Characteristics of HCCI Engine Operating in the Negative-Valve-Overlap Mode

Characteristics of un-throttled HCCI engine using negative valve overlap were examined under steady state and step-load change operations. The analysis employed a combined heat release analysis of the pressure data and a cycle simulation with a 1D gas exchange model to extract the residual fraction and the compression temperature from the experimental data. The residual gas fraction decreased with increase in engine load; the compression temperature decreased correspondingly. Substantial pumping loss attributed to the heat transfer in the re-compression process and the gas exchange friction was observed. At “optimum” setting of the combustion phasing, the GIMEP was not sensitive to the cycle-to-cycle combustion phasing variation. Large step high-to-low change in load was found to be stable. The reverse, however, had combustion failure in the first cycle due to unfavorable compression temperature and residual gas fraction.