Shamit Bakshi

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 Gasoline Direct Injection (GDI) engine typically operates on multiple fuel-preparation modes. In general, at higher loads a homogeneous mixture is favoured whereas a stratified mixture is preferred at part and low load conditions. This is usually achieved by altering the injection timing with respect to load and speed. In this paper the effect of injector configuration on the mixing process has been studied systematically. Two different injector configurations are considered, one with a central-hole injection and other with a 6-hole injection. The objective is to investigate the effect of initial fuel distribution inside the engine cylinder on charge preparation at the onset of ignition. This study also aims to explore a better solution for mixing in GDI engines by optimizing the GDI injector for both stratified and homogeneous mode of operations. An engine with a pentroof combustion chamber with centrally mounted injector and upright straight intake port and flat piston is selected. The computation begins from the start of the induction process and continued till the point of ignition. The dynamics of the mixing process is studied by grouping the in-cylinder charge in different bins in terms of the equivalence ratio. The temporal variation of the fraction of the mixture in different bins is studied as a function of time to understand the dynamics of the mixing process. Results from the parametric study indicate the possibility of switching the modes of mixing with respect to the operating conditions.

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 paper reports on experimental and theoretical investigations of the impact of a droplet onto a spherical target. Spatial and temporal variation of film thickness on the target surface is measured. Three distinct temporal phases of the film dynamics are clearly visible from the experimental results, namely the initial drop deformation phase, the inertia dominated phase, and the viscosity dominated phase. Experiments are also conducted to study the effect of droplet Reynolds number and target-to-drop size ratio on the dynamics of the film flow on the surface of the target. It is observed that for a given target-to-drop size ratio, the nondimensional temporal variation of film thickness collapses onto a single curve in the first and second phases. The transition to the viscosity dominated regime occurs earlier for the low Reynolds number cases and residual thickness is also larger. A simplified quasi-one-dimensional approach has been used to model the flow on the spherical target. The theory accounts for the inertial and viscous effects. Gravity and the curvature of the target are also taken into account. An analytical expression for the time-dependent film profile on the sphere is obtained for the inviscid, inertia dominated phase of spreading. Then, the evolution equation for the film thickness near the north pole in the viscosity dominated phase is obtained and solved. Good agreement is observed between the theoretical predictions and the measurements when the values of the drop and target diameters are comparable. No adjustable parameters have been used in the model. © 2007 American Institute of Physics.

A new air-assisted injection system-based two-stroke engine has been developed at the Indian Institute of Science, Bangalore over the past few years and shows the potential to meet emission norms such as Euro II and Euro III and yet deliver satisfactory performance. The 70 cc engine works on the direct mixture injection principle with scavenging performed by air alone instead of an air-fuel mixture. A small 20 cc pump driven off the engine is used for mixture preparation prior to in-cylinder injection of the mixture. In the present study, the mixture injection and subsequent charge stratification process inside the engine cylinder is modelled. A three-dimensional compressible flow code with a standard k-ε turbulence model with wall functions is developed and used for this modelling. 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 modelling 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, the sensitivity of two critical parameters in the mixing and stratification is investigated. The suggested parameters substantially enhance the flammable proportion at the onset of combustion. The predicted pressure-crank angle history from a combustion simulation supports this recommendation. © IMechE 2007.

In this work, three-dimensional fuel-air mixing inside a conventional spark ignition engine cylinder is simulated under direct injection conditions. The motivation is to explore retrofitting of conventional engines for direct injection to take advantage of low emissions and high thermal efficiency of the direct injection concept. Fuel-air mixing is studied at different loads by developing and applying a model based on the Lagrangian-drop and Eulerian-fluid (LDEF) procedure for modelling the two-phase flow. The Taylor Analogy Breakup (TAB) model for modelling the hollow cone spray and appropriate models for droplet impingement, drag and evaporation are used. Moving boundary algorithm and two-way interaction between both phases are implemented. Fuel injection timing and quantity is varied with load. Results show that near-stoichiometric fuel-air ratio region is observed at different locations depending on the load. The model developed serves to predict the fuel-air mixing spatially and temporally, and hence is a useful tool in design and optimization of direct injection engines with regards to injector and spark plug locations. Simulations over a range of speed and load indicate the need for a novel ignition strategy involving dual spark plugs and also provide guidelines in deciding spark plug locations. © Printed in India.

The possibility of multiple-injection in Common Rail Direct Injection (CRDI) engine allows achieving improved combination of oxides of nitrogen (NOx) and smoke emissions. In CRDI engines, the turbulent kinetic energy due to high pressure fuel injection is primarily responsible for fuel air mixing and hence the in-cylinder mixture formation. The air fuel mixing characteristics in the case of multiple-injection are quite different from that of single injection schedule. In this work a zero-dimensional model is proposed for mixing rate calculations with multiple-injection scheduling. The model considers generation and dissipation of in-cylinder turbulence through processes namely fuel injection, air swirl and combustion. The model constants are fine tuned with respect to the data available in existing literature. The model predictions are validated with the available data for the cylinder pressure and heat release rate histories on known single and multiple-injection schedules. These comparisons show good agreement to establish the role of mixing rate variations with multiple-injection. A single set of constants were found to match the cylinder pressure and heat release rate histories for single and multiple-injection from different sources in the literature. Further, the mixing rate and peak temperature predictions of the model are found to relate with the possible effect of specific injection scheduling on emission reductions reported in CRDI engine investigations. Copyright © 2009 by ASME.