1998-02-23

A Comparison of Time-Averaged Piston Temperatures and Surface Heat Flux Between a Direct-Fuel Injected and Carbureted Two-Stroke Engine 980763

Time-averaged temperatures at critical locations on the piston of a direct-fuel injected, two-stroke, 388 cm3, research engine were measured using an infrared telemetry device. The piston temperatures were compared to data [7] of a carbureted version of the two-stroke engine, that was operated at comparable conditions. All temperatures were obtained at wide open throttle, and varying engine speeds (2000-4500 rpm, at 500 rpm intervals). The temperatures were measured in a configuration that allowed for axial heat flux to be determined through the piston. The heat flux was compared to carbureted data [8] obtained using measured piston temperatures as boundary conditions for a computer model, and solving for the heat flux.The direct-fuel-injected piston temperatures and heat fluxes were significantly higher than the carbureted piston. On the exhaust side of the piston, the direct-fuel injected piston temperatures ranged from 33-73 °C higher than the conventional carbureted piston. On the intake side, the piston temperature varied, 52-85 °C between the two fuel supply strategies. Piston temperatures on the bottom surface of a direct-fuel injected engine are between 80-113°C higher than the carbureted engine. The highest recorded temperature, 363 °C, occurred in the central region of the piston crown.The heat flux was calculated at the piston crown edges, on the intake and exhaust side. At both locations, the heat flux increased with engine speed. Heat flux on the intake side was consistently higher than the exhaust side of the piston, and the magnitude of the heat flux varied from 0.6 to nearly 0.95 MW/m2. The difference between direct-fuel injection and carbureted heat fluxes decreases as engine speed increases, and the intake side is consistently higher than the exhaust side for all recorded speeds. However, heat flux through the bottom region of the direct-fuel injected piston center is less than the carbureted engine.

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