# Exhaust Gas Characteristics According to the Injection Conditions in Diesel and DME Engines
## 3 Results and Investigations  
### Effects of Atomization on Exhaust Gas  
Figure 3 shows the effect of high-pressure injection pressure on PM and NOx emissions. Many studies have been conducted by active researchers on the high-pressure engine; however, the problem of reducing PM and NOx emissions is still not solved. In the existing diesel (compression ignition) engines, the common rail high-pressure injection system has limitations in reducing PM and NOx emissions. Therefore, to solve the exhaust gas emission problem of the compression ignition engine, a compression ignition engine using an alternative fuel was studied [21; 22; 23; 24]. In this study, the exhaust gas problem, which cannot be solved by the existing common rail diesel compression ignition engine, was solved with the optimization of a DME engine system that can satisfy both efficiency and exhaust gas emission.  
Figure 2: Schematic diagram of the fuel injection control system.  
Table 2 presents the causes of PM and NO\({}_{\rm x}\) generation and the mitigation measures. To solve the problem of exhaust gas emission from conventional fossil fuels of compression ignition engines, DME, which is a natural gas reforming fuel, was used as an alternative fuel. The thermal efficiency of the compression ignition engines using the DME fuel was studied to determine the optimal injection conditions to maintain the current level of common rail diesel engines and simultaneously reduce the PM and NO\({}_{\rm x}\) emissions.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Emission** & **Methods** & **Effects of Reduction** \\ \hline \multirow{6}{*}{NO\({}_{\rm x}\)} & Injection timing delay & Lowering of combustion temperature [35] \\ \cline{2-3}  & Exhaust gas recirculation & Lowering of combustion temperature [36] \\ \cline{2-3}  & Lowering of oxygen thickness [37] \\ \cline{2-3}  & Water fulmination & Lowering of combustion temperature [38] \\ \cline{2-3}  & Fuel–water injection & Lowering of combustion rate in the first period [39] \\ \cline{2-3}  & Pilot injection & Lowering of combustion rate in the first period [40] \\ \cline{2-3}  & Improving cetane number & Lowering of combustion rate in the first period [40] \\ \cline{2-3}  & After treatment & NO\({}_{\rm x}\) recharge and resolve [41; 42; 43; 44; 45] \\ \hline \multirow{6}{*}{PM} & Spray improvement & Air inhalation increase in spray [46] \\ \cline{2-3}  & Mixing increase [47] \\ \cline{2-3}  & Optimization in & Mixing increase [48] \\ \cline{2-3}  & combustion chamber & Increase in air usage rate [49] \\ \cline{2-3}  & Confusion combustion & Mixing increase [50] \\ \cline{2-3}  & Increase of smoke oxidation [51] \\ \cline{2-3}  & Turbo charging & Lean burn combustion [52] \\ \cline{2-3}  & Air inhalation increase in spray [52] \\ \cline{2-3}  & Reduction in oil consumption & Reduction of SOF [53] \\ \hline Low sulfur fuel & Reduction of sulfur combination matter [53; 54; 55] \\ \hline After treatment & Smoke catching and SOF oxidation [56; 57] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Causes of PM and NO\({}_{\rm x}\) generation and mitigation measures.  
Figure 3: Effects of injection pressure on the exhaust gas.