Influence of mathematical simplifications on the dynamic and energetic performance of an engine/motorcycle integrated model

Abstract

Brazil is a major producer and consumer of motorcycles. In this context, the Department of Mechanical Engineering at the Federal University of Pernambuco offers three two-wheeled courses: Studies on Bicycles and Motorcycles (45 h, graduate students), Propulsion of Bicycles and Motorcycles (45 h, graduate students), and Motorcycle Engineering (60 h, under graduate students). All of them present a greater or lesser mixture of general topics (e.g. accidents, culture, market, history) and technical ones (e.g., technology description and mathematical modeling). On those courses, the calculations are made using empirical correlations, commercial packages, and also simple methods, which, although quantitatively weaker, have both didactic and theoretical advantages, as they consider the essence of the phenomena and reveal the strongest relations between the variables. In this paper, we present an integrated engine/motorcycle simple model that permits the manipulation of parameters, such as the combustion time, heat losses, drag and inertial resistances, gear shifting and others. Those model parameters are then varied to study their influence on the motorcycle behavior. Manipulating this model, students learn that both engine and motorcycle inefficiencies have the same order of influence on motorcycle economy, ethanol is less volumetrically efficient than gasoline, the change of sprockets can increase the maximal speed while deteriorating the mean speed, and other interesting practical concepts. The success of the courses can be gauged by the students’ enrollment, by the professors’ evaluation by the students, class participation, and by the strong commitment of the students to the final projects. Other highly probable cause for the success is the motorcycle itself, always a passionate subject for young people in general, and mechanical engineers in particular.