Search Results

The majority of hydrocarbon (HC) emissions in the FTP cycles are generated during cold starts when the catalyst is cold, and a large percentage of the injected fuel does not vaporize well. D Dduring this portion of the test, a wall film builds on the intake ports, fuel drips into the cylinder, and manifold pressure changes cause excursions in the air/fuel ratio (AFR). This paper presents the concept of heating fuel inside an injector to enhance vaporization in the intake manifold. Different injector parameters, such as heater temperature and injector tip geometry, were analyzed for different flow rates. The heat transfer inside the injector was investigated experimentally and numerically, using computational fluid dynamics (CFD) modeling. The Sauter Mean Diameter (SMD) of the fuel spray was measured and evaluated under different vacuum conditions using a Phase Doppler Particle Analyzer (PDPA).

For a better understanding of how soot is generated due to fuel films, a constant volume vessel was used together with four visualization techniques due to their high spatial (2D) and time resolution: Schlieren, natural luminosity, diffused back illumination and OH* chemiluminescence. The analysis was performed keeping the injection pressure at 30 bar and changing the plate temperature on which the spray impacts: 80, 120, 160 and 200 °C. The fuel is a mixture of iso-octane, hexane, toluene and 1-methylnaphthalene, which presents similar properties to commercial gasoline. Valuable insights were gained from the results that infer the real nature of the radiation observed during combustion events in gasoline direct injection (GDI) engines due to the presence of a fuel films which are conventionally described as “pool fires”. The results show that the highest quantity of soot is generated between plate temperatures of 80 and 120 °C.