Effect of Gasoline Fuel Additives on Combustion and Engine Performance

3.1
 
Spray Investigation 
The combustion vessel had previously been designed and built for diesel spray 
investigations. Modifications were carried out to enable gasoline spray 
characterisation with additives. This included a new fuel delivery and control systems. 
3.1.1
 
Injection System 
The fuel injection system was built based on a gasoline direct injection (GDI) system. 
Although modern GDI systems make use of spray guided multi-hole injection systems, 

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3.1 Spray Investigation 
76 
a single-hole wall-guided DI injector was reasoned more suitable for the current study. 
This was due to factors described in Section 2.2 on interactions between spray plumes 
but also with combustion experiments in mind. Due to the very large volume in the 
combustion chamber with respect to engine conditions at the end of compression 
stroke and a single source of ignition, the wall-guided injection system was employed 
as a spray-guided injection system. The selected injector was a Bosch single-hole GDI 
injector rated at 110 bar injection pressure. A custom water-cooled injector mount was 
designed and manufactured for the chosen injector. The mounting assembly can be 
seen Figure 3.2.  
Figure 3.2: Injector mount assembly. Components as named in the figure 
It was anticipated that some if not all of the additives used in the testing might 
carry a memory effect. This would potentially distort results and as a result a full fuel 
system clean up using an ultrasonic bath was used between different additives. 
Consequently, the fuel was pressurised using an in-house designed fuel pressure 
accumulator [217]. A larger piston is pressurised directly from a nitrogen supply 
which then amplifies the pressure as the force is transferred to a smaller piston. This 
system allowed for nitrogen supply pressure to be stepped-up by a factor 7 while all 
components in contact with fuels could explicitly be cleaned. Cleaned components 

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3.1 Spray Investigation 
77 
included fuel injector, injector cap, high pressure fuel line, pressure transducer mount 
and fuel accumulator parts that were in contact with the fuel. This is presented in 
Figure 3.3.