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Particle image velocimetry (PIV) was used to study the velocity field characteristics in motored two-stroke ported engines. Measurements of the two-dimensional velocity field were made at the midplane of the clearance volume for bowl-in-head and disk combustion chamber geometries. Measurements were also obtained for two scavenging port geometries, i.e. a loop-scavenged engine and a loop-scavenged engine with a boost port. Results from this study show that in-cylinder geometry had a dominant effect on the flow structure observed at TDC. For example, with the boost-port scavenging crankcase, the disk-shaped chamber showed a turbulent flow-field at TDC with little large scale motion. In contrast, addition of a squish flow from the bowl-in-head geometry produced an organized cross-chamber flow. The addition of a boost port also changed the flow structure markedly. A large-scale swirl flow was observed in the engine that did not contain a boost port.

An in-cylinder optical sensor has been developed and tested for use in spark-ignition engine combustion analysis and control, This sensor measures the luminous emission in the near infrared region. Results of these tests show good correlation between the measured luminosity and traditional combustion parameters, such as location and magnitude of maximum cylinder pressure, and location and magnitude of maximum heat release. Engine performance indicators, such as the indicated mean effective pressure (IMEP), also can be determined accurately with the measured luminosity combined with other engine operating parameters, e.g. intake manifold pressure. In-cylinder air-fuel ratio can be determined with accuracy over an ensemble of 100 cycles.

Three different carburetor types have been tested to observe differences in the characteristics of the fuel/air mixtures produced. To characterize the fuel/air mixtures, two diagnostics have been applied: 1) High speed movies and subsequent analysis of the exit flow, and 2) measurement of the A/F ratio found in different positions within the intake manifold. The three different carburetor types that have been studied include a fixed-venturi, fixed-jet butterfly carburetor, a slide-valve carburetor, and a constant-velocity carburetor. Each carburetor type produced a unique set of exit flow characteristics, with differences in the optical density of fuel exiting the carburetor, and differences in the apparent amount of fuel on the intake manifold wall, entrained in the air flow, and in vapor phase.