Numerical Investigations of a Naturally Aspirated Cogeneration Engine Operating with Overexpanded Cycle and Optimised Intake System

Denis Neher; Maurice Kettner; Fino Scholl; Markus Klaissle; Danny Schwarz; Blanca Gimenez

doi:10.4271/2014-32-0109

Electrical power and efficiency are decisive factors to minimise payoff time of cogeneration units and thus increase their profitability. In the case of (small-scale) cogeneration engines, low-NO_x operation and high engine efficiency are frequently achieved through lean burn operation. Whereas higher diluted mixture enables future emission standards to be met, it reduces engine power. It further leads to poor combustion phasing, reducing engine efficiency.

In this work, an engine concept that improves the trade-off between engine efficiency, NO_x emissions and engine power, was investigated numerically. It combines individual measures such as lean burn operation, overexpanded cycle as well as a power- and efficiency-optimised intake system.

Miller and Atkinson valve timings were examined using a detailed 1D model (AVL BOOST). Indicated specific fuel consumption (ISFC) was improved while maintaining effective compression ratio constant. However, brake specific fuel consumption (BSFC) rises due to lower IMEP. In order to take advantage of the reduced ISFC, the intake section was optimised through virtual Design of Experiments (DoE). Subsequently, intake swirl was reduced, leading to further benefits in charging and engine efficiency. For both Miller and Atkinson cycle the efficiency was increased, while meeting the reference engine's baseline NO_x emissions and IMEP.

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Numerical Investigations of a Naturally Aspirated Cogeneration Engine Operating with Overexpanded Cycle and Optimised Intake System 2014-32-0109

SAE MOBILUS