# A Review of Early Injection Strategy in Premixed Combustion Engines
## 4 Injection Angle
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Author** & **First Injection Quantity** & **Fuel** & **BSFC** & **NOx** & **HC** & **CO** & **Soot** \\ \hline [PERSON] et al. [92] & 0–10 mg/cycle & Diesel & na & na & \(\uparrow\) & na & \(\downarrow\) \\ \hline [PERSON] et al. [90] & 1–5 mg/cycle & Diesel & \(\uparrow\) & \(\downarrow\) & \(\uparrow\) & na & \(\uparrow\) \\ \hline [PERSON] et al. [50] & 2–10 mg/cycle & Diesel & na & \(\downarrow\uparrow\) & na & na & \(\uparrow\) \\ \hline [PERSON] and [PERSON] [93] & 0–50\% & Diesel & na & \(\uparrow\downarrow\) & \(\uparrow\) & \(\uparrow\) & \(\downarrow\uparrow\) \\ \hline [PERSON] et al. [84] & 10–20\% & Diesel & na & \(\uparrow\) & \(\uparrow\) & \(\uparrow\) & \(\rightarrow\) \\ \hline [PERSON] et al. [79] & 10–50\% & Diesel & \(\uparrow\) & \(\uparrow\) & na & na & \(\uparrow\) \\ \hline [PERSON] et al. [91] & 15–35\% & Diesel & \(\uparrow\) & \(\uparrow\) & na & \(\uparrow\) & na \\ \hline [PERSON] et al. [77] & 20–60\% & Diesel & \(\uparrow\) & \(\downarrow\) & na & na & \(\rightarrow\) \\ \hline [PERSON] et al. [56] & 20–60\% & Diesel & na & \(\uparrow\) & na & na & \(\uparrow\) \\ \hline [PERSON] et al. [83] & 2–6 mm\({}^{3}\)/cycle & DDCL & na & \(\uparrow\) & na & na & \(\rightarrow\) \\ \hline \end{tabular}
\end{table} 
Table 6: Variation of performance and emissions after increasing the first injection quantity (two-stage). characteristics of mixture formation and combustion in a PCCI engine using an early multiple injection strategy. Four injection angles (150\({}^{\circ}\), 130\({}^{\circ}\), 100\({}^{\circ}\), and 70\({}^{\circ}\)) were tested. Results showed that when the spray impinged on the wall of the combustion chamber, IMEP decreased because of the incomplete combustion due to wall-wetting; IMEP increased as the injection angle decreased. As the injection angle decreased, the mass of fuel impinging on the bowl region increased and the mixture forming in the bowl region became richer, which caused increased smoke. [PERSON] et al. [66] investigated the combustion and emission characteristics of a single-cylinder PCCI engine using two-stage diesel fuel. Two injection angles (150\({}^{\circ}\) and 100\({}^{\circ}\)) were examined. In order to reduce the wall-wetting by spray over-penetration, the injector with a narrow injection angle was tested. Results showed that opacity was improved to a minimum of 7% because the spray impingement was reduced, and HC and CO concentrations were also reduced compared to the 150\({}^{\circ}\) injection angle, while the power output was increased. However, with the advance of early injection timing, NOx concentration highly increased with the narrow injection angle. [PERSON] and [PERSON] [75] computationally investigated the effects of injection angle on combustion characteristics, performance, and amount of pollutant emissions in a DI injection angle. Three injection angles (145\({}^{\circ}\), 105\({}^{\circ}\), and 90\({}^{\circ}\)) were studied. NOx emissions decreased with decreased injection angle. However, as the injection angle decreased, soot emissions first decreased and then increased, and there was a best injection angle for soot emissions, which probably depended on the interaction of the spray and the piston bowl. The trend of BSFC as the injection angle was changed was similar to the soot emissions. The increased BSFC was mainly caused by incomplete combustion of the wall film. [PERSON] [47] investigated the effects of varying injection angles on emissions and thermal efficiency using a DI diesel engine. Results showed that injection angles from 100\({}^{\circ}\) to 158\({}^{\circ}\) significantly changed the spray targeting the piston bowl. Soot emissions decreased sharply as the injection angle decreased. HC and CO emissions with the 100\({}^{\circ}\) injection angle were the minimum. Figure 11: Schematic diagrams of the tested combustion chamber and fuel spray: (**a**) conventional diesel engine; (**b**) modified engine configuration for early injection [62]. [PERSON] et al.