摘要:

Experiments were conducted in a T63 engine combustor to: (I) gain a better understanding of the roles played by fuel properties and atomization in ignition and (2) give experimental verification of assumptions used in ignition models. Ten test fuels were used, some of which were specially blended to vary either viscosity or volatility while holding the other constant. Six atomizers were used to vary the fuel spray characteristics, and average drop sizes, represented by Sauler mean diameter (SMD), were measured. Air temperatures were varied from 239 to 310K. Ignition comparisons were made by the minimum fuel-air ratios required to achieve light-off. Measurements of gas velocity and fuel-air ratio were made at the spark gap. Approximate ignition delay times were determined from high-speed photographs of the ignition process. Significant results for this combustor included: (1) viscosity, which determined atomization characteristics, was more important than volatility in the ignition process, (2) ignition depended more on achieving a critical drop size than on reaching the lean-limit fuel-air ratio. (3) fuel temperature was found to be more important than air temperature for low-temperature ignition, an effect due principally lo viscosity and atomization rather than evaporation. A practical implication is that fuel heating would give a greater improvement in cold-start performance than heating the combustor inlet air.

ISSN:0010-2202    

DOI:10.1080/00102209108951784

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Numerical simulations of the spontaneous ignition and subsequent detonation of propane-air mixtures caused by a weak shock in a partially confined volume containing an obstacle are performed to study potential hazards from a leaking storage container. The numerical model combines a solution of the compressible equations of fluid dynamics with a phenomenological chemical induction model for species conversion and energy release. The purpose of the simulations is to study the mechanism of the ignition and detonation processes due to shock reflections from the wall boundaries. Nonreactive simulations show how the obstacle partially blocks the flow such that one portion of the shock front reflects off of the obstacle and another portion is transmitted. Reactive-flow simulations of stoichiometric propane-air show spontaneous ignition behind the shock reflected from the obstacle and later transition to detonation in the direction of the transmitted wave. A series of computations performed to study the effect of obstacle height show the various mechanisms responsible for the transition to detonation for the different obstacle sizes considered. Simulations in a mixture with variable stoichiometry around the obstacle, a more realistic picture of the physical scenario, show decay of the transmitted shock and then re-ignition as the shock reaches the stoichiometric region. Two separate areas of ignition eventually combine and transition to detonation. As this detonation propagates into the lean region far from the obstacle, it decays into a shock wave followed by a decaying flame front.

ISSN:0010-2202    

DOI:10.1080/00102209108951785

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Vortical structures arc investigated experimentally for combusting flow from a 2-D slot burner. A combination of a fast reactive system producing TiO2seed particles and a 2-D sheet lighting method was used to visualize the vortical structures. At a fixed air flow rate, three regimes were observed—depending on the fuel flow. These three regimes depend on whether the fuel penetrates the recirculating zones and are designated aspre-penetration, penetration-transition, and penetrationregime. In each regime, the flame and vortical structures are described and vortical shedding frequency is measured. It was found that the “petal” structures observed in a flame consist of vortical pairs of opposite sign. It is believed that these “petals” may be the precursor of flamelets seen in turbulent combustion.

ISSN:0010-2202    

DOI:10.1080/00102209108951786

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A model for time-dependent nonplanar propagation is derived in the limit of large activation energy, and is used to study the stability of a planar travelling wave in counter flow filtration combustion,i.e., where an exothermic reaction from passes through a porous solid medium that reacts with a forced inflow of gas to form a porous solid, and where the direction of propagation of the front is opposite to that of the incoming gas.

ISSN:0010-2202    

DOI:10.1080/00102209108951787

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The use of decomposed methanol,i.e., hydrogen and carbon monoxide, in spark-ignition engines is reviewed. The emphasis is on onboard decomposition and the paper docs not deal with engines fueled by stored hydrogen. The paper concentrates mostly on the experimental work performed using catalytically decomposed methanol, where the methanol is used as a hydrogen carrier. The greatest potential for this type of engine, besides the low energy consumption, lies in the low emissions of nitrogen oxides when running at lean air/fuel ratios.

ISSN:0010-2202    

DOI:10.1080/00102209108951788

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Ignitability of fuel droplets, relevant to the performance of liquid-fueled combustor, is investigated. Explicit ignition criterion of a fuel droplet which is not only in an unbounded oxidizing environment but also in spray interior has been expressed. A general discussion has been conducted as far as the exponent of fuel concentration. Based on the analytical solutions in the limiting situations as well as numerical results in the literature, approximate ignition criteria have been expressed in explicit form in obtaining the expressions of the ignition criteria, both simplicity in the expression and applicability for the widely-varing parameters have been taken into account. Fair expressions have been obtained with 8% error at the most.

ISSN:0010-2202    

DOI:10.1080/00102209108951789

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The present paper describes research to determine the lift and drag forces on a single heptane droplet in a non-uniform flow field over a range of Reynolds numbers of 1-30. Experiments are described for droplels (90-320μm) entering a jet of air (≈ 1 m/s) and fallowing unsteady curvilinear trajectories (for which few experimental studies and no theory exist). The lift and drag forces acting on the droplet are compared to those predicted by the most closely related theory and engineering formulae. The results support standard correlations and suggest that additional effects such as Basset forces reach not more than ten percent in these experiments.

ISSN:0010-2202    

DOI:10.1080/00102209108951790

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor