# A Review of Early Injection Strategy in Premixed Combustion Engines
## 3 Injection Timing
### Single Early Injection
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Author** & **Injection Pressure (bar)** & **Fuel** & **BSFC** & **NOx** & **HC** & **CO** & **Soot** \\ \hline [PERSON] et al. [50] & 500–900 & Diesel & na & \(\rightarrow\) & na & na & \(\downarrow\) \\ \hline [PERSON] et al. [52] & 600/1000 & Diesel & na & \(\uparrow\) & na & na & \(\downarrow\) \\ \hline [PERSON] et al. [48] & 300–1200 & Diesel & \(\downarrow\uparrow\) & \(\downarrow\) & \(\uparrow\) & \(\uparrow\) & \(\rightarrow\) \\ \hline [PERSON] et al. [49] & 800/1400 & Diesel & \(\downarrow\) & \(\uparrow\) & \(\downarrow\) & \(\rightarrow\) & \(\downarrow\) \\ \hline [PERSON] et al. [55] & 600–1400 & Diesel & na & na & na & na & \(\rightarrow\) \\ \hline [PERSON] et al. [56] & 1000–1400 & Diesel & \(\downarrow\) & \(\uparrow\) & na & na & \(\downarrow\) \\ \hline [PERSON] [47] & 800–1600 & Diesel & \(\downarrow\) & na & \(\downarrow\) & \(\downarrow\) & \(\downarrow\) \\ \hline [PERSON] et al. [51] & 400/1200 & \
\begin{tabular}{c} Bioethanol \\ blends \\ \end{tabular} & \(\downarrow\) & \(\uparrow\) & \(\uparrow\) & \(\uparrow\) & \(\downarrow\) \\ \hline [PERSON] et al. [57] & 200–240 &
\begin{tabular}{c} Carbon \\ black–water–diesel \\ \end{tabular} & na & \(\downarrow\)\(\uparrow\) & \(\downarrow\)\(\uparrow\) & \(\downarrow\)\(\uparrow\) & \(\downarrow\)\(\uparrow\) \\ \hline [PERSON] et al. [58] & 200–240 & Biodiesel & \(\downarrow\) & \(\uparrow\) & \(\downarrow\) & \(\downarrow\) \\ \hline \end{tabular} \(\uparrow\), increase; \(\downarrow\), decrease; \(\downarrow\)\(\uparrow\), first decrease then increase; \(\uparrow\)\(\downarrow\), first increase then decrease; \(\rightarrow\), no significant effect; na, data not available.  
\end{table} 
Table 2: Variation of performance and emissions after increasing the injection pressure. BSFC, brake-specific fuel consumption. mixture, which promoted soot generation. HC and CO emissions were also increased due to the spray overshoot. [PERSON] et al. (2019) studied the impact of injection timing on the performance and emissions of an HCCI diesel engine. The results indicated thermal efficiency and IMEP decreased with advanced injection timing. Injection timing earlier than 30\({}^{\circ}\) BTDC resulted in higher smoke emissions. This could be affected by the fuel impinging on the piston surface and splashing to the crevices, causing a rich-fuel zone. NOx emissions were lower with earlier injection timing. With the injection timing advanced, CO and HC emissions increased dramatically, owing to the wall-wetting. [PERSON] and [PERSON] (2016) examined the influence of injection timing on the performance and NOx emissions of an HCCI diesel engine. Results showed that IMEP decreased rapidly as the injection timing was advanced beyond 20\({}^{\circ}\) BTDC. When the injection timing was set between 30\({}^{\circ}\) and 50\({}^{\circ}\) BTDC, IMEP was approximately half of that of conventional diesel combustion. NOx emissions were strongly affected by the injection timing. As the injection timing was advanced beyond 30\({}^{\circ}\) BTDC, NOx emissions fell near to nearly 0. [PERSON] et al. (2016); [PERSON] et al. (2016) investigated the effect of injection timing on the characteristics of mixture formation and combustion in an HCCI engine. The injection timing was set from 90\({}^{\circ}\) to 40\({}^{\circ}\) BTDC. Results showed that in the case of early injection, the spray directly impinged upon the wall, a rich mixture was formed near the wall, and a lean mixture was formed in the center of the combustion chamber and the piston bowl zone, as seen in Figure 5. This led to incomplete combustion and decreased IMEP. On the other hand, earlier injection timing means a longer time for soot oxidation, which is beneficial for soot reduction. NOx emissions were also decreased with earlier injection timing. [PERSON] et al. (2016) modeled the combustion process in a direct injection compression ignition engine employing very early injection timing from 180\({}^{\circ}\) to 20\({}^{\circ}\) BTDC.