Emission Control Using Oxygen

Emission Control Using Oxygen

Abstract

Diesel engines posses the advantage of high fuel economy, reliability and torque. However they have the problems of high smoke and NOx emissions. The combustion process in the diesel engine is complex. Premixed combustion of the fuel follows the ignition delay period and is influenced by it significantly. An increase in the fraction of the fuel burned in this phase will lead to a reduction in smoke level. This phase is mainly responsible for NOx emissions and high rate of pressure rise normally encountered in diesel engines. A decrease in delay period leads to more fuel being burned in the diffusion combustion phase, which follows the premixed combustion phase. The diffusion combustion phase mainly contributes smoke and particulates. An increase in the concentration of oxygen in the inducted charge will enhance the combustion rate in both the phases. It will also reduce the ignition delay and this will lower the mass fraction of the fuel burned in the premixed phase. The presence of enhanced concentration of O2 will reduce HC, CO & smoke and could also improve the brake thermal efficiency. It will also affect the formation of NOx directly and indirectly.
Enhancing the concentration of oxygen in the intake charge:
Increases the brake thermal efficiency at all loads till an oxygen concentration of 27%
Decrease HC and CO level significantly
Drastically decreases smoke
Increases NO level significantly.
Decrease the ignition delay and increase peak pressure and maximum rate of pressure rise.
Rises the peak heat release till 25% oxygen and decreases it further due to reduction in ignition delay.
On the whole it can be concluded that oxygen enrichment of the intake air could lead to significant improvements in performance and a drastic reduction in smoke, HC, CO emissions of a diesel engine. However it has an adverse effect on NOx emissions thus is has to be combined with other methods if overall improvement is desired.