The Development And Experiment Of Rapid Compression-Expansion Machine

The mechanism of knock is still unclear although tremendous researches andefforts have engaged in knock study. In order to study knock mechanism a rapidcompression-expansion machine (RCEM) based on hydraulic system was developed.Firstly, the design idea and working principle were introduced. Driven section,combustion chamber and heating section and mixture making section were presentedin detail. The RCEM has advantages of wide visible zone, high compression ratio,relative compact structure and fairly short compression time. Then a1-dimensinalmodel was established in Amesim in order to simulate the RCEM performance. Theeffects of unidirectional restricting valve, restricting valve lift and diameter ofrestricting hole, hydraulic source pressure, moving mass and ignition phase werestudied. Knock duration and equivalence revs were defined to compare with revs ofcrankshaft engine. The results show that：the expansion time increases and pistonfluctuation decreases while the diameter of unidirectional restricting hole decreases;The combination of adjusting restricting valve and lower hydraulic source pressure inorder to low down the piston velocity of theoretically Top Dead Center(TDC) canincrease knock duration; larger moving mass can also lead to longer knock duration;Combustion and ignition phase have little influence on compression but canincrease expansion distance. At last pure air compression experiment and HCCIcombustion fueled with ether were conducted to assess the performance of RCEM.The in-cylinder pressure of experiment agrees very well with simulation, but the peakpressure of in-cylinder differs mainly due to compression ratio estimation error andheat transfer difference. The pressure consistency reaches an excellent level with amaximum peak pressure discrepancy ratio7.5%. The in-cylinder peak pressuredecreases while damp which consists of restricting valve lift and diameter ofrestricting hole increases. High fluctuation frequency of in-cylinder pressure of11kHzwas observed while HCCI combustion fueled with ether taken place in combustionchamber. The capability of RCEM for further knock and HCCI study was validatedby experiment.