Naitoh, K., Ohara, S., Onuma, Y., Kojima, K. et al., "High Thermal Efficiency Obtained with a Single-Point Autoignition Gasoline Engine Prototype Having Pulsed Supermulti-Jets Colliding in an Asymmetric Double Piston Unit," SAE Technical Paper 2016-01-2336, 2016, doi:10.4271/2016-01-2336.
A single-point autoignition gasoline engine (Fugine) proposed by us previously has a strongly asymmetric double piston unit without poppet valves, in which pulsed multi-jets injected from eight suction nozzles collide around the combustion chamber center. Combustion experiments conducted on this engine at a low operating speed of 2000 rpm using gasoline as the test fuel under lean burn conditions showed both high thermal efficiency comparable to that of diesel engines and silent combustion comparable to that of conventional spark-ignition gasoline engines. This gasoline engine was tested with a weak level of point compression generated by negative pressure of about 0.04 MPa and also at an additional mechanical homogeneous compression ratio of about 8:1 without throttle valves. After single-point autoignition, turbulent flame propagation may occur at the later stage of heat release. Loss of work necessary for generating negative pressure is relatively small because the period for negative pressure is relatively short and also because dissipation is less than the loss due to throttle valves. It is stressed that this prototype engine employs a low-cost gasoline injector for port injection, which results in an almost homogeneous charge of fuel vapor. Because of port injection, the gasoline injector injects fuel at lower pressures than in a direct-injection engine, so it is less expensive. Thus, homogeneous vapor fuel and autoignition will produce lower levels of NOx and soot. Moreover, some interesting experimental data on spark-assisted autoignition of gasoline were obtained, which suggest more stable combustion can be achieved by optimizing the autoignition timing.