Experimental Study of Spark-Assisted Auto-Ignition Gasoline Engine with Octagonal Colliding Pulsed Supermulti-Jets and Asymmetric Double Piston Unit

Much effort has been devoted to studies on auto-ignition engines of gasoline including homogeneous-charge combustion ignition engines over 30 years, which will lead to lower exhaust energy loss due to high-compression ratio and less dissipation loss due to throttle-less device. However, the big problem underlying gasoline auto-ignition is knocking phenomenon leading to strong noise and vibration. In order to overcome this problem, we propose the principle of colliding pulsed supermulti-jets. In a prototype engine developed by us, octagonal pulsed supermulti-jets collide and compress the air around the center point of combustion chamber, which leads to a hot spot area far from chamber walls. After generating the hot spot area, the mechanical compression of an asymmetric double piston unit is added in four-stroke operation, which brings auto-ignition of gasoline. In our previous report (SAE paper 2016-01-2336) using gasoline, there were only some engine cycles indicating high thermal efficiency comparable to that of diesel engines. In the present report, we show that spark-assisted auto-ignition combustion optimized with the hot spot area generated by octagonal pulsed supermulti-jets indicates potential of high thermal efficiency averaged during many cycles, which is about the same level of diesel engines. Mechanical compression ratio is about from 7.8:1 to 11:1 and engine speed is 2,000 rpm under the part load whose exhaust air-fuel ratio is about from 20 to 30. Moreover, experimental data obtained also show the increasing rate of pressure after combustion is less than the knocking limit of reciprocating engines. And we have made a new prototype engine whose asymmetric double piston unit moves non-sinusoidally. We intend to report progress of this new prototype engine.