Investigating the Effect of Spray Targeting and Impingement on Diesel Engine Cold Start

Analysis of the cold-starting performance of diesel engines requires the development of advanced models to describe the multicomponent nature of the fuel as well as the spray impingement and wall film behavior. A new approach to modeling the multicomponent nature of commercial fuels was implemented. This model is based on a continuous distribution using a probability density function, rather than the use of discrete components, to capture more accurately the entire range of composition in commercial fuels. The model was applied to single droplet calculations to validate the predictions against experimental results. Previous discrete component wall-film modeling has been extended to include the continuous multicomponent fuel representation. A significant factor that has received little attention in analyzing the cold-start performance of diesel engines is the spray impingement angle and location. This has been investigated using the modified KIVA code. The predictions show the importance of including both the multicomponent nature of the fuel, as well as a detailed model of the wall-film and spray-wall interaction. The multicomponent fuel modeling is critical to capturing the correct vaporization trends, and the spray-film interaction modeling is crucial to capturing the spray impingement and subsequent secondary atomization that produces smaller drops. The spray targeting, by way of enhanced secondary atomization (splashing), was found to be a powerful way of enhancing cold start. However, optimal spray targeting for cold-start performance may lead to deteriorated performance at other operating conditions.