Experimental study of spark-assisted auto-ignition gasoline engine with octagonal colliding pulsed supermulti-jets and asymmetric double piston unit 2018-32-0004
Much effort has been devoted to studies on auto-ignition engines of gasoline including homogeneous-charge combustion ignition engines over 30 years. The two key aims are 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 far from chamber walls. After those, the mechanical compression of an asymmetric double piston unit which moves with nearly sigmoidal mode is added, which brings auto-ignition of gasoline. In the year before last （in our SAE paper 2016-01-2336）, there are some engine cycles indicating high thermal efficiency due to spark-assisted auto-ignition combustion. In the present report, we show that spark-assisted auto-ignition combustion optimized indicates 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.