The maximum pressure rise rate is >10 bar/[degrees]CA and the HRPD ~0.32 stays almost constant till EF: 0.4.
With HRPD > 0.5, the soot emissions drop below the target value of 0.01 g/kWh.
It is important to note that the start of reduction in the CO emissions coincides with the HRPD approaching a value of 0.50.
The above results indicate that the HRPD is able to capture the transition to homogeneous combustion or in other words, the de-coupling of the NOx and soot trade-off.
The performance of the HRPD parameter in identifying the minimum required ethanol fraction was evaluated at 11 bar IMEP and 2 bar abs boost pressure.
The HRPD was almost constant at low EF and then started to increase as the EF approached a value of 0.5.
It is interesting to note that with HRPD at 0.51 (EF: 0.57), the trends in the maximum rate of pressure rise and the CO emissions were found to be consistent to those presented in Figure 3 and Figure 4.
These test results also highlight the potential benefit of the HRPD parameter to optimize the fuel quantity distribution between the two fuels for low emissions and high efficiency.
The HRPD profiles demonstrate that the parameter can provide useful feedback, independent of the SOI timing.
Noted, the HRPD value for both these EFs was -0.42.
The HRPD for the twin-pilot PPAC was 0.66 compared to the HRPD of 0.42 for the single-injection PPAC.
The pilot injection quantity needs to be minimized by modulating the ethanol fraction using HRPD feedback to ensure that stable combustion can be achieved with minimal soot emission penalty.