# A Review of Early Injection Strategy in Premixed Combustion Engines
## 3 Injection Timing
### Two-Stage Early Injection
#### 3.2.2 Second Injection Timing
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Author** & **First Injection** & **Second Injection** & **Feuel** & **BSFC** & **NOx** & **HC** & **CO** & **Soot** \\  & **Timing** (\({}^{\circ}\) **BTDC**) & **Timing** & \({}^{\circ}\) **BTDC** & & & & & \\ \hline [PERSON] et al. [74] & 30-9 & \(-\)14 & Diesel & na & \(\downarrow\uparrow\) & na & na & \(\downarrow\) \\ [PERSON] and [PERSON] [75] & 30-15 & 9 & Diesel & \(\uparrow\) & \(\uparrow\) & na & na & na \\ [PERSON] et al. [77] & 34-26 & 18 & Diesel & \(\uparrow\) & \(\downarrow\) & na & na & \(\downarrow\) \\ [PERSON] et al. [78] & 35-10 & TDC & Diesel & \(\uparrow\) & \(\downarrow\) & \(\uparrow\) & na & na & \(\downarrow\) \\ [PERSON] et al. [50] & 70–20 & \(-\)5 & Diesel & \(\uparrow\) & \(\downarrow\) & \(\uparrow\) & \(\uparrow\) & \(\rightarrow\) \\ [PERSON] et al. [79] & 70–45 & \(-\)5 & Diesel & \(\downarrow\) & \(\downarrow\) & na & na & \(\downarrow\) \\ [PERSON] and [PERSON] [80] & 110-70 & na & Diesel & \(\uparrow\) & \(\downarrow\) & na & na & \(\downarrow\) \\ [PERSON] and [PERSON] [81] & 250-80 & 20 & Diesel & \(\downarrow\) & \(-\) & \(\rightarrow\) & \(\uparrow\) & \(\downarrow\) \\ [PERSON] et al. [68] & 35-15 & 5 & DME & \(\uparrow\) & \(\downarrow\) & \(\uparrow\) & \(\uparrow\) & \(\downarrow\) \\ [PERSON] et al. [82] & 42-21 & 5 & non-butanol & na & na & na & \(\uparrow\) & \(\downarrow\) \\ [PERSON] et al. [83] & 45-8.5 & \(-\)1 & Diesel from Direct Coal & \(\uparrow\) & \(\downarrow\) & na & na & \(\downarrow\) \\ [PERSON] et al. [84] & 65–25 & 14 & B3/G3/DCB & na & \(\downarrow\)\(\uparrow\) & \(\uparrow\) & \(\uparrow\) & \(\downarrow\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Variation of performance and emissions after advancing the first injection timing (two-stage). strategy on improving exhaust emissions in an HCCI diesel engine. Second injection timing was varied from TDC to 20\({}^{\circ}\) ATDC under a fixed first injection timing of 60\({}^{\circ}\) BTDC. When the second injection was delayed, the location and shape of the first-stage heat release from the first injected fuel almost unchanged, while the second stage heat release of diffusive combustion occurred later and the heat release rate was slowed. At the retarded second injection timing, the major combustion event was shifted to later than TDC, which obtained a decrease of NOx emissions because of the low charge temperature and decreased IMEP. Total HC and CO emissions increased as the second injection timing was retarded. [PERSON] et al. [21] investigated the effect of second injection timing on a PCCI diesel engine. With the first injection timing fixed at 56\({}^{\circ}\) BTDC, the second injection timing was changed from 5\({}^{\circ}\) to 18\({}^{\circ}\) BTDC. Results showed that retarding the second injection timing shortened the ignition delay of the second injection due to the high ambient temperature, which increased the portion of diffusive combustion and resulted in significantly increased soot emissions. Retarding the second injection timing also decreased IMEP due to the shift of combustion to the late side. [PERSON] et al. [82] experimentally investigated the effects of second injection timing on the performance and emissions of two-stage injection heavy duty (HD) diesel fueled by n-butanol/diesel. The first injection timing was fixed at 42\({}^{\circ}\) BTDC, and the second injection was varied from 10\({}^{\circ}\) to \(-\)2.5\({}^{\circ}\) BTDC. Soot emissions declined with retarded second injection timing. However, CO emissions were just the opposite. In addition, BSFC increased when the second injection timing was retarded. [PERSON] et al. [86] investigated the effect of second injection timing on the emissions of a DME HCCI engine. The first injection timing was fixed at 80\({}^{\circ}\) BTDC, and the second injection timing was varied from 20\({}^{\circ}\) BTDC to TDC. Results showed that HC emission increased slightly as the second injection was retarded near TDC.