3.2. NO₂

3.2.1. Fuel-lean conditions ( = 0.833)

3.2.2. Stoichiometric conditions ( = 1.000)

Figure 130: Experimental readings of NO₂ from experiments of sulphur addition from the fuels investigated at = 1.000

Experimental readings of NO₂ in stoichiometric conditions were intermediate between those at other equivalence ratios.

Maximum readings of NO₂ were obtained from fuel G1 (68.3 ppm-wet without SO₂ injection), whereas fuel M1 produced intermediate values (35.6 ppm-wet) and fuel G2 gave the lowest readings (31.4 ppm-wet). A graph of the experimental readings can be seen in Figure 130.

The effect of addition of sulphur dioxide in stoichiometric conditions is to cause a drastic increase of NO₂ emissions from all fuels investigated. The nominal increases of NO₂ emissions can be seen in Figure 131. This graph clearly shows that the largest increases of NO₂ emissions were obtained from fuel M1, whereas smaller reductions were obtained from the heavy vacuum gas oils.

Figure 131: Nominal change in NO₂ emissions at = 1.000 from experiments of sulphur addition from the fuels investigated

Emissions from fuel G1 increased by 31.7 ppm-wet (ie 46.4 % of the emissions without addition of S) whereas G2 produced the smallest nominal increases of NO₂ (16.3 ppm-wet, ie 52 %). The extent of the increase followed the order of nitrogen content of the fuels. The nitrogen content of fuel M1 is 0.32 %, whereas it is 0.13 % for fuel G1 and 0.06 % for fuel G2.

3.2.3. Fuel-rich conditions ( = 1.200)

Figure 132: Experimental readings of NO₂ from experiments of sulphur addition from the fuels investigated at = 1.200

The experimental readings of nitrogen dioxide at fuel-rich conditions were highest among all conditions investigated. Fuel M1 (0.32 % N) produced 253 ppm-wet NO₂ without the addition of SO₂, whereas lower amounts were obtained from other fuels with lower nitrogen contents: 149 ppm-wet from fuel G1 (0.13 % N) and 98 ppm-wet from fuel G2 (0.06 % N). The experimental results are shown in Figure 132.

The effect of SO₂ addition to the combustion system had varying results, according to the fuel. Fuels M1 and G2 experienced increases of NO₂ emissions, whereas fuel G1 did not change its emissions appreciably.

Figure 133 shows this effect in greater detail. Fuel M1 showed increases of up to 37 ppm-wet on addition of 2 % fuel-S as SO₂. This represented a 14.6 % increase over the figures in absence of SO₂. Fuel G2 exhibited a smaller increase of NO₂ emissions, 12.1 ppm-wet (6.4 % per 1 % S added), whereas fuel G1 had a negligible variation of NO₂ emissions with SO₂ addition.

Figure 133: Nominal change in NO₂ emissions at = 1.200 from experiments of sulphur addition from the fuels investigated

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