Combustion experiment of silent single-point auto-ignition engine: Fugine

The new compressive combustion concept based on supermulti-jets colliding with pulse, which was proposed by computer simulations in our previous reports (SAE papers & AIAA papers, 2011-2015), has a potential of high thermal efficiency over 50% even for engines having combustion chambers smaller than 100cc, because the supermulti-jets colliding at chamber center encase burned gas around the chamber center, which lead to complete air insulation. It is also stressed that this supermulti-jets colliding at chamber center also brings encasing of combustion noise and that single-point auto-ignition at chamber center can relatively accomplish silent combustion at very high compression, whereas traditional auto-ignition engines such as diesel one use rapid heat release due to multi-point ignition, leading to strong noise. Recently, we originally developed a small prototype engine system for gasoline, having a strongly-asymmetric double piston and the supermulti-jets colliding with pulse, although there are no poppet valves and no throttle valves. This prototype engine, in which the number of jets colliding is eight while both of bore and stroke are about 40mm, can widely vary point compression strength due to the supermulti-jets and mechanical homogeneous compression level due to pistons, by changing the phase of two gears between the double piston. For air-fuel ratios between 20:1 and 40:1 (lean conditions), steady-state experiments of combustion for this small gasoline engine having a medium level of the point compression with an additional mechanical homogeneous compression ratio of about 8:1 show apparent increase of exhaust temperature over 100 degrees and pressures over 2.0 MPa, even at the situations without any plugs, while liquid fuel of gasoline is injected in intake-port (Injection pressure=0.35MPa), leading to homogeneous-charge of air-fuel mixture. It should also be emphasized that time histories of pressure after auto-ignition are similar to those for conventional SI gasoline engine, which implies silent auto-ignition of gasoline. For some partial loads at engine speed of 2,000rpm, the present new silent engine often results in thermal efficiency comparable to that of Diesel one, while cheap fuel injectors of low injection pressures are setting in intake ports. Silent auto-ignition of gasoline occurs, because single-point ignition in the early stage and turbulent flame propagation at the later stage of heat release may occur. Then, the present homogeneous-charge silent auto-ignition will also bring low emissions such as NOx comparable to those of conventional SI gasoline engines.