Comparative study on combustion and particulate emissions for diesel-biodiesel and diesel-diglyme blends

Experiments were conducted on a 4-cylinder direct-injection diesel engine using ultralow sulfur diesel blended with biodiesel or diglyme to investigate the influence on combustion and particulate emission characteristics. Five biodiesel blends and five diglyme blends with oxygen concentrations of 2%, 4%, 6%, 8% and 10% were prepared respectively and tested separately at five engine loads of maximum torque speed of 2400 rpm with same boundary condition. With the increase of oxygen content, in-cylinder pressure and heat release curve advanced for both blends but the peak values were lower than of diesel, the trend was more obvious for diglyme blends. Besides combustion centre was slightly varied for biodiesel fuels but postponed significantly for diglyme blends. Meanwhile, smoke opacity, brake specific particulate emissions and the geometric mean diameter of particle decreased accompanying with the increase in soluble organic fraction proportion, and biodiesel blends had more obvious variations. In addition, the total particle number concentration and the particle smaller than 100 nm in diameter increased gradually and unidirectionally for biodiesel blended fuels, but for diglyme blends, the peak value of the total particle was found from the blend containing 2% oxygen and the particles from all diglyme blends were higher than that from diesel. Compared with biodiesel, diglyme fuels had more particulate and particles emissions on the same oxygen base.