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Transfer-port and in-cylinder flow fields have been mapped in a crankcase-compression, loop-scavenged two-stroke engine under motored conditions (1600 r/min; delivery ratio: 0.5). The impulsive, high-velocity flow (initially ≳2200 m/s) issuing from the transfer ports is fairly uniform and symmetric in space. ...Detailed LDV measurements of the port-efflux velocity field in a two-port, loop-scavenged model engine have recently been carried out under both steady flow [21] and motored (blown, 200 r/min) conditions [22] at The Queen's University of Belfast; little in-cylinder velocity data have been presented, however [21].

High-speed (12 kHz) imaging of combustion luminosity (enhanced by using a sodium fuel additive) has been analyzed and compared to crank angle resolved heat release rates and mass fraction burn profiles in a spray-guided spark-ignited direct-injection (SG-SIDI) optical single-cylinder engine. The addition of a sodium-containing additive to gasoline greatly increases the combustion luminosity, which allows unintensified high-speed (12 kHz) imaging of early partially premixed flame kernel growth and overall flame propagation with excellent signal-to-noise ratio for hundreds of consecutive engine cycles. Ignition and early flame kernel growth are known to be key to understanding and eliminating poor burn cycles in SG-SIDI engines.

Two- and three-dimensional images of fuel distributions in a continuously firing direct-injection stratified-charge engine have been recorded under moderate-load conditions using planar laser-induced fluorescence (LIF) from commercial gasoline. Cyclic variations in the fuel concentration at the spark gap (deduced from individual-cycle two-dimensional images) appear sufficient to account for the observed incidence of misfires and partial burns. Tomographic three-dimensional LIF images of the average fuel distribution at the time of spark indicate that ignitable mixture is present only in a thin shell around the periphery of the fuel cloud. Differences in power output and combustion stability during engine warm-up observed with two injectors of the same type are reflected in systematic differences in the fuel concentration near the spark gap as inferred from LIF data.

Crevice flows of hydrocarbon fuel (both liquid and vapor) have been observed directly from fuel-injector mounting and nozzle-exit crevices in an optically-accessible single-cylinder direct-injection two-stroke engine burning commercial gasoline. Fuel trapped in crevices escapes combustion during the high-pressure portions of the engine cycle, exits the crevice as the cylinder pressure decreases, partially reacts when mixed with hot combustion gases in the cylinder, and contributes to unburned hydrocarbon emissions. High-speed laser Mie-scattering imaging reveals substantial liquid crevice flow in a cold engine at light load, decreasing as the engine warms up and as load is increased. Single-shot laser induced fluorescence imaging of fuel (both vapor and liquid) shows that substantial fuel vapor emanates from fuel injector crevices during every engine cycle and for all operating conditions.

Fluid-motion and turbulence phenomena important to fuel-spray dynamics, mixing, and combustion have been examined in a motored direct-injection engine using photon-correlation laser-Doppler velocimetry. Operating at 11:1 compression ratio, the engine incorporated a centrally located, cylindrical piston bowl and an off-axis, directed intake port.