# Effects of Ethanol-Diesel on the Combustion and Emissions from a Diesel Engine at a Low Idle Speed
## 3 Results and Discussion
### Emissions Characteristics  
#### 3.2.1. Gaseous Emissions  
The mixture of ethanol has a very substantial effect on combustion. The properties of ethanol, such as its low cetane number, lower LHV, high latent heat of evaporation and low viscosity, affect the generation of exhaust pollutants. Figure 8 shows the emissions characteristics of exhaust pollutants on the gaseous emissions of the test fuel conditions. Figure 8a shows NOx and PM, (b) shows the emission rates of NO2 and NO2/NOx, and (c) shows the emission characteristics of HC and CO by test fuel conditions. Figure 8: Emissions of (**a**) NOx and soot opacity, (**b**) NO2 and NO2/NOx, and (**c**) HC and CO.  
Figure 7: (**a**) Distributions of the IMEP and (**b**) the COV of the IMEP. NOx was emitted at 872 ppm under the conditions of DE_0. With the ethanol-mixed fuel DE_3, NOx was reduced by 3.5% to 841 ppm; with DE_5, it decreased by 6.5% to 815 ppm; and with DE_10, NOx decreased 6.9% to 812 ppm. As the ethanol blend ratio increases, the emissions of NOx tend to decrease. It was judged that NOx decreases in this manner because the low LHV and high latent heat of evaporation of ethanol reduce the combustion temperature, even though the pre-mixed combustion is increased due to the longer ignition delay caused by the low cetane number of ethanol. Many studies [13; 16; 19; 20] have also reported that the blend of ethanol or alcohol fuels reduces the production of NOx due to their lower LHV and high latent heat of evaporation, which makes the splitting of nitrogen molecules less likely. In the studies of [PERSON] et al. [16], the generation of NOx was reduced by blending ethanol in fuels, due to the high latent heat of vaporization and low LHV, and the suppression of thermal NO generation by the trace amounts of H\({}_{2}\)O in ethanol-blended fuel. Also, [PERSON] et al. [20] reported NOx reduction by ethanol blending for a low engine load condition. [PERSON] explained that the reason for NOx reduction is that the evaporation and lower LHV of ethanol in the blends after injection reduced the gas temperature in the cylinder. [PERSON] et al. [19] showed that NOx decreased by 14.1% and 6.1% at low engine loads (0.08 MPa and 0.2 MPa) when using ethanol-diesel blend fuels. In the study of [PERSON] et al., using a single-cylinder direct-injection engine, NOx concentrations decreased by 2.2% and 4.2%, respectively, when using 10% and 15% ethanol-diesel fuels. [PERSON] [13] reported that the emission of NOx was the same or very slightly lower, when an ethanol-blended fuel was used, than that of pure diesel fuel. The reasons were that the oxygen content and the longer ignition delay from the low cetane number of ethanol, and the low combustion temperature due to the lower caloric value of ethanol, counterbalanced each other for NOx generation. On the other hand, there are other studies [14; 22] that show that NOx increases with the blend of ethanol. [PERSON] [14] showed that NOx emissions increased with the use of ethanol and methanol blends, and explained that the NOx increase was due to the fact that the low cetane number and oxygen content were more effective than the latent heat vaporization. Based on the studies above, several factors affect the generation of NOx. First, the high combustion temperature caused by the high oxygen content of the alcohol generates thermal NOx. Second, the reduced combustion temperature caused by the cooling effect of the high evaporation cooling of alcohol reduces NOx. More NOx is produced with the rapid increase of the combustion temperature caused by the increase of premixed combustion, which is related to the low cetane number of ethanol. [PERSON] et al. [22] reported that the generation of NOx increased with the increase in the ethanol blending ratio, and that it was discharged to a maximum of 5.5 g/kWh from 30% ethanol-diesel fuel. Another reason for the decrease in NOx is the hydrous ethanol that can occur during fuel production or management. Due to its molecular structure, ethanol can be dissolved in water [37]. [PERSON] et al.