Performance and emissions of a compression ignition engine fueled with diesel/oxygenate blends for various fuel delivery advance angles

Oxygenated blends were prepared by adding methanol and solvent to diesel fuel, and engine performance and emissions of the oxygenated blends under various fuel delivery advance angles were conducted in a compression ignition engine. The results showed that the engine thermal efficiency increased and the diesel-equivalent brake specific fuel consumption decreased as the fuel delivery advance angle for the oxygenated blends increased, and the behavior had a tendency to be more obvious at high engine speed. The NO_x concentration in the oxygenated blends increased as the fuel delivery advance angle increased. For a specific fuel delivery advance angle, the NO_x concentration increased as the oxygenate mass fraction in the fuel blends increased, whereas a large addition of oxygenates in the diesel fuel reduced the NO_x concentration. The addition of oxygenate in the diesel fuel had a strong influence on the NO_x concentration at high engine load, whereas it had little influence at low engine load. The CO content decreased as the fuel delivery advance angle at high engine load became retarded, whereas at middle and low loads, the CO concentration varied little with variation of the fuel delivery advance angle but presented a low value for the diesel/oxygenate blends. The fuel delivery advance angle had little influence on the exhaust hydrocarbon (HC) content for the diesel/ oxygenate blends. The amount of smoke can be decreased remarkably by the addition of oxygenate in diesel fuel at the setting of various fuel delivery advance angles. The amount of smoke decreased as the fuel delivery advance angles for both diesel fuel and diesel/oxygenate blends increased; this phenomenon would be due to the increase in the fraction of fuel burned in the premixed burning phase and the decrease in the fraction of fuel burned in diffusive combustion phase, as well as the improvement of the diffusive combustion in the presence of oxygenated blends. The study also showed that a flat NO_x/smoke trade-off curve existed when the oxygenated blends were used.