Experimental measurements of n-heptane liquid length and spray cone angle for early direct-injection low-temperature conditions relevant to diesel engines in an optically accessible constant-pressure flow vessel
The prevalence of direct-injection fuel sprays in engines and power-generation systems and, in particular, the emergencies of advanced combustion strategies that involve unconventional conditions have made detailed study of fuel sprays necessary. In some of these strategies, fuel is injected early in the compression stroke when in-cylinder temperature and density are both much lower than for conventional operation, thus increasing the potential for wall impingement and wall wetting due to slower vaporization of the fuel. This thesis reports liquid penetration lengths and spray cone angles of n-heptane measured using high-speed imaging of elastic light scattering in a constant-pressure flow vessel (CPFV). Experiments were conducted for a range of injection pressures and injection durations, and more importantly for a range of steady ambient thermodynamic conditions, including velocity, temperature, and density of the air flow. Air temperatures included well below, near, and well above saturation temperatures of n-heptane at the various pressures studied, which should provide some insight into spray behavior of diesel fuel components for early-injection conditions that also could potentially range from below to above saturation. Results strongly suggest that well-accepted models, based on mixing-limited vaporization of fuel, are not sufficient for these conditions relevant to early direct-injection. More work is clearly necessary to develop new models to predict such behavior. Future work is expected to include studies of multi-component blends of hydrocarbons, such as gasoline, diesel, and biodiesel fuels and comprehensive experiments will be conducted to observe multiple-injection fuel spray phenomena.