|M.Sc Student||Amiel Ran|
|Subject||Knock Phenomenon in UAV Spark-Ignition Engines and Ways|
of Its Prevention
|Department||Department of Mechanical Engineering||Supervisor||Professor Leonid Tartakovsky|
|Full Thesis text|
Abnormal combustion such as knock and surface ignition are one of the main challenges in ICE power development for decades. Those phenomena can lead to increased emissions, deterioration in fuel consumption and power output and even to destruction of the engine. In this study, the knock phenomenon peculiarities in a UAV engine were investigated.
For the purpose of a theoretical study of knock phenomenon in a UAV engine, a computer model was developed and validated, using measured data gained by the author in the experimental part of the research. The model served for computational analysis of knock physics, investigation of factors leading to knock occurrence in UAV engines and choosing the proper solutions for the knock problem.
The engineering solutions that were finally considered after preliminary analysis and screening are intercooling (IC), ignition timing (IT), exhaust gas recirculation (EGR), and water injection. IC and water injection showed the best results in knock elimination and engine performance, whereas IC and IT showed the best fit, if one takes into account knock elimination but also a quick response, simple installation and design simplicity.
A novel approach for knock prediction and monitoring was developed. The method is based on developing a set of equations that best describe the joint influence on knock occurrence of engine operating parameters and environmental conditions relevant to aerial platforms. With these equations, it is possible to predict the chance of reaching knock and the knock intensity during flight and before takeoff, and to close a control circuit and implement knock prevention control algorithm at real-time.
Another approach for knock identification that was investigated is engine’s block vibration analysis. In this method, the engine's block vibrations are monitored and analyzed. While the engine is knocking, the vibration signal is changing due to the pressure waves inside the cylinders and is detected by an acceleration sensor mounted on the engine's block. This method showed good results, but also false alarms and sometimes more than 1.5 minutes delay in knock warning. Thus, it is not enough for a stand-alone solution, if a low knock threshold alert is needed.