Electronic Control of Air-Fuel Ratios in a Carburator for Two-Wheeler Application

The simple design and low cost of the carburator makes it an attractive proposition to be used for two-wheeler applications in India and other countries. However, stringent emission standards pose greater challenge in carburator matching for different vehicle applications. The use of electronics for controlling the air-fuel ratio in a carburator with closed-loop control to meet Euro-III standards is the driving force to undertake this project. The goal is to achieve the best catalytic converter efficiency when the air-fuel-ratio is maintained at stoichiometric within a close band.

Inherent variations in manufacturing of carburators can cause the air-fuel ratio to drift from stoichiometric and have an adverse effect on catalytic converter efficiency.

The most efficient method of maintaining air-fuel ratio within a close band near stoichiometric is through closed-loop control. This method is widely used in passenger cars with fuel injection. However, the need for a low cost system for two-wheeler is well known. Electronic closed-loop control system has been developed for carburator used in a 90cc 4-stroke two-wheeler for meeting the Euro-III emission norms.

This paper illustrates some of the research done to adapt electronic carburetion with closed-loop control to meet the Euro-III emission standards.