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We have proposed the engine featuring a new compressive combustion principle based on pulsed supermulti-jets colliding through a focusing process in which the jets are injected from the chamber walls to the chamber center. This principle has the potential for achieving relatively silent high compression around the chamber center because autoignition occurs far from the chamber walls and also for stabilizing ignition due to this plug-less approach without heat loss on mechanical plugs including compulsory plasma ignition systems. Then, burned high temperature gas is encased by nearly complete air insulation, because the compressive flow shrinking in focusing process gets over expansion flow generated by combustion.

The authors have previously proposed a plume ignition and combustion concept (i.e., PCC combustion), in which a hydrogen fuel is directly injected to the combustion chamber in the latter half of compression stroke and forms a richer mixture plume. By combusting the plume, both cooling losses and NOx formation are reduced. In this study, thermal efficiency was substantially improved and NOx formation was reduced with PCC combustion by optimizing such characteristics as direction and diameter of the jets in combination with combustion of lean mixture. Output power declined due to the lean mixture, however, was recovered by supercharging while keeping NOx emissions at the same level. Thermal efficiency was further improved by slightly re-optimizing the jet conditions.