Fluctuations in the Energetic Properties of a Spark-Ignition Engine Model with Variability

• Main Authors: Fernando Angulo-Brown, Alejandro Medina, Lev Guzmán-Vargas, Antonio Calvo-Hernández, Pedro L. Curto-Risso
• Format: Article
• Language: English
• Published: MDPI AG 2013-08-01
• Series: Entropy
• Subjects: spark ignition engine; quasi-dimensional simulations; cycle-to-cycle variability; energetics
• Online Access: http://www.mdpi.com/1099-4300/15/8/3277

We study the energetic functions obtained in a simulated spark-ignited engine that incorporates cyclic variability through a quasi-dimensional combustion model. Our analyses are focused on the effects of the fuel-air equivalence ratio of the mixture simultaneously over the cycle-to-cycle fluctuations of heat release (QR) and the performance outputs, such as the power (P) and the efficiency (QR). We explore the fluctuant behavior for QR, P and n related to random variations of the basic physical parameters in an entrainment or eddy-burning combustion model. P and n show triangle shaped first return maps, while QR exhibits a structured map, especially at intermediated fuel-air ratios. Structure disappears to a considerable extent in the case of heat release and close-to-stoichiometry fuel-air ratios. By analyzing the fractal dimension to explore the presence of correlations at different scales, we find that whereas QR displays short-range correlations for intermediate values of the fuel ratio, both P and n are characterized by a single scaling exponent, denoting irregular fluctuations. A novel noisy loop-shaped P vs. n plot for a large number of engine cycles is obtained. This plot, which evidences different levels of irreversibilities as the fuel ratio changes, becomes the observed loop P vs. n curve when fluctuations are disregarded, and thus, only the mean values for efficiency and power are considered.