Homogeneous Charge Preparation of Diesel Fuel by Spray Impingement onto a Hot Surface at Intake Manifold 2006-01-3322
A segment of steel tube with the inner diameter of 60 mm and length of 100 mm was fixed between the intake manifold and cylinder head in a direct injection natural aspirated diesel engine. The surface of the tube could be heated to be above 400 °C by the heater enwrapped outside within several minutes under the power less than 600 W. The tip of an injector traditionally used for in-cylinder diesel direct injection was extended to the axis of the tube. The diesel sprays could impinge onto the hot inner surface of the tube and atomize quickly if the temperature of the tube was high enough. Then the fuel-air mixture would be sucked into the cylinder, and HCCI combustion could be fulfilled. The vaporization ratio of the impinged diesel sprays was estimated by fuel consumption, intake air flux and excess air coefficient (λ) calculated from the volumetric concentration of O2, CO2 and CO emissions. The NOx emission was always very low. The exhaust opacity (PM) was lower than 5% in the range of λ = 4 ∼ 5 at the engine speed of 700 ∼ 1000 r/min, when the hot surface temperature is higher than 370 °C. The main composition of PM emission should be liquid fuel. Intake heating would decrease the PM emission efficiently at lower loads due to the elevated gas temperature and EGR would reduce PM distinctly at higher loads due to the prolonged time available for liquid fuel drops evaporation.