Search Results

This study focuses on the development of an autoignition model for diesel sprays that is applicable to phenomenological multi-zone combustion models. These models typically use a single-step Arrhenius expression to represent the low-temperature chemistry leading up to autoignition. There has been a substantial amount of work done in the area of n-heptane autoignition in homogeneous mixtures. Reduced kinetic mechanisms with ten reactions or less have been proposed in the literature to represent the complex low-temperature oxidation of n-heptane. These kinetic models are attractive for multi-zone simulations because of the low number of reactions involved. However, these kinetic mechanisms and the multi-zone treatment of the fuel spray do not account for the effect of turbulence/chemistry interactions on the chemical reaction rate.

Multidimensional models that are used for engine computations must include spray sub-models when the fuel is injected into the cylinder in liquid form. One of these spray sub-models is the droplet interaction model, which is separated into two parts: first, calculation of a collision rate between drops, and second, calculation of the outcome once a collision has occurred. This paper focuses on the problem of calculating the collision rate between drops accurately. Computing the collision rate between drops or particles when they are non-uniformly distributed and sharp gradients are present in their distribution is a challenging task. Traditionally the collisions between parcels of drops have been computed using the same spatial grid as is used for the Eulerian gas-phase calculations. Recently it has been proposed to use a secondary grid for the collision rate calculation that is independent of the gas-phase grid, as is done in the NTC collision algorithm.

This paper describes the results of experiments that were performed using a Ground Research Vehicle (GRV) at the National Aeronautics and Space Administration's (NASA) Dryden Flight Research Center in Edwards, CA and a comparison with computational results. The GRV is a modified 1984 General Motors (GMC) van and measures 40 feet long and 9 feet high, with a base area of 83 by 83, and it weighs 10260 lbs and holds a crew of up to three. Air data is measured from a nose-boom, 2 global positioning (GPS) units, and an absolute Honeywell Pressure Transducer with 4 Electronic Signal Processor (ESP) scanners and 64 surface pressure ports. This allows for detailed measurements of the surface pressure profiles around the vehicle. The total vehicle drag is estimated from coast-down tests, while the pressure component of the drag force may be calculated by integrating the pressure profiles on the front and base of the vehicle.