Zhanli Mao

Bio: Zhanli Mao is an academic researcher from Chinese People's Armed Police Force Academy. The author has contributed to research in topics: Combustion & Large eddy simulation. The author has an hindex of 1, co-authored 1 publications receiving 7 citations.

Experimental and LES investigation of flame propagation in a hydrogen/air mixture in a combustion vessel

Abstract: This work presents an experimental and numerical investigation of premixed flame propagation in a hydrogen/air mixture in a closed combustion vessel. In the experiment, high-speed schlieren video photography and pressure sensor are used to examine the flame dynamics and pressure transient. In the numerical study, a large eddy simulation (LES) based on a RNG sub-grid approach and a LES combustion model is applied to reproduce experimental observations. The effects of four physical phenomena on the burning velocity are considered in the combustion model, and the impact of grid type on the combustion dynamics is examined in the LES calculations. The flame experiences four stages both in experiment and LES calculations with structured and unstructured grids, i.e., spherical flame, finger-shaped flame, flame with its skirt in contact with the sidewalls, and tulip-shaped flame. The flame speed and pressure in the vessel develop with periodical oscillations in both the experiment and LES simulations due to the interaction of flame front with pressure wave. The numerical simulations compare well with the detailed experimental measurements, especially in term of the flame shape and position, pressure build-up, and periodical oscillation behaviors. The LES combustion model is successfully validated against the bench-scale experiment. It is put into evidence that mesh type has an impact to a certain extent on the numerical combustion dynamics, and the LES calculation on structured grid can predict the flame dynamics and pressure rise more accurately than that on unstructured grid with the same mesh resolution. The flame shape is more asymmetrical in the LES on an unstructured grid than that on a structured grid, and both the flame speed and the pressure rise at the later flame stage are underestimated in the LES on the unstructured grid.

Premixed flame propagation in hydrogen explosions

Abstract: Hydrogen as an energy carrier is a very promising alternative fuel in the future. Accidental hydrogen explosions remain one of the major concerns in hydrogen energy utilization and process industries. This paper summarizes recent experimental and numerical efforts towards understanding combustion wave propagation in hydrogen explosions, including flame instabilities, flame acceleration, deflagrations, and deflagration-to-detonation transition (DDT). The fundamental problems involve understanding physical mechanisms that significantly influence the dynamic flame behavior in hydrogen explosions, such as combustion/hydrodynamic instabilities, vortex motion, pressure waves and flow turbulence. Advances achieved over recent years in new experimental observations, theoretical models and numerical simulations are discussed. Future research is required to quantitatively understand flame instabilities, turbulence properties and DDT in hydrogen explosions and improve reliability of theoretical and numerical predictions for hydrogen safety applications.

The constant-volume propagating spherical flame method for laminar flame speed measurement

Abstract: Laminar flame speed is one of the most important intrinsic properties of a combustible mixture. Due to its importance, different methods have been developed to measure the laminar flame speed. This paper reviews the constant-volume propagating spherical flame method for laminar flame speed measurement. This method can be used to measure laminar flame speed at high pressures and temperatures which are close to engine-relevant conditions. First, the propagating spherical flame method is introduced and the constant-volume method (CVM) and constant-pressure method (CPM) are compared. Then, main groups using the constant-volume propagating spherical flame method are introduced and large discrepancies in laminar flame speeds measured by different groups for the same mixture are identified. The sources of discrepancies in laminar flame speed measured by CVM are discussed and special attention is devoted to the error encountered in data processing. Different correlations among burned mass fraction, pressure, temperature and flame speed, which are used by different researchers to obtain laminar flame speed, are summarized. The performance of these correlations are examined, based on which recommendations are given. Finally, recommendations for future studies on the constant-volume propagating spherical flame method for laminar flame speed measurement are presented.

Review on Large Eddy Simulation of Turbulent Premixed Combustion in Tubes

Abstract: This paper reviews the existing knowledge on the large eddy simulation (LES) of turbulent premixed combustion in empty tubes and obstructed tubes. From the view of model development in LES, this review comprehensively analyzes the development history and applicability of the important Sub-Grid Scale (SGS) viscosity models and SGS combustion models. LES is also used to combine flow and combustion models to reproduce industrial explosion including deflagration and detonation and the transition from deflagration to detonation (DDT). The discussion about models and applications presented here, leads readers to understand the progress of LES in the explosion of tube and reveals the deficiencies in this area.

Auto-ignition of biomass synthesis gas in shock tube at elevated temperature and pressure

Abstract: Ignition delay times of multi-component biomass synthesis gas (bio-syngas) diluted in argon were measured in a shock tube at elevated pressure (5, 10 and 15 bar, 1 bar = 105 Pa), wide temperature ranges (1,100–1,700 K) and various equivalence ratios (0.5, 1.0, 2.0). Additionally, the effects of the variations of main constituents (H2:CO = 0.125–8) on ignition delays were investigated. The experimental results indicated that the ignition delay decreases as the pressure increases above certain temperature (around 1,200 K) and vice versa. The ignition delays were also found to rise as CO concentration increases, which is in good agreement with the literature. In addition, the ignition delays of bio-syngas were found increasing as the equivalence ratio rises. This behavior was primarily discussed in present work. Experimental results were also compared with numerical predictions of multiple chemical kinetic mechanisms and Li’s mechanism was found having the best accuracy. The logarithmic ignition delays were found nonlinearly decrease with the H2 concentration under various conditions, and the effects of temperature, equivalence ratio and H2 concentration on the ignition delays are all remarkable. However, the effect of pressure is relatively smaller under current conditions. Sensitivity analysis and reaction pathway analysis of methane showed that R1 (H + O2 = O + OH) is the most sensitive reaction promoting ignition and R13 (H + O2 (+M) = HO2 (+M)), R53 (CH3 + H (+M) = CH4 (+M)), R54 (CH4 + H = CH3 + H2) as well as R56 (CH4 + OH = CH3 + H2O) are key reactions prohibiting ignition under current experimental conditions. Among them, R53 (CH3 + H (+M) = CH4 (+M)), R54 (CH4 + H = CH3 + H2) have the largest positive sensitivities and the high contribution rate in rich mixture. The rate of production (ROP) of OH of R1 showed that OH ROP of R1 decreases sharply as the mixture turns rich. Therefore, the ignition delays become longer as the equivalence ratio increases.

High-sensitivity fiber optic hydrogen sensor in air by optimizing a self-referenced demodulating method.

Abstract: Self-referenced demodulating methods of fiber optic hydrogen sensors based on WO3–Pd2Pt–Pt composite film are studied in this paper. By employing the proper baseline intensity as sensing parameters, fluctuations of the sensing signal of the hydrogen sensor can be obviously depressed, and sensitivity can be greatly improved. Experimental results show that the resolution of the hydrogen sensor can reach 3 parts per million (ppm) when the hydrogen concentration is lower than 1000 ppm. Additionally, the hydrogen sensor shows better sensitivity toward lower concentrations of hydrogen, enabling a hydrogen threshold down to 10 ppm in air at room temperature. To the best of our knowledge, this is the lowest threshold reported for an optical hydrogen sensor operated at room temperature in air. Moreover, the sensor has good repeatability during hydrogen response. This work proposes a simple and novel method to improve the performance of fiber optic hydrogen sensors, which can greatly promote their potential application in various fields.