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Diffusion flame
About: Diffusion flame is a research topic. Over the lifetime, 9266 publications have been published within this topic receiving 233522 citations.
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TL;DR: In this article, the use of small injector tip orifices was shown to enable non-sooting and low flame temperature combustion in two different ways as summarized below, while the injector was fully open (i.e. during the mixing-controlled phase of heat release for diesel combustion).
Abstract: Methods of producing non-sooting, low flame temperature diesel combustion were investigated in an optically-accessible, quiescent constant-volume combustion vessel under mixing-controlled diesel combustion conditions. Combustion and soot processes of single, isolated fuel jets were studied after auto-ignition and transient premixed combustion and while the injector was fully-open (i.e. during the mixing-controlled phase of heat release for diesel combustion). The investigation showed that small injector tip orifices could be used to produce non-sooting and low flame temperature combustion simultaneously. The use of small orifices was shown to enable non-sooting and low flame temperature combustion in two different ways as summarized below. A more detailed description of the experimental methods and results is provided in Ref. [1-3]. First, using an injector tip with a 50 micron orifice and ambient oxygen concentrations as low as 10% (simulating the use of extensive EGR), a fuel jet was non-sooting at typical diesel ambient temperatures (1000 K). Second, using the same injector tip at a reduced ambient gas temperature (850 K), but with 21% oxygen, it was shown that non-sooting, mixing-controlled combustion occurred at the lift-off length in a fuel-air mixture with a cross-sectional average equivalence ratio of approximately 0.6-suggesting that the quasi-steady combustion was fuel-lean andmore » thereby avoided the formation of a diffusion flame. The adiabatic flame temperature with reduced ambient oxygen concentration or fuel-lean combustion was approximately 2000 K, compared to typical diesel flame temperatures that exceed 2600 K. The 50 micron orifice results above were obtained using a No.2 diesel fuel. However, using an oxygenated fuel (20 wt% oxygen), the investigation showed that the same low temperature combustion, either with reduced ambient oxygen concentration or fuel-lean combustion, was realized with a 100 micron orifice. Although these single, isolated jets do not have jet-jet interactions that would occur in realistic engines, the results are useful for understanding limiting-case behavior of single-jet mixing and combustion during an injection event. The non-sooting and low flame temperature mixing-controlled combustion realized using small orifice tips suggests that the use of small orifices offers the potential for a simultaneous soot and NOx reduction in an engine, much like diesel HCCI combustion. However, further research is needed to determine whether these methods could be successfully implemented in real engines.« less
232 citations
TL;DR: In this paper, the effects of changes in intake temperature and pressure on the pre-ignition of turbo-charged engines were investigated. But the results were limited to the case of turbocharged engines, and they were concluded from the evidence of engine pressure records.
Abstract: Earlier studies of pre-ignitions at hot surfaces are first reviewed. The concept of a critical radius of a hot pocket of gas, closely related to the laminar flame thickness, that is necessary to initiate a propagating flame, has been used successfully to predict relative tendencies of different fuel–air mixtures to pre-ignite. As the mixture is compressed, the thickness of potential laminar flames decreases, and when this becomes of the order of the thermal sheath thickness at the hottest surface, pre-ignition can occur there, creating a propagating flame. Measured engine pre-ignition ratings are shown to correlate well with laminar flame thicknesses. Predictions are made concerning the effects of changes in intake temperature and pressure on the pre-ignition of different fuels.A growing current concern is occasional gas-phase, autoignitive, pre-ignitions that can occur in turbo-charged engines, giving rise to very severe autoignition and knock. It is concluded from the evidence of engine pressure records...
229 citations
TL;DR: In this paper, an analytical theory of flame acceleration is developed, which determines the growth rate, the total acceleration time, and the maximal increase of the flame surface area, and direct numerical simulations of the process are performed for the complete set of combustion equations.
229 citations
TL;DR: In this article, the premixed stoichiometric turbulent methane flames are investigated on a piloted Bunsen burner with a nozzle diameter of 12 mm and mean nozzle exit velocities of 65, 50, and 30 m/s.
228 citations
TL;DR: In this article, a free spherical or cylindrical laminar flame from a weak source of ignition, in the absence of any significant perturbations (rigid wall, obstacles, buoyancy forces), does indeed become unstable, turbulent, and self-accelerating, but for Re e 103-105.
Abstract: L. D. Landau believed that hydrodynamic instability of a flame, which he discovered theoretically [i], should in itself lead to the appearance of turbulent motion and to turbulent propagation of the combustion front already for Reynolds numbers Re = unR/v ~ 1 (u n is the normal rate of combustion and R is the radius of the visible front). Experiments show that a free spherical or cylindrical laminar flame from a weak source of ignition, in the absence of any significant perturbations (rigid wall, obstacles, buoyancy forces), does indeed become unstable, turbulent, and self-accelerating, but for Re e 103-105 .
228 citations