One of the promising results from oxygen enrichment is the significant decrease in smoke density in the exhaust. Agglomeration of soot particle in the diesel exhaust is the major source of smoke in diesel engine. It is formed mainly due to incomplete combustion of fuel hydrocarbons and some is contributed by lubricating oil. Soot formation is strongly dependent on the stoichiometry, temperature, pressure and mixing [18]. Soot in the exhaust gas is dominated by soot formation as well as oxidation. One of the main effects of oxygen enrichment is to increase oxygen–fuel ratio, which in turn improves the oxidation of fuel and suppress the soot formation. Oxygen enrichment also reduces the ignition delay, meaning higher burning rate and shorter combustion duration [15] which further reduces soot formation. The minimum reduction of smoke opacity in oxygen enrichment is 15% at full load with 27% oxygen enrichment, while the maximum reduction is 60% at no load 27% oxygen enrichment. Consistently there is reduction of smoke opacity levels at all loads and oxygen concentration levels as reported in Fig. 9.