Research On Knock Recognition And Suppression Strategy Of The Two-stroke Kerosene Engine

At present,two-stroke engines are commonly used in some special military vehicles and small and medium-sized UAVs in our country.Under the background of fuel simplification in our army,aviation kerosene is often used as fuel for these power devices because it is easy to be stored and transported.However,due to its unique physical and chemical characteristics,aviation kerosene has a slow flame propagation speed during combustion,and is more likely to knock than gasoline under low-speed and high-load conditions.Therefore the recognition and suppression of engine knock is an urgent problem in the research of two-stroke kerosene engine.Based on the project of a two-stroke kerosene engine,this paper designs a knock electronic control system of kerosene engine and the corresponding detonation suppression strategy by analyzing the vibration signal of kerosene engine block.The main works are as follows:(1)The two stroke kerosene engine test bench is built to collect cylinder pressure signal and body vibration signal in bench test.The time-domain analysis and frequency-domain analysis of the body vibration signal are carried out.The characteristics of vibration signals of engine block during knock are extracted.The results show that the knock of the engine mainly occurs from 10°CA to 80°CA after the TDC,and the knock characteristic frequency of the engine is near 11.3 kHz.(2)The knock electronic control system of two-stroke kerosene engine is designed and the design principle of hardware circuit and software flow of knock electronic control system are sorted out.Finally,the output voltage of HIP9011 is analyzed.The results show that when the output voltage of HIP9011 is more than 1.12 times of the average output voltage of the first 10 cycles,the knock of kerosene engine can be judged.(3)A one-dimensional numerical calculation model is built by GT-POWER.Variable parameters of air-fuel ratio,compression ratio and ignition advance angle are simulated.The results show that the engine has the greatest knock tendency near the theoretical air-fuel ratio,and the knock can be suppressed when the air-fuel ratio is far away from the theoretical air-fuel ratio.Increasing the compression ratio in a certain range can improve the power and economy of the engine,but it will increase the possibility of knock.The knock can be eliminated by delaying the ignition advance angle.There is an optimal ignition advance angle under specific conditions,which makes the engine obtain good economy,power and emission.Therefore,the influence of ignition advance angle on engine performance and emission index should be taken into account when designing knock suppression strategy.(4)Knock intensity is defined by the method of cyclic occupancy and the knock suppressionstrategy is designed.At the same time,a simulation test bench is built to verify the function of the engine knock control system designed in this paper.The results show that the electronic control system of two-stroke kerosene engine designed in this paper can realize ignition timing control.The knock of the engine can be identified by processing the vibration signal of the engine block.After the knock occurs,the ignition advance angle can be postponed according to the knock suppression strategy,so that the two stroke kerosene engine can always work at the knock edge condition.