Delayed Charging: A Means to Improve Two-Stroke Engine Characteristics

We have developed and patented a new simple device which reduces the amount of short-circuited fresh charge in two-stroke cycle engines and produces stratified charging and - combustion. The principle consists in scavenging the burnt gases with fresh air and delaying the introduction of the fresh charge in the cylinder. A numerical simulation showed a good promise of consumption and pollution improvement for this configuration. Then, preliminary bench tests have been carried out with a 50 cc production engine and the same modified engine including a delay-circuit.

Due to delayed charging:

• brake specific fuel consumption shows a mean 20% reduction down to a maximum of 25% comparing to production engine figures,
• unburnt hydrocarbons show a mean 35% reduction down to more than 50%,
• carbon-monoxide production decreases to a mean 1% concentration.
• torque increases at low r.p.m., but lowers at higher speeds of revolution due to the diminished permeability of this first prototype engine.