Anand T.N.C.

In this paper, detailed computational study is presented which helps to understand and improve the fuel-air mixing in a new direct-mixture-injection two-stroke engine. This new air-assisted injection system-based two-stroke engine is being developed at the Indian Institute of Science, Bangalore over the past few years. It shows the potential to meet emission norms such as EURO-II and EURO-III and also deliver satisfactory performance. This work proposes a comprehensive strategy to study the air-fuel mixing process in this engine and shows that this strategy can be potentially used to improve the engine performance. A three-dimensional compressible flow code with standard k - ε turbulence model with wall functions is developed and used for this modeling. To account for the moving boundary or piston in the engine cylinder domain, a non-stationary and deforming grid is used in this region with stationary cells in the ports and connecting ducts. A flux conservation scheme is used in the domain interface to allow the in-cylinder moving mesh to slide past the fixed port meshes. The initial conditions for flow parameters are taken from the output of a three-dimensional scavenging simulation. The state of the inlet charge is obtained from a separate modeling of the air-assisted injection system of this engine. The simulation results show that a large, near-stoichiometric region is present at most operating conditions in the cylinder head plane. The state of the in-cylinder charge at the onset of ignition is studied leading to a good understanding of the mixing process. In addition, sensitivity of two critical parameters on the mixing and stratification is investigated. The suggested parameters substantially enhance the flammable proportion at the onset of combustion. The predicted P - θ from a combustion simulation supports this recommendation. Copyright © 2005 by ASME.

A large number of studies in the literature have looked at secondary atomization of Newtonian liquids such as n-Heptane, water, ethyl alcohol, mercury and glycerol solutions, and ‘drop deformation and breakup regime maps’ have been plotted based on the studies. The aim of the present research is to study the secondary atomization of heated liquids. One of the liquids that was studied is molten beeswax which is a shear-thinning non-Newtonian liquid. A mono-disperse stream generator equipped with a piezo-stack and a heater produced mono-disperse droplets of molten beeswax and their breakup due to cross-flow was captured using backlit imaging. The continuous jet method was used in this study. The Weber number was varied by changing the velocity of air jet, and bag breakup, multimode breakup and sheet-thinning breakup were observed in the range studied.

It is known from recent studies that evaporation induces flow around a droplet at atmospheric conditions. This flow is visible even for slowly evaporating liquids like water. In the present study, we investigate the influence of the ambient gas on the evaporating droplet. We observe from the experiments that the rate of evaporation at atmospheric temperature and pressure decreases in a heavier ambient gas. The evaporation-induced flow in these gases for different liquids is measured using particle image velocimetry and found to be very different from each other. However, the width of the disturbed zone around the droplet is seen to be independent of the evaporating liquid and the size of the needle (for the range of needle diameters studied), and only depends on the ambient gas used.

Experiments are carried out on an evaporating pendant droplet and the flow induced around the droplet due to evaporation is studied for different ambient gases. A pendant drop of ethanol is formed on a steel needle in a closed chamber maintained at room temperature (301 K). The chamber is filled with a pure gas (nitrogen, oxygen, argon or carbon dioxide). The evaporating droplet causes a flow due to thermal buoyancy (due to the temperature difference caused by evaporative cooling) and solutal buoyancy (due to the difference in molecular weight between the evaporating liquid and surrounding gas). This flow around the evaporating droplet is characterized by using PIV (particle image velocimetry) technique. From these experiments, it is observed that the flow characteristics such as the velocity and penetration length of the flow changes depending upon the molecular weight of the ambient gas. It is observed that the flow penetrates significantly in case of a lower molecular weight gas (e.g. nitrogen) and the penetration decreases with increasing molecular. This, in turn, affects the evaporation rate of the suspended droplet.

The combustion characteristics and emissions in IC engines are influenced by the fuel injection rate. The study of fuel injection rate profile thus becomes essential to improve engine performance. In the present study, the injection rate of GDI injectors was measured in terms of the instantaneous mass flow rate of fuel. A setup was fabricated to obtain the injection rate based on Bosch tube method. Multi-hole GDI injectors of two different manufacturers were used in this study and their performances were measured up to 175 bar of injection pressure. The injector energizing current, wave pressure and rail pressure data were acquired at the rate of 500 kHz on a common time scale. The injected mass value per pulse, obtained by integrating the discharge rate profile was compared with the average values of mass injected measured using a mass balance for both the injectors and their performance were compared. The hydraulic delay measured during injector closing was found to be more than that during injector opening for both the injectors. Injection rate values for any given energizing time was found to be higher for one of the injectors by both the rate profile method and the mass balance averaging method.

A simple computational model was created to predict the vaporization rates of droplets of urea-water-solution (UWS) evaporating in a hot air stream. A single-component evaporation model, which was based on Abramzon-Sirignano's vaporization model, was adapted to handle UWS droplets, and the governing equations were solved numerically in MATLAB®. The temperature and species concentrations within the droplet were assumed to be uniform, and various methods available in literature were employed to estimate important thermophysical properties such as saturation vapor pressures, partial pressures, vaporization enthalpy, and vapor diffusivities. The suitability and limitations of the computational model were assessed by comparing the results with experimental data on UWS droplets evaporating under forced convective conditions. The temperatures considered in this study ranged from 373 K to 673 K, and the corresponding relative air velocities were between 1.5 m/s and 4.3 m/s. The model was found to be able to capture the two-stage vaporization behavior of the UWS droplet (except crystallization, puffing and micro-explosion) with reasonable accuracy. While the first-stage vaporization rates, predicted by the model, were accurate to within 1.8% to 17.7%, the accuracies of the second-stage vaporization rates were significantly dependent on the methods used to estimate fluid properties such as the vapor pressures and the vaporization enthalpy.

This work reports the measured spray structure and droplet size distributions of ethanol-gasoline blends for a low-pressure, multi-hole, port fuel injector (PFI). This study presents previously unavailable data for this class of injectors which are widely used in automotive applications. Specifically, gasoline, ethanol, and gasoline-ethanol blends containing 10%, 20% and 50% ethanol were studied using laser backlight imaging, and particle/droplet image analysis (PDIA) techniques. The fuel mass injected, spray structure and tip penetrations, droplet size distributions, and Sauter mean diameter were determined for the blends, at two different injection pressures. Results indicate that the gasoline and ethanol sprays have similar characteristics in terms of spray progression and droplet sizes in spite of the large difference in viscosity. It appears that the complex mode of atomization utilized in these injectors involving interaction of multiple fuel jets is fairly insensitive to the fuel viscosity over a range of values. This result has interesting ramifications for existing gasoline fuel systems which need to handle blends and even pure ethanol, which is one of the renewable fuels of the future. © 2012 Elsevier Ltd. All rights reserved.

In this paper, detailed computational study is presented which helps to understand and improve the fuel-air mixing in a new direct-mixture-injection two-stroke engine. This new air-assisted injection system-based two-stroke engine is being developed at the Indian Institute of Science, Bangalore over the past few years. It shows the potential to meet emission norms such as EURO-II and EURO-III and also deliver satisfactory performance. This work proposes a comprehensive strategy to study the air-fuel mixing process in this engine and shows that this strategy can be potentially used to improve the engine performance. A three-dimensional compressible flow code with standard k−2 turbulence model with wall functions is developed and used for this modeling. To account for the moving boundary or piston in the engine cylinder domain, a non-stationary and deforming grid is used in this region with stationary cells in the ports and connecting ducts. A flux conservation scheme is used in the domain interface to allow the in-cylinder moving mesh to slide past the fixed port meshes. The initial conditions for flow parameters are taken from the output of a three-dimensional scavenging simulation. The state of the inlet charge is obtained from a separate modeling of the air-assisted injection system of this engine. The simulation results show that a large, near-stoichiometric region is present at most operating conditions in the cylinder head plane. The state of the in-cylinder charge at the onset of ignition is studied leading to a good understanding of the mixing process. In addition, sensitivity of two critical parameters on the mixing and stratification is investigated. The suggested parameters substantially enhance the flammable proportion at the onset of combustion. The predicted P - θ from a combustion simulation supports this recommendation. EF/proceedings.

This article presents work carried out on a small, 4-stroke, SI engine, incorporated with an ultrasonic atomizer-based fueling system. A disc-type ultrasonic atomizer having good atomization characteristics was incorporated in the air intake path of a single cylinder, two-wheeler engine, replacing the conventional carburetor. This new fueling system was introduced with the aim of reducing the engine fuel consumption, while looking for a possible reduction in exhaust emissions. An electronic control mechanism was devised to change the atomization rate, in order to set the desired equivalence ratio for optimum engine operation. Test results indicate a significant improvement in fuel consumption and brake thermal efficiency, with a good control over the equivalence ratio. The system also allows engine operation at equivalence ratios as low as 0.5, and hence could be adopted for ultra-lean engines. This atomizer fueling system allows the use of closed loop lambda control which is required for meeting stringent automotive emission norms.

This paper reports results of an experimental study on various fluid patterns produced by two symmetric impinging Newtonian liquid jets. Water–glycerol mixtures with viscosities of 5 mPa·s, 15 mPa·s, and 40 mPa·s were used to study the effect of viscosity on fluid patterns. Two liquid jets with a diameter of 0.76 mm each were made to impinge on each other. Images in the plane perpendicular to both liquid jets were captured using a backlight direct imaging method using a 4 MPixel CCD camera. New types of periodic patterns, which to date have not been reported for Newtonian liquids, were observed in this study. It was observed that the velocity at which periodic patterns start to appear depends on the liquid viscosity. A fish-bone-like periodic structure was observed only with the 5 mPa·s liquid, while periodic shedding of droplets from the rim is not observed with the 40 mPa·s viscosity liquid. Periodic patterns were observed for all the liquids only at an impinging angle of 60 o , unlike in earlier studies where the patterns were observed with an impinging angle of 90 o . It was also observed that significant asymmetry between the liquid jets is not necessary for the formation of periodic patterns.