Effect of Gasoline Fuel Additives on Combustion and Engine Performance

2.2.2
 
Gasoline Indirect Injection 
Gasoline indirect injection refers to pressure atomiser systems where the air-
fuel mixture is created outside the combustion chamber. This can be achieved through 
either a single-point injection system or more commonly a multi-point injection/port 

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2.2 Fuel Metering Systems 
44 
fuel injection (PFI) system. In single-point systems, one injector per engine is used in 
the intake manifold, whilst PFI systems use an injector per cylinder whereby fuel is 
injected directly behind the inlet valves on each of the cylinders. Typical fuel pressures 
are 2-3 bar above atmospheric. Using injectors instead of carburettors enables much 
greater control over fuel quantities used and further improves atomisation 
characteristics of fuel sprays. Control mechanisms for PFI systems include continuous 
mechanical systems such as Bosch KE-Jetronic where injectors open mechanically 
under sufficient fuel supply pressure and a fuel distributer is used, or electronically 
controlled systems such as Bosch L-Jetronic where electromagnetically actuated 
injectors are employed [105].
Due to low fuel pressures, relatively simple and inexpensive electronic control 
units can be employed. Injecting fuel into the intake manifolds allows for sufficient 
time periods during which fuel vaporisation and air-fuel mixing can occur and leads 
to achieving homogeneous mixtures prior to combustion. This enables maximisation 
of power output but lacks the capability of running an engine at very lean conditions 
that would help with fuel economy. As such, the future of injection technologies, 
especially when applied to road going vehicles, is seen in direct injection systems 
although issues with increased particulate matter emissions need to be resolved.