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Recently, methyl pentanoate (MPe) has been considered an alternative fuel or additive in gasoline and diesel. Therefore, before its adoption in combustion devices, its combustion characteristics have to be thoroughly understood. Intrinsic flame instability and cellularity are combustion characteristics that influence the performance of combustion devices. In this light, the intrinsic instability and cellularity of MPe/air flames were investigated at the initial pressures of 1, 2, and 4 bar, temperatures of 453 K and 483 K, and equivalence ratios of 0.7-1.4 in a constant volume combustion chamber to understand the various combustion dynamics of MPe. The instability and cellularity were examined using physicochemical characteristics such as the stretch rate, Markstein length, Lewis number, thermal expansion ratio, and flame thickness. There were slight differences in the Markstein length at the various pressures, but generally, according to the Markstein length, MPe flames were unstable at higher pressures. The Lewis number revealed that MPe flames were thermal-diffusively stable, whereas the flame thickness showed MPe flames were more unstable at 483 K and 4 bar. Also, the MPe premixed flame growth rate and stability curves were obtained using theoretical analysis. The stability curves showed that at high initial pressures and temperatures, MPe flame instability occurs early at a smaller flame radius. Moreover, the experimental and theoretical critical radii agreed well. The research results provide a concrete foundation for advancing the knowledge of methyl pentanoate combustion. Refereed/Peer-reviewed

Ethyl acetate/hydrogen/air (EA/H2/air) premixed flame combustion characteristics were investigated at the initial pressures of 1 bar, 2 bar, and 3 bar and a temperature of 358 K using H2 in air volumetric fractions of 0 %, 4 %, 8 %, and 12 %. Specifically, the laminar burning speed (LBS) and intrinsic flame instabilities of the EA/H2/air premixed flames were investigated. The laminar burning speed follows the order of 0 % < 4 % < 8 % < 12 %. The maximum laminar burning speeds of 0.85 m/s, 0.78 m/s, and 0.70 m/s were measured at the initial pressures of 1, 2, and 3 bar, respectively, when a 12 % concentration of hydrogen was added to EA. Reactions R98: H + O2 ⟺ O + OH and R136: CH3 + H (+M) ⟺ CH4 (+M) significantly promoted and inhibited EA/H2/air LBS, respectively. Furthermore, the decreased flame thickness or curvature effect mainly caused the instability and cellularity of the EA/H2/air premixed flames when the concentration of hydrogen and the initial pressure increased. Theoretically, EA/H2/air premixed flames were thermal-diffusively stable and hydrodynamically unstable. This study provides a profound understanding of the combustion characteristics of EA/H2/air relevant to its application in combustors. Refereed/Peer-reviewed

The laminar burning velocity of 2-methylfuran was investigated using the constant volume method (CVM) at high initial pressure and temperature conditions. The so-called, linear x(p) approximation and a non-linear analytical x(p) relation were used to study the laminar burning velocities of 2-methylfuran fuel. The CVM results were compared to the constant pressure method (CPM) data and numerical results. The CVM and CPM results showed a consistent trend. A percentage deviation of between −8.9% and 8.2% as well as −6% and 8% were observed at initial pressures of 1 and 2 bar when the CVM results were compared to the CPM data while the difference was between −12% and 6% at 4 bar. The numerical results predicted higher laminar burning velocities at all initial conditions when compared to the CVM results. Laminar burning velocity correlations have been obtained from the combined experimental data as a function of the various unburned mixture pressures and temperatures at equivalence ratios of 0.7–1.4. Laminar burning velocities at high unburned mixture temperature and pressure measurement up to 421 K and 8 bar can be obtained from the few experimental data using the correlation in this study.

Combustion/explosion characteristics of 2-ethylfuran (2-EF) have been investigated using the constant volume combustion analysis at the initial pressures of 1, 2, 3, and 4 bar, initial temperatures of 373, 403, and 433 K over a wide range of equivalence ratios of 0.7–1.4. More specifically, the laminar burning velocity, peak explosion pressure, and maximum pressure rise rate of 2-EF were investigated. The peak explosion pressure was investigated using numerical and experimental analysis; the experimental data were slightly lower than the numerical results due to heat loss to the combustion chamber walls in the course of the experiment. As expected, the peak explosion pressure increased as the initial pressure increased and the initial temperature decreased. Similarly, the maximum pressure rise rate increased as the initial pressure increased but the maximum pressure rise rate was somehow close at the different initial temperatures. The burning velocity investigations showed that the maximum burning velocity occurred at the equivalence ratio of 1.1, except for conditions whereby the flame was unstable. The constant volume method (CVM) was used to obtain burning velocities at elevated pressures and temperatures up to 10 bar and 548 K for the 2-EF premixture. Finally, sensitivity analysis was done to evaluate the most sensitive reactions that influenced 2-EF premixture combustion/explosion.

Biomass energy is an emerging alternative energy source with an attractive carbon balance in its life cycle. Recently, a biomass fast pyrolysis fuel was produced from rice husk, and it was further upgraded using supercritical ethanol with a 5%Pt/SO 4 2− /ZrO 2 /SBA-15 catalyst in a hydrogen atmosphere. This upgraded biomass pyrolysis fuel is mainly composed of ethers, esters, alcohols and ketones. After analysing the composition of this upgraded biomass pyrolysis fuel, the authors reproduced a mixed fuel to mimic the upgraded biomass pyrolysis fuel. This mixed fuel contained ethanol, ethyl acetate, diethyl ether, acetone, and 2-butanone, with mass ratios of 9:6:2:1:1. This fuel has been used in a gasoline engine with some minor modifications; however, there is no data available for its laminar burning characteristics. In this study, the laminar burning characteristics of this mixed fuel were investigated in a constant volume combustion chamber (CVCC) at an initial pressure of 0.1 MPa and initial temperatures of 358, 388 and 418 K), and at an initial temperature of 358 K and initial pressures of 0.1, 0.2 and 0.4 MPa. By using a Schlieren high-speed imaging technique and a linear extrapolation method, laminar burning characteristics including the unstretched flame propagation speed, laminar burning velocity and other key parameters were calculated and discussed. Experiments were also conducted for two main components, ethanol and ethyl acetate, and results were used as benchmarks. The results indicated that the peak laminar burning velocity of the mixed fuel can be observed near the equivalence ratio of 1.1 under the tested conditions. At the same equivalence ratio, the laminar burning velocity was increased as initial temperature was increased, and it was decreased as initial pressure was increased. Markstein length decreased as equivalence ratio was increased, and it dropped below zero when the equivalence ratio was 1.4, indicating increased flame instability with equivalence ratio increased. Among the three examined fuels, the laminar burning velocity ranking was: ethanol > mixed fuel > ethyl acetate.

The cellular instability of ethyl acetate (EA) premixed flame has been studied theoretically and experimentally under different initial temperature, pressure and equivalence ratio. The constant pressure method (CPM) was used to determine the laminar burning velocity of EA spherical expanding flame in this research. In addition, the cellular evolution image of EA spherical expansion flame surface was obtained using high-speed schlieren technology. The image processing technology combined with three-dimensional reconstruction algorithm was used to extract and reconstruct the flame surface crack length, the number of cells on the flame surface, cellular area and cellular length scale. From the quantitative analysis of surface crack and cellular structure of EA flame, it can be seen that the evolution of flame surface crack and surface cellular structure is largely affected by equivalence ratio and initial pressure. With the increase of initial pressure or equivalence ratio, the earlier the flame surface cracks and cell formation. Furthermore, according to the cellular length scale in different radius, the wavenumber was deduced, and compared with the theoretical curve, it is found that the experimental wave numbers have the same evolution trend. Although, when the equivalence ratio is 1.4 with high Peclet number, the experimental wave numbers are somewhat beyond the boundary of the peninsula curve due to the influence of the nonlinear effects, the trend is consistent with the theoretical results.

The intrinsic flame instability of ethyl acetate (ETAC) spherically expanding premixture flame has been investigated and discussed using experimental and theoretical analysis at the initial temperature and pressure of 358 K, 388 K, 418 K and 1 bar, 2 bar, and 4 bar as well as the equivalence ratio of 0.8–1.6 using the constant volume combustion chamber (CVCC). When a premixture flame becomes unstable and cellularized the flame surface is wrinkled which further facilitates the rapid accelerative motion of the flame. Considering this, the wrinkling factor of the premixture was assessed. It was revealed that the wrinkling factor increases as the Peclet number increases. Comparative analysis of the experimental and theoretical Peclet number showed that the experimental data was smaller than the theoretical data, however, their trend was consistent. Flame instability was also investigated using the critical Peclet number ( Pe c ) and the Markstein number ( M b ) and empirical correlation Pe c = 52.31 M b + 260.43 was attained. In conclusion, an empirical correlation Ka c = 0.04704 e ( - 0.33466 M b ) and Ka cl = 0.04959 e ( - 0.25775 M b ) was established in terms of the Karlovitz numbers ( Ka ) and the Markstein number ( M b ).