Entropy 2013, 15, 3277-3296; doi:10.3390/e15083367 OPEN ACCESS entropy ISSN 1099-4300 www.mdpi.com/journal/entropy Article Fluctuations in the Energetic Properties of a Spark-Ignition Engine Model with Variability Pedro L. Curto-Risso 1, Alejandro Medina 2, Antonio Calvo-Hernandez´ 3, Lev Guzman-Vargas´ 4;* and Fernando Angulo-Brown 5 1 Instituto de Ingenier´ıa Mecanica´ y Produccion´ Industrial, Universidad de la Republica,´ Montevideo 11300, Uruguay; E-Mail: pcurto@fing.edu.uy 2 Departamento de F´ısica Aplicada, Universidad de Salamanca, Salamanca 37008, Spain; E-Mail:
[email protected] 3 Departamento de F´ısica Aplicada and IUFFYM, Universidad de Salamanca, Salamanca 37008, Spain; E-Mail:
[email protected] 4 Unidad Profesional Interdisciplinaria en Ingenier´ıa y Tecnolog´ıas Avanzadas, Instituto Politecnico´ Nacional, Av. IPN 2580, L. Ticoman,´ Mexico D.F. 07340, Mexico 5 Departamento de F´ısica, Escuela Superior de F´ısica y Matematicas,´ Instituto Politecnico´ Nacional, Edif. No. 9 U.P. Zacatenco, Mexico D. F. 07738, Mexico; E-Mail:
[email protected] * Author to whom correspondence should be addressed; E-Mail:
[email protected]; Tel.: +52-55-57296000 ext. 56873; Fax: +52-55-57529318. Received: 8 June 2013; in revised form: 30 July 2013 / Accepted: 13 August 2013 / Published: 19 August 2013 Abstract: 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 (η).