Engine cold-start testing

Fuel distribution and combustion are examined for direct- and port-fuel-injection systems during cold start.

Attention has been drawn to the gasoline direct-injection (GDI) engine due to various potential advantages (see Box). The precise estimation of in-cylinder fuel distribution can provide critical input for the design of GDI engines. Laser diagnostic methods such as planar laser-induced fluorescence (PLIF), which have been developed in the last decade, allow the direct measurement of fuel distribution in optically-accessible engines.

Regardless of the operating strategy used, one of the key advantages of a direct-injection (DI) engine is the reduction in unburned hydrocarbon (UHC) emissions during cold start. This reduction is due to elimination of the liquid-film-vaporization process in the intake ports of conventional port-fuel-injection (PFI) engines. An important factor to consider when evaluating the two DI operating strategies for cold start is “fast light-off” of the catalytic-converter system. Fast light-off requires high exhaust-gas temperatures that can be achieved with an early-injection, homogeneous-charge strategy. A more-complete understanding of DI engine cold-start behavior is critical to achieve even lower UHC emissions, and particularly to compete with developments in PFI engines using sophisticated fuel-metering systems.