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exhaust gas recirculation seminar report free download

Abstract

In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline and diesel engines. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. This dilutes the O2 in the incoming air stream and provides gases inert to combustion to act as absorbents of combustion heat to reduce peak in-cylinder temperatures. NOx is produced in a narrow band of high cylinder temperatures and pressures.In a gasoline engine, this inert exhaust displaces the amount of combustible matter in the cylinder. In a diesel engine, the exhaust gas replaces some of the excess oxygen in the pre-combustion mixture.Because NOx forms primarily when a mixture of nitrogen and oxygen is subjected to high temperature, the lower combustion chamber temperatures caused by EGR reduces the amount of NOx the combustion generates (though at some loss of engine efficiency).Gasses re-introduced from EGR systems will also contain near equilibrium concentrations of NOx and CO; the small fraction initially within the combustion chamber inhibits the total net production of these and other pollutants when sampled on a time average. Most modern engines now require exhaust gas recirculation to meet emissions standards.

Introduction

A pollutant that has not yet received as much public or regulatory attention as gaseous or solid particulate emissions is engine generated noise. Excessive levels of noise can, however, be as harmful to human health and the environment as noxious gases. In a well-designed engine, mechanical noise can be kept to a minimum but the combustion process itself still generates noise, “combustion noise”. Thus, if the combustion process is modified for exhaust emission control it can be expected that the level of noise generated by combustion will also be affected, albeit not necessarily adversely. As exhaust gas recirculation (EGR) is becoming an essential technology for NOx emission control in diesel engines, and, as this technique modifies the combustion process, it is important that the effects of using EGR on noise generation be identified