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A series of designed experiments (DOE) was used to optimize the seat and orifice designs in a multi stream gasoline direct injector. The goal of the experiments was to minimize the effects of fuel deposits on the injector performance. Two different engines were used in the test campaign. One engine, a centrally injected turbocharged 1.6L four cylinder, was used to run a three factor full factorial DOE that tested the effects of SAC volume design, tip design and combustion seal position. Another, a centrally injected turbocharged 3.0L six cylinder, was used to run a three factor full factorial and a four factor half factorial DOE. The three factors in the full factorial were orifice hole divergence, orifice hole surface finish and the use of an inert amorphous silicon coating. A fourth factor, hydro erosive grinding of the orifice holes, was added to facilitate the calculation of a four factor half factorial DOE with only four additional engine tests.

The impact of fuel composition (ethanol and aromatic content) and injector design on particulate number generation was studied in a 1.0L displacement direct injection spark ignition engine. Two types of engine tests that mimic real-life vehicle operation were carried out using a matrix of eight fuels and two injectors. It was found that the DISI injector design had the biggest impact on the extent of particulate number generation. An injector prototype designed to meet Euro 6c specifications for PN (6*1011 particles/km) resulted in much lower PN values compared to those obtained using a production injector currently available in the market. The impact of fuel composition on PN was apparent only during engine operation with the production injector. Overall, qualitative trends were observed but no statistically significant differences were observed for the impact of ethanol (E10 fuel match-blended for aromatics and octane quality) and aromatic content (19-28%) variation.

Vehicle manufactures are significantly increasing the production of Direct Injection Gasoline (DIG) engines to help meet the requirements of governmental regulations and the demands of consumers. While DIG powertrains offer multiple advantages over conventional gasoline engines they can be susceptible to fuel related deposit formation, specifically within the fuel injector nozzle. Fuel injector deposits have been linked to a number of negative effects that can impact the normal operation of the engine. A DIG deposit test has been developed to evaluate Deposit Control Additives (DCA) and their effect on injector deposits. Multiple metrics for evaluating fuel injector deposits were investigated to determine a suitable method for quantifying deposit formation. Interrogation of the vehicle On-Board Diagnostic (OBD) system was identified as the optimal method for quantifying deposit formation throughout the duration of the test.

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.