# 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
[38] reported that aqueous ethanol could reduce NOx. In the study, the combustion of aqueous ethanol and natural gas was compared using a Swirl burner, and the NOx generated by the combustion of aqueous ethanol was found to be reduced by 25%. [PERSON] explained that this was because the low cetane number of the blended ethanol increased the ignition delay. It is noted that NOx includes both NO and NO\({}_{2}\). NO\({}_{2}\) reacts with volatile organic compounds (VOCs) in the atmosphere to generate optical smog, known as fine dust [39; 40]. As shown in Figure 8b, NOx decreases but NO\({}_{2}\) increases as the ethanol mix increases. This is due to the increase in NO\({}_{2}\) generation due to the added oxygen from the ethanol in the mixture. The smoke opacity is reduced by ethanol blending, as shown in Figure 8a. The levels of smoke opacity were reduced from 5.3% for DE_0 to 3% for DE_10 by ethanol blending, and slightly decreased as the ethanol blending ratio increased. This is because of the effect of oxygen from ethanol blending resulting in more complete combustion. The HC emissions, addressed by Figure 8c, initially decrease as 3% ethanol is added to pure diesel fuel, and then increase as the ethanol blending ratio increases. The HC at DE_0 was 34 ppm, and these levels were reduced by 50% to 17 ppm for DE_3, by 44% to 19 ppm for DE_5 and by 15% (vs. diesel) to 29 ppm for DE_10. By blending ethanol, the HC emissions are lower than the diesel fuel condition. Under idle conditions with a low rotational speed and low fuel injection pressure, slightly rich combustion conditions are created for the stability of combustion. Blending ethanol with diesel reduces HC emissions because of the reduction of partial fuel-rich areas due to the effect of the oxygen and the improved atomization caused by the reduced viscosity of the injection fuel. Also, according to the report of [PERSON] (2014), the addition of alcohol increases the laminar flame speed, which reduces the temperature of the combustion but promotes the oxidation of the HC. However, in this study, the level of HC increases with the further increase in the ethanol blending ratio. This is believed to be caused by the partial over-lean area being increased by the blending of ethanol and the bulk quenching caused by the high latent heat of the evaporation of ethanol. Most studies (2014; 2015; 2016; 2017; 2018; 2019; 2020; 2021) also report an increase in HC as the blending ratio of ethanol increases. CO emissions increased as the blending ratio of ethanol increased. The CO concentration at DE_0 was 252 ppm, that of DE_3 increased by 5%to 266 ppm, DE5 increased by 13.5% to 286 ppm, DE10 increased by 27.4% to 321 ppm. Figure 8c shows that CO emissions for the blended fuels are higher than for unmixed diesel fuel. Several studies have reported that CO increases with the blending of ethanol. [PERSON] et al. (2018) explained that the increase in CO due to the ethanol mixture is caused by the incomplete combustion caused by the higher latent heat of the evaporation of ethanol. On the other hand, several other studies have reported that CO decreases with ethanol blending. [PERSON] (2014) reported that the addition of alcohol adds oxygen to the combustion gas, resulting in a partially leaner fuel, which converts more CO to CO\({}_{2}\) than under the diesel fuel conditions.