Abstract
The present work reports the effect of a nozzle placed upstream of the compressor of a high-speed direct-injection diesel engine. It has been observed that mounting a nozzle at the compressor inlet can lead to a shift in the compressor surge line to lower mass flowrates. In order to study the effect of the nozzle on the engine performance a set of experimental investigations has been conducted including characterization of the nozzle alone using a flow test rig up to sonic conditions and characterization of the nozzle—compressor unit by determining its operation map in a turbocharger test bench. The distortions in the compressor inlet are usually considered as a disadvantage, as they affect the efficiency and the behaviour of the turbocharger. However, the comparison between the original compressor map (provided by the manufacturer) and the nozzle—compressor map given in the present paper shows that the change in the flow pattern caused by the nozzle improves the engine—turbocharger coupling and thus reduces the air mass flowrate, leading to a surge by 30 per cent, for a given pressure ratio.
The improvement in turbocharging does not necessarily increase the performance of the engine. Nevertheless, the possibility of increasing the boost pressure allows elevated fuel flowrates to be applied while still maintaining the combustion efficiency, thus increasing the power of the engine
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