Emissions from a diesel engine with an air intake system under obstructed conditions.

Incomplete combustion in internal combustion engines leads to efficiency losses and increases in pollutant emission levels. For combustion to be complete, a well-balanced air-fuel mixture is essential, and this balance depends on the characteristics of the air intake system. In this context, the present study investigated the effect of five restriction levels (0%, 20%, 40%, 60%, and 80%) applied to the air intake duct on diesel engine emissions. To this end, a 75-hp tractor was coupled to an AW Nebraska 800 dynamometer, and gaseous emissions (oxygen, carbon monoxide, carbon dioxide, and nitrogen oxides) were recorded at five engine speeds (1250, 1500, 1750, 2000, and 2250 rpm). The relationship between intake system restriction and combustion quality was assessed, and mild restrictions (up to 20%) promoted more complete combustion under the evaluated operating conditions, as indicated by lower residual oxygen and carbon monoxide concentrations and higher carbon dioxide levels in the exhaust. In contrast, the 60% restriction produced the lowest NOx concentration. Regarding engine speed, higher engine speeds (1500 to 2250 rpm) favored more efficient combustion, with lower oxygen and carbon monoxide levels and higher CO₂ and NOx concentrations. Thus, restricting airflow was found to significantly alter the emissions profile, making it crucial to optimize air intake to balance efficiency and pollutant control.