3.4.4. Effect of n-Butanol Blending Ratio on NOx Reaction Rate

Figure 14 shows the effect of n-butanol blending ratio on the chemical reaction rate of NO produced at the maximum combustion temperature in the cylinder. The main reaction paths of NO generation at the in-cylinder combustion peak temperature are indicated by the following chemical equations:

$$\text{HNO} + \text{N}\_2 \leftrightarrow \text{NO} + \text{NNH} \tag{1}$$

$$\text{NO}\_2 \leftrightarrow \text{NO} + \text{O} \tag{2}$$

$$\text{NO}\_2 + \text{OH} \leftrightarrow \text{NO} + \text{HO}\_2 \tag{3}$$

$$\text{N}\_2 + \text{O} \leftrightarrow \text{NO} + \text{N} \tag{4}$$

It can be seen that the reaction rate of NO decreases significantly with the increase of n-butanol mixing ratio. The maximum reduction of NO production rate can reach about 48.8%. The main reason is that the increase of n-butanol mixing ratio leads to a decrease in the total heating value of the mixed fuel, which reduces the in-cylinder combustion temperature. The lower combustion temperature suppresses the perturbation of the gas in the cylinder. Therefore, the production rate and emissions of NO are reduced effectively.

Figure 15 shows the effect of n-butanol blending ratio on the chemical reaction rate of NO2 produced at the maximum combustion temperature in the cylinder. The main reaction paths of NO2 generation at the in-cylinder combustion peak temperature are indicated by the following chemical equations:

$$\text{HONO} + \text{OH} \leftrightarrow \text{NO}\_2 + \text{H}\_2\text{O} \tag{5}$$

$$\text{NO} + \text{OH} \leftrightarrow \text{NO}\_2 + \text{H} \tag{6}$$

**Figure 15.** Effect of n-butanol mixing ratio on NO2 formation rate.

It's the same as the decrease of NO reaction rate, the total heating value of the mixed fuel decreases with the increase of n-butanol blending ratio, which reduces the combustion temperature in the cylinder. The lower combustion temperature suppresses the perturbation of the gas in the cylinder, the combustion reaction rate of NO2 decreases, which leads

to a reduction in NO2 emissions. The NO2 generation rate can be reduced by about 46.4% at most.

It can be seen that the combustion reaction rate and emissions of NOx reduces significantly with the increase of n-butanol mixing ratio. When the blending ratio of n-butanol reaches 40%, the production rate of NO and NO2 can be reduced by more than 40%. Therefore, NOx emissions can be reduced effectively by increasing n-butanol mixing ratio in a suitable range.
