Cylinder diameter direct injection gasoline engine

The efficiency of combustion engines, and especially of gasoline engines, can be increased through so-called downsizing. Through the combination of direct injection and supercharging, the displacement can be reduced without comprising engine power. Furthermore, as powertrains become increasingly hybrid, there is an increased need for small-volume engines. In this FVV project, the partners worked on developing a suitable cylinder head concept for small-volume, direct injection gasoline engines. To this aim, 3D Computational Fluid Dynamics (CFD) calculations and experimental work on an optical one-cylinder test engine were carried out. The 3V concept shows promising results to date: Further investigations on the carburetion and suitability of different injector positions are part of an ongoing research project. The use of laser induced exciplex fluorescence (LIEF) makes it possible to analyse carburetion with great precision.

Motivation

The trend towards lower rated engine classes in gasoline engines has various drivers. One driver is downsizing, which aims through a combination of direct injection and turbocharging for a smaller displacement without comprising engine power. Furthermore, hybridization spurs the development of engines with smaller displacement and cylinder dimensions. However, smaller dimensions have the disadvantage of increasing fuel spread and can result in greater emissions as well as engine lubricating oil thinning. The aim of the FVV project was to investigate the feasibility of direct injection with far smaller bore diameters than usual on the market today.

Methodology

Based on extensive preliminary studies, two cylinder head concepts – 3V (valve) and 4V concept – were implemented as prototypes and investigated experimentally on an engine test rig. On a transparent engine, which was fitted with LIEF, the carburetion of the prototypes was analysed metrologically. Using LIEF, the simultaneous measurement of the liquid and gas phase is possible. As part of the optical engine tests, the sources of particle emissions could also be identified. Furthermore, the suitability of a central injector position in the 3V concept could be investigated using 3D CFD calculations of carburetion.

Result

The 3V concept with lateral side-mounted injector positioning and the 4V concept with sideways injector positioning have proven themselves. Particle emission behaviour can be optimised through sideways injection variations, such as control start and injection patterns, as well as through a variation in intensity of load movement, so that the requirements on current combustion processes can be fulfilled. With respect to particle emissions, a comparison of both concepts shows that the 3V concept offers greater potential but is more sensitive to application parameters such as injection timing. The effects of wall moistening and a central injection position in the 3V concept are part of ongoing research work.

Documentation

GDI Boundary Bore | Investigation of the smallest possible cylinder bore combining small engine displacement with gasoline direct injection | Project No. 1047

GDI Boundary Bore II | Numerical and optical studies of carburation in a minimal-volume direct injection spark ignition engine with different injector positions | Project No. 1223

Themis