Submitted by
Karthik .S.N

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Two Stroke Engine Using Reed Valves
INTRODUCTION
In developing countries a large number of private vehicles used two stroke engines. A large percentage of them employ two stroke engines because of their simplicity, high power to weight ratio and low cost of maintenance. Although two stroke engines are less efficient and more polluting they may continue to popular due to low cost and maintenance.
The most serious drawback of a two stroke S.I. engine is its higher fuel consumption and higher unburned hydrocarbon emissions when compared with four stroke engine. Fresh charge loss during the scavenging process of a two stroke S.I engine is known to be the principal reason for its high specific fuel consumption and high hydrocarbon emissions. During scavenging process a part of the fresh charge mixes with the residual exhaust gas as it scavenges the cylinder while some of it is loss due to short circuiting. The net effect is that 25%-40% of the charge may be wasted resulting in high fuel consumptions. Also in two stroke engines oil is used to lubricate the engines. The excessive percentage of oil in the fresh charge increases hydrocarbon in the exhaust. It is estimated that up to 10%-15% of HC may be contributed by the lubricating oil.
PROPOSAL FOR MODIFICATION
In the existing engine, the air fuel mixture is induced in the crank case when the piston is at the top dead centre. From these the piston moves down, uncovers the exhaust port first and then the transfer port which contains slightly compressed charge at a pressure of about 130 kpa.This charge is transferred to the upper part of the cylinder through the transfer port. The piston is so shaped that fresh charge of fuel and air will sweep up to the top of the cylinder and push out the remaining exhaust gas through the exhaust port by means of a projection on the piston called deflector.
REED VALVES
A pair of reed valves was employed to introduce the air from out side to the top of transfer passages that would remain between the crank case content of live mixture and the closed transfer port to the cylinder. When the later opened, air would be pumped in a head of mixture forming a buffer screen of air between the burned gas and the fresh charge