Gasoline Combustion System Development for Volvo Cars All-New Engine Family

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Volvo Car Corporation has recently launched the first three members of a completely new engine family called Drive-E. It consists of four gasoline and four diesel engines that are characterized by high specific performance, low friction and low fuel consumption. The number of cylinders is limited to four, which implies that these down-sized, boosted engines will replace present five and six cylinder engines. This paper focuses on the development of the Drive-E gasoline combustion system, characterized by a centrally-mounted direct-injection fuel injector in combination with high-tumbling intake ports. The break-down of the large-scale tumble motion into a high level of turbulence leads to fast and stable combustion as well as excellent air/fuel mixing and limited wall wetting. The four gasoline engines span a wide range of power levels. This means that the engine at the entry power level needs to breathe less air than the 2.0 L engine at the highest power level (225 kW, 306 HP). Consequently, intake port design was an important part of the combustion system development. Different intake port geometries are applied at the different power levels, and this paper describes the trade-off between a design that sets up a strong tumble motion (leading to fast combustion and thus reduced fuel consumption), and a design that optimizes engine breathing (enabling class-leading specific power, while keeping fuel-efficiency at a good level).

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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.