However, CO emissions increase slightly at 60% and 80% load compared to low loads in HCRCCI primarily because of delayed combustion
phasing and reduced in-cylinder temperatures owing to addition of EGR which reduces CO oxidation rates.
The study also showed that the maximum pressure rise rate increased with higher compression ratio for early combustion timing and a reverse effect was seen with delayed combustion
As expected, the SoE shift to 704[degrees] CA resulted in a later SoC and delayed combustion with the lowest peak AHRR.
Moreover, the delayed combustion process decreased the in cylinder peak temperatures and thus the N[O.sub.x] emissions but also the indicated efficiency.
Conversely, ITE decreased due to a combination of degraded expansion efficiency from the delayed combustion
and an associated decrease in combustion efficiency.
In dry calibration, the substantially delayed combustion phasing, on one hand, provides reduced peak pressures (Figure 16) but, on the other, it determines rapidly increased exhaust gas temperatures at the turbine inlet, as reported in Figure 17.
* for the above reason, a delayed combustion phasing was required under WI operation, just to keep the maximum in-cylinder pressure below the specified threshold;
The higher oxygen concentration of the leaner mixture and the hotter burned gas temperature from delayed combustion
phasing increase the post-flame oxidation rates.
Figure 5 clearly points out that ISFC penalties correlate with the trends of Co[V.sub.IMEP] and Co[V.sub.pmax]; a delayed SA in fact induces a delayed combustion
The loss caused by delayed combustion
outweighs the benefit achieved for advanced CA50.
The reason for this delayed combustion
phasing was an effect of the much higher exhaust rebreathe used than the other fuels in order for the residual to actually reduce reactivity and help obtain the desired combustion noise target.
Increased viscosities will lead to more prolonged and delayed combustion
, increasing cylinder temperatures overall.