Search Results

With increasingly stringent emissions regulations and concurrent requirements for enhanced engine thermal efficiency, a comprehensive characterization of the automotive gasoline fuel spray has become essential. The acquisition of accurate and repeatable spray data is even more critical when a combustion strategy such as gasoline direct injection is to be utilized. Without industry-wide standardization of testing procedures, large variablilities have been experienced in attempts to verify the claimed spray performance values for the Sauter mean diameter, Dv90, tip penetration and cone angle of many types of fuel sprays. A new SAE Recommended Practice document, J2715, has been developed by the SAE Gasoline Fuel Injection Standards Committee (GFISC) and is now available for the measurement and characterization of the fuel sprays from both gasoline direct injection and port fuel injection injectors.

The combustion mechanism of a fuel droplet cloud was studied by numerical simulation. We investigated how the flame front speed and combustion products changed depending on the equivalence ratio and initial temperature. Modeling was performed using the KIVA-III software package, a three dimensional analysis software used mainly for internal combustion engine applications. The computational domain was a horizontal 1x1x100 cell sector of a spherical combustion chamber and the fuel was n-decane. Results showed that when all the fuel droplets were assumed to have evaporated, the flame front speed increased from 28 cm/s to 152 cm/s as the equivalence ratio increased. The maximum flame front speed was reached at ϕ=1.1, beyond which it decreased (at richer overall equivalence ratios). With a constant equivalence ratio, the flame front speed decreased near the outside region, because the unburned gas was compressed by the expanding burned gas.

The effects of upstream conditions, such as nozzle and entrance shapes, on external flow characteristics continue to challenge fuel injection modeling efforts, particularly in the case of high-pressure diesel sprays. In this research, flow details were investigated both experimentally and numerically in a fuel injector nozzle orifice using an integrated approach. Calculations using the SIMPLE algorithm were first performed for the scaled-up experimental nozzles with various length to diameter ratios (L/d). Measurements of internal flow velocities for these nozzles were made by laser Doppler velocimetry in order to verify the computational results. Mean and fluctuating velocities and discharge coefficients were obtained at various Reynolds numbers. The mean turbulence intensity and turbulent kinetic energy for a sharp inlet nozzle were generally higher than for a round inlet nozzle, except for the near-wall region beginning at about one nozzle diameter from the entrance.

A two-stroke diesel engine was outfitted for operation with an electronic solenoid-controlled unit injector and an additional solenoid-controlled air-assisted injector at the inlet ports. Access through an existing pressure transducer port allowed installation of a sapphire window to the combustion chamber with very little disturbance to the combustion system. A coherent fiber optic bundle permitted remote visualization of the combustion event. Use of a gateable intensified solid-state camera permitted imaging at high effective shutter speeds at arbitrary times in the engine cycle. Imaging and two-color temperature and soot concentrations measurements were performed. Imaging results indicated a low-intensity diffuse ignition, away from the injector tip, for both the pilot spray in pilot-main tests and the main spray in the main-only runs. Remnants of the burning pilot spray congregated near the injector tip where a region of flame remained until main injection arrived.

A two-stroke diesel engine was outfitted for operation with an electronic solenoid-controlled unit injector and an additional solenoid-controlled air-assisted injector at the inlet ports. Factorial experiments were designed in order to quantify, in a statistically representative manner, the effects of pilot (or ‘split’) and port auxiliary injection on main fuel combustion. Results indicated that interactions between experimental parameters (such as between pilot fuel quantity and pilot-to-main spacing), as well as main effects are important in analyzing auxiliary fuel injection. The bulk gas temperature at main injection was determined primarily by the experimental parameters acting independently of one another, which is a case where main effects only are important. Conversely, analysis of indicated specific fuel consumption and peak cylinder pressure involved interactions of the experimental parameters in both cases.