Design of Lean Burn Engine for Scooters

Abstract

Internal combustion engine powered vehicles are widely used all around the world for mobility. Scooter is the most commonly used two-wheeler by people of all age groups due to its easy handling and riding comfort. Due to gearless transmission, the mileage of scooter is low compared to gear transmission bikes. Nowadays increase in petrol price makes the mileage as the most important factor for internal combustion engines. Using lean air-fuel mixture for combustion in a engine increases the mileage as well as reduces the pollution. The air-fuel ratio is said to be lean when the ratio of air-fuel is greater than 15:1, the stoichiometric ratio of air-fuel is 14.7:1. In this Study, the clearance between the piston and cylinder of a 125cc engine is reduced from 0.5mm to 0.25mm to run in lean air-fuel mixture. The lean fuel-air mixture is achieved by supplying extra air into the engine by making an additional hole in the carburetor outlet and the air is supplied through it. The excess air is supplied to the engine after the vehicle reaches above 40 kilometer per hour. The extra air supply is controlled by an solenoid valve which is actuated by an electronic circuit. The lean mixture usage increases the engine temperature more than usual and it is controlled by using synthetic engine oil. The result shows increase in mileage from 40 - 45 kilometer per litre to 50 - 60 kilometer per litre and reduction in the emission of Carbon monoxide (CO) and Hydrocarbon (HC). Thus an overall increase in mileage is about 15 - 20% from existing vehicle but emission of Nitrogen Oxides (NOX) is slightly higher than usual. Combustion of lean air-fuel mixture produces less torque hence it cannot be used to move the vehicle from rest position, so lean mixture must be supplied to the engine after the vehicle reaches certain speed.