Equivalence Ratio Distribution Research Articles

An LIF equivalence ratio imaging technique for multicomponent fuels in an IC engine

A method for identifying fuel/tracer mixtures suitable for laser-induced fluorescence (LIF) measurements of in-cylinder equivalence ratios is presented. The concentrations of multiple LIF tracers are adjusted so that the total vapor-phase fluorescence is proportional to the instantaneous mass evaporation rate. In this way, LIF image intensities are proportional to local fuel mass, which in turn can be converted into local fuel equivalence ratios. Uncertainty generated by pressure and temperature dependencies of ketone tracers is assessed. A two-fuel-component mixture developed with the method is used to measure two-dimensional fuel equivalence ratios in an optically accessible direct-injection spark-ignition engine. Results are compared with the equivalence ratio distribution of a mixture with a single fuel component. It is found that the effect of fuel volatility on the equivalence ratio distribution at the time of spark becomes more distinct as the start-of-injection timing is retarded.

Mixing of Multiple Jets With a Confined Subsonic Crossflow: Part I—Cylindrical Duct

This paper summarizes NASA-supported experimental and computational results on the mixing of a row of jets with a confined subsonic crossflow in a cylindrical duct. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex three-dimensional flowfield in the combustion chambers in gas turbine engines. The principal observations were that the momentum-flux ratio and the number of orifices were significant variables. Jet penetration was critical, and jet penetration decreased as either the number of orifices increased or the momentum-flux ratio decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the number of orifices was proportional to the square root of the momentum-flux ratio. In the cylindrical geometry, planar variances are very sensitive to events in the near-wall region, so planar averages must be considered in context with the distributions. The mass-flow ratios and orifices investigated were often very large (mass-flow ratio >1 and ratio of orifice area-to-mainstream cross-sectional area up to 0.5), and the axial planes of interest were sometimes near the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations. The results shown also seem to indicate that nonreacting dimensionless scalar profiles can emulate the reacting flow equivalence ratio distribution reasonably well. The results cited suggest that further study may not necessarily lead to a universal “rule of thumb” for mixer design for lowest emissions, because optimization will likely require an assessment for a specific application.

Analysis of combustion chamber insulation effects on the performance and exhaust emissions of a DI diesel engine using a multi-zone model

A comprehensive two-dimensional multi-zone model of a diesel engine cycle is presented in this study, in order to examine the influence of insulating the combustion chamber on the performance and exhaust pollutants emissions of a naturally-aspirated, direct injection (DI), four-stroke, water-cooled diesel engine. The heat insulation is taken into account by the corresponding rise of wall temperature, since this is the final result of insulation useful for the study. It is found that there is no remarkable improvement of engine efficiency, since the decrease of volumetric efficiency has a greater influence on it than the decrease of heat loss to the coolant, which is converted mainly to exhaust gas enthalpy (significant rise of the exhaust gas temperature). As far as the concentration of exhaust pollutant emissions is concerned, it is found that the rising heat insulation leads to a significant increase of the exhaust nitric oxide (NO) and to a moderate increase of the exhaust soot concentration. Plots of temperature, equivalence ratio, NO and soot distributions at various instants of time inside the combustion chamber, emanating from the application of the multi-zone model, aid the correct interpretation of the insulation effects gaining insight into the underlying mechanisms involved.

Analysis of combustion and pollutants formation in a direct injection diesel engine using a multi-zone model

A two-dimensional multi-zone model for the calculation of the closed cycle of a direct injection (DI) diesel engine is presented. The fuel spray is divided into small packages and the effect of air velocity pattern on spray development is taken into account. The calculation of swirl intensity variations during the cycle is based on hybrid solid body-boundary layer rotation scheme. Application of the mass, energy and state equations in each zone yields local temperatures and cylinder pressure histories. For calculating the concentration of constituents in the exhaust gases, a chemical equilibrium scheme is adopted for the C-H-O system of the eleven species considered, together with chemical rate equations for the calculation of nitric oxide (NO). A model for the evaluation of soot formation and oxidation rates is incorporated. A comparison is made between the theoretical results from the computer program implementing the analysis, with experimental results from a vast experimental investigation conducted on a direct injection, Lister-Petter diesel engine, with very encouraging results. Plots of temperature, equivalence ratio, NO and soot distributions inside the combustion chamber are presented, elucidating the physical mechanisms governing combustion and pollutants formation.

Mixing and chemical kinetic constraints on PIC production during chlorocarbon combustion

The amount and composition of products of incomplete combustion (PICs) in combustion systems is controlled by the complex interactions of turbulent mixing and chemical kinetics. The current paper addresses this problem by focusing on the effects of incomplete turbulent mixing on the extent of reaction and on the distribution of the local equivalence ratio, and investigating the contributions of chlorocarbon inhibition of chemical reaction to the emission of PICs. The experimental facility has been designed to simulate the conditions in actual incinerator systems; it consists of a Toroidal Jet Stirred Reactor (TJSC) followed by a Plug Flow Reactor (PFR). The experimental conditions allow one to investigate the combined effects of turbulent mixing and chemical kinetic inhibition on PIC emissions. To address these issues methyl chloride is injected into a baseline flow of hot products flowing in the PFR. Instantaneous temperature measurement, obtained by application of a laser Rayleigh scattering diagnostic, and stable species concentrations are then measured at various distances from the point of injection. The temperature probability density functions (pdfs) for fuel-lean and fuel-rich conditions show evidence of mixing constraints. Stable species concentration measurements prove that both mixing and chemical kinetic constraints are present in the PFR environment. Detection of aromatic species is interpreted as an effect of the variation of the local value of the equivalence ratio due to imperfect mixing. Finally, in order to model the combined chemical kinetic and mixing constraints and to determine which constraints are responsible for PIC emission, results from a highly simplified turbulent reacting flow model are presented. The model can predict the trend and magnitude of methyl chloride burnout and CO CO 2 ratio. Species, such as aromatic compounds, having a strong non-linear dependence on the equivalence ratio can provide insights on the mixing history and might serve as diagnostics of failure modes in incinerators.

Effect of water content on pollutant formation in a burning spray of water-in-diesel fuel emulsion

The effect of varying the water content of a range of water-in-diesel fuel emulsions on the combustion process in a confined continuously burning spray, while keeping other parameters constant, is described. Experimental measurements of the concentrations of the products of combustion and of temperature have been made using a steady-state combustion installation. Results obtained close to the combustion chamber exit are presented for tests with diesel fuel and with water-in-diesel fuel emulsions of water content up to 15% by volume. The tests are at a combustion pressure of 653 kPa and at two input equivalence ratios (0.871 and 1.085) based on the air-diesel fuel component ratio. Under these operating conditions the soot emission appears to be minimised for the emulsion having a water content of 5% by volume. The magnitudes of temperature and of the concentrations of the various species measured along the axis of the chamber are presented, together with the spatial distributions of these parameters in the form of isotherms and iso-concentration contours within the combustion chamber, for diesel fuel and for the emulsion of optimum water content again at 653 kPa and at the higher input equivalence ratio. A marked reduction in soot formation is observed together with a more even distribution of the vapour equivalence ratio inside the chamber for the burning emulsion. Combustion appears to approach completion more rapidly than in the case of the diesel fuel.

Stabilization Mechanism of Turbulent Wake Flame Behind Bluff Bodies with Fuel Injection : 1st Report, Blow-off Limits

Stability of wake flames formed behind a bluff-body with fuel injection was investigated experimentally in various geometries of two-dimensional bluff-bodies such as cylinders with 10-20mm diameters, hemi-circle, 60°wedge and rectangular rods of 12.5mm width. The bluff-body was located in an air stream flowing 5-60m/s. Fuels used were propane, methane, ethylene and butane. Flame stability limits, length or geometry of recirculation zone, distribution of chemical species concentrations, temperature and equivalence ratio in the zone were measured. The results show that the equivalence ratio in the recirculation zone is important in determining the flame limit. The air velocity at blow-off is inversely proportional to the square root of the bluff-body width, and is independent of the direction of fuel injection and the geometry of flame holder except for the rectangular rod.

Modelling the Fuel Temperature Effect on Flame Spread Limits in Opposed Flow

Abstract A numerical model of flame spread on a thermally thin fuel in opposed flow (Frey and T'ien, 1979) has been used to study the effect of the initial fuel bulk temperature on the extinction limit. The distribution of temperature, fuel fraction, reactivity, and local equivalence ratio are presented and analyzed for the near-limit case. When the fuel temperature is decreased, the fuel pyrolysis rate near the pyrolysis front decreases, the flame spread rate drops, the pyrolysis length diminishes and the flame size is reduced. When the flame reaches a certain critical size, depending on a number of parameters, extinction occurs.