Emission and Fuel Consumption Reduction in a Two-Stroke Engine Using Delayed-Charging

To reduce fuel losses during the gas-exchange-process in a two-stroke engine cylinder, a simple Delayed-Charging Device was developed to first scavenge burnt gases with fresh air and then introduce a fresh charge. This paper presents recent work done on a 50cc engine (i. e. through geometry changes of the delayed-charging circuit) to reduce torque losses and further improve fuel consumption and hydrocarbon emission reduction:

• a fuel trapping efficiency up to 87% (to be compared to the 74% production engine's),
• a mean specific fuel consumption lower than 400 g/kW.h (a mean 200 g/kW.h reduction compared to the rich-carbureted production engine),
• a HC emission down to 45 g/kW.h (lower than 1 3%),
• a delivery ratio reduction, due to the device presence, less than 6%,
• a maximum torque loss of 8% for the best delayed-charging circuit geometry,

Moreover, an estimate of the delayed-charging device efficiency has been done by comparing the trapping efficiency of delayed-charging modified engines equipped with either classical carburation or with delayed-charging-duct carburation. The further improvement potentialities have been studied through combustion-used trapped-air evaluation and through simulation of the triple-carburation due to the device-produced burnt-gas back-flow.