Technical Paper
Effect of Active Piston-Movement Control on Thermal Efficiency in Different Heat Release Profiles
2005-10-12
2005-32-0067
In order to improve thermal efficiency of spark ignition engines, the authors have studied means to improve degree of constant volume. The ideal Otto cycle realizes the maximal degree of constant volume with an instantaneous combustion at TDC. However, it is actually impossible to achieve instantaneous combustion as the combustion speed is limited. Thereby, the authors thought of an idea to increase degree of constant volume. That is to make the piston speed slow during combustion period by active piston-movement control, allowing more time for combustion. As a result, degree of constant volume was improved, but indicated thermal efficiency, estimated by integrating P-V diagram, was deteriorated. A longer expansion stroke was found to keep a longer period of high temperature and then, heat loss increased, leading to a decrease in indicated work.