Effect of ethanol addition on cyclic variability in a simulated spark ignition gasoline engine

Autor: A. Calvo Hernández, Asok K. Sen, Alejandro Medina, P.L. Curto-Risso
Rok vydání: 2014
Předmět:
Zdroj: Meccanica. 49:2285-2297
ISSN: 1572-9648
0025-6455
DOI: 10.1007/s11012-014-9974-1
Popis: This study investigates the cycle-to-cycle variations (CCV) of heat release in a simulated spark ignition engine fueled by gasoline–ethanol blends. The equivalence ratio of the combustible mixture is changed from 0.7 to 0.9 and 1.0, i.e., from very lean to stoichiometric. Ethanol is added in the volumetric proportions of 5–25 %. For each equivalence ratio and for each ethanol fraction added, we calculate the coefficient of variation (COV) of the heat release time series. From the values of COV, we find that at a fixed equivalence ratio, the CCV of heat release decreases as the amount of ethanol addition is increased. We also find that for a fixed volume fraction of ethanol, the CCV increases with leaner mixtures. In addition, we use a continuous wavelet transform (CWT) to analyze the heat release time series. From the CWT, the dominant modes of the CCV are identified and the engine cycles over which these modes may persist are delineated. The results reveal that the CCV of heat release occur on multiple timescales and exhibit complex dynamics. With no ethanol added, high-frequency intermittent fluctuations together with more persistent low-frequency variations are observed. As the volume fraction of ethanol is increased, the low-frequency variations tend to become less persistent and more intermittent. Furthermore, at a fixed equivalence ratio, when ethanol fraction is increased, the overall spectral power is found to decrease significantly indicating that ethanol has a pronounced effect on reducing the CCV. An advantage of using a simulated model engine is that the computations can be easily carried out to a large number of cycles and thus determine the long term dynamics of the cyclic variations.
Databáze: OpenAIRE
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