Chapter 14 - Emission control

Abstract

This chapter deals with the aspect of emission control in engines. Emission control essentially refers to the detoxification of exhaust from the engine, such as unburnt hydrocarbons, carbon monoxide, and oxides of nitrogen. A basic essential for spark ignition engine emission control is a carburetor or injection system capable of extreme accuracy in metering the fuel supply relative to the air entering the engine. Irregular combustion must be avoided during idling and, on the overrun, the mixture must either be totally combustible or the fuel supply totally cut off. In the latter event a smooth return to normal combustion when the throttle is opened again is essential. Idling speeds are typically 750 rev/min with automatic, and 550 rev/min with manual transmission. A capsule sensitive to manifold depression could be used to retard the ignition in the slow-running condition, the manifold depression tapping being taken from a position immediately downstream from the edge of the throttle when it is closed. Emissions from a diesel engine include white smoke and black smoke in addition to hydrocarbons, carbon monoxide, and oxides of nitrogen. The chapter then describes the valve arrangements to minimize emission from engines. These valve arrangements are also explained diagrammatically. The influence of fuel quality on diesel exhaust emissions are discussed in a tabular form.