In order to utilise the whole potential of DGI and to avoid any shortcomings the injection has to take place in a certain window of the operation cycle. More precisely is has to be ensured that no moving parts like piston or valves are impinged by the injection spray and that there is sufficient time for mixture formation before ignition. These boundary conditions are shown in picture 'Optimal injection timing and limitations by piston impingement and homogenization problems due to late injection (PFI = Port Fuel Injection)'.
Above mentioned considerations lead to an optimal injection window for each engine operation point. Picture 'Injection timing' shows this window of opportunity and the resulting available injection time for full load operation over engine speed. Due to the limited time for injection at high engine speed a high flow rate of the injector is required to provide the amount of fuel which is required at wide open throttle (WOT) and rated speed. On the other hand at idle operation or low load a small amount of fuel has to be provided without major deviations. Therefore special injectors and a modulated fuel pressure are required see picture 'Dynamic range of injector'.
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