Reduction of Fresh Charge Losses by Selective Exhaust Gas Recirculation (SEGR) in Two-Stroke Engines

It has been well understood that the loss of fresh charge during scavenging process is the principal cause for high specific fuel consumption (sfc) and unburned hydrocarbon (HC) emissions in two stroke, spark ignition engines. A new concept of ‘Selective Exhaust Gas Recirculation (SEGR) has been developed for reduction of these fresh charge losses.

Investigations into the history of fresh charge losses in the exhaust showed that the HC concentration is maximum around top-dead-centre. Recirculation of the portion of the exhaust gases corresponding to the period it contains maximum HC concentration is the basis of SEGR. This could be accomplished by crank case suction. The SEGR system required a recirculation probe in the exhaust connected to the top of transfer passage through a one-way valve. Induction of the fresh charge was similar to that in the conventional engine.

Besides the concept, the paper will discuss the effect of air-fuel ratio, spark-timings and recirculation ratio on performance and emissions. The results compared with and without SEGR showed upto 34% reduction in HC emissions accompanied with about 12% improvements in sfc.