Search Results

A multi-zone model was used to predict the operating range of homogeneous charge compression ignition (HCCI) engine, the boundaries of the operating range were determined by knock (presented by ringing intensity), partial burn (presented by combustion efficiency) and cycle-to-cycle variations (presented by the sensitivity of indicated mean effective pressure to the initial temperature). A HCCI engine fueled with iso-octane was simulated, and it was found that the knock and cycle-to-cycle variations predicted by this model showed a satisfactory agreement with measurements under different initial temperatures and equivalence ratios, and the operating range was well reproduced by the model. Furthermore, the model was applied to develop the operating range for different engine speeds by changing initial temperature and equivalence ratio. Finally, the potential to expand the operating range of HCCI engines through two strategies, i.e. variable compression ratio and boost, were investigated.

The multi-zone model has been attracting growing attention as an efficient and accurate numerical model for homogeneous charge compression ignition (HCCI) combustion simulations. In this paper, a comparative study was carried out to clarify the effect of various sub-models on the prediction capability of the multi-zone model. The influences of the distribution of zones, heat transfer from the wall, mass and heat exchange between zones and boundary layer thickness on HCCI combustion and emissions were discussed based on the experimental data. The results indicate dividing the colder region into more zones can improve the emissions prediction, however, more zones in the hotter region has little effect on the predictions. The improved Woschni model significantly improves the prediction of heat transfer.

In situ adaptive tabulation (ISAT) has been implemented into HCCI multidimensional modeling with detailed chemical kinetics, and the performance of ISAT was discussed. The results indicate that ISAT can reduce the computational time remarkably, and the global error can be efficiently controlled. The ISAT without growth and a reversal traverse were tested to ISAT, but they didn't influence the performance of ISAT greatly. Taking account of the character issues of chemical reactions during HCCI combustion process, an enhanced approach, the partial ISAT (PaISAT), was presented, which can significantly improve the accuracy and speed-up factor. The memory occupancy needed by ISAT was reduced based on the dynamic trimming technique.