Estudo conceitual de um motor com cilindrada e taxa de compressão ajustáveis

Author(s)

Caio Henrique Rufino

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Mecânica
• Defense date: 2020-02-19

Examining board members

Janito Vaqueiro Ferreira; Rogério Gonçalves dos Santos; Carlos Eduardo Keutenedjian Mady; José Antonio Velázquez; José Eduardo Mautone Barros

• Advisor: Janito Vaqueiro Ferreira

Abstract

Internal combustion engines still possess a long future in the transportation sector as they present significant advantages in terms of mileage, costs and mass as compared to their competitor technologies. Besides, the use of those engines can be extended owing to new technological advances, bringing improvements in efficiency and pollutant emissions, adding to the possibility of operating with fuels from renewable sources, considerably reducing the emission of greenhouse effect gases. Given this motivation, a solution is proposed, with the objective of permitting higher flexibility for a spark--ignition engine. The innovative solution presented here consists of a multi-link mechanism, which allows the control on the piston kinematics, thus adjusting compression ratio and cubic capacity. The objective of this study is to present preliminary results obtained by simulations, indicating the gains of implementing the proposed solution. To perform the study, a kinematic model of the mechanism was firstly developed. The kinematic model was then incorporated to a thermodynamic model for simulation, known as the predictive model. This model consists of a phenomenological model of two-zones of combustion, which predicts the engine performance and knock onset. To ensure model accuracy, a combustion diagnosis was performed on experimental data obtained from a commercial engine. The diagnosis provided fundamental data for the understanding of combustion behaviour related to diverse engine parameters such as spark timing, load, engine speed, and air-fuel ratio. Additionally, a comparison between ethanol and gasoline was performed as a mean to indicate the differences between both fuels. The data obtained from the combustion diagnosis were used in the combustion modelling, implemented in the predictive model. After the implementation of the combustion model, the predictive model was validated by comparing results obtained from the simulation for the commercial engine using data obtained from the bench tests. With the validated simulation model, a calibration based on simulation was performed for the proposed engine operating with ethanol at stoichiometric condition in order to indicate the optimal combination of intake manifold pressure, cubic capacity, compression ratio, and spark timing with the objective of maximising indicated thermal efficiency for the engine. Results demonstrated that the main advantage of controlling compression ratio becomes evident at medium to high engine speeds, conditions at which the knock onset is not critical. A conventional engine with fixed compression ratio operates with low compression ratio as its compression ratio is fixed because of the critical conditions for knock onset whereas a variable compression ratio engine can operate with an optimal compression ratio in all conditions. The advantages of controlling cubic capacity become more evident for partial load conditions, at which the pump losses caused by throttling are mitigated by the reduced cubic capacity. By combining the control of compression ratio and cubic capacity, it was possible to obtain up to 20% of efficiency increase for full load conditions and high engine speed as also an increase in efficiency between 10% and 20% for partial load conditions (AU)

• FAPESP's process: 18/18859-1 - Conceptual study of an internal combustion engine with adjustable cubic capacity and compression ratio
• Grantee: Caio Henrique Rufino
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)