong, C.T.; McGrath, D; Hochgreb, S; University of Cambridge; Shanghai Jiao Tong University (2019-04)
      Biofuel combustion results in lower soot compared with petroleum fuels. There have been several studies of soot formation measurement in flames of biodiesel surrogates (methyl esters), but few quantitative measurements from real biodiesels. In this study, we use laser induced incandescence and extinction measurements to obtain soot volume fraction in co-flow stabilised pool flames fueled with four different real biodiesels and two methyl esters. The results show that the degree of unsaturation plays an important role in the soot yield of fuels. A SEM analysis shows that the biofuels with lower degree of unsaturation produce a lower amount and smaller soot particles comparing the more saturated fuel.
    • A mean free path approach to the micro/nanochannel gas flows

      Xie, Jianfei; University of Derby (Springer Nature, 2020-05-07)
      We investigate the gas flows near to solid surfaces in terms of the local spatial variation in the molecular mean free path (MFP). Molecular dynamics (MD) is the appropriate scientific tool for obtaining molecularly-accurate dynamic information in micro and nano-scale gas flows, and has been used to evaluate the molecular mean free path of gases. In the calibration procedure, the viscosity of a gas in the homogeneous case can be recovered in our MD simulations and reach good agreement with the theoretical prediction and data from NIST. In surface-bounded gas flows, if the collisions between gas molecules and walls are counted, a spatially-varying mean free path is presented, and for the first time we have observed that the distribution of the free paths deviates from the exponential one and spikes appear in their distributions at larger Kn, i.e. in the transition flow regime. Based on elementary kinetic theory, the effective viscosity of the gas derived from the mean free path has been incorporated into the framework of the continuum-fluid dynamics equations, and micro-Couette flows are performed to demonstrate this potential application.
    • Relative permeabilities of supercritical CO2 and brine in carbon sequestration by a two-phase lattice Boltzmann method

      Xie, Jianfei; He, S.; Zu, Y. Q.; Lamy-Chappuis, B.; Yardley, B. W. D.; University of Sheffield (Springer Nature, 2017-03-10)
    • Effect of various surface conditions on nanochannel flows past permeable walls

      Xie, Jianfei; Cao, Bing-Yang; Tsinghua University (Informa UK Limited, 2016-10-11)
    • Influence of travelling surface waves on nanofluidic viscosity

      Xie, Jianfei; Cao, Bing-Yang; Tsinghua University (Elsevier BV, 2018-01)
    • A test of the effectiveness of pore scale fluid flow simulations and constitutive equations for modelling the effects of mineral dissolution on rock permeability

      Lamy-Chappuis, Benoit; Yardley, Bruce W.D.; He, Shuisheng; Zu, Yingqing; Xie, Jianfei; University of Sheffield (Elsevier BV, 2018-04)
    • Natural convection of power-law fluids under wall vibrations: A lattice Boltzmann study

      Xie, Jianfei; Tsinghua University (Informa UK Limited, 2017-11-07)
    • Two approaches to modelling the heating of evaporating droplet

      Xie, Jianfei; University of Sheffield (Elsevier BV, 2014-08)
    • Nanochannel flow past permeable walls via molecular dynamics

      Xie, Jianfei; Cao, Bing-Yang; Tsinghua University (AIP Publishing, 2016-07)
    • Lattce Boltzmann mdoelling of natural convection of power-law fluids under wall vibrations

      Xie, Jianfei; Cao, Bing-Yang; Tsinghua University (Begellhouse, 2018-08)