Anastasios Karkanis

Boundary-orthogonal biharmonic grids via preconditioned gradient methods

A finite difference approximation of the biharmonic equation is solved using three preconditioned gradient methods for the generation of curvilinear boundary-orthogonal grids in two dimensions. The developed algorithms based on the conjugated gradient, the steepest descent, and the minimal residual method are applied in a number of domains of engineering interest for the purpose of comparison in terms of CPU time and number of iterations to convergence.

Measurements of three-way catalyst performance under a stepwise constant idle speed schedule

The present paper analyses the results from a series of experiments involving tests of catalysts under a stepwise constant engine idle speed schedule in the form of a step pyramid. This test speed schedule consists of an acceleration sequence formed by a number of abrupt speed increments followed by constant speed periods, and a deceleration sequence formed by the same speed changes executed in the reverse order. During the experiments the CO, HC, as well as the catalyst outlet-inlet temperature difference were monitored. The experimental results indicated that as the catalyst efficiency deteriorated with age, the rise of pollution levels was accompanied by significant changes in the CO and temperature difference signals. The HC signal wa snot as strongly affected. There are positive indications that the outlet-inlet temperature difference signal can be used as an input to a microcontrolled catalyst efficiency assessment system, capable of operating under driving conditions. However, further experimentation is required for the development of the catalyst efficiency evaluation algorithm, since under load the increased mass flow and exhaust gas temperature would strongly effect catalytic efficiency.

Conjugate method solutions of the biharmonic equation for the generation of boundary orthogonal grids

Abstract A finite difference approximation of the biharmonic equation is solved using a number of preconditioned conjugate gradient methods, for the generation of curvilinear boundary-orthogonal grids in two dimensions. The methods are applied in a number of domains of electrical engineering interest for the purpose of comparing CPU time. The solution algorithms may be easily extended for the generation of three-dimensional grids.

A Catalyst Surface Control Automation System for Emission Reduction During Cold Start

This paper presents and discusses experimental data obtained during test simulating the test cycle ECE-15 for a relatively simple method for the reduction of pollutant emissions during a cold start. During a cold start the volume of the exhaust gases is considerably smaller than the ones under full load. Therefore, only a small portion of the catalyst active surface is used to process the gases at the cold start phase. After the light-off at the initial surface the exhaust gases pass from the total catalytic surface which is already pre-heated from the first phase. The experimental results presented here indicate that there is a reduction of the pollutant emissions during the cold start of an engine. The developed system uses the 20% of the catalyst active surface during start-up and the rest of the catalyst surface after this phase, controlled by a proper automation system. At the cold start phase the system focusing the gas flow towards the center core of the monolith, so there is a quicker warm-up of the catalyst and a faster initiation of catalysis in this area. So when the remaining ceramic body of the catalytic converter is used, it is already warmed and the catalysis starts almost immediately.Copyright