In recent years, a new type of engine (Fugine) based on the colliding of pulsed supermulti-jets was proposed by us, which indicates the potential for attaining very high thermal efficiencies and also less combustion noise. A prototype engine with eight nozzles for injecting octagonal pulsed supermulti-jets, which was developed with a low-cost gasoline injector and a double piston system, showed high thermal efficiency comparable to that of diesel engines and also less combustion noise comparable to that of traditional spark-ignition gasoline engines. Another type of prototype piston-less engine having fourteen bioctagonal nozzles was also developed and test results confirmed the occurrence of combustion, albeit it was unstable. In this work, time histories of pressure were measured in the combustion chamber of the piston-less prototype engine under a cold flow condition without combustion in order to examine the compression level obtained with the colliding supermulti-jets. Pressure was measured with a piezoelectric sensor. Unsteady three-dimensional computations were also performed and compared with the experimental pressures. The results showed a relatively high pressure level at the cylinder center and low pressure at the walls, which provided evidence of silent autoignition. Moreover, the reason why combustion was unstable in the prototype piston-less engine was also clarified. The data obtained have led to a new technique for improving combustion stability at engine start.