Takuya Tezuka

Evaluation of the reactivity of ultra-lean PRF/air mixtures by weak flames in a micro flow reactor with a controlled temperature profile

ABSTRACT The reactivity of ultra-lean primary reference fuel (PRF)/air mixtures was investigated by weak flames in a vertical-type micro flow reactor (MFR) with a controlled temperature profile. In experiments, steady-separated weak flames were obtained at equivalence ratios between 0.5 and 1.0 for PRF80, 90, and 100. At leaner conditions, all the fuels showed hot flames at lower temperature regions, indicating higher reactivity. In one-dimensional steady simulations of the present micro flow reactor by modified Chemkin-Pro PREMIX, the LLNL PRF mechanism was able to reproduce the experimental tendency, while the KUCRS PRF mechanism showed the opposite trend. By analyzing major reactions leading to the hot flame, seven H–O reactions were identified that primarily control the hot flame response to a change of equivalence ratio. By exchanging the rate parameters of these seven reactions for more recent ones, the reactivity trend was brought to very good agreement with experimental results. This improvement was credited to a better spatial separation of intermediate- and high-temperature reactions in the MFR and emphasizes the strength of this investigation method.

Experimental and numerical study of premixed flame penetration and propagation in multichannel system

ABSTRACT Experimental and numerical results on premixed flame penetration and subsequent propagation in a multichannel burner are presented. The burner consists of the set of planar straight quartz channels which transverse sizes can be varied. It is found that, depending on mixture flow rate, equivalence ratio and channels transverse sizes a big variety of combustion regimes can be observed. These regimes include burner-stabilized flames, upstream propagating flames, and flames stabilized under the burner external surface. The placement of different combustion regimes in equivalence ratio/flow rate plane is plotted by means of experimental and numerical studies. In wide range of parameters, the flame pulsations consisting of repetitive stages of flame ignition, upstream propagation, and quenching take place. Results of numerical simulations obtained in the framework of simplified thermal-diffusion model are found to be in a good qualitative agreement with experimental data and allow to explain experimental findings.

Effects of n-butanol addition on sooting tendency and formation of C1 –C2 primary intermediates of n-heptane/air mixture in a micro flow reactor with a controlled temperature profile

ABSTRACT Effects of n-butanol addition on the sooting tendency and formations of C1 and C2 primary intermediates of n-heptane/air mixtures were studied in a micro flow reactor with a controlled temperature profile. Sooting tendency was investigated over equivalence ratios of 1.5–4.0 at a maximum wall temperature of 1300 K. Experimental observations indicated two types of flames: a flame alone (type I) or a flame with soot (type II). The critical sooting equivalence ratio, at which the flame switched from type I to type II, increased with the increase of butanol content in the fuel blend. Results show that the sooting tendency of n-heptane decreases as the amount of n-butanol is increased. Computational results obtained using the Chemical Reaction Engineering and Chemical Kinetics mechanism show fair agreement with measurement results obtained at equivalence ratio of 2.0 and the maximum wall temperature of 1166 K. The validity in initial-stage reaction progress of existing mechanisms was examined.

OH-LIF measurement of H2/O2/N2 flames in a micro flow reactor with a controlled temperature profile

This paper presents combustion and ignition characteristic of H2/O2/N2 flames in a micro flow reactor with a controlled temperature profile. OH-LIF measurement was conducted to capture flame images. Flame responses were investigated for variable inlet flow velocity, U, and equivalence ratio, . Three kinds of flame responses were experimentally observed for the inlet flow velocities: stable flat flames (normal flames) in the high inlet flow velocity regime; unstable flames called Flames with Repetitive Extinction and Ignition (FREI) in the intermediate flow velocity regime; and stable weak flames in the low flow velocity regime, at = 0.6, 1.0 and 1.2. On the other hand, weak flame was not observed at = 3.0 by OH-LIF measurement. Computational OH mole fractions showed lower level at the rich conditions than those at stoichiometric and lean conditions. To examine this response of OH signal to equivalence ratio, rate of production analysis was conducted and four kinds of major contributed reaction for OH production: R3(O + H2 H + OH); R38(H + O2 O + OH); R46(H + HO2 2OH); and R86(2OH O + H2O), were found. Three reactions among them, R3, R38 and R46, did not showed significant difference in rate of OH production for different equivalence ratios. On the other hand, rate of OH production from R86 at = 3.0 was extremely lower than those at = 0.6 and 1.0. Therefore, R86 was considered to be a key reaction for the reduction of the OH production at = 3.0.

Soot and PAH Formation Characteristics in a Micro Flow Reactor With a Controlled Temperature Profile

To examine soot and PAH formation processes for rich methane/air and acetylene/air mixtures, a micro flow reactor with a controlled temperature profile was employed. In the experiment for a methane/air mixture, four kinds of responses to the variations of flow velocity and equivalence ratio were observed as follows: soot formation without a flame; a flame with soot formation; a flame without soot formation; and neither flame nor soot formation. Soot formations were observed in low flow velocity and high equivalence ratio. Starting point of soot formation shifted to the upstream side, i.e., low-temperature side, of the micro flow reactor with the decrease of flow velocity. One-dimensional steady-state computation was conducted by a flame code. In high flow velocity, low mole fraction of C2 H2 and high mole fraction of OH were observed in the whole region of the micro flow reactor. Soot volume fraction did not increase in this case. On the other hand, in low flow velocity, high mole fraction of C2 H2 and low mole fraction of OH were observed at the downstream side of the micro flow reactor. Soot volume fraction increased in this case. Since significant soot formation was observed at the low flow velocity and the high equivalence ratio, experiments with gas sampling were conducted for acetylene/air mixture to investigate temperature and equivalence ratio dependence of soot precursor production in such condition. Volume fractions of benzene increased with an increase of temperature. They were larger at higher equivalence ratio at the same temperature. Volume fractions of styrene increased with an increase of temperature. They were larger at higher equivalence ratio when the temperature is less than 1000 K. However the tendency was changed at 1000 K, styrene volume fraction at equivalence ratio of 7.0 was larger than that at equivalence ratio of 8.0.© 2011 ASME