Computations and Experiments for Clarifying Compression Level and Stability of Colliding Pulsed Supermulti-Jets in a Piston-Less Single-Point Autoignition Engine

Unsteady three-dimensional computations and experiments of compression flow formed by collision of supermulti-jets

“…In Figs. 16-18, 200-500 µs is used, which will correspond to the order of pulse period generated by airfoils in cascades of traditional turbofan engines and also rotary valves employed for our new engines having the supermulti-jets colliding with pulse (Naitoh et al, 2016a(Naitoh et al, , 2016c. The high pulse speed produced by airfoils in cascades or rotary valve will also result in strong shock fronts for maximizing the collision pressure and temperature, because the Tsuru, Konagaya, Kawaguchi and Naitoh, Journal of Thermal Science and Technology, Vol.13, No.1 (2018) tip speeds of cascades or rotary valves become the level of sound speed and more.…”

“…9 to 18 present evidence of the stable compression due to the collision of supermulti-jets in whole one cycle. (At operating conditions that rotating speeds of rotary valves employed for our new engines having the supermulti-jets colliding with pulse (Naitoh et al, 2016a(Naitoh et al, , 2016c are lower, we can make longer between pulsed jets, i.e., for closing period of rotary valves. This long silent situation of valve closed during a long time will lead to very low speed of flow in chamber, which will result in a stabilization effect of axisymmetric collision for the next cycle.…”

“…Very high compression can occur, especially when the pulsed jets are injected by suddenly opening the valves. Although traditional diesel and pulse detonation engines employ multi-point autoignition, single-point auto-ignition due to the collision of the supermulti-jets produces less noise because the heat release rate is relatively small and the point of heat release is away from the cylinder walls (Naitoh, 2011(Naitoh, , 2012Naitoh et al, 2016aNaitoh et al, , 2016bNaitoh et al, , 2016cTsuru et al, 2016). (For air-breathing engines, the limited number of nozzles in Fig.…”

“…We also conducted combustion experiments on three prototype engines based on the collision of pulsed supermultijets (Naitoh et al, 2016a(Naitoh et al, , 2016c. Figure 4 shows one of the three prototype engines, which is piston-less and has fourteen nozzles for injecting supermulti-jets.…”

“…Experimental results show auto-ignition with pressure increases on the wall of about 0.3-0.7 MPa, implying high pressure at the chamber center of over 2 MPa as evaluated computationally. The temperature on wall stays atmospheric, which indicates a nearly complete air-insulation effect (Naitoh et al, 2016a(Naitoh et al, , 2016c. Emphasis is also placed on the fact that the pressure increase on the chamber wall of about 0.3-0.7 MPa is less than the knocking limit.…”