The Effect of Tumble Flow on Efficiency for a Direct Injected Turbocharged Downsized Gasoline Engine

Direct gasoline injection combined with turbo charging and down sizing is a cost effective concept to meet future requirements for emission reduction as well as increased efficiency for passenger cars. It is well known that turbulence induced by in-cylinder air motion can influence efficiency. In this study, the intake-generated flow field was varied for a direct injected turbo charged concept, with the intent to evaluate if further increase in tumble potentially could lead to higher efficiency compared to the baseline. A single cylinder head with flow separating walls in the intake ports and different restriction plates was used to allow different levels of tumble to be experimentally evaluated in a single cylinder engine. The different levels of tumble were quantified by flow rig experiments.

Two series of experiments were performed, one aiming to evaluate tumble in the region of low to medium load and engine speed, mainly focusing on efficiency, and one for the high load region to evaluate any negative consequences of increased tumble. The results indicate that tumble positively can influence the efficiency and emissions, however, the shape of the incoming flow dictate the level of impact significantly. Even for a relatively small change in tumble great differences in heat loss were seen. The efficiency increase seen originated mainly from lower heat loss through the exhaust gases. Additional gain came from lower in cylinder heat loss for the more favorable shape of the flow, where CFD indicates that the incoming air initially follows the cylinder head to a greater extent. Negative consequences are also associated with increased tumble. For instance, excessive pressure rise rates which can result in noise issues at higher loads. However, from a combustion perspective, the turbulence induced by the tumble positively effects the main parameters with reduced combustion duration, increased stability and increased exhaust gas recycling tolerance as well as increased combustion efficiency, features that are beneficial especially for a direct injected down sized turbo charged concept.