Liquid Fuel Composition Effects on Forced, Nonpremixed Ignition

Abstract

The effects of jet fuel composition on ignition probability have been studied in a flowfield that is relevant to turbine engine combustors, but also fundamental and conducive to modeling. In the experiments, a spark kernel is ejected from a wall and propagates transversely into a crossflow. The kernel first encounters an air-only stream before transiting into a second, flammable (premixed) stream. The two streams have matched velocities, as verified by hot-wire measurements. The liquid fuels span a range of physical and chemical kinetic properties. To focus on their chemical differences, the fuels are prevaporized in a carrier air flow before being injected into the experimental facility. Ignition probabilities at atmospheric pressure and elevated crossflow temperature were determined from optical measurements of a large number of spark events, and high-speed imaging was used to characterize the kernel evolution. Eight fuel blends were tested experimentally; all exhibited increasing ignition probability as equivalence ratio increased, at least up to the maximum value studied (∼0.8). Statistically significant differences between fuels were measured that have some correlation with fuel properties. To elucidate these trends, the forced ignition process was also studied with a reduced-order numerical model of an entraining kernel. The simulations suggest ignition is successful if sufficient heat release occurs before entrainment of colder crossflow fluid quenches the exothermic oxidation reactions. As the kernel is initialized in air, it remains extremely lean during the initial entrainment of the fuel–air mixture; thus, richer crossflows lead to quicker and higher exothermicity.

High-Speed Imaging of Forced Ignition Kernels in Nonuniform Jet Fuel/Air Mixtures

“…An industrial gas turbine engine igniter, utilized in previous studies [9,13], produced sparks with a nominal deposition energy of 1.25 J/spark at a frequency of 15 Hz. After each discharge, the resulting high pressure in the cavity ejects a high-temperature plasma kernel into the crossflow.…”

“…Physical properties of liquid fuels will affect atomization [3,11,12] and vaporization [2,11], thereby influencing local fuel-air ratios. Chemical components of various jet fuels blends have also been shown to have statistically significant effect on ignition probability [6,13]. For example, a study of forced ignition in a striated flow with a sunken fire igniter [13] compared various conventional and synthesized fuels.…”

“…Chemical components of various jet fuels blends have also been shown to have statistically significant effect on ignition probability [6,13]. For example, a study of forced ignition in a striated flow with a sunken fire igniter [13] compared various conventional and synthesized fuels. The fuels were prevaporized to remove the influence of physical properties and isolate chemical composition effects.…”

“…Therefore, the primary objective of this work is to elucidate the processes by which a forced ignition kernel evolves into a selfsustained flame in the early times after a spark discharge using high-speed imaging diagnostics. Additionally, this work examines the effect of fuel composition on forced ignition success by comparing the three fuels identified in the earlier study [13].…”

Performance and Emission Study on a Dual Fuel Engine with Modified Gas Inlet

“…LPG duel fuel engines have a good thermal efficiency at high output but the performance is less during part load conditions due to the poor utilization of charges. This problem can be solved by varying injection timing, composition of the gaseous fuel and intake charge conditions, for improving the performance, combustion and emissions of dual fuel engines [17]. The objective of the present work is to develop a dual fuel engine test rig operating on LPG-diesel fuel with some modifications in the intake manifold for better mixing of the secondary fuel and to compare the engine performance characteristics without modifications and along with sole fuel.…”