Precise control over mixture formation withhigh fuel pressure and multiple injections allows Gasoline Direct Injection (GDI) engines to be operated satisfactorily at extreme conditions wherePort Fuel Injection (PFI) engines wouldnormally struggle due to combustion instability issues.
Catalyst heating phase is one such important condition which is initiated after a cold engine start to improve the effectiveness of the three-way catalyst (TWC). For a given TWC specification, fast light-offof TWC is achieved in the catalyst heating phase by increasing the exhaust gas temperature with higher exhaust mass flow.
The duration of this phase must be as short as possible, as it is a trade-off between achieving sufficient TWC light off performance and fuel efficiency. Thanks to advanced spray targeting and high fuel pressure, stratifiedmode is achieved in GDI engines by injecting a part of the total injected fuel per cycle very late in the compression stroke which forms a combustible mixture around the sparkplug which in turn facilitates very retarded spark timings. This allows the combustion to initiate after the compression stroke and propagate well into the expansion stoke to increase the exhaust gas temperature without compromising on combustion stability.
This technical paper summarises the study conducted on a 1.2litre 3-cylinder turbocharged GDI engine to achieve superior catalyst heating using advanced mixture formation and combustion timing techniques.
Results indicate that light-off of the catalyst was achieved rapidly and consistently after engine start both in the case of 3000 km stabilized and 1,60,000 km aged catalyst in comparison to results of tests with catalyst heating turned OFF.