Study Of Liquid Fuel Film Transport And Its Effect On Cold Start Hydrocarbon Emissions In A Carburetted Engine

Abstract

The present work is concerned with fundamental studies on the liquid fuel transport in the intake manifold of small carburetted engines. This work is motivated by the need for development of technologies to meet the stringent cold-start emission norms that are to be prescribed for two-wheelers in particular. More specifically, visualization studies conducted in a transparent manifold made of quartz in a small four-stroke 110-cc two-wheeler engine have shown the presence of gasoline films on the walls of the inlet manifold under cold start conditions. Advanced Laser diagnostic techniques such as Planar Laser Induced Fluorescence (PLIF) have been utilized to measure the thickness of the fuel films. The Sauter Mean Diameter for the fuel droplets at the carburettor exit is measured using Laser Shadowgraphy technique. It is observed that the films are present both at idling conditions and under load. This large amount of liquid fuel entering the engine leads to incomplete combustion and higher emissions of unburned hydrocarbons. A detailed analysis of the effects of heating the inlet manifold has been performed. The potential of this manifold heating strategy in reducing hydrocarbon emissions has been assessed and found to be promising. In addition, a need of proper control of the fuel exiting the carburettor is shown to reduce emissions and increase fuel efficiency.