Combustion, ionization and sporadic pre-ignition in a turbocharged gasoline direct injection engine

This research is focused on the use of ionization of combustion products in hydrocarbons-air flames to gain a better understanding of the combustion process in turbocharged gasoline direct injection engines. A GM 2.0 L Ecotec GDI-T engine is used in this investigation. The ion current is measured simultaneously by two in-cylinder combustion sensors: the spark plug and the fuel injector. The characteristics of the ion current signals produced by the two sensors are analyzed and correlated with the characteristics of the rate of heat release computed from the cylinder gas pressure. Since this is the first time for a fuel injector to be used as an ion current sensor, it was possible to determine many features of combustion in the engine which could not be determined from the spark plug signal. For example, the phase shift between the two ion current signals was used to determine the burning velocity. The results are compared with the burning velocity measured in optically accessible port injected engine in which high speed imaging techniques were used. In addition, it was possible to investigate the impact of the burning velocity on the indicated thermal efficiency and indicated mean effective pressure at different speeds and loads. Also, this research included the use of the two ion current signals for the feedback closed loop control of the engine. The engine was able to consistently operate on MBT (Maximum Brake Torque) point by adjusting the ignition and injection timings. In addition, engine knock was detected and controlled by retarding the ignition timing using the ion current signals. The findings from the experimental investigations are supported by a 3D gasoline cycle simulation of combustion and the ion current produced at the locations of the spark plug and the injector.;The research include a detailed analysis of the factors that contribute to combustion instability and cycle-to-cycle variations. Finally, combustion ionization used to investigate the low speed sporadic pre-ignition phenomenon (LSPI) which is currently limiting the progress toward higher power density and more efficient turbocharged gasoline engines. The ionization technique used in this investigation detected the sporadic pre-ignition.