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The purpose of this study is to experimentally understand the cyclic variation of combustion state in a two-stroke engine with respect to the variations in scavenging flow and the CO and CO2 emissions. The criteria of grouping combustion states into misfiring were established using the in-cylinder pressure at the crankangle of maximum variability in peak pressure instead of indicated mean effective pressure. The CO and CO2 emissions and the flow velocity variations in the transfer port and the exhaust pipe were measured. Combustion of each cycle was grouped into misfiring, incomplete firing or firing by the criteria of the in-cylinder pressure. In the cycle before misfiring, the CO and CO2 concentration showed high level and the first peak of the exhaust flow showed large velocity and the positive velocity remained for long duration, and the exhaust and the transfer port flow were steeply decelerated to negative velocity midway between scavenge port opening and bottom dead center.

The purpose of this study is to experimentally investigate in-cylinder flows with cyclic variation in a practical part-loaded two-stroke engine. First, the in-cylinder LDV measurements are introduced, which were carried out above the port layout and the combustion chamber as well as the exhaust pipe or the transfer port together with the simultaneous pressure measurements. Second, the in-cylinder flow characteristics in different combustion groups were discussed. The in-cylinder flow and the combustion-chamber flow were not simply characterized by the pressure variation in the engine or the other passage flow in the exhaust pipe or the transfer port. Finally, the in-cylinder flow structure with three stages was shown using the vector variation analysis and the drawing of the velocity profiles in the engine parts.

The purpose of this study was to detect a misfiring cycle in terms of the transfer-passage and the exhaust-pipe flow rate by experimental measurements. Simultaneous measurements of flow rates and in-cylinder pressure were carried out. The flow rate data were grouped into the different combustion classes by the in-cylinder pressure. A large flow rate of exhaust blow-down and a large reverse flow rate were observed in the cycle before misfiring, compared with in the cycle before firing. It showed that high concentration of the residual burnt gas in the cylinder was the main source of misfiring, this feature was also demonstrated by the complementary measurement of CO and CO2 concentrations.

The velocity variations of the burnt exhaust gas in a practical fired two-stroke engine operating under wide-open-throttle conditions were measured by a fiber LDV ( FLDV ). The characteristics of the exhaust flow are discussed in comparison with those in motoring and in a transfer port. The relation between velocity variation and pressure wave propagation in the exhaust pipe are also investigated. The measured results show that the velocity distribution in the exhaust pipe can be characterized as pulsative flow. The flow characteristics had large influence by the combustion pressure wave propagation. During exhaust and transfer-port opening, the intake flow and the blow-down flow have similar velocity gradient and peak location. The velocity distribution in the exhaust pipe was also measured, which showed pulsative flow variation having no recirculating vortex.