Scavenging Measurements in a Direct-Injection Two-Stroke Engine

The scavenging process in a direct-injection two-stroke research engine was examined by using an electromagnetically controlled poppet valve to sample the trapped charge. A physical model was developed to characterize thescavenging based solely on the measured trapped gas composition. This method obviates the need to measure the post-combustion composition of the trapped charge, which significantly eases the sampling valve requirements. The valve that was developed proved to be very robust and was able to sample over 30% of the trapped mass at 3000 rpm. The measured scavenging efficiency was found to agree well with the non-isothermal two-zone perfect mixing limit of scavenging. The scavenging efficiency was found to increase with delivery ratio, and was nearly independent of speed. The scavenging efficiency was found to decrease with increasing air-fuel ratio at a constant delivery ratio, but the effect was found to be the result of the exhaust gas temperature reduction more than the increase in the blowdown pressure.

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