1994-03-01

Imaging and Spatially Resolved Two-Color Temperature Measurements Through a Coherent Fiberoptic: Observation of Auxiliary Fuel Injection Effects on Combustion in a Two-Stroke DI Diesel 940903

A two-stroke diesel engine was outfitted for operation with an electronic solenoid-controlled unit injector and an additional solenoid-controlled air-assisted injector at the inlet ports. Access through an existing pressure transducer port allowed installation of a sapphire window to the combustion chamber with very little disturbance to the combustion system. A coherent fiber optic bundle permitted remote visualization of the combustion event. Use of a gateable intensified solid-state camera permitted imaging at high effective shutter speeds at arbitrary times in the engine cycle. Imaging and two-color temperature and soot concentrations measurements were performed.
Imaging results indicated a low-intensity diffuse ignition, away from the injector tip, for both the pilot spray in pilot-main tests and the main spray in the main-only runs. Remnants of the burning pilot spray congregated near the injector tip where a region of flame remained until main injection arrived. The main fuel ignited upon injection into this region.
Temperature measurements indicated that pilot injection resulted in a region of 2300 K or greater flame temperature around the injector nozzle at the start of main injection. Neither temperatures nor soot concentrations were detectable during the two-stage ignition process of the port fuel with this measurement system. Small-scale variations on the order of 100 K were evident in most temperatures images. The soot concentration in the pilot flame did not increase appreciably during the pilot-main delay period.

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