Identification and analysis of the factors to realizing variable intake/exhaust phases in opposed-piston two-stroke diesel engines

The opposed-piston, two-stroke (OP2S) diesel engine is a potential power system to promote thermal efficiency, but the engine has an inferior scavenging performance. Through variable intake/exhaust times, the combustion process can be effectively facilitated. For example, the VVT technology is used in traditional engines. However, this technology has not been applied to OP2S diesel engines. This present work analyzed parameters influencing the intake/exhaust times to find a way to realize variable intake/exhaust times in OP2S diesel engines. These parameters affecting intake/exhaust times were mainly focused on, for example, crank to link ratio (CLR), piston phase difference (PPD), and port height (PH). Through investigating their influence on IMEP, scavenging efficiency, and trapping efficiency, we evaluated the different schemes from performance, intake/exhaust phases, and realization cost. The results show that the PH scheme significantly precedes the PPD and CLR schemes for realizing the variable intake/exhaust times. The PH scheme owns a more extensive phase adjustment range of 31 degrees CA, the IMEP of 0.75 MPa, and the scavenging efficiency of 0.74. To achieve better power and scavenging performance, the EPH should be 37.5% higher than IPH, and the PPD should be kept below 15 degrees CA.