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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-NOx 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, NOx 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.

A comparison between conventional and bio-derived fuel spray characteristics is described in this paper. Radial distributions of drop size, axial and radial velocity components were measured using a Phase-Doppler Anemometer (PDA). A digital visualization system including a CCD camera was used to estimate the spray tip penetration. Fuel was injected through a single hole diesel injector into a test section at ambient pressure. An empirical expression was found to estimate the spray tip penetration at ambient conditions.