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Year 2000 emission norms for Indian passenger cars, which have been notified requires major changes in the existing technologies being used in the passenger car vehicles on roads. Electronic fuel injection systems and catalytic converters are being used extensively abroad to meet stringent emission regulations. Even in India, major joint ventures in passenger car segment have introduced vehicles with single-point / multi-point fuel injection systems. It has become difficult to meet the mandated emission regulations with the conventional mechanical carburetted vehicles. Automotive Research Association of India alongwith M/s UCAL Fuel Systems has developed an electronic feedback carburettor system to use alongwith catalytic converter for a passenger car to meet the year 2000 emission norms. A closed loop system has been designed and developed which takes the input from a λ-sensor output and controls the additional air added in the intake manifold of the engine through a stepper motor.

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.

This paper describes the engine mapping work carried out on a 2.1 litre carburetted petrol engine.The purpose of this work was to improve upon the emission levels of the engine to meet 1996 emission norms with sufficient margin and to achieve best fuel economy possible. This paper deals with the strategy for the selection of speed load points required for mapping depending on engine operating zones, engine base data collection, methodology followed in engine mapping, variation of engine performance and emissions with respect to air/fuel ratio and spark timing etc. Further the mass emission predictions for different strategies like leaning the air/fuel mixture, retarding the ignition timing etc. are also discussed. Recalibration of the carburettor based on the above findings, its effect on vehicle performance are dealt with.