## 4 Discussion  
Here, the characteristics of nitrogen oxide and black carbon reduction, according to the water content of the emulsion fuel, were studied by the numerical method, and reducing fuel consumption was achieved by adjusting the turbocharger compression ratio. The study was conducted varying the exhaust gas and the fuel consumption rate by adjusting the moisture content. The results are as follows:  
1. Using the comprehensive results of the maximum pressure position of combustion versus the turbocharger compression ratio and the moisture content of the emulsion fuel, in the lower load region, the position of the maximum pressure of combustion was retarded in the model of the basic engine. In the region of more than 50% load, the position of the maximum pressure of combustion is advanced.
2. Characteristics of the turbocharger compression ratio and the emulsion fuel versus the position of maximum combustion pressure were studied. As a result, the turbocharger compression ratio is CR03 and the moisture content is 16%, according to the moisture content of the emulsion fuel. Due to this phenomenon, fuel atomization was accelerated, due to micro-explosion of water, and combustion time was shortened, due to sufficient air, in turn due to the increased compression ratio of the turbocharger.
3. As a result of comparing the turbocharger compression ratio and the fuel consumption, in the cases of including water and excluding water, for the three types of emulsified fuels, the fuel consumption of the emulsified fuel containing water tended to increase. However, as a result of comparing the consumption of pure fuel, excluding moisture contained in emulsified fuel, the fuel consumption rate decreased in the order of EMDO10 \(<\) EMDO13 \(<\) EMDO16.
4. The results of the combustion period characteristics, versus the three types of emulsion fuel and the turbocharger compression ratios, shows that the combustion period is shortened in the order of CR00 \(>\) CR01 \(>\) CR02 \(>\) CR03, according to the compression ratio of the turbocharger. As the fuel water content increases, the combustion period is shortened in the order of EMDO16 \(<\) EMDO13 \(<\) EMDO10.
5. The nitrogen oxide and black carbon reduction was because the combustion period increased, with increasing compression ratio, while the combustion period was shortened, with increasing moisture content of emulsion fuel. This causes the combustion temperature to be lowered due to latent evaporation, in turn due to a phase change under high temperature and high-pressure combustion conditions of water contained in the fuel. Additionally, it caused an increase in the combustion pressure and a shortening of the combustion period, due to the expansion of the volume, in turn due to the micro-explosion of water. This may be due to the shortening of the post combustion period and the reduction of black carbon emissions. In addition, combustion was accelerated in the order--CR00 \(>\) CR01\(>\) CR02\(>\) CR03.
6. As a result of reducing exhaust emissions, black carbon reduction was lowered as the compression ratio of the turbocharger was increased, but black carbon reduction was clearly shown as the water content of the emulsion fuel increased. By optimizing the water content of the emulsion fuel and the compression ratio of the turbocharger, versus the exhaust emissions and the combustion state, it is shown that not only is the fuel consumption rate reduced but also the output improvement is very significant.  
Conceptualization, I.C.; methodology, I.C.; investigation, C.L.; data curation, I.C.; writing--original draft preparation, C.L.; writing--review and editing, C.L. All authors have read and agreed to the published version of the manuscript.  
The APC was funded by the Pukyong National University Research Fund in 2019 (CD20191039)  
**Conflicts of Interest:** The authors declare no conflict of interest.