Optimization of a user-defined fractal combustion model and its application to the assessment of the behaviour of a heavy-duty ng engine equipped with VVA under steady-state and transient conditions

This paper presents part of the activity carried out by Politecnico di Torino and Fiat Research Center within the CORE project. The work focused on one hand on the use of innovative fuels in heavy-duty (HD) vehicles, on the other hand on increasing the engine efficiency. The adoption of variable valve actuation devices is effective in enhancing the spark-ignition engine efficiency, however, low exhaust temperatures might arise in the catalyst warm-up phase. The paper is concerned with the development of an advanced air control and combustion system for a natural gas HD VVA engine. After a numerical steady-state analysis, the engine calibration was upgraded, then a variant of it for optimizing the catalyst warm-up phase was defined and tested, with specific reference to transient operations. The calculations were performed with the support of a GT-Power model which included a predictive combustion model, so as to guarantee a good result accuracy. Under steady-state conditions, within the considered operation range, the turbine discharge temperature could be increased by around 50-70 K, while increasing the fuel consumption by about 3.5%. In the considered portion of the WHTC the temperature benefit was about 33 K, and the fuel consumption penalty was around 4.5%.