Department of Mechanical Engineering

Indian Institute of Technology Palakkad&nbsp;(IIT Palakkad or IIT PKD) is a public autonomous&nbsp;engineering&nbsp;and&nbsp;research&nbsp;institute located in&nbsp;Palakkad,&nbsp;Kerala. It was&nbsp;one of the five new&nbsp;IITs&nbsp;proposed in the&nbsp;2014 Union budget of India. The campus was inaugurated on 3 August 2015. The institute has 94 faculty, 978 students, and 63 non-teaching staffs.

IT Palakkad currently offers four-year Bachelor of Technology (B.Tech) and two years MS programmes in 8 different engineering disciplines including&nbsp;Computer Science, Electrical, Mechanical, Civil among others.

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IIT Palakkad

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. Copyright © 2005 by ASME.

World University root node

ASME 2005 Internal Combustion Engine Division Fall Technical Conference, ICEF 2005

COMPUTATIONAL STUDIES ON CHARGE STRATIFICATION AND FUEL-AIR MIXING IN A NEW TWO-STROKE ENGINE

Multi-dimensional computational fluid dynamics simulations were carried out on the intake manifold and cylinder of a four-stroke single cylinder two-wheeler engine. The complex geometry of the manifold and the engine cylinder and the motion of the intake valve were taken into consideration. Both air flow and two-phase calculations were done to predict the trajectory of the liquid fuel and identify regions of impingement which could lead to film formation and high emissions at startup. The results show that the present geometry of the manifold is non-optimum as large recirculation zones are present. The two-phase simulations show that fuel transport is significantly affected due to the recirculation under idling conditions and significant impingement occurs. The numerical results obtained could be utilized to improve the flow in the manifold for lowering emissions. Copyright © 2005 by ASME.

MULTI-DIMENSIONAL, TRANSIENT FLUID FLOW SIMULATIONS IN THE MANIFOLD OF A FOUR-STROKE SINGLE CYLINDER ENGINE

Stiffness and damping coefficients of isothermal elastohydrodynamically lubricated point-contact problems are evaluated numerically with couple-stress fluids. A set of equations under steady-state and dynamic conditions is derived from the modified Reynolds equation using a linearized perturbation method. This paper is the second part of the present study; the modified Reynolds equation derived from the Stokes microcontinuum theory is used in the previous article. Dynamic pressures are found after solving the set of perturbed equations using the previously obtained steady-state pressure from the modified Reynolds equation. The stiffness and damping coefficients of the film are determined using the dynamic pressures. Then the overall stiffness and damping matrices of the ball bearing are obtained from load distribution, coordinate transformation, and compatibility relations. The bearing coefficients are introduced into a rotor system to simulate the response. It has been observed that the influence of couple-stress fluids on the dynamics of a rotor supported on lubricated ball bearings is marginal; hence, Newtonian theory can be used instead for simplicity. However, with increasing content of polymer additives in lubricant, for an accurate analysis the effect of couple stresses in a fluid should not be neglected. Copyright © Society of Tribologists and Lubrication Engineers.

Tribology Transactions

Elastohydrodynamically lubricated ball bearings with couple-stress fluids, part II: Dynamic analysis and application

The vibration in rotating machinery is mostly caused by unbalance, misalignment, mechanical looseness, shaft crack, and other malfunctions. The diagnostics of rotor faults have been gaining importance in recent years. Many papers in the literature have dealt with single fault identification, but, normally, more than one fault can occur in a rotor. In the present study a model-based method is proposed for the on-line identification of faults in a rotor. The fault-induced change of the rotor system is taken into account by equivalent loads in the mathematical model. The equivalent loads are virtual forces and moments acting on the linear undamaged system to generate a dynamic behavior identical to that measured in the damaged system. The rotor has been modeled using the finite element method with unbalance and crack as the considered faults. Different shape expansion methods are compared for fault identification. The identification process is also simulated when both unbalance and crack are acting simultaneously on the rotor. The fault size and location have been identified while the nature and symptoms of the faults are ascertained using fast Fourier transform. © 2005 Sage Publications.

JVC/Journal of Vibration and Control

Identification of unbalance and crack acting simultaneously in a rotor system: Modal expansion versus reduced basis dynamic expansion

We consider steady, fully developed flows of inelastic grains driven by gravity between identical bumpy walls. Bumpy walls provide a mechanism for the production or dissipation of fluctuation energy that can maintain a steady, fully-developed flow. Using balance equations, constitutive relations and boundary conditions that result from kinetic theory, we calculate the fields of mean velocity, fluctuation velocity and concentration across the chute, for a variety of flow rates, particle parameters and chute width. We find two qualitatively different steady flow regimes. One is a dense flow regime with low mean velocity while the other is one with a dilute flow and higher mean velocity. © 2005 Taylor & Francis Group.

Powders and Grains 2005 - Proceedings of the 5th International Conference on Micromechanics of Granular Media

Collisional flows of identical, smooth, nearly elastic spheres in a vertical chute

The dynamics and diagnostics of cracked rotor have been gaining importance in recent years. In the present study a model-based method is proposed for the on-line identification of cracks in a rotor. The fault-induced change of the rotor system is taken into account by equivalent loads in the mathematical model. The equivalent loads are virtual forces and moments acting on the linear undamaged system to generate a dynamic behaviour identical to the measured one of the damaged system. The rotor has been modelled using finite element method, while the crack is considered through local flexibility change. The crack has been identified for its depth and location on the shaft. The nature and symptoms of the fault, that is crack, are ascertained using the fast fourier transform. © 2003 Elsevier Ltd.

Journal of Sound and Vibration

Crack identification in a rotor system: A model-based approach

A numerical solution for the stiffness and damping characteristics of an isothermal, elastohydrodynamically lubricated point contact is presented considering the surface roughness effect and variation in viscosity with pressure. An attempt has been made to derive empirical formulae for the calculation of stiffness and damping coefficients of lubricated point contacts with a non-linear least-squares curve-fitting technique using different numerically evaluated data, thereby avoiding time-consuming numerical calculations. From this the overall stiffness and damping matrices of the ball bearing are obtained with a proper load distribution. A comparative study on the dynamics of a rotor-bearing system is carried out for a dry contact ball bearing, a lubricated contact ball bearing and a plain journal bearing. © IMechE 2004.

Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology

Stiffness and damping characteristics of lubricated ball bearings considering the surface roughness effect. Part 2. Numerical results and application

The stiffness and damping characteristics of isothermal, elastohydrodynamically lubricated point contact problems are evaluated numerically considering the surface roughness effect and variation in viscosity with pressure. A set of equations under steady-state and dynamic conditions is derived from the classical Reynolds equation using the linear perturbation method. The elasticity equation and steady-state Reynolds equation are solved simultaneously using the finite difference method with the successive over-relaxation scheme, whereas the dynamic pressures are found after solving the set of perturbed equations using the previously obtained steady-state pressures. The load capacity is obtained from the steady-state pressure distribution. The stiffness and damping coefficients of the contact are determined using the dynamic pressures. Then the overall stiffness and damping matrices of the ball bearing are obtained from the load distribution, coordinate transformation, and compatibility relations. © IMechE 2004.

Stiffness and damping characteristics of lubricated ball bearings considering the surface roughness effect. Part 1: Theoretical formulation

A Jeffcott rotor with a transverse crack has been considered in the present study. Equations of motion for transient response have been developed and dynamic analysis has been carried out to consider the effects of fluid film bearings. The coast-down phenomenon was analysed by considering the dissipation through the journal film and by evaluating the deceleration for each speed. Characteristic sub-critical response peaks have been found when the cracked rotor decelerates through its critical speed. The continuous wavelet transform (CWT) has been used as a tool to extract the above sub-harmonics from the time domain signals. The use of CWT has been suggested for crack detection and monitoring in a rotor system coasting down through its critical speed. © 2003 Elsevier Ltd. All rights reserved.

Tribology International

Detection and monitoring of crack in a coast-down rotor supported on fluid film bearings

The dynamics and diagnostics of rotor with vaults have been gaining importance in recent years. In the present study a model-based method is proposed for the on-line identification of faults In a rotor. The fault-induced change of the rotor system is taken into account by equivalent loads in the mathematical model. The equivalent loads are virtual forces and moments acting on the linear undamaged system to generate a dynamic behaviour identical to the measured one of the damaged system. The rotor has been modelled using FEM. Each fault has been identified for its size and location on the shaft for transient and steady rotors. The nature and symptoms of the fault are ascertained using FFT or Wavelet transforms. For on-line rotor fault identification a combined (hybrid) model and signal-based approach is suggested.