Eliminating Rating Effects on Turbocharged Diesel Response 840134
It is well known that the response of turbocharged diesel engines deteriorates as rated mean effective pressure (BMEP) Increases, for a given maximum power output. This is a problem for diesel generating sets but is now also causing concern on vehicle engines as ratings increase.
The objective of the paper is to present the trade-off between increased BMEP (rating) and response and to outline methods of improving response. A sophisticated and detailed transient engine simulation is first validated against test data for a high BMEP engine and is then used to compare the response of 16, 12, 8, 6 and 4 cylinder derivatives of the same 4-stroke diesel engine, when all are rated at the same maximum speed and power. Thus, rated speed BMEP increases from the naturally aspirated V16 (6.78 bar) through turbocharged V12, turbocharged and charge cooled V8 and L6 engines to a 2-stage turbocharged and charge cooled L4 (27.1 bar). The acceleration time of these engines varies greatly, the 4 cylinder taking 2.4 times as long to achieve maximum speed.
Various methods of improving response are examined, some well known and others novel. Some, such as reduced inertia and variable geometry are developments for which the turbocharger manufacturer is responsible. Others, such as variable fuel injection timing or valve timing, can be developed by the engine maker. It is shown that several options for development can substantially improve response until it is close to that of a naturally aspirated engine, whatever the rating of the engine.